Most recent papers

Abstract: The Porous Structure Of Snow Becomes Denser With Time Under Gravity, Primarily Due To The Creep Of Its Ice Matrix With Viscoplasticity. Despite Investigation Of This Behavior At The Macroscopic Scale, The Driving Microscopic Mechanisms Are Still Not Well Understood. Thanks To High-Performance Computing And Dedicated Solvers, We Modeled Snow Elasto-Viscoplasticity With 3D Images Of Its Microstructure And Different Mechanical Models Of Ice. The Comparison Of Our Numerical Experiments To Oedometric Compression Tests Measured By Tomography Showed That Ice In Snow Rather Behaves As A Heterogeneous Set Of Ice Crystals Than As Homogeneous Polycrystalline Ice. Similarly To Dense Ice, The Basal Slip System Contributed At Most, In The Simulations, To The Total Snow Deformation. However, In The Model, The Deformation Accommodation Between Crystals Was Permitted By The Pore Space And Did Not Require Any Prismatic And Pyramidal Slips, Whereas The Latter Are Pre-Requisite For The Simulation Of Dense Ice. Knowledge Of Snow Settlement Is Essential For Many Applications, Such As Paleoclimatology And Avalanche Forecasting. Snow Densification Is Mainly Driven By Time Dependent And Irreversible Deformations. Simulating This Highly Nonlinear Behavior For Intricate Microstructures Is Time-Consuming, Leading To A Scarcity Of Studies And A Limited Understanding Of The Underlying Microscale Mechanisms. In This Study, We Took Advantage Of An Advanced Numerical Solver To Calculate The Behavior Of 3D Imaged Snow Samples And Compared It With In Situ Experiments. Our Analysis Has Shown That The Crystalline Structure Must Be Taken Into Account, But The Discrepancy Between Experiments And Simulations Suggests The Existence Of Other Mechanisms, Particularly Between Snow Grains. Interestingly, Deformation Mechanisms Other Than Those Required To Simulate Dense Ice Have Been Observed. Ice In Snow Cannot Be Considered As Homogeneous, Individual Crystals Are Shown To Impact Snow Creep The Models Shows That Basal Glide Of A Few Ice Zones Supports Most Of The Snow Deformation In The Simulations, The Contribution Of The Hard Slip Systems Is Negligible, And Deformation Accommodation Is Enabled By The Pore Space

Abstract: Charging Of The Ice-Vapor Interface Is A Well-Studied Topic In Ice Physics And Atmospheric Electrification. However, These Effects Were Not Yet Considered To Examine Chemical Processes In Snow In Polar Regions Because Electric Potentials At Ice Surfaces Have So Far Been Considered Insufficient To Initiate Chemical Reactions And Processes. In This Review, We Analyze Literature Data To Estimate Levels Of Electrification In Snow And Other Frozen Objects That Can Be Caused By Different Processes Occurring At The Earth'S Surface. This Analysis Demonstrates That Threshold Values Of Electric Field Strength Can Be Exceeded For The Appearance Of Corona Discharges And Even For The Formation Of Rayleigh Jets Due To Combined Effects Of Different Meteorological And Physical Processes. The Accumulation Of Electrical Charges Can Lead To Different Chemical Modifications Such As Electroosmotic Phenomena Or The Accumulation Of Impurities From The Atmosphere In Growing Ice Crystals. Moreover, Highly Energetic States That Occur And Dissipate In Microseconds As “Hot Spots” Have The Potential To Initiate Free Radical Processes And Even The Production Of Charged Aerosols. The Review Also Discusses In Detail Selected Field Observations To Point Out How Processes Driven By Electrical Charging May Help To Interpret These Observations, Which Are At Least Partly Inconsistent With Our Present Understanding Of Snow And Ice Chemistry. Finally, Some Approaches Are Presented How These Effects Can Be Studied In Field And Laboratory Experiments. A Further Development Of This New Field At The Intersection Of Ice Physics And Snow Chemistry Seems Very Promising For A Better Understanding Of Relevant Chemical Processes Related To The Cryosphere. Different Processes Can Lead To High Electrical Field Strengths In Snow And Ice In Polar Regions With The Potential To Initiate Free Radical Processes And A Number Of Other Chemical Modifications.

Abstract: Microwave Brightness Temperatures Observed In Antarctica At 89 Ghz From The Advanced Microwave Sounding Unit B (Amsu-B) Point Out An Exceptional Decrease Of 57 K At Dome Fuji ( 77.31(Degrees)S, 39.70(Degrees)E) During The 2019-2020 Summer. The Grain Size Index (Gsi) Based On 89 And 150 Ghz From Amsu-B And Independent Observations At 89 Ghz From The Advanced Microwave Scanning Radiometer 2 (Amsr-2) Also Show Concurrent Unusual Values. To Explain Such Event, A Theoretical Analysis Was Carried Out By Means Of A Radiative Transfer Model. We Explore The Sensitivity Of Brightness Temperature To Surface Snow Properties Focusing On December, Just Before The Decrease, And April, At Its End. Results Confirm That This Variation Is Mainly Related To An Increase In Snow Grain Size. A Decrease In Snow Density Is Also Involved As Suggested By The Increase In Brightness Temperature At 1.4 Ghz From Soil Moisture And Ocean Salinity (Smos) And In The Polarization Ratio At 36 Ghz From Amsr-2. Extreme Values Observed At Multiple Frequencies, As Well As Peculiar Atmospheric Conditions Explored In A Previous Study, Confirm The Uniqueness Of This Event At Least On Decennial Scale.

Abstract: This Study Evaluates The Performance Of Two Planetary Boundary Parameterizations In Simulating The Mean Climate Of West Africa Using The Regional Climate Model Version 5 (Regcm5). These Planetary Boundary Parameterizations Are The Holtslag Scheme And The University Of Washington Scheme. Two Sets Of Three One-Year Simulations Were Carried Out At 25 Km Horizontal Resolution With Three Different Initial Conditions. The First Set Of Simulations Used The Holtslag Scheme (Hereafter Referred To As Hol), While The Second Used The University Of Washington (Uw) Scheme (Hereafter Referred To As Uw). The Results Displayed In This Study Are An Average Of The Three Simulations. During The Jjas Rainy Season, With Respect To Gpcp, Both Models Overestimated Total Rainfall In The Orographic Regions. The Uw Experiment Represented Total Rainfall Fairly Well Compared To Its Counterpart, Hol. Both Models Reproduced Convective Rainfall Well, With A Relatively Weak Dry Bias Over The Guinean Coast Subregion. Globally, Uw Performed Better Than Hol In Simulating Precipitation. The Pattern Of Near-Surface Temperature In Both Models Was Well Reproduced With A Higher Bias With Hol Than With Uw. Indeed, The Uw Scheme Led To A Cooling Effect Owing To The Reduction In Eddy Heat Diffusivity In The Lower Troposphere Contributing To Reduce The Bias. As A Consequence, The Height Of The Planetary Boundary Layer (Pbl) Was Best Simulated Using The Uw Scheme But Was Underestimated Compared To Era5, While Using The Hol Scheme Failed To Capture The Height Of The Pbl. This Is Coherent With The Distribution Of Total Cloud Cover, Which Was Better Simulated With The Uw Scheme Compared To The Hol Scheme. This Study Shows That Use Of Both Planetary Boundary Parameterizations Leads To A Good Simulation Of Most Of The Climatological Characteristics Of The West African Region. Nevertheless, Use Of The Uw Scheme Contributes To A Better Performance Than Use Of The Hol Scheme, And The Differentiation Between The Two Schemes Is Significant Along The Guinea Coast And In Orographic Regions. In These Topographically Complex Regions, Uw Appears To Be More Appropriate Than Hol. This Study Emphasizes The Importance Of Planetary Boundary Parameterizations For Accurately Simulating Climate Variables And For Improving Climate Forecasts And Projections In West Africa.

Abstract: This Study Is Anchored In The H2020 Seamless Project (Https://Www.Seamlessproject.Org, Last Access: 29 January 2024), Which Aims To Develop Ensemble Assimilation Methods To Be Implemented In Copernicus Marine Service Monitoring And Forecasting Systems, In Order To Operationally Estimate A Set Of Targeted Ecosystem Indicators In Various Regions, Including Uncertainty Estimates. In This Paper, A Simplified Approach Is Introduced To Perform A 4D (Space-Time) Ensemble Analysis Describing The Evolution Of The Ocean Ecosystem. An Example Application Is Provided, Which Covers A Limited Time Period In A Limited Subregion Of The North Atlantic (Between 31 And 21 Circle W, Between 44 And 50.5 Circle N, Between 15 March And 15 June 2019, At A 1/4 Circle And A 1 D Resolution). The Ensemble Analysis Is Based On Prior Ensemble Statistics From A Stochastic Nemo (Nucleus For European Modelling Of The Ocean)-Pisces Simulator. Ocean Colour Observations Are Used As Constraints To Condition The 4D Prior Probability Distribution.As Compared To Classic Data Assimilation, The Simplification Comes From The Decoupling Between The Forward Simulation Using The Complex Modelling System And The Update Of The 4D Ensemble To Account For The Observation Constraint. The Shortcomings And Possible Advantages Of This Approach For Biogeochemical Applications Are Discussed In The Paper. The Results Show That It Is Possible To Produce A Multivariate Ensemble Analysis Continuous In Time And Consistent With The Observations. Furthermore, We Study How The Method Can Be Used To Extrapolate Analyses Calculated From Past Observations Into The Future. The Resulting 4D Ensemble Statistical Forecast Is Shown To Contain Valuable Information About The Evolution Of The Ecosystem For A Few Days After The Last Observation. However, As A Result Of The Short Decorrelation Timescale In The Prior Ensemble, The Spread Of The Ensemble Forecast Increases Quickly With Time. Throughout The Paper, A Special Emphasis Is Given To Discussing The Statistical Reliability Of The Solution.Two Different Methods Have Been Applied To Perform This 4D Statistical Analysis And Forecast: The Analysis Step Of The Ensemble Transform Kalman Filter (With Domain Localization) And A Monte Carlo Markov Chain (Mcmc) Sampler (With Covariance Localization), Both Enhanced By The Application Of Anamorphosis To The Original Variables. Despite Being Very Different, The Two Algorithms Produce Very Similar Results, Thus Providing Support To Each Other'S Estimates. As Shown In The Paper, The Decoupling Of The Statistical Analysis From The Dynamical Model Allows Us To Restrict The Analysis To A Few Selected Variables And, At The Same Time, To Produce Estimates Of Additional Ecological Indicators (In Our Example: Phenology, Trophic Efficiency, Downward Flux Of Particulate Organic Matter). This Approach Can Easily Be Appended To Existing Operational Systems To Focus On Dedicated Users' Requirements, At A Small Additional Cost, As Long As A Reliable Prior Ensemble Simulation Is Available. It Can Also Serve As A Baseline To Compare With The Dynamical Ensemble Forecast And As A Possible Substitute Whenever Useful.

Abstract: The Chemical Composition Of Pm 10 And Non-Overlapping Pm 2.5 Was Studied At The Summit Of Mt. Chacaltaya (5380 M A.S.L., Lat. – 16.346950 Degrees, Long. – 68.128250 Degrees) Providing A Unique Long-Term Record Spanning From December 2011 To March 2020. The Chemical Composition Of Aerosol At The Chacaltaya Global Atmosphere Watch (Gaw) Site Is Representative Of The Regional Background, Seasonally Affected By Biomass Burning Practices And By Nearby Anthropogenic Emissions From The Metropolitan Area Of La Paz-El Alto. Concentration Levels Are Clearly Influenced By Seasons With Minima Occurring During The Wet Season (December To March) And Maxima Occurring During The Dry And Transition Seasons (April To November). Ions, Total Carbon (Ec + Oc), And Saccharide Interquartile Ranges For Concentrations Are 558-1785, 384-1120, And 4.3-25.5 Ng M – 3 For Bulk Pm 10 And 917-2308, 519-1175, And 3.9-24.1 Ng M – 3 For Pm 2.5 , Respectively, With Most Of The Aerosol Seemingly Present In The Pm 2.5 Fraction. Such Concentrations Are Overall Lower Compared To Other High-Altitude Stations Around The Globe But Higher Than Amazonian Remote Sites (Except For Oc). For Pm 10 , There Is Dominance Of Insoluble Mineral Matter (33 %-56 % Of The Mass), Organic Matter (7 %-34 %), And Secondary Inorganic Aerosol (15 %-26 %). Chemical Composition Profiles Were Identified For Different Origins: Ec, No 3 – , Nh 4 + , Glucose, And C 2 O 4 2 – For The Nearby Urban And Rural Areas; Oc, Ec, No 3 – , K + , Acetate, Formate, Levoglucosan, And Some F – And Br – For Biomass Burning; Meso 3 – , Na + , Mg 2 + , K + , And Ca 2 + For Aged Marine Emissions From The Pacific Ocean; Arabitol, Mannitol, And Glucose For Biogenic Emissions; Na + , Ca 2 + , Mg 2 + , And K + For Soil Dust; And So 4 2 – , F – , And Some Cl – For Volcanism. Regional Biomass Burning Practices Influence The Soluble Fraction Of The Aerosol Between June And November. The Organic Fraction Is Present All Year Round And Has Both Anthropogenic (Biomass Burning And Other Combustion Sources) And Natural (Primary And Secondary Biogenic Emissions) Origins, With The Oc / Ec Mass Ratio Being Practically Constant All Year Round (10.5 +/- 5.7, Iqr 8.1-13.3). Peruvian Volcanism Has Dominated The So 4 2 – Concentration Since 2014, Though It Presents Strong Temporal Variability Due To The Intermittence Of The Sources And Seasonal Changes In The Transport Patterns. These Measurements Represent Some Of The First Long-Term Observations Of Aerosol Chemical Composition At A Continental High-Altitude Site In The Tropical Southern Hemisphere.

Abstract: Humans Are Exposed To Toxic Methylmercury Mainly By Consuming Marine Fish. While Reducing Mercury Emissions And Releases Aims To Protect Human Health, It Is Unclear How This Affects Methylmercury Concentrations In Seawater And Marine Biota. We Compiled Existing And Newly Acquired Mercury Concentrations In Tropical Tunas From The Global Ocean To Explore Multidecadal Mercury Variability Between 1971 And 2022. We Show The Strong Inter-Annual Variability Of Tuna Mercury Concentrations At The Global Scale, After Correcting For Bioaccumulation Effects. We Found Increasing Mercury Concentrations In Skipjack In The Late 1990S In The Northwestern Pacific, Likely Resulting From Concomitant Increasing Asian Mercury Emissions. Elsewhere, Stable Long-Term Trends Of Tuna Mercury Concentrations Contrast With An Overall Decline In Global Anthropogenic Mercury Emissions And Deposition Since The 1970S. Modeling Suggests That This Limited Response Observed In Tunas Likely Reflects The Inertia Of Surface Ocean Mercury With Respect To Declining Emissions, As It Is Supplied By Legacy Mercury That Accumulated In The Subsurface Ocean Over Centuries. To Achieve Measurable Declines In Mercury Concentrations In Highly Consumed Pelagic Fish In The Near Future, Aggressive Emission Reductions And Long-Term And Continuous Mercury Monitoring In Marine Biota Are Needed.

Abstract: The Bio-Maido (Bio-Physicochemistry Of Tropical Clouds At Maido: Processes And Impacts On Secondary Organic Aerosols Formation) Campaign Was Conducted From 13 March To 4 April 2019 On The Tropical Island Of Reunion. The Main Objective Of The Project Was To Improve Understanding Of Cloud Impacts On The Formation Of Secondary Organic Aerosols (Soa) From Biogenic Volatile Organic Compound (Bvoc) Precursors In A Tropical Environment. Instruments Were Deployed At Five Sites: A Receptor Site, Maido Observatory (Mo) At 2165 M A.S.L. And Four Sites Along The Slope Of The Maido Mountain. Observations Include Measurements Of Volatile Organic Compounds (Vocs) And Characterization Of The Physical, Chemical And Biological (Bacterial Diversity And Culture-Based Approaches) Properties Of Aerosols And Cloud Water. Turbulent Parameters Of The Boundary Layer, Radiative Fluxes And Emissions Fluxes Of Bvocs From The Surrounding Vegetation Were Measured To Help Interpret Observed Chemical Concentrations In The Different Phases. Dynamical Analyses Showed Two Preferred Trajectory Routes For Air Masses Arriving At Mo During The Daytime. Both Trajectories Correspond To Return Branches Of The Trade Winds Associated With Upslope Thermal Breezes, Where Air Masses Likely Encountered Cloud Processing. The Highest Mixing Ratios Of Oxygenated Vocs (Ovocs) Were Measured Above The Site Located In The Endemic Forest And The Highest Contribution Of Ovocs To Total Vocs At Mo. Chemical Compositions Of Particles During Daytime Showed Higher Concentrations Of Oxalic Acid, A Tracer Of Cloud Processing And Photochemical Aging, And A More Oxidized Organic Aerosol At Mo Than At Other Sites. Approximately 20 % Of The Dissolved Organic Compounds Were Analyzed. Additional Analyses By Ultra-High-Resolution Mass Spectrometry Will Explore The Complexity Of The Missing Cloud Organic Matter.

Abstract: For Over 25 Years, Satellite Altimetry Has Provided Invaluable Information About The Ocean Dynamics At Many Scales. In Particular, Gridded Sea Surface Height (Ssh) Maps Allow Us To Estimate The Mesoscale Geostrophic Circulation In The Ocean. However, Conventional Interpolation Techniques Rely On Static Optimal Interpolation Schemes, Hence Limiting The Estimation Of Non-Linear Dynamics At Scales Not Well Sampled By Altimetry (I.E., Below 150-200Km At Mid-Latitudes). To Overcome This Limitation In The Resolution Of Small-Scale Ssh Structures (And Thus Small-Scale Geostrophic Currents), A Back-And-Forth Nudging Algorithm Combined With A Quasi-Geostrophic Model, A Technique Called Bfn-Qg, Has Been Successfully Applied On Simulated Ssh Data In Observing System Simulation Experiments (Osses). The Result Is A Significant Reduction In Interpolation Error And An Improvement In The Space-Time Resolutions Of The Experimental Gridded Product Compared To Those Of Operational Products. In This Study, We Propose That The Bfn-Qg Be Applied To Real Altimetric Ssh Data In A Highly Turbulent Region Spanning A Part Of The Agulhas Current. The Performances Are Evaluated Within Observing System Experiments (Oses) That Use Independent Data (Such As Independent Ssh, Sea Surface Temperature And Drifter Data) As Ground Truth. By Comparing The Mapping Performances To The Ones Obtained With Operational Products, We Show That The Bfn-Qg Improves The Mapping Of Short, Energetic Mesoscale Structures And Associated Geostrophic Currents Both In Space And Time. In Particular, The Bfn-Qg Improves (I) The Spatial Effective Resolution Of The Ssh Maps By A Factor Of 20%, (Ii) The Zonal And (Especially) The Meridional Geostrophic Currents, And (Iii) The Prediction Of Lagrangian Transport For Lead Times Up To 10D. Unlike The Results Obtained In The Osses, The Oses Reveal More Contrasting Performances In Low-Variability Regions, Which Are Discussed In The Paper.

Abstract: The Future Of Tidewater Glaciers In Response To Climate Warming Is One Of The Largest Sources Of Uncertainty In The Contribution Of The Greenland Ice Sheet To Global Sea-Level Rise. In This Study, We Investigate The Ability Of An Ice-Sheet Model To Reproduce The Past Evolution Of The Velocity And Surface Elevation Of A Tidewater Glacier, Upernavik Isstrom, By Prescribing Front Positions. To Achieve This, We Run Two Ensembles Of Simulations With A Weertman And A Regularised-Coulomb Friction Law. We Show That The Ice-Flow Model Has To Include A Reduction In Friction In The First 15 Km Upstream Of The Ice Front In Fast-Flowing Regions To Capture The Trends Observed During The 1985-2019 Period. Without This Process, The Ensemble Model Overestimates The Ice Flow Before The Retreat Of The Front In 2005 And Does Not Fully Reproduce Its Acceleration During The Retreat. This Results In An Overestimation Of The Total Mass Loss Between 1985 And 2019 Of 50% (300 Vs 200 Gt). Using A Variance-Based Sensitivity Analysis, We Show That Uncertainties In The Friction Law And The Ice-Flow Law Have A Greater Impact On The Model Results Than Surface Mass Balance And Initial Surface Elevation.

Abstract: Improving Our Understanding Of The Controls On Antarctic Precipitation Is Critical For Gaining Insights Into Past And Future Polar And Global Environmental Changes. Here We Develop Innovative Water Tracing Diagnostics In The Atmospheric General Circulation Model Echam6. These Tracers Provide New Detailed Information On Moisture Source Locations And Properties Of Antarctic Precipitation. In The Preindustrial Simulation, Annual Mean Antarctic Precipitation Originating From The Open Ocean Has A Source Latitude Range Of 49-35 Circle S, A Source Sea Surface Temperature Range Of 9.8-16.3 Circle C, A Source 2 M Relative Humidity Range Of 75.6 %-83.3 %, And A Source 10 M Wind Velocity (Vel10) Range Of 10.1 To 11.3 Ms-1. These Results Are Consistent With Estimates From Existing Literature. Central Antarctic Precipitation Is Sourced From More Equatorward (Distant) Sources Via Elevated Transport Pathways Compared To Coastal Antarctic Precipitation. This Has Been Attributed To A Moist Isentropic Framework; I.E. Poleward Vapour Transport Tends To Follow Constant Equivalent Potential Temperature. However, We Find Notable Deviations From This Tendency Especially In The Lower Troposphere, Likely Due To Radiative Cooling. Heavy Precipitation Is Sourced By Longer-Range Moisture Transport: It Comes From 2.9 Circle (300 Km, Averaged Over Antarctica) More Equatorward (Distant) Sources Compared To The Rest Of Precipitation. Precipitation During Negative Phases Of The Southern Annular Mode (Sam) Also Comes From More Equatorward Moisture Sources (By 2.4 Circle, Averaged Over Antarctica) Compared To Precipitation During Positive Sam Phases, Likely Due To Amplified Planetary Waves During Negative Sam Phases. Moreover, Source Vel10 Of Annual Mean Precipitation Is On Average 2.1 Ms-1 Higher Than Annual Mean Vel10 At Moisture Source Locations From Which The Precipitation Originates. This Shows That The Evaporation Of Moisture Driving Antarctic Precipitation Occurs Under Windier Conditions Than Average. We Quantified This Dynamic Control Of Southern Ocean Surface Wind On Moisture Availability For Antarctic Precipitation. Overall, The Innovative Water Tracing Diagnostics Enhance Our Understanding Of The Controlling Factors Of Antarctic Precipitation.

Abstract: High Elevation Headwater Catchments Are Complex Hydrological Systems That Seasonally Buffer Water And Release It In The Form Of Snow And Ice Melt, Modulating Downstream Runoff Regimes And Water Availability. In High Mountain Asia (Hma), Where A Wide Range Of Climates From Semi-Arid To Monsoonal Exist, The Importance Of The Cryospheric Contributions To The Water Budget Varies With The Amount And Seasonal Distribution Of Precipitation. Losses Due To Evapotranspiration And Sublimation Are To Date Largely Unquantified Components Of The Water Budget In Such Catchments, Although They Can Be Comparable In Magnitude To Glacier Melt Contributions To Streamflow. Here, We Simulate The Hydrology Of Three High Elevation Headwater Catchments In Distinct Climates In Hma Over 10 Years Using An Ecohydrological Model Geared Towards High-Mountain Areas Including Snow And Glaciers, Forced With Reanalysis Data. Our Results Show That Evapotranspiration And Sublimation Together Are Most Important At The Semi-Arid Site, Kyzylsu, On The Northernmost Slopes Of The Pamir Mountain Range. Here, The Evaporative Loss Amounts To 28% Of The Water Throughput, Which We Define As The Total Water Added To, Or Removed From The Water Balance Within A Year. In Comparison, Evaporative Losses Are 19% At The Central Himalayan Site Langtang And 13% At The Wettest Site, 24 K, On The Southeastern Tibetan Plateau. At The Three Sites, Respectively, Sublimation Removes 15%, 13% And 6% Of Snowfall, While Evapotranspiration Removes The Equivalent Of 76%, 28% And 19% Of Rainfall. In Absolute Terms, And Across A Comparable Elevation Range, The Highest Et Flux Is 413 Mm Yr-1 At 24 K, While The Highest Sublimation Flux Is 91 Mm Yr-1 At Kyzylsu. During Warm And Dry Years, Glacier Melt Was Found To Only Partially Compensate For The Annual Supply Deficit.

Abstract: The Greenland Ice Sheet Is A Key Contributor To Sea Level Rise. By Melting, The Ice Sheet Thins, Inducing Higher Surface Melt Due To Lower Surface Elevations, Accelerating The Melt Coming From Global Warming. This Process Is Called The Melt-Elevation Feedback And Can Be Considered By Using Two Types Of Models: Either (1) Atmospheric Models, Which Can Represent The Surface Mass Balance (Smb), Or Smb Estimates Resulting From Simpler Models Such As Positive Degree Day Models Or (2) Ice Sheet Models Representing The Surface Elevation Evolution. The Latter Ones Do Not Represent The Surface Mass Balance Explicitly As Well As Polar-Oriented Climate Models. A New Coupling Between The Mar (Modele Atmospherique Regional) Regional Climate Model And The Pism (Parallel Ice Sheet Model) Ice Sheet Model Is Presented Here Following The Cesm2 (Community Earth System Model; Ssp5-8.5, Shared Socioeconomic Pathway) Scenario Until 2100 At The Mar Lateral Boundaries. The Coupling Is Extended To 2200 With A Stabilised Climate (+7 Circle C Compared To 1961-1990) By Randomly Sampling The Last 10 Years Of Cesm2 To Force Mar And Reaches A Sea Level Rise Contribution Of 64 Cm. The Fully Coupled Simulation Is Compared To A One-Way Experiment Where Surface Topography Remains Fixed In Mar. However, The Surface Mass Balance Is Corrected For The Melt-Elevation Feedback When Interpolated On The Pism Grid By Using Surface Mass Balance Vertical Gradients As A Function Of Local Elevation Variations (Offline Correction). This Method Is Often Used To Represent The Melt-Elevation Feedback And Prevents A Coupling Which Is Too Expensive In Computation Time. In The Fully Coupled Mar Simulation, The Ice Sheet Morphology Evolution (Changing Slope And Reducing The Orographic Barrier) Induces Changes In Local Atmospheric Patterns. More Specifically, Wind Regimes Are Modified, As Well As Temperature Lapse Rates, Influencing The Melt Rate Through Modification Of Sensible Heat Fluxes At The Ice Sheet Margins. We Highlight Mitigation Of The Melt Lapse Rate On The Margins By Modifying The Surface Morphology. The Lapse Rates Considered By The Offline Correction Are No Longer Valid At The Ice Sheet Margins. If Used (One-Way Simulation), This Correction Implies An Overestimation Of The Sea Level Rise Contribution Of 2.5 %. The Mitigation Of The Melt Lapse Rate On The Margins Can Only Be Corrected By Using A Full Coupling Between An Ice Sheet Model And An Atmospheric Model.

Abstract: We Use An Observationally Calibrated Ice-Sheet Model To Investigate The Future Trajectory Of The Antarctic Ice Sheet Related To Uncertainties In The Future Balance Between Sub-Shelf Melting And Ice Discharge, On The One Hand, And The Surface Mass Balance, On The Other. Our Ensemble Of Simulations, Forced By A Panel Of Climate Models From The Sixth Phase Of The Coupled Model Intercomparison Project (Cmip6), Suggests That The Ocean Will Be The Primary Driver Of Short-Term Antarctic Mass Loss, Initiating Ice Loss In West Antarctica Already During This Century. The Atmosphere Initially Plays A Mitigating Role Through Increased Snowfall, Leading To An Antarctic Contribution To Global Mean Sea-Level Rise By 2100 Of 6 (-8 To 15) Cm Under A Low-Emission Scenario And 5.5 (-10 To 16) Cm Under A Very High-Emission Scenario. However, Under The Very High-Emission Pathway, The Influence Of The Atmosphere Shifts Beyond The End Of The Century, Becoming An Amplifying Driver Of Mass Loss As The Ice Sheet'S Surface Mass Balance Decreases. We Show That This Transition Occurs When Antarctic Near-Surface Warming Exceeds A Critical Threshold Of +7.5 Circle C, At Which The Increase In Surface Runoff Outweighs The Increase In Snow Accumulation, A Signal That Is Amplified By The Melt-Elevation Feedback. Therefore, Under The Very High-Emission Scenario, Oceanic And Atmospheric Drivers Are Projected To Result In A Complete Collapse Of The West Antarctic Ice Sheet Along With Significant Grounding-Line Retreat In The Marine Basins Of The East Antarctic Ice Sheet, Leading To A Median Global Mean Sea-Level Rise Of 2.75 (6.95) M By 2300 (3000). Under A More Sustainable Socio-Economic Pathway, We Find That The Antarctic Ice Sheet May Still Contribute To A Median Global Mean Sea-Level Rise Of 0.62 (1.85) M By 2300 (3000). However, The Rate Of Sea-Level Rise Is Significantly Reduced As Mass Loss Is Likely To Remain Confined To The Amundsen Sea Embayment, Where Present-Day Climate Conditions Seem Sufficient To Commit To A Continuous Retreat Of Thwaites Glacier.

Abstract: Previous Paleo-Glacial Studies On Kerguelen Showed A Singular Pattern Of Holocene Glacier Evolution On This Archipelago In Comparison With Other Southern Mid-Latitude Glacier Records. In This Study, We Aim To Test This Singularity On A Longer Timescale, Based On 26 New In Situ-Produced 36Cl Ages From Pre-Holocene Glaciogeomorphic Features. Samples From Moraine Boulders And Glacially Polished Bedrock Were Extracted At Six Different Sites, Located Near The Port-Aux-Francais Scientific Station (Paf Site), On Longue Island, Australia Island, On The Port-Jeanne D'Arc Peninsula (Pjda Site), On The Gallieni Peninsula At Baie Larose (Blr Site) And The Mcmurdo Island. The Moraine Ages Indicate That Glacier Culminations Occurred During Marine Isotopic Stage 3 (Mis 3) At 42.2 +/- 4.9 Ka On The Paf Site, And During The Global Last Glacial Maximum (Glgm) At 21.5 +/- 3.2 Ka On The Pjda Site And At 21.4 +/- 3.7 Ka And 19.4 +/- 2.6 On Baie Larose Site. This Is The First Time That Late Pleistocene Glacier Culminations Are Evidenced On Kerguelen By Direct Moraine Dating, Thus Allowing Comparison With Other Moraine Records From The Southern Mid-Latitudes. While It Remains Speculative Whether Or Not The Mis 3 Glacial Maximum At -42.2 Ka Is In Phase With Other Glaciers At This Latitude (Due To High Age Uncertainties), The Glgm Glacial Maximum Is Synchronous With That In Other Southern Mid-Latitude Regions. 36Cl Cre Ages Of Glacially Polished Bedrock Surfaces Sampled In Different Locations Of The Archipelago Vary From -39 Ka To -19 Ka. We Interpret These Results As Reflecting Periods Of Deglaciation That Occurred In Between The Two Glacier Culminations And Right After The Glgm On Kerguelen. These Ages Also Suggest That Some Places Of The Archipelago Were Free Of Ice At Least Since – 39 Ka. The Presence Of A Mis 3 Moraine At Paf Site That Has Not Been Obliterated By A Glgm Advance Suggests That The – 42.2 Ka Glacier Extent Was At Least As Large As Glgm Glacial Maxima On The Archipelago. The Glacier Culmination During Mis 3 Being Larger Than That During The Glgm On The Kerguelen Archipelago Matches Observations In Other Southern Mid-Latitude Regions. Late Pleistocene Glacier Culminations On Kerguelen May Have Been In Phase With Cold Temperatures Recorded In Sst Records, Which Suggest A Cooling Around Kerguelen. However, Climate Drivers Responsible For The Larger Mis 3 Glacier Culmination On Kerguelen Still Remain Unclear Even If We Hypothesize That Changes In Precipitation May Have Superimposed On Temperature Changes.