2024 |
Amato, F., Van Drooge, B., Jaffrezo, J., Favez, O., Colombi, C., Cuccia, E., et al. (2024). Aerosol Source Apportionment Uncertainty Linked To The Choice Of Input Chemical Components. Environment International, 1841.
Abstract: For A Positive Matrix Factorization (Pmf) Aerosol Source Apportionment (Sa) Studies There Is No Standard Procedure To Select The Most Appropriate Chemical Components To Be Included In The Input Dataset For A Given Site Typology, Nor Specific Recommendations In This Direction. However, These Choices Are Crucial For The Final Sa Outputs Not Only In Terms Of Number Of Sources Identified But Also, And Consequently, In The Source Contributions Estimates. In Fact, Pmf Tends To Reproduce Most Of Pm Mass Measured Independently And Introduced As A Total Variable In The Input Data, Regardless Of The Percentage Of Pm Mass Which Has Been Chemically Characterized, So That The Lack Of Some Specific Source Tracers (E.G. Levoglucosan) Can Potentially Affect The Results Of The Whole Source Apportionment Study. The Present Study Elaborates Further On The Same Concept, Evaluating Quantitatively The Impact Of Lacking Specific Sources' Tracers On The Whole Source Apportionment, Both In Terms Of Identified Sources And Source Contributions. This Work Aims To Provide First Recommendations On The Most Suitable And Critical Components To Be Included In Pmf Analyses In Order To Reduce Pmf Output Uncertainty As Much As Possible, And Better Represent The Most Commons Pm Sources Observed In Many Sites In Western Countries. To This Aim, We Performed Three Sensitivity Analyses On Three Different Datasets Across Eu, Including Extended Sets Of Organic Tracers, In Order To Cover Different Types Of Urban Conditions (Mediterranean, Continental, And Alpine), Source Types, And Pm Fractions. Our Findings Reveal That The Vehicle Exhaust Source Resulted To Be Less Sensitive To The Choice Of Analytes, Although Source Contributions Estimates Can Deviate Significantly Up To 44 %. On The Other Hand, For The Detection Of The Non-Exhaust One Is Clearly Necessary To Analyze Specific Inorganic Elements. The Choice Of Not Analysing Non-Polar Organics Likely Causes The Loss Of Separation Of Exhaust And Non-Exhaust Factors, Thus Obtaining A Unique Road Traffic Source, Which Provokes A Significant Bias Of Total Contribution. Levoglucosan Was, In Most Cases, Crucial To Identify Biomass Burning Contributions In Milan And In Barcelona, In Spite Of The Presence Of Pahs In Barcelona, While For The Case Of Grenoble, Even Discarding Levoglucosan, The Presence Of Pahs Allowed Identifying The Bb Factor. Modifying The Rest Of Analytes Provoke A Systematic Underestimation Of Biomass Burning Source Contributions. Sia Factors Resulted To Be Generally Overestimated With Respect To The Base Case Analysis, Also In The Case That Ions Were Not Included In The Pmf Analysis. Trace Elements Were Crucial To Identify Shipping Emissions (V And Ni) And Industrial Sources (Pb, Ni, Br, Zn, Mn, Cd And As). When Changing The Rest Of Input Variables, The Uncertainty Was Narrow For Shipping But Large For Industrial Processes. Major And Trace Elements Were Also Crucial To Identify The Mineral/Soil Factor At All Cities. Biogenic Soa And Anthropogenic Soa Factors Were Sensitive To The Presence Of Their Molecular Tracers, Since The Availability Of Oc Alone Is Unable To Separate A Soa Factor. Arabitol And Sorbitol Were Crucial To Detecting Fungal Spores While Odd Number Of Higher Alkanes (C27 To C31) For Plant Debris.
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Aroskay, A., Martin, E., Bekki, S., Le Pennec, J., Savarino, J., Temel, A., et al. (2024). Geological Evidence Of Extensive N- Fixation By Volcanic Lightning During Very Large Explosive Eruptions. Proceedings Of The National Academy Of Sciences Of The United States Of America, 1211(7).
Abstract: Most Of The Nitrogen (N) Accessible For Life Is Trapped In Dinitrogen (N2), The Most Stable Atmospheric Molecule. In Order To Be Metabolized By Living Organisms, N2 Has To Be Converted Into Biologically Assimilable Forms, So – Called Fixed N. Nowadays, Nearly All The N- Fixation Is Achieved Through Biological And Anthropogenic Processes. However, In Early Prebiotic Environments Of The Earth, N- Fixation Must Have Occurred Via Natural Abiotic Processes. One Of The Most Invoked Processes Is Electrical Discharges, Including From Thunderstorms And Lightning Associated With Volcanic Eruptions. Despite The Frequent Occurrence Of Volcanic Lightning During Explosive Eruptions And Convincing Laboratory Experimentation, No Evidence Of Substantial N- Fixation Has Been Found In Any Geological Archive. Here, We Report On The Discovery Of A Significant Amount Of Nitrate In Volcanic Deposits From Neogene Caldera- Forming Eruptions, Which Are Well Correlated With The Concentrations Of Species Directly Emitted By Volcanoes (Sulfur, Chlorine). The Multi- Isotopic Composition (Delta 18O, Delta 17O) Of The Nitrates Reveals That They Originate From The Atmospheric Oxidation Of Nitrogen Oxides Formed By Volcanic Lightning. According To These First Geological Volcanic Nitrate Archive, We Estimate That, On Average, About 60 Tg Of N Can Be Fixed During A Large Explosive Event. Our Findings Hint At A Unique Role Potentially Played By Subaerial Explosive Eruptions In Supplying Essential Ingredients For The Emergence Of Life On Earth.
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Marsal, A., Sauvain, J., Thomas, A., Lyon-Caen, S., Borlaza, L., Philippat, C., et al. (2024). Effects Of Personal Exposure To The Oxidative Potential Of Pm<Sub>2.5</Sub> On Oxidative Stress Biomarkers In Pregnant Women. Science Of The Total Environment, 9119.
Abstract: Oxidative Stress Is A Prominent Pathway For The Health Effects Associated With Fine Particulate Matter (Pm2.5) Exposure. Oxidative Potential (Op) Of Pm Has Been Associated To Several Health Endpoints, But Studies On Its Impact On Biomarkers Of Oxidative Stress Remains Insufficient. 300 Pregnant Women From The Sepages Cohort (France) Carried Personal Pm2.5 Samplers For A Week And Op Was Measured Using Ascorbic Acid (Aa) And Dithiothreitol (Dtt) Assays, And Normalized By 1) Pm2.5 Mass (Opm) And 2) Sampled Air Volume (Opv). A Pool Of Three Urine Spots Collected On The 7Th Day Of Pm Sampling Was Analyzed For Biomarkers, Namely 8-Hydroxy-2-Deoxyguanosine (8-Ohdg), Malondialdehyde (Mda) And 8-Isoprostaglandin-F2 Alpha (8-Isopgf2 Alpha). Associations Were Investigated Using Adjusted Multiple Linear Regressions. Op Effects Were Additionally Investigated By Stratifying By Median Pm2.5 Concentration (14 Mu G M(-3)). In The Main Models, No Association Was Observed With 8-Isopgf2 Alpha, Nor Mda. An Interquartile Range (Iqr) Increase In Opmaa Exposure Was Associated With Increased 8-Ohdg (Percent Change: 6.2 %; 95 % Ci: 0.2 % To 12.6 %). In The Stratified Analysis, Exposure To Opmaa Was Associated With 8-Ohdg For Participants Exposed To Low Levels Of Pm2.5 (Percent Change: 11.4 %; 95 % Ci: 3.3 % To 20.1 %), But Not For Those Exposed To High Levels (Percent Change: -1.0 %; 95 % Ci: -10.6 % To 9.6 %). Associations For Opmdtt Also Followed A Similar Pattern (P-Values For Opmaa-Pm And Opmdtt-Pm Interaction Terms Were 0.12 And 0.11, Respectively). Overall, Our Findings Suggest That Opmaa May Be Associated With Increased Dna Oxidative Damage. This Association Was Not Observed With Pm2.5 Mass Concentration Exposure. The Effects Of Opmaa In 8-Ohdg Tended To Be Stronger At Lower (Below Median) Vs. Higher Concentrations Of Pm2.5. Further Epidemiological, Toxicological And Aerosol Research Are Needed To Further Investigate The Opmaa Effects On 8-Ohdg And The Potential Modifying Effect Of Pm Mass Concentration On This Association.
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2023 |
Bekaert, D., Blard, P., Raoult, Y., Pik, R., Kipfer, R., Seltzer, A., et al. (2023). Last Glacial Maximum Cooling Of 9 Degrees C In Continental Europe From A 40 Kyr-Long Noble Gas Paleothermometry Record. Quaternary Science Reviews, .
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Bouchet, M., Landais, A., Grisart, A., Parrenin, F., Prié, F., Jacob, R., et al. (2023). The Antarctic Ice Core Chronology 2023 (Aicc2023) Chronological Framework And Associated Timescale For The European Project For Ice Coring In Antarctica (Epica) Dome C Ice Core. Climate Of The Past, 191(111), 2257–2286.
Abstract: The Epica (European Project For Ice Coring In Antarctica) Dome C (Edc) Ice Core Drilling In East Antarctica Reaches A Depth Of 3260 M. The Reference Edc Chronology, The Aicc2012 (Antarctic Ice Core Chronology 2012), Provides An Age Vs. Depth Relationship Covering The Last 800 Kyr (Thousands Of Years), With An Absolute Uncertainty Rising Up To 8000 Years At The Bottom Of The Ice Core. The Origins Of This Relatively Large Uncertainty Are Twofold: (1) The Delta 18 O Atm , Delta O 2 / N 2 And Total Air Content (Tac) Records Are Poorly Resolved And Show Large Gaps Over The Last 800 Kyr, And (2) Large Uncertainties Are Associated With Their Orbital Targets. Here, We Present New Highly Resolved Delta 18 O Atm , Delta O 2 / N 2 And Delta 15 N Measurements For The Edc Ice Core Covering The Last Five Glacial-Interglacial Transitions; A New Low-Resolution Tac Record Over The Period 440-800 Ka Bp (Ka: 1000 Years Before 1950); And Novel Absolute 81 Kr Ages. We Have Compiled Chronological And Glaciological Information Including Novel Orbital Age Markers From New Data On The Edc Ice Core As Well As Accurate Firn Modeling Estimates In A Bayesian Dating Tool To Construct The New Aicc2023 Chronology. For The First Time, Three Orbital Tools Are Used Simultaneously. Hence, It Is Possible To Observe That They Are Consistent With Each Other And With The Other Age Markers Over Most Of The Last 800 Kyr (70 %). This, In Turn, Gives Us Confidence In The New Aicc2023 Chronology. The Average Uncertainty In The Ice Chronology Is Reduced From 1700 To 900 Years In Aicc2023 Over The Last 800 Kyr ( 1 Sigma ). The New Timescale Diverges From Aicc2012 And Suggests Age Shifts Reaching 3800 Years Towards Older Ages Over Marine Isotope Stages (Miss) 5, 11 And 19. But The Coherency Between The New Aicc2023 Timescale And Independent Chronologies Of Other Archives (Italian Lacustrine Succession From Sulmona Basin, Dome Fuji Ice Core And Northern Alpine Speleothems) Is Improved By 1000 To 2000 Years Over These Time Intervals.
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Brun, F., King, O., Reveillet, M., Amory, C., Planchot, A., Berthier, E., et al. (2023). Everest South Col Glacier Did Not Thin During The Period 1984-2017. Cryosphere, 171(8), 3251–3268.
Abstract: The South Col Glacier Is A Small Body Of Ice And Snow (Approx. 0.2 Km(2)) Located At The Very High Elevation Of 8000Ma.S.L. (Above Sea Level) On The Southern Ridge Of Mt. Everest. A Recent Study By Potocki Et Al. (2022) Proposed That South Col Glacier Is Rapidly Losing Mass. This Is In Contradiction To Our Comparison Of Two Digital Elevation Models Derived From Aerial Photographs Taken In December 1984 And A Stereo Pleiades Satellite Acquisition From March 2017, From Which We Estimate A Mean Elevation Change Of 0.01 +/- 0.05M A(-1). To Reconcile These Results, We Investigate Some Aspects Of The Surface Energy And Mass Balance Of South Col Glacier. From Satellite Images And A Simple Model Of Snow Compaction And Erosion, We Show That Wind Erosion Has A Major Impact On The Surface Mass Balance Due To The Strong Seasonality In Precipitation And Wind And That It Cannot Be Neglected. Additionally, We Show That The Melt Amount Predicted By A Surface Energy And Mass Balance Model Is Very Sensitive To The Model Structure And Implementation. Contrary To Previous Findings, Melt Is Likely Not A Dominant Ablation Process On This Glacier, Which Remains Mostly Snow-Covered During The Monsoon.
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Celli, G., Cairns, W., Scarchilli, C., Cuevas, C., Saiz-Lopez, A., Savarino, J., et al. (2023). Bromine, Iodine And Sodium Along The Eaiist Traverse: Bulk And Surface Snow Latitudinal Variability. Environmental Research, 2392.
Abstract: During The East Antarctic International Ice Sheet Traverse (Eaiist, December 2019), In An Unexplored Part Of The East Antarctic Plateau, Snow Samples Were Collected To Expand Our Knowledge Of The Latitudinal Variability Of Iodine, Bromine And Sodium As Well As Their Relation In Connection With Emission Processes And Photochemical Activation In This Unexplored Area. A Total Of 32 Surface (0-5 Cm) And 32 Bulk (Average Of 1 M Depth) Samples Were Taken And Analysed By Inductively Coupled Plasma Mass Spectrometry (Icp-Ms). Our Results Show That There Is No Relevant Latitudinal Trend For Bromine And Sodium. For Bromine They Also Show That It Has No Sig-Nificant Post-Depositional Mechanisms While Its Inland Surface Snow Concentration Is Influenced By Spring Coastal Bromine Explosions. Iodine Concentrations Are Several Orders Of Magnitude Lower Than Bromine And Sodium And They Show A Decreasing Trend In The Surface Samples Concentration Moving Southward. This Suggests That Other Processes Affect Its Accumulation In Surface Snow, Probably Related To The Radial Reduction In The Ozone Layer Moving Towards Central Antarctica. Even Though All Iodine, Bromine And Sodium Present Similar Long-Range Transport From The Dominant Coastal Antarctic Sources, The Annual Seasonal Cycle Of The Ozone Hole Over Antarctica Increases The Amount Of Uv Radiation (In The 280-320 Nm Range) Reaching The Surface, Thereby Affecting The Surface Snow Photoactivation Of Iodine. A Comparison Between The Bulk And Surface Samples Supports The Conclusion That Iodine Undergoes Spring And Summer Snow Recycling That Increases Its Atmospheric Lifetime, While It Tends To Accumulate During The Winter Months When Photochemistry Ceases.
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Chaillot, J., Dasari, S., Fleurbaey, H., Daeron, M., Savarino, J., & Kassi, S. (2023). High-Precision Laser Spectroscopy Of H<Sub>2</Sub>S For Simultaneous Probing Of Multiple-Sulfur Isotopes. Environmental Science-Advances, 2(1), 78–86.
Abstract: The Simultaneous Monitoring Of The Triple Stable S-Isotopes (S-32, S-33 And S-34) Of Hydrogen Sulfide Has Been Conducted With A Vcof-Crds Set-Up (A V-Shaped Cavity For Optical Feedback Coupled To A Cavity Ring Down Spectrometer). The Spectroscopic Investigation Of H2S Was Performed For The First Time In The Near-Infrared Region (Approximate To 1.6 Mu M) With A Stabilized Laser Of Linewidth < 1 Khz And An Optical Pathlength Of 90 Km, Providing Unparalleled Sensitivity And Precision. Pressure Dependencies Of The System Were Explored To As Low As 0.1 Mbar Revealing The Lamb Dip Feature Of The Isotopologue Transitions. A Model Was Developed To Fit Experimental Spectra With Accuracy Better By One Order Of Magnitude Than What The Literature Provides. The S-Isotope Composition Delta S-34 And S-Isotope Anomaly Delta S-33 Are Determined With An Uncertainty Of 5 X 10(-6) Within 10 Seconds, Limited By H2S Reactivity Inside The Measurement Cell. Such High Precision Represents A New Benchmark For Laser Spectroscopy Of H2S And Optical Determination Of Isotopic Measurements And Makes Vcof-Crds A Promising Tool For A Plethora Of Future Applications.
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Chung, A., Parrenin, F., Steinhage, D., Mulvaney, R., Martín, C., Cavitte, M., et al. (2023). Stagnant Ice And Age Modelling In The Dome C Region, Antarctica. Cryosphere, 171(8), 3461–3483.
Abstract: The European Beyond Epica Project Aims To Extract A Continuous Ice Core Of Up To 1.5 Ma, With A Maximum Age Density Of 20 Kyr M(-1) At Little Dome C (Ldc). We Present A 1D Numerical Model Which Calculates The Age Of The Ice Around Dome C. The Model Inverts For Basal Conditions And Accounts Either For Melting Or For A Layer Of Stagnant Ice Above The Bedrock. It Is Constrained By Internal Reflecting Horizons Traced In Radargrams And Dated Using The Epica Dome C (Edc) Ice Core Age Profile. We Used Three Different Radar Datasets Ranging From A 10 000 Km(2) Airborne Survey Down To 5 Km Long Ground-Based Radar Transects Over Ldc. We Find That Stagnant Ice Exists In Many Places, Including Above The Ldc Relief Where The New Beyond Epica Drill Site (Beldc) Is Located. The Modelled Thickness Of This Layer Of Stagnant Ice Roughly Corresponds To The Thickness Of The Basal Unit Observed In One Of The Radar Surveys And In The Autonomous Phase-Sensitive Radio-Echo Sounder (Apres) Dataset. At Beldc, The Modelled Stagnant Ice Thickness Is 198 +/- 44 M And The Modelled Oldest Age Of Ice Is 1.45 +/- 0.16 Ma At A Depth Of 2494 +/- 30 M. This Is Very Similar To All Sites Situated On The Ldc Relief, Including That Of The Million Year Ice Core Project Being Conducted By The Australian Antarctic Division. The Model Was Also Applied To Radar Data In The Area 10-15 Km North Of Edc (North Patch), Where We Find Either A Thin Layer Of Stagnant Ice (Generally <60 M) Or A Negligible Melt Rate (<0.1 Mm Yr(-1)). The Modelled Maximum Age At North Patch Is Over 2 Ma In Most Places, With Ice At 1.5 Ma Having A Resolution Of 9-12 Kyr M(-1), Making It An Exciting Prospect For A Future Oldest Ice Drill Site.
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Dasari, S., Paris, G., Pei, Q., Cong, Z., & Widory, D. (2023). Tracing The Origin Of Elevated Springtime Atmospheric Sulfate On The Southern Himalayan-Tibetan Plateau. Environmental Science-Advances, 2(8), 1110–1118.
Abstract: The Himalayan Tibetan Plateau (Htp) Is One Of The World'S Most Climate-Sensitive Regions Outside The Polar Regions. Here, The Climate-Air Quality-Hydrological Cycle Affecting Sulfate Aerosols Remains Sparsely Investigated, With Their Source Origin(S) Requiring Further Investigation. We Tracked The Evolution Of Sulfur Mass-Independent Isotope Fractionation [S-Mif I.E., Delta S-33 Not Equal 0]-As A Potential Source Tracer-In Springtime Aerosol Sulfate Over The Southern Htp. In A First, At The Southern Htp High-Altitude Receptor Site Qomolangma-Mt. Everest Station, Qoms, Similar To 4300 M A.S.L., Elevated Sulfate Concentrations And S-Mif Were Both Found To Be Associated With Biomass Burning Aerosols (So42- And Delta S-33 Vs. K+: R-2 = 0.92 [P < 0.001] And 0.61[P < 0.005], Respectively). This Is In Stark Contrast To Delta S-33 Aerosol Records From The Central Htp And A Downwind Mountainous Site Wherein Anomalous Sulfur Has Been Linked To Stratospheric Intrusions In The Past, And Geological Lake Records From The Region Which Link The Origin Of Modern Sulfate On The Htp To The Influx Of Mineral Dust, Respectively. The Findings Suggest That There Are Yet Unknown Biomass Combustion-Related Processes (E.G., Crop-Residue And Waste Burning, Wildfires) Plausibly Generating Positive Mif In Sulfur, Which Could Have Implications For Historical S-Isotope Records. Comparing The Triple-S-Isotope Imprint In Aerosol Sulfate On The Htp And Its Surrounding Regions Reveals The Existence Of Spatial Heterogeneity In The Dominance Of Competing Sulfate Transport And Formation Processes With Implications For The Regional Tropospheric Chemical And Radiation Budgets.
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Eichler, A., Legrand, M., Jenk, T., Preunkert, S., Andersson, C., Eckhardt, S., et al. (2023). Consistent Histories Of Anthropogenic Western European Air Pollution Preserved In Different Alpine Ice Cores. Cryosphere, , 211922–213722.
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Erhardt, T., Jensen, C., Adolphi, F., Kjær, H., Dallmayr, R., Twarloh, B., et al. (2023). High-Resolution Aerosol Data From The Top 3.8 Kyr Of The East Greenland Ice Coring Project (Egrip) Ice Core. Earth System Science Data, 151(111), 5079–5091.
Abstract: Here We Present The High-Resolution Continuous Flow Analysis (Cfa) Data From The Top 479 M Of The East Greenland Ice Coring Project (Egrip) Ice Core Covering The Past 3.8 Kyr. The Data Consist Of 1 Mm Depth-Resolution Profiles Of Calcium, Sodium, Ammonium, Nitrate, And Electrolytic Conductivity As Well As Decadal Averages Of These Profiles. The Nominally 1 Mm Data Represent An Oversampling Of The Record As The True Resolution Is Limited By The Analytical Setup To Approximately 1 Cm. Alongside The Data We Provide A Description Of The Measurement Setup, Procedures, The Relevant References For The Specific Methods As Well As An Assessment Of The Precision Of The Measurements, The Sample-To-Depth Assignment, And The Depth And Temporal Resolution Of The Data Set. The Error In Absolute Depth Assignment Of The Data May Be On The Order Of 2 Cm; However, Relative Depth Offsets Between The Records Of The Individual Species Are Only On The Order Of 1 Mm. The Presented Data Have Sub-Annual Resolution Over The Entire Depth Range And Have Already Formed Part Of The Data For An Annually Layer-Counted Timescale For The Egrip Ice Core Used To Improve And Revise The Multi-Core Greenland Ice-Core Chronology (Gicc05) To A New Version, Gicc21 (Sinnl Et Al., 2022). The Data Are Available In Full 1 Mm Resolution And Decadal Averages On Pangaea (Https://Doi.Org/10.1594/Pangaea.945293, Erhardt Et Al., 2022B).
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Faïn, X., Etheridge, D., Fourteau, K., Martinerie, P., Trudinger, C., Rhodes, R., et al. (2023). Southern Hemisphere Atmospheric History Of Carbon Monoxide Over The Late Holocene Reconstructed From Multiple Antarctic Ice Archives. Climate Of The Past, 191(111), 2287–2311.
Abstract: Carbon Monoxide (Co) Is A Naturally Occurring Atmospheric Trace Gas, A Regulated Pollutant, And One Of The Main Components Determining The Oxidative Capacity Of The Atmosphere. Evaluating Climate-Chemistry Models Under Different Conditions Than Today And Constraining Past Co Sources Requires A Reliable Record Of Atmospheric Co Mixing Ratios ([Co]) That Includes Data Since Preindustrial Times. Here, We Report The First Continuous Record Of Atmospheric [Co] For Southern Hemisphere (Sh) High Latitudes Over The Past 3 Millennia. Our Continuous Record Is A Composite Of Three High-Resolution Antarctic Ice Core Gas Records And Firn Air Measurements From Seven Antarctic Locations. The Ice Core Gas [Co] Records Were Measured By Continuous Flow Analysis (Cfa), Using An Optical Feedback Cavity-Enhanced Absorption Spectrometer (Of-Ceas), Achieving Excellent External Precision (2.8-8.8 Ppb; 2 Sigma ) And Consistently Low Blanks (Ranging From 4.1 +/- 1.2 To 7.4 +/- 1.4 Ppb), Thus Enabling Paleo-Atmospheric Interpretations. Six New Firn Air [Co] Antarctic Datasets Collected Between 1993 And 2016 Ce At The De08-2, Dssw19K, Dssw20K, South Pole, Aurora Basin North (Abn), And Lock-In Sites (And One Previously Published Firn Co Dataset At Berkner) Were Used To Reconstruct The Atmospheric History Of Co From Similar To 1897 Ce, Using Inverse Modeling That Incorporates The Influence Of Gas Transport In Firn. Excellent Consistency Was Observed Between The Youngest Ice Core Gas [Co] And The [Co] From The Base Of The Firn And Between The Recent Firn [Co] And Atmospheric [Co] Measurements At Mawson Station (Eastern Antarctica), Yielding A Consistent And Contiguous Record Of Co Across These Different Archives. Our Antarctic [Co] Record Is Relatively Stable From – 835 To 1500 Ce, With Mixing Ratios Within A 30-45 Ppb Range (2 Sigma ). There Is A Similar To 5 Ppb Decrease In [Co] To A Minimum At Around 1700 Ce During The Little Ice Age. Co Mixing Ratios Then Increase Over Time To Reach A Maximum Of Similar To 54 Ppb By Similar To 1985 Ce. Most Of The Industrial Period [Co] Growth Occurred Between About 1940 To 1985 Ce, After Which There Was An Overall [Co] Decrease, As Observed In Greenland Firn Air And Later At Atmospheric Monitoring Sites And Attributed Partly To Reduced Co Emissions From Combustion Sources. Our Antarctic Ice Core Gas Co Observations Differ From Previously Published Records In Two Key Aspects. First, Our Mixing Ratios Are Significantly Lower Than Reported Previously, Suggesting That Previous Studies Underestimated Blank Contributions. Second, Our New Co Record Does Not Show A Maximum In The Late 1800S. The Absence Of A [Co] Peak Around The Turn Of The Century Argues Against There Being A Peak In Southern Hemisphere Biomass Burning At This Time, Which Is In Agreement With (I) Other Paleofire Proxies Such As Ethane Or Acetylene And (Ii) Conclusions Reached By Paleofire Modeling. The Combined Ice Core And Firn Air [Co] History, Spanning – 835 To 1992 Ce, Extended To The Present By The Mawson Atmospheric Record, Provides A Useful Benchmark For Future Atmospheric Chemistry Modeling Studies.
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Grilli, R., Delsontro, T., Garnier, J., Jacob, F., & Nemery, J. (2023). A Novel High-Resolution In Situ Tool For Studying Carbon Biogeochemical Processes In Aquatic Systems: The Lake Aiguebelette Case Study. Journal Of Geophysical Research-Biogeosciences, 1281(121).
Abstract: Lakes And Reservoirs Are A Significant Source Of Atmospheric Methane (Ch4), With Emissions Comparable To The Largest Global Ch4 Emitters. Understanding The Processes Leading To Such Significant Emissions From Aquatic Systems Is Therefore Of Primary Importance For Producing Accurate Projections Of Emissions In A Changing Climate. In This Work, We Present The First Deployment Of A Novel Membrane Inlet Laser Spectrometer (Mils) For Fast Simultaneous Detection Of Dissolved Ch4, Ethane (C2H6) And The Stable Carbon Isotope Of Methane (Delta 13Ch4). During A 1-Day Field Campaign, We Performed 2D Mapping Of Surface Water Of Lake Aiguebelette (France). Average Dissolved Ch4 Concentrations And Delta 13Ch4 Were 391.9 +/- 156.3 Nmol L-1 And -67.3 +/- 3.4 Parts Per Thousand In The Littoral Area And 169.8 +/- 26.6 Nmol L-1 And -61.5 +/- 3.6 Parts Per Thousand In The Pelagic Area. The Dissolved Ch4 Concentration In The Pelagic Zone Was 50 Times Larger Than The Concentration Expected At Equilibrium With The Atmosphere, Confirming An Oversaturation Of Dissolved Ch4 In Surface Waters Over Shallow And Deep Areas. The Results Suggest The Presence Of Ch4 Sources Less Enriched In 13C In The Littoral Zone (Presumably The Littoral Sediments). The Ch4 Pool Became More Enriched In 13C With Distance From Shore, Suggesting That Oxidation Prevailed Over Epilimnetic Ch4 Production And It Was Further Confirmed By An Isotopic Mass Balance Technique With The High-Resolution Data. This New In Situ Fast Response Sensor Allows One To Obtain Unique High-Resolution And High-Spatial Coverage Data Sets Within A Limited Amount Of Survey Time. This Tool Will Be Useful In The Future For Studying Processes Governing Ch4 Dynamics In Aquatic Systems. High-Resolution Mapping Of Surface Methane And Its Isotopic Signature Enables Accurate Characterization Of Aquatic Systems And Discrimination Of Biochemical Processes At Work. At Lake Aiguebelette, This New In Situ Tool Allowed Us To Conclude That Methane Present At The Surface Comes Mainly From Shallow Littoral Areas, Where Sediments, Which Are A Source Of Methane, Are Closer To The Surface. During Lateral Transport Of Water Masses From The Littoral Zone, The Change In Isotopic Signature Reveals That Methane Oxidation Prevails Over Local In Situ Production. Comparison With Previous Studies Validates The Importance Of High-Resolution Measurements (Particularly To Capture The High Variability In The Littoral Zone) And Showed That Smaller Lakes Experience Stronger Methane Isotopic Signature Changes For A Given Methane Concentration Variation. This Can Be Explained By The Fact That The Smaller Lake Has A Larger Littoral-To-Total Surface Area. This New Tool Will Be Useful In The Nearby Future To Study The Processes Governing Ch4 Dynamics In Aquatic Systems. Fast In Situ Measurements Of Dissolved Methane And Its Stable Carbon Isotopehigh-Spatial Resolution Mapping Of Dissolved Methane And Its Stable Carbon Isotopeimproved Production/Oxidation Process Identification Over Discrete Sampling
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Heintzenberg, J., Legrand, M., Gao, Y., Hara, K., Huang, S., Humphries, R., et al. (2023). Spatio-Temporal Distributions Of The Natural Non-Sea-Salt Aerosol Over The Southern Ocean And Coastal Antarctica And Its Potential Source Regions. Tellus Series B-Chemical And Physical Meteorology, 757(1).
Abstract: More Than 40 Years Of Aerosol Data Including Concentrations Of Particle Number And Of Nine Major Ions Collected Over The Southern Ocean And Coastal Stations Have Been Aggregated And Filtered With Back Trajectories To Reduce The Risk Of Influence From Adjacent Continents. That Provided A Rich Dataset Including Latitudinal Distribution And Seasonality Of Physical And Chemical Aerosol Parameters That Allow Insights Into Aerosol Sources Over The Southern Ocean. These Data Together With Statistics Of Back Trajectory Paths Of High (75% Percentile) And Low (25% Percentile) Concentrations Of The Studied Aerosol Parameters Were Used To Identify Potential Source Regions Of The Respective Compounds. For Particle Number Concentrations, Msa, And The Non-Sea-Salt Fractions Of Ca And Potassium The Most Prominent Source Regions Were Found In High Dms-Areas Close To Antarctica, Whereas The Potential Source Regions Of Nh4 And The Non-Sea-Salt Fraction Of Mg Were Located In Part Further North Over The Southern Ocean. These Geographical Differences Would Reflect Differences In The Marine Biota.
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Jourdain, B., Vincent, C., Réveillet, M., Rabatel, A., Brun, F., Six, D., et al. (2023). A Method To Estimate Surface Mass-Balance In Glacier Accumulation Areas Based On Digital Elevation Models And Submergence Velocities. Journal Of Glaciology, 696(2772), 1403–1418.
Abstract: Measuring Surface Mass-Balance In The Accumulation Areas Of Glaciers Is Challenging Because Of The High Spatial Variability Of Snow Accumulation And The Difficulty Of Conducting Annual Field Glaciological Measurements. Here, We Propose A Method That Can Solve Both These Problems For Many Locations. Ground-Penetrating Radar Measurements And Firn Cores Extracted From A Site In The French Alps Were First Used To Reconstruct The Topography Of A Buried End-Of-Summer Snow Horizon From A Past Year. Using These Data And Surface Elevation Observations From Lidar And Global Navigation Satellite System Instruments, We Calculated The Submergence Velocities Over The Period Between The Buried Horizon And More Recent Surface Elevation Observations. The Differences Between The Changes In Surface Elevation And The Submergence Velocities Were Then Used To Calculate The Annual Surface Mass-Balances With An Accuracy Of +/- 0.34 M W.E. Assuming That The Submergence Velocities Remain Stable Over Several Years, The Surface Mass-Balance Can Be Reconstructed For Subsequent Years From The Differences In Surface Elevation Alone. As Opposed To The Glaciological Method That Requires Substantial Fieldwork Year After Year To Provide Only Point Observations, This Method, Once Submergence Velocities Have Been Calculated, Requires Only Remote-Sensing Data To Provide Spatially Distributed Annual Mass-Balances In Accumulation Areas.
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Lamothe, A., Savarino, J., Ginot, P., Soussaintjean, L., Gautier, E., Akers, P., et al. (2023). An Extraction Method For Nitrogen Isotope Measurement Of Ammonium In Alow-Concentration Environment. Atmospheric Measurement Techniques, 161(171), 4015–4030.
Abstract: Ammonia (Nh3) Participates In The Nucleation And Growth Of Aerosols And Thus Plays A Major Role In Atmospheric Transparency, Pollution, Health, And Climate-Related Issues. Understanding Its Emission Sources Through Nitrogen Stable Isotopes Is Therefore A Major Focus Of Current Work To Mitigate The Adverse Effects Of Aerosol Formation. Since Ice Cores Can Preserve The Past Chemical Composition Of The Atmosphere For Centuries, They Are A Top Tool Of Choice For Understanding Past Nh3 Emissions Through Ammonium (Nh4+), The Form Of Nh3 Archived In Ice. However, The Remote Or High-Altitude Sites Where Glaciers And Ice Sheets Are Typically Localized Have Relatively Low Fluxes Of Atmospheric Nh4+ Deposition, Which Makes Ice Core Samples Very Sensitive To Laboratory Nh3 Contamination. As A Result, Accurate Techniques For Identifying And Tracking Nh3 Emissions Through Concentration And Isotopic Measurements Are Highly Sought To Constrain Uncertainties In Nh3 Emission Inventories And Atmospheric Reactivity Unknowns. Here, We Describe A Solid-Phase Extraction Method For Nh4+ Samples Of Low Concentration That Limits External Contamination And Produces Precise Isotopic Results. By Limiting Nh3Atm Exposure With A Scavenging Fume Hood And Concentrating The Targeted Nh4+ Through Ion Exchange Resin, We Successfully Achieve Isotopic Analysis Of 50 Nmol Nh4+ Samples With A 0.6 Parts Per Thousand Standard Deviation. This Extraction Method Is Applied To An Alpine Glacier Ice Core From Col Du Dome, Mont Blanc, Where We Successfully Demonstrate The Analytical Approach Through The Analysis Of Two Replicate 8 M Water Equivalent Ice Cores Representing 4 Years Of Accumulation With A Reproducibility Of +/- 2.1 Parts Per Thousand. Applying This Methodology To Other Ice Cores In Alpine And Polar Environments Will Open New Opportunities For Understanding Past Changes In Nh3 Emissions And Atmospheric Chemistry.
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Legrain, E., Blard, P., Kageyama, M., Charreau, J., Leduc, G., Bourdin, S., et al. (2023). Moisture Amplification Of The High-Altitude Deglacial Warming. Quaternary Science Reviews, 3183.
Abstract: In Response To Anthropogenic Warming, Glaciers Are Shrinking Almost Everywhere, Endangering Water Accessibility In Areas Located Downstream. Glacier Fluctuations Are At First Order Controlled By Local Precipitation And Temperature, But Large Uncertainties Persist On The Potential Role Of Local Moisture In Amplifying Or Dampening Temperature Changes At High-Elevation. Here, We Combine Glacier Extents And Sea Surface Temperature (Sst) During The Last Glacial Maximum (Lgm) To Quantify Altitudinal Thermal Gradients (Lapse Rate) From 40N To 40S Along The American Cordillera. We Also Constrain Modern Lapse Rates Based On Present Day Temperature And Sst Database To Explore How The Lapse Rate Has Changed Since The Lgm Along This North South Transect. Based On Proxy-Based Quantitative Paleo-Precipitation Estimations Above 2000 M, We Investigate How These Lapse Rate Changes Compare With Moisture Modifications Around The Cordillera And Discuss The Mechanisms That Potentially Controlled Lapse Rate Changes During The Post-Lgm Deglacial Warming. We Find That Lapse Rate Changes Are Linearly Related To Changes In Precipitation And Derive A Quantitative Relationship Between These Two Parameters. To Further Explore The Processes Involved In Controlling Lapse Rate Variations, We Use The Ipsl Global Climate Model Outputs, For The Lgm And Pre-Industrial States In This Region. The Ipsl Model Also Yields A Shallower Modern Lapse Rate In The Wetter Tropical Region, Confirming The Observed Correlation Between Precipitation Changes And Lapse Rate Variations. The Ipsl Model Also Supports A Close Coupling Of Continental Relative Moisture And Mean Annual Precipitation In The Studied Area, Indicating That Moisture Is Involved In The Precipitation – Lapse Rate Relationship. Our Results Suggest That Future Warming May Be Enhanced In High Altitude Regions Where Precipitation Is Expected To Increase. Using Our Most Reliable Relationship Linking Precipitation And Lapse Rate Changes, We Conclude That, Assuming A 1 C-Degrees Warming At Sea Level, A Mean Annual Precipitation Increases Of 500 Mm.A(-1) Could Lead To A Warming Amplification Of 4.1 +/- 0.8 C At 4000 M Asl (Mean Elevation Of Modern Glaciers). In This Case, A 2 C-Degrees Warming At Sea Level Would Yield >6 C Degrees Warming At 4000 M Asl. This Study Therefore Confirms That Special Attention Should Be Given To The Climate Projections Of Glacier Melting In Tropical And Mid Latitude Regions.
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Legrain, E., Parrenin, F., & Capron, E. (2023). A Gradual Change Is More Likely To Have Caused The Mid-Pleistocene Transition Than An Abrupt Event. Communications Earth & Environment, .
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Legrand, M., Mcconnell, J., Bergametti, G., Plach, A., Desboeufs, K., Chellman, N., et al. (2023). A Two-Fold Increase Of Phosphorus In Alpine Ice Over The Twentieth Century: Contributions From Dust, Primary Biogenic Emissions, Coal Burning, And Pig Iron Production. Journal Of Geophysical Research-Atmospheres, 1281(191).
Abstract: Phosphorus (P) Is A Key Nutrient For Many Organisms But Its Global Atmospheric Budget Is Largely Unconstrained. Estimates Of Major Emissions Sources Such As Fossil-Fuel Combustion Range From Similar To 0.02 To 1.1 Tg Yr-1, And Primary Biogenic Emissions Range From 0.16 To 1.0 Tg Yr-1. Here We Used Detailed Measurements Of Phosphorus In Alpine Ice Cores Extracted From The Col Du Dome (Cdd) Glacier Located Near The Mont Blanc Summit And Atmospheric Model Simulations To Evaluate Changes In Western European Emissions From Pre-Industrial (Pi) To Modern Times. The Ice-Core Records Show That P Concentrations During The Pi Were About 0.9 Ng G-1, Of Which One Third Was Of Crustal Origin And Two Thirds The Result Of Primary Biogenic Emissions. Concentrations Were Higher Throughout The 20Th Century, Reaching 2.5 Ng G-1 In The 1980S. Analysis Of Source Tracers Measured In The Same Ice, Commodity Productions Statistics, And Other Information Suggest That The Increase In P Throughout The 20Th Century Was Caused By Enhanced Emissions From Natural And Anthropogenic Sources. Coal Burning And Steel Industry Represented The Main Anthropogenic Sources During The First And Second Half Of The Century, Respectively. After 1950, The Increase In P Was Also Caused By Enhanced Dust Emissions, With Increased Biogenic Emissions Caused By Recent Changes Of Use-Land Also Contributing. These Findings Provide Important Constraints On The Atmospheric P Budget At The Scale Of Western Europe During The Recent Centuries. Phosphorus Is An Important Nutrient For Terrestrial And Aquatic Flora And Fauna. Whereas Dust Aerosol Emissions Are The Dominant Atmospheric Source Of Phosphorus On A Global Scale, Other Sources Such As Biogenic Particles Emitted By Vegetation, As Well As Fossil-Fuel Combustion, May Represent Important Sources In Less-Dusty Industrialized Regions. Estimates Of These Non-Crustal Sources Are Uncertain, However, With Values Often Varying By An Order Of Magnitude Or More. Comparison With Long-Term Pollution Records Extracted From Well-Dated Ice Cores Provides A Means Of Evaluating These Estimates. Here, We Analyzed Phosphorus In Ice Cores Extracted Near The Mont Blanc Summit In The French Alps To Develop An 1850 To 2000 Record. Phosphorus Deposition Doubled During This Period, With Increases Attributed To Enhancement Of Both Natural (Dust And Biogenic Particles Emitted By Vegetation) And Anthropogenic (Mainly Coal Burning And The Steel Industry) Emissions. A Doubling Of Phosphorus In Alpine Ice Deposited Between 1850 And 2000 From Increasing Natural And Anthropogenic Emissionsphosphorus Deposition Trends From 1900 To 1975 Mainly Attributed To Coal Burning And Pig Iron Industry Emissionsnatural European Phosphorus Sources Dominated By Primary Emissions Of Biogenic (70%) And Dust (30%) Particles That Were Enhanced After 1975
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Legrand, M., Mcconnell, J., Bergametti, G., Plach, A., Desboeufs, K., Chellman, N., et al. (2023). A Two-Fold Increase Of Phosphorus In Alpine Ice Over The Twentieth Century: Contributions From Dust, Primary Biogenic Emissions, Coal Burning, And Pig Iron Production. Journal Of Geophysical Research-Atmospheres, 1281(191).
Abstract: Phosphorus (P) Is A Key Nutrient For Many Organisms But Its Global Atmospheric Budget Is Largely Unconstrained. Estimates Of Major Emissions Sources Such As Fossil-Fuel Combustion Range From Similar To 0.02 To 1.1 Tg Yr(-1), And Primary Biogenic Emissions Range From 0.16 To 1.0 Tg Yr(-1). Here We Used Detailed Measurements Of Phosphorus In Alpine Ice Cores Extracted From The Col Du D & Ocirc;Me (Cdd) Glacier Located Near The Mont Blanc Summit And Atmospheric Model Simulations To Evaluate Changes In Western European Emissions From Pre-Industrial (Pi) To Modern Times. The Ice-Core Records Show That P Concentrations During The Pi Were About 0.9 Ng G(-1), Of Which One Third Was Of Crustal Origin And Two Thirds The Result Of Primary Biogenic Emissions. Concentrations Were Higher Throughout The 20Th Century, Reaching 2.5 Ng G(-1) In The 1980S. Analysis Of Source Tracers Measured In The Same Ice, Commodity Productions Statistics, And Other Information Suggest That The Increase In P Throughout The 20Th Century Was Caused By Enhanced Emissions From Natural And Anthropogenic Sources. Coal Burning And Steel Industry Represented The Main Anthropogenic Sources During The First And Second Half Of The Century, Respectively. After 1950, The Increase In P Was Also Caused By Enhanced Dust Emissions, With Increased Biogenic Emissions Caused By Recent Changes Of Use-Land Also Contributing. These Findings Provide Important Constraints On The Atmospheric P Budget At The Scale Of Western Europe During The Recent Centuries.
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Legrand, M., Mcconnell, J., Bergametti, G., Plach, A., Desboeufs, K., Chellman, N., et al. (2023). A Two-Fold Increase Of Phosphorus In Alpine Ice Over The Twentieth Century: Contributions From Dust, Primary Biogenic Emissions, Coal Burning, And Pig Iron Production. Journal Of Geophysical Research-Atmospheres, 1281(191).
Abstract: Phosphorus (P) Is A Key Nutrient For Many Organisms But Its Global Atmospheric Budget Is Largely Unconstrained. Estimates Of Major Emissions Sources Such As Fossil-Fuel Combustion Range From Similar To 0.02 To 1.1 Tg Yr(-1), And Primary Biogenic Emissions Range From 0.16 To 1.0 Tg Yr(-1). Here We Used Detailed Measurements Of Phosphorus In Alpine Ice Cores Extracted From The Col Du D & Ocirc;Me (Cdd) Glacier Located Near The Mont Blanc Summit And Atmospheric Model Simulations To Evaluate Changes In Western European Emissions From Pre-Industrial (Pi) To Modern Times. The Ice-Core Records Show That P Concentrations During The Pi Were About 0.9 Ng G(-1), Of Which One Third Was Of Crustal Origin And Two Thirds The Result Of Primary Biogenic Emissions. Concentrations Were Higher Throughout The 20Th Century, Reaching 2.5 Ng G(-1) In The 1980S. Analysis Of Source Tracers Measured In The Same Ice, Commodity Productions Statistics, And Other Information Suggest That The Increase In P Throughout The 20Th Century Was Caused By Enhanced Emissions From Natural And Anthropogenic Sources. Coal Burning And Steel Industry Represented The Main Anthropogenic Sources During The First And Second Half Of The Century, Respectively. After 1950, The Increase In P Was Also Caused By Enhanced Dust Emissions, With Increased Biogenic Emissions Caused By Recent Changes Of Use-Land Also Contributing. These Findings Provide Important Constraints On The Atmospheric P Budget At The Scale Of Western Europe During The Recent Centuries.
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Legrand, M., Mcconnell, J., Bergametti, G., Preunkert, S., Chellman, N., Desboeufs, K., et al. (2023). Alpine-Ice Record Of Bismuth Pollution Implies A Major Role Of Military Use During World War Ii. Scientific Reports, .
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Mardoñez, V., Pandolfi, M., Borlaza, L., Jaffrezo, J., Alastuey, A., Besombes, J., et al. (2023). Source Apportionment Study On Particulate Air Pollution In Two High-Altitude Bolivian Cities: La Paz And El Alto. Atmospheric Chemistry And Physics, 232(181), 10325–10347.
Abstract: La Paz And El Alto Are Two Fast-Growing, High-Altitude Bolivian Cities Forming The Second-Largest Metropolitan Area In The Country. Located Between 3200 And 4050 M A.S.L. (Above Sea Level), These Cities Are Home To A Burgeoning Population Of Approximately 1.8 Million Residents. The Air Quality In This Conurbation Is Heavily Influenced By Urbanization; However, There Are No Comprehensive Studies Evaluating The Sources Of Air Pollution And Their Health Impacts. Despite Their Proximity, The Substantial Variation In Altitude, Topography, And Socioeconomic Activities Between La Paz And El Alto Result In Distinct Sources, Dynamics, And Transport Of Particulate Matter (Pm). In This Investigation, Pm10 Samples Were Collected At Two Urban Background Stations Located In La Paz And El Alto Between April 2016 And June 2017. The Samples Were Later Analyzed For A Wide Range Of Chemical Species Including Numerous Source Tracers (Oc, Ec, Water-Soluble Ions, Sugar Anhydrides, Sugar Alcohols, Trace Metals, And Molecular Organic Species). The United States Environmental Protection Agency (U.S. Epa) Positive Matrix Factorization (Pmf V.5.0) Receptor Model Was Employed For The Source Apportionment Of Pm10. This Is One Of The First Source Apportionment Studies In South America That Incorporates An Extensive Suite Of Organic Markers, Including Levoglucosan, Polycyclic Aromatic Hydrocarbons (Pahs), Hopanes, And Alkanes, Alongside Inorganic Species. The Multisite Pmf Resolved 11 Main Sources Of Pm. The Largest Annual Contribution To Pm10 Came From The Following Two Major Sources: The Ensemble Of The Four Vehicular Emissions Sources (Exhaust And Non-Exhaust), Accountable For 35 % And 25 % Of The Measured Pm In La Paz And El Alto, Respectively; And Dust, Which Contributed 20 % And 32 % To The Total Pm Mass. Secondary Aerosols Accounted For 22 % (24 %) In La Paz (El Alto). Agricultural Smoke Resulting From Biomass Burning In The Bolivian Lowlands And Neighboring Countries Contributed To 9 % (8 %) Of The Total Pm10 Mass Annually, Increasing To 17 % (13 %) Between August-October. Primary Biogenic Emissions Were Responsible For 13 % (7 %) Of The Measured Pm10 Mass. Additionally, A Profile Associated With Open Waste Burning Occurring From May To August Was Identified. Although This Source Contributed Only To 2 % (5 %) Of The Total Pm10 Mass, It Constitutes The Second Largest Source Of Pahs, Which Are Compounds Potentially Hazardous To Human Health. Our Analysis Additionally Resolved Two Different Traffic-Related Factors, A Lubricant Source (Not Frequently Identified), And A Non-Exhaust Emissions Source. Overall, This Study Demonstrates That Pm10 Concentrations In La Paz And El Alto Region Are Predominantly Influenced By A Limited Number Of Local Sources. In Conclusion, To Improve Air Quality In Both Cities, Efforts Should Primarily Focus On Addressing Dust, Traffic Emissions, Open Waste Burning, And Biomass Burning.
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Marsal, A., Slama, R., Lyon-Caen, S., Borlaza, L., Jaffrezo, J., Boudier, A., et al. (2023). Prenatal Exposure To Pm2.5 Oxidative Potential And Lung Function In Infants And Preschool- Age Children: A Prospective Study. Environmental Health Perspectives, 1311(1).
Abstract: Background: Fine Particulate Matter (Pm2.5) Has Been Found To Be Detrimental To Respiratory Health Of Children, But Few Studies Have Examined The Effects Of Prenatal Pm2.5 Oxidative Potential (Op) On Lung Function In Infants And Preschool Children.Objectives: We Estimated The Associations Of Personal Exposure To Pm2.5 And Op During Pregnancy On Offspring Objective Lung Function Parameters And Compared The Strengths Of Associations Between Both Exposure Metrics.Methods: We Used Data From 356 Mother-Child Pairs From The Sepages Cohort. Pm Filters Collected Twice During A Week Were Analyzed For Op, Using The Dithiothreitol (Dtt) And The Ascorbic Acid (Aa) Assays, Quantifying The Exposure Of Each Pregnant Woman. Lung Function Was Assessed With Tidal Breathing Analysis (Tbfvl) And Nitrogen Multiple-Breath Washout (N2Mbw) Test, Performed At 6 Wk, And Airwave Oscillometry (Aos) Performed At 3 Y. Associations Of Prenatal Pm2.5 Mass And Op With Lung Function Parameters Were Estimated Using Multiple Linear Regressions.Results: In Neonates, An Interquartile (Iqr) Increase In Opdttv (0.89 Nmol/Min/M3) Was Associated With A Decrease In Functional Residual Capacity (Frc) Measured Byn2Mbw [Beta = – 2.26 Ml; 95% Confidence Interval (Ci): -4.68, 0.15]. Associations With Pm2.5 Showed Similar Patterns In Comparison With Opdtt V But Of Smaller Magnitude. Lung Clearance Index (Lci) And Tbfvl Parameters Did Not Show Any Clear Association With The Exposures Considered. At 3 Y, Increased Frequency-Dependent Resistance Of The Lungs (Rrs7-19) From Aos Tended To Be Associated With Higher Opdtt V (Beta = 0.09 Hpa X S/L; 95% Ci: -0.06, 0.24) And Opaav (Iqr =1.14 Nmol/Min/M3; Beta = 0.12 Hpa X S/L; 95% Ci: -0.04, 0.27) But Not With Pm2.5 (Iqr = 6.9 Mu G/M3; Beta = 0.02 Hpa X S/L; 95% Ci: -0.13, 0.16). Results For Frc And Rrs7-19 Remained Similar In Op Models Adjusted On Pm2.5.Discussion: Prenatal Exposure To Opdtt V Was Associated With Several Offspring Lung Function Parameters Over Time, All Related To Lung Volumes. Https://Doi.Org/10.1289/Ehp11155
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Mulvaney, R., Wolff, E., Grieman, M., Hoffmann, H., Humby, J., Nehrbass-Ahles, C., et al. (2023). The St22 Chronology For The Skytrain Ice Rise Ice Core – Part 2: An Age Model To The Last Interglacial And Disturbed Deep Stratigraphy. Climate Of The Past, , 85188–86488.
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Neubauer, C., Kantnerova, K., Lamothe, A., Savarino, J., Hilkert, A., Juchelka, D., et al. (2023). Discovering Nature?S Fingerprints: Isotope Ratio Analysis On Bioanalytical Mass Spectrometers. Journal Of The American Society For Mass Spectrometry, 343(4), 525–537.
Abstract: For A Generation Or More, The Mass Spectrometry That Developed At The Frontier Of Molecular Biology Was Worlds Apart From Isotope Ratio Mass Spectrometry, A Label-Free Approach Done On Optimized Gas-Source Magnetic Sector Instruments. Recent Studies Show That Electrospray-Ionization Orbitraps And Other Mass Spectrom-Eters Widely Used In The Life Sciences Can Be Fine-Tuned For High-Precision Isotope Ratio Analysis. Since Isotope Patterns Form Everywhere In Nature Based On Well-Understood Principles, Intramolecula R Isotope Measure-Ments Allow Unique Insights Into A Fascinating Range Of Research Topics. This Perspective Introduces A Wider Readership To Current Topics In Stable Isotope Research With The Aim Of Discussing How Soft-Ionization Mass Spectrometry Coupled With Ultrahigh Mass Resolution Can Enable Long-Envisioned Progress. We Highlight Novel Prospects Of Observing Isotopes In Intact Polar Compounds And Speculate On Future Directions Of This Adventure Into The Overlapping Realms Of Biology, Chemistry, And Geology.
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Oyabu, I., Kawamura, K., Fujita, S., Inoue, R., Motoyama, H., Fukui, K., et al. (2023). Temporal Variations Of Surface Mass Balance Over The Last 5000 Years Around Dome Fuji, Dronning Maud Land, East Antarctica. Climate Of The Past, 191(2), 293–321.
Abstract: We Reconstructed Surface Mass Balance (Smb) Around Dome Fuji, Antarctica, Over The Last 5000 Years Using The Data From 15 Shallow Ice Cores And Seven Snow Pits. The Depth-Age Relationships For The Ice Cores Were Determined By Synchronizing Them With A Layer-Counted Ice Core From West Antarctica (Wais Divide Ice Core) Using Volcanic Signals. The Reconstructed Smb Records For The Last 4000 Years Show Spatial Patterns That May Be Affected By Their Locations Relative To The Ice Divides Around Dome Fuji, Proximity To The Ocean, And Wind Direction. The Smb Records From The Individual Ice Cores And Snow Pits Were Stacked To Reconstruct The Smb History In The Dome Fuji Area. The Stacked Record Exhibits A Long-Term Decreasing Trend At -0.037 +/- 0.005 Kg M(-2) Per Century Over The Last 5000 Years In The Preindustrial Period. The Decreasing Trend May Be The Result Of Long-Term Surface Cooling Over East Antarctica And The Southern Ocean And Sea Ice Expansion In The Water Vapor Source Areas. The Multidecadal To Centennial Variations Of The Dome Fuji Smb After Detrending The Record Shows Four Distinct Periods During The Last Millennium: A Mostly Negative Period Before 1300 Ce, A Slightly Positive Period From 1300 To 1450 Ce, A Slightly Negative Period From 1450 To 1850 Ce With A Weak Maximum Around 1600 Ce, And A Strong Increase After 1850 Ce. These Variations Are Consistent With Those Of Previously Reconstructed Smb Records In The East Antarctic Plateau. The Low Accumulation Rate Periods Tend To Coincide With The Combination Of Strong Volcanic Forcings And Solar Minima For The Last 1000 Years, But The Correspondence Is Not Clear For The Older Periods, Possibly Because Of The Lack Of Coincidence Of Volcanic And Solar Forcings Or The Deterioration Of The Smb Record Due To A Smaller Number Of Stacked Cores.
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Ravanel, L., Guillet, G., Kaushik, S., Preunkert, S., Malet, E., Magnin, F., et al. (2023). Ice Aprons On Steep High-Alpine Slopes: Insights From The Mont-Blanc Massif, Western Alps. Journal Of Glaciology, .
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Servettaz, A., Orsi, A., Curran, M., Moy, A., Landais, A., Mcconnell, J., et al. (2023). A 2000-Year Temperature Reconstruction On The East Antarctic Plateau From Argon-Nitrogen And Water Stable Isotopes In The Aurora Basin North Ice Core. Climate Of The Past, , 112511–115211.
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Wang, Z., Chung, A., Steinhage, D., Parrenin, F., Freitag, J., & Eisen, O. (2023). Mapping Age And Basal Conditions Of Ice In The Dome Fuji Region, Antarctica, By Combining Radar Internal Layer Stratigraphy And Flow Modeling. Cryosphere, 171(101), 4297–4314.
Abstract: The Dome Fuji (Df) Region In Antarctica Is A Potential Site For An Ice Core With A Record Of Over 1 Myr. Here, We Combine Large-Scale Internal Airborne Radar Stratigraphy With A 1-D Model To Estimate The Age Of Basal Ice In The Df Region. The Radar Data Used In The Study Were Collected In A Survey During The 2016-2017 Antarctic Season. We Transfer The Latest Age-Depth Scales From The Df Ice Core To Isochrones Traced In Radargrams In The Surrounding 500 Km X 550 Km Region. At Each Point Of The Survey The 1-D Model Uses The Ages Of Isochrones To Construct The Age-Depth Scale At Depths Where Dated Isochrones Do Not Exist, The Surface Accumulation Rate And The Basal Thermal Condition, Including Melt Rate And The Thickness Of Stagnant Ice. Our Resulting Age Distribution And Age Density Suggest That Several Promising Sites With Ice Older Than 1.5 Myr In The Df Region Might Exist. The Deduced Melt Rates And Presence Of Stagnant Ice Provide More Constraints For Locating Sites With A Cold Base. The Accumulation Rates Range From 0.015 To 0.038 M A-1 Ice Equivalent. Based On Sensitivity Studies We Find That The Number And Depth Of Picked Isochrones And The Timescale Of The Ice Core Severely Affect The Model Results. Our Study Demonstrates That Constraints From Deep Radar Isochrones And A Trustworthy Timescale Could Improve The Model Estimation To Find Old Ice In The Df Region.
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2022 |
Aviles, G. P. F., Spadini, L., Sacchi, E., Rossier, Y., Savarino, J., Ramos, O. E., et al. (2022). Hydrogeochemical and nitrate isotopic evolution of a semiarid mountainous basin aquifer of glacial-fluvial and paleolacustrine origin (Lake Titicaca, Bolivia): the effects of natural processes and anthropogenic activities. Hydrogeology Journal, 303(1), 181–201.
Abstract: A hydrogeochemical and stable isotopic (delta(15) N-NO3 and delta O-18(NO3)) multitracer approach was combined with previous geological and hydrogeological knowledge in a groundwater-dominated basin, located within the semiarid region of the Bolivian Altiplano (SE of Lake Titicaca). Major natural processes and anthropogenic impacts controlling water chemistry and isotopic compositions of groundwater were identified and corresponding aquifer impacted zones determined. The main natural processes are, by following water flowlines, (1) silicate weathering in the piedmont subsystem (similar to 4,600-3,910 m asl, Ca(Mg)HCO3 facies), (2) Na-Ca exchange within glacial-fluvial deposits overlying paleolacustrine deposits (similar to 3,910 to 3,860 m asl, Na-HCO3 facies), and (3) evaporite dissolution in the confined zone of the lacustrine plain (similar to 3,860-3,810 m asl, Na-Cl-SO4 facies). The highest contributions of anthropogenic nitrate in groundwater have been observed at 3,960-3,860 m asl in the piedmont subsystem and were isotopically associated with leaching from areas influenced by manure piles, synthetic N fertilizers, and sewage collector pipes. In this subsystem, natural water-rock interactions could be deciphered with minimal anthropogenic impact, allowing nitrate sources to be clearly identified. Denitrification, occurring in the topographic lows of the piedmont subsystem, was identified as the main natural attenuation process. The multitracer approach provided a consistent understanding of the major processes that take place along the groundwater flow system and confirmed the significant role of anthropogenic nitrate. This aquifer system thus represents an ideal model of the region's hydrochemical evolution along the gravity-driven flow caused by natural water-rock interaction processes and the influence of anthropogenic contamination.
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Barbero, A., Grilli, R., Frey, M., Blouzon, C., Helmig, D., Caillon, N., et al. (2022). Summer Variability Of The Atmospheric No2 : No Ratio A Dome C On The East Antarctic Plateau. Atmospheric Chemistry And Physics, 222(181), 12025–12054.
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Becagli, S., Barbaro, E., Bonamano, S., Caiazzo, L., di Sarra, A., Feltracco, M., et al. (2022). Factors Controlling Atmospheric Dms And Its Oxidation Products (Msa And nssSO(4)(2-)) in the aerosol at Terra Nova Bay, Antarctica. Atmospheric Chemistry And Physics, 222(141), 9245–9263.
Abstract: This paper presents the results of simultaneous high time-resolution measurements of biogenic aerosol (methane sulfonic acid (MSA), non-sea salt sulfate nssSO(4)(2-)) with its gaseous precursor dimethylsulfide (DMS), performed at the Italian coastal base Mario Zucchelli Station (MZS) in Terra Nova Bay (MZS) during two summer campaigns (2018-2019 and 2019-2020). Data on atmospheric DMS concentration are scarce, especially in Antarctica. The DMS maximum at MZS occurs in December, one month earlier than at other Antarctic stations. The maximum of DMS concentration is connected with the phytoplanktonic senescent phase following the bloom of Phaeocystis antarctica that occurs in the polynya when sea ice opens up. The second plankton bloom occurs in January and, despite the high dimethylsufoniopropionate (DMSP) concentration in seawater, atmospheric DMS remains low, probably due to its fast biological turnover in seawater in this period. The intensity and timing of the DMS evolution during the two years suggest that only the portion of the polynya close to the sampling site produces a discernible effect on the measured DMS. The closeness to the DMS source area and the occurrence of air masses containing DMS and freshly formed oxidation products allow us to study the kinetic of biogenic aerosol formation and the reliable derivation of the branch ratio between MSA and nssSO(4)(2-) from DMS oxidation that is estimated to be 0.84 +/- 0.06. Conversely, for aged air masses with low DMS content, an enrichment of nssSO(4)(2-) with respect to MSA, is observed. We estimate that the mean contribution of freshly formed biogenic aerosol to PM10 is 17 % with a maximum of 56 %. The high contribution of biogenic aerosol to the total PM10 mass in summer in this area highlights the dominant role of the polynya on biogenic aerosol formation. Finally, due to the regional and year-to-year variability of DMS and related biogenic aerosol formation, we stress the need for long-term measurements of seawater and atmospheric DMS and biogenic aerosol along the Antarctic coast and in the Southern Ocean.
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Bianchi, F., Sinclair, V. A., Aliaga, D., Zha, Q. Z., Scholz, W., Wu, C., et al. (2022). The Saltena Experiment Comprehensive Observations Of Aerosol Sources, Formation, and Processes in the South American Andes. Bulletin Of The American Meteorological Society, 1031(2), E212–E229.
Abstract: This paper presents an introduction to the Southern Hemisphere High Altitude Experiment on Particle Nucleation and Growth (SALTENA). This field campaign took place between December 2017 and June 2018 (wet to dry season) at Chacaltaya (CHC), a GAW (Global Atmosphere Watch) station located at 5,240 m MSL in the Bolivian Andes. Concurrent measurements were conducted at two additional sites in El Alto (4,000 m MSL) and La Paz (3,600 m MSL). The overall goal of the campaign was to identify the sources, understand the formation mechanisms and transport, and characterize the properties of aerosol at these stations. State-of-the-art instruments were brought to the station complementing the ongoing permanent GAW measurements, to allow a comprehensive description of the chemical species of anthropogenic and biogenic origin impacting the station and contributing to new particle formation. In this overview we first provide an assessment of the complex meteorology, airmass origin, and boundary layer-free troposphere interactions during the campaign using a 6-month high-resolution Weather Research and Forecasting (WRF) simulation coupled with Flexible Particle dispersion model (FLEXPART). We then show some of the research highlights from the campaign, including (i) chemical transformation processes of anthropogenic pollution while the air masses are transported to the CHC station from the metropolitan area of La Paz- El Alto, (ii) volcanic emissions as an important source of atmospheric sulfur compounds in the region, (iii) the characterization of the compounds involved in new particle formation, and (iv) the identification of long-range-transported compounds from the Pacific or the Amazon basin. We conclude the article with a presentation of future research foci. The SALTENA dataset highlights the importance of comprehensive observations in strategic high-altitude locations, especially the undersampled Southern Hemisphere.
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Cao, Y., Jiang, Z., Alexander, B., Cole-Dai, J., Savarino, J., Erbland, J., et al. (2022). On The Potential Fingerprint Of The Antarctic Ozone Hole In Ice-Core Nitrate Isotopes: A Case Study Based On A South Pole Ice Core. Atmospheric Chemistry And Physics, 222(202), 13407–13422.
Abstract: Column Ozone Variability Has Important Implications For Surface Photochemistry And The Climate. Ice-Core Nitrate Isotopes Are Suspected To Be Influenced By Column Ozone Variability And Delta N-15(No3-) Has Been Sought To Serve As A Proxy Of Column Ozone Variability. In This Study, We Examined The Ability Of Ice-Core Nitrate Isotopes To Reflect Column Ozone Variability By Measuring Delta N-15(No3-) And Delta O-17(No3-) In A Shallow Ice Core Drilled At The South Pole. The Ice Core Covers The Period 1944-2005, And During This Period Delta N-15(No3-) Showed Large Annual Variability ((59.2 +/- 29.3)Parts Per Thousand), But With No Apparent Response To The Antarctic Ozone Hole. Utilizing A Snow Photochemical Model, We Estimated 6.9 Parts Per Thousand Additional Enrichments In Delta N-15(No3-) Could Be Caused By The Development Of The Ozone Hole. Nevertheless, This Enrichment Is Small And Masked By The Effects Of The Snow Accumulation Rate At The South Pole Over The Same Period Of The Ozone Hole. The Delta O-17(No3-) Record Has Displayed A Decreasing Trend By Similar To 3.4 Parts Per Thousand Since 1976. This Magnitude Of Change Cannot Be Caused By Enhanced Post-Depositional Processing Related To The Ozone Hole. Instead, The Delta O-17(No3-) Decrease Was More Likely Due To The Proposed Decreases In The O-3 / Hox Ratio In The Extratropical Southern Hemisphere. Our Results Suggest Ice-Core Delta N-15(No3-) Is More Sensitive To Snow Accumulation Rate Than To Column Ozone, But At Sites With A Relatively Constant Snow Accumulation Rate, Information Of Column Ozone Variability Embedded In Delta N-15(No3-) Should Be Retrievable.
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Dasari, S., & Widory, D. (2022). Radiocarbon (C-14) Analysis Of Carbonaceous Aerosols: Revisiting The Existing Analytical Techniques for Isolation of Black Carbon. Frontiers In Environmental Science, 101.
Abstract: Air pollution, a complex cocktail of different components, exerts an influence on climate/human; health both locally and away from source regions. The issue of air pollution is often closely linked; to carbonaceous aerosols, the assessment of climate/air quality/health impact of which remains associated with large uncertainties. Black carbon (BC)-a product of incomplete combustion-is a potent climate warming agent and one of the central components to this issue. An accurate; knowledge of BC emitting sources is necessary for devising appropriate mitigation strategies and; policies to reduce the associated climate/environmental burden. The radiocarbon isotope (C-14 or carbon-14) fingerprinting allows for an unambiguous and quantitative constraining of the BC sources and is therefore a well-popularized method. Here, we review the existing analytical techniques for the isolation of BC from a filter matrix for conducting C-14-based investigations. This work summarizes the protocols in use, provides an overarching perspective on the state-of- the-art and recommendations for certain aspects of future method development.
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Dasari, S., Paris, G., Saar, B., Pei, Q. M., Cong, Z. Y., & Widory, D. (2022). Sulfur Isotope Anomalies (Delta S-33) In Urban Air Pollution Linked To Mineral-Dust-Associated Sulfate. Environmental Science & Technology Letters, .
Abstract: Sulfur isotope analysis provides a unique probe for source-specific information and certain atmospheric reactions. Globally, atmospheric aerosols in urban locations exhibit significant sulfur mass-independent fractionation (i.e., S-MIF, Delta S-33 not equal 0). The origin(s) of these S-MIF anomalies remains unclear, thereby limiting the interpretation and/or application of such signals. Her; we conducted dual-isotope (Delta S-33 and delta S-34) fingerprinting of sulfate aerosols from summertime megacity Delhi in south Asia. A shift toward concomitantly high Delta S-33 (from 0.2 parts per thousand to 0.5 parts per thousand) and low delta S-34 (from 5 parts per thousand to 1 parts per thousand) values was observed with the influx of mineral dust. The Fe:Al ratio showed significant correlations with both sulfate loadings (R-2 = 0.84) and Delta S-33 signatures (R-2 = 0.77). Contrary to the prevailing paradigm, this observational evidence suggests that mineral-dust-associated sulfate exhibits S-MIF anomalies. Atmospheric processing of mineral dust plausibly leads to the production of these anomalies. Our evaluation suggests that an inherent mechanism(s) remains elusive. Although hindered by end-member uncertainties, we show that S-MIF signals can be source apportioned to quantitatively constrain the fraction of mineral-dust-associated sulfate in urban locations. The influx of mineral-dust-associated sulfate can influence urban air pollution affecting air quality and/or human health and as such requires monitoring. Urban Delta S-33 signals can therefore be used to trace this sulfate fraction, thereby improving our understanding of sulfate aerosol dynamics.
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Domine, F., Fourteau, K., Picard, G., Lackner, G., Sarrazin, D., & Poirier, M. (2022). Permafrost Cooled In Winter By Thermal Bridging Through Snow-Covered shrub branches. Nature Geoscience, 151(7), 554–+.
Abstract: Considerable expansion of shrubs across the Arctic tundra has been observed in recent decades. These shrubs are thought to have a warming effect on permafrost by increasing snowpack thermal insulation, thereby limiting winter cooling and accelerating thaw. Here, we use ground temperature observations and heat transfer simulations to show that low shrubs can actually cool the ground in winter by providing a thermal bridge through the snowpack. Observations from unmanipulated herb tundra and shrub tundra sites on Bylot Island in the Canadian high Arctic reveal a 1.21 degrees C cooling effect between November and February. This is despite a snowpack that is twice as insulating in shrubs. The thermal bridging effect is reversed in spring when shrub branches absorb solar radiation and transfer heat to the ground. The overall thermal effect is likely to depend on snow and shrub characteristics and terrain aspect. The inclusion of these thermal bridging processes into climate models may have an important impact on projected greenhouse gas emissions by permafrost. Arctic shrubs cool permafrost in winter by acting as a thermal bridge through the snowpack, according to ground temperature observations and heat transfer simulations.
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Fain, X., Rhodes, R. H., Place, P., Petrenko, V. V., Fourteau, K., Chellman, N., et al. (2022). Northern Hemisphere atmospheric history of carbon monoxide since preindustrial times reconstructed from multiple Greenland ice cores. Climate Of The Past, 181(3), 631–647.
Abstract: Carbon monoxide (CO) is a regulated pollutant and one of the key components determining the oxidizing capacity of the atmosphere. Obtaining a reliable record of atmospheric CO mixing ratios ([CO]) since preindustrial times is necessary to evaluate climate-chemistry models under conditions different from today and to constrain past CO sources. We present high-resolution measurements of CO mixing ratios from ice cores drilled at five different sites on the Greenland ice sheet that experience a range of snow accumulation rates, mean surface temperatures, and different chemical compositions. An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) was coupled with continuous melter systems and operated during four analytical campaigns conducted between 2013 and 2019. Overall, continuous flow analysis (CFA) of CO was carried out on over 700 m of ice. The CFA-based CO measurements exhibit excellent external precision (ranging from 3.3 to 6.6 ppbv, 1 sigma) and achieve consistently low blanks (ranging from 4.1 +/- 1.2 to 12.6 +/- 4.4 ppbv), enabling paleoatmospheric interpretations. However, the five CO records all exhibit variability that is too large and rapid to reflect past atmospheric mixing ratio changes. Complementary tests conducted on discrete ice samples demonstrate that these variations are not artifacts of the analytical method (i.e., production of CO from organics in the ice during melting) but are very likely related to in situ CO production within the ice before analysis. Evaluation of the signal resolution and co-investigation of high-resolution records of CO and total organic carbon (TOC) suggest that past atmospheric CO variations can be extracted from the records' baselines with accumulation rates higher than 20 cm w.e. yr(-1) (water equivalent per year). Consistent baseline CO records from four Greenland sites are combined to produce a multisite average ice core reconstruction of past atmospheric CO for the Northern Hemisphere high latitudes, covering the period from 1700 to 1957 CE. Such a reconstruction should be taken as an upper bound of past atmospheric CO abundance. From 1700 to 1875 CE, the record reveals stable or slightly increasing values in the 100-115 ppbv range. From 1875 to 1957 CE, the record indicates a monotonic increase from 114 +/- 4 to 147 +/- 6 ppbv. The ice core multisite CO record exhibits an excellent overlap with the atmospheric CO record from Green-land firn air which spans the 1950-2010 CE time period. The combined ice core and firn air CO history, spanning 1700-2010 CE, provides useful constraints for future model studies of atmospheric changes since the preindustrial period.
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Fleurbaey, H., Campargue, A., Da Silva, Y. C. M., Grilli, R., Kassi, S., & Mondelain, D. (2022). Characterization Of The H2O + Co2 Continuum Within The Infrared transparency windows. Journal Of Quantitative Spectroscopy & Radiative Transfer, 2822.
Abstract: Absorption spectra of humidified CO2 have been recorded at room temperature by cavity enhanced absorption techniques (CRDS and OFCEAS): (i) in three spectral ranges of the 1.6 μm window (5720-6045 cm (-1); 6390-6460 cm (-1) and 6570-6665 cm -1), (ii) in four narrow spectral intervals of the 2.3 μm window (4243-4255 cm(-1); 4301.3-4302 cm(-1); 4 421.5-4 4 40 cm(-1)and 4518-4535 cm( -1)), and (iii) around 2853 cm( -1). All these spectral ranges are situated in transparency windows of both H2O and CO2. The binary absorption coefficients (BC O-2-H2O +BH2O-C O-2) are retrieved from low pressure spectra ( < 1 atm) recorded with different molar fractions of water vapor in CO2 after subtracting the H2O and CO2 local monomer contributions and the self-continuum contribution of each species (i.e. H2O -H2O and CO2-CO2). Experimental room temperature binary coefficients are then compared to the only available empirical model based on line shape profiles with chi-factors. This model well reproduces our experimental values on the low-and high-frequency edges of the 1.6 μm window and gives a relatively good agreement for the 2853 cm( -1) data point. Larger differences are observed in the 2.3 μm window where the calculated values are underestimated by a factor of 3. Around 60 0 0 cm( -1), an additional absorption peak is observed which is tentatively interpreted as a collision induced absorption band due to the simultaneous excitation of the H2O and CO2 molecules. (C)& nbsp;2022 Elsevier Ltd. All rights reserved.
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Fleurbaey, H., Campargue, A., Da Silva, Y. C. M., Grilli, R., Kassi, S., & Mondelain, D. (2022). Characterization Of The H2O + Co2 Continuum Within The Infrared transparency windows. Journal Of Quantitative Spectroscopy & Radiative Transfer, 2822.
Abstract: Absorption spectra of humidified CO2 have been recorded at room temperature by cavity enhanced absorption techniques (CRDS and OFCEAS): (i) in three spectral ranges of the 1.6 μm window (5720-6045 cm (-1); 6390-6460 cm (-1) and 6570-6665 cm -1), (ii) in four narrow spectral intervals of the 2.3 μm window (4243-4255 cm(-1); 4301.3-4302 cm(-1); 4 421.5-4 4 40 cm(-1)and 4518-4535 cm( -1)), and (iii) around 2853 cm( -1). All these spectral ranges are situated in transparency windows of both H2O and CO2. The binary absorption coefficients (BC O-2-H2O +BH2O-C O-2) are retrieved from low pressure spectra ( < 1 atm) recorded with different molar fractions of water vapor in CO2 after subtracting the H2O and CO2 local monomer contributions and the self-continuum contribution of each species (i.e. H2O -H2O and CO2-CO2). Experimental room temperature binary coefficients are then compared to the only available empirical model based on line shape profiles with chi-factors. This model well reproduces our experimental values on the low-and high-frequency edges of the 1.6 μm window and gives a relatively good agreement for the 2853 cm( -1) data point. Larger differences are observed in the 2.3 μm window where the calculated values are underestimated by a factor of 3. Around 60 0 0 cm( -1), an additional absorption peak is observed which is tentatively interpreted as a collision induced absorption band due to the simultaneous excitation of the H2O and CO2 molecules. (C)& nbsp;2022 Elsevier Ltd. All rights reserved.
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Fleurbaey, H., Grilli, R., Mondelain, D., & Campargue, A. (2022). Measurements of the water vapor continuum absorption by OFCEAS at 3.50 μm and 2.32 μm. Journal Of Quantitative Spectroscopy & Radiative Transfer, 2782.
Abstract: Measurements of the water vapor absorption cross-sections at two spectral points of the 2.1 μm and 4.0 μm transparency windows are performed by optical feedback cavity enhanced absorption spectroscopy (OFCEAS). The self-continuum cross-section, C-s, is measured for temperature values of 30 and 47 degrees C (303 and 320 K) at the 2853 cm(-1) spectral point, corresponding to the lowest opacity region of the 4.0 μm transparency window. The C-s values derived from the pressure squared dependence of the self-continuum, are found consistent with previous CEAS measurements in the considered window but significantly smaller than measurements by Fourier transform spectroscopy (FTS). The C-s temperature dependence is discussed in relation with FTS measurements at high temperature. Foreign-continuum cross-sections, C-F, are newly obtained from OFCEAS spectra of moist air in flow regime at the 4302 cm(-1) spectral point of the low energy edge of the 2.1 μm window. After subtraction of the monomer and self-continuum contributions, C-F values are derived from the linear variation of the foreign-continuum absorption with the product of the water vapor and air partial pressures. The measurements were performed for temperature values of 34 and 47 degrees C (307 and 320 K) and no significant temperature dependency was observed. The present C-F value at 4302 cm(-1) is gathered with previous CEAS measurements at seven spectral points of the 2.1 μm window. This consistent set of C-F values is used to derive from a polynomial fit, the empirical frequency dependence of C-F(v) over the 4250-5000 cm(-1) range. Overall, the semi-empirical MTCKD3.5 values of C-F are significantly underestimated in the centre of the considered window. (C) 2021 Elsevier Ltd. All rights reserved.
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Han, C., Burn, L. J., Vallelonga, P., Do Hur, S., Boutron, C. F., Han, Y., et al. (2022). Lead Isotopic Constraints On The Provenance Of Antarctic Dust And Atmospheric Circulation Patterns Prior to the Mid-Brunhes Event (similar to 430 kyr ago). Molecules, 272(131).
Abstract: A lead (Pb) isotopic record, covering the two oldest glacial-interglacial cycles (similar to 572 to 801 kyr ago) characterized by lukewarm interglacials in the European Project for Ice Coring in Antarctica Dome C ice core, provides evidence for dust provenance in central East Antarctic ice prior to the Mid-Brunhes Event (MBE), similar to 430 kyr ago. Combined with published post-MBE data, distinct isotopic compositions, coupled with isotope mixing model results, suggest Patagonia/Tierra del Fuego (TdF) as the most important sources of dust during both pre-MBE and post-MBE cold and intermediate glacial periods. During interglacials, central-western Argentina emerges as a major contributor, resulting from reduced dust supply from Patagonia/TdF after the MBE, contrasting to the persistent dominance of dust from Patagonia/TdF before the MBE. The data also show a small fraction of volcanic Pb transferred from extra-Antarctic volcanoes during post-MBE interglacials, as opposed to abundant transfer prior to the MBE. These differences are most likely attributed to the enhanced wet removal efficiency with the hydrological cycle intensified over the Southern Ocean, associated with a poleward shift of the southern westerly winds (SWW) during warmer post-MBE interglacials, and vice versa during cooler pre-MBE ones. Our results highlight sensitive responses of the SWW and the associated atmospheric conditions to stepwise Antarctic warming.
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Jiang, Z., Savarino, J., Alexander, B., Erbland, J., Jaffrezo, J. L., & Geng, L. (2022). Impacts Of Post-Depositional Processing On Nitrate Isotopes In The Snow and the overlying atmosphere at Summit, Greenland. Cryosphere, 161(7), 2709–2724.
Abstract: The effect of post-depositional processing on the preservation of snow nitrate isotopes at Summit, Greenland, remains a subject of debate and is relevant to the quantitative interpretation of ice-core nitrate (isotopic) records at high snow accumulation sites. Here we present the first year-round observations of atmospheric nitrate and its isotopic compositions at Summit and compare them with published surface snow and snowpack observations. The atmospheric delta N-15(NO3-) remained negative throughout the year, ranging from -3.1 parts per thousand to -47.9 parts per thousand with a mean of (-14.8 +/- 7.3)parts per thousand (n = 54), and displayed minima in spring which are distinct from the observed spring delta N-15(NO3-) maxima in snowpack. The spring average atmospheric delta N-15(NO3-) was (-17.9 +/- 8.3) parts per thousand (n = 21), significantly depleted compared to the snowpack spring average of (4.6 +/- 2.1)parts per thousand, while the surface snow delta N-15(NO3-) of (-6.8 +/- 0.5)parts per thousand was in between the atmosphere and the snowpack. The differences in atmospheric, surface snow and snowpack delta N-15(NO3-) are best explained by the photo-driven post-depositional processing of snow nitrate, with potential contributions from fractionation during nitrate deposition. In contrast to delta N-15(NO3-) the atmospheric Delta O-1(7)(NO3-) was of a similar seasonal pattern and magnitude of change to that in the snowpack, suggesting little to no changes in Delta O-1(7)(NO3-) from photolysis, consistent with previous modeling results. The atmospheric delta O-18(NO3-) varied similarly to atmospheric Delta O-1(7)(NO3-), with summer low and winter high values. However, the difference between atmospheric and snow delta O-18(NO3-) was larger than that of Delta O-17(NO3-). We found a strong correlation between atmospheric delta O-18(NO3-) and Delta O-17(NO3-) that is very similar to previous measurements for surface snow at Summit, suggesting that atmospheric delta O-18(NO3-) versus Delta O-17(NO3-) relationships were conserved during deposition. However, we found the linear relationships between delta O-18 and Delta O-17(NO3-) were significantly different for snowpack compared to atmospheric samples. This likely suggests the oxygen isotopes are also affected before preservation in the snow at Summit, but the degree of change for delta O-18(NO3-) should be larger than that of Delta O-17(NO3-). This is because photolysis is a massdependent process that would directly affect delta O-18(NO3-) in snow but not Delta O-17(NO3-) as the latter is a mass-independent signal. Although there were uncertainties associated with the complied dataset, the results suggested that post-depositional processing at Summit can induce changes in nitrate isotopes, especially delta N-15(NO3-), consistent with a previous modeling study. This reinforces the importance of understanding the effects of post-depositional processing before ice-core nitrate isotope interpretation, even for sites with relatively high snow accumulation rates.
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Koenig, A. M., Sonke, J. E., Magand, O., Andrade, M., Moreno, I., Velarde, F., et al. (2022). Evidence For Interhemispheric Mercury Exchange In The Pacific Ocean Upper Troposphere. Journal Of Geophysical Research-Atmospheres, 1271(101).
Abstract: Even though anthropogenic mercury (Hg) emissions to the atmosphere are similar to 2.5 times higher in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH), atmospheric Hg concentrations in the NH are only similar to 1.5 times higher than in the SH. Global Hg models attribute this apparent discrepancy to large SH oceanic Hg emissions or to interhemispheric exchange of Hg through the atmosphere. However, no observational data set exists to serve as a benchmark to validate whether these coarse-resolution models adequately represent the complex dynamics of interhemispheric Hg exchange. During the 2015-2016 El Nino, we observed at mount Chacaltaya in the tropical Andes a similar to 50% increase in ambient Hg compared to the year before, coinciding with a shift in synoptic transport pathways. Using this event as a case study, we investigate the impact of interhemispheric exchange on atmospheric Hg in tropical South America. We use HYSPLIT to link Hg observations to long-range transport and find that the observed Hg increase relates strongly to air masses from the tropical Pacific upper troposphere (UT), a region directly impacted by interhemispheric exchange. Inclusion of the modeled seasonality of interhemispheric air mass exchange strengthens this relationship significantly. We estimate that interhemispheric exchange drives Hg seasonality in the SH tropical Pacific UT, with strongly enhanced Hg between July and October. We validate this seasonality with previously published aircraft Hg observations. Our results suggest that the transport of NH-influenced air masses to tropical South America via the Pacific UT occurs regularly but became more detectable at Chacaltaya in 2015-2016 because of a westward shift in air mass origin.
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Legrand, M., McConnell, J. R., Preunkert, S., Bergametti, G., Chellman, N. J., Desboeufs, K., et al. (2022). Thallium Pollution In Europe Over The Twentieth Century Recorded In Alpine Ice: Contributions From Coal Burning and Cement Production. Geophysical Research Letters, 494(131).
Abstract: Emission inventories indicate that thallium, a highly toxic metal, is emitted during coal burning and cement production. These estimates have been established only for the 1980s and 1990s but up to now they have not been compared to long-term observations. Here we used alpine ice cores to document thallium pollution over Europe since similar to 1850. Ice-core thallium concentrations increased from 1890 to 1910, and decreased after 1965 to concentrations that were half 1890 levels. Comparison of ice-core trends, estimated past emissions, and state-of-the-art atmospheric aerosol transport modeling suggest that coal burning was responsible for thallium pollution in Europe, particularly from 1920 to 1965 because of high coal consumption at that time. The subsequent decline resulted from decreased coal consumption and reduced emissions following technological improvements. The ice-core data suggest that the rapid growth of cement production that took place in Europe after 1950 had a limited impact on thallium pollution.
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Lim, S., Hwang, J., Lee, M., Czimczik, C. I., Xu, X. M., & Savarino, J. (2022). Robust Evidence Of C-14, C-13, And N-15 Analyses Indicating Fossil Fuel Sources for Total Carbon and Ammonium in Fine Aerosols in Seoul Megacity. Environmental Science & Technology, 565(111), 6894–6904.
Abstract: Carbon- and nitrogen-containing aerosols are ubiquitous in urban atmospheres and play important roles in air quality and climate change. We determined the C-14 fraction modern (f(M)) and delta C-13 of total carbon (TC) and delta N-15 of NH4+ in the PM2.5 collected in Seoul megacity during April 2018 to December 2019. The seasonal mean delta C-13 values were similar to -25.1% +/- 2.0% in warm and -24.2%+/- 0.82% in cold seasons. Mean delta N-15 values were higher in warm (16.4%+/- 2.8%) than in cold seasons (4.0%+/- 6.1%), highlighting the temperature effects on atmospheric NH3 levels and phase- equilibrium isotopic exchange during the conversion of NH3 to NH4+. While 37% +/- 10% of TC was apportioned to fossilfuel sources on the basis of f(M) values, delta N-15 indicated a higher contribution of emissions from vehicle exhausts and electricity generating units (power-plant NH3 slip) to NH3: 60% +/- 26% in warm season and 66% +/- 22% in cold season, based on a Bayesian isotope-mixing model. The collective evidence of multiple isotope analysis reasonably supports the major contribution of fossil-fuel-combustion sources to NH4+, in conjunction with TC, and an increased contribution from vehicle emissions during the severe PM2.5 pollution episodes. These findings demonstrate the efficacy of a multiple-isotope approach in providing better insight into the major sources of PM2.5 in the urban atmosphere.
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Lim, S., Lee, M., Savarino, J., & Laj, P. (2022). Oxidation Pathways And Emission Sources Of Atmospheric Particulate nitrate in Seoul: based on delta N-15 and Delta O-17 measurements. Atmospheric Chemistry And Physics, 222(8), 5099–5115.
Abstract: PM2.5 haze pollution driven by secondary inorganic NO3- has been a great concern in East Asia. It is, therefore, imperative to identify its sources and oxidation processes, for which nitrogen and oxygen stable isotopes are powerful tracers. Here, we determined the delta N-15 (NO3-) and Delta O-17 (NO3-) of PM2.5 in Seoul during the summer of 2018 and the winter of 2018-2019 and estimated quantitatively the relative contribution of oxidation pathways for particulate NO3- and investigated major NOx emission sources. In the range of PM2.5 mass concentration from 7.5 μg m(-3) (summer) to 139.0 μg m(-3) (winter), the mean delta N-15 was -0.7 parts per thousand +/- 3.3 parts per thousand and 3.8 parts per thousand +/- 3.7 parts per thousand, and the mean Delta O-17 was 23.2 parts per thousand +/- 2.2 parts per thousand and 27.7 parts per thousand +/- 2.2 parts per thousand in the summer and winter, respectively. While OH oxidation was the dominant pathway for NO3- during the summer (87 %), nighttime formation via N2O5 and NO3 was relatively more important (38 %) during the winter, when aerosol liquid water content (ALWC) and nitrogen oxidation ratio (NOR) were higher. Interestingly, the highest Delta O-17 was coupled with the lowest delta N-15 and highest NOR during the record-breaking winter PM2.5 episodes, revealing the critical role of photochemical oxidation process in severe winter haze development. For NOx sources, atmospheric delta N-15 (NOx) estimated from measured delta N-15 (NO3-) considering isotope fractionation effects indicates vehicle emissions as the most important emission source of NOx in Seoul. The contribution from biogenic soil and coal combustion was slightly increased in summer and winter, respectively. Our results built on a multiple-isotope approach provide the first explicit evidence for NO3- formation processes and major NOx emission sources in the Seoul megacity and suggest an effective mitigation measure to improve PM2.5 pollution.
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Moseid, K., Schulz, M., Eichler, A., Schwikowski, M., Mcconnell, J., Olivie, D., et al. (2022). Using Ice Cores To Evaluate Cmip6 Aerosol Concentrations Over The Historical Era. Journal Of Geophysical Research-Atmospheres, 1271(181).
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Oyabu, I., Kawamura, K., Buizert, C., Parrenin, F., Orsi, A., Kitamura, K., et al. (2022). The Dome Fuji Ice Core Df2021 Chronology (0-207 Kyr Bp). Quaternary Science Reviews, .
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Papazian, S., D'Agostino, L. A., Sadiktsis, I., Froment, J., Bonnefille, B., Sdougkou, K., et al. (2022). Nontarget mass spectrometry and in silico molecular characterization of air pollution from the Indian subcontinent. Communications Earth & Environment, 3(1).
Abstract: A combination of high-resolution mass spectrometry and computational molecular characterization techniques can structurally annotate up to 17% of organic compounds in fine particulate matter in highly polluted air sampled in the Maldives. Fine particulate-matter is an important component of air pollution that impacts health and climate, and which delivers anthropogenic contaminants to remote global regions. The complex composition of organic molecules in atmospheric particulates is poorly constrained, but has important implications for understanding pollutant sources, climate-aerosol interactions, and health risks of air pollution exposure. Here, comprehensive nontarget high-resolution mass spectrometry was combined with in silico structural prediction to achieve greater molecular-level insight for fine particulate samples (n = 40) collected at a remote receptor site in the Maldives during January to April 2018. Spectral database matching identified 0.5% of 60,030 molecular features observed, while a conservative computational workflow enabled structural annotation of 17% of organic structures among the remaining molecular dark matter. Compared to clean air from the southern Indian Ocean, molecular structures from highly-polluted regions were dominated by organic nitrogen compounds, many with computed physicochemical properties of high toxicological and climate relevance. We conclude that combining nontarget analysis with computational mass spectrometry can advance molecular-level understanding of the sources and impacts of polluted air.
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Picard, G., Lowe, H., Domine, F., Arnaud, L., Larue, F., Favier, V., et al. (2022). The Microwave Snow Grain Size: A New Concept To Predict Satellite Observations Over Snow-Covered Regions. Agu Advances, 3(4).
Abstract: Satellite observations of snow-covered regions in the microwave range have the potential to retrieve essential climate variables such as snow height. This requires a precise understanding of how microwave scattering is linked to snow microstructural properties (density, grain size, grain shape and arrangement). This link has so far relied on empirical adjustments of the theories, precluding the development of robust retrieval algorithms. Here we solve this problem by introducing a new microstructural parameter able to consistently predict scattering. This “microwave grain size” is demonstrated to be proportional to the measurable optical grain size and to a new factor describing the chord length dispersion in the microstructure, a geometrical property known as polydispersity. By assuming that the polydispersity depends on the snow grain type only, we retrieve its value for rounded and faceted grains by optimization of microwave satellite observations in 18 Antarctic sites, and for depth hoar in 86 Canadian sites using ground-based observations. The value for the convex grains (0.6) compares favorably to the polydispersity calculated from 3D micro-computed tomography images for alpine grains, while values for depth hoar show wider variations (1.2-1.9) and are larger in Canada than in the Alps. Nevertheless, using one value for each grain type, the microwave observations in Antarctica and in Canada can be simulated from in-situ measurements with good accuracy with a fully physical model. These findings improve snow scattering modeling, enabling future more accurate uses of satellite observations in snow hydrological and meteorological applications.
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2021 |
Albertin, S., Savarino, J., Bekki, S., Barbero, A., & Caillon, N. (2021). Measurement report: Nitrogen isotopes (delta N-15) and first quantification of oxygen isotope anomalies (Delta O-17, delta O-18) in atmospheric nitrogen dioxide. Atmospheric Chemistry And Physics, 21(13), 10477–10497.
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Alemany, O., Talalay, P., Boissonneau, P., Chappellaz, J., Chemin, J., Duphil, R., et al. (2021). The SUBGLACIOR drilling probe: hydraulic considerations. Annals Of Glaciology, 62(84), 131–142.
Abstract: Using significant technological breakthroughs and unconventional approaches, the goal of the in situ probing of glacier ice for a better understanding of the orbital response of climate (SUBGLACIOR) project is to advance ice core research by inventing, constructing and testing an in situ probe to evaluate if a target site is suitable for recovering ice as old as 1.5 million years. Embedding a laser spectrometer, the probe is intended to make its own way down into the ice and to measure, in real time and down to the bedrock, the depth profiles of the ice delta D water isotopes as well as the trapped CH4 gas concentration and dust concentration. The probe descent is achieved through electromechanical drilling combined with continuous meltwater sample production using a central melting finger in the drill head. A key aspect of the project lies in the design and implementation of an efficient method to continuously transfer to the surface the ice chips being produced by the drill head and from the refreezed water expulsed downstream from the melting finger, into the borehole. This paper presents a detailed calculation and analysis of the flow rates and pressure conditions required to overcome friction losses of the drilling fluid and to effectively transport ice chips to the surface.
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Arienzo, M., Legrand, M., Preunkert, S., Stohl, A., Chellman, N., Eckhardt, S., et al. (2021). Alpine Ice-Core Evidence of a Large Increase in Vanadium and Molybdenum Pollution in Western Europe During the 20th Century. Journal Of Geophysical Research-Atmospheres, 126(4).
Abstract: Pollutants emitted by industrial processes are deposited across the landscape. Ice core records from mid-latitude glaciers located close to emission sources document the history of local-to-regional pollution since preindustrial times. Such records underpin attribution of pollutants to specific emission sources critical to developing abatement policies. Previous ice core studies from the Alps document the overall magnitude and timing of pollution related to nitrogen and sulfur-derived species, as well as a few metals including lead. Here, we used subannually resolved measurements of vanadium (V) and molybdenum (Mo) in two ice cores from Col du Dome (French Alps), as well as atmospheric transport and deposition modeling, to investigate sources of pollution in the free European troposphere. The noncrustal V and Mo (ncV, ncMo) components were calculated by subtracting the crustal component from the total concentration. These ice core results showed a 32-fold increase in ncV and a 69-fold increase in ncMo from the preindustrial era (pre-1860) to the industrial concentration peaks. Anthropogenic V and Mo emissions in Europe were estimated using emission factors from oil and coal consumption and atmospheric transport and deposition modeling. When comparing ice core data to estimated anthropogenic V and Mo emissions in Europe, V was found to be sourced primarily from oil combustion emissions. Conversely, coal and oil combustion estimated emissions did not agree with the measured ice core Mo concentrations, suggesting that other anthropogenic Mo sources dominated coal-burning emissions, particularly after the 1950s. Noncoal-burning sources of Mo may include metallurgy although emission factors are poorly known.
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Bailey, H., Hubbard, A., Klein, E., Mustonen, K., Akers, P., Marttila, H., et al. (2021). Arctic sea-ice loss fuels extreme European snowfall. Nature Geoscience, .
Abstract: The loss of Arctic sea-ice enhances evaporation and fuels extreme European winter snowfall, according to an analysis of atmospheric water vapour isotope measurements. The loss of Arctic sea-ice has been implicated with severe cold and snowy mid-latitude winters. However, the mechanisms and a direct link remain elusive due to limited observational evidence. Here we present atmospheric water vapour isotope measurements from Arctic Finland during 'the Beast from the East'-a severe anticyclonic outbreak that brought heavy snowfall and freezing across Europe in February 2018. We find that an anomalously warm Barents Sea, with a 60% ice-free surface, supplied up to 9.3 mm d(-1) moisture flux to this cold northeasterly airflow. We demonstrate that approximately 140 gigatonnes of water was evaporated from the Barents Sea during the event, potentially supplying up to 88% of the corresponding fresh snow over northern Europe. Reanalysis data show that from 1979 to 2020, net March evaporation across the Barents Sea increased by approximately 70 kg per square metre of sea-ice lost (r(2) = 0.73, P < 0.01), concurrent with a 1.6 mm (water equivalent) per year increase in Europe's maximum snowfall. Our analysis directly links Arctic sea-ice loss with increased evaporation and extreme snowfall, and signifies that by 2080, an Atlantified ice-free Barents Sea will be a major source of winter moisture for continental Europe.
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Barbero, A., Savarino, J., Grilli, R., Blouzon, C., Picard, G., Frey, M., et al. (2021). New Estimation of the NOx Snow-Source on the Antarctic Plateau. Journal Of Geophysical Research-Atmospheres, 126(20).
Abstract: To fully decipher the role of nitrate photolysis on the atmospheric oxidative capacity in snow-covered regions, NOx flux must be determined with more precision than existing estimates. Here, we introduce a method based on dynamic flux chamber measurements for evaluating the NOx production by photolysis of snowpack nitrate in Antarctica. Flux chamber experiments were conducted for the first time in Antarctica, at the French-Italian station Concordia, Dome C (75 degrees 06'S, 123 degrees 20'E, 3233 m a.s.l) during the 2019-2020 summer campaign. Measurements were gathered with several snow samples of different ages ranging from newly formed drifted snow to 6-year-old firn. Contrary to existing literature expectations, the daily average photolysis rate coefficient, JNO3 over bar , did not significantly vary between differently aged snow samples, suggesting that the photolabile nitrate in snow behaves as a single-family source with common photochemical properties, where a JNO3 over bar = (2.37 +/- 0.35) x 10(-8) s(-1) (1 sigma) has been calculated from December 10(th) 2019 to January 7(th) 2020. At Dome C summer daily average NOx flux, FNOx, based on measured NOx production rates was estimated to be (4.3 +/- 1.2) x 10(8) molecules cm(-2) s(-1), which is 1.5-7 times less than the net NOx flux observed previously above snow at Dome C using the gradient flux method. Using these results, we extrapolated an annual continental snow sourced NOx budget of 0.017 +/- 0.003 Tg center dot N y(-1), similar to 2 times the nitrogen budget, (N-budget), of the stratospheric denitrification previously estimated for Antarctica. These quantifications of nitrate photolysis using flux chamber experiments provide a road-map toward a new parameterization of the sigma NO3-(lambda,T)phi(T,pH) product that can improve future global and regional models of atmospheric chemistry.
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Buizert, C., Fudge, T., Roberts, W., Steig, E., Sherriff-Tadano, S., Ritz, C., et al. (2021). Antarctic surface temperature and elevation during the Last Glacial Maximum. Science, 372(6546), 1097–+.
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Capron, E., Rasmussen, S., Popp, T., Erhardt, T., Fischer, H., Landais, A., et al. (2021). The anatomy of past abrupt warmings recorded in Greenland ice. Nature Communications, 12(1).
Abstract: Data availability and temporal resolution make it challenging to unravel the anatomy (duration and temporal phasing) of the Last Glacial abrupt climate changes. Here, we address these limitations by investigating the anatomy of abrupt changes using sub-decadal-scale records from Greenland ice cores. We highlight the absence of a systematic pattern in the anatomy of abrupt changes as recorded in different ice parameters. This diversity in the sequence of changes seen in ice-core data is also observed in climate parameters derived from numerical simulations which exhibit self-sustained abrupt variability arising from internal atmosphere-ice-ocean interactions. Our analysis of two ice cores shows that the diversity of abrupt warming transitions represents variability inherent to the climate system and not archive-specific noise. Our results hint that during these abrupt events, it may not be possible to infer statistically-robust leads and lags between the different components of the climate system because of their tight coupling. Palaeodata resolution and dating limit the study of the sequence of changes across Earth during past abrupt warmings. Here, the authors show tight decadal-scale coupling between Greenland climate, North Atlantic sea ice and atmospheric circulation during these past events using two highly resolved ice-core records.
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Crick, L., Burke, A., Hutchison, W., Kohno, M., Moore, K., Savarino, J., et al. (2021). New insights into the similar to 74 ka Toba eruption from sulfur isotopes of polar ice cores. Climate Of The Past, 17(5), 2119–2137.
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Crotti, I., Landais, A., Stenni, B., Bazin, L., Parrenin, F., Frezzotti, M., et al. (2021). An extension of the TALDICE ice core age scale reaching back to MIS 10.1. Quaternary Science Reviews, 266.
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Dasari, S., Andersson, A., Popa, M., Rockmann, T., Holmstrand, H., Budhavant, K., et al. (2021). Observational Evidence of Large Contribution from Primary Sources for Carbon Monoxide in the South Asian Outflow. Environmental Science & Technology, .
Abstract: South Asian air is among the most polluted in the world, causing premature death of millions and asserting a strong perturbation of the regional climate. A central component is carbon monoxide (CO), which is a key modulator of the oxidizing capacity of the atmosphere and a potent indirect greenhouse gas. While CO concentrations are declining elsewhere, South Asia exhibits an increasing trend for unresolved reasons. In this paper, we use dual-isotope (delta C-13 and (delta O-18) fingerprinting of CO intercepted in the South Asian outflow to constrain the relative contributions from primary and secondary CO sources. Results show that combustion-derived primary sources dominate the wintertime continental CO fingerprint (f(primary) similar to 79 +/- 4%), significantly higher than the pnmr global estimate (f(primary) similar to 55 +/- 5%). Satellite-based inventory estimates match isotope-constrained f(primary)-CO, suggesting observational convergence in source characterization and a prospect for model-observation reconciliation. This “ground-truthing” emphasizes the pressing need to mitigate incomplete combustion activities for climate/air quality benefits in South Asia.
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Davtian, N., Bard, E., Darfeuil, S., Menot, G., & Rostek, F. (2021). The Novel Hydroxylated Tetraether Index RI-OH ' as a Sea Surface Temperature Proxy for the 160-45 ka BP Period Off the Iberian Margin. Paleoceanography And Paleoclimatology, 36(3).
Abstract: RI-OH ' and RI-OH (ring index of hydroxylated tetraethers) are two novel organic paleothermometers which could either complement or replace more established paleothermometric proxies, such as U-K '(37) (C-37 ketone unsaturation ratio) and TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms). Despite a few promising attempts, the paleothermometric potential of RI-OH ' and RI-OH is not fully constrained. Here we present new high-resolution temperature records over the 160-45 ka BP (before present = year 1950 CE) period using four organic proxies (RI-OH ', RI-OH, TEX86, and U-K '(37)) from three deep sea sediment cores located in a north-south transect along the Iberian Margin. We analyzed all organic proxies from a single set of lipid extracts to optimize proxy-proxy comparisons and phase relationship studies. RI-OH ' responds to Dansgaard-Oeschger and Heinrich events, better resembles U-K '(37) than TEX86, and better records the influence of (sub)polar waters during Heinrich events than does RI-OH. While RI-OH ' gives realistic sea surface temperatures and latitudinal gradients coherent with those from independent paleothermometers, a more extensive RI-OH '-temperature calibration for the North Atlantic is clearly needed. However, the absence of a significant warm bias in RI-OH '-based temperatures compared to a shallow sea site suggests that endemic, deep-dwelling archeal communities affect TEX86 but not RI-OH ' in the Iberian Margin. TEX86 leads RI-OH ' and U-K '(37) during four Heinrich-like events, potentially due to background fluxes from deep waters for nonhydroxylated tetraethers summed with primary productivity dependent fluxes from surface waters for all investigated lipid classes. Relationships with Greenland temperatures further support RI-OH '-based paleothermometry.
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Favez, O., Weber, S., Petit, J., Alleman, L., Albinet, A., Riffault, V., et al. (2021). Overview of the French Operational Network for In Situ Observation of PM Chemical Composition and Sources in Urban Environments (CARA Program). Atmosphere, 12(2).
Abstract: The CARA program has been running since 2008 by the French reference laboratory for air quality monitoring (LCSQA) and the regional monitoring networks, to gain better knowledge-at a national level-on particulate matter (PM) chemistry and its diverse origins in urban environments. It results in strong collaborations with international-level academic partners for state-of-the-art, straightforward, and robust results and methodologies within operational air quality stakeholders (and subsequently, decision makers). Here, we illustrate some of the main outputs obtained over the last decade, thanks to this program, regarding methodological aspects (both in terms of measurement techniques and data treatment procedures) as well as acquired knowledge on the predominant PM sources. Offline and online methods are used following well-suited quality assurance and quality control procedures, notably including inter-laboratory comparison exercises. Source apportionment studies are conducted using various receptor modeling approaches. Overall, the results presented herewith underline the major influences of residential wood burning (during the cold period) and road transport emissions (exhaust and non-exhaust ones, all throughout the year), as well as substantial contributions of mineral dust and primary biogenic particles (mostly during the warm period). Long-range transport phenomena, e.g., advection of secondary inorganic aerosols from the European continental sector and of Saharan dust into the French West Indies, are also discussed in this paper. Finally, we briefly address the use of stable isotope measurements (delta N-15) and of various organic molecular markers for a better understanding of the origins of ammonium and of the different organic aerosol fractions, respectively.
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Fleurbaey, H., Grilli, R., Mondelain, D., Kassi, S., Yachmenev, A., Yurchenko, S., et al. (2021). Electric-quadrupole and magnetic-dipole contributions to the v(2) + v(3) band of carbon dioxide near 3.3 μm. Journal Of Quantitative Spectroscopy & Radiative Transfer, 266.
Abstract: The recent detections of electric-quadrupole (E2) transitions in water vapor and magnetic-dipole (M1) transitions in carbon dioxide have opened a new field in molecular spectroscopy. While in their present status, the spectroscopic databases provide only electric-dipole (E1) transitions for polyatomic molecules (H2O, CO2, N2O, CH4, O-3 ...), the possible impact of weak E2 and M1 bands to the modeling of the Earth and planetary atmospheres has to be addressed. This is especially important in the case of carbon dioxide for which E2 and M1 bands may be located in spectral windows of weak E1 absorption. In the present work, a high sensitivity absorption spectrum of CO2 is recorded by Optical-Feedback-Cavity Enhanced Absorption Spectroscopy (OFCEAS) in the 3.3 μm transparency window of carbon dioxide. The studied spectral interval corresponds to the region where M1 transitions of the v(2) + v(3) band of carbon dioxide were recently identified in the spectrum of the Martian atmosphere. Here, both M1 and E2 transitions of the v2 + v3 band are detected by OFCEAS. Using recent ab initio calculations of the E2 spectrum of (CO2,)-C-12-O-16 intensity measurements of five M1 lines and three E2 lines allow us to disentangle the M-1 and E-2 con-tributions. Indeed, E2 intensity values (on the order of a few 10(-29) cm/molecule) are found in reasonable agreement with ab initio calculations while the intensity of the M1 lines (including an E2 contribution) agree very well with recent very long path measurements by Fourier Transform spectroscopy. We thus conclude that both E2 and M1 transitions should be systematically incorporated in the CO2 line list pro-vided by spectroscopic databases. (C) 2021 Elsevier Ltd. All rights reserved.
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Gkinis, V., Vinther, B., Popp, T., Quistgaard, T., Faber, A., Holme, C., et al. (2021). A 120,000-year long climate record from a NW-Greenland deep ice core at ultra-high resolution. Scientific Data, 8(1).
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Guillet, G., Preunkert, S., Ravanel, L., Montagnat, M., & Friedrich, R. (2021). Investigation of a cold-based ice apron on a high-mountain permafrost rock wall using ice texture analysis and micro-C-14 dating: a case study of the Triangle du Tacul ice apron (Mont Blanc massif, France). Journal Of Glaciology, 67(266), 1205–1212.
Abstract: The current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years.
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Hattori, S., Iizuka, Y., Alexander, B., Ishino, S., Fujita, K., Zhai, S., et al. (2021). Isotopic evidence for acidity-driven enhancement of sulfate formation after SO2 emission control. Science Advances, 7(19).
Abstract: After the 1980s, atmospheric sulfate reduction is slower than the dramatic reductions in sulfur dioxide (SO2) emissions. However, a lack of observational evidence has hindered the identification of causal feedback mechanisms. Here, we report an increase in the oxygen isotopic composition of sulfate (Delta O-17(SO4)2-) in a Greenland ice core, implying an enhanced role of acidity-dependent in-cloud oxidation by ozone (up to 17 to 27%) in sulfate production since the 1960s. A global chemical transport model reproduces the magnitude of the increase in observed Delta O-17(SO4)2- with a 10 to 15% enhancement in the conversion efficiency from SO2 to sulfate in Eastern North America and Western Europe. With an expected continued decrease in atmospheric acidity, this feedback will continue in the future and partially hinder air quality improvements.
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Ishino, S., Hattori, S., Legrand, M., Chen, Q., Alexander, B., Shao, J., et al. (2021). Regional Characteristics of Atmospheric Sulfate Formation in East Antarctica Imprinted on O-17-Excess Signature. Journal Of Geophysical Research-Atmospheres, 126(6).
Abstract: O-17-excess (Delta O-17 = delta O-17 – 0.52 x delta O-18) of sulfate trapped in Antarctic ice cores has been proposed as a potential tool for assessing past oxidant chemistry, while insufficient understanding of atmospheric sulfate formation around Antarctica hampers its interpretation. To probe influences of regional specific chemistry, we compared year-round observations of Delta O-17 of non-sea-salt sulfate in aerosols (Delta O-17(SO42-)(nss)) at Dome C and Dumont d'Urville, inland and coastal sites in East Antarctica, throughout the year 2011. Although Delta O-17(SO42-)(nss) at both sites showed consistent seasonality with summer minima (similar to 1.0 parts per thousand) and winter maxima (similar to 2.5 parts per thousand) owing to sunlight-driven changes in the relative importance of O-3 oxidation to OH and H2O2 oxidation, significant intersite differences were observed in austral spring-summer and autumn. The cooccurrence of higher Delta O-17(SO42-)(nss) at inland (2.0 parts per thousand +/- 0.1 parts per thousand) than the coastal site (1.2 parts per thousand +/- 0.1 parts per thousand) and chemical destruction of methanesulfonate (MS-) in aerosols at inland during spring-summer (October-December), combined with the first estimated Delta O-17(MS-) of similar to 16 parts per thousand, implies that MS- destruction produces sulfate with high Delta O-17(SO42-)(nss) of similar to 12 parts per thousand. If contributing to the known postdepositional decrease of MS- in snow, this process should also cause a significant postdepositional increase in Delta O-17(SO42-)(nss) over 1 parts per thousand, that can reconcile the discrepancy between Delta O-17(SO42-)(nss) in the atmosphere and ice. The higher Delta O-17(SO42-)(nss) at the coastal site than inland during autumn (March-May) may be associated with oxidation process involving reactive bromine and/or sea-salt particles around the coastal region.
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Jiang, Z., Alexander, B., Savarino, J., Erbland, J., & Geng, L. (2021). Impacts of the photo-driven post-depositional processing on snow nitrate and its isotopes at Summit, Greenland: a model-based study. Cryosphere, 15(9), 4207–4220.
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Larue, F., Picard, G., Aublanc, J., Arnaud, L., Robledano-Perez, A., Le Meur, E., et al. (2021). Radar altimeter waveform simulations in Antarctica with the Snow Microwave Radiative Transfer Model (SMRT). Remote Sensing Of Environment, 263.
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Legrand, M., Mcconnell, J., Preunkert, S., Chellman, N., & Arienzo, M. (2021). Causes of Enhanced Bromine Levels in Alpine Ice Cores During the 20th Century: Implications for Bromine in the Free European Troposphere. Journal Of Geophysical Research-Atmospheres, 126(8).
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Legrand, M., Weller, R., Preunkert, S., & Jourdain, B. (2021). Ammonium in Antarctic Aerosol: Marine Biological Activity Versus Long-Range Transport of Biomass Burning. Geophysical Research Letters, 48(11).
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Levin, I., Hammer, S., Kromer, B., Preunkert, S., Weller, R., & Worthy, D. (2021). Radiocarbon In Global Tropospheric Carbon Dioxide. Radiocarbon, .
Abstract: Since the 1950s, observations of radiocarbon (C-14) in tropospheric carbon dioxide (CO2) have been conducted in both hemispheres, documenting the so-called nuclear “bomb spike” and its transfer into the oceans and the terrestrial biosphere, the two compartments permanently exchanging carbon with the atmosphere. Results from the Heidelberg global network of Delta C-14-CO2 observations are revisited here with respect to the insights and quantitative constraints they provided on these carbon exchange fluxes. The recent development of global and hemispheric trends of Delta C-14-CO2 are further discussed in regard to their suitability to continue providing constraints for C-14-free fossil CO2 emission changes on the global and regional scale.
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Lilien, D., Steinhage, D., Taylor, D., Parrenin, F., Ritz, C., Mulvaney, R., et al. (2021). Brief communication: New radar constraints support presence of ice older than 1.5 Myr at Little Dome C. Cryosphere, 15(4), 1881–1888.
Abstract: The area near Dome C, East Antarctica, is thought to be one of the most promising targets for recovering a continuous ice-core record spanning more than a million years. The European Beyond EPICA consortium has selected Little Dome C (LDC), an area similar to 35 km southeast of Concordia Station, to attempt to recover such a record. Here, we present the results of the final ice-penetrating radar survey used to refine the exact drill site. These data were acquired during the 2019-2020 austral summer using a new, multi-channel high-resolution very high frequency (VHF) radar operating in the frequency range of 170-230 MHz. This new instrument is able to detect reflectors in the near-basal region, where previous surveys were largely unable to detect horizons. The radar stratigraphy is used to transfer the timescale of the EPICA Dome C ice core (EDC) to the area of Little Dome C, using radar isochrones dating back past 600 ka. We use these data to derive the expected depth-age relationship through the ice column at the now-chosen drill site, termed BELDC (Beyond EPICA LDC). These new data indicate that the ice at BELDC is considerably older than that at EDC at the same depth and that there is about 375m of ice older than 600 kyr at BELDC. Stratigraphy is well preserved to 2565 m, similar to 93% of the ice thickness, below which there is a basal unit with unknown properties. An ice-flow model tuned to the isochrones suggests ages likely reach 1.5 Myr near 2500 m, similar to 65m above the basal unit and similar to 265m above the bed, with sufficient resolution (19 +/- 2 kyrm(-1)) to resolve 41 kyr glacial cycles.
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Lindau, F., Simoes, J., Delmonte, B., Ginot, P., Baccolo, G., Paleari, C., et al. (2021). Giant dust particles at Nevado Illimani: a proxy of summertime deep convection over the Bolivian Altiplano. Cryosphere, 15(3), 1383–1397.
Abstract: A deeper understanding of past atmospheric circulation variability in the Central Andes is a high-priority topic in paleoclimatology mainly because of the necessity to validate climate models used to predict future precipitation trends and to develop mitigation and/or adaptation strategies for future climate change scenarios in this region. Within this context, we here investigate an 18-year firn core drilled at Nevado Illimani in order to interpret its mineral dust record in relation to seasonal processes, in particular atmospheric circulation and deep convection. The core was dated by annual layer counting based on seasonal oscillations of dust, calcium, and stable isotopes. Geochemical and mineralogical data show that dust is regionally sourced in winter and summer. During austral summer (wet season), an increase in the relative proportion of giant dust particles (empty set > 20 μm) is observed, in association with oscillations of stable isotope records (delta D, delta O-18). It seems that at Nevado Illimani both the deposition of dust and the isotopic signature of precipitation are influenced by atmospheric deep convection, which is also related to the total amount of precipitation in the area. This hypothesis is corroborated by regional meteorological data. The interpretation of giant particle and stable isotope records suggests that downdrafts due to convective activity promote turbulent conditions capable of suspending giant particles in the vicinity of Nevado Illimani. Giant particles and stable isotopes, when considered together, can be therefore used as a new proxy for obtaining information about deep convective activity in the past.
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Schmidely, L., Nehrbass-Ahles, C., Schmitt, J., Han, J., Silva, L., Shin, J., et al. (2021). CH4 and N2O fluctuations during the penultimate deglaciation. Climate Of The Past, 17(4), 1627–1643.
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Thomas, M., Laube, J., Kaiser, J., Allin, S., Martinerie, P., Mulvaney, R., et al. (2021). Stratospheric carbon isotope fractionation and tropospheric histories of CFC-11, CFC-12, and CFC-113 isotopologues. Atmospheric Chemistry And Physics, 21(9), 6857–6873.
Abstract: We present novel measurements of the carbon isotope composition of CFC-11 (CCl3F), CFC-12 (CCl2F2), and CFC-113 (CF2ClCFCl2), three atmospheric trace gases that are important for both stratospheric ozone depletion and global warming. These measurements were carried out on air samples collected in the stratosphere – the main sink region for these gases – and on air extracted from deep polar firn snow. We quantify, for the first time, the apparent isotopic fractionation, epsilon(app)(C-13), for these gases as they are destroyed in the high- and mid-latitude stratosphere: epsilon(app)(CFC-12, high-latitude) = (-20.2 +/- 4.4) parts per thousand, and epsilon(app)(CFC-113, high-latitude) = (-9.4 +/- 4.4) parts per thousand, epsilon(app)(CFC-12, mid-latitude) = (30.3 +/- 10.7) parts per thousand, and epsilon(app)(CFC-113, mid-latitude) = (34.4 +/- 9.8) parts per thousand. Our CFC-11 measurements were not sufficient to calculate epsilon(app)(CFC-11), so we instead used previously reported photolytic fractionation for CFC-11 and CFC-12 to scale our epsilon(app)(CFC-12), resulting in epsilon(app)(CFC-11, high-latitude) = (-7.8 +/- 1.7) parts per thousand and epsilon(app)(CFC-11, mid-latitude) = (-11.7 +/- 4.2) parts per thousand. Measurements of firn air were used to construct histories of the tropospheric isotopic composition, delta(T)(C-13), for CFC-11 (1950s to 2009), CFC-12 (1950s to 2009), and CFC-113 (1970s to 2009), with delta(T)(C-13) increasing for each gas. We used epsilon(app)(high-latitude), which was derived from more data, and a constant isotopic composition of emissions, delta(E)(C-13), to model delta(T)(C-13, CFC-11), delta(T)(C-13, CFC-12), and delta(T)(C-13, CFC-113). For CFC-11 and CFC-12, modelled delta(T)(C-13) was consistent with measured delta(T)(C-13) for the entire period covered by the measurements, suggesting that no dramatic change in delta(E)(C-13, CFC-11) or delta(E)(C-13, CFC-12) has occurred since the 1950s. For CFC-113, our modelled delta(T)(C-13, CFC-113) did not agree with our measurements earlier than 1980. This discrepancy may be indicative of a change in delta(E)(C-13, CFC-113). However, this conclusion is based largely on a single sample and only just significant outside the 95% confidence interval. Therefore more work is needed to independently verify this temporal trend in the global tropospheric C-13 isotopic composition of CFC-113. Our modelling predicts increasing delta(T)(C-13, CFC-11), delta(T)(C-13, CFC-12), and delta(T)(C-13, CFC-113) into the future. We investigated the effect of recently reported new CFC-11 emissions on background delta(T)(C-13, CFC-11) by fixing model emissions after 2012 and comparing delta(T)(C-13, CFC-11) in this scenario to the model base case. The difference in delta(T)(C-13, CFC-11) between these scenarios was 1.4 parts per thousand in 2050. This difference is smaller than our model uncertainty envelope and would therefore require improved modelling and measurement precision as well as better quantified isotopic source compositions to detect.
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Xiao, C., Du, Z., Handley, M., Mayewski, P., Cao, J., Schupbach, S., et al. (2021). Iron in the NEEM ice core relative to Asian loess records over the last glacial-interglacial cycle. National Science Review, 8(7).
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Zhai, S., Wang, X., Mcconnell, J., Geng, L., Cole-Dai, J., Sigl, M., et al. (2021). Anthropogenic Impacts on Tropospheric Reactive Chlorine Since the Preindustrial. Geophysical Research Letters, 48(14).
Abstract: Tropospheric reactive gaseous chlorine (Cl-y) impacts the atmosphere's oxidation capacity with implications for chemically reduced gases such as methane. Here we use Greenland ice-core records of chlorine, sodium, and acidity, and global model simulations to show how tropospheric Cl-y has been impacted by anthropogenic emissions since the 1940s. We show that anthropogenic contribution of nonsea-salt chlorine significantly influenced total chlorine and its trends after the 1940s. The modeled regional 170% Cl-y increase from preindustrial to the 1970s was driven by acid displacement from sea-salt-aerosol, direct emission of hydrochloric acid (HCl) from combustion, and chemical reactions driven by anthropogenic nitrogen oxide (NOx) emissions. Since the 1970s, the modeled 6% Cl-y decrease was caused mainly by reduced anthropogenic HCl emissions from air pollution mitigation policies. Our findings suggest that anthropogenic emissions of acidic gases and their emission control strategies have substantial impacts on Cl-y with implications for tropospheric oxidants, methane, and mercury.
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2020 |
Barbero, A., Blouzon, C., Savarino, J., Caillon, N., Dommergue, A., & Grilli, R. (2020). A compact incoherent broadband cavity-enhanced absorption spectrometer for trace detection of nitrogen oxides, iodine oxide and glyoxal at levels below parts per billion for field applications. Atmospheric Measurement Techniques, 13(8), 4317–4331.
Abstract: We present a compact, affordable and robust instrument based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) for simultaneous detection of NOx, IO, CHOCHO and O-3 in the 400-475 nm wavelength region. The instrument relies on the injection of a high-power LED source in a high-finesse cavity (F similar to 33100), with the transmission signal being detected by a compact spectrometer based on a high-order diffraction grating and a charge-coupled device (CCD) camera. A minimum detectable absorption of 2.0 x 10(-10) cm(-1) was achieved within similar to 22 min of total acquisition, corresponding to a figure of merit of 1.8 x 10(-10) cm(-1) Hz(-1/2) per spectral element. Due to the multiplexing broadband feature of the setup, multi-species detection can be performed with simultaneous detection of NO2, IO, CHOCHO and O-3 achieving detection limits of 11, 0.3, 10 ppt (parts per trillion) and 47 ppb (parts per billion) (1 sigma) within 22 min of measurement, respectively (half of the time is spent on the acquisition of the reference spectrum in the absence of the absorber, and the other half is spent on the absorption spectrum). The implementation on the inlet gas line of a compact ozone generator based on electrolysis of water allows for the measurement of NOx (NO + NO2) and therefore an indirect detection of NO with detection limits for NOx and NO of 10 and 21 ppt (1 sigma), respectively. The device has been designed to fit in a 19 in., 3U (5.25 in.) rack-mount case; weighs 15 kg; and has a total electrical power consumption of < 300 W. The instrument can be employed to address different scientific objectives such as better constraining the oxidative capacity of the atmosphere, studying the chemistry of highly reactive species in atmospheric chambers as well as in the field and looking at the sources of glyoxal in the marine boundary layer to study possible implications on the formation of secondary aerosol particles.
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Fourteau, K., Arnaud, L., Fain, X., Martinerie, P., Etheridge, D., Lipenkov, V., et al. (2020). Historical porosity data in polar firn. Earth System Science Data, 12(2), 1171–1177.
Abstract: In the 1990s, closed and open porosity volumes of firn samples were measured by J.-M. Barnola using the technique of gas pycnometry, on firn from three different polar sites. They are the basis of a parameterization of closed porosity in polar firn, first introduced in Goujon et al. (2003) and used in several firn physics models (e.g., Buizert et al., 2012). However, these data and their processing have not been published in their own right yet. In this short article, we detail how they were processed by J.-M. Barnola and how the closed porosity parameterization was obtained. We show that the original data processing only partially accounts for the presence of reopened bubbles in the samples. Since the proper correction to apply for this effect is hard to estimate, we also processed the data without including a correction for reopened bubbles. Finally, we made these pycnometry data available in order to be used by the glaciology community, notably for the study of polar ice formation and of the composition of gas records in ice cores. They are hosted on the PANGAEA database: https://doi.org/10.1594/PANGAEA.907678 (Fourteau et al., 2019a).
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Fourteau, K., Gillet-Chaulet, F., Martinerie, P., & Fain, X. (2020). A Micro-Mechanical Model for the Transformation of Dry Polar Firn Into Ice Using the Level-Set Method. Frontiers In Earth Science, 8.
Abstract: Interpretation of greenhouse gas records in polar ice cores requires a good understanding of the mechanisms controlling gas trapping in polar ice, and therefore of the processes of densification and pore closure in firn (compacted snow). Current firn densification models are based on a macroscopic description of the firn and rely on empirical laws and/or idealized geometries to obtain the equations governing the densification and pore closure. Here, we propose a physically-based methodology explicitly representing the porous structure and its evolution over time. In order to handle the complex geometry and topological changes that occur during firn densification, we rely on a Level-Set representation of the interface between the ice and the pores. Two mechanisms are considered for the displacement of the interface: (i) mass surface diffusion driven by local pore curvature and (ii) ice dislocation creep. For the latter, ice is modeled as a viscous material and the flow velocities are solutions of the Stokes equations. First applications show that the model is able to densify firn and split pores. Using the model in cold and arid conditions of the Antarctic plateau, we show that gas trapping models do not have to consider the reduced compressibility of closed pores compared to open pores in the deepest part of firns. Our results also suggest that the mechanism of curvature-driven surface diffusion does not result in pore splitting, and that ice creep has to be taken into account for pores to close. Future applications of this type of model could help quantify the evolution and closure of firn porous networks for various accumulation and temperature conditions.
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Fourteau, K., Martinerie, P., Fain, X., Ekaykin, A., Chappellaz, J., & Lipenkov, V. (2020). Estimation of gas record alteration in very low-accumulation ice cores. Climate Of The Past, 16(2), 503–522.
Abstract: We measured the methane mixing ratios of enclosed air in five ice core sections drilled on the East Antarctic Plateau. Our work aims to study two effects that alter the recorded gas concentrations in ice cores: layered gas trapping artifacts and firn smoothing. Layered gas trapping artifacts are due to the heterogeneous nature of polar firn, where some strata might close early and trap abnormally old gases that appear as spurious values during measurements. The smoothing is due to the combined effects of diffusive mixing in the firn and the progressive closure of bubbles at the bottom of the firn. Consequently, the gases trapped in a given ice layer span a distribution of ages. This means that the gas concentration in an ice layer is the average value over a certain period of time, which removes the fast variability from the record. Here, we focus on the study of East Antarctic Plateau ice cores, as these low-accumulation ice cores are particularly affected by both layering and smoothing. We use high-resolution methane data to test a simple trapping model reproducing the layered gas trapping artifacts for different accumulation conditions typical of the East Antarctic Plateau. We also use the high-resolution methane measurements to estimate the gas age distributions of the enclosed air in the five newly measured ice core sections. It appears that for accumulations below 2 cm ice equivalent yr(-1) the gas records experience nearly the same degree of smoothing. We therefore propose to use a single gas age distribution to represent the firn smoothing observed in the glacial ice cores of the East Antarctic Plateau. Finally, we used the layered gas trapping model and the estimation of glacial firn smoothing to quantify their potential impacts on a hypothetical 1.5-million-year-old ice core from the East Antarctic Plateau. Our results indicate that layering artifacts are no longer individually resolved in the case of very thinned ice near the bedrock. They nonetheless contribute to slight biases of the measured signal (less than 10 ppbv and 0.5 ppmv in the case of methane using our currently established continuous CH4 analysis and carbon dioxide, respectively). However, these biases are small compared to the dampening experienced by the record due to firn smoothing.
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Grilli, R., Darchambeau, F., Chappellaz, J., Mugisha, A., Triest, J., & Umutoni, A. (2020). Continuous in situ measurement of dissolved methane in Lake Kivu using a membrane inlet laser spectrometer. Geoscientific Instrumentation Methods And Data Systems, 9(1), 141–151.
Abstract: We report the first high-resolution continuous profile of dissolved methane in the shallow water of Lake Kivu, Rwanda. The measurements were performed using an in situ dissolved gas sensor, called Sub-Ocean, based on a patented membrane-based extraction technique coupled with a highly sensitive optical spectrometer. The sensor was originally designed for ocean settings, but both the spectrometer and the extraction system were modified to extend the dynamical range up to 6 orders of magnitude with respect to the original prototype (from nmol L-1 to mmol L-1 detection) to fit the range of concentrations at Lake Kivu. The accuracy of the instrument was estimated to +/- 22 % (2 sigma) from the standard deviation of eight profiles at 80 m depth, corresponding to +/- 0.112 mbar of CH4 in water or +/- 160 nmol L-1 at 25 degrees C and 1 atm. The instrument was able to continuously profile the top 150 m of the water column within only 25 min The maximum observed mixing ratio of CH4 in the gas phase concentration was 77 %, which at 150 m depth and under thermal conditions of the lake corresponds to 3.5 mmol L-1. Deeper down, dissolved CH4 concentrations were too large for the methane absorption spectrum to be correctly retrieved. Results are in good agreement with discrete in situ measurements conducted with the commercial HydroC (R) sensor. This fast-profiling feature is highly useful for studying the transport, production and consumption of CH4 and other dissolved gases in aquatic systems. While the sensor is well adapted for investigating most environments with a concentration of CH4 up to a few millimoles per liter, in the future the spectrometer could be replaced with a less sensitive analytical technique possibly including simultaneous detection of dissolved CO2 and total dissolved gas pressure, for exploring settings with very high concentrations of CH4 such as the bottom waters of Lake Kivu.
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Helmig, D., Liptzin, D., Hueber, J., & Savarino, J. (2020). Impact of exhaust emissions on chemical snowpack composition at Concordia Station, Antarctica. Cryosphere, 14(1), 199–209.
Abstract: The chemistry of reactive gases inside the snowpack and in the lower atmosphere was investigated at Concordia Station (Dome C), Antarctica, from December 2012 to January 2014. Measured species included ozone, nitrogen oxides, gaseous elemental mercury (GEM), and formaldehyde, for study of photochemical reactions, surface exchange, and the seasonal cycles and atmospheric chemistry of these gases. The experiment was installed approximate to 1 km from the station main infrastructure inside the station clean air sector and within the station electrical power grid boundary. Ambient air was sampled continuously from inlets mounted above the surface on a 10m meteorological tower. In addition, snowpack air was collected at 30 cm intervals to 1.2m depth from two manifolds that had both above- and below-surface sampling inlets. Despite being in the clean air sector, over the course of the 1.2-year study, we observed on the order of 50 occasions when exhaust plumes from the camp, most notably from the power generation system, were transported to the study site. Continuous monitoring of nitrogen oxides (NOx) provided a measurement of a chemical tracer for exhaust plumes. Highly elevated levels of NOx (up to 1000 x background) and lowered ozone (down to approximate to 50 %), most likely from reaction of ozone with nitric oxide, were measured in air from above and within the snowpack. Within 5-15 min from observing elevated pollutant levels above the snow, rapidly increasing and long-lasting concentration enhancements were measured in snowpack air. While pollution events typically lasted only a few minutes to an hour above the snow surface, elevated NOx levels were observed in the snowpack lasting from a few days to approximate to 1 week. GEM and formaldehyde measurements were less sensitive and covered a shorter measurement period; neither of these species' data showed noticeable concentration changes during these events that were above the normal variability seen in the data. Nonetheless, the clarity of the NOx and ozone observations adds important new insight into the discussion of if and how snow photochemical experiments within reach of the power grid of polar research sites are possibly compromised by the snowpack being chemically influenced (contaminated) by gaseous and particulate emissions from the research camp activities. This question is critical for evaluating if snowpack trace chemical measurements from within the camp boundaries are representative for the vast polar ice sheets.
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Hmiel, B., Petrenko, V., Dyonisius, M., Buizert, C., Smith, A., Place, P., et al. (2020). Preindustrial (CH4)-C-14 indicates greater anthropogenic fossil CH4 emissions. Nature, 578(7795), 409–+.
Abstract: Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era(1). Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate(2,3). Carbon-14 in CH4 ((CH4)-C-14) can be used to distinguish between fossil (C-14-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct (CH4)-C-14 emissions from nuclear reactors have complicated this approach since the middle of the 20th century(4,5). Moreover, the partitioning of total fossil CH4 emissions (presently 172 to 195 teragrams CH4 per year)(2,3) between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH4 per year(6,7). Geological emissions were less than 15.4 teragrams CH4 per year at the end of the Pleistocene, about 11,600 years ago(8), but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core (CH4)-C-14 measurements to show that natural geological CH4 emissions to the atmosphere were about 1.6 teragrams CH4 per year, with a maximum of 5.4 teragrams CH4 per year (95 per cent confidence limit)-an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH4 emissions are underestimated by about 38 to 58 teragrams CH4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH4 budget, and will help to inform strategies for targeted emission reductions(9,10). Isotopic evidence from ice cores indicates that preindustrial-era geological methane emissions were lower than previously thought, suggesting that present-day emissions of methane from fossil fuels are underestimated.
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Lee, J., Brook, E., Bertler, N., Buizert, C., Baisden, T., Blunier, T., et al. (2020). An 83 000-year-old ice core from Roosevelt Island, Ross Sea, Antarctica. Climate Of The Past, 16(5), 1691–1713.
Abstract: In 2013 an ice core was recovered from Roosevelt Island, an ice dome between two submarine troughs carved by paleo-ice-streams in the Ross Sea, Antarctica. The ice core is part of the Roosevelt Island Climate Evolution (RICE) project and provides new information about the past configuration of the West Antarctic Ice Sheet (WAIS) and its retreat during the last deglaciation. In this work we present the RICE17 chronology, which establishes the depth-age relationship for the top 754m of the 763m core. RICE17 is a composite chronology combining annual layer interpretations for 0-343m (Winstrup et al., 2019) with new estimates for gas and ice ages based on synchronization of CH4 and delta O-18(atm) records to corresponding records from the WAIS Divide ice core and by modeling of the gas age-ice age difference. Novel aspects of this work include the following: (1) an automated algorithm for multiproxy stratigraphic synchronization of high-resolution gas records; (2) synchronization using centennial-scale variations in methane for preanthropogenic time periods (60-720 m, 1971 CE to 30 ka), a strategy applicable for future ice cores; and (3) the observation of a continuous climate record back to similar to 65 ka providing evidence that the Roosevelt Island Ice Dome was a constant feature throughout the last glacial period.
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Legrand, M., Mcconnell, J., Lestel, L., Preunkert, S., Arienzo, M., Chellman, N., et al. (2020). Cadmium Pollution From Zinc-Smelters up to Fourfold Higher Than Expected in Western Europe in the 1980s as Revealed by Alpine Ice. Geophysical Research Letters, 47(10).
Abstract: Estimates of past emission inventories suggest that toxic heavy metal pollution in Europe was highest in the mid-1970s for lead and in the mid-1960s for cadmium, but these previous estimates have not been compared to observations. Here, alpine ice-cores were used to document cadmium and lead pollution in western Europe between 1890 and 2000. The ice-core trends show that while lead pollution largely from leaded gasoline reached a maximum in similar to 1975 as expected, cadmium pollution primarily from zinc smelters peaked in the early-1980s rather than in similar to 1965 and was up to fourfold higher than estimated after 1975. Comparisons between ice-core trends, estimated past emissions, and state-of-the-art atmospheric aerosol transport and deposition modeling suggest that the estimated decreases in cadmium emissions after 1970 were based on overly optimistic emissions reductions from the introduction of pollution control devices and other technological improvements. Plain Language Summary Cadmium and lead are among the most toxic heavy-metal pollutants and identified by international conventions as priority contaminants for emissions reduction. Anthropogenic emissions in Europe previously estimated from commodity production statistics are uncertain; comparison with long-term pollution records extracted from well-dated ice cores provides a means of evaluating these estimates. Alpine ice-core records spanning 1890 to 2000 show that lead pollution, mainly related to leaded gasoline use since the mid-20th century, reached a maximum in the mid-1970s as predicted by estimated past emissions. Surprisingly, however, cadmium levels primarily arising from zinc smelter emissions were up to fourfold higher than expected and decreased only after 1980, suggesting that previous reconstructions of past cadmium pollution had assumed overly optimistic emissions reductions from the introduction of pollution control devices and other technological improvements particularly after 1975. Contrary to previous emissions estimates, these new alpine ice-core records show that western European pollution maxima for these two toxic metals coincided in the 1970s. This finding is important in terms of impact of Cd pollution on organisms that depends on concentration in the environment but also duration of exposure.
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Ming, A., Winton, V., Keeble, J., Abraham, N., Dalvi, M., Griffiths, P., et al. (2020). Stratospheric Ozone Changes From Explosive Tropical Volcanoes: Modeling and Ice Core Constraints. Journal Of Geophysical Research-Atmospheres, 125(11).
Abstract: Major tropical volcanic eruptions have emitted large quantities of stratospheric sulfate and are potential sources of stratospheric chlorine although this is less well constrained by observations. This study combines model and ice core analysis to investigate past changes in total column ozone. Historic eruptions are good analogs for future eruptions as stratospheric chlorine levels have been decreasing since the year 2000. We perturb the preindustrial atmosphere of a chemistry-climate model with high and low emissions of sulfate and chlorine. The sign of the resulting Antarctic ozone change is highly sensitive to the background stratospheric chlorine loading. In the first year, the response is dynamical, with ozone increases over Antarctica. In the high HCl (2Tg emission) experiment, the injected chlorine is slowly transported to the polar regions with subsequent chemical ozone depletion. These model results are then compared to measurements of the stable nitrogen isotopic ratio, delta N-15(NO3-), from a low snow accumulation Antarctic ice core from Dronning Maud Land (recovered in 2016-2017). We expect ozone depletion to lead to increased surface ultraviolet (UV) radiation, enhanced air-snow nitrate photochemistry and enrichment in delta N-15(NO3-) in the ice core. We focus on the possible ozone depletion event that followed the largest volcanic eruption in the past 1,000 years, Samalas in 1257. The characteristic sulfate signal from this volcano is present in the ice core but the variability in delta N-15(NO3-) dominates any signal arising from changes in ultraviolet from ozone depletion. Prolonged complete ozone removal following this eruption is unlikely to have occurred over Antarctica. Plain Language Summary Chlorine in the stratosphere destroys ozone that protects the Earth from harmful ultraviolet radiation. Volcanic eruptions in the tropics can emit sulfate and chlorine into the stratosphere. Chlorine levels are currently decreasing and to understand the impact of a volcanic eruption on stratospheric ozone in a future climate, historical eruptions are a useful analog since the preindustrial climate also had low chlorine levels. Using a chemistry-climate model, we run a set of experiments where we inject different amounts of sulfate and chlorine into the stratosphere over the tropics to simulate different types and strengths of explosive volcanoes and we find that the ozone over Antarctica initially increases over the first year following the eruption. If the volcano emits a large amount of chlorine, ozone then decreases over Antarctica in years two to four following the eruption. We also compare our results to ice core data around a large historic volcanic eruption, Samalas (1257).
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Nehrbass-Ahles, C., Shin, J., Schmitt, J., Bereiter, B., Joos, F., Schilt, A., et al. (2020). Abrupt CO2 release to the atmosphere under glacial and early interglacial climate conditions. Science, 369(6506), 1000–+.
Abstract: Pulse-like carbon dioxide release to the atmosphere on centennial time scales has only been identified for the most recent glacial and deglacial periods and is thought to be absent during warmer climate conditions. Here, we present a high-resolution carbon dioxide record from 330,000 to 450,000 years before present, revealing pronounced carbon dioxide jumps (CDJ) under cold and warm climate conditions. CDJ come in two varieties that we attribute to invigoration or weakening of the Atlantic meridional overturning circulation (AMOC) and associated northward and southward shifts of the intertropical convergence zone, respectively. We find that CDJ are pervasive features of the carbon cycle that can occur during interglacial climate conditions if land ice masses are sufficiently extended to be able to disturb the AMOC by freshwater input.
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Nour, A., Vallet-Coulomb, C., Bouchez, C., Ginot, P., Doumnang, J., Sylvestre, F., et al. (2020). Geochemistry of the Lake Chad Tributaries Under Strongly Varying Hydro-climatic Conditions. Aquatic Geochemistry, 26(1), 3–29.
Abstract: The Lake Chad Basin (LCB) is one of the main endorheic basins in the world and has undergone large-level and surface variations during the last decades, particularly during the Sahelian dry period in the 1970s and the 1980s. The Chari-Logone River system covers 25% of the LCB but accounts for up to 82% of the Lake Chad water supply. The aim of this study is to investigate the dissolved phase transported by the Chari-Logone system, in order (1) to elucidate the origin and the behavior of major elements and the weathering processes in the watershed; (2) to estimate the total dissolved flux, its variability over the last decades and the driving factors. To do so, samples were collected monthly between January 2013 and November 2016 at three representative sites of the basin: in the Chari River in “Chagoua,” in the Logone River in “Ngueli” just before the confluence of both rivers, and at a downstream site in “Douguia,” 30 km after the confluence. Concentrations in major elements displayed significant seasonal variations in the Chari and Logone waters. At the seasonal time scale, the comparison between the concentrations of chemical elements and the flow rates showed a hysteresis loop. This hysteresis behavior corresponds to a variable contribution over time of two water bodies, fast surface water, and slow groundwater, the latter carrying higher concentrations and Ca/Na ratio, which may result from the contribution of pedogenic carbonate weathering to the dominant signature of silicate weathering. At the annual time scale, similar average concentrations are observed in the Chari and Logone Rivers, despite contrasted annual runoff. In addition, an interannual stability of ionic concentrations was observed in the Chari-Logone River during the flood regime, both during the years covered by our monitoring (2013-2016) and during the pre-drought period (1969, 1972 and 1973). This situation corresponds to a chemostatic behavior, where the annual river discharge is the main factor controlling the interannual variation of chemical fluxes.
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Osmont, D., Brugger, S., Gilgen, A., Weber, H., Sigl, M., Modini, R., et al. (2020). Tracing devastating fires in Portugal to a snow archive in the Swiss Alps: a case study. Cryosphere, 14(11), 3731–3745.
Abstract: Recent large wildfires, such as those in Portugal in 2017, have devastating impacts on societies, economy, ecosystems and environments. However, wildfires are a natural phenomenon, which has been exacerbated by land use during the past millennia. Ice cores are one of the archives preserving information on fire occurrences over these timescales. A difficulty is that emission sensitivity of ice cores is often unknown, which constitutes a source of uncertainty in the interpretation of such archives. Information from specific and well-documented case studies is therefore useful to better understand the spatial representation of ice-core burning records. The wildfires near Pedrogao Grande in central Portugal in 2017 provided a test bed to link a fire event to its footprint left in a high-alpine snowpack considered a surrogate for high-alpine ice-core sites. Here, we (1) analysed black carbon (BC) and microscopic charcoal particles deposited in the snowpack close to the high-alpine research station Jungfraujoch in the Swiss Alps; (2) calculated backward trajectories based on ERA-Interim reanalysis data and simulated the transport of these carbonaceous particles using a global aerosol-climate model; and (3) analysed the fire spread, its spatial and temporal extent, and its intensity with remote-sensing (e.g. MODIS) Active Fire and Burned Area products. According to modelled emissions of the FINN v1.6 database, the fire emitted a total amount of 203.5 t BC from a total burned area of 501 km(2) as observed on the basis of satellite fire products. Backward trajectories unambiguously linked a peak of atmospheric-equivalent BC observed at the Jungfraujoch research station on 22 June – with elevated levels until 25 June – with the highly intensive fires in Portugal. The atmospheric signal is in correspondence with an outstanding peak in microscopic charcoal observed in the snow layer, depositing nearly as many charcoal particles as during an average year in other ice archives. In contrast to charcoal, the amount of atmospheric BC deposited during the fire episode was minor due to a lack of precipitation. Simulations with a global aerosol-climate model suggest that the observed microscopic charcoal particles originated from the fires in Portugal and that their contribution to the BC signal in snow was negligible. Our study revealed that microscopic charcoal can be transported over long distances (1500 km) and that snow and ice archives are much more sensitive to distant events than sedimentary archives, for which the signal is dominated by local fires. The findings are important for future ice-core studies as they document that, for BC as a fire tracer, the signal preservation depends on precipitation. Single events, like this example, might not be preserved due to unfavourable meteorological conditions.
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Petit, J., & Raynaud, D. (2020). Forty years of ice-core records of CO2. Nature, 579(7800), 505–506.
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Shin, J., Nehrbass-Ahles, C., Grilli, R., Beeman, J., Parrenin, F., Teste, G., et al. (2020). Millennial-scale atmospheric CO2 variations during the Marine Isotope Stage 6 period (190-135 ka). Climate Of The Past, 16(6), 2203–2219.
Abstract: Using new and previously published CO2 data from the EPICA Dome C ice core (EDC), we reconstruct a new high-resolution record of atmospheric CO2 during Marine Isotope Stage (MIS) 6 (190 to 135 ka) the penultimate glacial period. Similar to the last glacial cycle, where high-resolution data already exists, our record shows that during longer North Atlantic (NA) stadials, millennial CO2 variations during MIS 6 are clearly coincident with the bipolar seesaw signal in the Antarctic temperature record. However, during one short stadial in the NA, atmospheric CO2 variation is small (similar to 5 ppm) and the relationship between temperature variations in EDC and atmospheric CO2 is unclear. The magnitude of CO2 increase during Carbon Dioxide Maxima (CDM) is closely related to the NA stadial duration in both MIS 6 and MIS 3 (60-27 ka). This observation implies that during the last two glacials the overall bipolar seesaw coupling of climate and atmospheric CO2 operated similarly. In addition, similar to the last glacial period, CDM during the earliest MIS 6 show different lags with respect to the corresponding abrupt CH4 rises, the latter reflecting rapid warming in the Northern Hemisphere (NH). During MIS 6i at around 181.5 +/- 0.3 ka, CDM 6i lags the abrupt warming in the NH by only 240 +/- 320 years. However, during CDM 6iv (171.1 +/- 0.2 ka) and CDM 6iii (175.4 +/- 0.4 ka) the lag is much longer: 1290 +/- 540 years on average. We speculate that the size of this lag may be related to a larger expansion of carbonrich, southern-sourced waters into the Northern Hemisphere in MIS 6, providing a larger carbon reservoir that requires more time to be depleted.
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Svensson, A., Dahl-Jensen, D., Steffensen, J., Blunier, T., Rasmussen, S., Vinther, B., et al. (2020). Bipolar volcanic synchronization of abrupt climate change in Greenland and Antarctic ice cores during the last glacial period. Climate Of The Past, 16(4), 1565–1580.
Abstract: The last glacial period is characterized by a number of millennial climate events that have been identified in both Greenland and Antarctic ice cores and that are abrupt in Greenland climate records. The mechanisms governing this climate variability remain a puzzle that requires a precise synchronization of ice cores from the two hemispheres to be resolved. Previously, Greenland and Antarctic ice cores have been synchronized primarily via their common records of gas concentrations or isotopes from the trapped air and via cosmogenic isotopes measured on the ice. In this work, we apply ice core volcanic proxies and annual layer counting to identify large volcanic eruptions that have left a signature in both Greenland and Antarctica. Generally, no tephra is associated with those eruptions in the ice cores, so the source of the eruptions cannot be identified. Instead, we identify and match sequences of volcanic eruptions with bipolar distribution of sulfate, i.e. unique patterns of volcanic events separated by the same number of years at the two poles. Using this approach, we pinpoint 82 large bipolar volcanic eruptions throughout the second half of the last glacial period (12-60 ka). This improved ice core synchronization is applied to determine the bipolar phasing of abrupt climate change events at decadal-scale precision. In response to Greenland abrupt climatic transitions, we find a response in the Antarctic water isotope signals (delta O-18 and deuterium excess) that is both more immediate and more abrupt than that found with previous gas-based interpolar synchronizations, providing additional support for our volcanic framework. On average, the Antarctic bipolar seesaw climate response lags the midpoint of Greenland abrupt delta O-18 transitions by 122 +/- 24 years. The time difference between Antarctic signals in deuterium excess and delta O-18, which likewise informs the time needed to propagate the signal as described by the theory of the bipolar seesaw but is less sensitive to synchronization errors, suggests an Antarctic delta O-18 lag behind Greenland of 152 +/- 37 years. These estimates are shorter than the 200 years suggested by earlier gas-based synchronizations. As before, we find variations in the timing and duration between the response at different sites and for different events suggesting an interaction of oceanic and atmospheric teleconnection patterns as well as internal climate variability.
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Vecchiato, M., Gambaro, A., Kehrwald, N., Ginot, P., Kutuzov, S., Mikhalenko, V., et al. (2020). The Great Acceleration of fragrances and PAHs archived in an ice core from Elbrus, Caucasus. Scientific Reports, 10(1).
Abstract: The Great Acceleration of the anthropogenic impact on the Earth system is marked by the ubiquitous distribution of anthropogenic materials throughout the global environment, including technofossils, radionuclides and the exponential increases of methane and carbon dioxide concentrations. However, personal care products as direct tracers of human domestic habits are often overlooked. Here, we present the first research combining fragrances, as novel personal care products, and polycyclic aromatic hydrocarbons (PAHs) as combustion and industrial markers, across the onset of the Great Acceleration in the Elbrus, Caucasus, ice core. This archive extends from the 1930s to 2005, spanning the profound changes in the relationship between humans and the environment during the twentieth century. Concentrations of both fragrances and PAHs rose throughout the considered period, reflecting the development of the Anthropocene. However, within this rising trend, remarkable decreases of the tracers track the major socioeconomic crises that occurred in Eastern Europe during the second half of the twentieth century.
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Vincent, C., Gilbert, A., Jourdain, B., Piard, L., Ginot, P., Mikhalenko, V., et al. (2020). Strong changes in englacial temperatures despite insignificant changes in ice thickness at Dome du Gaiter glacier (Mont Blanc area). Cryosphere, 14(3), 925–934.
Abstract: The response of very-high-elevation glaciated areas on Mont Blanc to climate change has been analysed using observations and numerical modelling over the last 2 decades. Unlike the changes at low elevations, we observe very low glacier thickness changes, of about – 2.6 m on average since 1993. The slight changes in horizontal ice flow velocities and submergence velocities suggest a decrease of about 10 % in ice flux and surface mass balance. This is due to less snow accumulation and is consistent with the precipitation decrease observed in meteorological data. Conversely, measurements performed in deep boreholes since 1994 reveal strong changes in englacial temperature reaching a 1.5 degrees C increase at a depth of 50 m. We conclude that at such very high elevations, current changes in climate do not lead to visible changes in glacier thickness but cause invisible changes within the glacier in terms of englacial temperatures. Our analysis from numerical modelling shows that glacier near-surface temperature warming is enhanced by increasing melt frequency at high elevations although the impact on surface mass balance is low. This results in a non-linear response of englacial temperature to currently rising air temperatures. In addition, borehole temperature inversion including a new dataset confirms previous findings of similar air temperature changes at high and low elevations in the Alps.
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Winton, V., Ming, A., Caillon, N., Hauge, L., Jones, A., Savarino, J., et al. (2020). Deposition, recycling, and archival of nitrate stable isotopes between the air-snow interface: comparison between Dronning Maud Land and Dome C, Antarctica. Atmospheric Chemistry And Physics, 20(9), 5861–5885.
Abstract: The nitrogen stable isotopic composition in nitrate (delta N-15-NO3-) measured in ice cores from low-snow-accumulation regions in East Antarctica has the potential to provide constraints on past ultraviolet (UV) radiation and thereby total column ozone (TCO) due to the sensitivity of nitrate (NO3-) photolysis to UV radiation. However, understanding the transfer of reactive nitrogen at the air-snow interface in polar regions is paramount for the interpretation of ice core records of delta N-15-NO3- and NO3- mass concentrations. As NO 3 undergoes a number of post-depositional processes before it is archived in ice cores, site-specific observations of delta N-15-NO3- and air-snow transfer modelling are necessary to understand and quantify the complex photochemical processes at play. As part of the Isotopic Constraints on Past Ozone Layer Thickness in Polar Ice (ISOL-ICE) project, we report new measurements of NO3- mass concentration and delta N-15-NO3- in the atmosphere, skin layer (operationally defined as the top 5 mm of the snowpack), and snow pit depth profiles at Kohnen Station, Dronning Maud Land (DML), Antarctica. We compare the results to previous studies and new data, presented here, from Dome C on the East Antarctic Plateau. Additionally, we apply the conceptual 1D model of TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow (TRANSITS) to assess the impact of NO3- recycling on delta N-15-NO3- and NO3- mass concentrations archived in snow and firn. We find clear evidence of NO3- photolysis at DML and confirmation of previous theoretical, field, and laboratory studies that UV photolysis is driving NO3- recycling and redistribution at DML. Firstly, strong denitrification of the snowpack is observed through the delta N-15-NO3- signature, which evolves from the enriched snowpack (-3 parts per thousand to 100 parts per thousand), to the skin layer (-20 parts per thousand to 3 parts per thousand), to the depleted atmosphere (-50% to -2 parts per thousand), corresponding to mass loss of NO3- from the snowpack. Based on the TRANSITS model, we find that NO3- is recycled two times, on average, before it is archived in the snowpack below 15 cm and within 0.75 years (i.e. below the photic zone). Mean annual archived delta N-15-NO3- and NO3- mass concentration values are 50 parts per thousand and 60 ng g(-1), respectively, at the DML site. We report an e-folding depth (light attenuation) of 2-5 cm for the DML site, which is considerably lower than Dome C. A reduced photolytic loss of NO3- at DML results in less enrichment of delta N-15-NO3- than at Dome C mainly due to the shallower e-folding depth but also due to the higher snow accumulation rate based on TRANSITS-modelled sensitivities. Even at a relatively low snow accumulation rate of 6 cm yr(-1) (water equivalent; w.e. ), the snow accumulation rate at DML is great enough to preserve the seasonal cycle of NO3- mass concentration and delta N-15-NO3-, in contrast to Dome C where the depth profiles are smoothed due to longer exposure of surface snow layers to incoming UV radiation before burial. TRANSITS sensitivity analysis of delta N-15-NO3- at DML highlights that the dominant factors controlling the archived delta N-15-NO3- signature are the e-folding depth and snow accumulation rate, with a smaller role from changes in the snowfall timing and TCO. Mean TRANSITS model sensitivities of archived delta N-15-NO3- at the DML site are 100% for an e-folding depth change of 8 cm, 110% for an annual snow accumulation rate change of 8.5 cm yr(-1) w.e., 10% for a change in the dominant snow deposition season between winter and summer, and 10% for a TCO change of 100DU (Dobson units). Here we set the framework for the interpretation of a 1000-year ice core record of delta N-15-NO3- from DML. Ice core delta N-15-NO3- records at DML will be less sensitive to changes in UV than at Dome C; however the higher snow accumulation rate and more accurate dating at DML allows for higher-resolution delta N-15-NO3- records.
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2019 |
Akers, P., Brook, G., Railsback, L., Cherkinksy, A., Liang, F., Ebert, C., et al. (2019). Integrating U-Th, C-14, and Pb-210 methods to produce a chronologically reliable isotope record for the Belize River Valley Maya from a low-uranium stalagmite. Holocene, 29(7), 1234–1248.
Abstract: Social and environmental changes had great spatiotemporal variability in the Maya Lowlands during the Classic and Postclassic Periods, and stalagmites promise high-resolution paleoclimate data that can refine our understanding of this complex time. Unfortunately, stalagmites in this region are often difficult to date by U-Th methods because of low initial uranium concentrations. Other dating techniques can be used on such stalagmites, and we present here an age-depth model for BZBT1, a low-uranium stalagmite sampled from Box Tunich cave in the Belize River Valley. This age-depth model dates the growth of BZBT1 to between 400 and 1610 yr BP (340-1550 CE) by combining evidence from U-Th results, radiocarbon dating of both stalagmite CaCO3 and trapped organic material, and Pb-210 dating. The resulting stable isotope record from BZBT1 reveals paleoclimate changes that affected local Maya populations during the Classic and early Postclassic Periods. This record is further refined by isotopically tuning the BZBT1 data with two other regional stalagmite records. Our work offers additional paleoclimate insight into the relationship between the Maya and their environment from a stalagmite that would typically be disregarded for research purposes. Continued research into alternative dating techniques for speleothems can enable additional scientific discovery while promoting speleothem conservation.
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Akers, P., Brook, G., Railsback, L., Cherkinksy, A., Liang, F., Ebert, C., et al. (2019). Integrating U-Th, C-14, and Pb-210 methods to produce a chronologically reliable isotope record for the Belize River Valley Maya from a low-uranium stalagmite. Holocene, .
Abstract: Social and environmental changes had great spatiotemporal variability in the Maya Lowlands during the Classic and Postclassic Periods, and stalagmites promise high-resolution paleoclimate data that can refine our understanding of this complex time. Unfortunately, stalagmites in this region are often difficult to date by U-Th methods because of low initial uranium concentrations. Other dating techniques can be used on such stalagmites, and we present here an age-depth model for BZBT1, a low-uranium stalagmite sampled from Box Tunich cave in the Belize River Valley. This age-depth model dates the growth of BZBT1 to between 400 and 1610 yr BP (340-1550 CE) by combining evidence from U-Th results, radiocarbon dating of both stalagmite CaCO3 and trapped organic material, and Pb-210 dating. The resulting stable isotope record from BZBT1 reveals paleoclimate changes that affected local Maya populations during the Classic and early Postclassic Periods. This record is further refined by isotopically tuning the BZBT1 data with two other regional stalagmite records. Our work offers additional paleoclimate insight into the relationship between the Maya and their environment from a stalagmite that would typically be disregarded for research purposes. Continued research into alternative dating techniques for speleothems can enable additional scientific discovery while promoting speleothem conservation.
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Baroni, M., Bard, E., Petit, J., Viseur, S., Aumaitre, G., Bourles, D., et al. (2019). Persistent Draining of the Stratospheric Be-10 Reservoir After the Samalas Volcanic Eruption (1257 CE). Journal Of Geophysical Research-Atmospheres, 124(13), 7082–7097.
Abstract: More than 2,000 analyses of beryllium-10 (Be-10) and sulfate concentrations were performed at a nominal subannual resolution on an ice core covering the last millennium as well as on records from three sites in Antarctica (Dome C, South Pole, and Vostok) to better understand the increase in Be-10 deposition during stratospheric volcanic eruptions. A significant increase in Be-10 concentration is observed in 14 of the 26 volcanic events studied. The slope and intercept of the linear regression between Be-10 and sulfate concentrations provide different and complementary information. Slope is an indicator of the efficiency of the draining of Be-10 atoms by volcanic aerosols depending on the amount of SO2 released and the altitude it reaches in the stratosphere. Intercept gives an image of the Be-10 production in the stratospheric reservoir, ultimately depending on solar modulation. The Samalas event (1257 CE) stands out from the others as the biggest eruption of the last millennium with the lowest positive slope of all the events. We hypothetize that the persistence of volcanic aerosols in the stratosphere after the Samalas eruption has drained the stratospheric Be-10 reservoir for a decade, meaning that solar reconstructions based on Be-10 should be considered with caution during this period. The slope of the linear regression between Be-10 and sulfate concentrations can also be used to correct the Be-10 snow/ice signal of the volcanic disturbance.
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Beeman, J., Gest, L., Parrenin, F., Raynaud, D., Fudge, T., Buizert, C., et al. (2019). Antarctic temperature and CO2: near-synchrony yet variable phasing during the last deglaciation. Climate Of The Past, 15(3), 913–926.
Abstract: The last deglaciation, which occurred from 18 000 to 11 000 years ago, is the most recent large natural climatic variation of global extent. With accurately dated paleoclimate records, we can investigate the timings of related variables in the climate system during this major transition. Here, we use an accurate relative chronology to compare temperature proxy data and global atmospheric CO2 as recorded in Antarctic ice cores. In addition to five regional records, we compare a delta O-18 stack, representing Antarctic climate variations with the high-resolution robustly dated WAIS Divide CO2 record (West Antarctic Ice Sheet). We assess the CO2 and Antarctic temperature phase relationship using a stochastic method to accurately identify the probable timings of changes in their trends. Four coherent changes are identified for the two series, and synchrony between CO2 and temperature is within the 95% uncertainty range for all of the changes except the end of glacial termination 1 (T1). During the onset of the last deglaciation at 18 ka and the deglaciation end at 11.5 ka, Antarctic temperature most likely led CO2 by several centuries (by 570 years, within a range of 127 to 751 years, 68% probability, at the T1 onset; and by 532 years, within a range of 337 to 629 years, 68% probability, at the deglaciation end). At 14.4 ka, the onset of the Antarctic Cold Reversal (ACR) period, our results do not show a clear lead or lag (Antarctic temperature leads by 50 years, within a range of -137 to 376 years, 68% probability). The same is true at the end of the ACR (CO2 leads by 65 years, within a range of 211 to 117 years, 68% probability). However, the timings of changes in trends for the individual proxy records show variations from the stack, indicating regional differences in the pattern of temperature change, particularly in the WAIS Divide record at the onset of the deglaciation; the Dome Fuji record at the deglaciation end; and the EDML record after 16 ka (EPICA Dronning Maud Land, where EPICA is the European Project for Ice Coring in Antarctica). In addition, two changes – one at 16 ka in the CO2 record and one after the ACR onset in three of the isotopic temperature records – do not have high-probability counterparts in the other record. The likely-variable phasing we identify testify to the complex nature of the mechanisms driving the carbon cycle and Antarctic temperature during the deglaciation.
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Bourgeois, I., Clement, J., Caillon, N., & Savarino, J. (2019). Foliar uptake of atmospheric nitrate by two dominant subalpine plants: insights from in situ triple-isotope analysis. New Phytologist, 223(4), 1784–1794.
Abstract: The significance of foliar uptake of nitrogen (N) compounds in natural conditions is not well understood, despite growing evidence of its importance to plant nutrition. In subalpine meadows, N-limitation fosters the dominance of specific subalpine plant species, which in turn ensures the provision of essential ecosystems services. Understanding how these plants absorb N and from which sources is important in predicting ecological consequences of increasing N deposition. Here, we investigate the sources of N to plants from subalpine meadows with distinct land-use history in the French Alps, using the triple isotopes (Delta O-17, delta O-18, and delta N-15) of plant tissue nitrate (NO3-). We use this approach to evaluate the significance of foliar uptake of atmospheric NO3- (NO3atm-). The foliar uptake of NO3atm- accounted for 4-16% of the leaf NO3- content, and contributed more to the leaf NO3- pool after peak biomass. Additionally, the gradual N-15 enrichment of NO3- from the soil to the leaves reflected the contribution of NO3atm- assimilation to plants' metabolism. The present study confirms that foliar uptake is a potentially important pathway for NO3atm- into subalpine plants. This is of major significance as N emissions (and deposition) are predicted to increase globally in the future.
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Breant, C., Dos Santos, C., Agosta, C., Casado, M., Fourre, E., Goursaud, S., et al. (2019). Coastal water vapor isotopic composition driven by katabatic wind variability in summer at Dumont d'Urville, coastal East Antarctica. Earth And Planetary Science Letters, 514, 37–47.
Abstract: Dumont d'Urville station, located on the East coast of Antarctica in Adelie Land, is in one of the windiest coastal region on Earth, due to katabatic winds downslope from the East Antarctic ice sheet. In summer, the season of interest in this study, coastal weather is characterized by well-marked diel cycles in temperature and wind patterns. Our study aims at exploring the added value of water vapor stable isotopes in coastal Adelie Land to provide new information on the local atmospheric water cycle and climate. An important application is the interpretation of water isotopic profiles in snow and ice cores recently drilled in Adelie Land. We present the first continuous measurements of delta O-18 and d-excess in water vapor over Adelie Land. During our measurements period (26/12/2016 to 03/02/2017), we observed clear diel cycles in terms of temperature, humidity and isotopic composition. The cycles in isotopic composition are particularly large given the muted variations in temperature when compared to other Antarctic sites where similar monitoring have been performed. Based on data analyses and simulations obtained with the regional MAR model on the coastal Adelie Land, we suggest that the driver for delta O-18 and d-excess diel variability in summer at Dumont d'Urville is the variation of the strength of the wind coming from the continent: the periods with strong wind are associated with the arrival of relatively dry air with water vapor associated with low delta O-18 and high d-excess from the Antarctic plateau. Finally, in addition to the interpretation of snow and ice core isotopic profiles in the coastal regions, our study has implications for the evaluation of atmospheric models equipped with water isotopes. (C) 2019 Elsevier B.V. All rights reserved.
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Breant, C., Landais, A., Orsi, A., Martinerie, P., Extier, T., Prie, F., et al. (2019). Unveiling the anatomy of Termination 3 using water and air isotopes in the Dome C ice core, East Antarctica. Quaternary Science Reviews, 211, 156–165.
Abstract: Each glacial – interglacial transition of the Quaternary occurs in a different orbital context leading to various timing for the deglaciation and sequence of high vs low latitudes events. Termination 3, 250 kyears before present (ka), is an unusual deglaciation in the context of the last 9 deglaciations recorded in the old EPICA Dome C (EDC) Antarctic ice core: it exhibits a three-phase sequence, two warming phases separated by a small cooling, the last phase suggesting a particularly rapid temperature increase. We present here new high resolution delta N-15 and deuterium excess (d-excess) data from the EDC ice core to provide a detailed temperature change estimate during this termination. Then, we combined the delta D and delta O-18 to discuss the relationship between high and low latitude changes through the d-excess. We also provide the high vs low latitude sequence of events over this deglaciation without chronological uncertainty using low latitude ice core proxies. In agreement with previous studies based on speleothem analyses, we show that the first phase of Termination 3 (256-249 ka) is associated with small Heinrich like events linked to changes in ITCZ position, monsoon activity and teleconnections with Antarctica. In a context of minimum Northern Hemisphere insolation, this leads to a rather strong Antarctic warming, as observed in the delta N-15 record in contrast to the relatively small delta D increase. The second warming phase occurs during the rise of the Northern hemisphere insolation, with a large Heinrich like event leading to the characteristic Antarctic warming observed in the delta N-15 and delta D increase as for the more recent terminations. (C) 2019 Elsevier Ltd. All rights reserved.
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Brugger, S., Gobet, E., Osmont, D., Behling, H., Fontana, S., Hooghiemstra, H., et al. (2019). Tropical Andean glacier reveals colonial legacy in modern mountain ecosystems. Quaternary Science Reviews, 220, 1–13.
Abstract: The extent of pre-Columbian land use and its legacy on modern ecosystems, plant associations, and species distributions of the Americas is still hotly debated. To address this gap, we present a Holocene palynological record (pollen, spores, microscopic charcoal, SCP analyses) from Illimani glacier with exceptional temporal resolution and chronological control close to the center of Inca activities around Lake Titicaca in Bolivia. Our results suggest that Holocene fire activity was largely climate-driven and pre-Columbian agropastoral and agroforestry practices had moderate (large-scale) impacts on plant communities. Unprecedented human-shaped vegetation emerged after AD 1740 following the establishment of novel colonial land use practices and was reinforced in the modern era after AD 1950 with intensified coal consumption and industrial plantations of Pinus and Eucalyptus. Although agroforestry practices date back to the Incas, the recent vast afforestation with exotic monocultures together with rapid climate warming and associated fire regime changes may provoke unprecedented and possibly irreversible ecological and environmental alterations. (C) 2019 Elsevier Ltd. All rights reserved.
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Fourteau, K., Martinerie, P., Fain, X., Schaller, C., Tuckwell, R., Lowe, H., et al. (2019). Multi-tracer study of gas trapping in an East Antarctic ice core. Cryosphere, 13(12), 3383–3403.
Abstract: We study a firn and ice core drilled at the new “Lock-In” site in East Antarctica, located 136 km away from Concordia station towards Dumont d'Urville. High-resolution chemical and physical measurements were performed on the core, with a particular focus on the trapping zone of the firn where air bubbles are formed. We measured the air content in the ice, closed and open porous volumes in the firn, firn density, firn liquid conductivity, major ion concentrations, and methane concentrations in the ice. The closed and open porosity volumes of firn samples were obtained using the two independent methods of pycnometry and tomography, which yield similar results. The measured increase in the closed porosity with density is used to estimate the air content trapped in the ice with the aid of a simple gas-trapping model. Results show a discrepancy, with the model trapping too much air. Experimental errors have been considered but do not explain the discrepancy between the model and the observations. The model and data can be reconciled with the introduction of a reduced compression of the closed porosity compared to the open porosity. Yet, it is not clear if this limited compression of closed pores is the actual mechanism responsible for the low amount of air in the ice. High-resolution density measurements reveal the presence of strong layering, manifesting itself as centimeter-scale variations. Despite this heterogeneous stratification, all layers, including the ones that are especially dense or less dense compared to their surroundings, display similar pore morphology and closed porosity as a function of density. This implies that all layers close in a similar way, even though some close in advance or later compared to the bulk firn. Investigation of the chemistry data suggests that in the trapping zone, the observed stratification is partly related to the presence of chemical impurities.
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Gautier, E., Savarino, J., Hoek, J., Erbland, J., Caillon, N., Hattori, S., et al. (2019). 2600-years of stratospheric volcanism through sulfate isotopes. Nature Communications, 10.
Abstract: High quality records of stratospheric volcanic eruptions, required to model past climate variability, have been constructed by identifying synchronous (bipolar) volcanic sulfate horizons in Greenland and Antarctic ice cores. Here we present a new 2600-year chronology of stratospheric volcanic events using an independent approach that relies on isotopic signatures (Delta S-33 and in some cases Delta O-17) of ice core sulfate from five closely-located ice cores from Dome C, Antarctica. The Dome C stratospheric reconstruction provides independent validation of prior reconstructions. The isotopic approach documents several high-latitude stratospheric events that are not bipolar, but climatically-relevant, and diverges deeper in the record revealing tropospheric signals for some previously assigned bipolar events. Our record also displays a collapse of the Delta O-17 anomaly of sulfate for the largest volcanic eruptions, showing a further change in atmospheric chemistry induced by large emissions. Thus, the refinement added by considering both isotopic and bipolar correlation methods provides additional levels of insight for climate-volcano connections and improves ice core volcanic reconstructions.
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Gautier, E., Savarino, J., Hoek, J., Erbland, J., Caillon, N., Hattori, S., et al. (2019). 2600-years of stratospheric volcanism through sulfate isotopes (vol 10, 466, 2019). Nature Communications, 10.
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Geng, L., Savarino, J., Caillon, N., Gautier, E., Farquhar, J., Dottin, J., et al. (2019). Intercomparison measurements of two S-33-enriched sulfur isotope standards. Journal Of Analytical Atomic Spectrometry, 34(6), 1263–1271.
Abstract: Despite widespread applications of sulfur isotope mass-independent fractionation (MIF) signals for probing terrestrial and extra-terrestrial environments, there has been no international sulfur isotope reference material available for normalization of Delta S-33 and Delta S-36 data. International reference materials to anchor isotope values are useful for interlaboratory data comparisons and are needed to evaluate, e.g., whether issues exist associated with blanks and mass spectrometry when using different analytical approaches. We synthesized two sodium sulfate samples enriched in S-33 with different magnitudes, and termed them S-MIF-1 and S-MIF-2, respectively. The sulfur isotopic compositions of these two samples were measured in five different laboratories using two distinct techniques to place them on the V-CDT scale for delta S-34 and a provisional V-CDT scale for Delta S-33 and Delta S-36. We obtained average delta S-34 values of S-MIF-1 = 10.26 +/- 0.22 parts per thousand and S-MIF-2 = 21.53 +/- 0.26 parts per thousand (1 sigma, versus V-CDT). The average Delta S-33 and Delta S-36 values of S-MIF-1 were determined to be 9.54 +/- 0.09 parts per thousand and -0.11 +/- 0.25 parts per thousand, respectively, while the average Delta S-33 and Delta S-36 values of S-MIF-2 are 11.39 +/- 0.08 parts per thousand and -0.33 +/- 0.13 parts per thousand (1 sigma, versus V-CDT). The lack of variation among the interlaboratory isotopic values suggests sufficient homogeneity of S-MIF-1 and S-MIF-2, especially for Delta S-33. Although additional measurements may be needed to ensure the accuracy of the isotopic compositions of S-MIF-1 and S-MIF-2, they can serve as working standards for routine Delta S-33 analysis to improve data consistency, and have the potential to serve as secondary sulfur isotope reference materials to address issues such as scale contraction/expansion and for normalization and reporting of Delta S-33 and Delta S-36 between laboratories. For the same reasons as listed for sulfur isotopes, the same standards were also artificially enriched in O-17. The calibration is still in progress but first estimations gave Delta O-17 = 3.3 +/- 0.3 parts per thousand with unassigned delta O-18.
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Goursaud, S., Masson-Delmotte, V., Favier, V., Preunkert, S., Legrand, M., Minster, B., et al. (2019). Challenges associated with the climatic interpretation of water stable isotope records from a highly resolved firn core from Adelie Land, coastal Antarctica. Cryosphere, 13(4), 1297–1324.
Abstract: A new 21.3 m firn core was drilled in 2015 at a coastal Antarctic high-accumulation site in Adelie Land (66.78 degrees S; 139.56 degrees E, 602 m a.s.l.), named Terre Adelie 192A (TA192A). The mean isotopic values (-19.3 parts per thousand +/- 3.1 parts per thousand for delta O-18 and 5.4 parts per thousand +/- 2.2 parts per thousand for deuterium excess) are consistent with other coastal Antarctic values. No significant isotope-temperature relationship can be evidenced at any timescale. This rules out a simple interpretation in terms of local temperature. An observed asymmetry in the delta O-18 seasonal cycle may be explained by the precipitation of air masses coming from the eastern and western sectors in autumn and winter, recorded in the d-excess signal showing outstanding values in austral spring versus autumn. Significant positive trends are observed in the annual d-excess record and local sea ice extent (135-145 degrees E) over the period 1998-2014. However, process studies focusing on resulting isotopic compositions and particularly the deuterium excess-delta O-18 relationship, evidenced as a potential fingerprint of moisture origins, as well as the collection of more isotopic measurements in Adelie Land are needed for an accurate interpretation of our signals.
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Gutierrez, J., Maraun, D., Widmann, M., Huth, R., Hertig, E., Benestad, R., et al. (2019). An intercomparison of a large ensemble of statistical downscaling methods over Europe: Results from the VALUE perfect predictor cross-validation experiment. International Journal Of Climatology, 39(9), 3750–3785.
Abstract: VALUE is an open European collaboration to intercompare downscaling approaches for climate change research, focusing on different validation aspects (marginal, temporal, extremes, spatial, process-based, etc.). Here we describe the participating methods and first results from the first experiment, using “perfect” reanalysis (and reanalysis-driven regional climate model (RCM)) predictors to assess the intrinsic performance of the methods for downscaling precipitation and temperatures over a set of 86 stations representative of the main climatic regions in Europe. This study constitutes the largest and most comprehensive to date intercomparison of statistical downscaling methods, covering the three common downscaling approaches (perfect prognosis, model output statistics-including bias correction-and weather generators) with a total of over 50 downscaling methods representative of the most common techniques. Overall, most of the downscaling methods greatly improve (reanalysis or RCM) raw model biases and no approach or technique seems to be superior in general, because there is a large method-to-method variability. The main factors most influencing the results are the seasonal calibration of the methods (e.g., using a moving window) and their stochastic nature. The particular predictors used also play an important role in cases where the comparison was possible, both for the validation results and for the strength of the predictor-predictand link, indicating the local variability explained. However, the present study cannot give a conclusive assessment of the skill of the methods to simulate regional future climates, and further experiments will be soon performed in the framework of the EURO-CORDEX initiative (where VALUE activities have merged and follow on). Finally, research transparency and reproducibility has been a major concern and substantive steps have been taken. In particular, the necessary data to run the experiments are provided at and data and validation results are available from the VALUE validation portal for further investigation: .
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Ishino, S., Hattori, S., Savarino, J., Legrand, M., Albalat, E., Albarede, F., et al. (2019). Homogeneous sulfur isotope signature in East Antarctica and implication for sulfur source shifts through the last glacial-interglacial cycle. Scientific Reports, 9.
Abstract: Sulfate aerosol (SO42-) preserved in Antarctic ice cores is discussed in the light of interactions between marine biological activity and climate since it is mainly sourced from biogenic emissions from the surface ocean and scatters solar radiation during traveling in the atmosphere. However, there has been a paradox between the ice core record and the marine sediment record; the former shows constant nonsea-salt (nss-) SO42- flux throughout the glacial-interglacial changes, and the latter shows a decrease in biogenic productivity during glacial periods compared to interglacial periods. Here, by ensuring the homogeneity of sulfur isotopic compositions of atmospheric nss-SO42-(delta S-34(nss)) over East Antarctica, we established the applicability of the signature as a robust tool for distinguishing marine biogenic and nonmarine biogenic SO42. Our findings, in conjunction with existing records of nss-SO42- flux and (delta S-34(nss)) in Antarctic ice cores, provide an estimate of the relative importance of marine biogenic SO42- during the last glacial period to be 48 +/- 10% of nss-SO42-, slightly lower than 59 +/- 11% during the interglacial periods. Thus, our results tend to reconcile the ice core and sediment records, with both suggesting the decrease in marine productivity around Southern Ocean under the cold climate.
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Jansson, P., Triest, J., Grilli, R., Ferre, B., Silyakova, A., Mienert, J., et al. (2019). High-resolution underwater laser spectrometer sensing provides new insights into methane distribution at an Arctic seepage site. Ocean Science, 15(4), 1055–1069.
Abstract: Methane (CH4) in marine sediments has the potential to contribute to changes in the ocean and climate system. Physical and biochemical processes that are difficult to quantify with current standard methods such as acoustic surveys and discrete sampling govern the distribution of dissolved CH4 in oceans and lakes. Detailed observations of aquatic CH4 concentrations are required for a better understanding of CH4 dynamics in the water column, how it can affect lake and ocean acidification, the chemosynthetic ecosystem, and mixing ratios of atmospheric climate gases. Here we present pioneering high-resolution in situ measurements of dissolved CH4 throughout the water column over a 400 m deep CH4 seepage area at the continental slope west of Svalbard. A new fast-response underwater membraneinlet laser spectrometer sensor demonstrates technological advances and breakthroughs for ocean measurements. We reveal decametre-scale variations in dissolved CH4 concentrations over the CH4 seepage zone. Previous studies could not resolve such heterogeneity in the area, assumed a smoother distribution, and therefore lacked both details on and insights into ongoing processes. We show good repeatability of the instrument measurements, which are also in agreement with discrete sampling. New numerical models, based on acoustically evidenced free gas emissions from the seafloor, support the observed heterogeneity and CH4 inventory. We identified sources of CH4, undetectable with echo sounder, and rapid diffusion of dissolved CH4 away from the sources. Results from the continuous ocean laser-spectrometer measurements, supported by modelling, improve our understanding of CH4 fluxes and related physical processes over Arctic CH4 degassing regions.
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Klein, F., Abram, N., Curran, M., Goosse, H., Goursaud, S., Masson-Delmotte, V., et al. (2019). Assessing the robustness of Antarctic temperature reconstructions over the past 2 millennia using pseudoproxy and data assimilation experiments. Climate Of The Past, 15(2), 661–684.
Abstract: The Antarctic temperature changes over the past millennia remain more uncertain than in many other continental regions. This has several origins: (1) the number of high-resolution ice cores is small, in particular on the East Antarctic plateau and in some coastal areas in East Antarctica; (2) the short and spatially sparse instrumental records limit the calibration period for reconstructions and the assessment of the methodologies; (3) the link between isotope records from ice cores and local climate is usually complex and dependent on the spatial scales and timescales investigated. Here, we use climate model results, pseudoproxy experiments and data assimilation experiments to assess the potential for reconstructing the Antarctic temperature over the last 2 millennia based on a new database of stable oxygen isotopes in ice cores compiled in the framework of Antarctica2k (Stenni et al., 2017). The well-known covariance between delta O-18 and temperature is reproduced in the two isotope-enabled models used (ECHAM5/MPI-OM and ECHAM5-wiso), but is generally weak over the different Antarctic regions, limiting the skill of the reconstructions. Furthermore, the strength of the link displays large variations over the past millennium, further affecting the potential skill of temperature reconstructions based on statistical methods which rely on the assumption that the last decades are a good estimate for longer temperature reconstructions. Using a data assimilation technique allows, in theory, for changes in the delta O-18-temperature link through time and space to be taken into account. Pseudoproxy experiments confirm the benefits of using data assimilation methods instead of statistical methods that provide reconstructions with unrealistic variances in some Antarctic subregions. They also confirm that the relatively weak link between both variables leads to a limited potential for reconstructing temperature based on delta O-18. However, the reconstruction skill is higher and more uniform among reconstruction methods when the reconstruction target is the Antarctic as a whole rather than smaller Antarctic subregions. This consistency between the methods at the large scale is also observed when reconstructing temperature based on the real delta O-18 regional composites of Stenni et al. (2017). In this case, temperature reconstructions based on data assimilation confirm the long-term cooling over Antarctica during the last millennium, and the later onset of anthropogenic warming compared with the simulations without data assimilation, which is especially visible inWest Antarctica. Data assimilation also allows for models and direct observations to be reconciled by reproducing the east-west contrast in the recent temperature trends. This recent warming pattern is likely mostly driven by internal variability given the large spread of individual Paleoclimate Modelling Intercomparison Project (PMIP)/Coupled Model Intercomparison Project (CMIP) model realizations in simulating it. As in the pseudoproxy framework, the reconstruction methods perform differently at the subregional scale, especially in terms of the variance of the time series produced. While the potential benefits of using a data assimilation method instead of a statistical method have been highlighted in a pseudoproxy framework, the instrumental series are too short to confirm this in a realistic setup.
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Kokhanovsky, A., Lamare, M., Danne, O., Brockmann, C., Dumont, M., Picard, G., et al. (2019). Retrieval of Snow Properties from the Sentinel-3 Ocean and Land Colour Instrument. Remote Sensing, 11(19).
Abstract: The Sentinel Application Platform (SNAP) architecture facilitates Earth Observation data processing. In this work, we present results from a new Snow Processor for SNAP. We also describe physical principles behind the developed snow property retrieval technique based on the analysis of Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3A/B measurements over clean and polluted snow fields. Using OLCI spectral reflectance measurements in the range 400-1020 nm, we derived important snow properties such as spectral and broadband albedo, snow specific surface area, snow extent and grain size on a spatial grid of 300 m. The algorithm also incorporated cloud screening and atmospheric correction procedures over snow surfaces. We present validation results using ground measurements from Antarctica, the Greenland ice sheet and the French Alps. We find the spectral albedo retrieved with accuracy of better than 3% on average, making our retrievals sufficient for a variety of applications. Broadband albedo is retrieved with the average accuracy of about 5% over snow. Therefore, the uncertainties of satellite retrievals are close to experimental errors of ground measurements. The retrieved surface grain size shows good agreement with ground observations. Snow specific surface area observations are also consistent with our OLCI retrievals. We present snow albedo and grain size mapping over the inland ice sheet of Greenland for areas including dry snow, melted/melting snow and impurity rich bare ice. The algorithm can be applied to OLCI Sentinel-3 measurements providing an opportunity for creation of long-term snow property records essential for climate monitoring and data assimilation studies-especially in the Arctic region, where we face rapid environmental changes including reduction of snow/ice extent and, therefore, planetary albedo.
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Kutuzov, S., Legrand, M., Preunkert, S., Ginot, P., Mikhalenko, V., Shukurov, K., et al. (2019). The Elbrus (Caucasus, Russia) ice core record – Part 2: history of desert dust deposition. Atmospheric Chemistry And Physics, 19(22), 14133–14148.
Abstract: Ice cores are one of the most valuable paleoarchives. Records from ice cores provide information not only about the amount of dust in the atmosphere, but also about dust sources and their changes in the past. In 2009, a 182 m long ice core was recovered from the western plateau of Mt Elbrus (5115 ma.s.l.). This record was further extended after a shallow ice core was drilled in 2013. Here we analyse Ca2+ concentrations, a commonly used proxy of dust, recorded in these Elbrus ice records over the time period of 1774-2013 CE. The Ca2+ record reveals quasi-decadal variability with a generally increasing trend. Using multiple regression analysis, we found a statistically significant spatial correlation of the Elbrus Ca2+ summer concentrations with precipitation and soil moisture content in the Levant region (specifically Syria and Iraq). The Ca2+ record also correlates with drought indices in North Africa (r = 0.67, p<0.001) and Middle East regions (r = 0.71, p<0.001). Dust concentrations prominently increase in the ice core over the past 200 years, confirming that the recent droughts in the Fertile Crescent (1998-2012 CE) present the most severe aridity experienced in at least the past two centuries. For the most recent 33 years recorded (1979-2012 CE), significant correlations exist between Ca2+ and Pacific circulation indices (Pacific Decadal Oscillation, Southern Oscillation Index and Nino 4), which suggests that the increased frequency of extreme El Nino and La Nina events due to a warming climate has extended their influence to the Middle East. Evidence demonstrates that the increase in Ca2+ concentration in the ice core cannot be attributed to human activities, such as coal combustion and cement production.
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Lechevallier, L., Grilli, R., Kerstel, E., Romanini, D., & Chappellaz, J. (2019). Simultaneous detection of C2H6, CH4, and delta C-13-CH4 using optical feedback cavity-enhanced absorption spectroscopy in the mid-infrared region: towards application for dissolved gas measurements. Atmospheric Measurement Techniques, 12(6), 3101–3109.
Abstract: Simultaneous measurement of C2H6 and CH4 concentrations, and of the delta C-13-CH4 isotope ratio is demonstrated using a cavity-enhanced absorption spectroscopy technique in the mid-IR region. The spectrometer is compact and has been designed for field operation. It relies on optical-feedback-assisted injection of 3.3 μm radiation from an inter-band cascade laser (ICL) into a V-shaped high-finesse optical cavity. A minimum absorption coefficient of 2.8 x 10(9) cm(-1) is obtained in a single scan (0.1 s) over 0.7 cm(-1). Precisions of 3 ppbv, 11 ppbv, and 0.08% for C2H6, CH4, and delta C-13-CH4, respectively, are achieved after 400 s of integration time. Laboratory calibrations and tests of performance are reported here. They show the potential for the spectrometer to be embedded in a sensor probe for in situ measurements in ocean waters, which could have important applications for the understanding of the source and fate of hydrocarbons from the seabed and in the water column.
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Lee, K., Han, C., Hong, S., Jun, S., Han, Y., Xiao, C., et al. (2019). A 300-Year High-Resolution Greenland Ice Record of Large-Scale Atmospheric Pollution by Arsenic in the Northern Hemisphere. Environmental Science & Technology, 53(22), 12999–13008.
Abstract: We report the first high-resolution record of arsenic (As) observed in Greenland snow and ice for the periods 1711-1970 and 2003-2009 AD. The results show well-defined large-scale atmospheric pollution by this toxic element in the northern hemisphere, beginning as early as the 18th century. The most striking feature is an abrupt, unprecedented enrichment factor (EF) peak in the late 1890s, with an similar to 30-fold increase in the mean value above the Holocene natural level. Highly enriched As was evident until the late 1910s; a sharp decline was observed after the First World War, reaching a minimum in the early 1930s during the Great Depression. A subsequent increase lasted until the mid-1950s, before decreasing again. Comparisons between the observed variations and Cu smelting data indicate that Cu smelting in Europe and North America was the likely source of early anthropogenic As in Greenland. Despite a significant reduction of similar to 80% in concentration and similar to 60% in EF from the 1950s to the 2000s, more than 80% of present-day As in Greenland is of anthropogenic origin, probably due to increasing As emissions from coal combustion in China. This highlights the demand for the implementation of national and international environmental regulations to further reduce As emissions.
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Preunkert, S., Legrand, M., Kutuzov, S., Ginot, P., Mikhalenko, V., & Friedrich, R. (2019). The Elbrus (Caucasus, Russia) ice core record – Part 1: reconstruction of past anthropogenic sulfur emissions in south-eastern Europe. Atmospheric Chemistry And Physics, 19(22), 14119–14132.
Abstract: This study reports on the glaciochemistry of a deep ice core (182 m long) drilled in 2009 at Mount Elbrus in the Caucasus, Russia. Radiocarbon dating of the particulate organic carbon fraction in the ice suggests that the basal ice dates to 280 +/- 400 CE (Common Era). Based on chemical stratigraphy, the upper 168.6 m of the core was dated by counting annual layers. The seasonally resolved chemical records cover the years 1774-2009 CE, thus being useful to reconstruct many aspects of atmospheric pollution in south-eastern Europe from pre-industrial times to the present day. After having examined the extent to which the arrival of large dust plumes originating from the Sahara and Middle East modifies the chemical composition of the Elbrus (ELB) snow and ice layers, we focus on the dust-free sulfur pollution. The ELB dust-free sulfate levels indicate a 6- and 7-fold increase from 1774-1900 to 1980-1995 in winter and summer, respectively. Remaining close to 55 +/- 10 ppb during the 19th century, the annual dust-free sulfate levels started to rise at a mean rate of similar to 3 ppb per year from 1920 to 1950. The annual increase accelerated between 1950 and 1975 (8 ppb per year), with levels reaching a maximum between 1980 and 1990 (376 +/- 10 ppb) and subsequently decreasing to 270 +/- 18 ppb at the beginning of the 21st century. Long-term dust-free sulfate trends observed in the ELB ice cores are compared with those previously obtained in Alpine and Altai (Siberia) ice, with the most important differences consisting in a much earlier onset and a more pronounced decrease in the sulfur pollution over the last 3 decades in western Europe than south-eastern Europe and Siberia.
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Preunkert, S., Mcconnell, J., Hoffmann, H., Legrand, M., Wilson, A., Eckhardt, S., et al. (2019). Lead and Antimony in Basal Ice From Col du Dome (French Alps) Dated With Radiocarbon: A Record of Pollution During Antiquity. Geophysical Research Letters, 46(9), 4953–4961.
Abstract: Lead and antimony measurements in basal ice from the Col du Dome glacier document heavy metal pollution in western Europe associated with emissions from mining and smelting operations during European antiquity. Radiocarbon dating of the particulate organic carbon fraction in the ice suggests that the basal ice dates to similar to 5,000 +/- 600 cal years BP. In agreement with a precisely dated Greenland lead record, the Col du Dome record indicates two periods of significant lead pollution during the Roman period, that is, the last centuries before the Common Era to the second century of the Common Era. Atmospheric modeling and the Col du Dome record consistently show an overall magnitude of the lead perturbation 100 times larger than in the Greenland record. Antimony closely tracked lead, with antimony pollution about 2 orders of magnitude lower, consistent with European peat records. Plain Language Summary Measurements of radiocarbon on particulate organic matter trapped in ice showed that the deepest ice of the Mont Blanc glacier covers the entire period of antiquity (from 800 BCE to 250 CE). Lead measurements indicated significant metal pollution during the Roman Republican and the Imperial period, that is, during the last centuries before the Common Era to the second century of the Common Era, with much lower levels before and after. We show that the Roman-era emissions enhanced the natural lead level by at least a factor of 10, which was already significant compared to the modern enhancement by a factor of 100 due to lead emissions related to the use of leaded gasoline. This first ice record of pollution by antimony, another toxic heavy metal, during antiquity showing large Roman-era increases in parallel with lead, confirms that early mining and smelting activities had environmental implications beyond simply lead contamination.
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Walters, W., Michalski, G., Bohlkes, J., Alexander, B., Savarino, J., & Thiemens, M. (2019). Assessing the Seasonal Dynamics of Nitrate and Sulfate Aerosols at the South Pole Utilizing Stable Isotopes. Journal Of Geophysical Research-Atmospheres, 124(14), 8161–8177.
Abstract: Atmospheric nitrate (NO3- = particulate NO3- + gas-phase nitric acid [HNO3]) and sulfate (SO42-) are key molecules that play important roles in numerous atmospheric processes. Here, the seasonal cycles of NO3- and total suspended particulate sulfate (SO4(TSP)2-) were evaluated at the South Pole from aerosol samples collected weekly for approximately 10 months (26 January to 25 October) in 2002 and analyzed for their concentration and isotopic compositions. Aerosol NO3- was largely affected by snowpack emissions in which [NO3-] and delta N-15(NO3-) were highest (49.3 +/- 21.4 ng/m(3), n = 8) and lowest (-47.0 +/- 11.7 parts per thousand, n = 5), respectively, during periods of sunlight in the interior of Antarctica. The seasonal cycle of Delta O-17(NO3-) reflected tropospheric chemistry year-round with lower values observed during sunlight periods and higher values observed during dark periods, reflecting shifts from HOx- to O-3-dominated oxidation chemistry. SO4(TSP)2- concentrations were highest during austral summer and fall (86.7 +/- 73.7 ng/m(3), n = 18) and are indicated to be derived from dimethyl sulfide (DMS) emissions, as delta S-34(SO42-)((TSP)) values (18.5 +/- 1.0 parts per thousand, n = 10) were similar to literature delta S-34(DMS) values. The seasonal cycle of Delta O-17(SO42-)((TSP)) exhibited minima during austral summer (0.9 +/- 0.1 parts per thousand, n = 5) and maxima during austral fall (1.3 +/- 0.3 parts per thousand, n = 6) and austral spring (1.6 +/- 0.1 parts per thousand, n = 5), indicating a shift from HOx- to O-3-dominated chemistry in the atmospheric derived SO42- component. Overall, the budgets of NO3- and SO4(TSP)2- at the South Pole were complex functions of transport, localized chemistry, biological activity, and meteorological conditions, and these results will be important for interpretations of oxyanions in ice core records in the interior of Antarctica.
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Yeung, L., Murray, L., Martinerie, P., Witrant, E., Hu, H., Banerjee, A., et al. (2019). Isotopic constraint on the twentieth-century increase in tropospheric ozone. Nature, 570(7760), 224–+.
Abstract: Tropospheric ozone (O-3) is a key component of air pollution and an important anthropogenic greenhouse gas(1). During the twentieth century, the proliferation of the internal combustion engine, rapid industrialization and land-use change led to a global-scale increase in O-3 concentrations(2,3); however, the magnitude of this increase is uncertain. Atmospheric chemistry models typically predict(4-7) an increase in the tropospheric O-3 burden of between 25 and 50 per cent since 1900, whereas direct measurements made in the late nineteenth century indicate that surface O-3 mixing ratios increased by up to 300 per cent(8-10) over that time period. However, the accuracy and diagnostic power of these measurements remains controversial(2). Here we use a record of the clumped-isotope composition of molecular oxygen ((OO)-O-18-O-18 in O-2) trapped in polar firn and ice from 1590 to 2016 ad, as well as atmospheric chemistry model simulations, to constrain changes in tropospheric O-3 concentrations. We find that during the second half of the twentieth century, the proportion of (OO)-O-18-O-18 in O-2 decreased by 0.03 +/- 0.02 parts per thousand (95 per cent confidence interval) below its 1590-1958 ad mean, which implies that tropospheric O-3 increased by less than 40 per cent during that time. These results corroborate model predictions of global-scale increases in surface pollution and vegetative stress caused by increasing anthropogenic emissions of O-3 precursors(4,5,11). We also estimate that the radiative forcing of tropospheric O-3 since 1850 ad is probably less than +0.4 watts per square metre, consistent with results from recent climate modelling studies(12).
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2018 |
Baggenstos, D., Severinghaus, J., Mulvaney, R., Mcconnell, J., Sigl, M., Maselli, O., et al. (2018). A Horizontal Ice Core From Taylor Glacier, Its Implications for Antarctic Climate History, and an Improved Taylor Dome Ice Core Time Scale. Paleoceanography And Paleoclimatology, 33(7), 778–794.
Abstract: Ice core records from Antarctica show mostly synchronous temperature variations during the last deglacial transition, an indication that the climate of the entire continent reacted as one unit to the global changes. However, a record from the Taylor Dome ice core in the Ross Sea sector of East Antarctica has been suggested to show a rapid warming, similar in style and synchronous with the Oldest Dryas-Bolling warming in Greenland. Since publication of the Taylor Dome record, a number of lines of evidence have suggested that this interpretation is incorrect and reflects errors in the underlying time scale. The issues raised regarding the dating of Taylor Dome currently linger unresolved, and the original time scale remains the de facto chronology. We present new water isotope and chemistry data from nearby Taylor Glacier to resolve the confusion surrounding the Taylor Dome time scale. We find that the Taylor Glacier record is incompatible with the original interpretation of the Taylor Dome ice core, showing that the warming in the area was gradual and started at similar to 18 ka BP (before 1950) as seen in other East Antarctic ice cores. We build a consistent, up-to-date Taylor Dome chronology from 0 to 60 ka BP by combining new and old age markers based on synchronization to other ice core records. The most notable feature of the new TD2015 time scale is a gas age-ice age difference of up to 12,000 years during the Last Glacial Maximum, by far the largest ever observed.
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Bourgeois, I., Savarino, J., Caillon, N., Angot, H., Barbero, A., Delbart, F., et al. (2018). Tracing the Fate of Atmospheric Nitrate in a Subalpine Watershed Using Delta O-17. Environmental Science & Technology, 52(10), 5561–5570.
Abstract: Nitrogen is an essential nutrient for life on Earth, but in excess, it can lead to environmental issues (e.g., N saturation, loss of biodiversity, acidification of lakes, etc.). Understanding the nitrogen budget (i.e., inputs and outputs) is essential to evaluate the prospective decay of the ecosystem services (e.g., freshwater quality, erosion control, loss of high patrimonial-value plant species, etc.) that subalpine headwater catchments provide, especially as these ecosystems experience high atmospheric nitrogen deposition. Here, we use a multi-isotopic tracer (Delta O-17, delta N-15 and delta O-18) of nitrate in aerosols, snow, and streams to assess the fate of atmospherically deposited nitrate in the subalpine watershed of the Lautaret Pass (French Alps). We show that atmospheric N deposition contributes significantly to stream nitrate pool year-round, either by direct inputs (up to 35%) or by in situ nitrification of atmospheric ammonium (up to 35%). Snowmelt in particular leads to high exports of atmospheric nitrate, most likely fast enough to impede assimilation by surrounding ecosystems. Yet, in a context of climate change, with shorter snow seasons, and increasing nitrogen emissions, our results hint at possibly stronger ecological consequences of nitrogen atmospheric deposition in the close future.
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Bourgeois, I., Savarino, J., Nemery, J., Caillon, N., Albertin, S., Delbart, F., et al. (2018). Atmospheric nitrate export in streams along a montane to urban gradient. Science Of The Total Environment, 633, 329–340.
Abstract: Nitrogen (N) emissions associated with urbanization exacerbate the atmospheric N influx to remote ecosystems – like mountains -, leading to well-documented detrimental effects on ecosystems (e.g., soil acidification, pollution of freshwaters). Here, the importance and fate of N deposition in a watershed was evaluated along a montane to urban gradient, using a multi-isotopic tracers approach (Delta O-17, delta N-15, delta O-18 of nitrate, delta H-2 and delta O-18 of water). In this setting, the montane streams had higher proportions of atmospheric nitrate compared to urban streams, and exported more atmospheric nitrate on a yearly basis (0.35 vs 0.10 kg-N ha(-1) yr(-1)). In urban areas, nitrate exports were driven by groundwater, whereas in the catchment head nitrate exports were dominated by surface runoff. The main sources of nitrate to the montane streams were microbial nitrification and atmospheric deposition, whereas microbial nitrification and sewage leakage contributed most to urban streams. Based on the measurement of delta N-15 and delta O-18-NO3-, biological processes such as denitrification or N assimilation were not predominant in any streams in this study. The observed low delta N-15 and delta O-18 range of terrestrial nitrate (i.e., nitrate not coming from atmospheric deposition) in surface water compared to literature suggests that atmospheric deposition may be underestimated as a direct source of N. (c) 2018 Elsevier B.V. All rights reserved.
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Buizert, C., Sigl, M., Severi, M., Markle, B., Wettstein, J., Mcconnell, J., et al. (2018). Abrupt ice-age shifts in southern westerly winds and Antarctic climate forced from the north. Nature, 563(7733), 681–+.
Abstract: The mid-latitude westerly winds of the Southern Hemisphere play a central role in the global climate system via Southern Ocean upwelling(1), carbon exchange with the deep ocean(2), Agulhas leakage (transport of Indian Ocean waters into the Atlantic)(3) and possibly Antarctic ice-sheet stability(4). Meridional shifts of the Southern Hemisphere westerly winds have been hypothesized to occur(5,6) in parallel with the well-documented shifts of the intertropical convergence zone(7) in response to Dansgaard-Oeschger (DO) events-abrupt North Atlantic climate change events of the last ice age. Shifting moisture pathways to West Antarctica(8) are consistent with this view but may represent a Pacific teleconnection pattern forced from the tropics(9). The full response of the Southern Hemisphere atmospheric circulation to the DO cycle and its impact on Antarctic temperature remain unclear(10). Here we use five ice cores synchronized via volcanic markers to show that the Antarctic temperature response to the DO cycle can be understood as the superposition of two modes: a spatially homogeneous oceanic 'bipolar seesaw' mode that lags behind Northern Hemisphere climate by about 200 years, and a spatially heterogeneous atmospheric mode that is synchronous with abrupt events in the Northern Hemisphere. Temperature anomalies of the atmospheric mode are similar to those associated with present-day Southern Annular Mode variability, rather than the Pacific-South American pattern. Moreover, deuterium-excess records suggest a zonally coherent migration of the Southern Hemisphere westerly winds over all ocean basins in phase with Northern Hemisphere climate. Our work provides a simple conceptual framework for understanding circum-Antarctic temperature variations forced by abrupt Northern Hemisphere climate change. We provide observational evidence of abrupt shifts in the Southern Hemisphere westerly winds, which have previously documented(1-3) ramifications for global ocean circulation and atmospheric carbon dioxide. These coupled changes highlight the necessity of a global, rather than a purely North Atlantic, perspective on the DO cycle.
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Bulat, S., Doronin, M., Pavlov, G., Karlov, D., Marie, D., & Petit, J. (2018). Unknown Widespread Iron- and Sulfur-Oxidizing Bacteria beneath the East Antarctic Ice Sheet. Paleontological Journal, 52(10), 1196–1203.
Abstract: Comparative analysis of the Vostok ice core (Central East Antarctica; one horizon, three boreholes) and D10 ice core (shoreline nearby the French Dumont d'Urville station) has reliably revealed three phylotypes (species) of aerobic iron-oxidizing betaproteobacteria of the family Gallionellaceae (closely related at the genus level to Sideroxydans lithotrophicus and Ferriphaselus amnicola), one of which has been detected from both the Vostok (borehole 5G-3) and D10 cores. In addition, the phylotype related to sulfur-oxidizing bacteria Tumebacillus sp. has been detected from both the Vostok (borehole 5G-2) and D10 cores. The both ice cores are almost equal in age, about 20000 years; however, they differ in origin: the ice from Dumont d'Urville is atmospheric, while that from Vostok is a lake ice. The ice samples greatly vary in the storage time before treatment in the laboratory (from 0.5 to 40 years) and in intervals between treatments (from 1 to 5 years). The drilling sites are more than 1000 km apart. No evident hydrological links (the transfer of water beneath the ice sheet) between the Lake Vostok and Dumont D'Urville station have been found. This coincidence can be explained by the fact that minerals from the bedrock under the glacier, containing ferrous iron and reduced sulfur compounds, as well as physical and chemical conditions in both sites, liquid fresh water at a temperature near the freezing point, are similar. These and other assumptions are considered in the present article.
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Burr, A., Ballot, C., Lhuissier, P., Martinerie, P., Martin, C. L., & Philip, A. (2018). Pore morphology of polar firn around closure revealed by X-ray tomography. Cryosphere, 12(7), 2481–2500.
Abstract: Understanding the slow densification process of polar firn into ice is essential in order to constrain the age difference between the ice matrix and entrapped gases. The progressive microstructure evolution of the firn column with depth leads to pore closure and gas entrapment. Air transport models in the firn usually include a closed porosity profile based on available data. Pycnometry or melting-refreezing techniques have been used to obtain the ratio of closed to total porosity and air content in closed pores, respectively. X-ray-computed tomography is complementary to these methods, as it enables one to obtain the full pore network in 3-D. This study takes advantage of this nondestructive technique to discuss the morphological evolution of pores on four different Antarctic sites. The computation of refined geometrical parameters for the very cold polar sites Dome C and Lock In (the two Antarctic plateau sites studied here) provides new information that could be used in further studies. The comparison of these two sites shows a more tortuous pore network at Lock In than at Dome C, which should result in older gas ages in deep firn at Lock In. A comprehensive estimation of the different errors related to X-ray tomography and to the sample variability has been performed. The procedure described here may be used as a guideline for further experimental characterization of firn samples. We show that the closed-to-total porosity ratio, which is classically used for the detection of pore closure, is strongly affected by the sample size, the image reconstruction, and spatial heterogeneities. In this work, we introduce an alternative parameter, the connectivity index, which is practically independent of sample size and image acquisition conditions, and that accurately predicts the close-off depth and density. Its strength also lies in its simple computation, without any assumption of the pore status (open or close). The close-off prediction is obtained for Dome C and Lock In, without any further numerical simulations on images (e.g., by permeability or diffusivity calculations).
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Cavitte, M. G. P., Parrenin, F., Ritz, C., Young, D. A., Van Liefferinge, B., Blankenship, D. D., et al. (2018). Accumulation patterns around Dome C, East Antarctica, in the last 73 kyr. Cryosphere, 12(4), 1401–1414.
Abstract: We reconstruct the pattern of surface accumulation in the region around Dome C, East Antarctica, since the last glacial. We use a set of 18 isochrones spanning all observable depths of the ice column, interpreted from various ice-penetrating radar surveys and a 1-D ice flow model to invert for accumulation rates in the region. The shallowest four isochrones are then used to calculate paleoaccumulation rates between isochrone pairs using a 1-D assumption where horizontal advection is negligible in the time interval of each layer. We observe that the large-scale (100s km) surface accumulation gradient is spatially stable through the last 73 kyr, which reflects current modeled and observed precipitation gradients in the region. We also observe small-scale (10 s km) accumulation variations linked to snow redistribution at the surface, due to changes in its slope and curvature in the prevailing wind direction that remain spatially stationary since the last glacial.
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Chambers, S., Preunkert, S., Weller, R., Hong, S., Humphries, R., Tositti, L., et al. (2018). Characterizing Atmospheric Transport Pathways to Antarctica and the Remote Southern Ocean Using Radon-222. Frontiers In Earth Science, 6.
Abstract: We discuss remote terrestrial influences on boundary layer air over the Southern Ocean and Antarctica, and the mechanisms by which they arise, using atmospheric radon observations as a proxy. Our primary motivation was to enhance the scientific community's ability to understand and quantify the potential effects of pollution, nutrient or pollen transport from distant land masses to these remote, sparsely instrumented regions. Seasonal radon characteristics are discussed at 6 stations (Macquarie Island, King Sejong, Neumayer, Dumont d'Urville, Jang Bogo and Dome Concordia) using 1-4 years of continuous observations. Context is provided for differences observed between these sites by Southern Ocean radon transects between 45 and 67 degrees S made by the Research Vessel Investigator. Synoptic transport of continental air within the marine boundary layer (MBL) dominated radon seasonal cycles in the mid-Southern Ocean site (Macquarie Island). MBL synoptic transport, tropospheric injection, and Antarctic outflow all contributed to the seasonal cycle at the sub-Antarctic site (King Sejong). Tropospheric subsidence and injection events delivered terrestrially influenced air to the Southern Ocean MBL in the vicinity of the circumpolar trough (or “Polar Front”). Katabatic outflow events from Antarctica were observed to modify trace gas and aerosol characteristics of the MBL 100-200 km off the coast. Radon seasonal cycles at coastal Antarctic sites were dominated by a combination of local radon sources in summer and subsidence of terrestrially influenced tropospheric air, whereas those on the Antarctic Plateau were primarily controlled by tropospheric subsidence. Separate characterization of long-term marine and katabatic flow air masses at Dumont d'Urville revealed monthly mean differences in summer of up to 5 ppbv in ozone and 0.3 ng m(-3) in gaseous elemental mercury. These differences were largely attributed to chemical processes on the Antarctic Plateau. A comparison of our observations with some Antarctic radon simulations by global climate models over the past two decades indicated that: (i) some models overestimate synoptic transport to Antarctica in the MBL, (ii) the seasonality of the Antarctic ice sheet needs to be better represented in models, (iii) coastal Antarctic radon sources need to be taken into account, and (iv) the underestimation of radon in subsiding tropospheric air needs to be investigated.
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Galeazzo, T., Bekki, S., Martin, E., Savarino, J., & Arnold, S. (2018). Photochemical box modelling of volcanic SO2 oxidation: isotopic constraints. Atmospheric Chemistry And Physics, 18(24), 17909–17931.
Abstract: The photochemical box model CiTTyCAT is used to analyse the absence of oxygen mass-independent anomalies (O-MIF) in volcanic sulfates produced in the troposphere. An aqueous sulfur oxidation module is implemented in the model and coupled to an oxygen isotopic scheme describing the transfer of O-MIF during the oxidation of SO2 by OH in the gas-phase, and by H2O2, O-3 and O-2 catalysed by TMI in the liquid phase. Multiple model simulations are performed in order to explore the relative importance of the various oxidation pathways for a range of plausible conditions in volcanic plumes. Note that the chemical conditions prevailing in dense volcanic plumes are radically different from those prevailing in the surrounding background air. The first salient finding is that, according to model calculations, OH is expected to carry a very significant O-MIF in sulfur-rich volcanic plumes and, hence, that the volcanic sulfate produced in the gas phase would have a very significant positive isotopic enrichment. The second finding is that, although H2O2 is a major oxidant of SO2 throughout the troposphere, it is very rapidly consumed in sulfur-rich volcanic plumes. As a result, H2O2 is found to be a minor oxidant for volcanic SO2. According to the simulations, oxidation of SO2 by O-3 is negligible because volcanic aqueous phases are too acidic. The model predictions of minor or negligible sulfur oxidation by H2O2 and O-3, two oxidants carrying large O-MIF, are consistent with the absence of O-MIF seen in most isotopic measurements of volcanic tropospheric sulfate. The third finding is that oxidation by O-2/TMI in volcanic plumes could be very substantial and, in some cases, dom- H2O2 and O-3 are vastly reduced in a volcanic plume compared to the background air. Only cases where sulfur oxidation by O-2/TMI is very dominant can explain the isotopic composition of volcanic tropospheric sulfate.
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Gautier, E., Savarino, J., Erbland, J., & Farquhar, J. (2018). SO2 Oxidation Kinetics Leave a Consistent Isotopic Imprint on Volcanic Ice Core Sulfate. Journal Of Geophysical Research-Atmospheres, 123(17), 9801–9812.
Abstract: This work presents measurements of time-resolved mass-independently fractionated sulfate of volcanic origin from Antarctic ice core records that cover the last 2,600years. These measurements are used to evaluate the time dependence of the deposited isotopic signal and to extract the isotopic characteristics of the reactions yielding sulfate from stratospheric volcanic eruptions in the modern atmosphere. Time evolution of the signal in snow (years) with respect to the fast SO2 oxidation in the stratosphere suggests that photochemically produced condensed phase is rapidly and continuously separated from the gas phase and preserved during transportation and deposition on the polar ice cap. On some eruptions, a nonzero isotopic mass balance highlights that a part of the signal can be lost during transport and/or deposition. The large number of volcanic events studied allows the S-33 versus S-36 and S-34 versus S-33 slopes to be constrained at -1.56 (1 sigma=0.25) and 0.09 (1 sigma=0.02), respectively. The S-33 versus S-36 slope refines a prior determinations of S-36/S-33=-4 and overlaps the range observed for sulfur seen in early Earth samples (Archean). In recent volcanogenic sulfate, the S-33 versus S-34 differs, however, from the Archean record. The similitude for S-36/S-33 and the difference for S-33/S-34 suggest similar mass-independently fractionated sulfate processes to the Archean atmosphere. Using a simple model, we highlight that a combination of several mechanisms is needed to reproduce the observed isotopic trends and suggest a greater contribution from mass-dependent oxidation by OH in the modern atmosphere. Plain Language Summary Large volcanic eruptions inject sulfurous gases in the stratosphere, where they rapidly form sulfuric acid aerosols. These aerosols can reside in the stratosphere for years, cover the entire globe, and profoundly modify the climate by scattering and absorbing solar radiation. Sulfuric acid aerosols formed by this process acquire an isotopic anomaly that traces these processes and allows identification of these eruptions in ice core records, providing a means to distinguish between high and low climatic impact eruptions in ice core volcanic deposits. This study provides a characterization of this time-dependent isotopic signature that is used to constrain its origin and to understand the processes underlying its production and evolution.
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Geng, L., Savarino, J., Savarino, C. A., Caillon, N., Cartigny, P., Hattori, S., et al. (2018). A simple and reliable method reducing sulfate to sulfide for multiple sulfur isotope analysis. Rapid Communications In Mass Spectrometry, 32(4), 333–341.
Abstract: RationalePrecise analysis of four sulfur isotopes of sulfate in geological and environmental samples provides the means to extract unique information in wide geological contexts. Reduction of sulfate to sulfide is the first step to access such information. The conventional reduction method suffers from a cumbersome distillation system, long reaction time and large volume of the reducing solution. We present a new and simple method enabling the process of multiple samples at one time with a much reduced volume of reducing solution. MethodsOne mL of reducing solution made of HI and NaH2PO2 was added to a septum glass tube with dry sulfate. The tube was heated at 124 degrees C and the produced H2S was purged with inert gas (He or N-2) through gas-washing tubes and then collected by NaOH solution. The collected H2S was converted into Ag2S by adding AgNO3 solution and the co-precipitated Ag2O was removed by adding a few drops of concentrated HNO3. ResultsWithin 2-3h, a 100% yield was observed for samples with 0.2-2.5mol Na2SO4. The reduction rate was much slower for BaSO4 and a complete reduction was not observed. International sulfur reference materials, NBS-127, SO-5 and SO-6, were processed with this method, and the measured against accepted S-34 values yielded a linear regression line which had a slope of 0.99 0.01 and a R-2 value of 0.998. ConclusionsThe new methodology is easy to handle and allows us to process multiple samples at a time. It has also demonstrated good reproducibility in terms of H2S yield and for further isotope analysis. It is thus a good alternative to the conventional manual method, especially when processing samples with limited amount of sulfate available.
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Goursaud, S., Masson-Delmotte, V., Favier, V., Orsi, A., & Werner, M. (2018). Water stable isotope spatio-temporal variability in Antarctica in 1960-2013: observations and simulations from the ECHAM5-wiso atmospheric general circulation model. Climate Of The Past, 14(6), 923–946.
Abstract: Polar ice core water isotope records are commonly used to infer past changes in Antarctic temperature, motivating an improved understanding and quantification of the temporal relationship between delta O-18 and temperature. This can be achieved using simulations performed by atmospheric general circulation models equipped with water stable isotopes. Here, we evaluate the skills of the high-resolution water-isotope-enabled atmospheric general circulation model ECHAM5-wiso (the European Centre Hamburg Model) nudged to European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis using simulations covering the period 1960-2013 over the Antarctic continent. We compare model outputs with field data, first with a focus on regional climate variables and second on water stable isotopes, using our updated dataset of water stable isotope measurements from precipitation, snow, and firn-ice core samples. ECHAM5-wiso simulates a large increase in temperature from 1978 to 1979, possibly caused by a discontinuity in the European Reanalyses (ERA) linked to the assimilation of remote sensing data starting in 1979. Although some model-data mismatches are observed, the (precipitation minus evaporation) outputs are found to be realistic products for surface mass balance. A warm model bias over central East Antarctica and a cold model bias over coastal regions explain first-order delta O-18 model biases by too-strong isotopic depletion on coastal areas and underestimated depletion inland. At the second order, despite these biases, ECHAM5-wiso correctly captures the observed spatial patterns of deuterium excess. The results of model-data comparisons for the inter-annual delta O-18 standard deviation differ when using precipitation or ice core data. Further studies should explore the importance of deposition and post-deposition processes affecting ice core signals and not resolved in the model. These results build trust in the use of ECHAM5-wiso outputs to investigate the spatial, seasonal, and inter-annual delta O-18-temperature relationships. We thus make the first Antarctica-wide synthesis of prior results. First, we show that local spatial or seasonal slopes are not a correct surrogate for inter-annual temporal slopes, leading to the conclusion that the same isotope-temperature slope cannot be applied for the climatic interpretation of Antarctic ice core for all timescales. Finally, we explore the phasing between the seasonal cycles of deuterium excess and delta O-18 as a source of information on changes in moisture sources affecting the delta O-18-temperature relationship. The few available records and ECHAM5-wiso show different phase relationships in coastal, intermediate, and central regions. This work evaluates the use of the ECHAM5-wiso model as a tool for the investigation of water stable isotopes in Antarctic precipitation and calls for extended studies to improve our understanding of such proxies.
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Grilli, R., Triest, J., Chappellaz, J., Calzas, M., Desbois, T., Jansson, P., et al. (2018). Sub-Ocean: Subsea Dissolved Methane Measurements Using an Embedded Laser Spectrometer Technology. Environmental Science & Technology, 52(18), 10543–10551.
Abstract: We present a novel instrument, the Sub-Ocean probe, allowing in situ and continuous measurements of dissolved methane in seawater. It relies on an optical feedback cavity enhanced absorption technique designed for trace gas measurements and coupled to a patent-pending sample extraction method. The considerable advantage of the instrument compared with existing ones lies in its fast response time of the order of 30 s, that makes this probe ideal for fast and continuous 3D-mapping of dissolved methane in water. It could work up to 40 MPa of external pressure, and it provides a large dynamic range, from subnmol of CH4 per liter of seawater to mmol L-1. In this work, we present laboratory calibration of the instrument, intercomparison with standard method and field results on methane detection. The good agreement with the headspace equilibration technique followed by gas-chromatography analysis supports the utility and accuracy of the instrument. A continuous 620-m depth vertical profile in the Mediterranean Sea was obtained within only 10 min, and it indicates background dissolved CH4 values between 1 and 2 nmol L-1 below the pycnocline, similar to previous observations conducted in different ocean settings. It also reveals a methane maximum at around 6 m of depth, that may reflect local production from bacterial transformation of dissolved organic matter.
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Hoffmann, H., Preunkert, S., Legrand, M., Leinfelder, D., Bohleber, P., Friedrich, R., et al. (2018). A New Sample Preparation System For Micro-C-14 Dating Of Glacier Ice With A First Application To A High Alpine Ice Core From Colle Gnifetti (Switzerland). Radiocarbon, 60(2), 517–533.
Abstract: Radiometric dating of glacier ice is an essential tool where stratigraphic dating methods cannot be applied. This study focuses on Alpine glacier ice and presents a new sample preparation system for dating of glacier ice samples via radiocarbon (C-14) dating of the microscopic particulate organic carbon (POC) fraction incorporated in the ice matrix. An adaptable, low-cost inline filtration-oxidation-unit (REFILOX) has been developed, which for the first time unifies all sample preparation steps from ice filtration to CO2 quantification in one closed setup. A systematic C-14 investigation of modern European aerosol samples revealed that a POC combustion temperature of 340 degrees C provides the best representation of the real sample age. A very low process blank of maximally 0.3 +/- 0.1 μgC now enables C-14 dating of high Alpine ice samples, where POC concentrations are generally low (typically 10-50 μgC/kg), in an ice sample mass range of 300-500 g. In a first successful application, the method was used to obtain age constraints for an ice core from the cold, high Alpine firn saddle Colle Gnifetti (Switzerland). Analysis of the bottom ice core sections revealed a basal age of 4171-3923 cal yr BP but also a so far enigmatic discontinuity in the age-depth relationship.
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Jean-Baptiste, P., Fourre, E., Petit, J. R., Lipenkov, V., Bulat, S., Chetverikov, Y., et al. (2018). Helium and Neon in the Accreted Ice of the Subglacial Antarctic Lake Vostok. Geophysical Research Letters, 45(10), 4927–4932.
Abstract: We analyzed helium and neon in 24 samples from between 3,607 and 3,767m (i.e., down to 2m above the lake-ice interface) of the accreted ice frozen to the ceiling of Lake Vostok. Within uncertainties, the neon budget of the lake is balanced, the neon supplied to the lake by the melting of glacier ice being compensated by the neon exported by lake ice. The helium concentration in the lake is about 12 times more than in the glacier ice, with a measured He-3/He-4 ratio of 0.120.01R(a). This shows that Lake Vostok's waters are enriched by a terrigenic helium source. The He-3/He-4 isotope ratio of this helium source was determined. Its radiogenic value (0.057xR(a)) is typical of an old continental province, ruling out any magmatic activity associated with the tectonic structure of the lake. It corresponds to a low geothermal heat flow estimated at 51mW/m(2). Plain Language Summary Extending over 15,000km(2) in a deep trough north of Vostok station, Lake Vostok is the largest and the deepest among the many subglacial lakes to have been discovered in Antarctica. Its ice ceiling is tilted, with an ice thickness of 3,750m in the south and 4,300m in the north. As the melting point is pressure dependent, the base of the glacier melts on the thick side (northern region) whereas lake water refreezes in the south, where the Vostok station is located. Unlike most gases, helium and neon can be incorporated into the crystal structure of ice during freezing. This property makes helium and neon isotopes in the accreted ice a valuable source of information on the concentration and isotope composition of both gases in the lake water itself. Between 2006 and 2012, we collected 24 samples from between 3,607 and 3,767m (i.e., down to 2m above the lake-ice interface) of the accreted ice frozen to the ceiling of Lake Vostok (lake ice) for analyzing helium and neon. Within uncertainties, the neon concentration measured in the lake ice is equal to that in the glacier ice. This indicates that the neon budget of the lake is balanced, the neon supply to the lake by the melting of glacier ice being compensated by the Ne export by lake ice. This confirms earlier suggestions from radar data and GPS measurements of surface ice velocity that the water added to the lake by the melting of glacier ice is balanced by the lake ice, which is exported by the glacier's movement out of the lake. Helium isotopes (He-3 and He-4) are sensitive indicators of tectonic-magmatic activity. In continental areas of recent tectonic-magmatic activity such as geothermal areas, the ratio He-3/He-4 is at its highest, accompanied by excess heat flow. On the contrary, in stable continental areas, low He-3/He-4 ratios are found. The low He-3/He-4 ratio in Lake Vostok clearly demonstrates the absence of volcanic and/or magmatic activity associated with the tectonic structure of the lake, in agreement with the absence of magnetic anomaly. The helium concentration in the lake is about 12 times the concentration measured in the glacier ice. This shows that the Lake Vostok's waters are enriched from beneath by a flux of helium typical of an old stable continental province. Helium isotopes points to a low geothermal heat flow beneath the lake. We estimate this heat flow at 51mW/m(2). This value is fully consistent with the heat flow map for Antarctica inferred from satellite magnetic data and corresponds to the baseline heat fl
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Lechevallier, L., Vasilchenko, S., Grilli, R., Mondelain, D., Romanini, D., & Campargue, A. (2018). The water vapour self-continuum absorption in the infrared atmospheric windows: new laser measurements near 3.3 and 2.0 μm. Atmospheric Measurement Techniques, 11(4), 2159–2171.
Abstract: The amplitude, the temperature dependence, and the physical origin of the water vapour absorption continuum are a long-standing issue in molecular spectroscopy with direct impact in atmospheric and planetary sciences. In recent years, we have determined the self-continuum absorption of water vapour at different spectral points of the atmospheric windows at 4.0, 2.1, 1.6, and 1.25 μm, by highly sensitive cavity-enhanced laser techniques. These accurate experimental constraints have been used to adjust the last version (3.2) of the semi-empirical MTCKD model (MlawerTobinClough-Kneizys-Davies), which is widely incorporated in atmospheric radiative-transfer codes. In the present work, the self-continuum cross-sections, C-S, are newly determined at 3.3 μm (3007 cm(-1)) and 2.0 μm (5000 cm(-1)) by optical-feedback-cavity enhanced absorption spectroscopy (OFCEAS) and cavity ring-down spectroscopy (CRDS), respectively. These new data allow extending the spectral coverage of the 4.0 and 2.1 μm windows, respectively, and testing the recently released 3.2 version of the MT_CKD continuum. By considering high temperature literature data together with our data, the temperature dependence of the selfcontinuum is also obtained.
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Legrand, M., Mcconnell, J., Preunkert, S., Arienzo, M., Chellman, N., Gleason, K., et al. (2018). Alpine ice evidence of a three-fold increase in atmospheric iodine deposition since 1950 in Europe due to increasing oceanic emissions. Proceedings Of The National Academy Of Sciences Of The United States Of America, 115(48), 12136–12141.
Abstract: Iodine is an important nutrient and a significant sink of tropospheric ozone, a climate-forcing gas and air pollutant. Ozone interacts with seawater iodide, leading to volatile inorganic iodine release that likely represents the largest source of atmospheric iodine. Increasing ozone concentrations since the preindustrial period imply that iodine chemistry and its associated ozone destruction is now substantially more active. However, the lack of historical observations of ozone and iodine means that such estimates rely primarily on model calculations. Here we use seasonally resolved records from an Alpine ice core to investigate 20th century changes in atmospheric iodine. After carefully considering possible postdepositional changes in the ice core record, we conclude that iodine deposition over the Alps increased by at least a factor of 3 from 1950 to the 1990s in the summer months, with smaller increases during the winter months. We reproduce these general trends using a chemical transport model and show that they are due to increased oceanic iodine emissions, coupled to a change in iodine speciation over Europe from enhanced nitrogen oxide emissions. The model underestimates the increase in iodine deposition by a factor of 2, however, which may be due to an underestimate in the 20th century ozone increase. Our results suggest that iodine's impact on the Northern Hemisphere atmosphere accelerated over the 20th century and show a coupling between anthropogenic pollution and the availability of iodine as an essential nutrient to the terrestrial biosphere.
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Passalacqua, O., Cavitte, M., Gagliardini, O., Gillet-Chaulet, F., Parrenin, F., Ritz, C., et al. (2018). Brief communication: Candidate sites of 1.5 Myr old ice 37 km southwest of the Dome C summit, East Antarctica. Cryosphere, 12(6), 2167–2174.
Abstract: The search for ice as old as 1.5 Myr requires the identification of places that maximize our chances to retrieve old, well-resolved, undisturbed and datable ice. One of these locations is very likely southwest of the Dome C summit, where elevated bedrock makes the ice thin enough to limit basal melting. A 3-D ice flow simulation is used to calculate five selection criteria, which together delineate the areas with the most appropriate glaciological properties. These selected areas (a few square kilometers) lie on the flanks of a bedrock high, where a balance is found between risks of basal melting, stratigraphic disturbances and sufficient age resolution. Within these areas, several sites of potential 1.5 Myr old ice are proposed, situated on local bedrock summits or ridges. The trajectories of the ice particles towards these locations are short, and the ice flows over a smoothly undulating bedrock. These sites will help to choose where new high-resolution ground radar surveys should be conducted in upcoming field seasons.
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Schupbach, S., Fischer, H., Bigler, M., Erhardt, T., Gfeller, G., Leuenberger, D., et al. (2018). Greenland records of aerosol source and atmospheric lifetime changes from the Eemian to the Holocene. Nature Communications, 9.
Abstract: The Northern Hemisphere experienced dramatic changes during the last glacial, featuring vast ice sheets and abrupt climate events, while high northern latitudes during the last interglacial (Eemian) were warmer than today. Here we use high-resolution aerosol records from the Greenland NEEM ice core to reconstruct the environmental alterations in aerosol source regions accompanying these changes. Separating source and transport effects, we find strongly reduced terrestrial biogenic emissions during glacial times reflecting net loss of vegetated area in North America. Rapid climate changes during the glacial have little effect on terrestrial biogenic aerosol emissions. A strong increase in terrestrial dust emissions during the coldest intervals indicates higher aridity and dust storm activity in East Asian deserts. Glacial sea salt aerosol emissions in the North Atlantic region increase only moderately (50%), likely due to sea ice expansion. Lower aerosol concentrations in Eemian ice compared to the Holocene are mainly due to shortened atmospheric residence time, while emissions changed little.
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Song, S., Angot, H., Selin, N., Gallee, H., Sprovieri, F., Pirrone, N., et al. (2018). Understanding mercury oxidation and air-snow exchange on the East Antarctic Plateau: a modeling study. Atmospheric Chemistry And Physics, 18(21), 15825–15840.
Abstract: Distinct diurnal and seasonal variations of mercury (Hg) have been observed in near-surface air at Concordia Station on the East Antarctic Plateau, but the processes controlling these characteristics are not well understood. Here, we use a box model to interpret the Hg-0 (gaseous elemental mercury) measurements in thes year 2013. The model includes atmospheric Hg-0 oxidation (by OH, O-3, or bromine), surface snow Hg-II (oxidized mercury) reduction, and air-snow exchange, and is driven by meteorological fields from a regional climate model. The simulations suggest that a photochemically driven mercury diurnal cycle occurs at the air-snow interface in austral summer. The fast oxidation of Hg-0 in summer may be provided by a two-step bromine-initiated scheme, which is favored by low temperature and high nitrogen oxides at Concordia. The summertime diurnal variations of Hg-0 (peaking during daytime) may be confined within several tens of meters above the snow surface and affected by changing mixed layer depths. Snow re-emission of Hg-0 is mainly driven by photoreduction of snow HgII in summer. Intermittent warming events and a hypothesized reduction of Hg-II occurring in snow in the dark may be important processes controlling the mercury variations in the non-summer period, although their relative importance is uncertain. The Br-initiated oxidation of Hg-0 is expected to be slower at Summit Station in Greenland than at Concordia (due to their difference in temperature and levels of nitrogen oxides and ozone), which may contribute to the observed differences in the summertime diurnal variations of Hg-0 between these two polar inland stations.
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Spolaor, A., Angot, H., Roman, M., Dommergue, A., Scarchilli, C., Varde, M., et al. (2018). Feedback mechanisms between snow and atmospheric mercury: Results and observations from field campaigns on the Antarctic plateau. Chemosphere, 197, 306–317.
Abstract: The Antarctic Plateau snowpack is an important environment for the mercury geochemical cycle. We have extensively characterized and compared the changes in surface snow and atmospheric mercury concentrations that occur at Dome C. Three summer sampling campaigns were conducted between 2013 and 2016. The three campaigns had different meteorological conditions that significantly affected mercury deposition processes and its abundance in surface snow. In the absence of snow deposition events, the surface mercury concentration remained stable with narrow oscillations, while an increase in precipitation results in a higher mercury variability. The Hg concentrations detected confirm that snowfall can act as a mercury atmospheric scavenger. A high temporal resolution sampling experiment showed that surface concentration changes are connected with the diurnal solar radiation cycle. Mercury in surface snow is highly dynamic and it could decrease by up to 90% within 4/6 h. A negative relationship between surface snow mercury and atmospheric concentrations has been detected suggesting a mutual dynamic exchange between these two environments. Mercury concentrations were also compared with the Br concentrations in surface and deeper snow, results suggest that Br could have an active role in Hg deposition, particularly when air masses are from coastal areas. This research presents new information on the presence of Hg in surface and deeper snow layers, improving our understanding of atmospheric Hg deposition to the snow surface and the possible role of re-emission on the atmospheric Hg concentration. (C) 2018 Elsevier Ltd. All rights reserved.
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Tzedakis, P., Drysdale, R., Margari, V., Skinner, L., Menviel, L., Rhodes, R., et al. (2018). Enhanced climate instability in the North Atlantic and southern Europe during the Last Interglacial. Nature Communications, 9.
Abstract: Considerable ambiguity remains over the extent and nature of millennial/centennial-scale climate instability during the Last Interglacial (LIG). Here we analyse marine and terrestrial proxies from a deep-sea sediment sequence on the Portuguese Margin and combine results with an intensively dated Italian speleothem record and climate-model experiments. The strongest expression of climate variability occurred during the transitions into and out of the LIG. Our records also document a series of multi-centennial intra-interglacial arid events in southern Europe, coherent with cold water-mass expansions in the North Atlantic. The spatial and temporal fingerprints of these changes indicate a reorganization of ocean surface circulation, consistent with low-intensity disruptions of the Atlantic meridional overturning circulation (AMOC). The amplitude of this LIG variability is greater than that observed in Holocene records. Episodic Greenland ice melt and runoff as a result of excess warmth may have contributed to AMOC weakening and increased climate instability throughout the LIG.
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Weller, R., Legrand, M., & Preunkert, S. (2018). Size distribution and ionic composition of marine summer aerosol at the continental Antarctic site Kohnen. Atmospheric Chemistry And Physics, 18(4), 2413–2430.
Abstract: We measured aerosol size distributions and conducted bulk and size-segregated aerosol sampling during two summer campaigns in January 2015 and January 2016 at the continental Antarctic station Kohnen (Dronning Maud Land). Physical and chemical aerosol properties differ conspicuously during the episodic impact of a distinctive low-pressure system in 2015 (LPS15) compared to the prevailing clear sky conditions. The approximately 3-day LPS15 located in the eastern Weddell Sea was associated with the following: marine boundary layer air mass intrusion; enhanced condensation particle concentrations (1400 +/- 700 cm(-3) compared to 250 +/- 120 cm(-3) under clear sky conditions; mean +/- SD); the occurrence of a new particle formation event exhibiting a continuous growth of particle diameters (D-p) from 12 to 43 nm over 44 h (growth rate 0.6 nm h(-1)); peaking methane sulfonate (MS-), non-sea-salt sulfate (nss-SO42-), and Na+ concentrations (190 ng m(-3) MS-, 137 ng m(-3) nss-SO42-, and 53 ng m(-3) Na+ compared to 24 +/- 15, 107 +/- 20, and 4.1 +/- 2.2 ng m(-3), respectively, during clear sky conditions); and finally an increased MS- / nss-SO42- mass ratio beta(MS) of 0.4 up to 2.3 (0.21 +/- 0.1 under clear sky conditions) comparable to typical values found at coastal Antarctic sites. Throughout the observation period a larger part of MS could be found in super-micron aerosol compared to nss-SO42-, i.e., (10 +/- 2) % by mass compared to (3.2 +/- 2) %, respectively. On the whole, under clear sky conditions aged aerosol characterized by usually mono-modal size distributions around D-p = 60 nm was observed. Although our observations indicate that the sporadic impacts of coastal cyclones were associated with enhanced marine aerosol entry, aerosol deposition on-site during austral summer should be largely dominated by typical steady clear sky conditions.
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Barbante, C., Spolaor, A., Cairns, W. R. L., & Boutron, C. (2017). Man's footprint on the Arctic environment as revealed by analysis of ice and snow. Earth-Science Reviews, 168, 218–231.
Abstract: The date of the definitive start to the Anthropocene is still under debate, and although a lot of progress has been made, currently available data is not precise enough to define the start of the human-dominated geological epoch. We know that during and after the industrial revolution, humans started having a much greater impact on the Earth's environment. Increases in population have led to increases in resource and fossil fuel use, leaving a marked impact on our planet. This impact, in the Northern hemisphere, is effectively recorded in the snow and ice of the Arctic. Human activity has changed various biogeochemical cycles to such an extent, that the climate has started to change. This has disturbed the biosphere, pushing it to adapt in response to these changes through evolutionary pressure. The Arctic is a particularly vulnerable environment and mankind is having a profound impact on its fragile equilibrium. Higher concentrations of heavy metals, organic compounds and radionuclides have been detected in ice cores as well as snow. Although climatic changes are evident on a global scale, in the Arctic these changes have been amplified. Advances in laboratory analysis methods have been applied to ice cores and surface snow samples to help us understand the mechanisms governing this fragile environment and to evaluate the impact and amplitude of human activity. Despite these advances, the fluxes and distributions over time of anthropogenic organic compounds is largely unknown. Hopefully advances in analytical methods will mean that this is not the case in the future. (C) 2017 Elsevier B.V. All rights reserved.
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Bock, M., Schmitt, J., Beck, J., Seth, B., Chappellaz, J., & Fischer, H. (2017). Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4 ice core records. Proceedings Of The National Academy Of Sciences Of The United States Of America, 114(29), E5778–E5786.
Abstract: Atmospheric methane (CH4) records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere. Here, we present dual stable isotopic methane records [delta(CH4)-C-13 and delta D(CH4)] from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima. The changes in these sources are steered by variations in temperature, precipitation, and the water table as modulated by insolation, (local) sea level, and monsoon intensity. Based on our delta D(CH4) constraint, it seems that geologic emissions of methane may play a steady but only minor role in atmospheric CH4 changes and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 y compared with older time periods. This shift cannot be explained by climatic changes. Rather, our isotopic methane budget points to a marked increase in fire activity, possibly caused by biome changes and accumulation of fuel related to the late Pleistocene megafauna extinction, which took place in the course of the last glacial.
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Breant, C., Martinerie, P., Orsi, A., Arnaud, L., & Landais, A. (2017). Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities. Climate Of The Past, 13(7), 833–853.
Abstract: The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas-ice age difference is essential to documenting the phasing between CO2 and temperature changes, especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using delta N-15 of air measured in ice cores. All firn densification models applied to deglaciations show a large disagreement with delta N-15 measurements at several sites in East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas delta N-15 suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model-data mismatch for the gas trapping depth evolution over the last deglaciation at the coldest sites in East Antarctica (Vostok, Dome C), while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured delta N-15 evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in the coldest conditions. The inclusion of im-purity effects improves the agreement between modelled and measured delta N-15 at cold East Antarctic sites during the last deglaciation, but deteriorates the agreement between modelled and measured delta N-15 evolution at Greenland and Antarctic sites with high accumulation unless threshold effects are taken into account. We thus do not provide a definite solution to the firnification at very cold Antarctic sites but propose potential pathways for future studies.
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Delmonte, B., Paleari, C. I., Ando, S., Garzanti, E., Andersson, P. S., Petit, J. R., et al. (2017). Causes of dust size variability in central East Antarctica (Dome B): Atmospheric transport from expanded South American sources during Marine Isotope Stage 2. Quaternary Science Reviews, 168, 55–68.
Abstract: We here investigate the spatial and temporal variability of eolian dust particle sorting recorded in the Dome B (77 degrees 05' S, 94 55' E) ice core, central East Antarctica, during Marine Isotope Stage (MIS) 2. We address the question whether such changes reflect variable transport pathways from a unique source area or rather a variable apportionment from diverse Southern Hemisphere sources transported at different elevation in the troposphere. The Sr-Nd radiogenic isotope composition of glacial dust samples as well as single-particle Raman mineralogy support the hypothesis of a single dust provenance both for coarse and fine mode dust events at Dome B. The southern South American provenance of glacial dust in Antarctica deduced from these results indicate a dust composition coherent with a mixture of volcanic material and minerals derived from metamorphic and plutonic rocks. Additionally, Dome B glacial samples contain aragonite particles along with diatom valves of marine benthic/epiphytic species and freshwater species living today in the northern Antarctic Peninsula and southern South America. These data suggest contribution from the exposed Patagonian continental shelf and glacial outwash plains of southern Patagonia at the time when sea level reached its minimum. Our results confirm that dust sorting is controlled by the relative intensity of the two main patterns of tropospheric dust transport onto the inner Plateau, i.e. fast low-level advection and long-range high-altitude transport including air subsidence over Antarctica. (C) 2017 Elsevier Ltd. All rights reserved.
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Fourteau, K., Fain, X., Martinerie, P., Landais, A., Ekaykin, A. A., Lipenkov, V. Y., et al. (2017). Analytical constraints on layered gas trapping and smoothing of atmospheric variability in ice under low-accumulation conditions. Climate Of The Past, 13(12), 1815–1830.
Abstract: We investigate for the first time the loss and alteration of past atmospheric information from air trapping mechanisms under low-accumulation conditions through continuous CH4 (and CO) measurements. Methane concentration changes were measured over the Dansgaard-Oeschger event 17 (DO-17, similar to 60000 yrBP) in the Antarctic Vostok 4G-2 ice core. Measurements were performed using continuous-flow analysis combined with laser spectroscopy. The results highlight many anomalous layers at the centimeter scale that are unevenly distributed along the ice core. The anomalous methane mixing ratios differ from those in the immediate surrounding layers by up to 50 ppbv. This phenomenon can be theoretically reproduced by a simple layered trapping model, creating very localized gas age scale inversions. We propose a method for cleaning the record of anomalous values that aims at minimizing the bias in the overall signal. Once the layered-trapping-induced anomalies are removed from the record, DO-17 appears to be smoother than its equivalent record from the high-accumulation WAIS Divide ice core. This is expected due to the slower sinking and densification speeds of firn layers at lower accumulation. However, the degree of smoothing appears surprisingly similar between modern and DO-17 conditions at Vostok. This suggests that glacial records of trace gases from low-accumulation sites in the East Antarctic plateau can provide a better time resolution of past atmospheric composition changes than previously expected. We also developed a numerical method to extract the gas age distributions in ice layers after the removal of the anomalous layers based on comparison with a weakly smoothed record. It is particularly adapted for the conditions of the East Antarctic plateau, as it helps to characterize smoothing for a large range of very low-temperature and low-accumulation conditions.
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Geng, L., Murray, L. T., Mickley, L. J., Lin, P., Fu, Q., Schauer, A. J., et al. (2017). Isotopic evidence of multiple controls on atmospheric oxidants over climate transitions. Nature, 546(7656), 133–+.
Abstract: The abundance of tropospheric oxidants, such as ozone (O-3) and hydroxyl (OH) and peroxy radicals (HO2 + RO2), determines the lifetimes of reduced trace gases such as methane and the production of particulate matter important for climate and human health. The response of tropospheric oxidants to climate change is poorly constrained owing to large uncertainties in the degree to which processes that influence oxidants may change with climate(1) and owing to a lack of palaeo-records with which to constrain levels of atmospheric oxidants during past climate transitions(2). At present, it is thought that temperature-dependent emissions of tropospheric O-3 precursors and water vapour abundance determine the climate response of oxidants, resulting in lower tropospheric O-3 in cold climates while HOx (= OH + HO2 + RO2) remains relatively buffered(3). Here we report observations of oxygen-17 excess of nitrate (a proxy for the relative abundance of atmospheric O-3 and HOx) from a Greenland ice core over the most recent glacial-interglacial cycle and for two Dansgaard-Oeschger events. We find that tropospheric oxidants are sensitive to climate change with an increase in the O-3/HOx ratio in cold climates, the opposite of current expectations. We hypothesize that the observed increase in O-3/HOx in cold climates is driven by enhanced stratosphere-to-troposphere transport of O-3, and that reactive halogen chemistry is also enhanced in cold climates. Reactive halogens influence the oxidative capacity of the troposphere directly as oxidants themselves and indirectly(4) via their influence on O-3 and HOx. The strength of stratosphere-to-troposphere transport is largely controlled by the Brewer-Dobson circulation(5), which may be enhanced in colder climates owing to a stronger meridional gradient of sea surface temperatures(6), with implications for the response of tropospheric oxidants(7) and stratospheric thermal and mass balance(8). These two processes may represent important, yet relatively unexplored, climate feedback mechanisms during major climate transitions.
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Goursaud, S., Masson-Delmotte, V., Favier, V., Preunkert, S., Fily, M., Gallee, H., et al. (2017). A 60-year ice-core record of regional climate from Adelie Land, coastal Antarctica. Cryosphere, 11(1), 343–362.
Abstract: A 22.4 m-long shallow firn core was extracted during the 2006/2007 field season from coastal Adelie Land. Annual layer counting based on subannual analyses of delta O-18 and major chemical components was combined with 5 reference years associated with nuclear tests and non-retreat of summer sea ice to build the initial ice-core chronology (19462006), stressing uncertain counting for 8 years. We focus here on the resulting delta O-18 and accumulation records. With an average value of 21.8 +/- 6.9 cmw. e. yr(-1), local accumulation shows multi-decadal variations peaking in the 1980s, but no long-term trend. Similar results are obtained for delta O-18, also characterised by a remarkably low and variable amplitude of the seasonal cycle. The ice-core records are compared with regional records of temperature, stake area accumulation measurements and variations in sea-ice extent, and outputs from two models nudged to ERA (European Re-analysis) atmospheric reanalyses: the high-resolution atmospheric general circulation model (AGCM), including stable water isotopes ECHAM5-wiso (European Centre Hamburg model), and the regional atmospheric model Modele Atmospherique Regional (AR). A significant linear correlation is identified between decadal variations in delta O-18 and regional temperature. No significant relationship appears with regional sea-ice extent. A weak and significant correlation appears with Dumont d'Urville wind speed, increasing after 1979. The model-data comparison highlights the inadequacy of ECHAM5-wiso simulations prior to 1979, possibly due to the lack of data assimilation to constrain atmospheric reanalyses. Systematic biases are identified in the ECHAM5-wiso simulation, such as an overestimation of the mean accumulation rate and its interannual variability, a strong cold bias and an underestimation of the mean delta O-18 value and its interannual variability. As a result, relationships between simulated delta O-18 and temperature are weaker than observed. Such systematic precipitation and temperature biases are not displayed by MAR, suggesting that the model resolution plays a key role along the Antarctic ice sheet coastal topography. Interannual variations in ECHAM5-wiso temperature and precipitation accurately capture signals from meteorological data and stake observations and are used to refine the initial ice-core chronology within 2 years. After this adjustment, remarkable positive (negative) delta O-18 anomalies are identified in the ice-core record and the ECHAM5-wiso simulation in 1986 and 20
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Hattori, S., Savarino, J., Kamezaki, K., Ishino, S., Dyckmans, J., Fujinawa, T., et al. (2017). Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterial method and N2O decomposition by microwave discharge (vol 30, pg 2635, 2016). Rapid Communications In Mass Spectrometry, 31(4), 396.
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Ishino, S., Hattori, S., Savarino, J., Jourdain, B., Preunkert, S., Legrand, M., et al. (2017). Seasonal variations of triple oxygen isotopic compositions of atmospheric sulfate, nitrate, and ozone at Dumont d'Urville, coastal Antarctica. Atmospheric Chemistry And Physics, 17(5), 3713–3727.
Abstract: Triple oxygen isotopic compositions (Delta O-17 = delta O-17-0.52 x delta O-18) of atmospheric sulfate (SO42-) and nitrate (NO3-) in the atmosphere reflect the relative contribution of oxidation pathways involved in their formation processes, which potentially provides information to reveal missing reactions in atmospheric chemistry models. However, there remain many theoretical assumptions for the controlling factors of Delta O-17(SO42-) and Delta O-17(NO3-) values in those model estimations. To test one of those assumption that Delta O-17 values of ozone (O-3) have a flat value and do not influence the seasonality of Delta O-17(SO42-) and Delta O-17(NO3-) values, we performed the first simultaneous measurement of Delta O-17 values of atmospheric sulfate, nitrate, and ozone collected at Dumont d'Urville (DDU) Station (66 degrees 40 ' S, 140 degrees 01 ' E) throughout 2011. Delta O-17 values of sulfate and nitrate exhibited seasonal variation characterized by minima in the austral summer and maxima in winter, within the ranges of 0.9-3.4 and 23.0-41.9 %, respectively. In contrast, Delta O-17 values of ozone showed no significant seasonal variation, with values of 26 +/- 1% throughout the year. These contrasting seasonal trends suggest that seasonality in Delta O-17(SO42-) and Delta O-17(NO3-) values is not the result of changes in Delta O-17(O-3), but of the changes in oxidation chemistry. The trends with summer minima and are caused by sunlight-driven changes in the relative contribution of O3 oxidation to the oxidation by HOx, ROx, and H2O2. In addition to that general trend, by comparing Delta O-17(SO42-) and Delta O-17(NO3-) values to ozone mixing ratios, we found that Delta O-17(SO42-) values observed in spring (September to November) were lower than in fall (March to May), while there was no significant spring and fall difference in Delta O-17(NO3-) values. The relatively lower sensitivity of Delta O-17(SO42-) values to the ozone mixing ratio in spring compared to fall is possibly explained by (i) the increased contribution of SO2 oxidations by OH and H2O2 caused by NOx emission from snowpack and/ or (ii) SO2 oxidation by hypohalous acids (HOX = HOCl + HOBr) in the aqueous phase.
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Kawamura, K., Abe-Ouchi, A., Motoyama, H., Ageta, Y., Aoki, S., Azuma, N., et al. (2017). State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling. Science Advances, 3(2).
Abstract: Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instabilitywith bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.
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Kozachek, A., Mikhalenko, V., Masson-Delmotte, V., Ekaykin, A., Ginot, P., Kutuzov, S., et al. (2017). Large-scale drivers of Caucasus climate variability in meteorological records and Mt El'brus ice cores. Climate Of The Past, 13(5), 473–489.
Abstract: A 181.8 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt El'brus (43 degrees 20'53.9 '' N, 42 degrees 25'36.0 '' E; 5115m a.s.l.) in the Caucasus, Russia, in 2009 (Mikhalenko et al., 2015). Here, we report on the results of the water stable isotope composition from this ice core with additional data from the shallow cores. The distinct seasonal cycle of the isotopic composition allows dating by annual layer counting. Dating has been performed for the upper 126 m of the deep core combined with 20 m from the shallow cores. The whole record covers 100 years, from 2013 back to 1914. Due to the high accumulation rate (1380 mm w.e. year(-1)) and limited melting, we obtained isotopic composition and accumulation rate records with seasonal resolution. These values were compared with available meteorological data from 13 weather stations in the region and also with atmosphere circulation indices, back-trajectory calculations, and Global Network of Isotopes in Precipitation (GNIP) data in order to decipher the drivers of accumulation and ice core isotopic composition in the Caucasus region. In the warm season (May-October) the isotopic composition depends on local temperatures, but the correlation is not persistent over time, while in the cold season (November-April), atmospheric circulation is the predominant driver of the ice core's isotopic composition. The snow accumulation rate correlates well with the precipitation rate in the region all year round, which made it possible to reconstruct and expand the precipitation record at the Caucasus highlands from 1914 until 1966, when reliable meteorological observations of precipitation at high elevation began.
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Landais, A., Casado, M., Prie, F., Magand, O., Arnaud, L., Ekaykin, A., et al. (2017). Surface studies of water isotopes in Antarctica for quantitative interpretation of deep ice core data. Comptes Rendus Geoscience, 349(4), 139–150.
Abstract: Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (delta D or delta O-18) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. delta O-18 evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (similar to 0.7-0.8 parts per thousand. degrees C (1) for delta O-18 vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46 parts per thousand. degrees C (1)). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of delta O-18 in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the delta O-18 of snow and surface temperature, but is associated with a much slower delta O-18-vs-temperature slope than the slope observed in the seasonal precipitation. (3) Post-deposition effects clearly limit the archiving of high-resolution (seasonal) climatic variability in the polar snow, but we suggest that sites with an accumulation rate of the order of 40 kg.m (2).yr (1) may record a seasonal cycle at shallow depths. (C) 2017 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Legrand, M., Preunkert, S., Weller, R., Zipf, L., Elsasser, C., Merchel, S., et al. (2017). Year-round record of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) – Part 2: Biogenic sulfur (sulfate and methanesulfonate) aerosol. Atmospheric Chemistry And Physics, 17(22), 14055–14073.
Abstract: Multiple year-round (2006-2015) records of the bulk and size-segregated composition of aerosol were obtained at the inland site of Concordia located in East Antarctica. The well-marked maximum of non-sea salt sulfate (nssSO(4)) in January (100 +/- 28 ng m(-3) versus 4.4 +/- 2.3 ng m(-3) in July) is consistent with observations made at the coast (280 +/- 78 ng M-3 in January versus 16 +/- 9 ng m(-3) in July at Dumont d'Urville, for instance). In contrast, the well-marked maximum of MSA at the coast in January (60 +/- 23 ng M-3 at Dumont d'Urville) is not observed at Concordia (5.2 +/- 2.0 ng M-3 in January). Instead, the MSA level at Concordia peaks in October (5.6 +/- 1.9 ng m(-3)) and March (14.9 +/- 5.7 ng m(-3)). As a result, a surprisingly low MSA-to-nssSO(4) ratio (RMSA) is observed at Concordia in mid-summer (0.0 +/- 5 0.02 in January versus 0.25 +/- 0.09 in March). We find that the low value of RMSA in mid-summer at Concordia is mainly driven by a drop of MSA levels that takes place in submicron aerosol (0.3 pm diameter). The drop of MSA coincides with periods of high photochemical activity as indicated by high ozone levels, strongly suggesting the occurrence of an efficient chemical destruction of MSA over the Antarctic plateau in mid-summer. The relationship between MSA and nssSO(4) levels is examined separately for each season and indicates that concentration of non-biogenic sulfate over the Antarctic plateau does not exceed 1 ng M-3 in fall and winter and remains close to 5 ng M-3 in spring. This weak non-biogenic sulfate level is discussed in the light of radionuclides (Pb-210, Be-10, and Be-7) also measured on bulk aerosol samples collected at Concordia. The findings highlight the complexity in using MSA in deep ice cores extracted from inland Antarctica as a proxy of past dimethyl sulfide emissions from the Southern Ocean.
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Legrand, M., Preunkert, S., Wolff, E., Weller, R., Jourdain, B., & Wagenbach, D. (2017). Year-round records of bulk and size-segregated aerosol composition in central Antarctica (Concordia site) Part 1: Fractionation of sea-salt particles. Atmospheric Chemistry And Physics, 17(22), 14039–14054.
Abstract: Multiple year-round records of bulk and size segregated composition of aerosol were obtained at the inland site of Concordia located at Dome C in East Antarctica. In parallel, sampling of acidic gases on denuder tubes was carried out to quantify the concentrations of HCl and HNO3 present in the gas phase. These time series are used to examine aerosol present over central Antarctica in terms of chloride depletion relative to sodium with respect to freshly emitted sea-salt aerosol as well as depletion of sulfate relative to sodium with respect to the composition of seawater. A depletion of chloride relative to sodium is observed over most of the year, reaching a maximum of similar to 20 ngm(-3) in spring when there are still large sea-salt amounts and acidic components start to recover. The role of acidic sulfur aerosol and nitric acid in replacing chloride from sea-salt particles is here discussed. HCl is found to be around twice more abundant than the amount of chloride lost by sea-salt aerosol, suggesting that either HCl is more efficiently transported to Concordia than sea-salt aerosol or re-emission from the snow pack over the Antarctic plateau represents an additional significant HCl source. The size-segregated composition of aerosol collected in winter (from 2006 to 2011) indicates a mean sulfate to sodium ratio of sea-salt aerosol present over central Antarctica of 0.16 +/- 0.05, suggesting that, on average, the sea-ice and open-ocean emissions equally contribute to sea-salt aerosol load of the inland Antarctic atmosphere. The temporal variability of the sulfate depletion relative to sodium was examined at the light of air mass backward trajectories, showing an overall decreasing trend of the ratio (i.e., a stronger sulfate depletion relative to sodium) when air masses arriving at Dome C had traveled a longer time over sea ice than over open ocean. The findings are shown to be useful to discuss sea-salt ice records extracted at deep drilling sites located inland Antarctica.
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Lim, S., Fain, X., Ginot, P., Mikhalenko, V., Kutuzov, S., Paris, J. D., et al. (2017). Black carbon variability since preindustrial times in the eastern part of Europe reconstructed from Mt. Elbrus, Caucasus, ice cores. Atmospheric Chemistry And Physics, 17(5), 3489–3505.
Abstract: Black carbon (BC), emitted by fossil fuel combustion and biomass burning, is the second largest manmade contributor to global warming after carbon dioxide (Bond et al., 2013). However, limited information exists on its past emissions and atmospheric variability. In this study, we present the first high-resolution record of refractory BC (rBC, including mass concentration and size) reconstructed from ice cores drilled at a high-altitude eastern European site in Mt. Elbrus (ELB), Caucasus (5115ma. s.l.). The ELB ice core record, covering the period 1825-2013, reflects the atmospheric load of rBC particles at the ELB site transported from the European continent with a larger rBC input from sources located in the eastern part of Europe. In the first half of the 20th century, European anthropogenic emissions resulted in a 1.5-fold increase in the ice core rBC mass concentrations with respect to its level in the preindustrial era (before 1850). The summer (winter) rBC mass concentrations increased 5-fold (3.3-fold) in 1960-1980, followed by a decrease until similar to 2000. Over the last decade, the rBC signal for summertime slightly increased. We have compared the signal with the atmospheric BC load simulated using past BC emissions (ACCMIP and MACCity inventories) and taken into account the contribution of different geographical regions to rBC distribution and deposition at the ELB site. Interestingly, the observed rBC variability in the ELB ice core record since the 1960s is not in perfect agreement with the simulated atmospheric BC load. Similar features between the ice core rBC record and the best scenarios for the atmospheric BC load support anthropogenic BC increase in the 20th century being reflected in the ELB ice core record. However, the peak in BC mass concentration observed in similar to 1970 in the ice core is estimated to occur a decade later from past inventories. BC emission inventories for the period 1960s-1970s may be underestimating European anthropogenic emissions. Furthermore, for summertime snow layers of the 2000s, the slightly increasing trend of rBC deposition likely reflects recent changes in anthropogenic and biomass burning BC emissions in the eastern part of Europe. Our study highlights that the past changes in BC emissions of eastern Europe need to be considered in assessing ongoing air quality regulation.
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Narcisi, B., Petit, J. R., & Langone, A. (2017). Last glacial tephra layers in the Talos Dome ice core (peripheral East Antarctic Plateau), with implications for chronostratigraphic correlations and regional volcanic history. Quaternary Science Reviews, 165, 111–126.
Abstract: Tephra isochrons offer considerable potential for correlating diverse palaeoarchives and highlighting regional climatic differences. They are especially useful when applied to polar ice records encompassing the last glacial, as these clearly portray the pronounced millennial-scale climate variability that characterised this period. Here we present the continuous record of primary fallout tephra layers in the East Antarctic Talos Dome ice core (72 degrees 49 ' S, 159 degrees 11 ' E), developed upon examination of the core sections spanning the glacial period 16.5 to 71 ka. A total of ca. 45 discrete tephra deposits precisely positioned stratigraphically relative to the temperature record for the core and dated using the AICC2012 timescale, were identified. Quantitative grain size, particle morphology, major and trace element composition using Coulter Counter, SEM, EPMA-WDS, and LA-ICP-MS analytical methods were studied as diagnostic features for tephra characterisation. The tephrostratigraphic framework provides a reference for future precise comparison between ice and sediment sequences across the Antarctic continent. Indeed, several potential markers characterised by distinct volcanic glass geochemistry and/or particular stratigraphic location (e.g., a 17.6-ka ash layer deposited during the well-known major acidity event) are now available for the direct linkage of palaeoclimatic archives. The Talos Dome tephra sequence, dominated by mid distal pyroclastic products from the nearby Northern Victoria Land volcanoes, also represents the most comprehensive and best time-constrained record of regional Antarctic volcanism yet developed. It documents nearly continuous sustained explosive activity during the considered time interval and, combined with previous ice-core tephra results for the last and the current interglacial periods, suggests progressive compositional shift through time. (C) 2017 Elsevier Ltd. All rights reserved.
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Narcisi, B., Petit, J. R., & Langone, A. (2017). Last glacial tephra layers in the Talos Dome ice core (peripheral East Antarctic Plateau), with implications for chronostratigraphic correlations and regional volcanic history (vol 165, pg 111, 2017). Quaternary Science Reviews, 172, 142–143.
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Newland, M. J., Martinerie, P., Witrant, E., Helmig, D., Worton, D. R., Hogan, C., et al. (2017). Changes to the chemical state of the Northern Hemisphere atmosphere during the second half of the twentieth century. Atmospheric Chemistry And Physics, 17(13), 8269–8283.
Abstract: The NOx (NO and NO2) and HOx (OH and HO2) budgets of the atmosphere exert a major influence on atmospheric composition, controlling removal of primary pollutants and formation of a wide range of secondary products, including ozone, that can influence human health and climate. However, there remain large uncertainties in the changes to these budgets over recent decades. Due to their short atmospheric lifetimes, NOx and HOx are highly variable in space and time, and so the measurements of these species are of limited value for examining long-term, largescale changes to their budgets. Here, we take an alternative approach by examining long-term atmospheric trends of alkyl nitrates, the production efficiency of which is dependent on the atmospheric [NO] / [HO2] ratio. We derive long-term trends in the alkyl nitrates from measurements in firn air from the NEEM site, Greenland. Their mixing ratios increased by a factor of 3-5 between the 1970s and 1990s. This was followed by a steep decline to the sampling date of 2008. Moreover, we examine how the trends in the alkyl nitrates compare to similarly derived trends in their parent alkanes (i.e. the alkanes which, when oxidised in the presence of NOx, lead to the formation of the alkyl nitrates). The ratios of the alkyl nitrates to their parent alkanes increased from around 1970 to the late 1990s. This is consistent with large changes to the [NO] / [HO2] ratio in the Northern Hemisphere atmosphere during this period. Alternatively, they could represent changes to concentrations of the hydroxyl radical, OH, or to the transport time of the air masses from source regions to the Arctic.
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Parrenin, F., Bazin, L., Capron, E., Landais, A., Lemieux-Dudon, B., & Masson-Delmotte, V. (2017). Icechrono1: A Probabilistic Model To Compute A Common And Optimized Chronology For Several Ice Cores. Quaternaire, 28(2), 179–184.
Abstract: Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inference of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into IceChrono1 are modeling scenarios of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice- and air-dated horizons, ice and air depth intervals with known durations, Delta depth observations (depth shift between synchronous events recorded in the ice and in the air) and finally ice, air or mix stratigraphic links in between ice cores. the inference problem is formulated as a least squares optimisation, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm (thus assuming that the model is almost linear in the vicinity of the solution) and a numerical evaluation of the model's Jacobian. IceChrono1 is freely available under the General Public License v3 open source license.
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Parrenin, F., Cavitte, M. G. P., Blankenship, D. D., Chappellaz, J., Fischer, H., Gagliardini, O., et al. (2017). Is there 1.5-million-year-old ice near Dome C, Antarctica? Cryosphere, 11(6), 2427–2437.
Abstract: Ice sheets provide exceptional archives of past changes in polar climate, regional environment and global atmospheric composition. The oldest dated deep ice core drilled in Antarctica has been retrieved at EPICA Dome C (EDC), reaching similar to 800 000 years. Obtaining an older paleoclimatic record from Antarctica is one of the greatest challenges of the ice core community. Here, we use internal isochrones, identified from airborne radar coupled to ice-flow modelling to estimate the age of basal ice along transects in the Dome C area. Three glaciological properties are inferred from isochrones: surface accumulation rate, geothermal flux and the exponent of the Lliboutry velocity profile. We find that old ice (> 1.5 Myr, 1.5 million years) likely exists in two regions: one similar to 40 km south-west of Dome C along the ice divide to Vostok, close to a secondary dome that we name “Little Dome C” (LDC), and a second region named “North Patch” (NP) located 10-30 km north-east of Dome C, in a region where the geothermal flux is apparently relatively low. Our work demonstrates the value of combining radar observations with ice flow modelling to accurately represent the true nature of ice flow, and understand the formation of ice-sheet architecture, in the centre of large ice sheets.
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Passalacqua, O., Ritz, C., Parrenin, F., Urbini, S., & Frezzotti, M. (2017). Geothermal flux and basal melt rate in the Dome C region inferred from radar reflectivity and heat modelling. Cryosphere, 11(5), 2231–2246.
Abstract: Basal melt rate is the most important physical quantity to be evaluated when looking for an old-ice drilling site, and it depends to a great extent on the geothermal flux (GF), which is poorly known under the East Antarctic ice sheet. Given that wet bedrock has higher reflectivity than dry bedrock, the wetness of the ice-bed interface can be assessed using radar echoes from the bedrock. But, since basal conditions depend on heat transfer forced by climate but lagged by the thick ice, the basal ice may currently be frozen whereas in the past it was generally melting. For that reason, the risk of bias between present and past conditions has to be evaluated. The objective of this study is to assess which locations in the Dome C area could have been protected from basal melting at any time in the past, which requires evaluating GF. We used an inverse approach to retrieve GF from radar-inferred distribution of wet and dry beds. A 1-D heat model is run over the last 800 ka to constrain the value of GF by assessing a critical ice thickness, i.e. the minimum ice thickness that would allow the present local distribution of basal melting. A regional map of the GF was then inferred over a 80 km x 130 km area, with a N-S gradient and with values ranging from 48 to 60m Wm(-2). The forward model was then emulated by a polynomial function to compute a time-averaged value of the spatially variable basal melt rate over the region. Three main subregions appear to be free of basal melting, two because of a thin overlying ice and one, north of Dome C, because of a low GF.
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Petrenko, V. V., Mith, A. M. S., Chaefer, H. S., Riedel, K., Brook, E., Baggenstos, D., et al. (2017). Minimal geological methane emissions during the Younger Dryas-Preboreal abrupt warming event. Nature, 548(7668), 443–446.
Abstract: Methane (CH4) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions)(1) and top-down approaches (measuring atmospheric mole fractions and isotopes)(2) for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane ((CH4)-C-14) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today(3,4), our results indicate that current estimates of today's natural geological methane emissions (about 52 teragrams per year)(1,2) are too high and, by extension, that current estimates of anthropogenic fossil methane emissions(2) are too low. Our results also improve on and confirm earlier findings(5-7) that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas-Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates(8), permafrost(9) and methane trapped under ice(10)) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas-Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.
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Prokopiou, M., Martinerie, P., Sapart, C. J., Witrant, E., Monteil, G., Ishijima, K., et al. (2017). Constraining N2O emissions since 1940 using firn air isotope measurements in both hemispheres. Atmospheric Chemistry And Physics, 17(7), 4539–4564.
Abstract: N2O is currently the third most important anthropogenic greenhouse gas in terms of radiative forcing and its atmospheric mole fraction is rising steadily. To quantify the growth rate and its causes over the past decades, we performed a multi-site reconstruction of the atmospheric N2O mole fraction and isotopic composition using new and previously published firn air data collected from Greenland and Antarctica in combination with a firn diffusion and densification model. The multi-site reconstruction showed that while the global mean N2O mole fraction increased from (290 +/- 1) nmol mol(-1) in 1940 to (322 +/- 1) nmol mol(-1) in 2008, the isotopic composition of atmospheric N2O decreased by (-2.2 +/- 0.2)parts per thousand for delta N-15(av), (-1.0 +/- 0.3)parts per thousand for delta O-18, (-1.3 +/- 0.6)parts per thousand for delta N-15(alpha), and (-2.8 +/- 0.6)parts per thousand for delta N-15(beta) over the same period. The detailed temporal evolution of the mole fraction and isotopic composition derived from the firn air model was then used in a two-box atmospheric model (comprising a stratospheric box and a tropospheric box) to infer changes in the isotopic source signature over time. The precise value of the source strength depends on the choice of the N2O lifetime, which we choose to fix at 123 years. The average isotopic composition over the investigated period is delta N-15(av) = (-7.6 +/- 0.8)parts per thousand (vs. air-N-2), delta O-18 D (32.2 +/- 0.2)parts per thousand (vs. Vienna Standard Mean Ocean Water – VSMOW) for delta O-18, delta N-15(alpha) = (-3.0 +/- 1.9)parts per thousand and delta N-15(beta) = (-11.7 +/- 2.3) parts per thousand. delta N-15(av), and delta N-15(beta) show some temporal variability, while for the other signatures the error bars of the reconstruction are too large to retrieve reliable temporal changes. Possible processes that may explain trends in N-15 are discussed. The N-15 site preference (= delta N-15 alpha – delta N-15(beta)) provides evidence of a shift in emissions from denitrification to nitrification, although the uncertainty envelopes are large.
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Raisbeck, G. M., Cauquoin, A., Jouzel, J., Landais, A., Petit, J. R., Lipenkov, V. Y., et al. (2017). An improved north-south synchronization of ice core records around the 41 kyr Be-10 peak. Climate Of The Past, 13(3), 217–229.
Abstract: Using new high-resolution Be-10 measurements in the NGRIP, EDML and Vostok ice cores, together with previously published data from EDC, we present an improved synchronization between Greenland and Antarctic ice cores during the Laschamp geomagnetic excursion similar to 41 kyr ago. We estimate the precision of this synchronization to be +/- 20 years, an order of magnitude better than previous work. We discuss the implications of this new synchronization for making improved estimates of the depth difference between ice and enclosed gas of the same age (Delta depth), difference between age of ice and enclosed gas at the same depth (Delta age) in the EDC and EDML ice cores, spectral properties of the Be-10 profiles and phasing between Dansgaard-Oeschger-10 (in NGRIP) and AIM-10 (in EDML and EDC).
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Rhodes, R. H., Brook, E. J., McConnell, J. R., Blunier, T., Sime, L. C., Fain, X., et al. (2017). Atmospheric methane variability: Centennial-scale signals in the Last Glacial Period. Global Biogeochemical Cycles, 31(3), 575–590.
Abstract: In order to understand atmospheric methane (CH4) biogeochemistry now and in the future, we must apprehend its natural variability, without anthropogenic influence. Samples of ancient air trapped within ice cores provide the means to do this. Here we analyze the ultrahigh-resolution CH4 record of the West Antarctic Ice Sheet Divide ice core 67.2-9.8 ka and find novel, atmospheric CH4 variability at centennial time scales throughout the record. This signal is characterized by recurrence intervals within a broad 80-500 year range, but we find that age-scale uncertainties complicate the possible isolation of any periodic frequency. Lower signal amplitudes in the Last Glacial relative to the Holocene may be related to incongruent effects of firn-based signal smoothing processes. Within interstadial and stadial periods, the peak-to-peak signal amplitudes vary in proportion to the underlying millennial-scale oscillations in CH4 concentration-the relative amplitude change is constant. We propose that the centennial CH4 signal is related to tropical climate variability that influences predominantly low-latitude wetland CH4 emissions. Plain Language Summary Using a new method to measure methane concentrations of ancient air trapped in ice cores, we have detected variability in atmospheric methane concentration on centennial time scales in the Last Glacial Period for the first time. We know these signals represent past changes in atmospheric methane because they appear in several ice core records. We ropose that changes in methane emissions from tropical wetlands are responsible. How this new variability might be related to similar signals found in the late Holocene ice core records and the instrumental record of atmospheric methane is an open question.
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Stenni, B., Curran, M. A. J., Abram, N. J., Orsi, A., Goursaud, S., Masson-Delmotte, V., et al. (2017). Antarctic climate variability on regional and continental scales over the last 2000 years. Climate Of The Past, 13(11), 1609–1634.
Abstract: Climate trends in the Antarctic region remain poorly characterized, owing to the brevity and scarcity of direct climate observations and the large magnitude of interannual to decadal-scale climate variability. Here, within the framework of the PAGES Antarctica2k working group, we build an enlarged database of ice core water stable isotope records from Antarctica, consisting of 112 records. We produce both unweighted and weighted isotopic (delta O-18) composites and temperature reconstructions since 0 CE, binned at 5- and 10-year resolution, for seven climatically distinct regions covering the Antarctic continent. Following earlier work of the Antarctica2k working group, we also produce composites and reconstructions for the broader regions of East Antarctica, West Antarctica and the whole continent. We use three methods for our temperature reconstructions: (i) a temperature scaling based on the delta O-18-temperature relationship output from an ECHAM5-wiso model simulation nudged to ERA-Interim atmospheric reanalyses from 1979 to 2013, and adjusted for the West Antarctic Ice Sheet region to borehole temperature data, (ii) a temperature scaling of the isotopic normalized anomalies to the variance of the regional reanalysis temperature and (iii) a composite-plus-scaling approach used in a previous continent-scale reconstruction of Antarctic temperature since 1 CE but applied to the new Antarctic ice core database. Our new reconstructions confirm a significant cooling trend from 0 to 1900 CE across all Antarctic regions where records extend back into the 1st millennium, with the exception of the Wilkes Land coast and Weddell Sea coast regions. Within this long-term cooling trend from 0 to 1900 CE, we find that the warmest period occurs between 300 and 1000 CE, and the coldest interval occurs from 1200 to 1900 CE. Since 1900 CE, significant warming trends are identified for the West Antarctic Ice Sheet, the Dronning Maud Land coast and the Antarctic Peninsula regions, and these trends are robust across the distribution of records that contribute to the unweighted isotopic composites and also significant in the weighted temperature reconstructions. Only for the Antarctic Peninsula is this most recent century-scale trend unusual in the context of natural variability over the last 2000 years. However, projected warming of the Antarctic continent during the 21st century may soon see significant and unusual warming develop across other parts of the Antarctic continent. The extended Antarctica2k ice core isotope database developed by this working group opens up many avenues for developing a deeper understanding of the response of Antarctic climate to natural and anthropogenic climate forcings. The first long-term quantification of regional climate in Antarctica presented herein is a basis for data-model comparison and assessments of past, present and future driving factors of Antarctic climate.
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Traversi, R., Becagli, S., Brogioni, M., Caiazzo, L., Ciardini, V., Giardi, F., et al. (2017). Multi-year record of atmospheric and snow surface nitrate in the central Antarctic plateau. Chemosphere, 172, 341–354.
Abstract: Continuous all year-round samplings of atmospheric aerosol and surface snow at high (daily to 4-day) resolution were carried out at Dome C since 2004-05 to 2013 and nitrate records are here presented. Basing on a larger statistical data set than previous studies, results confirm that nitrate seasonal pattern is characterized by maxima during austral summer for both aerosol and surface snow, occurring in-phase with solar UV irradiance. This temporal pattern is likely due to a combination of nitrate sources and post-depositional processes whose intensity usually enhances during the summer. Moreover, it should be noted that a case study of the synoptic conditions, which took place during a major nitrate event, showed the occurrence of a stratosphere-troposphere exchange. The sampling of both matrices at the same time with high resolution allowed the detection of a an about one-month long recurring lag of summer maxima in snow with respect to aerosol. This result can be explained by deposition and post-deposition processes occurring at the atmosphere-snow interface, such as a net uptake of gaseous nitric acid and a replenishment of the uppermost surface layers driven by a larger temperature gradient in summer. This hypothesis was preliminarily tested by a comparison with surface layers temperature data in the 2012-13 period. The analysis of the relationship between the nitrate concentration in the gas phase and total nitrate obtained at Dome C (2012-13) showed the major role of gaseous HNO3 to the total nitrate budget suggesting the need to further investigate the gas-to-particle conversion processes. (C) 2017 Elsevier Ltd. All rights reserved.
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Ventrillard, I., Xueref-Remy, I., Schmidt, M., Kwok, C. Y., Fain, X., & Romanini, D. (2017). Comparison of optical-feedback cavity-enhanced absorption spectroscopy and gas chromatography for ground-based and airborne measurements of atmospheric CO concentration. Atmospheric Measurement Techniques, 10(5), 1803–1812.
Abstract: We present the first comparison of carbon monoxide (CO) measurements performed with a portable laser spectrometer that exploits the optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) technique, against a high-performance automated gas chromatograph (GC) with a mercuric oxide reduction gas detector (RGD). First, measurements of atmospheric CO mole fraction were continuously collected in a Paris (France) suburb over 1 week. Both instruments showed an excellent agreement within typically 2 ppb (part per billion in volume), fulfilling the World Meteorological Organization (WMO) recommendation for CO inter-laboratory comparison. The compact size and robustness of the OF-CEAS instrument allowed its operation aboard a small aircraft employed for routine tropospheric air analysis over the French Orleans forest area. Direct OF-CEAS real-time CO measurements in tropospheric air were then compared with later analysis of flask samples by the gas chromatograph. Again, a very good agreement was observed. This work establishes that the OF-CEAS laser spectrometer can run unattended at a very high level of sensitivity (< 1 ppb) and stability without any periodic calibration.
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2016 |
Bazin, L., Landais, A., Capron, E., Masson-Delmotte, V., Ritz, C., Picard, G., et al. (2016). Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores. Climate Of The Past, 12(3), 729–748.
Abstract: Orbital tuning is central for ice core chronologies beyond annual layer counting, available back to 60 ka (i.e. thousands of years before 1950) for Greenland ice cores. While several complementary orbital tuning tools have recently been developed using delta O-18(atm), delta O-2/N-2 and air content with different orbital targets, quantifying their uncertainties remains a challenge. Indeed, the exact processes linking variations of these parameters, measured in the air trapped in ice, to their orbital targets are not yet fully understood. Here, we provide new series of delta O-2/N-2 and delta O-18(atm) data encompassing Marine Isotopic Stage (MIS) 5 (between 100 and 160 ka) and the oldest part (340-800 ka) of the East Antarctic EPICA Dome C (EDC) ice core. For the first time, the measurements over MIS 5 allow an inter-comparison of delta O-2/N-2 and delta O-18(atm) records from three East Antarctic ice core sites (EDC, Vostok and Dome F). This comparison highlights some site-specific delta O-2/N-2 variations. Such an observation, the evidence of a 100 ka periodicity in the delta O-2/N-2 signal and the difficulty to identify extrema and mid-slopes in delta O-2/N-2 increase the uncertainty associated with the use of delta O-2/N-2 as an orbital tuning tool, now calculated to be 3-4 ka. When combining records of delta O-18(atm) and delta O-2/N-2 from Vostok and EDC, we find a loss of orbital signature for these two parameters during periods of minimum eccentricity (similar to 400 ka, 720-800 ka). Our data set reveals a time-varying offset between delta O-2/N-2 and delta O-18(atm) records over the last 800 ka that we interpret as variations in the lagged response of delta O-18(atm) to precession. The largest offsets are identified during Terminations II, MIS 8 and MIS 16, corresponding to periods of destabilization of the Northern polar ice sheets. We therefore suggest that the occurrence of Heinrich like events influences the response of delta O-18(atm) to precession.
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Berger, A., Crucifix, M., Hodell, D. A., Mangili, C., McManus, J. F., Otto-Bliesner, B., et al. (2016). Interglacials of the last 800,000years. Reviews Of Geophysics, 54(1), 162–219.
Abstract: Interglacials, including the present (Holocene) period, are warm, low land ice extent (high sea level), end-members of glacial cycles. Based on a sea level definition, we identify eleven interglacials in the last 800,000years, a result that is robust to alternative definitions. Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (last interglacial) and 11c (similar to 400ka ago) were globally strong (warm), while MIS 13a (similar to 500ka ago) was cool at many locations. A step change in strength of interglacials at 450ka is apparent only in atmospheric CO2 and in Antarctic and deep ocean temperature. The onset of an interglacial (glacial termination) seems to require a reducing precession parameter (increasing Northern Hemisphere summer insolation), but this condition alone is insufficient. Terminations involve rapid, nonlinear, reactions of ice volume, CO2, and temperature to external astronomical forcing. The precise timing of events may be modulated by millennial-scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere. A variety of temporal trends is observed, such that maxima in the main records are observed either early or late in different interglacials. The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes. Interglacials have been typically 10-30ka long. The combination of minimal reduction in northern summer insolation over the next few orbital cycles, owing to low eccentricity, and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future.
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Bock, J., Savarino, J., & Picard, G. (2016). Air-snow exchange of nitrate: a modelling approach to investigate physicochemical processes in surface snow at Dome C, Antarctica. Atmospheric Chemistry And Physics, 16(19), 12531–12550.
Abstract: Snowpack is a multiphase (photo) chemical reactor that strongly influences the air composition in polar and snow-covered regions. Snowpack plays a special role in the nitrogen cycle, as it has been shown that nitrate undergoes numerous recycling stages (including photolysis) in the snow before being permanently buried in the ice. However, the current understanding of these physicochemical processes remains very poor. Several modelling studies have attempted to reproduce (photo) chemical reactions inside snow grains, but these have relied on strong assumptions to characterise snow reactive properties, which are not well defined. Air-snow exchange processes such as adsorption, solid-state diffusion, or co-condensation also affect snow chemical composition. Here, we present a physically based model of these processes for nitrate. Using as input a 1-year-long time series of atmospheric nitrate concentration measured at Dome C, Antarctica, our model reproduces with good agreement the nitrate measurements in the surface snow. By investigating the relative importance of the main exchange processes, this study shows that, on the one hand, the combination of bulk diffusion and co-condensation allows a good reproduction of the measurements (correlation coefficient r = 0.95), with a correct amplitude and timing of summer peak concentration of nitrate in snow. During winter, nitrate concentration in surface snow is mainly driven by thermodynamic equilibrium, whilst the peak observed in summer is explained by the kinetic process of co-condensation. On the other hand, the adsorption of nitric acid on the surface of the snow grains, constrained by an already existing parameterisation for the isotherm, fails to fit the observed variations. During winter and spring, the modelled concentration of adsorbed nitrate is respectively 2.5 and 8.3-fold higher than the measured one. A strong diurnal variation driven by the temperature cycle and a peak occurring in early spring are two other major features that do not match the measurements. This study clearly demonstrates that co-condensation is the most important process to explain nitrate incorporation in snow undergoing temperature gradient metamorphism. The parameterisation developed for this process can now be used as a foundation piece in snowpack models to predict the inter-relationship between snow physical evolution and snow nitrate chemistry.
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Brovkin, V., Bruecher, T., Kleinen, T., Zaehle, S., Joos, F., Roth, R., et al. (2016). Comparative carbon cycle dynamics of the present and last interglacial. Quaternary Science Reviews, 137, 15–32.
Abstract: Changes in temperature and carbon dioxide during glacial cycles recorded in Antarctic ice cores are tightly coupled. However, this relationship does not hold for interglacials. While climate cooled towards the end of both the last (Eemian) and present (Holocene) interglacials, CO2 remained stable during the Eemian while rising in the Holocene. We identify and review twelve biogeochemical mechanisms of terrestrial (vegetation dynamics and CO2 fertilization, land use, wildfire, accumulation of peat, changes in permafrost carbon, subaerial volcanic outgassing) and marine origin (changes in sea surface temperature, carbonate compensation to deglaciation and terrestrial biosphere regrowth, shallow-water carbonate sedimentation, changes in the soft tissue pump, and methane hydrates), which potentially may have contributed to the CO2 dynamics during interglacials but which remain not well quantified. We use three Earth System Models (ESMs) of intermediate complexity to compare effects of selected mechanisms on the interglacial CO2 and delta(CO2)-C-13 changes, focusing on those with substantial potential impacts: namely carbonate sedimentation in shallow waters, peat growth, and (in the case of the Holocene) human land use. A set of specified carbon cycle forcings could qualitatively explain atmospheric CO2 dynamics from 8 ka BP to the pre-industrial. However, when applied to Eemian boundary conditions from 126 to 115 ka BP, the same set of forcings led to disagreement with the observed direction of CO2 changes after 122 ka BP. This failure to simulate late-Eemian CO2 dynamics could be a result of the imposed forcings such as prescribed CaCO3 accumulation and/or an incorrect response of simulated terrestrial carbon to the surface cooling at the end of the interglacial. These experiments also reveal that key natural processes of interglacial CO2 dynamics – shallow water CaCO3 accumulation, peat and permafrost carbon dynamics are not well represented in the current ESMs. Global-scale modeling of these long-term carbon cycle components started only in the last decade, and uncertainty in parameterization of these mechanisms is a main limitation in the successful modeling of interglacial CO2 dynamics. (C) 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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Cavitte, M. G. P., Blankenship, D. D., Young, D. A., Schroeder, D. M., Parrenin, F., Lemeur, E., et al. (2016). Deep radiostratigraphy of the East Antarctic plateau: connecting the Dome C and Vostok ice core sites. Journal Of Glaciology, 62(232), 323–334.
Abstract: Several airborne radar-sounding surveys are used to trace internal reflections around the European Project for Ice Coring in Antarctica Dome C and Vostok ice core sites. Thirteen reflections, spanning the last two glacial cycles, are traced within 200 km of Dome C, a promising region for million-year-old ice, using the University of Texas Institute for Geophysics High-Capacity Radar Sounder. This provides a dated stratigraphy to 2318 m depth at Dome C. Reflection age uncertainties are calculated from the radar range precision and signal-to-noise ratio of the internal reflections. The radar stratigraphy matches well with the Multichannel Coherent Radar Depth Sounder (MCoRDS) radar stratigraphy obtained independently. We show that radar sounding enables the extension of ice core ages through the ice sheet with an additional radar-related age uncertainty of similar to 1/3-1/2 that of the ice cores. Reflections are extended along the Byrd-Totten Glacier divide, using University of Texas/Technical University of Denmark and MCoRDS surveys. However, core-to-core connection is impeded by pervasive aeolian terranes, and Lake Vostok's influence on reflection geometry. Poor radar connection of the two ice cores is attributed to these effects and suboptimal survey design in affected areas. We demonstrate that, while ice sheet internal radar reflections are generally isochronal and can be mapped over large distances, careful survey planning is necessary to extend ice core chronologies to distant regions of the East Antarctic ice sheet.
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Crichton, K. A., Bouttes, N., Roche, D. M., Chappellaz, J., & Krinner, G. (2016). Permafrost carbon as a missing link to explain CO2 changes during the last deglaciation. Nature Geoscience, 9(9), 683–+.
Abstract: The atmospheric concentration of CO2 increased from 190 to 280 ppm between the last glacial maximum 21,000 years ago and the pre-industrial era(1,2). This CO2 rise and its timing have been linked to changes in the Earth's orbit, ice sheet configuration and volume, and ocean carbon storage(2,3). The ice-core record of delta(CO2)-C-13 (refs 2,4) in the atmosphere can help to constrain the source of carbon, but previous modelling studies have failed to capture the evolution of delta(CO2)-C-13 over this period(5). Here we show that simulations of the last deglaciation that include a permafrost carbon component can reproduce the ice core records between 21,000 and 10,000 years ago. We suggest that thawing permafrost, due to increasing summer insolation in the northern hemisphere, is the main source of CO2 rise between 17,500 and 15,000 years ago, a period sometimes referred to as the Mystery Interval(6). Together with a fresh water release into the North Atlantic, much of the CO2 variability associated with the Bolling-Allerod/Younger Dryas period similar to 15,000 to similar to 12,000 years ago can also be explained. In simulations of future warming we find that the permafrost carbon feedback increases global mean temperature by 10-40% relative to simulations without this feedback, with the magnitude of the increase dependent on the evolution of anthropogenic carbon emissions.
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Dommergue, A., Martinerie, P., Courteaud, J., Witrant, E., & Etheridge, D. M. (2016). A new reconstruction of atmospheric gaseous elemental mercury trend over the last 60 years from Greenland firn records. Atmospheric Environment, 136, 156–164.
Abstract: This study presents measurements of gaseous elemental mercury (GEM) concentrations in the 80 m of firn air at the international drilling site of NEEM in Greenland (2452 m, 77 degrees 25.8 N, 51 degrees 06.4 W). Using inverse modeling, we were able to reconstruct the atmospheric GEM trend at this Arctic site over the last 60 years. We show discrepancies between this record and the previous firn record of Summit. This could be attributed to experimental biases and/or differences in air mass transport. A multisite inverse model was used to derive an atmospheric scenario reconciling the two firn records. We show that GEM seasonal variations are very limited at these high altitude sites and thus probably unaffected by spring/summer photochemistry. The firn reconstructions suggest an increase of GEM concentrations since the 1950s peaking in the late 1960s and early 1970s. A decrease is then observed with minimum GEM concentrations around 1995-2000. The reconstruction compares well with historical mercury (Hg) releases and recent simulations of atmospheric Hg. Our optimal GEM scenario does not allow to categorically conclude on recent trends for GEM concentrations over the 2000-2010 decade. (C) 2016 Elsevier Ltd. All rights reserved.
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Francois, B., Borga, M., Creutin, J. D., Hingray, B., Raynaud, D., & Sauterleute, J. F. (2016). Complementarity between solar and hydro power: Sensitivity study to climate characteristics in Northern-Italy. Renewable Energy, 86, 543–553.
Abstract: Climate related energy sources such as wind, solar and runoff sources are variable in time and space, following their driving weather variables. High penetration of such energy sources might be facilitated by using their complementarity in order to increase the balance between energy load and generation. This study presents the analysis of the effect of a 100% renewable energy mix composed by solar and run-of-the-river energy in Northern Italy where these two energy sources are the main alternative energy sources. Along a climate gradient from the Alpine crest (snow melt dominated area) to the Veneto plain (rainfall dominated area), solar power is generated in the flat plain, and run-of-the-river hydropower at two mountainous locations. Covering all possible mixes of these two sources, we analyze their complementarity across different temporal scales using two indicators: the standard deviation of the energy balance and the theoretical storage required for balancing generation and load. Results show that at small temporal scale (hourly), a high share of run-of-the-river power allows minimizing the energy balance variability. The opposite is obtained at larger temporal scales (daily and monthly) essentially because of lower variability of solar power generation, which also implies a lower storage requirement. (C) 2015 Elsevier Ltd. All rights reserved.
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Francois, B., Hingray, B., Raynaud, D., Borga, M., & Creutin, J. D. (2016). Increasing climate-related-energy penetration by integrating run-of-the river hydropower to wind/solar mix. Renewable Energy, 87, 686–696.
Abstract: The penetration rate of Climate Related Energy sources like solar-power, wind-power and hydro-power source is potentially low as a result of the large space and time variability of their driving climatic variables. Increased penetration rates can be achieved with mixes of sources. Optimal mixes, i.e. obtained with the optimal share for each source, are being identified for a number of regions worldwide. However, they often consider wind and solar power only. Based on 33 years of daily data (1980-2012) for a set of 12 European regions, we re-estimate the optimal mix when wild run-of-the-river energy is included in the solar/wind mix. It is found to be highly region dependent but the highest shares are often obtained for run-of-the-river, ranging from 35% to 65% in Belarus and England. High solar shares (>40%) are found in southern countries but solar shares drop to less than 15% in northern countries. Wind shares range from 10 to 35% with the exception of Norway where it reaches 50%. These results put in perspective the optimal 60%-40% wind/solar mix currently used for Europe. For all regions, including run-of-the-river in the mix allows increasing the penetration rate of CREs (from 1 to 8% points). (C) 2015 Elsevier Ltd. All rights reserved.
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Gautier, E., Savarino, J., Erbland, J., Lanciki, A., & Possenti, P. (2016). Variability of sulfate signal in ice core records based on five replicate cores. Climate Of The Past, 12(1), 103–113.
Abstract: Current volcanic reconstructions based on ice core analysis have significantly improved over the past few decades by incorporating multiple-core analyses with a high temporal resolution from different parts of the polar regions into a composite common volcanic eruption record. Regional patterns of volcanic deposition are based on composite records, built from cores taken at both poles. However, in many cases only a single record at a given site is used for these reconstructions. This assumes that transport and regional meteorological patterns are the only source of the dispersion of the volcanic products. Here we evaluate the local-scale variability of a sulfate profile in a low-accumulation site (Dome C, Antarctica), in order to assess the representativeness of one core for such a reconstruction. We evaluate the variability with depth, statistical occurrence, and sulfate flux deposition variability of volcanic eruptions detected in five ice cores, drilled 1m apart from each other. Local-scale variability, essentially attributed to snow drift and surface roughness at Dome C, can lead to a non-exhaustive record of volcanic events when a single core is used as the site reference, with a bulk probability of 30% of missing volcanic events and close to 65% uncertainty on one volcanic flux measurement (based on the standard deviation obtained from a five-core comparison). Averaging n records reduces the uncertainty of the deposited flux mean significantly (by a factor 1/root n); in the case of five cores, the uncertainty of the mean flux can therefore be reduced to 29 %.
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Hattori, S., Savarino, J., Kamezaki, K., Ishino, S., Dyckmans, J., Fujinawa, T., et al. (2016). Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterialmethod and N2O decomposition by microwave discharge. Rapid Communications In Mass Spectrometry, 30(24), 2635–2644.
Abstract: RATIONALE: Triple oxygen and nitrogen isotope ratios in nitrate are powerful tools for assessing atmospheric nitrate formation pathways and their contribution to ecosystems. N2O decomposition using microwave-induced plasma (MIP) has been used only for measurements of oxygen isotopes to date, but it is also possible to measure nitrogen isotopes during the same analytical run. METHODS: The main improvements to a previous system are (i) an automated distribution system of nitrate to the bacterial medium, (ii) N2O separation by gas chromatography before N2O decomposition using the MIP, (iii) use of a corundumtube for microwave discharge, and (iv) development of an automated system for isotopic measurements. Three nitrate standards with sample sizes of 60, 80, 100, and 120 nmol were measured to investigate the sample size dependence of the isotope measurements. RESULTS: The delta O-17, delta O-18, and Delta O-17 values increased with increasing sample size, although the delta N-15 value showed no significant size dependency. Different calibration slopes and intercepts were obtained with different sample amounts. The slopes and intercepts for the regression lines in different sample amounts were dependent on sample size, indicating that the extent of oxygen exchange is also dependent on sample size. The sample-size-dependent slopes and intercepts were fitted using natural log (ln) regression curves, and the slopes and intercepts can be estimated to apply to any sample size corrections. When using 100 nmol samples, the standard deviations of residuals from the regression lines for this system were 0.5 parts per thousand, 0.3 parts per thousand, and 0.1 parts per thousand, respectively, for the delta O-18, Delta O-17, and delta N-15 values, results that are not inferior to those from other systems using gold tube or gold wire. CONCLUSIONS: An automated system was developed to measure triple oxygen and nitrogen isotopes in nitrate using N2O decomposition by MIP. This system enables us to measure both triple oxygen and nitrogen isotopes in nitrate with comparable precision and sample throughput (23 min per sample on average), and minimal manual treatment. Copyright (C) 2016 John Wiley & Sons, Ltd.
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Laube, J. C., Hanif, N. M., Martinerie, P., Gallacher, E., Fraser, P. J., Langenfelds, R., et al. (2016). Tropospheric observations of CFC-114 and CFC-114a with a focus on long-term trends and emissions. Atmospheric Chemistry And Physics, 16(23), 15347–15358.
Abstract: Chlorofluorocarbons (CFCs) are ozone-depleting substances as well as strong greenhouse gases, and the control of their production and use under the Montreal Protocol has had demonstrable benefits to both mitigation of increasing surface UV radiation and climate forcing. A global ban on consumption came into force in 2010, but there is evidence of continuing emissions of certain CFCs from a range of sources. One compound has received little attention in the literature, namely CFC-114 (C2Cl2F4). Of particular interest here is the differentiation between CFC-114 (CClF2CClF2) and its asymmetric isomeric form CFC-114a (CF3CCl2F) as atmospheric long-term measurements in the peer-reviewed literature to date have been assumed to represent the sum of both isomers with a time-invariant isomeric speciation. Here we report the first long-term measurements of the two isomeric forms separately, and find that they have different origins and trends in the atmosphere. Air samples collected at Cape Grim (41 degrees S), Australia, during atmospheric background conditions since 1978, combined with samples collected from deep polar snow (firn) enable us to obtain a near-complete record of both gases since their initial production and release in the 1940s. Both isomers were present in the unpolluted atmosphere in comparably small amounts before 1960. The mixing ratio of CFC-114 doubled from 7.9 to 14.8 parts per trillion (ppt) between the start of the Cape Grim record in 1978 and the end of our record in 2014, while over the same time CFC-114a trebled from 0.35 to 1.03 ppt. Mixing ratios of both isomers are slowly decreasing by the end of this period. This is consistent with measurements of recent aircraft-based samples showing no significant interhemispheric mixing ratio gradient. We also find that the fraction of CFC-114a mixing ratio relative to that of CFC-114 increased from 4.2 to 6.9% over the 37-year period. This contradicts the current tacit assumption used in international climate change and ozone depletion assessments that both isomers have been largely co-emitted and that their atmospheric concentration ratio has remained approximately constant in time. Complementary observations of air collected in Taiwan indicate a persisting source of CFC-114a in South East Asia which may have been contributing to the changing balance between the two isomers. In addition we present top-down global annual emission estimates of CFC-114 and CFC-114a derived from these measurements using a two-dimensional atmospheric chemistry-transport model. In general, the emissions for both compounds grew steadily during the 1980s, followed by a substantial reduction from the late 1980s onwards, which is consistent with the reduction of emission in response to the Montreal Protocol, and broadly consistent with bottom-up estimates derived by industry. However, we find that small but significant emissions of both isomers remain in 2014. Moreover the inferred changes to the ratio of emissions of the two isomers since the 1990s also indicate that the sources of the two gases are, in part, independent.
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Legrand, M., McConnell, J., Fischer, H., Wolff, E. W., Preunkert, S., Arienzo, M., et al. (2016). Boreal fire records in Northern Hemisphere ice cores: a review. Climate Of The Past, 12(10).
Abstract: Here, we review different attempts made since the early 1990s to reconstruct past forest fire activity using chemical signals recorded in ice cores extracted from the Greenland ice sheet and a few mid-northern latitude, high-elevation glaciers. We first examined the quality of various inorganic (ammonium, nitrate, potassium) and organic (black carbon, various organic carbon compounds including levoglucosan and numerous carboxylic acids) species proposed as fire proxies in ice, particularly in Greenland. We discuss limitations in their use during recent vs. pre-industrial times, atmospheric lifetimes, and the relative importance of other non-biomass-burning sources. Different high-resolution records from several Greenland drill sites and covering various timescales, including the last century and Holocene, are discussed. We explore the extent to which atmospheric transport can modulate the record of boreal fires from Canada as recorded in Greenland ice. Ammonium, organic fractions (black and organic carbon), and specific organic compounds such as formate and vanillic acid are found to be good proxies for tracing past boreal fires in Greenland ice. We show that use of other species – potassium, nitrate, and carboxylates (except formate) – is complicated by either post-depositional effects or existence of large non-biomass-burning sources. The quality of levoglucosan with respect to other proxies is not addressed here because of a lack of high-resolution profiles for this species, preventing a fair comparison. Several Greenland ice records of ammonium consistently indicate changing fire activity in Canada in response to past climatic conditions that occurred during the last millennium and since the last large climatic transition. Based on this review, we make recommendations for further study to increase reliability of the reconstructed history of forest fires occurring in a given region.
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Legrand, M., Preunkert, S., Savarino, J., Frey, M. M., Kukui, A., Helmig, D., et al. (2016). Inter-annual variability of surface ozone at coastal (Dumont d'Urville, 2004-2014) and inland (Concordia, 2007-2014) sites in East Antarctica. Atmospheric Chemistry And Physics, 16(12), 8053–8069.
Abstract: Surface ozone has been measured since 2004 at the coastal East Antarctic site of Dumont d'Urville (DDU), and since 2007 at the Concordia station located on the high East Antarctic plateau. This paper discusses long-term changes, seasonal and diurnal cycles, as well as inter-annual summer variability observed at these two East Antarctic sites. At Concordia, near-surface ozone data were complemented by balloon soundings and compared to similar measurements done at the South Pole. The DDU record is compared to those obtained at the coastal site of Syowa, also located in East Antarctica, as well as the coastal sites of Neumayer and Halley, both located on the coast of the Weddell Sea in West Antarctica. Surface ozone mixing ratios exhibit very similar seasonal cycles at Concordia and the South Pole. However, in summer the diurnal cycle of ozone is different at the two sites with a drop of ozone in the afternoon at Concordia but not at the South Pole. The vertical distribution of ozone above the snow surface also differs. When present, the ozone-rich layer located near the ground is better mixed and deeper at Concordia (up to 400aEuro-m) than at the South Pole during sunlight hours. These differences are related to different solar radiation and wind regimes encountered at these two inland sites. DDU appears to be the coastal site where the impact of the late winter/spring bromine chemistry is the weakest, but where the impact of elevated ozone levels caused by NOx snow emissions from the high Antarctic plateau is the highest. The highest impact of the bromine chemistry is seen at Halley and Neumayer, and to a lesser extent at Syowa. These three sites are only weakly impacted by the NOx chemistry and the net ozone production occurring on the high Antarctic plateau. The differences in late winter/spring are attributed to the abundance of sea ice offshore from the sites, whereas those in summer are related to the topography of East Antarctica that promotes the katabatic flow bringing oxidant-rich inland air masses to the site. There appears to be a decreasing change in summer surface ozone at the two East Antarctic sites of Concordia and DDU over the most recent period (2004-2014 and 2007-2014). Further research, including continued monitoring, is needed at these two sites to better separate the effect of synoptic transport from possible change of NOx snow emissions in response to recovery of the stratospheric ozone layer leading to penetration of more UV radiation to the surface.
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Legrand, M., Yang, X., Preunkert, S., & Theys, N. (2016). Year-round records of sea salt, gaseous, and particulate inorganic bromine in the atmospheric boundary layer at coastal (Dumont d'Urville) and central (Concordia) East Antarctic sites. Journal Of Geophysical Research-Atmospheres, 121(2), 997–1023.
Abstract: Multiple year-round records of bulk and size-segregated compositions of aerosol were obtained at the coastal Dumont d'Urville (DDU) and inland Concordia sites located in East Antarctica. They document the sea-salt aerosol load and composition including, for the first time in Antarctica, the bromide depletion of sea-salt aerosol relative to sodium with respect to seawater. In parallel, measurements of bromide trapped in mist chambers and denuder tubes were done to investigate the concentrations of gaseous inorganic bromine species. These data are compared to simulations done with an off-line chemistry transport model, coupled with a full tropospheric bromine chemistry scheme and a process-based sea-salt production module that includes both sea-ice-sourced and open-ocean-sourced aerosol emissions. Observed and simulated sea-salt concentrations sometime differ by up to a factor of 2 to 3, particularly at DDU possibly due to local wind pattern. In spite of these discrepancies, both at coastal and inland Antarctica, the dominance of sea-ice-related processes with respect to open ocean emissions for the sea-salt aerosol load in winter is confirmed. For summer, observations and simulations point out sea salt as the main source of gaseous inorganic bromine species. Investigations of bromide in snow pit samples do not support the importance of snowpack bromine emissions over the Antarctic Plateau. To evaluate the overall importance of the bromine chemistry over East Antarctica, BrO simulations were also discussed with respect data derived from GOME-2 satellite observations over Antarctica.
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Lipenkov, V. Y., Ekaykin, A. A., Polyakova, E. V., & Raynaud, D. (2016). Characterization of subglacial Lake Vostok as seen from physical and isotope properties of accreted ice. Philosophical Transactions Of The Royal Society A-Mathematical Physical And Engineering Sciences, 374(2059).
Abstract: Deep drilling at the Vostok Station has reached the surface of subglacial Lake Vostok (LV) twice-in February 2012 and January 2015. As a result, three replicate cores from boreholes 5G-1, 5G-2 and 5G-3 became available for detailed and revalidation analyses of the 230 m thickness of the accreted ice, down to its contact with water at 3769 m below the surface. The study reveals that the concentration of gases in the lake water beneath Vostok is unexpectedly low. A clear signature of the melt water in the surface layer of the lake, which is subject to refreezing on the icy ceiling of LV, has been discerned in the three different properties of the accreted ice: the ice texture, the isotopic and the gas content of the ice. These sets of data indicate in concert that poor mixing of the melt (and hydrothermal) water with the resident lake water and pronounced spatial and/or temporal variability of local hydrological conditions are likely to be the characteristics of the southern end of the lake. The latter implies that the surface water may be not representative enough to study LV's behaviour, and that direct sampling of the lake at different depths is needed in order to move ahead with our understanding of the lake's hydrological regime.
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Nakano, S., Suzuki, K., Kawamura, K., Parrenin, F., & Higuchi, T. (2016). A sequential Bayesian approach for the estimation of the age-depth relationship of the Dome Fuji ice core. Nonlinear Processes In Geophysics, 23(1), 31–44.
Abstract: A technique for estimating the age-depth relationship in an ice core and evaluating its uncertainty is presented. The age-depth relationship is determined by the accumulation of snow at the site of the ice core and the thinning process as a result of the deformation of ice layers. However, since neither the accumulation rate nor the thinning process is fully known, it is essential to incorporate observational information into a model that describes the accumulation and thinning processes. In the proposed technique, the age as a function of depth is estimated by making use of age markers and delta O-18 data. The age markers provide reliable age information at several depths. The data of delta O-18 are used as a proxy of the temperature for estimating the accumulation rate. The estimation is achieved using the particle Markov chain Monte Carlo (PMCMC) method, which is a combination of the sequential Monte Carlo (SMC) method and the Markov chain Monte Carlo method. In this hybrid method, the posterior distributions for the parameters in the models for the accumulation and thinning process are computed using the Metropolis method, in which the likelihood is obtained with the SMC method, and the posterior distribution for the age as a function of depth is obtained by collecting the samples generated by the SMC method with Metropolis iterations. The use of this PMCMC method enables us to estimate the age-depth relationship without assuming either linearity or Gaussianity. The performance of the proposed technique is demonstrated by applying it to ice core data from Dome Fuji in Antarctica.
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Narcisi, B., Petit, J. R., Langone, A., & Stenni, B. (2016). A new Eemian record of Antarctic tephra layers retrieved from the Talos Dome ice core (Northern Victoria Land). Global And Planetary Change, 137, 69–78.
Abstract: Polar ice sheets are remarkable repositories of tephra layers. The Talos Dome ice core (72 degrees 49'5, 159 degrees 11'E), drilled at the edge of the East Antarctic Plateau, close to Late Quaternary volcanoes, offers considerable potential to extend the current tephra time-stratigraphic framework. A tephrochronological study was undertaken of the ice core sections related to the Last Interglacial and the transition to the subsequent glacial period. Thirteen macroscopically visible layers, interpreted to be related to primary deposition of fallout tephra, have been analysed for quantitative grain size and glass shard geochemistry. The layers, precisely framed within the climate (6180) record for the core, span in age from 111.6 +/- 1.9 to 123.3 +/- 22 ka. Coarse particle size suggests origin from regional sources. Indeed, the vast majority of the samples display an alkaline affinity and trachytic composition that are both typical geochemical features of rifting Antarctic volcanism. Using subtle differences in the geochemical signatures and the comparison with data from previous studies, a few layers are attributed to known coeval Mt. Melbourne eruptions. Another sample subset is consistent with derivation from The Pleiades and Mt. Rittmann volcanoes. One peculiar trachytic glass population appears to be related to activity of the more distant Marie Byrd land volcanoes. The newly detected tephras provide stratigraphic markers that could facilitate future synchronisation and dating of palaeoclimatic records. The Talos Dome tephra inventory also contributes significantly to the reconstruction of the Northern Victoria Land explosive volcanism, for which chronostratigraphic data for the last Interglacial temporal segment are poor. (C) 2015 Elsevier B.V. All rights reserved.
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Parrenin, F., Fujita, S., Abe-Ouchi, A., Kawamura, K., Masson-Delmotte, V., Motoyama, H., et al. (2016). Climate dependent contrast in surface mass balance in East Antarctica over the past 216 ka. Journal Of Glaciology, 62(236), 1037–1048.
Abstract: Documenting past changes in the East Antarctic surface mass balance is important to improve ice core chronologies and to constrain the ice-sheet contribution to global mean sea-level change. Here we reconstruct past changes in the ratio of surface mass balance (SMB ratio) between the EPICA Dome C (EDC) and Dome Fuji (DF) East Antarctica ice core sites, based on a precise volcanic synchronization of the two ice cores and on corrections for the vertical thinning of layers. During the past 216 000 a, this SMB ratio, denoted SMBEDC/SMBDF, varied between 0.7 and 1.1, being small during cold periods and large during warm periods. Our results therefore reveal larger amplitudes of changes in SMB at EDC compared with DF, consistent with previous results showing larger amplitudes of changes in water stable isotopes and estimated surface temperature at EDC compared with DF. Within the last glacial inception (Marine Isotope Stages, MIS-5c and MIS-5d), the SMB ratio deviates by up to 0.2 from what is expected based on differences in water stable isotope records. Moreover, the SMB ratio is constant throughout the late parts of the current and last interglacial periods, despite contrasting isotopic trends.
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Passalacqua, O., Gagliardini, O., Parrenin, F., Todd, J., Gillet-Chaulet, F., & Ritz, C. (2016). Performance and applicability of a 2.5-D ice-flow model in the vicinity of a dome. Geoscientific Model Development, 9(7), 2301–2313.
Abstract: Three-dimensional ice flow modelling requires a large number of computing resources and observation data, such that 2-D simulations are often preferable. However, when there is significant lateral divergence, this must be accounted for (2.5-D models), and a flow tube is considered (volume between two horizontal flowlines). In the absence of velocity observations, this flow tube can be derived assuming that the flowlines follow the steepest slope of the surface, under a few flow assumptions. This method typically consists of scanning a digital elevation model (DEM) with a moving window and computing the curvature at the centre of this window. The ability of the 2.5-D models to account properly for a 3-D state of strain and stress has not clearly been established, nor their sensitivity to the size of the scanning window and to the geometry of the ice surface, for example in the cases of sharp ridges. Here, we study the applicability of a 2.5-D ice flow model around a dome, typical of the East Antarctic plateau conditions. A twin experiment is carried out, comparing 3-D and 2.5-D computed velocities, on three dome geometries, for several scanning windows and thermal conditions. The chosen scanning window used to evaluate the ice surface curvature should be comparable to the typical radius of this curvature. For isothermal ice, the error made by the 2.5-D model is in the range 0-10aEuro-% for weakly diverging flows, but is 2 or 3 times higher for highly diverging flows and could lead to a non-physical ice surface at the dome. For non-isothermal ice, assuming a linear temperature profile, the presence of a sharp ridge makes the 2.5-D velocity field unrealistic. In such cases, the basal ice is warmer and more easily laterally strained than the upper one, the walls of the flow tube are not vertical, and the assumptions of the 2.5-D model are no longer valid.
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Rhodes, R. H., Fain, X., Brook, E. J., McConnell, J. R., Maselli, O. J., Sigl, M., et al. (2016). Local artifacts in ice core methane records caused by layered bubble trapping and in situ production: a multi-site investigation. Climate Of The Past, 12(4), 1061–1077.
Abstract: Advances in trace gas analysis allow localised, non-atmospheric features to be resolved in ice cores, superimposed on the coherent atmospheric signal. These high frequency signals could not have survived the low-pass filter effect that gas diffusion in the firn exerts on the atmospheric history and therefore do not result from changes in the atmospheric composition at the ice sheet surface. Using continuous methane (CH4) records obtained from five polar ice cores, we characterise these non-atmospheric signals and explore their origin. Isolated samples, enriched in CH4 in the Tunul3 (Greenland) record are linked to the presence of melt layers. Melting can enrich the methane concentration due to a solubility effect, but we find that an additional in situ process is required to generate the full magnitude of these anomalies. Furthermore, in all the ice cores studied there is evidence of reproducible, decimetre-scale CH4 variability. Through a series of tests, we demonstrate that this is an artifact of layered bubble trapping in a heterogeneous density firn column; we use the term “trapping signal” for this phenomenon. The peak -to -peak amplitude of the trapping signal is typically 5 ppb, but may exceed 40 ppb. Signal magnitude increases with atmospheric CH4 growth rate and seasonal density contrast, and decreases with accumulation rate. Significant annual periodicity is present in the CH4 variability of two Greenland ice cores, suggesting that layered gas trapping at these sites is controlled by regular, seasonal variations in the physical properties of the firn. Future analytical campaigns should anticipate high -frequency artifacts at high -melt ice core sites or during time periods with high atmospheric CH4 growth rate in order to avoid misinterpretation of such features as past changes in atmospheric composition.
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Riveiros, N. V., Govin, A., Waelbroeck, C., Mackensen, A., Michel, E., Moreira, S., et al. (2016). Mg/Ca thermometry in planktic foraminifera: Improving paleotemperature estimations for G. bulloides and N. pachyderma left. Geochemistry Geophysics Geosystems, 17(4), 1249–1264.
Abstract: Planktic foraminiferal Mg/Ca ratios have become a fundamental seawater temperature proxy in past climate reconstructions, due to the temperature dependence of Mg uptake into foraminiferal calcite. However, empirical calibrations for single species from methodologically consistent data are still lacking. Here we present species -specific calibrations of Mg/Ca versus calcification temperature for two commonly used species of planktic foraminifera: Globigerina bulloides and Neogloboquadrina pachyderma left, based on a series of Southern Ocean and North Atlantic core tops. Combining these new data with previously published data, we derive an integrated G. bulloides Mg/Ca-temperature calibration for mid and high latitudes of both hemispheres between 2 and 18 degrees C, where Mg/Ca = 1.006 +/- 0.032* e(0.065 +/- 0.003)*(Tiso) (R-2=0.82). G. bulloides is found to calcify deeper in the Southern Ocean ( 200 m) than in the North Atlantic (top 50 m). We also propose a Mg/Ca temperature calibration to describe the temperature response in N. pachyderma left that calcified away from the influence of sea ice in the Southern Ocean, valid between similar to -1 and 9 degrees C, of the form Mg/Ca = 0.580 +/- 0.016 * e(0.084) (+/-) (0.006)*(Tisa) (R-2 = 0.70). These calibrations account for uncertainties on Mg/Ca measurements and calcification temperature that were carefully estimated and propagated using Monte Carlo iterations. The la propagated error in Mg/Ca-derived temperatures is 1.1 degrees C for G. bulloides and 0.9 degrees C for N. pachyderma left for the presented data sets. Geographical extension of genotypes must be assessed when choosing to develop regional or global calibrations.
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Savarino, J., Vicars, W. C., Legrand, M., Preunkert, S., Jourdain, B., Frey, M. M., et al. (2016). Oxygen isotope mass balance of atmospheric nitrate at Dome C, East Antarctica, during the OPALE campaign. Atmospheric Chemistry And Physics, 16(4), 2659–2673.
Abstract: Variations in the stable oxygen isotope composition of atmospheric nitrate act as novel tools for studying oxidative processes taking place in the troposphere. They provide both qualitative and quantitative constraints on the pathways determining the fate of atmospheric nitrogen oxides (NO + NO2 = NOx). The unique and distinctive O-17 excess (Delta O-17 = delta O-17-0.52 x delta O-18) of ozone, which is transferred to NOx via oxidation, is a particularly useful isotopic fingerprint in studies of NOx transformations. Constraining the propagation of O-17 excess within the NOx cycle is critical in polar areas, where there exists the possibility of extending atmospheric investigations to the glacial-interglacial timescale using deep ice core records of nitrate. Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C (East Antarctic Plateau) during the austral summer of 2011/2012. Nitrate isotope analysis has been here combined for the first time with key precursors involved in nitrate production (NOx, O-3, OH, HO2, RO2, etc.) and direct observations of the transferrable Delta O-17 of surface ozone, which was measured at Dome C throughout 2012 using our recently developed analytical approach. Assuming that nitrate is mainly produced in Antarctica in summer through the OH + NO2 pathway and using concurrent measurements of OH and NO2, we calculated a Delta O-17 signature for nitrate on the order of (21-22 + 3) %. These values are lower than the measured values that ranged between 27 and 31 %. This discrepancy between expected and observed Delta O-17(NO3-)values suggests the existence of an unknown process that contributes significantly to the atmospheric nitrate budget over this East Antarctic region. However, systematic errors or false isotopic balance transfer functions are not totally excluded.
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Sigl, M., Fudge, T. J., Winstrup, M., Cole-Dai, J., Ferris, D., McConnell, J. R., et al. (2016). The WAIS Divide deep ice core WD2014 chronology – Part 2: Annual-layer counting (0-31 ka BP). Climate Of The Past, 12(3), 769–786.
Abstract: We present the WD2014 chronology for the upper part (0-2850 m; 31.2 ka BP) of the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core. The chronology is based on counting of annual layers observed in the chemical, dust and electrical conductivity records. These layers are caused by seasonal changes in the source, transport, and deposition of aerosols. The measurements were interpreted manually and with the aid of two automated methods. We validated the chronology by comparing to two high-accuracy, absolutely dated chronologies. For the Holocene, the cosmogenic isotope records of Be-10 from WAIS Divide and C-14 for IntCal13 demonstrated that WD2014 was consistently accurate to better than 0.5% of the age. For the glacial period, comparisons to the Hulu Cave chronology demonstrated that WD2014 had an accuracy of better than 1% of the age at three abrupt climate change events between 27 and 31 ka. WD2014 has consistently younger ages than Greenland ice core chronologies during most of the Holocene. For the Younger Dryas-Preboreal transition (11.595 ka; 24 years younger) and the Bolling-Allerod Warming (14.621 ka; 7 years younger), WD2014 ages are within the combined uncertainties of the timescales. Given its high accuracy, WD2014 can become a reference chronology for the Southern Hemisphere, with synchronization to other chronologies feasible using high-quality proxies of volcanism, solar activity, atmospheric mineral dust, and atmospheric methane concentrations.
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Touzeau, A., Landais, A., Stenni, B., Uemura, R., Fukui, K., Fujita, S., et al. (2016). Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters. Cryosphere, 10(2), 837–852.
Abstract: The isotopic compositions of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second-order parameters (d-excess and O-17-excess) are related to delta O-18 and how they are controlled. d-excess increases in the interior of the continent (i.e., when delta O-18 decreases), due to the distillation process, whereas O-17-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over 1 year at Dome C and Vostok, as well as in surface snow at Dome C. We note that the slope of the delta O-18 vs. temperature (T) relationship decreases in these samples compared to those from the traverses, and thus caution is advocated when using spatial slopes for past climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active and that their interpretation in terms of source climatic parameters is strongly complicated by local temperature effects in East Antarctica. Finally we check if the same relationships between delta O-18 and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to delta O-18 in most snow pits, the O-17-excess is no longer positively correlated to delta O-18 and even shows anti-correlation to delta O-18 at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes.
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Trudinger, C. M., Fraser, P. J., Etheridge, D. M., Sturges, W. T., Vollmer, M. K., Rigby, M., et al. (2016). Atmospheric abundance and global emissions of perfluorocarbons CF4, C2F6 and C3F8 since 1800 inferred from ice core, firn, air archive and in situ measurements. Atmospheric Chemistry And Physics, 16(18), 11733–11754.
Abstract: Perfluorocarbons (PFCs) are very potent and long-lived greenhouse gases in the atmosphere, released predominantly during aluminium production and semiconductor manufacture. They have been targeted for emission controls under the United Nations Framework Convention on Climate Change. Here we present the first continuous records of the atmospheric abundance of CF4 (PFC-14), C2F6 (PFC-116) and C3F8 (PFC-218) from 1800 to 2014. The records are derived from high-precision measurements of PFCs in air extracted from polar firn or ice at six sites (DE08, DE08-2, DSSW20K, EDML, NEEM and South Pole) and air archive tanks and atmospheric air sampled from both hemispheres. We take account of the age characteristics of the firn and ice core air samples and demonstrate excellent consistency between the ice core, firn and atmospheric measurements. We present an inversion for global emissions from 1900 to 2014. We also formulate the inversion to directly infer emission factors for PFC emissions due to aluminium production prior to the 1980s. We show that 19th century atmospheric levels, before significant anthropogenic influence, were stable at 34.1 +/- 0.3 ppt for CF4 and below detection limits of 0.002 and 0.01 ppt for C2F6 and C3F8, respectively. We find a significant peak in CF4 and C2F6 emissions around 1940, most likely due to the high demand for aluminium during World War II, for example for construction of aircraft, but these emissions were nevertheless much lower than in recent years. The PFC emission factors for aluminium production in the early 20th century were significantly higher than today but have decreased since then due to improvements and better control of the smelting process. Mitigation efforts have led to decreases in emissions from peaks in 1980 (CF4) or early-to-mid-2000s (C2F6 and C3F8) despite the continued increase in global aluminium production; however, these decreases in emissions appear to have recently halted. We see a temporary reduction of around 15% in CF4 emissions in 2009, presumably associated with the impact of the global financial crisis on aluminium and semiconductor production.
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Wolff, E. W., Bigler, M., Curran, M. A. J., Dibb, J. E., Frey, M. M., Legrand, M., et al. (2016). Comment on “Low time resolution analysis of polar ice cores cannot detect impulsive nitrate events” by DF Smart et al. Journal Of Geophysical Research-Space Physics, 121(3), 1920–1924.
Abstract: Smart et al. (2014) suggested that the detection of nitrate spikes in polar ice cores from solar energetic particle (SEP) events could be achieved if an analytical system with sufficiently high resolution was used. Here we show that the spikes they associate with SEP events are not reliably recorded in cores from the same location, even when the resolution is clearly adequate. We explain the processes that limit the effective resolution of ice cores. Liquid conductivity data suggest that the observed spikes are associated with sodium or another nonacidic cation, making it likely that they result from deposition of sea salt or similar aerosol that has scavenged nitrate, rather than from a primary input of nitrate in the troposphere. We consider that there is no evidence at present to support the identification of any spikes in nitrate as representing SEP events. Although such events undoubtedly create nitrate in the atmosphere, we see no plausible route to using nitrate spikes to document the statistics of such events.
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Zannoni, N., Gros, V., Lanza, M., Sarda, R., Bonsang, B., Kalogridis, C., et al. (2016). OH reactivity and concentrations of biogenic volatile organic compounds in a Mediterranean forest of downy oak trees. Atmospheric Chemistry And Physics, 16(3), 1619–1636.
Abstract: Total OH reactivity, defined as the total loss frequency of the hydroxyl radical in the atmosphere, has proved to be an excellent tool to identify the total loading of reactive species in ambient air. High levels of unknown reactivity were found in several forests worldwide and were often higher than at urban sites. Our study presents atmospheric mixing ratios of biogenic compounds and total OH reactivity measured during late spring 2014 at the forest of downy oak trees of the Observatoire de Haute Provence (OHP), France. Air masses were sampled at two heights: 2 m, i.e., inside the canopy, and 10 m, i.e., above the canopy, where the mean canopy height is 5 m. We found that the OH reactivity at the site mainly depended on the main primary biogenic species emitted by the forest, which was isoprene and to a lesser extent by its degradation products and long-lived atmospheric compounds (up to 26% during daytime). During daytime, no significant missing OH reactivity was reported at the site, either inside or above the canopy. However, during two nights we determined a missing fraction of OH reactivity up to 50 %, possibly due to unmeasured oxidation products. We confirmed that no significant oxidation of the primary species occurred within the canopy; primary compounds emitted by the forest were fast transported to the atmosphere. Finally, the OH reactivity at this site was maximum 69 s(-1), which is a high value for a forest characterized by a temperate climate. Observations in various and diverse forests in the Mediterranean region are therefore needed to better constrain the impact of reactive gases over this area.
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Zatko, M., Erbland, J., Savarino, J., Geng, L., Easley, L., Schauer, A., et al. (2016). The magnitude of the snow-sourced reactive nitrogen flux to the boundary layer in the Uintah Basin, Utah, USA. Atmospheric Chemistry And Physics, 16(21), 13837–13851.
Abstract: Reactive nitrogen(N-r = NO, NO2, HONO) and volatile organic carbon emissions from oil and gas extraction activities play a major role in wintertime ground-level ozone exceedance events of up to 140 ppb in the Uintah Basin in eastern Utah. Such events occur only when the ground is snow covered, due to the impacts of snow on the stability and depth of the boundary layer and ultraviolet actinic flux at the surface. Recycling of reactive nitrogen from the photolysis of snow nitrate has been observed in polar and mid-latitude snow, but snow-sourced reactive nitrogen fluxes in mid-latitude regions have not yet been quantified in the field. Here we present vertical profiles of snow nitrate concentration and nitrogen isotopes (delta N-15) collected during the Uintah Basin Winter Ozone Study 2014 (UBWOS 2014), along with observations of insoluble light-absorbing impurities, radiation equivalent mean ice grain radii, and snow density that determine snow optical properties. We use the snow optical properties and nitrate concentrations to calculate ultraviolet actinic flux in snow and the production of N-r from the photolysis of snow nitrate. The observed delta N-15(NO3-) is used to constrain modeled fractional loss of snow nitrate in a snow chemistry column model, and thus the source of N-r to the overlying boundary layer. Snow-surface delta N-15(NO3-) measurements range from -5 to 10% and suggest that the local nitrate burden in the Uintah Basin is dominated by primary emissions from anthropogenic sources, except during fresh snowfall events, where remote NOx sources from beyond the basin are dominant. Modeled daily averaged snow-sourced N-r fluxes range from 5.6 to 71 x 10(7) molec cm(-2) s(-1) over the course of the field campaign, with a maximum noontime value of 3.1 x 10(9) molec cm(-2) s(-1). The top-down emission estimate of primary, anthropogenic NOx in Uintah and Duchesne counties is at least 300 times higher than the estimated snow NOx emissions presented in this study. Our results suggest that snow-sourced reactive nitrogen fluxes are minor contributors to the N-r boundary layer budget in the highly polluted Uintah Basin boundary layer during winter 2014.
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Allin, S. J., Laube, J. C., Witrant, E., Kaiser, J., McKenna, E., Dennis, P., et al. (2015). Chlorine isotope composition in chlorofluorocarbons CFC-11, CFC-12 and CFC-113 in firn, stratospheric and tropospheric air. Atmospheric Chemistry And Physics, 15(12), 6867–6877.
Abstract: The stratospheric degradation of chlorofluorocarbons (CFCs) releases chlorine, which is a major contributor to the destruction of stratospheric ozone (O-3). A recent study reported strong chlorine isotope fractionation during the breakdown of the most abundant CFC (CFC-12, CCl2F2, Laube et al., 2010a), similar to effects seen in nitrous oxide (N2O). Using air archives to obtain a long-term record of chlorine isotope ratios in CFCs could help to identify and quantify their sources and sinks. We analyse the three most abundant CFCs and show that CFC-11 (CCl3F) and CFC-113 (CClF2CCl2F) exhibit significant stratospheric chlorine isotope fractionation, in common with CFC-12. The apparent isotope fractionation (epsilon(app)) for mid- and high-latitude stratospheric samples are respectively -2.4 (0.5) and -2.3 (0.4) parts per thousand for CFC-11, -12.2 (1.6) and -6.8 (0.8) parts per thousand for CFC-12 and -3.5 (1.5) and -3.3 (1.2) parts per thousand for CFC-113, where the number in parentheses is the numerical value of the standard uncertainty expressed in per mil. Assuming a constant isotope composition of emissions, we calculate the expected trends in the tropospheric isotope signature of these gases based on their stratospheric Cl-37 enrichment and stratosphere-troposphere exchange. We compare these projections to the long-term delta (Cl-37) trends of all three CFCs, measured on background tropospheric samples from the Cape Grim air archive (Tasmania, 1978-2010) and tropospheric firn air samples from Greenland (North Greenland Eemian Ice Drilling (NEEM) site) and Antarctica (Fletcher Promontory site). From 1970 to the present day, projected trends agree with tropospheric measurements, suggesting that within analytical uncertainties, a constant average emission isotope delta (delta) is a compatible scenario. The measurement uncertainty is too high to determine whether the average emission isotope delta has been affected by changes in CFC manufacturing processes or not. Our study increases the suite of trace gases amenable to direct isotope ratio measurements in small air volumes (approximately 200 mL), using a single-detector gas chromatography-mass spectrometry (GC-MS) system.
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Amogu, O., Esteves, M., Vandervaere, J. P., Abdou, M. M., Panthou, G., Rajot, J. L., et al. (2015). Runoff evolution due to land-use change in a small Sahelian catchment. Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 60(1), 78–95.
Abstract: Land-use changes have been significant these last decades in West Africa, particularly in the Sahel region; in this area, climatic and demographic factors have led to a rise in cropped areas in recent decades causing strong changes in the water cycle and in river regimes. This study compares the rainfall-runoff relationships for two periods (1991-1994 and 2004-2011) in two small and similar neighbouring Sahelian catchments (approx 0.1 km(2) each). This allows identification of the different hydrological consequences of land-use/land-cover change, particularly the fallow shortening and the consequent degradation of topsoil. The main land surface change is a 75% increase in crusted soil area. Runoff increased by more than 20% on average between the two periods while flood duration decreased by 50% on average. However, runoff values remained largely constant in the lower part of the northern basin due to a strong increase in in-channel infiltration. Editor D. Koutsoyiannis; Associate editor T. Wagener
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Bereiter, B., Eggleston, S., Schmitt, J., Nehrbass-Ahles, C., Stocker, T. F., Fischer, H., et al. (2015). Revision of the EPICA Dome C CO2 record from 800 to 600kyr before present. Geophysical Research Letters, 42(2), 542–549.
Abstract: The European Project for Ice Coring in Antarctica Dome ice core from Dome C (EDC) has allowed for the reconstruction of atmospheric CO2 concentrations for the last 800,000years. Here we revisit the oldest part of the EDC CO2 record using different air extraction methods and sections of the core. For our established cracker system, we found an analytical artifact, which increases over the deepest 200m and reaches 10.12.4ppm in the oldest/deepest part. The governing mechanism is not yet fully understood, but it is related to insufficient gas extraction in combination with ice relaxation during storage and ice structure. The corrected record presented here resolves partly – but not completely – the issue with a different correlation between CO2 and Antarctic temperatures found in this oldest part of the records. In addition, we provide here an update of 800,000years atmospheric CO2 history including recent studies covering the last glacial cycle.
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Berhanu, T. A., Savarino, J., Erbland, J., Vicars, W. C., Preunkert, S., Martins, J. F., et al. (2015). Isotopic effects of nitrate photochemistry in snow: a field study at Dome C, Antarctica. Atmospheric Chemistry And Physics, 15(19), 11243–11256.
Abstract: Stable isotope ratios of nitrate preserved in deep ice cores are expected to provide unique and valuable information regarding paleoatmospheric processes. However, due to the post-depositional loss of nitrate in snow, this information may be erased or significantly modified by physical or photochemical processes before preservation in ice. We investigated the role of solar UV photolysis in the post-depositional modification of nitrate mass and stable isotope ratios at Dome C, Antarctica, during the austral summer of 2011/2012. Two 30 cm snow pits were filled with homogenized drifted snow from the vicinity of the base. One of these pits was covered with a plexiglass plate that transmits solar UV radiation, while the other was covered with a different plexiglass plate having a low UV transmittance. Samples were then collected from each pit at a 2-5 cm depth resolution and a 10-day frequency. At the end of the season, a comparable nitrate mass loss was observed in both pits for the top-level samples (0-7 cm) attributed to mixing with the surrounding snow. After excluding samples impacted by the mixing process, we derived an average apparent nitrogen isotopic fractionation ((15)epsilon(app)) of -67.8 +/- 12% for the snow nitrate exposed to solar UV using the nitrate stable isotope ratios and concentration measurements. For the control samples in which solar UV was blocked, an apparent average (15)epsilon(app) value of -12.0 +/- 1.7% was derived. This difference strongly suggests that solar UV photolysis plays a dominant role in driving the isotopic fractionation of nitrate in snow. We have estimated a purely photolytic nitrogen isotopic fractionation ((15)epsilon(photo)) of -55.8 +/- 12.0% from the difference in the derived apparent isotopic fractionations of the two experimental fields, as both pits were exposed to similar physical processes except exposure to solar UV. This value is in close agreement with the (15)epsilon(photo) value of -47.9 +/- 6.8% derived in a laboratory experiment simulated for Dome C conditions (Berhanu et al., 2014). We have also observed an insensitivity of (15)epsilon with depth in the snowpack under the given experimental setup. This is due to the uniform attenuation of incoming solar UV by snow, as (15)epsilon is strongly dependent on the spectral distribution of the incoming light flux. Together with earlier work, the results presented here represent a strong body of evidence that solar UV photolysis is the most relevant post-depositional process modifying the stable isotope ratios of snow nitrate at low-accumulation sites, where many deep ice cores are drilled. Nevertheless, modeling the loss of nitrate in snow is still required before a robust interpretation of ice core records can be provided.
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Crichton, K. A., Anderson, K., Bennie, J. J., & Milton, E. J. (2015). Characterizing peatland carbon balance estimates using freely available Landsat ETM plus data. Ecohydrology, 8(3), 493–503.
Abstract: We demonstrate the potential of using freely available satellite data from the Landsat ETM+ sensor for generating carbon balance estimates for lowland peatlands. We used a lowland ombrotrophic peatland in the UK as our test site representing a range of peatland conditions. A literature survey was undertaken to identify the simplest classification schema that could be used to distinguish ecohydrological classes for carbon sequestration on the peatland surface. These were defined as: active raised bog, Eriophorum-dominated bog, milled unvegetated peat and drained or degraded bog, with bracken and Carr woodland to define the bog edges. A maximum likelihood classifier (MLC) was used to map the spatial distribution of the six classes on the peatland surface. A Landsat ETM+ band-5 derived brightness-texture layer created using geostatistical methods greatly improved classification accuracies. The results showed the best accuracy of the MLC, when compared to finer scale methods, with Landsat ETM+ bands alone was 74%, which increased to 93% when including the brightness-texture layer. An estimate of carbon sequestration status of the site was performed that showed good agreement with the results of a finer-scale-based estimate. The coarse-scale map estimating -12000kg carbon and fine scale map estimating +23000kg carbon per annum. We conclude that with further development of our tool, if textural measures are used alongside optical data in MLC, it is possible to achieve good quality estimates of carbon balance status for peatland landscapes. This represents a potentially powerful operational toolkit for land managers and policy makers who require spatially distributed information on carbon storage and release for carbon pricing and effective land management. Copyright (c) 2014 John Wiley & Sons, Ltd.
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Erbland, J., Savarino, J., Morin, S., France, J. L., Frey, M. M., & King, M. D. (2015). Air-snow transfer of nitrate on the East Antarctic Plateau – Part 2: An isotopic model for the interpretation of deep ice-core records. Atmospheric Chemistry And Physics, 15(20), 12079–12113.
Abstract: Unraveling the modern budget of reactive nitrogen on the Antarctic Plateau is critical for the interpretation of ice-core records of nitrate. This requires accounting for nitrate recycling processes occurring in near-surface snow and the overlying atmospheric boundary layer. Not only concentration measurements but also isotopic ratios of nitrogen and oxygen in nitrate provide constraints on the processes at play. However, due to the large number of intertwined chemical and physical phenomena involved, numerical modeling is required to test hypotheses in a quantitative manner. Here we introduce the model TRANSITS (TRansfer of Atmospheric Nitrate Stable Isotopes To the Snow), a novel conceptual, multi-layer and one-dimensional model representing the impact of processes operating on nitrate at the air-snow interface on the East Antarctic Plateau, in terms of concentrations (mass fraction) and nitrogen (delta N-15) and oxygen isotopic composition (O-17 excess, Delta O-17) in nitrate. At the air-snow interface at Dome C (DC; 75 degrees 06'S, 123 degrees 19'E), the model reproduces well the values of delta N-15 in atmospheric and surface snow (skin layer) nitrate as well as in the delta N-15 profile in DC snow, including the observed extraordinary high positive values (around +300 %) below 2 cm. The model also captures the observed variability in nitrate mass fraction in the snow. While oxygen data are qualitatively reproduced at the air-snow interface at DC and in East Antarctica, the simulated Delta O-17 values underestimate the observed Delta O-17 values by several per mill. This is explained by the simplifications made in the description of the atmospheric cycling and oxidation of NO2 as well as by our lack of understanding of the NOx chemistry at Dome C. The model reproduces well the sensitivity of delta N-15, Delta O-17 and the apparent fractionation constants ((15)epsilon(app), E-17(app)) to the snow accumulation rate. Building on this development, we propose a framework for the interpretation of nitrate records measured from ice cores. Measurement of nitrate mass fractions and delta N-15 in the nitrate archived in an ice core may be used to derive information about past variations in the total ozone column and/or the primary inputs of nitrate above Antarctica as well as in nitrate trapping efficiency (defined as the ratio between the archived nitrate flux and the primary nitrate input flux). The Delta O-17 of nitrate could then be corrected from the impact of cage recombination effects associated with the photolysis of nitrate in snow. Past changes in the relative contributions of the Delta O-17 in the primary inputs of nitrate and the Delta O-17 in the locally cycled NO2 and that inherited from the additional O atom in the oxidation of NO2 could then be determined. Therefore, information about the past variations in the local and long-range processes operating on reactive nitrogen species could be obtained from ice cores collected in low-accumulation regions such as the Antarctic Plateau.
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Fujita, S., Parrenin, F., Severi, M., Motoyama, H., & Wolff, E. W. (2015). Volcanic synchronization of Dome Fuji and Dome C Antarctic deep ice cores over the past 216 kyr. Climate of the Past, 11(10), 1395–1416.
Abstract: Two deep ice cores, Dome Fuji (DF) and EPICA Dome C (EDC), drilled at remote dome summits in Antarctica, were volcanically synchronized to improve our understanding of their chronologies. Within the past 216 kyr, 1401 volcanic tie points have been identified. DFO2006 is the chronology for the DF core that strictly follows O-2/N-2 age constraints with interpolation using an ice flow model. AICC2012 is the chronology for five cores, including the EDC core, and is characterized by glaciological approaches combining ice flow modelling with various age markers. A precise comparison between the two chronologies was performed. The age differences between them are within 2 kyr, except at Marine Isotope Stage (MIS) 5. DFO2006 gives ages older than AICC2012, with peak values of 4.5 and 3.1 kyr at MIS 5d and MIS 5b, respectively. Accordingly, the ratios of duration (AICC2012/DFO2006) range between 1.4 at MIS 5e and 0.7 at MIS 5a. When making a comparison with accurately dated speleothem records, the age of DFO2006 agrees well at MIS 5d, while the age of AICC2012 agrees well at MIS 5b, supporting their accuracy at these stages. In addition, we found that glaciological approaches tend to give chronologies with younger ages and with longer durations than age markers suggest at MIS 5d-6. Therefore, we hypothesize that the causes of the DFO2006-AICC2012 age differences at MIS 5 are (i) overestimation in surface mass balance at around MIS 5d-6 in the glaciological approach and (ii) an error in one of the O-2/N-2 age constraints by similar to 3 kyr at MIS 5b. Overall, we improved our knowledge of the timing and duration of climatic stages at MIS 5. This new understanding will be incorporated into the production of the next common age scale. Additionally, we found that the deuterium signals of ice, delta D-ice, at DF tends to lead the one at EDC, with the DF lead being more pronounced during cold periods. The lead of DF is by +710 years (maximum) at MIS 5d, -230 years (minimum) at MIS 7a and +60 to +126 years on average.
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Gallee, H., Preunkert, S., Argentini, S., Frey, M. M., Genthon, C., Jourdain, B., et al. (2015). Characterization of the boundary layer at Dome C (East Antarctica) during the OPALE summer campaign. Atmospheric Chemistry And Physics, 15(11), 6225–6236.
Abstract: Regional climate model MAR (Modele Atmospherique Regional) was run for the region of Dome C located on the East Antarctic plateau, during Antarctic summer 2011-2012, in order to refine our understanding of meteorological conditions during the OPALE tropospheric chemistry campaign. A very high vertical resolution is set up in the lower troposphere, with a grid spacing of roughly 2 m. Model output is compared with temperatures and winds observed near the surface and from a 45m high tower as well as sodar and radiation data. MAR is generally in very good agreement with the observations, but sometimes underestimates cloud formation, leading to an underestimation of the simulated downward long-wave radiation. Absorbed short-wave radiation may also be slightly overestimated due to an underestimation of the snow albedo, and this influences the surface energy budget and atmospheric turbulence. Nevertheless, the model provides sufficiently reliable information about surface turbulent fluxes, vertical profiles of vertical diffusion coefficients and boundary layer height when discussing the representativeness of chemical measurements made nearby the ground surface during field campaigns conducted at Concordia station located at Dome C (3233m above sea level).
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Govin, A., Capron, E., Tzedakis, P. C., Verheyden, S., Ghaleb, B., Hillaire-Marcel, C., et al. (2015). Sequence of events from the onset to the demise of the Last Interglacial: Evaluating strengths and limitations of chronologies used in climatic archives. Quaternary Science Reviews, 129, 1–36.
Abstract: The Last Interglacial (LIG) represents an invaluable case study to investigate the response of components of the Earth system to global warming. However, the scarcity of absolute age constraints in most archives leads to extensive use of various stratigraphic alignments to different reference chronologies. This feature sets limitations to the accuracy of the stratigraphic assignment of the climatic sequence of events across the globe during the LIG. Here, we review the strengths and limitations of the methods that are commonly used to date or develop chronologies in various climatic archives for the time span (similar to 140 -100 ka) encompassing the penultimate deglaciation, the LIG and the glacial inception. Climatic hypotheses underlying record alignment strategies and the interpretation of tracers are explicitly described. Quantitative estimates of the associated absolute and relative age uncertainties are provided. Recommendations are subsequently formulated on how best to define absolute and relative chronologies. Future climato-stratigraphic alignments should provide (1) a clear statement of climate hypotheses involved, (2) a detailed understanding of environmental parameters controlling selected tracers and (3) a careful evaluation of the synchronicity of aligned paleoclimatic records. We underscore the need to (1) systematically report quantitative estimates of relative and absolute age uncertainties, (2) assess the coherence of chronologies when comparing different records, and (3) integrate these uncertainties in paleoclimatic interpretations and comparisons with climate simulations. Finally, we provide a sequence of major climatic events with associated age uncertainties for the period 140-105 ka, which should serve as a new benchmark to disentangle mechanisms of the Earth system's response to orbital forcing and evaluate transient climate simulations. (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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Lemieux-Dudon, B., Bazin, L., Landais, A., Kele, H. T. M., Guillevic, M., Kindler, P., et al. (2015). Implementation of counted layers for coherent ice core chronology. Climate Of The Past, 11(6), 959–978.
Abstract: A recent coherent chronology has been built for four Antarctic ice cores and the NorthGRIP (NGRIP) Greenland ice core (Antarctic Ice Core Chronology 2012, AICC2012) using a Bayesian approach for ice core dating (Datice). When building the AICC2012 chronology, and in order to prevent any confusion with official ice core chronology, the AICC2012 chronology for NGRIP was forced to fit exactly the GICC05 chronology based on layer counting. However, such a strong tuning did not satisfy the hypothesis of independence of background parameters and observations for the NGRIP core, as required by Datice. We present here the implementation in Datice of a new type of markers that is better suited for constraints deduced from layer counting: the duration constraints. Estimating the global error on chronology due to such markers is not straightforward and implies some assumption on the correlation between individual counting errors for each interval of duration. We validate this new methodological implementation by conducting twin experiments and a posteriori diagnostics on the NGRIP ice core. Several sensitivity tests on marker sampling and correlation between counting errors were performed to provide some guidelines when using such a method for future dating experiments. Finally, using these markers for NGRIP in a five-core dating exercise with Datice leads to new chronologies that do not differ by more than 410 years from AICC2012 for Antarctic ice cores and 150 years from GICC05 for NGRIP over the last 60 000 years.
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Mamadou, I., Gautier, E., Descroix, L., Noma, I., Moussa, I. B., Maiga, O. F., et al. (2015). Exorheism growth as an explanation of increasing flooding in the Sahel. Catena, 131, 130–139.
Abstract: For two decades, the Niamey area, in Niger, has undergone the creation of several new wadis (“koris” in hausa, the most spoken language in West Africa). The significant runoff increase in the Sahelian reach of Niger river makes us interested in the behavior of the basins of the tributary koris of Niger River in the Niamey area, in Niger. These koris generally formed during a single storm event, within depressions previously occupied by ponds; these ponds are overflown creating a new “kori”. This study examines in detail the causes of this new exorheism mechanism. The main explanation of this evolution has been determined as being the strong runoff increase, related to an extension of crusted soils due to agricultural practices, mostly the reduction of fallow duration. The degradation of their structural stability leads to crusting and a strong reduction of their hydraulic conductivity. This is linked to water and sediment balance at the catchment scale. (C) 2015 Elsevier B.V. All rights reserved.
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Michoud, V., Doussin, J. F., Colomb, A., Afif, C., Borbon, A., Camredon, M., et al. (2015). Strong HONO formation in a suburban site during snowy days. Atmospheric Environment, 116, 155–158.
Abstract: Nitrous acid measurements were carried out during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) winter field campaign at the SIRTA observatory in Paris surroundings from the 20th of January to the 15th of February 2010. At the end of the campaign, significant snow events occurred leading to snow accumulation at the sampling site during the last days. These specific conditions gave the opportunity to examine the HONO budget with and without the presence of snow at ground. Much higher HONO sources were found for the days when the site was covered by snow. This provides evidence for the existence of a large snowpack source of HONO in mid-latitude polluted regions that needs to be investigated for a better understanding of wintertime photochemistry. (C) 2015 Elsevier Ltd. All rights reserved.
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Mikhalenko, V., Sokratov, S., Kutuzov, S., Ginot, P., Legrand, M., Preunkert, S., et al. (2015). Investigation of a deep ice core from the Elbrus western plateau, the Caucasus, Russia. Cryosphere, 9(6), 2253–2270.
Abstract: A 182m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt. Elbrus (43 degrees 20' 53.9 '' N, 42 degrees 25'36.0 '' E; 5115ma.s.l.) in the Caucasus, Russia, in 2009. This is the first ice core in the region that represents a paleoclimate record that is practically undisturbed by seasonal melting. Relatively high snow accumulation rates at the drilling site enabled the analysis of the intraseasonal variability in climate proxies. Borehole temperatures ranged from -17 degrees C at 10m depth to -2.4 degrees C at 182 m. A detailed radio-echo sounding survey showed that the glacier thickness ranged from 45m near the marginal zone of the plateau up to 255m at the glacier center. The ice core has been analyzed for stable isotopes (delta O-18 and delta D), major ions (K+, Na+, Ca2+, Mg2+, NH4+, SO42-, NO3-, Cl-, F-), succinic acid (HOOCCH2COOH), and tritium content. The mean annual net accumulation rate of 1455mmw : e : for the last 140 years was estimated from distinct annual oscillations of delta O-18, delta D, succinic acid, and NH4+. Annual layer counting also helped date the ice core, agreeing with the absolute markers of the tritium 1963 bomb horizon located at the core depth of 50.7mw : e : and the sulfate peak of the Katmai eruption (1912) at 87.7mw : e : According to mathematical modeling results, the ice age at the maximum glacier depth is predicted to be similar to 660 years BP. The 2009 borehole is located downstream from this point, resulting in an estimated basal ice age of less than 350-400 years BP at the drilling site. The glaciological and initial chemical analyses from the Elbrus ice core help reconstruct the atmospheric history of the European region.
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Parrenin, F., Bazin, L., Capron, E., Landais, A., Lemieux-Dudon, B., & Masson-Delmotte, V. (2015). IceChrono1: a probabilistic model to compute a common and optimal chronology for several ice cores. Geoscientific Model Development, 8(5), 1473–1492.
Abstract: Polar ice cores provide exceptional archives of past environmental conditions. The dating of ice cores and the estimation of the age-scale uncertainty are essential to interpret the climate and environmental records that they contain. It is, however, a complex problem which involves different methods. Here, we present IceChrono1, a new probabilistic model integrating various sources of chronological information to produce a common and optimized chronology for several ice cores, as well as its uncertainty. IceChrono1 is based on the inversion of three quantities: the surface accumulation rate, the lock-in depth (LID) of air bubbles and the thinning function. The chronological information integrated into the model are models of the sedimentation process (accumulation of snow, densification of snow into ice and air trapping, ice flow), ice-and air-dated horizons, ice and air depth intervals with known durations, Delta depth observations (depth shift between synchronous events recorded in the ice and in the air) and finally air and ice stratigraphic links in between ice cores. The optimization is formulated as a least squares problem, implying that all densities of probabilities are assumed to be Gaussian. It is numerically solved using the Levenberg-Marquardt algorithm and a numerical evaluation of the model's Jacobian. IceChrono follows an approach similar to that of the Datice model which was recently used to produce the AICC2012 (Antarctic ice core chronology) for four Antarctic ice cores and one Greenland ice core. IceChrono1 provides improvements and simplifications with respect to Datice from the mathematical, numerical and programming point of views. The capabilities of IceChrono1 are demonstrated on a case study similar to the AICC2012 dating experiment. We find results similar to those of Datice, within a few centuries, which is a confirmation of both IceChrono1 and Datice codes. We also test new functionalities with respect to the original version of Datice: observations as ice intervals with known durations, correlated observations, observations as air intervals with known durations and observations as mixed ice-air stratigraphic links. IceChrono1 is freely available under the General Public License v3 open source license.
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Preunkert, S., Legrand, M., Frey, M. M., Kukui, A., Savarino, J., Gallee, H., et al. (2015). Formaldehyde (HCHO) in air, snow, and interstitial air at Concordia (East Antarctic Plateau) in summer. Atmospheric Chemistry And Physics, 15(12), 6689–6705.
Abstract: During the 2011/12 and 2012/13 austral summers, HCHO was investigated for the first time in ambient air, snow, and interstitial air at the Concordia site, located near Dome C on the East Antarctic Plateau, by deploying an Aerolaser AL-4021 analyzer. Snow emission fluxes were estimated from vertical gradients of mixing ratios observed at 1 cm and 1 m above the snow surface as well as in interstitial air a few centimeters below the surface and in air just above the snowpack. Typical flux values range between 1 and 2 x 10(12) molecules m(-2) s(-1) at night and 3 and 5 x 10(12) molecules m(-2) s(-1) at noon. Shading experiments suggest that the photochemical HCHO production in the snowpack at Concordia remains negligible compared to temperature-driven air-snow exchanges. At 1 m above the snow surface, the observed mean mixing ratio of 130 pptv and its diurnal cycle characterized by a slight decrease around noon are quite well reproduced by 1-D simulations that include snow emissions and gas-phase methane oxidation chemistry. Simulations indicate that the gas-phase production from CH4 oxidation largely contributes (66%) to the observed HCHO mixing ratios. In addition, HCHO snow emissions account for 30% at night and 10% at noon to the observed HCHO levels.
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Quiquet, A., Archibald, A. T., Friend, A. D., Chappellaz, J., Levine, J. G., Stone, E. J., et al. (2015). The relative importance of methane sources and sinks over the Last Interglacial period and into the last glaciation. Quaternary Science Reviews, 112, 1–16.
Abstract: All recent climatic projections for the next century suggest that we are heading towards a warmer climate than today (Intergovernmental Panel on Climate Change; Fifth Assessment Report), driven by increasing atmospheric burdens of anthropogenic greenhouse gases. In particular, the volume mixing ratio of methane, the second-most important anthropogenic greenhouse gas, has increased by a factor of similar to 2.5 from the beginning of the European Industrial Revolution. Due to their complex responses to climatic factors, understanding of the dynamics of future global methane emissions and sinks is crucial for the next generation of climate projections. Of relevance to this problem, the Earth likely experienced warmer average temperatures than today during the Last Interglacial (LIG) period (130-115 kaBP). Interestingly, ice cores do not indicate a different methane mixing ratio from the Pre-Industrial Holocene (PIH), in other words the current interglacial period prior to anthropogenic influence. This is surprising as warmer temperatures might be expected to increase methane emissions. The present study aims to improve our understanding of the changes in the global methane budget through quantifying the relative importance of sources and sinks of methane during the last full glacial interglacial cycle. A fairly limited number of studies have investigated this cycle at the millenium time scale with most of them examining the doubling in CH4 from the Last Glacial Maximum (LGM) to the PIH. Though it is still a matter of debate, a general consensus suggests a predominant role to the change in methane emissions from wetlands and only a limited change in the oxidising capacity of the atmosphere. In the present study we provide an estimate of the relative importance of sources and sinks during the LIG period, using a complex climate chemistry model to quantify the sinks, and a methane emissions model included in a global land surface model, for the sources. We are not aware of any previous studies that have explicitly tackled sources and sinks of methane in the previous interglacial. Our results suggest that both emissions and sinks of methane were higher during the LIG period, relative to the PIH, resulting in similar atmospheric concentrations of methane. Our simulated change in methane lifetime is primarily driven by climate (i.e. air temperature and humidity). However, a significant part of the reduced methane lifetime is also attributable to the impact of changes in NO emissions from lightning. An increase in biogenic emissions of non-methane volatile organic compounds during the LIG seems unlikely to have compensated for the impact of temperature and humidity. Surface methane emissions from wetlands were higher in northern latitudes due to an increase of summer temperature, whilst the change in the tropics is less certain. Simulated methane emissions are strongly sensitive to the atmospheric forcing, with most of this sensitivity related to changes in wetland extent. (C) 2015 Elsevier Ltd. All rights reserved.
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Tison, J. L., de Angelis, M., Littot, G., Wolff, E., Fischer, H., Hansson, M., et al. (2015). Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core. Cryosphere, 9(4), 1633–1648.
Abstract: An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (delta D-delta O-18(ice), delta O-18(atm), total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the “basal clean ice facies”. Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate “from within”, and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future “oldest ice” drilling location in Antarctica.
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Wegner, A., Fischer, H., Delmonte, B., Petit, J. R., Erhardt, T., Ruth, U., et al. (2015). The role of seasonality of mineral dust concentration and size on glacial/interglacial dust changes in the EPICA Dronning Maud Land ice core. Journal Of Geophysical Research-Atmospheres, 120(19).
Abstract: We present a record of particulate dust concentration and size distribution in subannual resolution measured on the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land (EDML) ice core drilled in the Atlantic sector of the East Antarctic plateau. The record reaches from present day back to the penultimate glacial until 145,000 years B.P. with subannual resolution from 60,000 years B.P. to the present. Mean dust concentrations are a factor of 46 higher during the glacial (similar to 850-4600 ng/mL) compared to the Holocene (similar to 16-112 ng/mL) with slightly smaller dust particles during the glacial compared to the Holocene and with an absolute minimum in the dust size at 16,000 years B.P. The changes in dust concentration are mainly attributed to changes in source conditions in southern South America. An increase in the modal value of the dust size suggests that at 16,000 years B.P. a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the EDML drill site. We find a clear in-phase relation of the seasonal variation in dust mass concentration and dust size during the glacial (r(conc,size) = 0.8) but no clear phase relationship during the Holocene (0 < r(conc,size)< 0.4). With a simple conceptual 1-D model describing the transport of the dust to the ice sheet using the size as an indicator for transport intensity, we find that the effect of the changes in the seasonality of the source emission strength and the transport intensity on the dust decrease over Transition 1 can significantly contribute to the large decrease of dust concentration from the glacial to the Holocene.
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Weihaupt, J. G., Van Der Hoeven, F. G., Chambers, F. B., Lorius, C., Wyckoff, J. W., & Castendyk, D. (2015). The Wilkes Land Anomaly revisited. Antarctic Science, 27(3), 290–304.
Abstract: The Wilkes Land Gravity Anomaly, first reported in 1959-60, is located in northern Victoria Land in the Pacific Ocean sector of East Antarctica, 1400 km west of the Ross Sea and centred at 70 degrees 00'S-140 degrees 00'E. Initially described on the basis of ground-based seismic and gravity survey, and estimated at the time to have a diameter of 243 km, the original data are now supplemented by data from airborne radiosound survey, airborne gravity survey, airborne magnetic survey and satellite remote sensing. These new data enable us to expand upon the original data, and reveal that the structure has a diameter of some 510 km, is accompanied by ice streams and a chaotically disturbed region of the continental ice sheet, has a subglacial topographical relief of >= 1500 m, and exhibits a negative free air gravity anomaly associated with a larger central positive free air gravity anomaly. The feature has been described as a volcanic structure, an igneous intrusion, an ancient igneous diapir, a subglacial sedimentary basin, a glacially eroded subglacial valley, a tectonic feature and a meteorite impact crater. We re-examine the feature on the basis of these collective data, with emphasis on the free air gravity anomaly signs, magnitudes and patterns, magnetic signature magnitudes and patterns, and the size, shape, dimensions and morphology of the structure. This enhanced view adds substantially to the original description provided at the time of discovery, and suggests several explanations for the origin of the Wilkes Land Anomaly. However, the importance of this feature lies not only in determining its origin but by the fact that this part of the Wilkes Subglacial Basin is one of the most prominent regional negative geoid and associated gravity anomalies of the Antarctic continent.
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