2024 |
Cantera, I., Carteron, A., Guerrieri, A., Marta, S., Bonin, A., Ambrosini, R., et al. (2024). The Importance Of Species Addition 'Versus' Replacement Varies Over Succession In Plant Communities After Glacier Retreat. Nature Plants, .
Abstract: The Mechanisms Underlying Plant Succession Remain Highly Debated. Due To The Local Scope Of Most Studies, We Lack A Global Quantification Of The Relative Importance Of Species Addition 'Versus' Replacement. We Assessed The Role Of These Processes In The Variation (Beta-Diversity) Of Plant Communities Colonizing The Forelands Of 46 Retreating Glaciers Worldwide, Using Both Environmental Dna And Traditional Surveys. Our Findings Indicate That Addition And Replacement Concur In Determining Community Changes In Deglaciated Sites, But Their Relative Importance Varied Over Time. Taxa Addition Dominated Immediately After Glacier Retreat, As Expected In Harsh Environments, While Replacement Became More Important For Late-Successional Communities. These Changes Were Aligned With Total Beta-Diversity Changes, Which Were More Pronounced Between Early-Successional Communities Than Between Late-Successional Communities (>50 Yr Since Glacier Retreat). Despite The Complexity Of Community Assembly During Plant Succession, The Observed Global Pattern Suggests A Generalized Shift From The Dominance Of Facilitation And/Or Stochastic Processes In Early-Successional Communities To A Predominance Of Competition Later On.
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Guillemot, A., Bontemps, N., Larose, E., Teodor, D., Faller, S., Baillet, L., et al. (2024). Investigating Subglacial Water-Filled Cavities By Spectral Analysis Of Ambient Seismic Noise: Results On The Polythermal Tête-Rousse Glacier (Mont Blanc, France). Geophysical Research Letters, 515(4).
Abstract: Polythermal Glaciers Can Trap Considerable Volumes Of Liquid Water With The Potential To Generate Devastating Outburst Floods. This Study Aims To Identify Water-Filled Subglacial Reservoirs From Ambient Seismic Noise Collected By Moderate-Cost Surveys. The Horizontal-To-Vertical Spectral Ratio Technique Is Highly Sensitive To Impedance Contrasts At Interfaces, Thus Commonly Used To Estimate Glacier Thickness. Here, We Focus On The Inverse Ratio, That Is, The V/H Spectral Ratio (Vhsr), Whose High Values Indicate A Low Impedance Volume Beneath The Surface, Suggesting Subglacial Cavities. We Analyze Vhsr Peaks From A Seismic Array Of 60 Nodes Installed On The Tete-Rousse Glacier (Mont Blanc Massif, French Alps); Data Were Gathered Over 15 Days. Mapping The Vhsr Amplitude Over The Free Surface Reveals The Main Cavity Locations And The Basal Areas Affected By Melting Within The Glacier. Results Obtained In The Field Are Supported By A Conceptual Model Based On 3D Finite-Element Simulations. Considerable Volumes Of Liquid Water May Be Trapped Within Cavities In Polythermal Glaciers. If These Cavities Rupture, The Resulting Outburst Flood Has The Potential To Cause Devastation In Populated Mountain Areas. With The Aim Of Testing Methods To Locate Such Cavities, We Installed 60 Small 3-Component Seismic Sensors On The Tete-Rousse Glacier (Mont Blanc Massif, French Alps), Which Is Known To Contain Such Cavities. We Used These Sensors To Test A Detection Method Based On Ambient Seismic Noise. For 3 Weeks, The Sensors Recorded Vibrations Within The Glacier. On A Glacier Without Cavities, These Vibrations Ought To Be Predominantly In The Horizontal Direction. In The Presence Of A Cavity, We Expect The Ice Above The Cavity To Vibrate Mostly Vertically-Like A Bridge. In This Paper, We Highlight Areas On The Glacier Where Vertical Vibrations Were Stronger Than Horizontal Vibrations. These Areas Fit Well With The Locations Of The Main Known Cavities In This Glacier, And With Areas Affected By Basal Melting. We Supported Our Field Observations With Modeling Based On 3D Simulations, Paving The Way To A New Method To Locate Water-Filled Cavities Within Glaciers. Spectral Analysis From Ambient Seismic Noise Is Complementary To Other Geophysical Methods For Investigating Glaciers At Depth Results Suggest That The Vertical-To-Horizontal Spectral Ratio Is A Reliable Proxy To Locate Subglacial Cavities Experimental Results Were Confirmed Using A Simplified Numerical Model
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Lapere, R., Thomas, J., Favier, V., Angot, H., Asplund, J., Ekman, A., et al. (2024). Polar Aerosol Atmospheric Rivers: Detection, Characteristics, And Potential Applications. Journal Of Geophysical Research-Atmospheres, 1291(2).
Abstract: Aerosols Play A Key Role In Polar Climate, And Are Affected By Long-Range Transport From The Mid-Latitudes, Both In The Arctic And Antarctic. This Work Investigates Poleward Extreme Transport Events Of Aerosols, Referred To As Polar Aerosol Atmospheric Rivers (P-Aar), Leveraging The Concept Of Atmospheric Rivers (Ar) Which Signal Extreme Transport Of Moisture. Using Reanalysis Data, We Build A Detection Catalog Of P-Aars For Black Carbon, Dust, Sea Salt And Organic Carbon Aerosols, For The Period 1980-2022. First, We Describe The Detection Algorithm, Discuss Its Sensitivity, And Evaluate Its Validity. Then, We Present Several Extreme Transport Case Studies, In The Arctic And In The Antarctic, Illustrating The Complementarity Between Ars And P-Aars. Despite Similarities In Transport Pathways During Co-Occurring Ar/P-Aar Events, Vertical Profiles Differ Depending On The Species, And Large-Scale Transport Patterns Show That Moisture And Aerosols Do Not Necessarily Originate From The Same Areas. The Complementarity Between Ar And P-Aar Is Also Evidenced By Their Long-Term Characteristics In Terms Of Spatial Distribution, Seasonality And Trends. P-Aar Detection, As A Complement To Ar, Can Have Several Important Applications For Better Understanding Polar Climate And Its Connections To The Mid-Latitudes. The Extreme Transport Of Aerosol-Containing Air Masses, From The Mid-Latitudes To The Polar Regions, Can Be Characterized And Quantified By Leveraging Polar Aerosol Atmospheric Rivers (P-Aars). This Is Similar To The Atmospheric Rivers (Ars) Which Carry Large Amounts Of Water To The Poles And Affect The Overall Stability Of Polar Ecosystems. In This Work, We Establish A Detection Algorithm For P-Aars And Evaluate It For Different Well-Known Aerosol Intrusions Or Ar Events. The Areas Most Affected By P-Aars Are Described, Their Trends Are Investigated And We Discuss The Potential Applications Of P-Aar Detection For A Better Understanding Of Polar Climate. A Catalog Of Polar Aerosol Atmospheric Rivers (P-Aar) Is Provided For 1980-2022 By Adapting An Atmospheric River (Ar) Detection Schemeimportant P-Aar Events, Representing Rapid Poleward Transport Of Aerosol-Enriched Air Masses, Are Presentedcombining Ar And P-Aar Can Improve Our Understanding Of The Links Between Mid- And Polar-Latitudes, In The Past, Present And Future Climate
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Uroz, L., Yan, Y., Benoit, A., Rabatel, A., Giffard-Roisin, S., & Lin-Kwong-Chon, C. (2024). Using Deep Learning For Glacier Thickness Estimation At A Regional Scale. Ieee Geoscience And Remote Sensing Letters, 212.
Abstract: Mountain Glaciers Play A Critical Role For Mountain Ecosystems And Society With Major Concerns Related To Their Future Evolution And Related Water Resources. Modeling Glacier Future Evolution Allows Anticipating Climate Change Impacts And Informing Policy Decisions. It Relies On Accurate Ice Thickness Estimation At Regional Scales. This Letter Proposes A Deep Learning-Based Approach In A Supervised Learning Framework For Ice Thickness Estimation At A Regional Scale From Surface Ice Velocity Measurements And A Digital Elevation Model (Dem). A Neural Network Model Built Upon A Resnet Architecture Is Proposed Based On The Trade-Off Between The Model Complexity And The Prediction Efficiency. Promising Results Are Obtained From Data Including 1400 Glaciers In The Swiss Alps, Highlighting The Potential Of Deep Learning-Based Approach For Large-Scale Ice Thickness Estimation. The Incorporation Of Expert'S Knowledge Into The Neural Network Model Further Helps Refine The Model Prediction And Improve The Model Relevance. The Ice Volume Difference Between The Reference Issued From Ground Penetrating Radar (Gpr) Measurements And The Predictions By The Proposed Neural Network Model Varies Between 0.5% And 16% Of The Reference Volume. Larger Ice Volume Difference Is Mainly Related To Over-Deepening Of The Bedrock Resulting From Past Larger Extent Of The Glacier, Which Information Is Not Included In The Data.
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Zimmer, A., Beach, T., Luzzadder-Beach, S., Rabatel, A., Encarnación, R., Robles, J., et al. (2024). Soil Temperature And Local Initial Conditions Drive Carbon And Nitrogen Build-Up In Young Proglacial Soils In The Tropical Andes And European Alps. Catena, 2352.
Abstract: Climate Warming Has Accelerated The Retreat Of Mountain Glaciers Worldwide, Exposing New Areas To Weathering, Vegetation Colonization, And Soil Formation. In Light Of Probable Climate Changes Such As Warming And New Extremes, Understanding The Factors That Control Soil Organic Carbon (Soc) And Nitrogen Build-Up Is Crucial To Comprehend Proglacial Soils And Ecosystem Formation. To This End, We Examine The Evolution Of Soc, Nitrogen (Total N And Nh4+), And Phosphorus (Available P) Along Nine 120-Year Chronosequences Of Deglacierization Distributed Between The European Alps And Tropical Andes. Our Dataset Includes Geochemical Analyses Of 188 Soil Samples, In Situ Soil Temperature Data For The Period 2019-2022, And Hydrographic Variables. Although Time Controls Proglacial Soil Development At All Sites, Our Study Highlights Distinct Pedogenesis Dynamics Between Proglacial Landscapes Depending On The Micro And Macro Environmental Context. Differences In Soil Development Were Strongly Driven By Growing Degree Days (Gdd), Maximum Soil Temperature, And Parent Material. Notably, We Identified A Positive Effect Of Gdd On Soc And N (Total N And Nh4+), While Our Results Indicate A Negative Effect Of Maximum Soil Temperature On Soc And Nh4+, Suggesting That Overly High Temperatures Reduce Microbial Mineralization And Organic Matter Input To The Soil Matrix. We Reported The Presence Of Higher Initial Soc, Total N, And Nh4+ In The Andean Sites Than In The Alps Sites, Suggesting Enhanced Soil Development At The Andean Locations. This Comparative Study Suggests The Relative Importance Of Maximum Temperature And Initial Site Conditions (E.G., Parent Materials, Glacier Biomes) During Proglacial Pedogenesis. Our Findings Highlight That Soil Temperature Modulates Pedogenesis In A Complex Way And Suggest Avoiding Simply Associating Greater Soil Development With Higher Soil Temperature In Proglacial Landscapes.
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Zimmer, A., Beach, T., Luzzadder-Beach, S., Rabatel, A., Robles, J., Encarnaci, R., et al. (2024). Physico-Chemical Properties And Toxicity Of Young Proglacial Soils In The Tropical Andes And Alps. Catena, 2372.
Abstract: New Soils Formed After Glacier Retreat Can Provide Insights Into The Rates Of Soil Formation In The Context Of Accelerated Warming Due To Climate Change. Recently Deglacierized Terrains (Since The Little Ice Age) Are Subject To Weathering And Pedogenesis, And Freshly Exposed Sediments Are Prone To React Readily With The Environment. This Study Aims To Determine The Impact Of Parent Material And Time On Soil Physical And Chemical Properties Of Nine Proglacial Landscapes Distributed In The Tropical Andes And Alps. A Total Of 188 Soil Samples Were Collected Along Chronosequences Of Deglacierization And From Sites That Differed In Terms Of Parent Material And Classified Following Three Parent Material Groups: (1) Granodiorite-Tonalite (Gt), (2) Gneiss-Shales-Schists (Gss), And (3) Mont-Blanc Granite (Mbg). We Determined Physical And Chemical Soil Properties Such As Contents Of Clay, Silt, Sand, Organic Carbon, Bulk Density (Bd), Ph, Extractable Cation (Exca, Exmg, Exk), Elemental Composition By Xray Fluorescence (Al, Si, P, S, K, Ca, Mn, Fe, Cu, Zn, As, Mo, Hg, Pb) And Icp-Ms (Al, Ca, Cu, Fe, K, Mg, Mn, Mo, Na, P, S, Zn), And Mineral Phase (Xrd Diffraction Analysis). Parent Material-Controlled Particle-Size Distribution, Soc, Ph, Available P, Exca, And Exmg, Whereas Time Since Deglacierization Only Affected Soc And P, And Exmg Globally. Most Of The Significant Differences In Soil Properties Between Parent Material Groups Occurred Within The First 17 Years After Deglacierization, And Then We Observed A Homogenization Between Sites. While The Higher Soc And P Contents Observed Within The Gt Andean Sites Might Be Due To The Parent Material Composition Leading To Faster Initial Soil Formation, We Identified Potential As, Cu, Mo, And Mn Toxicity Within Those Soils. Our Study Highlights The Need To Investigate Further Proglacial Soil'S Buffering Capacity And Carbon Sequestration To Globally Inform The Conservation And Management Of Novel Proglacial Ecosystems.
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2023 |
Al-Yaari, A., Condom, T., Junquas, C., Rabatel, A., Ramseyer, V., Sicart, J., et al. (2023). Climate Variability And Glacier Evolution At Selected Sites Across The World: Past Trends And Future Projections. Earths Future, 111(101).
Abstract: The Availability Of Freshwater From Glaciers And Snowmelt Is Of Vital Importance For People And Ecosystems In The Context Of Global Climate Change. Here, We Focus On 25 Glaciers Located In Different Climates And Latitudes And Investigate Their Recent (1958-2020) And Future Projected Trends (2020-2050 And 2070-2100) In Monthly Precipitation (Pr), Maximum And Minimum Temperatures, Ice Mass Loss, And Their Relationships With Cloud Properties. The Study Sites Are Located In Temperate Europe (France), The Inner (Ecuador, Venezuela, And Colombia) And Outer Tropics (Bolivia And Peru), Central America (Mexico), Tropical Southeast Asia (Indonesia), Equatorial Africa (Uganda), And The Southern Dry And Patagonian Andes (Chile And Argentina). The Climate Analyses Are Based On Terraclimate Data (Monthly Climate And Climatic Water Balance For Global Terrestrial Surfaces) And 28 Cordex (Coordinated Regional Climate Downscaling Experiment) Climate Simulations. Our Findings Reveal That, Extrapolating Current Glacier Volume Change Trends, Almost Half Of The Studied Glaciers Are Likely To Vanish (95%-100% Volume Loss) By 2050, With Widespread Warming And Drying Trends Since 1958. A Shift Toward Wetter Conditions At Pico Humboldt (Venezuela) And Martial Este (Argentina) Identifiable In The Cordex Simulation Will Very Likely Not Have A Limiting Impact On Glacier Mass Loss Owing To Increasing Temperatures, Which Will Raise The Elevation Of The Rain/Snow Limit. Our Results Provide Useful New Information To Better Understand Glacier-Climate Relationships And Future Scenarios Dominated By Ice Mass Loss Trends Across The Globe. These Findings Suggest Serious Consequences For Future Water Availability, Which Exacerbate The Vulnerability Of Local Populations And Ecosystems.
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Autin, P., Sicart, J., Rabatel, A., Hock, R., & Jomelli, V. (2023). Climate Reconstruction Of The Little Ice Age Maximum Extent Of The Tropical Zongo Glacier Using A Distributed Energy Balancemodel. Comptes Rendus Geoscience, 3553, 381–398.
Abstract: This Study Assessed The Climate Conditions That Caused The Tropical Zongo Glacier (16 Degrees S, Bolivia) To Reach Its Little Ice Age (Lia) Maximum Extent In The Late 17Th Century. We Carried Out Sensitivity Analyses Of The Annual Surface Mass Balance To Different Physically Coherent Climate Scenarios Constrained By Information Taken From Paleoclimate Proxies And Sensitivity Studies Of Past Glacier Advances. These Scenarios Were Constrained By A 1.1 K Cooling And A 20% Increase In Annual Precipitation Compared To The Current Climate. Seasonal Precipitation Changes Were Constructed Using Shuffled Input Data For The Model: Measurements Of Air Temperature And Relative Humidity, Precipitation, Wind Speed, Incoming Short And Longwave Radiation Fluxes, And Assessed Using A Distributed Energy Balance Model. They Were Considered Plausible If Conditions Close To Equilibrium Glacier-Wide Mass Balance Were Obtained. Results Suggest That On Top Of A 1.1 K Cooling And Similar To 20% Increase In Annual Precipitation, Only Two Seasonal Precipitation Patterns Allow Lia Equilibrium: Evenly Distributed Precipitation Events Across The Year And An Early Wet Season Onset.
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Bayle, A., Carlson, B., Zimmer, A., Vallee, S., Rabatel, A., Cremonese, E., et al. (2023). Local Environmental Context Drives Heterogeneity Of Early Succession Dynamics In Alpine Glacier Forefields. Biogeosciences, , 164911–166911.
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Berthier, E., Vincent, C., & Six, D. (2023). Exceptional Thinning Through The Entire Altitudinal Range Of Mont-Blanc Glaciers During The 2021/22 Mass Balance Year. Journal Of Glaciology, .
Abstract: Widespread Glacier Losses Have Been Observed In Most Glaciated Regions On Earth During Recent Decades, With A Typical Pattern Of Strong Thinning In Their Lower Reaches And Limited Elevation Changes In Their Accumulation Areas. Here, We Use Pleiades Satellite Stereo-Images Of The Mont-Blanc Massif (Alps) To Reveal That Thinning Took Place Through The Entire Elevation Range During The Exceptional 2021/22 Mass-Balance Year. Above 3000 M A.S.L. On Argentiere Glacier And Mer De Glace, Thinning Rates Exceeded 3.5 M A-1 While Almost No Change Occurred During The Previous 9 Years. Below 3000 M A.S.L., These Anomalous Thinning Rates Are Essentially Explained By Changes In Surface Mass Balance. At Higher Altitudes, Other Processes Such As Firn Densification May Play A Role. Our Analysis Shows That High Altitude Glaciers, Mostly Stable During The Last 100 Years, Are Now Responding To The Impact Of Climate Change.
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Bouttes, N., Lhardy, F., Quiquet, A., Paillard, D., Goosse, H., & Roche, D. (2023). Deglacial Climate Changes As Forced By Different Ice Sheet Reconstructions. Climate Of The Past, , 102711–104211.
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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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Burgard, C., Jourdain, N., Mathiot, P., Smith, R., Schaefer, R., Caillet, J., et al. (2023). Emulating Present And Future Simulations Of Melt Rates At The Base Of Antarctic Ice Shelves With Neural Networks. Journal Of Advances In Modeling Earth Systems, 151(121).
Abstract: Melt Rates At The Base Of Antarctic Ice Shelves Are Needed To Drive Projections Of The Antarctic Ice Sheet Mass Loss. Current Basal Melt Parameterizations Struggle To Link Open Ocean Properties To Ice-Shelf Basal Melt Rates For The Range Of Current Sub-Shelf Cavity Geometries Around Antarctica. We Present A Proof Of Concept Exploring The Potential Of Simple Deep Learning Techniques To Parameterize Basal Melt. We Train A Simple Feedforward Neural Network, Or Multilayer Perceptron, Acting On Each Grid Cell Separately, To Emulate The Behavior Of Circum-Antarctic Cavity-Resolving Ocean Simulations. We Find That This Kind Of Emulator Produces Reasonable Basal Melt Rates For Our Training Ensemble, At Least As Close As Or Closer To The Reference Than Traditional Parameterizations. On An Independent Ensemble Of Simulations That Was Produced With The Same Ocean Model But With Different Model Parameters, Cavity Geometries And Forcing, The Neural Network Yields Similar Results To Traditional Parameterizations On Present Conditions. In Much Warmer Conditions, Both Traditional Parameterizations And Neural Network Struggle, But The Neural Network Tends To Produce Basal Melt Rates Closer To The Reference Than A Majority Of Traditional Parameterizations. While This Shows That Such A Neural Network Is At Least As Suitable For Century-Scale Antarctic Ice-Sheet Projections As Traditional Parameterizations, It Also Highlights That Tuning Any Parameterization On Present-Like Conditions Can Introduce Biases And Should Be Used With Care. Nevertheless, This Proof Of Concept Is Promising And Provides A Basis For Further Development Of A Deep Learning Basal Melt Parameterization. A Warmer Ocean Around Antarctica Leads To Higher Melting Of The Floating Ice Shelves, Which Influence The Ice Loss From The Antarctic Ice Sheet And Therefore Sea-Level Rise. In Computer Simulations Of The Ocean, These Ice Shelves Are Often Not Represented. For Simulations Of The Ice Sheet, So-Called Parameterizations Are Used To Link The Oceanic Properties In Front Of The Shelf And The Melt At Their Base. We Show That This Link Can Be Emulated With A Simple Neural Network, Which Performs At Least As Well As Traditional Physical Parameterizations Both For Present And Much Warmer Conditions. This Study Also Proposes Several Potential Ways Of Further Improving The Use Of Deep Learning To Parameterize Basal Melt. We Show That Simple Neural Networks Produce Reasonable Basal Melt Rates By Emulating Circum-Antarctic Cavity-Resolving Ocean Simulationspredicted Melt Rates For Present And Warmer Conditions Are Similar Or Closer To The Reference Simulation Than Traditional Parameterizationswe Show That Neural Networks Are Suited To Be Used As Basal Melt Parameterizations For Century-Scale Ice-Sheet Projections
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Burgard, C., Jourdain, N., Mathiot, P., Smith, R., Schäfer, R., Caillet, J., et al. (2023). Emulating Present And Future Simulations Of Melt Rates At The Base Of Antarctic Ice Shelves With Neural Networks. Journal Of Advances In Modeling Earth Systems, 151(121).
Abstract: Melt Rates At The Base Of Antarctic Ice Shelves Are Needed To Drive Projections Of The Antarctic Ice Sheet Mass Loss. Current Basal Melt Parameterizations Struggle To Link Open Ocean Properties To Ice-Shelf Basal Melt Rates For The Range Of Current Sub-Shelf Cavity Geometries Around Antarctica. We Present A Proof Of Concept Exploring The Potential Of Simple Deep Learning Techniques To Parameterize Basal Melt. We Train A Simple Feedforward Neural Network, Or Multilayer Perceptron, Acting On Each Grid Cell Separately, To Emulate The Behavior Of Circum-Antarctic Cavity-Resolving Ocean Simulations. We Find That This Kind Of Emulator Produces Reasonable Basal Melt Rates For Our Training Ensemble, At Least As Close As Or Closer To The Reference Than Traditional Parameterizations. On An Independent Ensemble Of Simulations That Was Produced With The Same Ocean Model But With Different Model Parameters, Cavity Geometries And Forcing, The Neural Network Yields Similar Results To Traditional Parameterizations On Present Conditions. In Much Warmer Conditions, Both Traditional Parameterizations And Neural Network Struggle, But The Neural Network Tends To Produce Basal Melt Rates Closer To The Reference Than A Majority Of Traditional Parameterizations. While This Shows That Such A Neural Network Is At Least As Suitable For Century-Scale Antarctic Ice-Sheet Projections As Traditional Parameterizations, It Also Highlights That Tuning Any Parameterization On Present-Like Conditions Can Introduce Biases And Should Be Used With Care. Nevertheless, This Proof Of Concept Is Promising And Provides A Basis For Further Development Of A Deep Learning Basal Melt Parameterization. A Warmer Ocean Around Antarctica Leads To Higher Melting Of The Floating Ice Shelves, Which Influence The Ice Loss From The Antarctic Ice Sheet And Therefore Sea-Level Rise. In Computer Simulations Of The Ocean, These Ice Shelves Are Often Not Represented. For Simulations Of The Ice Sheet, So-Called Parameterizations Are Used To Link The Oceanic Properties In Front Of The Shelf And The Melt At Their Base. We Show That This Link Can Be Emulated With A Simple Neural Network, Which Performs At Least As Well As Traditional Physical Parameterizations Both For Present And Much Warmer Conditions. This Study Also Proposes Several Potential Ways Of Further Improving The Use Of Deep Learning To Parameterize Basal Melt. We Show That Simple Neural Networks Produce Reasonable Basal Melt Rates By Emulating Circum-Antarctic Cavity-Resolving Ocean Simulationspredicted Melt Rates For Present And Warmer Conditions Are Similar Or Closer To The Reference Simulation Than Traditional Parameterizationswe Show That Neural Networks Are Suited To Be Used As Basal Melt Parameterizations For Century-Scale Ice-Sheet Projections
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Burgos-Cuevas, A., Ruiz-Angulo, A., Ramos-Musalem, K., Palacios-Morales, C., & Garcia-Molina, C. (2023). Experimental Downslope Gravity Currents Over A Synthetic Topography. Atmosfera, 373, 383–399.
Abstract: Experimental Lock-Release Gravity Currents Are Investigated As They Propagate Downslope Over Varying Synthetic Topography. We Emulate And Investigate The Dynamics Of Thermally Driven Winds That Propagate Downslope While Interacting With The Roughness Of A Complex Topographic Surface. The Mixing Processes Between The Gravity Currents And Their Surroundings Are Studied With Particle Image Velocimetry (Piv), And Entrainment Is Quantified. The Magnitude Of The Entrainment Coefficient Is Shown To Increase As The Roughness Of The Slope Increases. Shadowgraph Visualizations Qualitatively Reproduce This Behavior. Finally, Pressure Fields Are Estimated From Velocity Fields, And Pressure Time Series Are Obtained Over Synthetic Stations Along The Topographic Surface. The Arrival Of Gravity Currents Is Shown To Be Detected In The Pressure Time Series. This Last Result May Help Detect Atmospheric Gravity Currents Using Only Surface Pressure Measurements.
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Caillet, J., Jourdain, N., Mathiot, P., Hellmer, H., & Mouginot, J. (2023). Drivers And Reversibility Of Abrupt Ocean State Transitions In The Amundsen Sea, Antarctica. Journal Of Geophysical Research-Oceans, 1281(1).
Abstract: Ocean Warming Around Antarctica Has The Potential To Trigger Marine Ice-Sheet Instabilities. It Has Been Suggested That Abrupt And Irreversible Cold-To-Warm Ocean Tipping Points May Exist, With Possible Domino Effect From Ocean To Ice-Sheet Tipping Points. A 1/4 & Deg; Ocean Model Configuration Of The Amundsen Sea Sector Is Used To Investigate The Existence Of Ocean Tipping Points, Their Drivers, And Their Potential Impact On Ice-Shelf Basal Melting. We Apply Idealized Atmospheric Perturbations Of Either Heat, Freshwater, Or Momentum Fluxes, And We Characterize The Key Physical Processes At Play In Warm-To-Cold And Cold-To-Warm Climate Transitions. Relatively Weak Perturbations Of Any Of These Fluxes Are Able To Switch The Amundsen Sea To An Intermittent Or Permanent Cold State, That Is, With Ocean Temperatures Close To The Surface Freezing Point And Very Low Ice-Shelf Melt Rate. The Transitions Are Reversible, That Is, Canceling The Atmospheric Perturbation Brings The Ocean System Back To Its Unperturbed State Within A Few Decades. All The Transitions Are Primarily Driven By Changes In Surface Buoyancy Fluxes Resulting From The Freshwater Flux Perturbation Or From Modified Net Sea-Ice Production Due To Either Heat Flux Or Sea-Ice Advection Anomalies. These Changes Affect The Vertical Ocean Stratification Over The Continental Shelf And Thereby The Eastward Undercurrent At The Shelf Break, Which Both Impact Ice-Shelf Melting. As Sea-Ice Induced Deep Convection Is Already Quite Limited In Present-Day Conditions, Surface Buoyancy Gain In A Warmer Climate Has Relatively Little Effect On Deep Ocean Properties Compared To Colder Climate Conditions.
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Cassel, M., Navratil, O., Liebault, F., Recking, A., Vazquez-Tarrio, D., Bakker, M., et al. (2023). Assessment Of Pebble Virtual Velocities By Combining Active Rfid Fixed Stations With Geophones. Earth Surface Processes And Landforms, .
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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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Clauzel, L., Menegoz, M., Gilbert, A., Gagliardini, O., Six, D., Gastineau, G., et al. (2023). Sensitivity Of Glaciers In The European Alps To Anthropogenic Atmospheric Forcings: Case Study Of The Argentiere Glacier. Geophysical Research Letters, .
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Cook, S., Gillet-Chaulet, F., & Fuerst, J. (2023). Robust Reconstruction Of Glacier Beds Using Transient 2D Assimilation With Stokes. Journal Of Glaciology, .
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Cook, S., Jouvet, G., Millan, R., Rabatel, A., Zekollari, H., & Dussaillant, I. (2023). Committed Ice Loss In The European Alps Until 2050 Using A Deep-Learning-Aided 3D Ice-Flow Model With Data Assimilation. Geophysical Research Letters, 505(232).
Abstract: Modeling The Short-Term (<50 Years) Evolution Of Glaciers Is Difficult Because Of Issues Related To Model Initialization And Data Assimilation. However, This Timescale Is Critical, Particularly For Water Resources, Natural Hazards, And Ecology. Using A Unique Record Of Satellite Remote-Sensing Data, Combined With A Novel Optimisation And Surface-Forcing-Calculation Method Within The Framework Of The Deep-Learning Based Instructed Glacier Model, We Are Able To Ameliorate Initialization Issues. We Thus Model The Committed Evolution Of All Glaciers In The European Alps Up To 2050 Using Present-Day Climate Conditions, Assuming No Future Climate Change. We Find That The Resulting Committed Ice Loss Exceeds A Third Of The Present-Day Ice Volume By 2050, With Multi-Kilometer Frontal Retreats For Even The Largest Glaciers. Our Results Show The Importance Of Modeling Ice Dynamics To Accurately Retrieve The Ice-Thickness Distribution And To Predict Future Mass Changes. Thanks To High-Performance Gpu Processing, We Also Demonstrate Our Method'S Global Potential.
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Cusicanqui, D., Bodin, X., Duvillard, P., Schoeneich, P., Revil, A., Assier, A., et al. (2023). Glacier, Permafrost And Thermokarst Interactions In Alpine Terrain: Insights From Seven Decades Of Reconstructed Dynamics Of The Chauvet Glacial And Periglacial System (Southern French Alps). Earth Surface Processes And Landforms, .
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Da Silva, E., Woolliams, E., Picot, N., Poisson, J., Skourup, H., Moholdt, G., et al. (2023). Towards Operational Fiducial Reference Measurement (Frm) Data For The Calibration And Validation Of The Sentinel-3 Surface Topography Mission Over Inland Waters, Sea Ice, And Land Ice. Remote Sensing, 151(191).
Abstract: The Copernicus Sentinel-3 Surface Topography Mission (Stm) Land Altimetry Provides Valuable Surface Elevation Information Over Inland Waters, Sea Ice, And Land Ice, Thanks To Its Synthetic Aperture Radar (Sar) Altimeter And Its Orbit That Covers High-Latitude Polar Regions. To Ensure That These Measurements Are Reliable And To Maximise The Return On Investment, Adequate Validation Of The Geophysical Retrieval Methods, Processing Algorithms, And Corrections Must Be Performed Using Independent Observations. The Eu-Esa Project St3Tart (Started July 2021) Aims To Generalise The Concept Of Fiducial Reference Measurements (Frms) For The Copernicus Sentinel-3 Stm. This Work Has Gathered Existing Data, Made New Observations During Field Campaigns, And Ensured That These Observations Meet The Criteria Of Frm Standards So That They Can Be Used To Validate Sentinel-3 Stm Land Altimetry Products Operationally. A Roadmap For The Operational Provision Of The Frm, Including The Definition, Consolidation, And Identification Of The Most Relevant And Cost-Effective Methods And Protocols To Be Maintained, Supported, Or Implemented, Has Been Developed. The Roadmap Includes Guidelines For Si Traceability, Definitions Of Frm Measurement Procedures, Processing Methods, And Uncertainty Budget Estimations.
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Fremand, A., Fretwell, P., Bodart, J., Pritchard, H., Aitken, A., Bamber, J., et al. (2023). Antarctic Bedmap Data: Findable, Accessible, Interoperable, And Reusable (Fair) Sharing Of 60 Years Of Ice Bed, Surface, And Thickness Data. Earth System Science Data, 151(7), 2695–2710.
Abstract: One Of The Key Components Of This Research Has Been The Mapping Of Antarctic Bed Topography And Ice Thickness Parameters That Are Crucial For Modelling Ice Flow And Hence For Predicting Future Ice Loss And The Ensuing Sea Level Rise. Supported By The Scientific Committee On Antarctic Research (Scar), The Bedmap3 Action Group Aims Not Only To Produce New Gridded Maps Of Ice Thickness And Bed Topography For The International Scientific Community, But Also To Standardize And Make Available All The Geophysical Survey Data Points Used In Producing The Bedmap Gridded Products. Here, We Document The Survey Data Used In The Latest Iteration, Bedmap3, Incorporating And Adding To All Of The Datasets Previously Used For Bedmap1 And Bedmap2, Including Ice Bed, Surface And Thickness Point Data From All Antarctic Geophysical Campaigns Since The 1950S. More Specifically, We Describe The Processes Used To Standardize And Make These And Future Surveys And Gridded Datasets Accessible Under The Findable, Accessible, Interoperable, And Reusable (Fair) Data Principles. With The Goals Of Making The Gridding Process Reproducible And Allowing Scientists To Re-Use The Data Freely For Their Own Analysis, We Introduce The New Scar Bedmap Data Portal (Https://Bedmap.Scar.Org, Last Access: 1 March 2023) Created To Provide Unprecedented Open Access To These Important Datasets Through A Web-Map Interface. We Believe That This Data Release Will Be A Valuable Asset To Antarctic Research And Will Greatly Extend The Life Cycle Of The Data Held Within It. Data Are Available From The Uk Polar Data Centre: Https://Data.Bas.Ac.Uk (Last Access: 5 May 2023 ). See The Data Availability Section For The Complete List Of Datasets.
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Gilbert, A., Gimbert, F., Gagliardini, O., & Vincent, C. (2023). Inferring The Basal Friction Law From Long Term Changes Of Glacier Length, Thickness And Velocity On An Alpine Glacier. Geophysical Research Letters, 505(161).
Abstract: Basal Sliding Of Glaciers And Ice Sheets Remains A Source Of Uncertainty In Simulating The Long-Term Evolution Of Ice Masses. In Particular, The Response Of Ice Flow To Changes In Driving Stress Depends Strongly On The Value Of The Exponent M In Nonlinear Friction Laws (E.G., Weertman'S Law), Which Is Poorly Constrained By Observations. Here We Constrain The Friction Law At A Natural Scale On Argentiere Glacier (French Alps, Hard-Bed), Taking Advantage Of Well-Resolved Observations Of Glacier Mass Balance, Geometry And Basal Sliding Over Time Spans That Include Large Changes In Driving Stress. By Combining Three Different Independent Methods Based On (A) Surface Velocity Inversion, (B) Transient Length Change Modeling, And (C) Direct Local Sliding Measurements, We Consistently Find A Value Of M = 3.1 +/- 0.3. We Suggest That Weertman'S Law Is Suitable For Modeling The Long-Term Evolution Of Hard-Bedded Glaciers And Ice Sheets.
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Gilbert, A., Gimbert, F., Gagliardini, O., & Vincent, C. (2023). Inferring The Basal Friction Law From Long Term Changes Of Glacier Length, Thickness And Velocity On An Alpine Glacier. Geophysical Research Letters, 505(161).
Abstract: Basal Sliding Of Glaciers And Ice Sheets Remains A Source Of Uncertainty In Simulating The Long-Term Evolution Of Ice Masses. In Particular, The Response Of Ice Flow To Changes In Driving Stress Depends Strongly On The Value Of The Exponent M In Nonlinear Friction Laws (E.G., Weertman'S Law), Which Is Poorly Constrained By Observations. Here We Constrain The Friction Law At A Natural Scale On Argentiere Glacier (French Alps, Hard-Bed), Taking Advantage Of Well-Resolved Observations Of Glacier Mass Balance, Geometry And Basal Sliding Over Time Spans That Include Large Changes In Driving Stress. By Combining Three Different Independent Methods Based On (A) Surface Velocity Inversion, (B) Transient Length Change Modeling, And (C) Direct Local Sliding Measurements, We Consistently Find A Value Of M = 3.1 +/- 0.3. We Suggest That Weertman'S Law Is Suitable For Modeling The Long-Term Evolution Of Hard-Bedded Glaciers And Ice Sheets.
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Gonzalez, A., Fontaine, F., Barruol, G., Recking, A., Burtin, A., Join, J., et al. (2023). Seismic Signature Of A River Flooding In La R & Prime;Eunion Island During The Tropical Cyclone Dumazile (March 2018). Journal Of Applied Geophysics, 2152.
Abstract: Monitoring Of Sediment Transport During Extreme Flood Events Is Difficult And Often Impossible. Fluvial Seismology Can Provide Constraints On The Mechanisms Of This Transport And On The Seismic Sources But Few Cases Of Application In Context Of Extreme Events Such As Tropical Cyclones Were Realized. Recordings From Three Seismic Stations Temporarily Installed Along A River (The Rivie`Re Du Ma<Sic>T) Located In La Re & Prime;Union Island (Indian Ocean) Are Analysed To Characterize High-Frequency (> 1 Hz) Seismic Noise Induced By The Extreme Flood Generated By The Tropical Cyclone Dumazile (March 2018). We Evidence A Good Correlation (R2 = 0.94) Between The Amplitude Of The Seismic Signal And The Water Level At Lower Frequencies (2-7 Hz), Particularly During The Rising Limb Of The River Flood. The Relationship Between Seismic Amplitude And Water Level Measurements Tested At Multiple Frequency Ranges Are Consistent With A Signal Dominated By Water Flow At Lower Frequencies And By Sediment Transport At Higher Frequencies (15-45 Hz). We Show That The Use Of Seismic Measurement, Particularly At Stations Located Very Close To The Riverbed Can Provide Comprehensive Information On The Mechanisms Involved During Sediment Transport Associated With Extreme Flood Events When Direct Measurements Are Not Possible.
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Halas, P., Mouginot, J., De Fleurian, B., & Langebroek, P. (2023). Impact Of Seasonal Fluctuations Of Ice Velocity On Decadal Trends Observed In Southwest Greenland. Remote Sensing Of Environment, 2852.
Abstract: By Tracking The Feature Displacement Between Satellite Images Spaced Approximately One Year Apart, Surface Runoff Has Been Shown To Have A Long-Term Impact On The Average Ice Flow Of A Land-Terminating Sector Of Greenland. In This Study, We Revisit The Multi-Year Trends In Ice Flow By Assessing More Carefully The Impact Of Seasonal Fluctuation In Velocity On The Annual Mean Ice Velocity. We Find That, Depending On The Length And Period Used To Measure Displacement, Seasonal Fluctuations Do Have An Impact On Observed Velocities On Up To 15%, And Can Affect Decadal Trends. Nevertheless, The Magnitude Of This Fluctuation Is Small Enough To Confirm The General Slowdown Observed During The 2000-2012 Period. Between 2012 And 2019, We Find Significant Re-Acceleration Of Low-Lying Glaciers Tongue But Velocity Trends Elsewhere Are Generally Insignificant And Not Spatially Consistent. Finally, We Propose A More Selective Approach To Recovering Velocity Trends Using Satellite Imagery That Involves Using Only Measurements Where The Image Pair Starting Date Is Before Summer, In Order To Have Comparable Measurements For Every Year, Sampling A Melt Season And The Following Winter.
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Hill, E., Urruty, B., Reese, R., Garbe, J., Gagliardini, O., Durand, G., et al. (2023). The Stability Of Present-Day Antarctic Grounding Lines – Part 1: No Indication Of Marine Ice Sheet Instability In The Current Geometry. Cryosphere, 171(9), 3739–3759.
Abstract: Theoretical And Numerical Work Has Shown That Under Certain Circumstances Grounding Lines Of Marine-Type Ice Sheets Can Enter Phases Of Irreversible Advance And Retreat Driven By The Marine Ice Sheet Instability (Misi). Instances Of Such Irreversible Retreat Have Been Found In Several Simulations Of The Antarctic Ice Sheet. However, It Has Not Been Assessed Whether The Antarctic Grounding Lines Are Already Undergoing Misi In Their Current Position. Here, We Conduct A Systematic Numerical Stability Analysis Using Three State-Of-The-Art Ice Sheet Models: Ua, Elmer/Ice, And The Parallel Ice Sheet Model (Pism). For The First Two Models, We Construct Steady-State Initial Configurations Whereby The Simulated Grounding Lines Remain At The Observed Present-Day Positions Through Time. The Third Model, Pism, Uses A Spin-Up Procedure And Historical Forcing Such That Its Transient State Is Close To The Observed One. To Assess The Stability Of These Simulated States, We Apply Short-Term Perturbations To Submarine Melting. Our Results Show That The Grounding Lines Around Antarctica Migrate Slightly Away From Their Initial Position While The Perturbation Is Applied, And They Revert Once The Perturbation Is Removed. This Indicates That Present-Day Retreat Of Antarctic Grounding Lines Is Not Yet Irreversible Or Self-Sustained. However, Our Accompanying Paper (Part 2, ) Shows That If The Grounding Lines Retreated Further Inland, Under Present-Day Climate Forcing, It May Lead To The Eventual Irreversible Collapse Of Some Marine Regions Of West Antarctica.
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Hutchinson, K., Deshayes, J., Ethe, C., Rousset, C., De Lavergne, C., Vancoppenolle, M., et al. (2023). Improving Antarctic Bottom Water Precursors In Nemo For Climate Applications. Geoscientific Model Development, , 362933–365033.
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Jones, N., Strozzi, T., Rabatel, A., Ducasse, E., & Mouginot, J. (2023). Surface Instability Mapping In Alpine Paraglacial Environments Using Sentinel-1 Dinsar Techniques. Ieee Journal Of Selected Topics In Applied Earth Observations And Remote Sensing, 161, 45.
Abstract: Current Climate Warming Leads To Widespread Glacier Shrinkage In High Alpine Terrains And Associated Changes In Surface Dynamics Of Deglacierized Environments. In Consequence, Slope Instabilities Increasingly Develop Along Retreating Glaciers Through Debuttressing Effects Or Degrading Permafrost Conditions. In The Context Of Associated Hazards To The Local Environment And Infrastructure, A Thorough Analysis Of Slope Instabilities Is Highly Relevant. Affected Regions Are Mostly Inaccessible And Cover Large Areas, Therefore Remote Sensing Techniques Such As Differential Interferometric Synthetic Aperture Radar (Dinsar) Are Valuable Tools To Monitor Surface Movements And Assess Their Evolution. We Apply Standard And Advanced Dinsar Methods Using Sentinel-1 Sar Data From 2015 Until Late 2021 To Map And Classify Slope Instabilities In Three Glacierized Regions In The European Alps. The Final Products Include An Inventory Per Region, With A Total Of 815 Mapped Slope Instabilities, Of Which 38% Move <3, 9% Move 3-10, 42% Move 10-30, And 11% Move >30 Cm/Yr. An Additional Assessment Of Four Landslides Occurring Along Shrinking Glaciers Shows Time Series With Recent Accelerations In 2018/19. Validation Of Sentinel-1 Derived Slope Movement Products Is Performed By Comparison With Shorter Wavelength Terrasar-X And Optical Sentinel-2 Derived Data Using Offset Tracking. Results Clearly Show The Suitability Of Sentinel-1 Dinsar Methods To Detect A Range Of Slope Movements In High Alpine Terrain, Yet Also Highlight The Limitations. We Therefore Recommend A Combination Of Advanced Sentinel-1 Dinsar And Sentinel-2 Offset Tracking Methods To Develop A Comprehensive Inventory Of Alpine Slope Motion.
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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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Law, R., Christoffersen, P., Mackie, E., Cook, S., Haseloff, M., & Gagliardini, O. (2023). Complex Motion Of Greenland Ice Sheet Outlet Glaciers With Basal Temperate Ice. Science Advances, 9(6).
Abstract: Uncertainty Associated With Ice Sheet Motion Plagues Sea Level Rise Predictions. Much Of This Uncertainty Arises From Imperfect Representations Of Physical Processes Including Basal Slip And Internal Ice Deformation, With Ice Sheet Models Largely Incapable Of Reproducing Borehole-Based Observations. Here, We Model Isolated Three-Dimensional Domains From Fast-Moving (Sermeq Kujalleq/Store Glacier) And Slow-Moving (Isunnguata Sermia) Ice Sheet Settings In Greenland. By Incorporating Realistic Geostatistically Simulated Topography, We Show That A Spatially Highly Variable Layer Of Temperate Ice (Much Softer Ice At The Pressure-Melting Point) Forms Naturally In Both Settings, Alongside Ice Motion Patterns Which Diverge Substantially From Those Obtained Using Smoothly Varying Bedmachine Topography. Temperate Ice Is Vertically Extensive (>100 Meters) In Deep Troughs But Thins Notably (<5 Meters) Over Bedrock Highs, With Basal Slip Rates Reaching >90 Or <5% Of Surface Velocity Dependent On Topography And Temperate Layer Thickness. Developing Parameterizations Of The Net Effect Of This Complex Motion Can Improve The Realism Of Predictive Ice Sheet Models.
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Le Cozannet, G., Nicholls, R., Durand, G., Slangen, A., Lincke, D., & Chapuis, A. (2023). Adaptation To Multi-Meter Sea-Level Rise Should Start Now. Environmental Research Letters, 181(9).
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Lecavalier, B., Tarasov, L., Balco, G., Spector, P., Hillenbrand, C., Buizert, C., et al. (2023). Antarctic Ice Sheet Paleo-Constraint Database. Earth System Science Data, 151(8), 3573–3596.
Abstract: We Present A Database Of Observational Constraints On Past Antarctic Ice Sheet Changes During The Last Glacial Cycle Intended To Consolidate The Observations That Represent Our Understanding Of Past Antarctic Changes And For State-Space Estimation And Paleo-Model Calibrations. The Database Is A Major Expansion Of The Initial Work Of Briggs And Tarasov (2013). It Includes New Data Types And Multi-Tier Data Quality Assessment. The Updated Constraint Database, Antice2 (Https://Theghub.Org/Resources/4884, Lecavalier Et Al., 2022), Consists Of Observations Of Past Grounded- And Floating-Ice-Sheet Extent, Past Ice Thickness, Past Relative Sea Level, Borehole Temperature Profiles, And Present-Day Bedrock Displacement Rates. In Addition To Paleo-Observations, The Present-Day Ice Sheet Geometry And Surface Ice Velocities Are Incorporated To Constrain The Present-Day Ice Sheet Configuration. The Method By Which The Data Are Curated Using Explicitly Defined Criteria Is Detailed. Moreover, The Observational Uncertainties Are Specified. The Methodology By Which The Constraint Database Can Be Applied To Evaluate A Given Ice Sheet Reconstruction Is Discussed. The Implementation Of The Antice2 Database For Antarctic Ice Sheet Model Calibrations Will Improve Antarctic Ice Sheet Predictions During Past Warm And Cold Periods And Yield More Robust Paleo-Model Spin Ups For Forecasting Future Ice Sheet Changes.
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Maclennan, M., Lenaerts, J., Shields, C., Hoffman, A., Wever, N., Thompson-Munson, M., et al. (2023). Climatology And Surface Impacts Of Atmospheric Rivers On West Antarctica. Cryosphere, 171(2), 865–881.
Abstract: Atmospheric Rivers (Ars) Transport Large Amounts Of Moisture From The Mid- To High-Latitudes And They Are A Primary Driver Of The Most Extreme Snowfall Events, Along With Surface Melting, In Antarctica. In This Study, We Characterize The Climatology And Surface Impacts Of Ars On West Antarctica, Focusing On The Amundsen Sea Embayment And Marie Byrd Land. First, We Develop A Climatology Of Ars In This Region, Using An Antarctic-Specific Ar Detection Tool Combined With The Modern-Era Retrospective Analysis For Research And Applications, Version 2 (Merra-2) And The European Centre For Medium-Range Weather Forecasts (Ecmwf) Reanalysis V5 (Era5) Atmospheric Reanalyses. We Find That While Ars Are Infrequent (Occurring 3 % Of The Time), They Cause Intense Precipitation In Short Periods Of Time And Account For 11 % Of The Annual Surface Accumulation. They Are Driven By The Coupling Of A Blocking High Over The Antarctic Peninsula With A Low-Pressure System Known As The Amundsen Sea Low. Next, We Use Observations From Automatic Weather Stations On Thwaites Eastern Ice Shelf With The Firn Model Snowpack And Interferometric Reflectometry (Ir) To Examine A Case Study Of Three Ars That Made Landfall In Rapid Succession From 2 To 8 February 2020, Known As An Ar Family Event. While Accumulation Dominates The Surface Impacts Of The Event On Thwaites Eastern Ice Shelf (> 100 Kgm(-2) Or Millimeters Water Equivalent), We Find Small Amounts Of Surface Melt As Well (< 5 Kgm(-2)). The Results Presented Here Enable Us To Quantify The Past Impacts Of Ars On West Antarctica'S Surface Mass Balance (Smb) And Characterize Their Interannual Variability And Trends, Enabling A Better Assessment Of Future Ar-Driven Changes In The Smb.
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Maier, N., Andersen, J., Mouginot, J., Gimbert, F., & Gagliardini, O. (2023). Wintertime Supraglacial Lake Drainage Cascade Triggers Large-Scale Ice Flow Response In Greenland. Geophysical Research Letters, 505(4).
Abstract: Surface Melt Forces Summertime Ice-Flow Accelerations On Glaciers And Ice Sheets. Here, We Show That Large Meltwater-Forced Accelerations Also Occur During Wintertime In Greenland. We Document Supraglacial Lakes (Sgls) Draining In Cascades At Unusually High Elevation, Causing An Expansive Flow Acceleration Over A Similar To 5,200 Km(2) Region During Winter. The Three-Component Interferometric Surface Velocity Field And Decomposition Modeling Reveal The Underlying Flood Propagation With Unprecedented Detail As It Traveled Over 160 Km From The Drainage Site To The Margin, Providing Novel Constraints On Subglacial Water Pathways, Drainage Morphology, And Links With Basal Sliding. The Triggering Sgls Continuously Grew Over 40 Years And Suddenly Released Decades Of Stored Meltwater, Demonstrating Surface Melting Can Impact Dynamics Well Beyond Melt Production. We Show These Events Are Likely Common And Thus Their Cumulative Impact On Dynamics Should Be Further Evaluated.
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Mathiot, P., & Jourdain, N. (2023). Southern Ocean Warming And Antarctic Ice Shelf Melting In Conditions Plausible By Late 23Rd Century In A High-End Scenario. Ocean Science, 191(6), 1595–1615.
Abstract: How Much Antarctic Ice Shelf Basal Melt Rates Can Increase In Response To Global Warming Remains An Open Question. Here We Describe The Response Of The Southern Ocean And Ice Shelf Cavities To An Abrupt Change To High-End Atmospheric Conditions Plausible By The Late 23Rd Century Under The Ssp5-8.5 Scenario. To Achieve This Objective, We First Present And Evaluate A New 0.25 Circle Global Configuration Of The Nemo Nucleus For European Modelling Of The Ocean Ocean And Sea Ice Model. Our Present-Day Simulations Demonstrate Good Agreement With Observational Data For Key Variables Such As Temperature, Salinity, And Ice Shelf Melt Rates, Despite The Remaining Difficulties To Simulate The Interannual Variability In The Amundsen Sea. The Ocean Response To The High-End Atmospheric Perturbation Includes A Strengthening And Extension Of The Ross And Weddell Gyres And A Quasi-Disappearance Of Sea Ice, With A Subsequent Decrease In Production Of High Salinity Shelf Water And Increased Intrusion Of Warmer Water Onto The Continental Shelves Favoured By Changes In Baroclinic Currents At The Shelf Break. We Propose To Classify The Perturbed Continental Shelf As A “Warm-Fresh Shelf”. This Induces A Substantial Increase In Ice Shelf Basal Melt Rates, Particularly In The Coldest Seas, With A Total Basal Mass Loss Rising From 1180 To 15 700 Gt Yr – 1 And An Antarctica Averaged Melt Rate Increasing From 0.8 To 10.6 M Yr – 1 . In The Perturbed Simulation, Most Ice Shelves Around Antarctica Experience Conditions That Are Currently Found In The Amundsen Sea, While The Amundsen Sea Warms By 2 Circle C. These Idealised Projections Can Be Used As A Base To Calibrate Basal Melt Parameterisations Used In Long-Term Ice Sheet Projections.
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Mosbeux, C., Padman, L., Klein, E., Bromirski, P., & Fricker, H. (2023). Seasonal Variability In Antarctic Ice Shelf Velocities Forced By Sea Surfaceheight Variations. Cryosphere, , 258522–260622.
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Mouginot, J., Rabatel, A., Ducasse, E., & Millan, R. (2023). Optimization Of Cross Correlation Algorithm For Annual Mapping Of Alpine Glacier Flow Velocities; Application To Sentinel-2. Ieee Transactions On Geoscience And Remote Sensing, 616.
Abstract: Nowadays, Satellite Observations Cover Most Of The Earth'S Surface In A Repetitive Manner. This Information Is Crucial For Documenting Variability And Environmental Changes Such As Glacier Surface Velocity. With This In Mind, Digital Image Processing Has Been Developed And Improved Over The Past Decades. The Processing Challenges Are Now Related To Optimizing Parameters That Account For The High Variability Of Natural Processes, As Well As Filtering And Aggregating The Results To Provide Useful Products To End-Users. Based On The Normalized Cross Correlation (Ncc) Method Applied To Sentinel-2 Optical Satellite Observations Up To 400 Days Apart, We Present A Series Of Tests To Derive Optimal Parameter Values For The Quantification Of Alpine Glacier Ice Velocity That We Have Applied To The Mont-Blanc Massif Where In Situ Measurements Are Available. We Found That A Search Distance Adapted To The Temporal Baseline, A 16X16 Pixel Window Size, And A 5X5 Pixels Sampling Provide An Appropriate Combination Of Parameters To Process Sentinel-2 With The Ncc Method When Applied To Small Alpine Glaciers. Combining Several Spatial And Temporal Filters Applied To A Large Set Of More Than 18 000 Displacement Maps Obtained Between 2015 And 2021, Then Aggregating These Filtered Maps Using Statistical Or Linear Regressions Into Annual Maps, Yields Near-Complete Maps Of The Test Region With A Root Mean Square Error (Rmse) Reduced To About 10 M.Yr(-1) Compared To In Situ Measurements.
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Otosaka, I., Shepherd, A., Ivins, E., Schlegel, N., Amory, C., Van Den Broeke, M., et al. (2023). Mass Balance Of The Greenland And Antarctic Ice Sheets From 1992 To 2020. Earth System Science Data, , 159711–161611.
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Piantini, M., Gimbert, F., Korkolis, E., Rousseau, R., Bellot, H., & Recking, A. (2023). Solid Concentration As A Main Proxy For Basal Force Fluctuations Generated By Highly Concentrated Sediment Flows. Geophysical Research Letters, 505(1).
Abstract: Sediment Flows Generate Ground Vibrations By Exerting Force Fluctuations On The Riverbed. Linking Force Fluctuations To Properties Of Highly Concentrated Sediment Flows, However, Remains Particularly Challenging Due To Complexities Arising From Grain-To-Grain Interactions. Here, We Conduct Downscaled Flume Experiments In Which We Specifically Measure Force Fluctuations And Local Seismic Vibrations Together With Flow Properties Of Highly Concentrated Sediment Flows At High Spatial And Temporal Resolution. We Observe Hysteresis Behaviors Between Force Fluctuations Amplitude And Flow Surface Elevation And Mass That Occur During Complex Changes In Internal Flow Dynamics. By Contrast, Force Fluctuations Amplitude Exhibits A Unique Negative Relationship With Solid Concentration. We Suggest This Is Due To The Rheology Of Dense Granular Flows, Where Solid Concentration Is A Proxy For Particle Agitation. We Therefore Advance That Solid Concentration Should Be Incorporated In Seismic Models Of Such Sediment Flows As A Key Parameter Describing Inter-Particle Collisions And Impacts To The Bed.
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Piantini, M., Gimbert, F., Korkolis, E., Rousseau, R., Bellot, H., & Recking, A. (2023). Solid Concentration As A Main Proxy For Basal Force Fluctuations Generated By Highly Concentrated Sediment Flows. Geophysical Research Letters, .
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Pohl, B., Prince, H., Wille, J., Kingston, D., Cullen, N., & Fauchereau, N. (2023). Atmospheric Rivers And Weather Types In Aotearoa New Zealand: A Two-Way Story. Journal Of Geophysical Research-Atmospheres, 1281(151).
Abstract: Here, We Analyze The Inter-Relationships Between Weather Types (Wts) And Atmospheric Rivers (Ars) Around Aotearoa New Zealand (Anz), Their Respective Properties, As Well As Their Combined And Separate Influence On Daily Precipitation Amounts And Extremes. Results Show That Ars Are Often Associated With 3-4 Wts, But These Wts Change Depending On The Regions Where Ars Landfall. The Wts Most Frequently Associated With Ars Generally Correspond To Those Favoring Anomalously Strong Westerly Wind In The Mid-Latitudes, Especially For Southern Regions Of Anz, Or Northwesterly Anomalies Favoring Moisture Export From The Lower Latitudes, Especially For The Northern Regions. Wts And Ars Show Strong Within-Type And Inter-Event Diversity. The Synoptic Patterns Of The Wts Significantly Differ When They Are Associated With Ar Occurrences, With Atmospheric Centers Of Actions Being Shifted So That Moisture Fluxes Toward Anz Are Enhanced. The Location, Angle, And Persistence Of Ars Appear Strongly Driven By The Synoptic Configurations Of The Wts. Although Total Moisture Transport Shows Weaker Wt-Dependency, It Appears Strongly Related To Zonal Wind Speed To The South Of Anz, Or The Moisture Content Of The Air Mass To The North. Finally, Wt Influence On Daily Precipitation May Completely Change Depending On Their Association, Or Lack Thereof, With Ar Events. Wts Traditionally Considered As Favorable To Wet Conditions May Conceal Daily Precipitation Extremes Occurring During Ar Days, And Anomalously Dry Days Or Near-Climatological Conditions During Non-Ar Days.
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Rabatel, A., Ducasse, E., Millan, R., & Mouginot, J. (2023). Satellite-Derived Annual Glacier Surface Flow Velocity Products For The European Alps, 2015-2021. Data, .
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Rabatel, A., Ducasse, E., Ramseyer, V., & Millan, R. (2023). State And Fate Of Glaciers In The Val Veny (Mont- Blanc Range, Italy): Contribution Of Optical Satellite Products. Revue De Geographie Alpine-Journal Of Alpine Research, 1111(2).
Abstract: The Glaciers Of The Val Veny (Italian Side Of The Mont-Blanc Massif) Have Been The Site Of Numerous Field Observations During The Last Decades, In Particular For The Study Of Glacial Fluctuations Or Surface Processes Related To The Debris Cover. Here, We Propose To Examine How Satellite Observations Can Complement Field Measurements On The State And Fate Of The Val Veny Glaciers. Indeed, Satellite Products Obtained In A Quasi-Systematic Way Allow To Account Not Only For The Loss Of Surface And Volume, But Also For The Changes In Their Flow Velocities. The Overall Pattern We Document Is A Glacier Thinning And Slowdown Of The Ice Flow, With An Estimated Shrinkage Of 25% By 2050 And A Volume Loss Ranging Between 30 And 43% Depending On The Data Source Used For The Estimation Of The Initial Volume. In Such A Context, A Portion Of The Upper Reaches Of Brenva Glacier Shows An Unexpected Pattern Of Thickening And Increase In Ice Flow That Rises Questions On Its Origin. Finally, The Uncertainties In The Estimation Of Ice Thicknesses Remain Important And Have Repercussions On The Future Evolution Of The Glaciers And Their Contribution From A Hydrological Point Of View. By 2050, We Estimate That The Water Contribution Due To The Volume Loss Of Val Veny Glaciers Could Decrease By 40%.
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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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Reese, R., Garbe, J., Hill, E., Urruty, B., Naughten, K., Gagliardini, O., et al. (2023). The Stability Of Present-Day Antarctic Grounding Lines – Part 2: Onset Of Irreversible Retreat Of Amundsen Sea Glaciers Under Current Climate On Centennial Timescales Cannot Be Excluded. Cryosphere, 171(9), 3761–3783.
Abstract: Observations Of Ocean-Driven Grounding-Line Retreat In The Amundsen Sea Embayment In Antarctica Raise The Question Of An Imminent Collapse Of The West Antarctic Ice Sheet. Here We Analyse The Committed Evolution Of Antarctic Grounding Lines Under The Present-Day Climate. To This Aim, We First Calibrate A Sub-Shelf Melt Parameterization, Which Is Derived From An Ocean Box Model, With Observed And Modelled Melt Sensitivities To Ocean Temperature Changes, Making It Suitable For Present-Day Simulations And Future Sea Level Projections. Using The New Calibration, We Run An Ensemble Of Historical Simulations From 1850 To 2015 With A State-Of-The-Art Ice Sheet Model To Create Model Instances Of Possible Present-Day Ice Sheet Configurations. Then, We Extend The Simulations For Another 10 000 Years To Investigate Their Evolution Under Constant Present-Day Climate Forcing And Bathymetry. We Test For Reversibility Of Grounding-Line Movement In The Case That Large-Scale Retreat Occurs. In The Amundsen Sea Embayment We Find Irreversible Retreat Of The Thwaites Glacier For All Our Parameter Combinations And Irreversible Retreat Of The Pine Island Glacier For Some Admissible Parameter Combinations. Importantly, An Irreversible Collapse In The Amundsen Sea Embayment Sector Is Initiated At The Earliest Between 300 And 500 Years In Our Simulations And Is Not Inevitable Yet – As Also Shown In Our Companion Paper Part 1,. In Other Words, The Region Has Not Tipped Yet. With The Assumption Of Constant Present-Day Climate, The Collapse Evolves On Millennial Timescales, With A Maximum Rate Of 0.9 Mma-1 Sea-Level-Equivalent Ice Volume Loss. The Contribution To Sea Level By 2300 Is Limited To 8 Cm With A Maximum Rate Of 0.4 Mma-1 Sea-Level-Equivalent Ice Volume Loss. Furthermore, When Allowing Ice Shelves To Regrow To Their Present Geometry, We Find That Large-Scale Grounding-Line Retreat Into Marine Basins Upstream Of The Filchner-Ronne Ice Shelf And The Western Siple Coast Is Reversible. Other Grounding Lines Remain Close To Their Current Positions In All Configurations Under Present-Day Climate.
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Seroussi, H., Verjans, V., Nowicki, S., Payne, A., Goelzer, H., Lipscomb, W., et al. (2023). Insights Into The Vulnerability Of Antarctic Glaciers From The Ismip6 Ice Sheet Model Ensemble And Associated Uncertainty. Cryosphere, 171(121), 5197–5217.
Abstract: The Antarctic Ice Sheet Represents The Largest Source Of Uncertainty In Future Sea Level Rise Projections, With A Contribution To Sea Level By 2100 Ranging From – 5 To 43 Cm Of Sea Level Equivalent Under High Carbon Emission Scenarios Estimated By The Recent Ice Sheet Model Intercomparison For Cmip6 (Ismip6). Ismip6 Highlighted The Different Behaviors Of The East And West Antarctic Ice Sheets, As Well As The Possible Role Of Increased Surface Mass Balance In Offsetting The Dynamic Ice Loss In Response To Changing Oceanic Conditions In Ice Shelf Cavities. However, The Detailed Contribution Of Individual Glaciers, As Well As The Partitioning Of Uncertainty Associated With This Ensemble, Have Not Yet Been Investigated. Here, We Analyze The Ismip6 Results For High Carbon Emission Scenarios, Focusing On Key Glaciers Around The Antarctic Ice Sheet, And We Quantify Their Projected Dynamic Mass Loss, Defined Here As Mass Loss Through Increased Ice Discharge Into The Ocean In Response To Changing Oceanic Conditions. We Highlight Glaciers Contributing The Most To Sea Level Rise, As Well As Their Vulnerability To Changes In Oceanic Conditions. We Then Investigate The Different Sources Of Uncertainty And Their Relative Role In Projections, For The Entire Continent And For Key Individual Glaciers. We Show That, In Addition To Thwaites And Pine Island Glaciers In West Antarctica, Totten And Moscow University Glaciers In East Antarctica Present Comparable Future Dynamic Mass Loss And High Sensitivity To Ice Shelf Basal Melt. The Overall Uncertainty In Additional Dynamic Mass Loss In Response To Changing Oceanic Conditions, Compared To A Scenario With Constant Oceanic Conditions, Is Dominated By The Choice Of Ice Sheet Model, Accounting For 52 % Of The Total Uncertainty Of The Antarctic Dynamic Mass Loss In 2100. Its Relative Role For The Most Dynamic Glaciers Varies Between 14 % For Macayeal And Whillans Ice Streams And 56 % For Pine Island Glacier At The End Of The Century. The Uncertainty Associated With The Choice Of Climate Model Increases Over Time And Reaches 13 % Of The Uncertainty By 2100 For The Antarctic Ice Sheet But Varies Between 4 % For Thwaites Glacier And 53 % For Whillans Ice Stream. The Uncertainty Associated With The Ice-Climate Interaction, Which Captures Different Treatments Of Oceanic Forcings Such As The Choice Of Melt Parameterization, Its Calibration, And Simulated Ice Shelf Geometries, Accounts For 22 % Of The Uncertainty At The Ice Sheet Scale But Reaches 36 % And 39 % For Institute Ice Stream And Thwaites Glacier, Respectively, By 2100. Overall, This Study Helps Inform Future Research By Highlighting The Sectors Of The Ice Sheet Most Vulnerable To Oceanic Warming Over The 21St Century And By Quantifying The Main Sources Of Uncertainty.
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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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Trabattoni, A., Barruol, G., Dreo, R., & Boudraa, A. (2023). Ship Detection And Tracking From Single Ocean-Bottom Seismic And Hydroacoustic Stations. Journal Of The Acoustical Society Of America, 1531(1), 260–273.
Abstract: We Report In This Study How Ocean-Bottom Seismometers (Obs) Can Be Used As Passive Sonars To Automatically Detect, Localize, And Track Moving Acoustic Sources At The Ocean Surface. We Developed Single-Station Methods Based On Direction Of Arrival And On Multi-Path Interference Measurements Capable Of Handling Continuous Erratic Signals Emitted By Ships. Based On A Bayesian Mathematical Framework, We Developed An Azimuthal Detector And A Radial Detector And Combined Them Into A Fully Automatic Tracker. We Tested The Developed Algorithm On Seismic And Hydroacoustic Data Recorded In The Indian Ocean By An Obs Deployed At 4300 M Depth, 200 Km West Of La Reunion Island. We Quantified The Performances Using Archives Of Commercial-Vessel Trajectories In The Area Provided By The Automatic Identification System. Detectors Demonstrate Capabilities In The Detection Range Up To 100 Km From The Obs With Azimuthal Accuracies Of A Few Degrees And With Distance Accuracies Of A Few Hundred Of Meters. We Expect The Method To Be Easily Transposed To Any Other Kind Of Sources (Such As Marine Mammals).
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Umlauft, J., Johnson, C., Roux, P., Trugman, D., Lecointre, A., Walpersdorf, A., et al. (2023). Mapping Glacier Basal Sliding Applying Machine Learning. Journal Of Geophysical Research-Earth Surface, 1281(111).
Abstract: During The Resolve Project (“High-Resolution Imaging In Subsurface Geophysics: Development Of A Multi-Instrument Platform For Interdisciplinary Research”), Continuous Surface Displacement And Seismic Array Observations Were Obtained On Glacier D'Argentiere In The French Alps For 35 Days In May 2018. The Data Set Is Used To Perform A Detailed Study Of Targeted Processes Within The Highly Dynamic Cryospheric Environment. In Particular, The Physical Processes Controlling Glacial Basal Motion Are Poorly Understood And Remain Challenging To Observe Directly. Especially In The Alpine Region For Temperate Based Glaciers Where The Ice Rapidly Responds To Changing Climatic Conditions And Thus, Processes Are Strongly Intermittent In Time And Heterogeneous In Space. Spatially Dense Seismic And Global Positioning System (Gps) Measurements Are Analyzed Applying Machine Learning To Gain Insight Into The Processes Controlling Glacial Motions Of Glacier D'Argentiere. Using Multiple Bandpass-Filtered Copies Of The Continuous Seismic Waveforms, We Compute Energy-Based Features, Develop A Matched Field Beamforming Catalog And Include Meteorological Observations. Features Describing The Data Are Analyzed With A Gradient Boosting Decision Tree Model To Directly Estimate The Gps Displacements From The Seismic Noise. We Posit That Features Of The Seismic Noise Provide Direct Access To The Dominant Parameters That Drive Displacement On The Highly Variable And Unsteady Surface Of The Glacier. The Machine Learning Model Infers Daily Fluctuations And Longer Term Trends. The Results Show On-Ice Displacement Rates Are Strongly Modulated By Activity At The Base Of The Glacier. The Techniques Presented Provide A New Approach To Study Glacial Basal Sliding And Discover Its Full Complexity.
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Vincent, C., & Thibert, E. (2023). Brief Communication: Non-Linear Sensitivity Of Glacier Mass Balance To Climate Attested By Temperature-Index Models. Cryosphere, , 198911–199511.
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2022 |
Argueso, D., Di Luca, A., Jourdain, N., Romero, R., & Homar, V. (2022). Mechanisms For Extreme Precipitation Changes In A Tropical Archipelago. Journal Of Climate, 353(171), 5519–5536.
Abstract: The Maritime Continent Is One Of The Most Challenging Regions For Atmospheric Models. Processes That Modulate Deep Convection Are Poorly Represented In Models, Which Affects Their Ability To Simulate Precipitation Features Accurately. Thus, Future Projections Of Precipitation Over The Region Are Prone To Large Uncertainties. One Of The Key Players In Modeling Tropical Precipitation Is The Convective Representation, And Hence Convection-Permitting Experiments Have Contributed To Improve Aspects Of Precipitation In Models. This Improvement Creates Opportunities To Explore The Physical Processes That Govern Rainfall In The Maritime Continent, As Well As Their Role In A Warming Climate. Here, We Examine The Response To Climate Change Of Models With Explicit And Parameterized Convection And How That Reflects In Precipitation Changes. We Focus On The Intensification Of Spatial Contrasts As Precursors Of Changes In Mean And Extreme Precipitation In The Tropical Archipelago. Our Results Show That The Broad Picture Is Similar In Both Model Setups, Where Islands Will Undergo An Increase In Mean And Extreme Precipitation In A Warmer Climate And The Ocean Will See Less Rain. However, The Magnitude And Spatial Structure Of Such Changes, As Well As The Projection Of Rainfall Percentiles, Are Different Across Model Experiments. We Suggest That While The Primary Effect Of Climate Change Is Thermodynamical And It Is Similarly Reproduced By Both Model Configurations, Dynamical Effects Are Represented Quite Differently In Explicit And Parameterized Convection Experiments. In This Study, We Link Such Differences To Horizontal And Vertical Spatial Contrasts And How Convective Representations Translate Them Into Precipitation Changes.
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Autin, P., Sicart, J. E., Rabatel, A., Soruco, A., & Hock, R. (2022). Climate Controls On The Interseasonal And Interannual Variability Of The Surface Mass and Energy Balances of a Tropical Glacier (Zongo Glacier, Bolivia, 16 degrees S): New Insights From the Multi-Year Application of a Distributed Energy Balance Model. Journal Of Geophysical Research-Atmospheres, 1271(7).
Abstract: The application of a distributed energy balance model over nine years at an hourly time step to a 20 x 20 m grid cell over Glacier Zongo (Bolivia, 16 degrees S) enabled assessment of the climate factors that control the interseasonal and interannual variability of its surface mass balance. The model was validated by comparing the measured and simulated discharge at the outlet, albedo at the Automatic Weather Station, surface state and annual mass balance both glacier-wide and as a function of altitude. Analysis of the mean monthly energy fluxes highlighted the importance of the meteorological conditions over October and November on the variability of the annual surface mass balance. Two sensitivity analyses are presented, one of the distribution of precipitation over time which maintains a physical coherence between the different meteorological variables and one of the impact of prolonged periods of intense cloud radiative forcing on the surface mass balance. The distribution of precipitation events over time and their associated amounts are the main drivers of the interannual variability of the surface mass balance via an albedo feedback effect. Additionally, prolonged periods of negative cloud radiative forcing, specifically over the month of November, notably reduce the melt rate.
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Bakker, M., Legout, C., Gimbert, F., Nord, G., Boudevillain, B., & Freche, G. (2022). Seismic Modelling And Observations Of Rainfall. Journal Of Hydrology, 6106.
Abstract: Rainfall is a key driver of geomorphological processes ranging from impacting drops that lead to the small-scale dislodgement of soil particles to large-scale morphogenic floods and rainfall-induced hillslope processes. Although rainfall has been identified in seismic records, the associated power spectral density and its quantitative relation to the underlying physical processes have not yet been studied. Here, we analyze nearly 2 years of combined seismic and optical disdrometer measurements, where the latter enables the drop-based quantification of rainfall physical properties. Our measurements confirm the broadband observation of ground velocity power spectral density due to rainfall, allowing the seismic identification of rainfall at intensities as low as 1 mm/h. Seismic power, P, shows a power-law scaling with rainfall intensity, I, and kinetic energy, E: P proportional to I-2.1 and P proportional to E-1.6. The observed scaling relations are consistent between the three monitored sites although there are absolute differences in seismic power of about 1 order of magnitude, which are likely due to variability in landcover and subsurface seismic properties. With a physical model, we demonstrate that the observed power-law relations are set by an underlying linear relation between seismic power and rainfall impulse power, and that the associated exponent values of I and E are due to the covariance of the raindrop size distribution with the total number of drops. The largest raindrop fractions, whose relative contribution increases with rainfall intensity, dominate the seismic signal where, in our case, 90% of the seismic power is attributed to drops larger than 3 mm. Using our model, we estimate the contributing area of rainfall to seismic observations to be within a radial distance of -5-25 m. The spatially integrated nature of the seismic measurements and their sensitivity to large raindrops, which control the disaggregation and the mobilization of soil particles, make seismic records well-suited for the investigation of soil erosion processes. More generally, our work provides a basis for the temporally-resolved seismic quantification of rainfall that drives the dynamics of various hydro-geomorphological processes.
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Bakker, M., Legout, C., Gimbert, F., Nord, G., Boudevillain, B., & Freche, G. (2022). Seismic Modelling And Observations Of Rainfall. Journal Of Hydrology, 6106.
Abstract: Rainfall is a key driver of geomorphological processes ranging from impacting drops that lead to the small-scale dislodgement of soil particles to large-scale morphogenic floods and rainfall-induced hillslope processes. Although rainfall has been identified in seismic records, the associated power spectral density and its quantitative relation to the underlying physical processes have not yet been studied. Here, we analyze nearly 2 years of combined seismic and optical disdrometer measurements, where the latter enables the drop-based quantification of rainfall physical properties. Our measurements confirm the broadband observation of ground velocity power spectral density due to rainfall, allowing the seismic identification of rainfall at intensities as low as 1 mm/h. Seismic power, P, shows a power-law scaling with rainfall intensity, I, and kinetic energy, E: P proportional to I-2.1 and P proportional to E-1.6. The observed scaling relations are consistent between the three monitored sites although there are absolute differences in seismic power of about 1 order of magnitude, which are likely due to variability in landcover and subsurface seismic properties. With a physical model, we demonstrate that the observed power-law relations are set by an underlying linear relation between seismic power and rainfall impulse power, and that the associated exponent values of I and E are due to the covariance of the raindrop size distribution with the total number of drops. The largest raindrop fractions, whose relative contribution increases with rainfall intensity, dominate the seismic signal where, in our case, 90% of the seismic power is attributed to drops larger than 3 mm. Using our model, we estimate the contributing area of rainfall to seismic observations to be within a radial distance of -5-25 m. The spatially integrated nature of the seismic measurements and their sensitivity to large raindrops, which control the disaggregation and the mobilization of soil particles, make seismic records well-suited for the investigation of soil erosion processes. More generally, our work provides a basis for the temporally-resolved seismic quantification of rainfall that drives the dynamics of various hydro-geomorphological processes.
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Basantes-Serrano, R., Rabatel, A., Francou, B., Vincent, C., Soruco, A., Condom, T., et al. (2022). New Insights Into The Decadal Variability In Glacier Volume Of A Tropical Ice Cap, Antisana (0 Degrees 29 ' S, 78 Degrees 09 ' W), Explained By The Morpho-Topographic And Climatic Context. Cryosphere, 161(111), 4659–4677.
Abstract: We Present A Comprehensive Study Of The Evolution Of The Glaciers On The Antisana Ice Cap (Tropical Andes) Over The Period 1956-2016. Based On Geodetic Observations Of Aerial Photographs And High-Resolution Satellite Images, We Explore The Effects Of Morpho-Topographic And Climate Variables On Glacier Volumes. Contrasting Behaviour Was Observed Over The Whole Period, With Two Periods Of Strong Mass Loss, 1956-1964 (-0.72 M W.E. Yr(-1)) And 1979-1997 (-0.82 M W.E. Yr(-1)), And Two Periods With Slight Mass Loss, 1965-1978 (0.10 M W.E. Yr(-1)) And 1998-2016 (-0.26 M W.E. Yr(-1)). There Was A 42 % Reduction In The Total Surface Area Of The Ice Cap. Individually, Glacier Responses Were Modulated By Morpho-Topographic Variables (E.G. Maximum And Median Altitude And Surface Area), Particularly In The Case Of The Small Tongues Located At Low Elevations (Glacier 1, 5 And 16) Which Have Been Undergoing Accelerated Disintegration Since The 1990S And Will Likely Disappear In The Coming Years. Moreover, Thanks To The Availability Of Aerial Data, A Surging Event Was Detected On The Antisana Glacier 8 (G8) In The 2009-2011 Period; Such An Event Is Extremely Rare In This Region And Deserves A Dedicated Study. Despite The Effect Of The Complex Topography, Glaciers Have Reacted In Agreement With Changes In Climate Forcing, With A Stepwise Transition Towards Warmer And Alternating Wet-Dry Conditions Since The Mid-1970S. Long-Term Decadal Variability Is Consistent With The Warm-Cold Conditions Observed In The Pacific Ocean Represented By The Southern Oscillation Index.
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Becquet, J., Lamouroux, N., Condom, T., Gouttevin, I., Forcellini, M., Launay, B., et al. (2022). Macroinvertebrate Distribution Associated With Environmental Variables In Alpine Streams. Freshwater Biology, .
Abstract: Ongoing Hydrological Alterations Due To Climate Change And Anthropogenic Uses Of Water Have Major Implications For Freshwater Biodiversity. Quantifying The Relative Effects Of Environmental Variables On Macroinvertebrates Is Required To Predict Biological Responses To Hydrological Alterations. To Date, No Study Simultaneously Examined The Effects Of Physico-Chemistry, Hydraulics, And Hydrology On The Distribution Of Alpine Macroinvertebrate Communities And Taxa. In This Study, We Aimed To Quantify The Relative Correlation Between These Environmental Variables And Macroinvertebrate Community Composition And Structure. We Sampled Macroinvertebrates At 66 Stream Sites Located In Three Catchments In The French Alps. We Characterised The Proximate Habitat At Each Site Using 11 Variables Describing Measured Physico-Chemistry And Hydraulics, And Simulation-Based Hydrology. We Described Relationships Between Community Structure And The Environment Using A Co-Inertia Analysis And Modelled Individual Taxa Abundance With Generalised Linear Mixed Models. The Co-Inertia Revealed A Significant Co-Structure Between The Environmental And Macroinvertebrate Matrices. Glacier-Influenced Sites With High Turbidity And Summer Flow Exhibited Similar Community Composition With Low Total Abundance. Sources At High Altitude And Sites With Low Glacial Influence, Exhibiting High Summer Flow And Flow Velocity, Were Dominated By Diamesinae, Rhithrogena Spp., Dictyogenus Spp., And Baetis Alpinus. Streams Fed By Rainfall/Snowmelt And Valley Sources, Associated With Higher Temperature, Conductivity, And Monthly Discharge Variability Were Characterised By Higher Richness And Abundances. Models Indicated That The Three Types Of Proximate Habitat Variables Significantly Contributed To The Macroinvertebrate Distribution. Turbidity Was Strongly Negatively Associated With Macroinvertebrate Abundances. Increasing Flow Velocity And Summer Flow Had Significant (Mainly Negative) Effect In 43% Of Models. The Co-Structure Between Communities And Proximate Habitat Variables Was Shared By The Three Catchments. For Most Individual Taxa, Catchment Identity Did Not Influence Abundance Models And Cross-Validations Indicated Transferable Effects Of Proximate Habitat Variables Among Alpine Catchments. Our Results Can Be Used To Infer Responses Of Alpine Macroinvertebrates To Multivariate Environmental Changes. Understanding The Relationships Between Macroinvertebrates And Environmental Variables Help To Predict How Communities And Taxa Will Be Affected By Habitat Alterations Due To Ongoing Hydrological Changes And Resulting Physico-Chemical Conditions.
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Beraud, L., Cusicanqui, D., Rabatel, A., Brun, F., Vincent, C., & Six, D. (2022). Glacier-Wide Seasonal And Annual Geodetic Mass Balances From Pleiades Stereo Images: Application To The Glacier D'Argentiere, French Alps. Journal Of Glaciology, .
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Bernard, A., Hagenmuller, P., Montagnat, M., & Chambon, G. (2022). Disentangling Creep And Isothermal Metamorphism During Snow Settlement With X-Ray Tomography. Journal Of Glaciology, .
Abstract: Once Fallen, Snow Settles Due To The Combined Effects Of Metamorphism And Deformation Of The Ice Matrix Under Gravity. To Understand How These Coupled Processes Affect Snow Evolution, We Performed Oedometric Compression Tests And Continuously Monitored The Snow Microstructure.With X-Ray Tomography. Centimetric Samples With An Initial Density Between 200 And 300 Kgm(-3) Were Followed During An Initial Sintering Phase And Under Two Different Loads Of 2.1 And 4.7 Kpa At -8 Degrees C For Similar To 1 Week. The Microstructure Captured At A Voxel Size Of 8.5 Mu M Was Characterized By Density, Specific Surface Area (Ssa) And Two Metrics Related To Bond Network, Namely The Euler Characteristic And The Minimum Cut Surface. Load-Induced Creep Of The Ice Matrix Was Observed Only For Sufficiently Low Values Of Initial Density (<290 Kgm(-3) In Our Tests), And Was Shown To Be Associated To A Significant Increase Of The Number Of Bonds. Application Of The Load, However, Did Not Affect The Individual Bond Size Nor The Ssa, Which Appeared To Be Mainly Controlled By Isothermal Metamorphism. The Uniaxial Compression Did Not Induce Any Creation Of Anisotropy On The Microstructural Characteristics. Overall, Our Results Show That, For The Considered Conditions, The Deformation Of The Ice Matrix Mainly Leads To A Reduction Of The Pore Space And An Increase Of The Coordination Number, While Metamorphism Mainly Affects The Grain And Bond Sizes.
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Bolibar, J., Rabatel, A., Gouttevin, I., Zekollari, H., & Galiez, C. (2022). Nonlinear sensitivity of glacier mass balance to future climate change unveiled by deep learning. Nature Communications, 131(1).
Abstract: Glaciers and ice caps are experiencing strong mass losses worldwide, challenging water availability, hydropower generation, and ecosystems. Here, we perform the first-ever glacier evolution projections based on deep learning by modelling the 21st century glacier evolution in the French Alps. By the end of the century, we predict a glacier volume loss between 75 and 88%. Deep learning captures a nonlinear response of glaciers to air temperature and precipitation, improving the representation of extreme mass balance rates compared to linear statistical and temperature-index models. Our results confirm an over-sensitivity of temperature-index models, often used by large-scale studies, to future warming. We argue that such models can be suitable for steep mountain glaciers. However, glacier projections under low-emission scenarios and the behaviour of flatter glaciers and ice caps are likely to be biased by mass balance models with linear sensitivities, introducing long-term biases in sea-level rise and water resources projections. Deep learning unveils a nonlinear sensitivity of glacier mass changes to future climate warming, with important implications for water resources and sea-level rise coming from glaciers and particularly ice caps.
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Burgard, C., Jourdain, N., Reese, R., Jenkins, A., & Mathiot, P. (2022). An Assessment Of Basal Melt Parameterisations For Antarctic Ice Shelves. Cryosphere, 161(121), 4931–4975.
Abstract: Ocean-Induced Ice-Shelf Melt Is One Of The Largest Uncertainty Factors In The Antarctic Contribution To Future Sea-Level Rise. Several Parameterisations Exist, Linking Oceanic Properties In Front Of The Ice Shelf To Melt At The Base Of The Ice Shelf, To Force Ice-Sheet Models. Here, We Assess The Potential Of A Range Of These Existing Basal Melt Parameterisations To Emulate Basal Melt Rates Simulated By A Cavity-Resolving Ocean Model On The Circum-Antarctic Scale. To Do So, We Perform Two Cross-Validations, Over Time And Over Ice Shelves Respectively, And Re-Tune The Parameterisations In A Perfect-Model Approach, To Compare The Melt Rates Produced By The Newly Tuned Parameterisations To The Melt Rates Simulated By The Ocean Model. We Find That The Quadratic Dependence Of Melt To Thermal Forcing Without Dependency On The Individual Ice-Shelf Slope And The Plume Parameterisation Yield The Best Compromise, In Terms Of Integrated Shelf Melt And Spatial Patterns. The Box Parameterisation, Which Separates The Sub-Shelf Circulation Into Boxes, The Picop Parameterisation, Which Combines The Box And Plume Parameterisation, And Quadratic Parameterisations With Dependency On The Ice Slope Yield Basal Melt Rates Further From The Model Reference. The Linear Parameterisation Cannot Be Recommended As The Resulting Integrated Ice-Shelf Melt Is Comparably Furthest From The Reference. When Using Offshore Hydrographic Input Fields In Comparison To Properties On The Continental Shelf, All Parameterisations Perform Worse; However, The Box And The Slope-Dependent Quadratic Parameterisations Yield The Comparably Best Results. In Addition To The New Tuning, We Provide Uncertainty Estimates For The Tuned Parameters.
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Calonne, N., Burr, A., Philip, A., Flin, F., & Geindreau, C. (2022). Effective coefficient of diffusion and permeability of firn at Dome C and Lock In, Antarctica, and of various snow types – estimates over the 100-850 kg m(-3) density range. Cryosphere, 161(3), 967–980.
Abstract: Modeling air transport through the entire firn column of polar ice sheets is needed to interpret climate archives. To this end, different regressions have been proposed in the past to estimate the effective coefficient of diffusion and permeability of firn. These regressions are often valid for specific depth or porosity ranges only. Also, they constitute a source of uncertainty as evaluations have been limited by the lack of reliable data of firn transport properties. To contribute with a new dataset, this study presents the effective coefficient of diffusion and the permeability at Dome C and Lock In, Antarctica, from the near-surface to the close-off (23 to 133 m depth). Also, microstructure is characterized based on density, specific surface area, closed porosity ratio, connectivity index, and structural anisotropy through the correlation lengths. All properties were estimated based on pore-scale computations from 3D tomographic images of firn samples. The normalized diffusion coefficient ranges from 1.9 x 10(-1) to 8.3 x 10(-5) , and permeability ranges from 1.2 x 10(-9) to 1.1 x 10(-12) m(2), for densities between 565 and 888 kg m(-3). No or little anisotropy is reported. Next, we investigate the relationship of the transport properties with density over the firn density range (550-850 kg m(-3)), as well as over the entire density range encountered in the ice sheets (100-850 kg m(-3)), by extending the datasets with transport properties of alpine and artificial snow from previous studies. Classical analytical models and regressions from literature are evaluated against the estimates from pore-scale simulations. For firn, good agreements are found for permeability and the diffusion coefficient with two existing regressions of the literature based on open porosity despite the rather different site conditions (Greenland). Over the entire 100-850 kg m(-3) density range, permeability is accurately reproduced by the Carman-Kozeny and self-consistent (spherical bi-composite) models when expressed in terms of a rescaled porosity, phi(res) = (phi – phi(off)) – (1 – phi(off)), to account for pore clo- sure, where q5off is the close-off porosity. For the normalized diffusion coefficient, none of the evaluated formulas were satisfactory, so we propose a new regression based on the rescaled porosity that reads D / D-air = (phi(res))(1.61).
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Charrier, L., Yan, Y., Trouve, E., Koeniguer, E., Mouginot, J., & Millan, R. (2022). Fusion Of Multitemporal Multisensor Velocities Using Temporal Closure Of Fractions Of Displacements. Ieee Geoscience And Remote Sensing Letters, 191.
Abstract: Numerous Glacier Velocity Observations, Derived From Spaceborne Imagery, Are Available Online, But It Remains Difficult To Analyze Them Because They Are Measured With Different Temporal Baselines, By Various Sensors. In This Study, We Propose A Novel Formulation Of The Temporal Closure To Fuse Multitemporal Multisensor Velocity Observations Without Prior Information On The Displacement Behavior And The Data Uncertainty. We Establish A System Of Linear Equations Between Combinations Of Displacement Observations And Fractions Of Estimated Displacements. The Proposed Approach Provides A Velocity Time-Series With A Regular And Optimal Temporal Sampling, The Latter Representing A Compromise Between The Temporal Resolution And The Signal-To-Noise Ratio. The Proposed Approach Is First Evaluated On Synthetic Datasets And Second On Sentinel-2 And Venus Velocity Observations Over The Fox Glacier In New Zealand. The Results Show The Intra-Annual Variability Of Fox Glacier Surface Velocity With A Reduced Uncertainty And Complete Temporal Coverage.
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Cheng, G., Morlighem, M., Mouginot, J., & Cheng, D. (2022). Helheim Glacier's Terminus Position Controls Its Seasonal and Inter-Annual Ice Flow Variability. Geophysical Research Letters, 494(5).
Abstract: Over the past decade, one of the largest contributors to total ice discharge across the Greenland ice sheet, Helheim Glacier, has experienced large fluctuations in ice velocity. In this study, we simulate the dynamics of Helheim, from 2007 to 2020, using the Ice-sheet and Sea-level System Model to identify the drivers of these large changes in ice discharge. By quantifying the impact of individual external forcing and model parameters on Helheim's modeled velocity, we find that the position of the calving front alone explains the dynamic variability of the glacier, as it has a direct and large impact on Helheim's ice velocity. The seasonal to inter-annual variability of Helheim Glacier is, however, relatively insensitive to the choice of friction law or ice rheology factor. This study shows that more research on calving dynamics and ice-ocean interactions is required to project the future of this sector of Greenland.
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Chmiel, M., Godano, M., Piantini, M., Brigode, P., Gimbert, F., Bakker, M., et al. (2022). Brief Communication: Seismological Analysis Of Flood Dynamics And hydrologically triggered earthquake swarms associated with Storm Alex. Natural Hazards And Earth System Sciences, 222(5), 1541–1558.
Abstract: On 2 October 2020, the Maritime Alps in southern France were struck by the devastating Storm Alex, which caused locally more than 600 mm of rain in less than 24 h. The extreme rainfall and flooding destroyed regional rain and stream gauges. That hinders our understanding of the spatial and temporal dynamics of rainfall-runoff processes during the storm. Here, we show that seismological observations from permanent seismic stations constrain these processes at a catchment scale. The analysis of seismic power, peak frequency, and the back azimuth provides us with the timing and velocity of the propagation of flash-flood waves associated with bedload-dominated phases of the flood on the Vesubie River. Moreover, the combined short-term average to long-term average ratio and template-matching earthquake detection reveal that 114 local earthquakes between local magnitude M-L = -0.5 and M-L = 2 were triggered by the hydrological loading and/or the resulting in situ underground pore pressure increase. This study shows the impact of Storm Alex on the Earth's surface and deep-layer processes and paves the way for future works that can reveal further details of these processes.
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Collow, A. B. M., Shields, C. A., Guan, B., Kim, S., Lora, J. M., McClenny, E. E., et al. (2022). An Overview Of Artmip'S Tier 2 Reanalysis Intercomparison: Uncertainty in the Detection of Atmospheric Rivers and Their Associated Precipitation. Journal Of Geophysical Research-Atmospheres, 1271(8).
Abstract: Atmospheric rivers, or long but narrow regions of enhanced water vapor transport, are an important component of the hydrologic cycle as they are responsible for much of the poleward transport of water vapor and result in precipitation, sometimes extreme in intensity. Despite their importance, much uncertainty remains in the detection of atmospheric rivers in large datasets such as reanalyses and century scale climate simulations. To understand this uncertainty, the Atmospheric River Tracking Method Intercomparison Project (ARTMIP) developed tiered experiments, including the Tier 2 Reanalysis Intercomparison that is presented here. Eleven detection algorithms submitted hourly tags--binary fields indicating the presence or absence of atmospheric rivers--of detected atmospheric rivers in the Modern Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) and European Centre for Medium-Range Weather Forecasts' Reanalysis Version 5 (ERA5) as well as six-hourly tags in the Japanese 55-year Reanalysis (JRA-55). Due to a higher climatological mean for integrated water vapor transport in MERRA-2, atmospheric rivers were detected more frequently relative to the other two reanalyses, particularly in algorithms that use a fixed threshold for water vapor transport. The finer horizontal resolution of ERA5 resulted in narrower atmospheric rivers and an ability to detect atmospheric rivers along resolved coastlines. The fraction of hemispheric area covered by ARs varies throughout the year in all three reanalyses, with different atmospheric river detection tools having different seasonal cycles.
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Crotti, I., Quiquet, A., Landais, A., Stenni, B., Wilson, D., Severi, M., et al. (2022). Wilkes Subglacial Basin Ice Sheet Response To Southern Ocean Warming During Late Pleistocene Interglacials. Nature Communications, 131(1).
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Dofal, A., Michon, L., Fontaine, F., Rindraharisaona, E., Barruol, G., & Tkalcic, H. (2022). Imaging The Lithospheric Structure And Plumbing System Below Themayotte Volcanic Zone. Comptes Rendus Geoscience, 3543, 47–64.
Abstract: Teleseismic Receiver-Functions And Rayleigh-Wave Dispersion Curves Are Jointly Inverted For Quantifying S-Wave Velocity Profiles Beneath The Active Volcanic Zone Off Mayotte. We Show That The Lithosphere In The East-Northeast Quadrant Is Composed Of Fourmain Layers, Interpreted As The Volcanic Edifice, The Crust With Underplating, The Lithospheric Mantle, And The Asthenosphere, The Latter Two Presenting A Main Low-Velocity Zone. The Depths Of The Old (10-11 Km) And New Moho (28-31 Km) Coincide With The Two Magma Reservoirs Evidenced By Recent Seismological And Petrological Methods. We Propose That The Main Magma Reservoir Composed Of Mush With An Increasing Amount Of Liquid Extends Down To 54 Km Depth. This Magma Storage Develops From A Rheological Contrast Between The Ductile Lower And Brittle Upper Lithospheric Mantle And Accounts For Most Of The Volcanic Eruptionrelated Seismicity. Finally, The Abnormally Small Thickness Of The Lithosphericmantle (33 Km) Is Likely A Result Of A Thermal Thinning Since The Onset Of Cenozoic Magmatism.
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Durand, G., van den Broeke, M. R., Le Cozannet, G., Edwards, T. L., Holland, P. R., Jourdain, N. C., et al. (2022). Sea-Level Rise: From Global Perspectives to Local Services. Frontiers In Marine Science, 8.
Abstract: Coastal areas are highly diverse, ecologically rich, regions of key socio-economic activity, and are particularly sensitive to sea-level change. Over most of the 20th century, global mean sea level has risen mainly due to warming and subsequent expansion of the upper ocean layers as well as the melting of glaciers and ice caps. Over the last three decades, increased mass loss of the Greenland and Antarctic ice sheets has also started to contribute significantly to contemporary sea-level rise. The future mass loss of the two ice sheets, which combined represent a sea-level rise potential of similar to 65 m, constitutes the main source of uncertainty in long-term (centennial to millennial) sea-level rise projections. Improved knowledge of the magnitude and rate of future sea-level change is therefore of utmost importance. Moreover, sea level does not change uniformly across the globe and can differ greatly at both regional and local scales. The most appropriate and feasible sea level mitigation and adaptation measures in coastal regions strongly depend on local land use and associated risk aversion. Here, we advocate that addressing the problem of future sea-level rise and its impacts requires (i) bringing together a transdisciplinary scientific community, from climate and cryospheric scientists to coastal impact specialists, and (ii) interacting closely and iteratively with users and local stakeholders to co-design and co-build coastal climate services, including addressing the high-end risks.
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Ershadi, M. R., Drews, R., Martin, C., Eisen, O., Ritz, C., Corr, H., et al. (2022). Polarimetric Radar Reveals The Spatial Distribution Of Ice Fabric At domes and divides in East Antarctica. Cryosphere, 161(5), 1719–1739.
Abstract: Ice crystals are mechanically and dielectrically anisotropic. They progressively align under cumulative deformation, forming an ice-crystal-orientation fabric that, in turn, impacts ice deformation. However, almost all the observations of ice fabric are from ice core analysis, and its influence on the ice flow is unclear. Here, we present a non-linear inverse approach to process co- and cross-polarized phase-sensitive radar data. We estimate the continuous depth profile of georeferenced ice fabric orientation along with the reflection ratio and horizontal anisotropy of the ice column. Our method approximates the complete second-order orientation tensor and all the ice fabric eigenvalues. As a result, we infer the vertical ice fabric anisotropy, which is an essential factor to better understand ice deformation using anisotropic ice flow models. The approach is validated at two Antarctic ice core sites (EPICA (European Project for Ice Coring in Antarctica) Dome C and EPICA Dronning Maud Land) in contrasting flow regimes. Spatial variability in ice fabric characteristics in the dome-to-flank transition near Dome C is quantified with 20 more sites located along with a 36 km long cross-section. Local horizontal anisotropy increases under the dome summit and decreases away from the dome summit We suggest that this is a consequence of the nonlinear rheology of ice, also known as the Raymond effect. On larger spatial scales, horizontal anisotropy increases with increasing distance from the dome. At most of the sites, the main driver of ice fabric evolution is vertical compression, yet our data show that the horizontal distribution of the ice fabric is consistent with the present horizontal flow. This method uses polarimetric-radar data, which are suitable for profiling radar applications and are able to constrain ice fabric distribution on a spatial scale comparable to ice flow observations and models.
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Gilbert, A., Gimbert, F., Thogersen, K., Schuler, T. V., & Kaab, A. (2022). A Consistent Framework For Coupling Basal Friction With Subglacial Hydrology on Hard-Bedded Glaciers. Geophysical Research Letters, 494(131).
Abstract: Below hard-bedded glaciers, both basal friction and distributed subglacial drainage are thought to be controlled by a network of cavities. Previous coupled hydro-mechanical models, however, describe cavity-driven friction and hydraulic transmissivity independently, resulting in a physically inconsistent cavity evolution between the two components of the models. Here, we overcome this issue by describing the hydro-mechanical system using a common cavity-evolution description, that governs both transient friction and hydraulic transmissivity. We show that our coupling approach is superior to previous formulations in explaining a unique observation record of glacier sliding speed from the French Alps. We find that, at multi-day to multi-decadal timescales, sliding speed can be expressed as a direct function of basal shear stress and water discharge, without accounting for water pressure, which simply adjusts to maintain the cavitation ratio needed to accommodate the water supply.
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Grima, C., Mouginot, J., Kofman, W., Herique, A., & Beck, P. (2022). The Basal Detectability of an Ice-Covered Mars by MARSIS. Geophysical Research Letters, 494(2).
Abstract: The detection of anomalously strong relative basal reflectivity beneath the Martian South Polar Layered Deposits (SPLD) from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) has led to hypotheses suggesting the presence of basal materials such as liquid water. Here, we propose a forward approach to assess whether such a high signal could be produced by a Martian terrain currently exposed at the surface without liquid water. We convert existing MARSIS surface reflectivity measurements into a basal reflectivity as if it were overlaid by an SPLD-like ice deposit. 0.3%-2% of the surface could produce basal reflections of magnitude similar to the SPLD measurements in the assumption of a 10% impure ice. An ice loss tangent > $ > $0.01 is required to prevent any of the current Martian surface from producing a bright SPLD-like basal reflection. The detected bright terrains are gathered within volcanic constructs of diverse geologic epoch.
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Huot, P. V., Kittel, C., Fichefet, T., Jourdain, N. C., & Fettweis, X. (2022). Effects of ocean mesoscale eddies on atmosphere-sea ice-ocean interactions off Adelie Land, East Antarctica. Climate Dynamics, .
Abstract: Heat and momentum exchanges at the Southern Ocean surface are crucial for the Earth's Climate, but the importance of the small-scale spatial variability of these surface fluxes is poorly understood. Here, we explore how small-scale heterogeneities of the surface conditions due in particular to ocean eddies affect the atmosphere-sea ice-ocean interactions off Adelie Land, in East Antarctica. To this end, we use a high-resolution regional atmosphere-sea ice-ocean coupled model based on the NEMO-LIM and MAR models. We explore how the atmosphere responds to small-scale heterogeneity of the ocean or sea ice surface conditions, how eddies affect the sea ice and atmosphere, and how the eddy-driven surface fluxes impact the heat, freshwater, and momentum budget of the ocean. The atmosphere is found to be more sensitive to small-scale surface temperature gradients above the ice-covered than above the ice-free ocean. Sea ice concentration is found to be weaker above anticyclonic than cyclonic eddies due to increased sea ice melting or freezing (0.8 cm/day) partly compensated by sea ice convergence or divergence. The imprint of ice-free eddies on the atmosphere is weak, but in the presence of sea ice, air warming (+ 0.3 degrees C) and wind intensification (+ 0.1 m/s) are found above anticyclonic eddies, while cyclonic eddies have the opposite effects. Removing the interactions of eddies with the sea ice or atmosphere does not affect the total sea ice volume, but increases the ocean kinetic energy by 8% and weakens northward advection of sea ice, leading to a 15% decrease in freshwater flux north of 62.5 degrees S and weaker ocean restratification.
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Jomelli, V., Swingedouw, D., Vuille, M., Favier, V., Goehring, B., Shakun, J., et al. (2022). In-phase millennial-scale glacier changes in the tropics and North Atlantic regions during the Holocene. Nature Communications, 131(1).
Abstract: Glaciers showed a similar evolution in Greenland, Europe, the US and the tropical Andes during the Holocene. The authors propose the Atlantic Meridional Ocean Overturning Circulation as a key driver of this trend. Based on new and published cosmic-ray exposure chronologies, we show that glacier extent in the tropical Andes and the north Atlantic regions (TANAR) varied in-phase on millennial timescales during the Holocene, distinct from other regions. Glaciers experienced an early Holocene maximum extent, followed by a strong mid-Holocene retreat and a re-advance in the late Holocene. We further explore the potential forcing of TANAR glacier variations using transient climate simulations. Since the Atlantic Meridional Overturning Circulation (AMOC) evolution is poorly represented in these transient simulations, we develop a semi-empirical model to estimate the “AMOC-corrected” temperature and precipitation footprint at regional scales. We show that variations in the AMOC strength during the Holocene are consistent with the observed glacier changes. Our findings highlight the need to better constrain past AMOC behavior, as it may be an important driver of TANAR glacier variations during the Holocene, superimposed on other forcing mechanisms.
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Jourdain, N., Mathiot, P., Burgard, C., Caillet, J., & Kittel, C. (2022). Ice Shelf Basal Melt Rates In The Amundsen Sea At The End Of The 21St Century. Geophysical Research Letters, 494(222).
Abstract: Antarctic Ice Sheet Projections Show The Highest Sensitivity To Increased Basal Melting In The Amundsen Sea. However, Little Is Known About The Processes That Control Future Increase In Melt Rates. We Build An Ensemble Of Three Ocean-Sea-Ice-Ice-Shelf Simulations For Both The Recent Decades And The Late 21St Century, Constrained By Regional Atmosphere Simulations And The Multi-Model Mean Climate Change Of The Fifth Climate Model Intercomparison Project Under The Rcp8.5 Scenario. The Ice-Shelf Melt Rates Are Typically Multiplied By 1.4-2.2 From Present Day To Future, For A Total Basal Mass Loss Increased By 346 Gt Yr(-1) On Average. This Is Equally Explained By Advection Of Warmer Water From Remote Locations And Regional Changes In Ekman Downwelling And In The Ice-Shelf Melt-Induced Circulation, While Increased Iceberg Melt Plays No Significant Role. Our Simulations Suggest That High-End Melt Projections Previously Used To Constrain Recent Sea Level Projections May Have Been Significantly Overestimated.
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Junquas, C., Heredia, M. B., Condom, T., Ruiz-Hernandez, J. C., Campozano, L., Dudhia, J., et al. (2022). Regional climate modeling of the diurnal cycle of precipitation and associated atmospheric circulation patterns over an Andean glacier region (Antisana, Ecuador). Climate Dynamics, .
Abstract: A multi-experiment ensemble is performed using the WRF (Weather Research and Forecasting) model at high spatial resolution (1 km) over the Antisana glacier region (Ecuador), during the year 2005. Our goal is to identify the best model configurations to simulate atmospheric processes at diurnal and seasonal scales. The model is able to reproduce the complex zonal gradient of precipitation between the wet Amazon and the drier inter-Andean region. The main precipitation biases are (i) an overestimation in the afternoon (up to 6 mm/day) in the Antisana region related to local surface circulation patterns and (ii) a nighttime overestimation (up to 20 mm/day) in the Andes-Amazon transition zone associated with the regional circulation. Changing the microphysics scheme and/or the cumulus scheme primarily affect nighttime processes, while changing the topography forcing and activating slope radiation and shading options mostly affects afternoon processes. An adequate choice of the model configuration allows a correct representation of the diurnal cycle of precipitation, and in particular: (i) the mid-level easterly regional flow, (ii) the local moisture transport along and across the valleys, and (iii) the orographic mountain waves on the Antisana summit. For this specific area and year, the best configuration retained defined as “dSRTM_LRad” shows nighttime (daytime) precipitation biases smaller than 2 mm/day (3 mm/day); it is based on non-smoothed SRTM digital elevation model (dSRTM), Lin Purdue microphysics (L), and slope and shading radiation options (Rad). This 1-km resolution configuration requires the activation of the cumulus scheme, that improves the regional nighttime convection induced by the easterly regional flow on the Amazon-Andes transition region. It allows also a realistic strengthening of the daytime upward moisture transport. This study demonstrates that in the Antisana region, 1 km is a resolution still too coarse to deactivate cumulus schemes for a correct representation of cloud convection.
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Kenny, G., Hyde, W., Storey, M., Garde, A., Whitehouse, M., Beck, P., et al. (2022). Ar-40/Ar-39 And Zircon U-Pb Analyses Date The Hiawatha Impact Structure, Northwest Greenland, To The Late Paleocene. Meteoritics & Planetary Science, 575.
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Kenny, G. G., Hyde, W. R., Storey, M., Garde, A. A., Whitehouse, M. J., Beck, P., et al. (2022). A Late Paleocene age for Greenland's Hiawatha impact structure. Science Advances, 8(101).
Abstract: The similar to 31-km-wide Hiawatha structure, located beneath Hiawatha Glacier in northwestern Greenland, has been proposed as an impact structure that may have formed after the Pleistocene inception of the Greenland Ice Sheet. To date the structure, we conducted Ar-40/Ar-39 analyses on glaciofluvial sand and U-Pb analyses on zircon separated from glaciofluvial pebbles of impact melt rock, all sampled immediately downstream of Hiawatha Glacier. Unshocked zircon in the impact melt rocks dates to similar to 1915 million years (Ma), consistent with felsic intrusions found in local bedrock. The Ar-40/Ar-39 data indicate Late Paleocene resetting and shocked zircon dates to 57.99 +/- 0.54 Ma, which we interpret as the impact age. Consequently, the Hiawatha impact structure far predates Pleistocene glaciation and is unrelated to either the Paleocene-Eocene Thermal Maximum or flood basalt volcanism in east Greenland. However, it was contemporaneous with the Paleocene Carbon Isotope Maximum, although the impact's exact paleoenvironmental and climatic significance awaits further investigation.
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Khan, S., Choi, Y., Morlighem, M., Rignot, E., Helm, V., Humbert, A., et al. (2022). Extensive Inland Thinning And Speed-Up Of Northeast Greenland Ice Stream. Nature, 6116(79377), 727–+.
Abstract: Over The Past Two Decades, Ice Loss From The Greenland Ice Sheet (Gris) Has Increased Owing To Enhanced Surface Melting And Ice Discharge To The Ocean(1-5). Whether Continuing Increased Ice Loss Will Accelerate Further, And By How Much, Remains Contentious(6-9). A Main Contributor To Future Ice Loss Is The Northeast Greenland Ice Stream (Negis), Greenland'S Largest Basin And A Prominent Feature Of Fast-Flowing Ice That Reaches The Interior Of The Gris(10-)(12). Owing To Its Topographic Setting, This Sector Is Vulnerable To Rapid Retreat, Leading To Unstable Conditions Similar To Those In The Marine-Based Setting Of Ice Streams In Antarctica(13-20). Here We Show That Extensive Speed-Up And Thinning Triggered By Frontal Changes In 2012 Have Already Propagated More Than 200 Km Inland. We Use Unique Global Navigation Satellite System (Gnss) Observations, Combined With Surface Elevation Changes And Surface Speeds Obtained From Satellite Data, To Select The Correct Basal Conditions To Be Used In Ice Flow Numerical Models, Which We Then Use For Future Simulations. Our Model Results Indicate That This Marine-Based Sector Alone Will Contribute 13.5-15.5 Mm Sea-Level Rise By 2100 (Equivalent To The Contribution Of The Entire Ice Sheet Over The Past 50 Years) And Will Cause Precipitous Changes In The Coming Century. This Study Shows That Measurements Of Subtle Changes In The Ice Speed And Elevation Inland Help To Constrain Numerical Models Of The Future Mass Balance And Higher-End Projections Show Better Agreement With Observations.
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Kittel, C., Amory, C., Hofer, S., Agosta, C., Jourdain, N. C., Gilbert, E., et al. (2022). Clouds Drive Differences In Future Surface Melt Over The Antarctic Ice shelves. Cryosphere, 161(7), 2655–2669.
Abstract: Recent warm atmospheric conditions have damaged the ice shelves of the Antarctic Peninsula through surface melt and hydrofracturing and could potentially initiate future collapse of other Antarctic ice shelves. However, model projections with similar greenhouse gas scenarios suggest large differences in cumulative 21st-century surface melting. So far it remains unclear whether these differences are due to variations in warming rates in individual models or whether local feedback mechanisms of the surface energy budget could also play a notable role. Here we use the polar-oriented regional climate model MAR (Modele Atmospherique Regional) to study the physical mechanisms that would control future surface melt over the Antarctic ice shelves in high-emission scenarios RCP8.5 and SSP5-8.5. We show that clouds enhance future surface melt by increasing the atmospheric emissivity and longwave radiation towards the surface. Furthermore, we highlight that differences in meltwater production for the same climate warming rate depend on cloud properties and particularly cloud phase. Clouds containing a larger amount of supercooled liquid water lead to stronger melt, subsequently favouring the absorption of solar radiation due to the snowmelt-albedo feedback. As liquid-containing clouds are projected to increase the melt spread associated with a given warming rate, they could bea major source of uncertainties in projections of the future Antarctic contribution to sea level rise.
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Labedz, C. R., Bartholomaus, T. C., Amundson, J. M., Gimbert, F., Karplus, M. S., Tsai, V. C. C., et al. (2022). Seismic Mapping of Subglacial Hydrology Reveals Previously Undetected Pressurization Event. Journal Of Geophysical Research-Earth Surface, 1271(3).
Abstract: Understanding the dynamic response of glaciers to climate change is vital for assessing water resources and hazards, and subglacial hydrology is a key player in glacier systems. Traditional observations of subglacial hydrology are spatially and temporally limited, but recent seismic deployments on and around glaciers show the potential for comprehensive observation of glacial hydrologic systems. We present results from a high-density seismic deployment spanning the surface of Lemon Creek Glacier, Alaska. Our study coincided with a marginal lake drainage event, which served as a natural experiment for seismic detection of changes in subglacial hydrology. We observed glaciohydraulic tremor across the surface of the glacier that was generated by the subglacial hydrologic system. During the lake drainage, the relative changes in seismic tremor power and water flux are consistent with pressurization of the subglacial system of only the upper part of the glacier. This event was not accompanied by a significant increase in glacier velocity; either some threshold necessary for rapid basal motion was not attained, or, plausibly, the geometry of Lemon Creek Glacier inhibited speedup. This pressurization event would have likely gone undetected without seismic observations, demonstrating the power of cryoseismology in testing assumptions about and mapping the spatial extent of subglacial pressurization.
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Maclennan, M., Lenaerts, J., Shields, C., & Wille, J. (2022). Contribution Of Atmospheric Rivers To Antarctic Precipitation. Geophysical Research Letters, 494(181).
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Maier, N., Gimbert, F., & Gillet-Chaulet, F. (2022). Threshold Response To Melt Drives Large-Scale Bed Weakening In Greenland. Nature, 6076(79207), 714–+.
Abstract: Ice speeds in Greenland are largely set by basal motion(1), which is modulated by meltwater delivery to the ice base(2-4). Evidence suggests that increasing melt rates enhance the subglacial drainage network's capacity to evacuate basal water, increasing bed friction and causing the ice to slow(5-10). This limits the potential of melt forcing to increase mass loss as temperatures increase(11). Here we show that melt forcing has a pronounced influence on dynamics, but factors besides melt rates primarily control its impact. Using a method to examine friction variability across the entirety of western Greenland, we show that the main impact of melt forcing is an abrupt north-to-south change in bed strength that cannot be explained by changes in melt production. The southern ablation zone is weakened by 20-40 per cent compared with regions with no melt, whereas in northern Greenland the ablation zone is strengthened. We show that the weakening is consistent with persistent basal water storage and that the threshold is linked to differences in sliding and hydropotential gradients, which exert primary control on the pressures within drainage pathways that dewater the bed. These characteristics are mainly set by whether a margin is land or marine terminating, suggesting that dynamic changes that increase mass loss are likely to occur in northern Greenland as temperatures increase. Our results point to physical representations of these findings that will improve simulated ice-sheet evolution at centennial scales.
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Milillo, P., Rignot, E., Rizzoli, P., Scheuchl, B., Mouginot, J., Bueso-Bello, J. L., et al. (2022). Rapid glacier retreat rates observed in West Antarctica. Nature Geoscience, 151(1), 48–+.
Abstract: The Pope, Smith and Kohler glaciers, in the Amundsen Sea Embayment of West Antarctica, have experienced enhanced ocean-induced ice-shelf melt, glacier acceleration, ice thinning and grounding-line retreat in the past 30 years. Here we present observations of the grounding-line retreat of these glaciers since 2014 using a constellation of interferometric radar satellites combined with precision surface elevation data. We find that the grounding lines develop spatially variable, kilometre-scale, tidally induced migration zones. After correction for tidal effects, we detect a sustained pattern of retreat coincident with high melt rates of ungrounded ice, marked by episodes of more rapid retreat. In 2017, Pope Glacier retreated 3.5 km in 3.6 months, or 11.7 km yr(-1). In 2016-2018, Smith West retreated at 2 km yr(-1) and Kohler at 1.3 km yr(-1). While the retreat slowed in 2018-2020, these retreat rates are faster than anticipated by numerical models on yearly timescales. We hypothesize that the rapid retreat is caused by unrepresented, vigorous ice-ocean interactions acting within newly formed cavities at the ice-ocean boundary. The Pope, Smith and Kohler glaciers in West Antarctica have exhibited faster than expected retreat rates in recent years, according to grounding-line observations from satellite radar interferometry.
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Millan, R., Mouginot, J., Rabatel, A., & Morlighem, M. (2022). Ice velocity and thickness of the world's glaciers. Nature Geoscience, 151(2), 124–+.
Abstract: The effect of climate change on water resources and sea-level rise is largely determined by the size of the ice reservoirs around the world and the ice thickness distribution, which remains uncertain. Here, we present a comprehensive high-resolution mapping of ice motion for 98% of the world's total glacier area during the period 2017-2018. We use this mapping of glacier flow to generate an estimate of global ice volume that reconciles ice thickness distribution with glacier dynamics and surface topography. The results suggest that the world's glaciers have a potential contribution to sea-level rise of 257 +/- 85 mm, which is 20% less than previously estimated. At low latitudes, our findings highlight notable changes in freshwater resources, with 37% more ice in the Himalayas and 27% less ice in the tropical Andes of South America, affecting water availability for local populations. This mapping of glacier flow and thickness redefines our understanding of global ice-volume distribution and has implications for the prediction of glacier evolution around the world, since accurate representations of glacier geometry and dynamics are of prime importance to glacier modelling. Potential sea-level rise from the world's glaciers is 20% less than previously thought, according to an estimate based on high-resolution maps of glacier ice velocity and thickness.
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Millan, R., Mouginot, J., Rabatel, A., & Morlighem, M. (2022). Ice Velocity And Thickness Of The World'S Glaciers (Vol 15, Pg 124, 2022). Nature Geoscience, .
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Nanni, U., Roux, P., Gimbert, F., & Lecointre, A. (2022). Dynamic Imaging Of Glacier Structures At High-Resolution Using Source Localization With a Dense Seismic Array. Geophysical Research Letters, 494(6).
Abstract: Dense seismic array monitoring combined with advanced processing can help retrieve and locate a variety of seismic sources with unprecedented resolution and spatial coverage. We present a methodology that goes beyond classical localization algorithms through gathering various types of sources (impulsive or continuous) using a single scheme based on a gradient-descent optimization and evaluating different levels of phase coherence. We apply our methodology on an Alpine glacier and demonstrate that we can retrieve the dynamics of active crevasses with a metric resolution using sources associated with high phase coherence; the presence of diffracting materials (e.g., rocks) trapped in transverse crevasses using sources with moderate phase coherence; and the two-dimensional time evolution of the subglacial hydrology system using sources with low phase coherence. Our study highlights the strength of using an appropriate and systematic seismological approach to image a wide range of subsurface structures and phenomena in settings with complex wavefields.
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Piantini, M., Gimbert, F., Bakker, M., Recking, A., & Nanni, U. (2022). Using A Dense Seismic Array To Study Fluvial Processes In A Braided river reach under flood conditions. Lhb-Hydroscience Journal, , 2053314.
Abstract: Dense seismic array monitoring has recently allowed the detailed investigation of sources of ground vibrations and their spatiotemporal dynamics. In a context where traditional monitoring techniques for fluvial processes often do not provide data with adequate temporal and spatial resolution, the use of dense arrays could allow the identification and tracking of different sources of river-induced seismic ground vibrations (e.g. turbulence and bedload transport). Here, we study the potential of dense seismic array monitoring by investigating a high-flow event that occurred in summer 2019 along a 600-m-long braided reach of the Severaisse River (French Alps). We use a network of 80 seismometers deployed on both river banks, and we supplement the seismic observations with flow gauging measurements and time-lapse imagery. During this event, we observe impulsive signals that are coherently detected over the array, and which we interpret as being associated with the bedload transport of clusters of coarse grains (blocks). Through phase-delay analysis we are able to locate these seismic events on the bend apex of an active branch of the reach. These results demonstrate the capability of such a method to locate bedload activity at high spatiotemporal resolution, providing crucial information for geomorphological investigations and natural risk management.
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Piantini, M., Gimbert, F., Bakker, M., Recking, A., & Nanni, U. (2022). Using A Dense Seismic Array To Study Fluvial Processes In A Braided river reach under flood conditions. Lhb-Hydroscience Journal, .
Abstract: Dense seismic array monitoring has recently allowed the detailed investigation of sources of ground vibrations and their spatiotemporal dynamics. In a context where traditional monitoring techniques for fluvial processes often do not provide data with adequate temporal and spatial resolution, the use of dense arrays could allow the identification and tracking of different sources of river-induced seismic ground vibrations (e.g. turbulence and bedload transport). Here, we study the potential of dense seismic array monitoring by investigating a high-flow event that occurred in summer 2019 along a 600-m-long braided reach of the Severaisse River (French Alps). We use a network of 80 seismometers deployed on both river banks, and we supplement the seismic observations with flow gauging measurements and time-lapse imagery. During this event, we observe impulsive signals that are coherently detected over the array, and which we interpret as being associated with the bedload transport of clusters of coarse grains (blocks). Through phase-delay analysis we are able to locate these seismic events on the bend apex of an active branch of the reach. These results demonstrate the capability of such a method to locate bedload activity at high spatiotemporal resolution, providing crucial information for geomorphological investigations and natural risk management.
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Prieur, C., Rabatel, A., Thomas, J., Farup, I., & Chanussot, J. (2022). Machine Learning Approaches To Automatically Detect Glacier Snow Lines On Multi-Spectral Satellite Images. Remote Sensing, 141(161).
Abstract: Documenting The Inter-Annual Variability And The Long-Term Trend Of The Glacier Snow Line Altitude Is Highly Relevant To Document The Evolution Of Glacier Mass Changes. Automatically Identifying The Snow Line On Glaciers Is Challenging; Recent Developments In Machine Learning Approaches Show Promise To Tackle This Issue. This Manuscript Presents A Proof Of Concept Of Machine Learning Approaches Applied To Multi-Spectral Images To Detect The Snow Line And Quantify Its Average Altitude. The Tested Approaches Include The Combination Of Different Image Processing And Classification Methods, And Takes Into Account Cast Shadows. The Efficiency Of These Approaches Is Evaluated On Mountain Glaciers In The European Alps By Comparing The Results With Manually Annotated Data. Solutions Provided By The Different Approaches Are Robust When Compared To The Ground Truth'S Snow Lines, With A Pearson'S Correlation Ranging From 79% To 96% Depending On The Method. However, The Tested Approaches May Fail When Snow Lines Are Not Continuous Or Exhibit A Strong Change Of Elevation. The Major Advantage Over The State Of The Art Is That The Proposed Approach Does Not Require One Calibration Per Glacier.
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Ravanel, L., Lacroix, E., Le Meur, E., Batoux, P., & Malet, E. (2022). Multiparameter Monitoring Of Crevasses On An Alpine Glacier To Understand Formation And Evolution Of Snow Bridges. Cold Regions Science And Technology, 2032.
Abstract: On Glaciers, The Snow Bridges That Form Above Crevasses Have Hardly Been Considered By Researchers Up To Now, Despite Their Importance For High Mountain Activities (Skiing, Mountaineering) And The Risks That Their Possible Failure Poses To Practitioners. In Order To Improve Our Understanding Of The Formation And Evolution Of These Fragile Snow Structures, We Monitored During Two Years A Succession Of Three Crevasses Located At 3450 M A.S.L. In The Mont-Blanc Massif (France) Using A Set Of Sensors Including An Automatic Camera, Air Temperature Sensors, A Wind Vane-Anemometer, And An Extensometer. Geophysical Profiles (Ground Penetrating Radar) Were Also Carried Out To Clarify The Glacial Context. Despite Particularly Extreme Monitoring Conditions, At The Level Of A Bump Formed By The Bedrock Under An Ice Thickness Of C. 25 M, We Have Shown That A Wind Event Parallel To The Crevasse Favours Its Filling By Snow While A Strong Wind Making A Significant Angle With The Crevasse Under Largely Negative Temperatures Can Rapidly Create A Snow Bridge By Cornice Accretion That Grows By Extending Leeward. High Temperatures Are Responsible For Most Of The Natural Failures Of Sbs. These Elements Are Already Used For Risk Mitigation.
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Rignot, E., Mouginot, J., Scheuchl, B., & Jeong, S. (2022). Changes In Antarctic Ice Sheet Motion Derived From Satellite Radar Interferometry Between 1995 And 2022. Geophysical Research Letters, 494(232).
Abstract: Ice Motion And Boundaries Are Critical Information For Ice Sheet Models That Project Ice Evolution In A Warming Climate. We Present Four Historical, Continent-Wide, Maps Of Antarctic-Wide Ice Motion And Boundaries For The Time Period 1995-2022. The Results Reveal No Change In The Interior Region Of East Antarctica, Iceberg Detachments At Ice Shelf Fronts, And Widespread Glacier Speedup That Propagates 100 Km'S Inland In West Antarctica And The Antarctic Peninsula. Speedup Affects The Entire Drainage Of The Amundsen Sea Embayment Sector; The Entire West Coast Of The Antarctic Peninsula Down To Georgevi Ice Shelf; The East Coast Down To Larsen C Ice Shelf; Getz Ice Shelf, Hull And Land Glaciers In West Antarctica; Matusevitch, Ninnis, Mertz And Denman Glaciers, Glaciers In Porpoise And Vincennes Bay; And Robert, Wilma And Rayner Glaciers In Enderby Land, In East Antarctica. We Attribute The Observed Glacier Changes To Increased Melting By Warmer Ocean Waters.
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Rohmer, J., Thieblemont, R., Le Cozannet, G., Goelzer, H., & Durand, G. (2022). Improving Interpretation Of Sea-Level Projections Through A Machine-Learning-Based Local Explanation Approach. Cryosphere, 161(111), 4637–4657.
Abstract: Process-Based Projections Of The Sea-Level Contribution From Land Ice Components Are Often Obtained From Simulations Using A Complex Chain Of Numerical Models. Because Of Their Importance In Supporting The Decision-Making Process For Coastal Risk Assessment And Adaptation, Improving The Interpretability Of These Projections Is Of Great Interest. To This End, We Adopt The Local Attribution Approach Developed In The Machine Learning Community Known As “Shap” (Shapley Additive Explanations). We Apply Our Methodology To A Subset Of The Multi-Model Ensemble Study Of The Future Contribution Of The Greenland Ice Sheet To Sea Level, Taking Into Account Different Modelling Choices Related To (1) Numerical Implementation, (2) Initial Conditions, (3) Modelling Of Ice-Sheet Processes, And (4) Environmental Forcing. This Allows Us To Quantify The Influence Of Particular Modelling Decisions, Which Is Directly Expressed In Terms Of Sea-Level Change Contribution. This Type Of Diagnosis Can Be Performed On Any Member Of The Ensemble, And We Show In The Greenland Case How The Aggregation Of The Local Attribution Analyses Can Help Guide Future Model Development As Well As Scientific Interpretation, Particularly With Regard To Spatial Model Resolution And To Retreat Parametrisation.
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Smith, A., Jahn, A., Burgard, C., & Notz, D. (2022). Improving Model-Satellite Comparisons Of Sea Ice Melt Onset With A Satellite Simulator. Cryosphere, 161(8), 3235–3248.
Abstract: Seasonal Transitions In Arctic Sea Ice, Such As The Melt Onset, Have Been Found To Be Useful Metrics For Evaluating Sea Ice In Climate Models Against Observations. However, Comparisons Of Melt Onset Dates Between Climate Models And Satellite Observations Are Indirect. Satellite Data Products Of Melt Onset Rely On Observed Brightness Temperatures, While Climate Models Do Not Currently Simulate Brightness Temperatures, And Must Therefore Define Melt Onset With Other Modeled Variables. Here We Adapt A Passive Microwave Sea Ice Satellite Simulator, The Arctic Ocean Observation Operator (Arc3O), To Produce Simulated Brightness Temperatures That Can Be Used To Diagnose The Timing Of The Earliest Snowmelt In Climate Models, As We Show Here Using Community Earth System Model Version 2 (Cesm2) Ocean-Ice Hindcasts. By Producing Simulated Brightness Temperatures And Earliest Snowmelt Estimation Dates Using Cesm2 And Arc3O, We Facilitate New And Previously Impossible Comparisons Between The Model And Satellite Observations By Removing The Uncertainty That Arises Due To Definition Differences. Direct Comparisons Between The Model And Satellite Data Allow Us To Identify An Early Bias Across Large Areas Of The Arctic At The Beginning Of The Cesm2 Ocean-Ice Hindcast Melt Season, As Well As Improve Our Understanding Of The Physical Processes Underlying Seasonal Changes In Brightness Temperatures. In Particular, The Arc3O Allows Us To Show That Satellite Algorithm-Based Melt Onset Dates Likely Occur After Significant Snowmelt Has Already Taken Place.
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Stokes, C., Abram, N., Bentley, M., Edwards, T., England, M., Foppert, A., et al. (2022). Response Of The East Antarctic Ice Sheet To Past And Future Climate Change. Nature, 6086(79227), 275–+.
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Verfaillie, D., Pelletier, C., Goosse, H., Jourdain, N. C., Bull, C. Y. S., Dalaiden, Q., et al. (2022). The Circum-Antarctic Ice-Shelves Respond To A More Positive Southern Annular Mode with regionally varied melting. Communications Earth & Environment, 3(1).
Abstract: The Southern Hemisphere cryosphere has recently shown regionally-contrasted responses to climate change, in particular to the positive phases of the Southern Annular Mode. However, the understanding of the impacts of this mode on ice-shelf basal melt at a circum-Antarctic scale is still limited. Here, we performed idealized experiments with a pan-Antarctic regional ice-shelf cavity-resolving ocean-sea-ice model for different phases of the Southern Annular Mode. We show that positive phases lead to increased upwelling and subsurface ocean temperature and salinity close to ice shelves, while the opposite occurs for negative phases. A one-standard-deviation increase of the Southern Annular Mode leads to a net basal mass loss of 40 Gt yr(-1), with strong regional contrasts: increased ice-shelf basal melt in the Bellingshausen and Western Pacific sectors and the opposite response in the Amundsen sector. Estimates of 1000-1200 and 2090-2100 ice-shelf basal melt changes due to the Southern Annular Mode are -86.6 Gt yr(-1) and 55.0 to 164.9 Gt yr(-1), respectively, compared to the present. Positive phases of the Southern Annular Mode lead to enhanced basal melt overall in the Antarctic ice shelves, with strong losses in the Bellingshausen and Western Pacific sectors and gains in the Amundsen Sea, according to ice-ocean model experiments.
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Vincent, C., Gilbert, A., Walpersdorf, A., Gimbert, F., Gagliardini, O., Jourdain, B., et al. (2022). Evidence Of Seasonal Uplift In The Argentiere Glacier (Mont Blanc Area, France). Journal Of Geophysical Research-Earth Surface, 1271(7).
Abstract: The hydromechanical processes by which basal water controls sliding at the glacier bed are poorly known, despite glacier basal motion being responsible for a large part of ice flux in temperate alpine glaciers. Previous studies suggest that sliding strongly relates to the quantity of water being stored at the ice-bedrock interface. However, this water storage is difficult to quantify accurately on the basis of surface-motion observations, given that uplift can also be affected by changes in vertical-strain rates and sliding velocity change. Here, we use a comprehensive data set of in situ measurements performed over 2 years on the Argentiere Glacier in the French Alps to investigate the relationships between horizontal and vertical velocities, basal sliding, subglacial runoff and bed separation. We observe strikingly large uplifts varying spatially between 0.20 and 0.90 m over the winter/spring seasons between January and June and with a consistent spatial pattern from 1 year to another. We show, based on observations and three dimensional ice-flow modeling, that these large uplifts cannot be explained solely by changes in strain rates or in sliding up an inclined bed. Our results reveal that more than 80% of the observed uplift is related to enhanced bed separation through cavitation, allowing us to estimate the volume occupied by water-filled subglacial cavities. Our interpretation of uplift being mainly caused by increased cavitation is also consistent with an associated increase in the observed surface horizontal velocity. These findings provide important observational constraints for testing subglacial hydrological models.
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2021 |
An, L., Rignot, E., Wood, M., Willis, J., Mouginot, J., & Khan, S. (2021). Ocean melting of the Zachariae Isstrom and Nioghalvfjerdsfjorden glaciers, northeast Greenland. Proceedings Of The National Academy Of Sciences Of The United States Of America, 118(2).
Abstract: Zachariae Isstrom (ZI) and Nioghalvfjerdsfjorden (79N) are marine-terminating glaciers in northeast Greenland that hold an ice volume equivalent to a 1.1-m global sea level rise. ZI lost its floating ice shelf, sped up, retreated at 650 m/y, and experienced a 5-gigaton/y mass loss. Glacier 79N has been more stable despite its exposure to the same climate forcing. We analyze the impact of ocean thermal forcing on the glaciers. A three-dimensional inversion of airborne gravity data reveals an 800-m-deep, broad channel that allows subsurface, warm, Atlantic Intermediate Water (AIW) (+1.25 degrees C) to reach the front of ZI via two sills at 350-m depth. Subsurface ocean temperature in that channel has warmed by 1.3 +/- 0.5 degrees C since 1979. Using an ocean model, we calculate a rate of ice removal at the grounding line by the ocean that increased from 108 m/y to 185 m/y in 1979-2019. Observed ice thinning caused a retreat of its flotation line to increase from 105 m/y to 217 m/y, for a combined grounding line retreat of 13 km in 41 y that matches independent observations within 14%. In contrast, the limited access of AIW to 79N via a narrower passage yields lower grounded ice removal (53 m/y to 99 m/y) and thinning-induced retreat (27 m/y to 50 m/y) for a combined retreat of 4.4 km, also within 12% of observations. Ocean-induced removal of ice at the grounding line, modulated by bathymetric barriers, is therefore a main driver of ice sheet retreat, but it is not incorporated in most ice sheet models.
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Beaumet, J., Deque, M., Krinner, G., Agosta, C., Alias, A., & Favier, V. (2021). Significant additional Antarctic warming in atmospheric bias-corrected ARPEGE projections with respect to control run. Cryosphere, 15(8), 3615–3635.
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Beaumet, J., Menegoz, M., Morin, S., Gallee, H., Fettweis, X., Six, D., et al. (2021). Twentieth century temperature and snow cover changes in the French Alps. Regional Environmental Change, 21(4).
Abstract: Changes in snow cover associated with the warming of the French Alps greatly influence social-ecological systems through their impact on water resources, mountain ecosystems, economic activities, and glacier mass balance. In this study, we investigated trends in snow cover and temperature over the twentieth century using climate model and reanalysis data. The evolution of temperature, precipitation and snow cover in the European Alps has been simulated with the Modele Atmospherique Regional (MAR) applied with a 7-km horizontal resolution and driven by ERA-20C (1902-2010) and ERA5 (1981-2018) reanalyses data. Snow cover duration and snow water equivalent (SWE) simulated with MAR are compared to the SAFRAN – SURFEX-ISBA-Crocus – MEPRA meteorological and snow cover reanalysis (S2M) data across the French Alps (1958-2018) and in situ glacier mass balance measurements. MAR outputs provide a realistic distribution of SWE and snow cover duration as a function of elevation in the French Alps. Large disagreements are found between the datasets in terms of absolute warming trends over the second part of the twentieth century. MAR and S2M trends are in relatively good agreement for the decrease in snow cover duration, with higher decreases at low elevation (similar to 5-10%/decade). Consistent with other studies, the highest warming rates in MAR occur at low elevations (< 1000 m a.s.l) in winter, whereas they are found at high elevations (> 2000 m a.s.l) in summer. In spring, warming trends show a maximum at intermediate elevations (1500 to 1800 m). Our results suggest that higher warming at these elevations is mostly linked to the snow-albedo feedback in spring and summer caused by the disappearance of snow cover at higher elevation during these seasons. This work has evidenced that depending on the season and the period considered, enhanced warming at higher elevations may or may not be found. Additional analysis in a physically comprehensive way and more high-quality dataset, especially at high elevations, are still required to better constrain and quantify climate change impacts in the Alps and its relation to elevation.
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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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Bull, C., Jenkins, A., Jourdain, N., Vankova, I., Holland, P., Mathiot, P., et al. (2021). Remote Control of Filchner-Ronne Ice Shelf Melt Rates by the Antarctic Slope Current. Journal Of Geophysical Research-Oceans, 126(2).
Abstract: Recent work on the Filchner-Ronne Ice Shelf (FRIS) system has shown that a redirection of the coastal current in the southeastern Weddell Sea could lead to a regime change in which an intrusion of warm Modified Circumpolar Deep Water results in large increases in the basal melt rate. Work to date has mostly focused on how increases in the Modified Circumpolar Deep Water crossing the continental shelf break leads directly to heat driven changes in melting in the ice-shelf cavity. In this study, we introduce a Weddell Sea regional ocean model configuration with static ice shelves. We evaluate a reference simulation against radar observations of melting, and find good agreement between the simulated and observed mean melt rates. We analyze 28 sensitivity experiments that simulate the influence of changes in remote water properties of the Antarctic Slope Current on basal melting in the FRIS. We find that remote changes in salinity quasi-linearly modulate the mean FRIS net melt rate. Changes in remote temperature quadratically vary the FRIS net melt rate. In both salinity and temperature perturbations, the response is rapid and transient, with a recovery time-scale of 5-15 years dependent on the size/type of perturbation. We show that the two types of perturbations lead to different changes on the continental shelf, and that ultimately different factors modulate the melt rates in the FRIS cavity. We discuss how these results, are relevant for ocean hindcast simulations, sea level, and melt rate projections of the FRIS.
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Cavitte, M., Young, D., Mulvaney, R., Ritz, C., Greenbaum, J., Ng, G., et al. (2021). A detailed radiostratigraphic data set for the central East Antarctic Plateau spanning from the Holocene to the mid-Pleistocene. Earth System Science Data, 13(10), 4759–4777.
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Charton, J., Jomelli, V., Schimmelpfennig, I., Verfaillie, D., Favier, V., Mokadem, F., et al. (2021). A debris-covered glacier at Kerguelen (49 degrees S, 69 degrees E) over the past 15 000 years. Antarctic Science, 33(1), 103–115.
Abstract: Debris-covered glaciers constitute a large part of the world's cryosphere. However, little is known about their long-term response to multi-millennial climate variability, in particular in the Southern Hemisphere. Here, we provide first insights into the response of a debris-covered glacier to multi-millennial climate variability in the sub-Antarctic Kerguelen Archipelago, which can be compared to that of recently investigated debris-free glaciers. We focus on the Gentil Glacier and present 13 new Cl-36 cosmic-ray exposure ages from moraine boulders. The Gentil Glacier experienced at least two glacial advances: the first one during the Late Glacial (19.0-11.6 ka) at similar to 14.3 ka and the second one during the Late Holocene at similar to 2.6 ka. Both debris-covered and debris-free glaciers advanced broadly synchronously during the Late Glacial, most probably during the Antarctic Cold Reversal event (14.5-12.9 ka). This suggests that both glacier types at Kerguelen were sensitive to abrupt temperature changes recorded in Antarctic ice cores, associated with increased moisture. However, during the Late Holocene, the advance at similar to 2.6 ka was not observed in other glaciers and seems to be an original feature of the debris-covered Gentil Glacier, related to either distinct dynamics or to distinct sensitivity to precipitation changes.
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Cook, S., Christoffersen, P., Truffer, M., Chudley, T., & Abellan, A. (2021). Calving of a Large Greenlandic Tidewater Glacier has Complex Links to Meltwater Plumes and Melange. Journal Of Geophysical Research-Earth Surface, 126(4).
Abstract: Calving and solid ice discharge into fjords account for approximately half of the annual net ice loss from the Greenland ice sheet, but these processes are rarely observed. To gain insights into the spatiotemporal nature of calving, we use a terrestrial radar interferometer to derive a 3-week record of 8,026 calving events from Sermeq Kujalleq (Store Glacier, West Greenland), including the transition between a melange-filled and ice-free fjord. We show that calving rates double across this transition and that the interferometer record is in good agreement with volumetric estimates of calving losses from contemporaneous unmanned aerial vehicle surveys. We report significant variations in calving activity over time, which obfuscate any simple power-law relationship. While there is a statistically significant relationship between surface melt and the number of calving events, no such relationship exists between surface melt and the volume of these events. Similarly, we find a 70% increase in the number of calving events in the presence of visible meltwater plumes but only a 3% increase in calving volumes. While calving losses appear to have no clear single control, we find a bimodal distribution of iceberg sizes due to small blocks breaking off the subaerial part of the glacier front and large capsizing icebergs forming by full-thickness failure. Whereas previous work has hypothesized that tidewater glaciers can be grouped according to whether they calve predominantly by the former or latter mechanism, our observations indicate that calving here inherently comprises both and that the dominant process can change over relatively short periods.
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Cook, S. J., Christoffersen, P., & Todd, J. (2021). A fully-coupled 3D model of a large Greenlandic outlet glacier with evolving subglacial hydrology, frontal plume melting and calving. Journal Of Glaciology, .
Abstract: We present the first fully coupled 3D full-Stokes model of a tidewater glacier, incorporating ice flow, subglacial hydrology, plume-induced frontal melting and calving. We apply the model to Store Glacier (Sermeq Kujalleq) in west Greenland to simulate a year of high melt (2012) and one of low melt (2017). In terms of modelled hydrology, we find perennial channels extending 5 km inland from the terminus and up to 41 and 29 km inland in summer 2012 and 2017, respectively. We also report a hydrodynamic feedback that suppresses channel growth under thicker ice inland and allows water to be stored in the distributed system. At the terminus, we find hydrodynamic feedbacks exert a major control on calving through their impact on velocity. We show that 2012 marked a year in which Store Glacier developed a fully channelised drainage system, unlike 2017, where it remained only partially developed. This contrast in modelled behaviour indicates that tidewater glaciers can experience a strong hydrological, as well as oceanic, control, which is consistent with observations showing glaciers switching between types of behaviour. The fully coupled nature of the model allows us to demonstrate the likely lack of any hydrological or ice-dynamic memory at Store Glacier.
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Crockart, C., Vance, T., Fraser, A., Abram, N., Criscitiello, A., Curran, M., et al. (2021). El Nino-Southern Oscillation signal in a new East Antarctic ice core, Mount Brown South. Climate Of The Past, 17(5), 1795–1818.
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Cusicanqui, D., Rabatel, A., Vincent, C., Bodin, X., Thibert, E., & Francou, B. (2021). Interpretation of Volume and Flux Changes of the Laurichard Rock Glacier Between 1952 and 2019, French Alps. Journal Of Geophysical Research-Earth Surface, 126(9).
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Derkacheva, A., Gillet-Chaulet, F., Mouginot, J., Jager, E., Maier, N., & Cook, S. (2021). Seasonal evolution of basal environment conditions of Russell sector, West Greenland, inverted from satellite observation of surface flow. Cryosphere, 15(12), 5675–5704.
Abstract: Due to increasing surface melting on the Greenland ice sheet, better constraints on seasonally evolving basal water pressure and sliding speed are required by models. Here we assess the potential of using inverse methods on a dense time series of surface speeds to recover the seasonal evolution of the basal conditions in a well-documented region in southwest Greenland. Using data compiled from multiple satellite missions, we document seasonally evolving surface velocities with a temporal resolution of 2 weeks between 2015 and 2019. We then apply the inverse control method using the ice flow model Elmer/Ice to infer the basal sliding and friction corresponding to each of the 24 surface velocity data sets. Near the margin where the uncertainty in the velocity and bed topography are small, we obtain clear seasonal variations that can be mostly interpreted in terms of an effective-pressure-based hard-bed friction law. We find for valley bottoms or “troughs” in the bed topography that the changes in modelled basal conditions directly respond to local modelled water pressure variations, while the link is more complex for subglacial “ridges” which are often non-locally forced. At the catchment scale, in-phase variations in the water pressure, surface velocities, and surface runoff variations are found. Our results show that time series inversions of observed surface velocities can be used to understand the evolution of basal conditions over different timescales and could therefore serve as an intermediate validation for subglacial hydrology models to achieve better coupling with ice flow models.
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Donat-Magnin, M., Jourdain, N., Kittel, C., Agosta, C., Amory, C., Gallee, H., et al. (2021). Future surface mass balance and surface melt in the Amundsen sector of the West Antarctic Ice Sheet. Cryosphere, 15(2), 571–593.
Abstract: We present projections of West Antarctic surface mass balance (SMB) and surface melt to 2080-2100 under the RCP8.5 scenario and based on a regional model at 10 km resolution. Our projections are built by adding a CMIP5 (Coupled Model Intercomparison Project Phase 5) multi-model-mean seasonal climate-change anomaly to the present-day model boundary conditions. Using an anomaly has the advantage to reduce CMIP5 model biases, and a perfect-model test reveals that our approach captures most characteristics of future changes despite a 16 %-17 % underestimation of projected SMB and melt rates. SMB over the grounded ice sheet in the sector between Getz and Abbot increases from 336 Gt yr(-1) in 1989-2009 to 455 Gt yr(-1) in 2080-2100, which would reduce the global sea level changing rate by 0.33 mm yr(-1). Snowfall indeed increases by 7.4 % degrees C-1 to 8.9 % degrees C-1 of near-surface warming due to increasing saturation water vapour pressure in warmer conditions, reduced sea-ice concentrations, and more marine air intrusion. Ice-shelf surface melt rates increase by an order of magnitude in the 21st century mostly due to higher downward radiation from increased humidity and to reduced albedo in the presence of melting. There is a net production of surface liquid water over eastern ice shelves (Abbot, Cosgrove, and Pine Island) but not over western ice shelves (Thwaites, Crosson, Dotson, and Getz). This is explained by the evolution of the melt-to-snowfall ratio: below a threshold of 0.60 to 0.85 in our simulations, firn air is not entirely depleted by melt water, while entire depletion and net production of surface liquid water occur for higher ratios. This suggests that western ice shelves might remain unaffected by hydrofracturing for more than a century under RCP8.5, while eastern ice shelves have a high potential for hydrofracturing before the end of this century.
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Edwards, T., Nowicki, S., Marzeion, B., Hock, R., Goelzer, H., Seroussi, H., et al. (2021). Projected land ice contributions to twenty-first-century sea level rise. Nature, 593(7857), 74–+.
Abstract: Efficient statistical emulation of melting land ice under various climate scenarios to 2100 indicates a contribution from melting land ice to sea level increase of at least 13 centimetres sea level equivalent. The land ice contribution to global mean sea level rise has not yet been predicted(1) using ice sheet and glacier models for the latest set of socio-economic scenarios, nor using coordinated exploration of uncertainties arising from the various computer models involved. Two recent international projects generated a large suite of projections using multiple models(2-8), but primarily used previous-generation scenarios(9) and climate models(10), and could not fully explore known uncertainties. Here we estimate probability distributions for these projections under the new scenarios(11,12) using statistical emulation of the ice sheet and glacier models. We find that limiting global warming to 1.5 degrees Celsius would halve the land ice contribution to twenty-first-century sea level rise, relative to current emissions pledges. The median decreases from 25 to 13 centimetres sea level equivalent (SLE) by 2100, with glaciers responsible for half the sea level contribution. The projected Antarctic contribution does not show a clear response to the emissions scenario, owing to uncertainties in the competing processes of increasing ice loss and snowfall accumulation in a warming climate. However, under risk-averse (pessimistic) assumptions, Antarctic ice loss could be five times higher, increasing the median land ice contribution to 42 centimetres SLE under current policies and pledges, with the 95th percentile projection exceeding half a metre even under 1.5 degrees Celsius warming. This would severely limit the possibility of mitigating future coastal flooding. Given this large range (between 13 centimetres SLE using the main projections under 1.5 degrees Celsius warming and 42 centimetres SLE using risk-averse projections under current pledges), adaptation planning for twenty-first-century sea level rise must account for a factor-of-three uncertainty in the land ice contribution until climate policies and the Antarctic response are further constrained.
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Farinotti, D., Brinkerhoff, D., Furst, J., Gantayat, P., Gillet-Chaulet, F., Huss, M., et al. (2021). Results from the Ice Thickness Models Intercomparison eXperiment Phase 2 (ITMIX2). Frontiers In Earth Science, 8.
Abstract: Knowing the ice thickness distribution of a glacier is of fundamental importance for a number of applications, ranging from the planning of glaciological fieldwork to the assessments of future sea-level change. Across spatial scales, however, this knowledge is limited by the paucity and discrete character of available thickness observations. To obtain a spatially coherent distribution of the glacier ice thickness, interpolation or numerical models have to be used. Whilst the first phase of the Ice Thickness Models Intercomparison eXperiment (ITMIX) focused on approaches that estimate such spatial information from characteristics of the glacier surface alone, ITMIX2 sought insights for the capability of the models to extract information from a limited number of thickness observations. The analyses were designed around 23 test cases comprising both real-world and synthetic glaciers, with each test case comprising a set of 16 different experiments mimicking possible scenarios of data availability. A total of 13 models participated in the experiments. The results show that the inter-model variability in the calculated local thickness is high, and that for unmeasured locations, deviations of 16% of the mean glacier thickness are typical (median estimate, three-quarters of the deviations within 37% of the mean glacier thickness). This notwithstanding, limited sets of ice thickness observations are shown to be effective in constraining the mean glacier thickness, demonstrating the value of even partial surveys. Whilst the results are only weakly affected by the spatial distribution of the observations, surveys that preferentially sample the lowest glacier elevations are found to cause a systematic underestimation of the thickness in several models. Conversely, a preferential sampling of the thickest glacier parts proves effective in reducing the deviations. The response to the availability of ice thickness observations is characteristic to each approach and varies across models. On average across models, the deviation between modeled and observed thickness increase by 8.5% of the mean ice thickness every time the distance to the closest observation increases by a factor of 10. No single best model emerges from the analyses, confirming the added value of using model ensembles.
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Forquin, P., Blasone, M., Georges, D., & Dargaud, M. (2021). Continuous and discrete methods based on X-ray computed-tomography to model the fragmentation process in brittle solids over a wide range of strain-rates-application to three brittle materials. Journal Of The Mechanics And Physics Of Solids, 152.
Abstract: In the present work, two methods, named “continuous” and “discrete”, are proposed to model the fragmentation process in brittle solids. Both methods rely on a preliminary analysis of the existing flaws population in scanned samples with X-ray micro-Computed Tomography (microCT). By converting the size of defects into critical stresses, the density of critical defects versus the applied stress level is deduced and used as an input of both a continuum and a discrete method. To do so, the concept of critical defects obscuration is implemented. Introduced in the DFH (DenoualForquin-Hild) micromechanics model, this concept consists in describing how cracks propagating from triggered flaws prevent neighbouring flaws from being activated. This obscuration phenomenon is implemented in the present work by using the flaws population determined via microCT analysis as an input. In the continuous method, the differential equation of the obscuration probability provided in the DFH model is integrated. In the discrete method, a cubic subvolume of the scanned volume is considered and the growth of obscuration volumes is numerically simulated considering the real location of each critical defect and their stress of activation. Both methods provide predictions for the material dynamic strength and final cracking density according to the applied strain-rate. These two methods are applied to three types of brittle materials: an Ultra-High Performance Concrete (UHPC), a porous polycrystalline ice and a silicon carbide with spherical “fuse-flaws”. Finally, the obtained predictions are compared to the closedform solution of the DFH model, which is based on a Weibull distribution of the critical flaws identified from bending tests. Whereas the three approaches match very well at low strain-rates, the continuous and discrete methods diverge from the DFH closed-form solution at high strainrates, due to the activation of smaller and more numerous defects that could not be activated in the quasi-static bending tests.
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Georges, D., Saletti, D., Montagnat, M., Forquin, P., & Hagenmuller, P. (2021). Influence of Porosity on Ice Dynamic Tensile Behavior as Assessed by Spalling Tests. Journal Of Dynamic Behavior Of Materials, .
Abstract: The impact of ice on structures is a strong concern, in particular for aeronautical or space crafts that are strongly damaged by the impact of atmospheric ice, and more specifically by hailstones during hailstorms. During the impact, the hailstone is submitted to a complex loading including a strong dynamic tensile component that is responsible for its fragmentation and influences the mechanical loading transmitted to the impacted structure. However, up to now, very limited work were conducted on the tensile strength of ice under dynamic loading and the microstructure influence was out the scope of most studies. In particular the presence of porosity in ice as observed in hailstones is thought to significantly affect the ice mechanical response. The aim of this paper is to investigate the role of porosity on the tensile behavior of polycrystalline ice at high strain rates. To do so, spalling tests with a Hopkinson bar apparatus were conducted on microstructures characterized by porosities with two different pore size distributions. The dynamic tensile strength was computed by the use of the so-called Novikov formula and several indicators were used to assess the quality of each test. A whole set of high porosity samples was tested and additional tests were performed on low porosity ice, expanding the existing results in the literature. The fragmentation processes occuring during the spalling tests were observed by means of an ultra high speed camera and the influence of porosity on the main fracture planes was investigated by analysing post-spalling samples with an automatic ice texture analyser and X-ray tomography. Tensile strength is shown to increase with strain rate over the range 24 s(-1) to 120 s(-1) and to decrease with increasing porosity. The presence of large porosities in the high porosity samples appear to contribute preferentially to this strength decrease. Relevant observations concerning the detected cracks, the tortuosity of crack paths and the presence of porosities on the crack surfaces seem to validate the hypothesis of porosities playing a key role for crack initiation and propagation during ice fragmentation.
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Gimbert, F., Gilbert, A., Gagliardini, O., Vincent, C., & Moreau, L. (2021). Do Existing Theories Explain Seasonal to Multi-Decadal Changes in Glacier Basal Sliding Speed? Geophysical Research Letters, 48(15).
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Gimbert, F., Nanni, U., Roux, P., Helmstetter, A., Garambois, S., Lecointre, A., et al. (2021). A Multi-Physics Experiment with a Temporary Dense Seismic Array on the Argentiere Glacier, French Alps: The RESOLVE Project. Seismological Research Letters, 92(2), 1185–1201.
Abstract: Recent work in the field of cryo-seismology demonstrates that high-frequency (> 1 Hz) seismic waves provide key constraints on a wide range of glacier processes, such as basal friction, surface crevassing, or subglacial water flow. Establishing quantitative links between the seismic signal and the processes of interest, however, requires detailed characterization of the wavefield, which, at high frequencies, necessitates the deployment of large and dense seismic arrays. Although dense seismic array monitoring has recently become increasingly common in geophysics, its application to glaciated environments remains limited. Here, we present a dense seismic array experiment made of 98 three-component seismic stations continuously recording during 35 days in early spring 2018 on the Argentiere Glacier, French Alps. The seismic dataset is supplemented with a wide range of complementary observations obtained from ground-penetrating radar, drone imagery, Global Navigation Satellite Systems positioning, and in situ measurements of basal glacier sliding velocities and subglacial water discharge. We present first results through conducting spectral analysis, template matching, matched-field processing, and eikonal-wave tomography. We report enhanced spatial resolution on basal stick slip and englacial fracturing sources as well as novel constraints on the heterogeneous nature of the noise field generated by subglacial water flow and on the link between crevasse properties and englacial seismic velocities. We outline in which ways further work using this dataset could help tackle key remaining questions in the field.
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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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Haq, M., Azam, M., & Vincent, C. (2021). Efficiency of artificial neural networks for glacier ice-thickness estimation: a case study in western Himalaya, India. Journal Of Glaciology, 67(264), 671–684.
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Huot, P., Fichefet, T., Jourdain, N., Mathiot, P., Rousset, C., Kittel, C., et al. (2021). Influence of ocean tides and ice shelves on ocean & ndash;ice interactions and dense shelf water formation in the D & rsquo;Urville Sea, Antarctica. Ocean Modelling, 162.
Abstract: The D'Urville Sea, East Antarctica, is a major source of Dense Shelf Water (DSW), a precursor of Antarctic Bottom Water (AABW). AABW is a key water mass involved in the worldwide ocean circulation and long-term climate variability. The properties of AABW in global climate models suffer from several biases, making climate projections uncertain. These models are potentially omitting or misrepresenting important mechanisms involved in the formation of DSW, such as tides and ocean-ice shelf interactions. Recent studies pointed out that tides and ice shelves significantly influence the coastal seas of Antarctica, where AABW originates from. Yet, the implications of these two processes in the formation and evolution of DSW are poorly understood, in particular in the D'Urville Sea. Using a series of NEMO-LIM numerical simulations, we assess the sensitivity of dense water formation in the D'Urville Sea to the representation of tides and ocean-ice shelf interactions during the years 2010-2015. We show that the ice shelves off Adelie Land are highly sensitive to tidal forcing, with a significant basal melt increase in the presence of tides. Ice shelf basal melt freshens and cools the ocean over significant portions of the coastal seas at the depth of the ice shelf draft. An opposite warming and increase in salinity are found in the upper layers. The influence of ice shelf basal melt on the ocean is largely increased in the presence of tides. However, the production of sea ice is found to be mostly unaffected by these two processes. Water mass transport out of polynyas and ice shelf cavities are then investigated, together with their sensitivity to tides and ocean-ice shelf interactions. Ice shelf basal melt impacts the volume of dense waters in two ways: (1) Dense Shelf Water and Modified Shelf Water are consumed to form water masses of intermediate density inside the ice shelf cavities, and (2) the freshening of the ocean subsurface makes its transformation into dense water by sea ice formation more difficult. These results suggest that ice shelf basal melt variability can explain part of the observed changes of dense water properties, and may also affect the production of dense water in a future climate.
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Huot, P., Kittel, C., Fichefet, T., Jourdain, N., Sterlin, J., & Fettweis, X. (2021). Effects of the atmospheric forcing resolution on simulated sea ice and polynyas off Adelie Land, East Antarctica. Ocean Modelling, 168.
Abstract: Coastal polynyas of the Southern Ocean play a central role in the ventilation of the deep ocean and affect the stability of ice shelves. It appears crucial to incorporate them into climate models, but it is unclear how to adequately simulate them. In particular, there is no consensus on the atmospheric forcing resolution needed to appropriately model the sea ice in coastal Antarctica. A high resolution might be required to represent the local winds such as katabatic winds which are key drivers of coastal polynyas. To fill in this gap, we have tested the sensitivity of sea ice and air-sea-ice interactions to the resolution of the atmospheric forcing in a high-resolution ocean-sea ice model. A set of regional atmospheric simulations at horizontal resolutions of 20, 10, and 5 km are performed with an atmospheric regional model and used to force three ocean-sea ice simulations in the Adelie Land sector, East Antarctica. Due to the better representation of topography with a refined grid, the offshore component of coastal winds becomes stronger at increased resolution. The wind intensification is particularly strong down valleys channelizing the katabatic flow, with increase in wind speed ranging between 1 and 3 m/s. Under a higher resolution forcing, polynyas open more frequently and are wider. This fosters the growth rate of sea ice in polynyas, while landfast ice and pack ice are weakly affected. In polynyas, the production of sea ice is increased by up to 30% at 5 km resolution compared to 20 km resolution. Polynyas downstream of the katabatic wind pathway are more affected than the ones driven by easterly winds, highlighting the importance of the local wind conditions. Brine rejection associated with these higher sea ice production rates affects the salinity budget of the ocean and enhances both the volume and density of the dense Shelf Water produced off Adelie Land. These results underpin the need to better account for local coastal winds and polynyas in ocean and climate models.
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Kaab, A., Jacquemart, M., Gilbert, A., Leinss, S., Girod, L., Huggel, C., et al. (2021). Sudden large-volume detachments of low-angle mountain glaciers more frequent than thought? Cryosphere, 15(4), 1751–1785.
Abstract: The detachment of large parts of low-angle mountain glaciers resulting in massive ice-rock avalanches have so far been believed to be a unique type of event, made known to the global scientific community first for the 2002 Kolka Glacier detachment, Caucasus Mountains, and then for the 2016 collapses of two glaciers in the Aru range, Tibet. Since 2016, several so-far unrecognized low-angle glacier detachments have been recognized and described, and new ones have occurred. In the current contribution, we compile, compare, and discuss 20 actual or suspected large-volume detachments of low-angle mountain glaciers at 10 different sites in the Caucasus, the Pamirs, Tibet, Altai, the North American Cordillera, and the Southern Andes. Many of the detachments reached volumes in the order of 10-100 millionm(3). The similarities and differences between the presented cases indicate that glacier detachments often involve a coincidental combination of factors related to the lowering of basal friction, high or increasing driving stresses, concentration of shear stress, or low resistance to exceed stability thresholds. Particularly soft glacier beds seem to be a common condition among the observed events as they offer smooth contact areas between the glacier and the underlying substrate and are prone to till-strength weakening and eventually basal failure under high pore-water pressure. Partially or fully thawed glacier bed conditions and the presence of liquid water could thus play an important role in the detachments. Surface slopes of the detached glaciers range between around 10 degrees and 20 degrees. This may be low enough to enable the development of thick and thus large-volume glaciers while also being steep enough to allow critical driving stresses to build up. We construct a simple slab model to estimate ranges of glacier slope and width above which a glacier may be able to detach when extensively losing basal resistance. From this model we estimate that all the detachments described in this study occurred due to a basal shear stress reduction of more than 50 %. Most of the ice-rock avalanches resulting from the detachments in this study have a particularly low angle of reach, down to around 5 degrees, likely due to their high ice content and connected liquefaction potential, the availability of soft basal slurries, and large amounts of basal water, as well as the smooth topographic setting typical for glacial valleys. Low-angle glacier detachments combine elements and likely also physical processes of glacier surges and ice break-offs from steep glaciers. The surge-like temporal evolution ahead of several detachments and their geographic proximity to other surge-type glaciers indicate the glacier detachments investigated can be interpreted as endmembers of the continuum of surge-like glacier instabilities. Though rare, glacier detachments appear to be more frequent than commonly thought and disclose, despite local differences in conditions and precursory evolutions, the fundamental and critical potential of low-angle soft glacier beds to fail catastrophically.
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Karlsson, N., Solgaard, A., Mankoff, K., Gillet-Chaulet, F., Macgregor, J., Box, J., et al. (2021). A first constraint on basal melt-water production of the Greenland ice sheet. Nature Communications, 12(1).
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Khedim, N., Cecillon, L., Poulenard, J., Barre, P., Baudin, F., Marta, S., et al. (2021). Topsoil organic matter build-up in glacier forelands around the world. Global Change Biology, .
Abstract: Since the last glacial maximum, soil formation related to ice-cover shrinkage has been one major sink of carbon accumulating as soil organic matter (SOM), a phenomenon accelerated by the ongoing global warming. In recently deglacierized forelands, processes of SOM accumulation, including those that control carbon and nitrogen sequestration rates and biogeochemical stability of newly sequestered carbon, remain poorly understood. Here, we investigate the build-up of SOM during the initial stages (up to 410 years) of topsoil development in 10 glacier forelands distributed on four continents. We test whether the net accumulation of SOM on glacier forelands (i) depends on the time since deglacierization and local climatic conditions (temperature and precipitation); (ii) is accompanied by a decrease in its stability and (iii) is mostly due to an increasing contribution of organic matter from plant origin. We measured total SOM concentration (carbon, nitrogen), its relative hydrogen/oxygen enrichment, stable isotopic (C-13, N-15) and carbon functional groups (C-H, C=O, C=C) compositions, and its distribution in carbon pools of different thermal stability. We show that SOM content increases with time and is faster on forelands experiencing warmer climates. The build-up of SOM pools shows consistent trends across the studied soil chronosequences. During the first decades of soil development, the low amount of SOM is dominated by a thermally stable carbon pool with a small and highly thermolabile pool. The stability of SOM decreases with soil age at all sites, indicating that SOM storage is dominated by the accumulation of labile SOM during the first centuries of soil development, and suggesting plant carbon inputs to soil (SOM depleted in nitrogen, enriched in hydrogen and in aromatic carbon). Our findings highlight the potential vulnerability of SOM stocks from proglacial areas to decomposition and suggest that their durability largely depends on the relative contribution of carbon inputs from plants.
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Kittel, C., Amory, C., Agosta, C., Jourdain, N., Hofer, S., Delhasse, A., et al. (2021). Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet. Cryosphere, 15(3), 1215–1236.
Abstract: The future surface mass balance (SMB) will influence the ice dynamics and the contribution of the Antarctic ice sheet (AIS) to the sea level rise. Most of recent Antarctic SMB projections were based on the fifth phase of the Coupled Model Intercomparison Project (CMIP5). However, new CMIP6 results have revealed a C1:3 degrees C higher mean Antarctic near-surface temperature than in CMIP5 at the end of the 21st century, enabling estimations of future SMB in warmer climates. Here, we investigate the AIS sensitivity to different warmings with an ensemble of four simulations performed with the polar regional climate model Modele Atmospherique Regional (MAR) forced by two CMIP5 and two CMIP6 models over 1981-2100. Statistical extrapolation enables us to expand our results to the whole CMIP5 and CMIP6 ensembles. Our results highlight a contrasting effect on the future grounded ice sheet and the ice shelves. The SMB over grounded ice is projected to increase as a response to stronger snowfall, only partly offset by enhanced meltwater run-off. This leads to a cumulated sealevel-rise mitigation (i.e. an increase in surface mass) of the grounded Antarctic surface by 5.1 +/- 1.9 cm sea level equivalent (SLE) in CMIP5-RCP8.5 (Relative Concentration Pathway 8.5) and 6.3 +/- 2.0 cm SLE in CMIP6-ssp585 (Shared Socioeconomic Pathways 585). Additionally, the CMIP6 low-emission ssp126 and intermediate-emission ssp245 scenarios project a stabilized surface mass gain, resulting in a lower mitigation to sea level rise than in ssp585. Over the ice shelves, the strong run-off increase associated with higher temperature is projected to decrease the SMB (more strongly in CMIP6-ssp585 compared to CMIP5-RCP8.5). Ice shelves are however predicted to have a close-to-present-equilibrium stable SMB under CMIP6 ssp126 and ssp245 scenarios. Future uncertainties are mainly due to the sensitivity to anthropogenic forcing and the timing of the projected warming. While ice shelves should remain at a close-to-equilibrium stable SMB under the Paris Agreement, MAR projects strong SMB decrease for an Antarctic near-surface warming above C2:5 degrees C compared to 1981-2010 mean temperature, limiting the warming range before potential irreversible damages on the ice shelves. Finally, our results reveal the existence of a potential threshold (C7:5 degrees C) that leads to a lower groundedSMB increase. This however has to be confirmed in following studies using more extreme or longer future scenarios.
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Lagarde, S., Dietze, M., Gimbert, F., Laronne, J., Turowski, J., & Halfi, E. (2021). Grain-Size Distribution and Propagation Effects on Seismic Signals Generated by Bedload Transport. Water Resources Research, 57(4).
Abstract: Bedload transport is a key process in fluvial morphodynamics, but difficult to measure. The advent of seismic monitoring techniques has provided an alternative to in-stream monitoring, which is often costly and cannot be utilized during large floods. Seismic monitoring is a method requiring several steps to convert seismic data into bedload flux data. State-of-the-art conversion approaches exploit physical models predicting the seismic signal generated by bedload transport. However, due to a lack of well-constrained validation data, the accuracy of the resulting inversions is unknown. We use field experiments to constrain a seismic bedload model and compare the results to high-quality independent bedload measurements. Constraining the Green's function (i.e., seismic ground properties) with an active seismic survey resulted in an average absolute difference between modeled and empirically measured seismic bedload power of 11 dB in the relevant frequency band. Using generically estimated Green's function parameters resulted in a difference of 20 dB, thus highlighting the importance of using actual field parameters. Water turbulence and grain hiding are unlikely to be the cause of differences between field observations and our analysis. Rather, they may be either due to the inverted model being particularly sensitive to the coarse tail of the grain-size distribution, which is least well constrained from field observations, or due to the seismic model underestimating effects of the largest grains.
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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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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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Lipscomb, W., Leguy, G., Jourdain, N., Asay-Davis, X., Seroussi, H., & Nowicki, S. (2021). ISMIP6-based projections of ocean-forced Antarctic Ice Sheet evolution using the Community Ice Sheet Model. Cryosphere, 15(2), 633–661.
Abstract: The future retreat rate for marine-based regions of the Antarctic Ice Sheet is one of the largest uncertainties in sea-level projections. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) aims to improve projections and quantify uncertainties by running an ensemble of ice sheet models with atmosphere and ocean forcing derived from global climate models. Here, the Community Ice Sheet Model (CISM) is used to run ISMIP6-based projections of ocean-forced Antarctic Ice Sheet evolution. Using multiple combinations of sub-ice-shelf melt parameterizations and calibrations, CISM is spun up to steady state over many millennia. During the spin-up, basal friction parameters and basin-scale thermal forcing corrections are adjusted to optimize agreement with the observed ice thickness. The model is then run forward for 550 years, from 1950-2500, applying ocean thermal forcing anomalies from six climate models. In all simulations, the ocean forcing triggers long-term retreat of the West Antarctic Ice Sheet, especially in the Filchner-Ronne and Ross sectors. Mass loss accelerates late in the 21st century and then rises steadily for several centuries without leveling off. The resulting ocean-forced sea-level rise at year 2500 varies from about 150 to 1300 mm, depending on the melt scheme and ocean forcing. Further experiments show relatively high sensitivity to the basal friction law, moderate sensitivity to grid resolution and the prescribed collapse of small ice shelves, and low sensitivity to the stress-balance approximation. The Amundsen sector exhibits threshold behavior, with modest retreat under many parameter settings but complete collapse under some combinations of low basal friction and high thermal forcing anomalies. Large uncertainties remain, as a result of parameterized sub-shelf melt rates, simplified treatments of calving and basal friction, and the lack of ice-ocean coupling.
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Maier, N., Gimbert, F., Gillet-Chaulet, F., & Gilbert, A. (2021). Basal traction mainly dictated by hard-bed physics over grounded regions of Greenland. Cryosphere, 15(3), 1435–1451.
Abstract: On glaciers and ice sheets, identifying the relationship between velocity and traction is critical to constrain the bed physics that controls ice flow. Yet in Greenland, these relationships remain unquantified. We determine the spatial relationship between velocity and traction in all eight major drainage catchments of Greenland. The basal traction is estimated using three different methods over large grid cells to minimize interpretation biases associated with unconstrained rheologic parameters used in numerical inversions. We find the relationships are consistent with our current understanding of basal physics in each catchment. We identify catchments that predominantly show Mohr-Coulomb-like behavior typical of deforming beds or significant cavitation, as well as catchments that predominantly show rate-strengthening behavior typical of Weertman-type hard-bed physics. Overall, the traction relationships suggest that the flow field and surface geometry of the grounded regions in Greenland is mainly dictated by Weertman-type hard-bed physics up to velocities of approximately 450m yr(-1), except within the Northeast Greenland Ice Stream and areas near floatation. Depending on the catchment, behavior of the fastest-flowing ice (similar to 1000 m yr(-1)) directly inland from marine-terminating outlets exhibits Weertman-type rate strengthening, Mohr-Coulomb-like behavior, or is not confidently resolved given our methodology. Given the complex basal boundary across Greenland, the relationships are captured reasonably well by simple traction laws which provide a parameterization that can be used to model ice dynamics at large scales. The results and analysis serve as a first constraint on the physics of basal motion over the grounded regions of Greenland and provide unique insight into future dynamics and vulnerabilities in a warming climate.
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Marta, S., Azzoni, R., Fugazza, D., Tielidze, L., Chand, P., Sieron, K., et al. (2021). The Retreat of Mountain Glaciers since the Little Ice Age: A Spatially Explicit Database. Data, 6(10).
Abstract: Most of the world's mountain glaciers have been retreating for more than a century in response to climate change. Glacier retreat is evident on all continents, and the rate of retreat has accelerated during recent decades. Accurate, spatially explicit information on the position of glacier margins over time is useful for analyzing patterns of glacier retreat and measuring reductions in glacier surface area. This information is also essential for evaluating how mountain ecosystems are evolving due to climate warming and the attendant glacier retreat. Here, we present a non-comprehensive spatially explicit dataset showing multiple positions of glacier fronts since the Little Ice Age (LIA) maxima, including many data from the pre-satellite era. The dataset is based on multiple historical archival records including topographical maps; repeated photographs, paintings, and aerial or satellite images with a supplement of geochronology; and own field data. We provide ESRI shapefiles showing 728 past positions of 94 glacier fronts from all continents, except Antarctica, covering the period between the Little Ice Age maxima and the present. On average, the time series span the past 190 years. From 2 to 46 past positions per glacier are depicted (on average: 7.8).</p> Dataset 10.6084/m9.figshare.13700215</p> Dataset License CC-BY-4.0</p>
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Matsuoka, K., Skoglund, A., Roth, G., De Pomereu, J., Griffiths, H., Headland, R., et al. (2021). Quantarctica, an integrated mapping environment for Antarctica, the Southern Ocean, and sub-Antarctic islands. Environmental Modelling & Software, 140.
Abstract: Quantarctica (https://www.npolar.no/quantarctica) is a geospatial data package, analysis environment, and visualization platform for the Antarctic Continent, Southern Ocean (>40oS), and sub-Antarctic islands. Quantarctica works with the free, cross-platform Geographical Information System (GIS) software QGIS and can run without an Internet connection, making it a viable tool for fieldwork in remote areas. The data package includes basemaps, satellite imagery, terrain models, and scientific data in nine disciplines, including physical and biological sciences, environmental management, and social science. To provide a clear and responsive user experience, cartography and rendering settings are carefully prepared using colour sets that work well for typical data combinations and with consideration of users with common colour vision deficiencies. Metadata included in each dataset provides brief abstracts for non-specialists and references to the original data sources. Thus, Quantarctica provides an integrated environment to view and analyse multiple Antarctic datasets together conveniently and with a low entry barrier.
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Misset, C., Recking, A., Legout, C., Bakker, M., Gimbert, F., Geay, T., et al. (2021). Using Continuous Turbidity and Seismic Measurements to Unravel Sediment Provenance and Interaction Between Suspended and Bedload Transport in an Alpine Catchment. Geophysical Research Letters, 48(4).
Abstract: Fine sediment transport results from the complexity of the interactions between the different modes of transport and the variety of possible sediment sources, from the river bed stocks remobilization to hillslopes erosion. From a 2-year period in an Alpine catchment, we show how the combined use of continuous turbidity and seismic measurements can help to address these issues. In the studied catchment, the signals are more strongly correlated during the high flows of the snowmelt period than during the summer period when the river bed is stable and the hillslopes are no longer protected by a snow cover during storms. This sheds light on the seasonal control exerted by the river bed mobility and the snow cover on suspended sediment dynamics in mountainous catchments. It also questions the potential shift of this dynamics from river bed to hillslope dominated in a context of global warming.
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Montagnat, M., Bourcier, M., Philip, A., Bons, P., Bauer, C., Deconinck, P., et al. (2021). Texture characterization of some large hailstones with an automated technique. Journal Of Glaciology, 67(266), 1190–1204.
Abstract: Hailstone structures have been studied for over a century, but so far mainly by manual optical means. This paper presents new texture and microstructure data (i.e. crystal lattice orientations, grain sizes and shapes) measured with an Automatic Ice Texture Analyzer, which gives access to high spatial and angular resolutions. The hailstones show two main characteristics: (1) they are structured with several concentric layers composed of alternating fine equiaxed grains and coarse elongated and radially oriented grains, and (2) they show two texture types with c-axes oriented either parallel or perpendicular to the radial direction. Such textures are compared with the ones observed in lake S1 and S2 ices, respectively. The S1 texture type (with c-axes parallel to the columnar crystals that grew in the radial direction) may result from epitaxial growth from a polycrystalline embryo, while the S2 texture (c-axes in the plane perpendicular to the column direction) may result from the growth from an embryo made of a few crystals with mainly one crystallographic orientation. Our novel high-resolution maps and measurements of both microstructure and texture may help to shed new light on the long-term discussion on the growth mechanisms of large hailstones.
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Nanni, U., Gimbert, F., Roux, P., & Lecointre, A. (2021). Observing the subglacial hydrology network and its dynamics with a dense seismic array. Proceedings Of The National Academy Of Sciences Of The United States Of America, 118(28).
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Payne, A., Nowicki, S., Abe-Ouchi, A., Agosta, C., Alexander, P., Albrecht, T., et al. (2021). Future Sea Level Change Under Coupled Model Intercomparison Project Phase 5 and Phase 6 Scenarios From the Greenland and Antarctic Ice Sheets. Geophysical Research Letters, 48(16).
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Piantini, M., Gimbert, F., Bellot, H., & Recking, A. (2021). Triggering and propagation of exogenous sediment pulses in mountain channels: insights from flume experiments with seismic monitoring. Earth Surface Dynamics, 9(6), 1423–1439.
Abstract: the upper part of mountain river catchments, large amounts of loose debris produced by mass-wasting processes can accumulate at the base of slopes and cliffs. Sudden destabilizations of these deposits are thought to trigger energetic sediment pulses that may travel in downstream rivers with little exchange with the local bed. The dynamics of these exogenous sediment pulses remain poorly known because direct field observations are lacking, and the processes that control their formation and propagation have rarely been explored. Here we carry out flume experiments with the aims of investigating (i) the role of sediment accumulation zones in the generation of sediment pulses, (ii) their propagation dynamics in low-order mountain channels, and (iii) the capability of seismic methods to unravel their physical properties. We use an original setup wherein we supply liquid and solid discharge to a low-slope storage zone acting like a natural sediment accumulation zone that is connected to a downstream 18% steep channel equipped with geophones. We show that the ability of the self-formed deposit to generate sediment pulses is controlled by the fine fraction of the mixture. In particular, when coarse grains coexist with a high content of finer particles, the storage area experiences alternating phases of aggradation and erosion strongly impacted by grain sorting. The upstream processes also influence the composition of the sediment pulses, which are formed by a front made of the coarsest fraction of the sediment mixture, a body composed of a high concentration of sand corresponding to the peak of solid discharge, and a diluted tail that exhibits a wide grain size distribution. Seismic measurements reveal that the front dominates the overall seismic noise, but we observe a complex dependency between seismic power and sediment pulse transport characteristics, which questions the applicability of existing seismic theories in such a context. These findings challenge the classical approach for which the sediment budget of mountain catchments is merely reduced to an available volume, since not only hydrological but also granular conditions should be considered to predict the occurrence and propagation of such sediment pulses.
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Pohl, B., Favier, V., Wille, J., Udy, D., Vance, T., Pergaud, J., et al. (2021). Relationship Between Weather Regimes and Atmospheric Rivers in East Antarctica. Journal Of Geophysical Research-Atmospheres, 126(24).
Abstract: Here, we define weather regimes in the East Antarctica-Southern Ocean sector based on daily anomalies of 700 hPa geopotential height derived from ERA5 reanalysis during 1979-2018. Most regimes and their preferred transitions depict synoptic-scale disturbances propagating eastwards off the Antarctic coastline. While regime sequences are generally short, their interannual variability is strongly driven by the polarity of the Southern Annular Mode (SAM). Regime occurrences are then intersected with atmospheric rivers (ARs) detected over the same region and period. ARs are equiprobable throughout the year, but clearly concentrate during regimes associated with a strong atmospheric ridges/blockings on the eastern part of the domain, which act to channel meridional advection of heat and moisture from the lower latitudes towards Antarctica. Both regimes and ARs significantly shape climate variability in Antarctica. Regimes favorable to AR occurrences are associated with anomalously warm and humid conditions in coastal Antarctica and, to a lesser extent, the hinterland parts of the Antarctic plateau. These anomalies are strongly enhanced during AR events, with warmer anomalies and dramatically amplified snowfall amounts. Large-scale conditions favoring AR development are finally explored. They show weak dependency to the SAM, but particularly strong atmospheric ridges/blockings over the Southern Ocean appear as the most favorable pattern, in which ARs can be embedded, and to which they contribute.
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Quiquet, A., Dumas, C., Paillard, D., Ramstein, G., Ritz, C., & Roche, D. (2021). Deglacial Ice Sheet Instabilities Induced by Proglacial Lakes. Geophysical Research Letters, 48(9).
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Reveillet, M., Vincent, C., Six, D., Rabatel, A., Sanchez, O., Piard, L., et al. (2021). Spatio-temporal variability of surface mass balance in the accumulation zone of the Mer de Glace, French Alps, from multitemporal terrestrial LiDAR measurements. Journal Of Glaciology, 67(261), 137–146.
Abstract: Spatio-temporal variability of the winter surface mass balance is a major uncertainty in the modelling of annual surface mass balance. Moreover, its measurement at high spatio-temporal resolution (sub-200 m) is very useful to force, calibrate or validate models. This study presents the results of year-round field campaigns to study the evolution of the surface mass balance in a 2 km(2) portion of the accumulation zone of the Mer de Glace (France). It is based on repeated LiDAR acquisitions, submergence-velocity measurements and meteorological records. The two methods used to quantify submergence velocities show good agreement. They present a linear temporal evolution without significant seasonal changes but display significant spatial variability. We conclude that a dense network of submergence velocity measurements is required to reduce the uncertainties when computing winter and annual surface mass balance from digital elevation model differencing. Finally, a hight spatio-temporal variability of the winter surface mass balance is highlighted (e.g., a std dev. of 0.92 m in April) even though the topography is homogeneous (std dev. of 25 m). Attempts to relate this variability to different morpho-topographic variables and wind-related indexes show the need for studies conducted at the snowfall event scale to obtain a better understanding of the variability in mass balance at the glacier scale.
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Rignot, E., An, L., Chauche, N., Morlighem, M., Jeong, S., Wood, M., et al. (2021). Retreat of Humboldt Gletscher, North Greenland, Driven by Undercutting From a Warmer Ocean. Geophysical Research Letters, 48(6).
Abstract: Humboldt Gletscher is a 100-km wide, slow-moving glacier in north Greenland which holds a 19-cm global sea level equivalent. Humboldt has been the fourth largest contributor to sea level rise since 1972 but the cause of its mass loss has not been elucidated. Multi-beam echo sounding data collected in 2019 indicate a seabed 200 m deeper than previously known. Conductivity temperature depth data reveal the presence of warm water of Atlantic origin at 0 degrees C at the glacier front and a warming of the ocean waters by 0.9 +/- 0.1 degrees C since 1962. Using an ocean model, we reconstruct grounded ice undercutting by the ocean, combine it with calculated retreat caused by ice thinning to floatation, and are able to fully explain the observed retreat. Two thirds of the retreat are caused by undercutting of grounded ice, which is a physical process not included in most ice sheet models.
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Rosero, P., Crespo-Perez, V., Espinosa, R., Andino, P., Barragan, A., Moret, P., et al. (2021). Multi-taxa colonisation along the foreland of a vanishing equatorial glacier. Ecography, 44(7), 1010–1021.
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Rounce, D., Hock, R., Mcnabb, R., Millan, R., Sommer, C., Braun, M., et al. (2021). Distributed Global Debris Thickness Estimates Reveal Debris Significantly Impacts Glacier Mass Balance. Geophysical Research Letters, 48(8).
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Royer, A., Picard, G., Vargel, C., Langlois, A., Gouttevin, I., & Dumont, M. (2021). Improved Simulation of Arctic Circumpolar Land Area Snow Properties and Soil Temperatures. Frontiers In Earth Science, 9.
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Ruiz-Hernandez, J., Condom, T., Ribstein, P., Le Moine, N., Espinoza, J., Junquas, C., et al. (2021). Spatial variability of diurnal to seasonal cycles of precipitation from a high-altitude equatorial Andean valley to the Amazon Basin. Journal Of Hydrology-Regional Studies, 38.
Abstract: Study region: The upper part of the Guayllabamba and Napo basins (78.2 degrees W, 0.3 degrees S; 18,500 km(2)) in the equatorial Andes, which are vulnerable to stress on the ecosystem services. Study focus: This paper analyses the diurnal cycle of precipitation over a transect from the Andes to the Amazon. The diurnal cycle is estimated as the diurnal distribution of precipitation for 2014-2019 using records from 80 stations. Cluster analysis performed on the diurnal cycle estimates depicts the spatial association between the diurnal and seasonal cycles of precipitation. New hydrological insights: A northwest-southeast spatial variation in the diurnal and seasonal cycles is identified with four groups of stations. In the western part, the seasonal cycles of Groups 1 and 2 are bimodal with precipitation maxima in the March-April and October-November seasons and a short drier season in July-August. In the eastern part, Group 3 also presents bimodality, but a weaker seasonal cycle. Conversely, Group 4 is unimodal with a peak in June. Distinct diurnal cycles are observed in both drier and wetter seasons of Groups 1-3; no marked diurnal cycle is observed in Group 4. Groups 3 and 4 are the most spatially heterogeneous, with an exceptional horizontal variation of 330 mm/yr/km. The analysis of these variations provides insight into the atmospheric dynamics driving precipitation in this zone, and may help to better optimize the water supply system.
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Scholzen, C., Schuler, T., & Gilbert, A. (2021). Sensitivity of subglacial drainage to water supply distribution at the Kongsfjord basin, Svalbard. Cryosphere, 15(6), 2719–2738.
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Serazin, G., Di Luca, A., Sen Gupta, A., Roge, M., Jourdain, N., Argueso, D., et al. (2021). East Australian Cyclones and Air-Sea Feedbacks. Journal Of Geophysical Research-Atmospheres, 126(20).
Abstract: The importance of resolving mesoscale air-sea interactions to represent cyclones impacting the East Coast of Australia, the so-called East Coast Lows (ECLs), is investigated using the Australian Regional Coupled Model based on NEMO-OASIS-WRF (NOW) at 1/4 degrees resolution. The fully coupled model is shown to be capable of reproducing correctly relevant features such as the seasonality, spatial distribution and intensity of ECLs while it partially resolves mesoscale processes, such as air-sea feedbacks over ocean eddies and fronts. The mesoscale thermal feedback (TFB) and the current feedback (CFB) are shown to influence the intensity of northern ECLs (north of 30 degrees S), with the TFB modulating the pre-storm sea surface temperature (SST) by shifting ECL locations eastwards and the CFB modulating the wind stress. By fully uncoupling the atmospheric model of NOW, the intensity of northern ECLs is increased due to the absence of the cold wake that provides a negative feedback to the cyclone. The number of ECLs might also be affected by the air-sea feedbacks but large interannual variability hampers significant results with short-term simulations. The TFB and CFB modify the climatology of SST (mean and variability) but no direct link is found between these changes and those noticed in ECL properties. These results show that the representation of ECLs, mainly north of 30 degrees S, depend on how air-sea feedbacks are simulated. This is particularly important for atmospheric downscaling of climate projections as small-scale SST interactions and the effects of ocean currents are not accounted for.
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Sierra, J., Junquas, C., Espinoza, J., Segura, H., Condom, T., Andrade, M., et al. (2021). Deforestation impacts on Amazon-Andes hydroclimatic connectivity. Climate Dynamics, .
Abstract: Amazonian deforestation has accelerated during the last decade, threatening an ecosystem where almost one third of the regional rainfall is transpired by the local rainforest. Due to precipitation recycling, the southwestern Amazon, including the Amazon-Andes transition region, is particularly sensitive to forest loss. This study evaluates the impacts of Amazonian deforestation on the hydro-climatic connectivity between the Amazon and the eastern tropical Andes during the austral summer (December-January-February) in terms of hydrological and energetic balances. Using 10-years high-resolution simulations (2001-2011) with the Weather Research and Forecasting Model, we analyze control and deforestation scenario simulations. Regionally, deforestation leads to a reduction in the surface net radiation, evaporation, moisture convergence and precipitation (similar to 20%) over the entire Amazon basin. In addition, during this season, deforestation increases the atmospheric subsidence over the southern Amazon and weakens the regional Hadley cell. Atmospheric stability increases over the western Amazon and the tropical Andes inhibiting convection in these areas. Consequently, major deforestation impacts are observed over the hydro-climate of the Amazon-Andes transition region. At local scale, nighttime precipitation decreases in Bolivian valleys (similar to 20-30%) due to a strong reduction in the humidity transport from the Amazon plains towards the Andes linked to the South American low-level jet. Over these valleys, a weakening of the daytime upslope winds is caused by local deforestation, which reduces the turbulent fluxes at lowlands. These alterations in rainfall and atmospheric circulation could impact the rich Andean ecosystems and its tropical glaciers.
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Vincent, C., Cusicanqui, D., Jourdain, B., Laarman, O., Six, D., Gilbert, A., et al. (2021). Geodetic point surface mass balances: a new approach to determine point surface mass balances on glaciers from remote sensing measurements. Cryosphere, 15(3), 1259–1276.
Abstract: Mass balance observations are very useful to assess climate change in different regions of the world. As opposed to glacier-wide mass balances which are influenced by the dynamic response of each glacier, point mass balances provide a direct climatic signal that depends on surface accumulation and ablation only. Unfortunately, major efforts are required to conduct in situ measurements on glaciers. Here, we propose a new approach that determines point surface mass balances from remote sensing observations. We call this balance the geodetic point surface mass balance. From observations and modelling performed on the Argentiere and Mer de Glace glaciers over the last decade, we show that the vertical ice flow velocity changes are small in areas of low bedrock slope. Therefore, assuming constant vertical velocities in time for such areas and provided that the vertical velocities have been measured for at least 1 year in the past, our method can be used to reconstruct annual point surface mass balances from surface elevations and horizontal velocities alone. We demonstrate that the annual point surface mass balances can be reconstructed with an accuracy of about 0.3?m of water equivalent per year (mw.e. a(-1)) using the vertical velocities observed over the previous years and data from unmanned aerial vehicle images. Given the recent improvements of satellite sensors, it should be possible to apply this method to high-spatial-resolution satellite images as well.
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Wagnon, P., Brun, F., Khadka, A., Berthier, E., Shrestha, D., Vincent, C., et al. (2021). Reanalysing the 2007-19 glaciological mass-balance series of Mera Glacier, Nepal, Central Himalaya, using geodetic mass balance. Journal Of Glaciology, 67(261), 117–125.
Abstract: The 2007-19 glaciological mass-balance series of Mera Glacier in the Everest Region, East Nepal, is reanalysed using the geodetic mass balance assessed by differencing two DEMs obtained from Pleiades stereo-images acquired in November 2012 and in October 2018. The glaciological glacier-wide annual mass balance of Mera Glacier has to be systematically decreased by 0.11 m w.e. a(-1) to match the geodetic mass balance. We attribute part of the positive bias of the glaciological mass balance to an over-estimation of the accumulation above 5520 m a.s.l., likely due to a measurement network unable to capture its spatial variability. Over the period 2007-19, Mera Glacier has lost mass at a rate of -0.41 +/- 0.20 m w.e. a(-1), in general agreement with regional averages for the central Himalaya. We observe a succession of negative mass-balance years since 2013.
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Wongchuig, S., Espinoza, J., Condom, T., Segura, H., Ronchail, J., Arias, P., et al. (2021). A regional view of the linkages between hydro-climatic changes and deforestation in the Southern Amazon. International Journal Of Climatology, .
Abstract: In the last four decades, the Southern Amazon (south of 8 degrees S) has shown changes in the spatial and temporal patterns of its hydro-climatic components, leading to drier conditions. Due to climate and land-use changes, this region is considered as a zone under biophysical transition processes. Previous studies have documented a complex interaction between climate and deforestation either on a large-scale or based on limited in situ data, typically covering the Brazilian Amazon. In this study, we analyse the relationships between hydro-climate, the surface water-energy partitioning and an index of regional forest cover change for the period 1981-2018. Additionally, we discretized three regions covering the Bolivian Amazon and the southern portions of the Peruvian and Brazilian Amazon due to their differences in the evolution of land use. In the Bolivian region, a high ratio of forest cover change, exceeding 40-50%, is related to a significant tendency to become water-limited. This change is associated with decreased rainfall, increased potential evapotranspiration and decreased actual evapotranspiration. Regardless of the region analysed, those that are characterized by a high ratio of forest cover change (>40-50%) show growing imbalance between increasing potential and decreasing actual evapotranspiration. However, in the Peruvian and Brazilian regions, hydro-climatic conditions remain energy-limited due to minor rainfall changes. The observed differences in surface water-energy partitioning behaviour evidence a complex dependence of both sub-regional (i.e., land cover changes) and large-scale (i.e., strengthening of the Walker and Hadley circulations) conditions. Our findings indicate a clear link between hydro-climatic changes and deforestation, providing a new perspective on their spatial variability on a sub-regional scale.
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Wood, M., Rignot, E., Fenty, I., An, L., Bjork, A., Van Den Broeke, M., et al. (2021). Ocean forcing drives glacier retreat in Greenland. Science Advances, 7(1).
Abstract: The retreat and acceleration of Greenland glaciers since the mid-1990s have been attributed to the enhanced intrusion of warm Atlantic Waters (AW) into fjords, but this assertion has not been quantitatively tested on a Greenland-wide basis or included in models. Here, we investigate how AW influenced retreat at 226 marine-terminating glaciers using ocean modeling, remote sensing, and in situ observations. We identify 74 glaciers in deep fjords with AW controlling 49% of the mass loss that retreated when warming increased undercutting by 48%. Conversely, 27 glaciers calving on shallow ridges and 24 in cold, shallow waters retreated little, contributing 15% of the loss, while 10 glaciers retreated substantially following the collapse of several ice shelves. The retreat mechanisms remain undiagnosed at 87 glaciers without ocean and bathymetry data, which controlled 19% of the loss. Ice sheet projections that exclude ocean-induced undercutting may underestimate mass loss by at least a factor of 2.
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2020 |
Bakker, M., Gimbert, F., Geay, T., Misset, C., Zanker, S., & Recking, A. (2020). Field Application and Validation of a Seismic Bedload Transport Model. Journal Of Geophysical Research-Earth Surface, 125(5).
Abstract: Bedload transport drives morphological changes in gravel-bed streams and sediment transfer in catchments. The large impact forces associated with bedload motion and its highly dynamic spatiotemporal nature make it difficult to monitor bedload transport in the field. In this study, we revise a physically-based model of bedload-induced seismic ground motion proposed by Tsai et al. (2012, ) and apply it to invert bedload flux from seismic measurements alongside an Alpine stream. First, we constrain the seismic response of a braided river reach with a simple active experiment using a series of large-rock impacts. This allows the characterization of surface wave propagation and attenuation with distance from the impact source. Second, we distinguish bedload-generated ground vibrations from those caused by turbulent flow using frequency-based scaling relationships between seismic power and discharge. Finally, absolute bedload transport rates are quantified from seismic measurements using inverse modeling based on a simplified formulation of bedload particle motion. The results are verified with a large data set of bedload samples, demonstrating that seismic measurements can provide an indirect measure for bedload flux with uncertainties within a factor of 5(+/- 1) for instantaneous measurements (between 0.01 and 1 kg/m/s). Larger deviations may be caused by uncertainties in the contribution of turbulent flow effects, particle impact velocity, and especially particle size that may vary with sediment supply and flow conditions. When constraining these uncertainties, instream sediment transport measurements are no longer necessarily required and seismic monitoring may provide an accurate and continuous means to investigate bedload dynamics in gravel-bed streams.
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Bolibar, J., Rabatel, A., Gouttevin, I., & Galiez, C. (2020). A deep learning reconstruction of mass balance series for all glaciers in the French Alps: 1967-2015. Earth System Science Data, 12(3), 1973–1983.
Abstract: Glacier mass balance (MB) data are crucial to understanding and quantifying the regional effects of climate on glaciers and the high-mountain water cycle, yet observations cover only a small fraction of glaciers in the world. We present a dataset of annual glacier-wide mass balance of all the glaciers in the French Alps for the 1967-2015 period. This dataset has been reconstructed using deep learning (i.e. a deep artificial neural network) based on direct MB observations and remote -sensing annual estimates, meteorological reanalyses and topographical data from glacier inventories. The method's validity was assessed previously through an extensive cross -validation against a dataset of 32 glaciers, with an estimated average error (RMSE) of 0.55 mw.e. a(-1), an explained variance (r(2)) of 75 % and an average bias of -0.021 m w.e. a(-1.) We estimate an average regional area-weighted glacier-wide MB of -0.69 +/- 0.21 (1 sigma) mw.e. a(-1) for the 1967-2015 period with negative mass balances in the 1970s (-0.44 m w.e. a-1), moderately negative in the 1980s (-0.16 m w.e. a(-1)) and an increasing negative trend from the 1990s onwards, up to -1.26 m w.e. a(-1) in the 2010s. Following a topographical and regional analysis, we estimate that the massifs with the highest mass losses for the 1967-2015 period are the Chablais (-0.93 mw.e. a(-1)), Champsaur (-0.86 m w.e. a(-1)), and Haute-Maurienne and Ubaye ranges (-0.84 mw.e. a(-1) each), and the ones presenting the lowest mass losses are the Mont-Blanc (-0.68 mw.e. a1), Oisans and Haute-Tarentaise ranges (-0.75 m w.e. a(-1) each). This dataset available at https://doi.org/10.5281/zenodo.3925378 (Bolibar et al., 2020a) provides relevant and timely data for studies in the fields of glaciology, hydrology and ecology in the French Alps in need of regional or glacier-specific annual net glacier mass changes in glacierized catchments.
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Brancato, V., Rignot, E., Milillo, P., Morlighem, M., Mouginot, J., An, L., et al. (2020). Grounding Line Retreat of Denman Glacier, East Antarctica, Measured With COSMO-SkyMed Radar Interferometry Data. Geophysical Research Letters, 47(7).
Abstract: Denman Glacier, East Antarctica, holds an ice volume equivalent to a 1.5 m rise in global sea level. Using satellite radar interferometry from the COSMO-SkyMed constellation, we detect a 5.4 0.3 km grounding line retreat between 1996 and 2017-2018. A novel reconstruction of the glacier bed topography indicates that the retreat proceeds on the western flank along a previously unknown 5 km wide, 1,800 m deep trough, deepening to 3,400 m below sea level. On the eastern flank, the grounding line is stabilized by a 10 km wide ridge. At tidal frequencies, the grounding line extends over a several kilometer-wide grounding zone, enabling warm ocean water to melt ice at critical locations for glacier stability. If warm, modified Circumpolar Deep Water reaches the sub-ice-shelf cavity and continues to melt ice at a rate exceeding balance conditions, the potential exists for Denman Glacier to retreat irreversibly into the deepest, marine-based basin in Antarctica. Plain Language Summary Using satellite radar data from the Italian COSMO-SkyMed constellation, we document the grounding line retreat of Denman Glacier, a major glacier in East Antarctica that holds an ice volume equivalent to a 1.5 m global sea level rise. The grounding line is retreating asymmetrically. On the eastern flank, the glacier is protected by a subglacial ridge. On the western flank, we find a deep and steep trough with a bed slope that makes the glacier conducive to rapid retreat. If warm water continues to induce high rates of ice melt near the glacier grounding zone, the potential exists for Denman Glacier to undergo a rapid and irreversible retreat, with major consequences for sea level rise.
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Braud, I., Chaffard, V., Coussot, C., Galle, S., Juen, P., Alexandre, H., et al. (2020). Building the information system of the French Critical Zone Observatories network: Theia/OZCAR-IS. Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, .
Abstract: The French Critical Zone research infrastructure, OZCAR-RI, gathers 20 observatories sampling various compartments of the critical zone, each having developed their own data management and distribution systems. A common information system (Theia/OZCAR IS) was built to make theirin situobservation FAIR (findable, accessible, interoperable, reusable). The IS architecture was designed after consultation of the users, data producers and IT teams involved in data management. A common data model based on various metadata standards was defined to create information fluxes between observatories' ISs and the Theia/OZCAR IS. Controlled vocabularies were defined to develop a data discovery web portal offering a faceted search with various criteria, including variables names and categories that were harmonized in a thesaurus published on the web. This paper describes the IS architecture, the pivot data model and open-source solutions used to implement data discovery, and future steps to implement data downloading and interoperability services.
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Brondex, J., Gagliardini, O., Gillet-Chaulet, F., & Chekki, M. (2020). Comparing the long-term fate of a snow cave and a rigid container buried at Dome C, Antarctica. Cold Regions Science And Technology, 180.
Abstract: Ice Memory is an international project aiming at creating a global ice archive sanctuary in Antarctica. The design of a perennial subsurface storage space for the cores is a cornerstone of this project. Here, we use an ice/firn flow model to investigate possible storage solutions that would meet the specific requirements of the project. To this end, we consider two extreme cases in terms of rigidity of the facility: an ice cave excavated into the firn and a perfectly rigid container buried within it. We focus on the rate of sinking of the facility as well as on the rate of closure of the cave and the evolution of the normal stresses supported by the container. Our results show that the lifetime of a cave is highly affected by the initial density of snow in its surrounding. On the other hand, the presence of the rigid container within the domain perturbs the flow of snow, creating patches of high density in its surrounding and leading to significant normal stresses on its walls. In particular, strong stress concentrations are obtained at the container angles. These results prove that unreinforced shipping containers are unsuited for this task.
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Bull, C., Kiss, A., Sen Gupta, A., Jourdain, N., Argueso, D., Di Luca, A., et al. (2020). Regional Versus Remote Atmosphere-Ocean Drivers of the Rapid Projected Intensification of the East Australian Current. Journal Of Geophysical Research-Oceans, 125(7).
Abstract: Like many western boundary currents, the East Australian Current (EAC) extension is projected to get stronger and warmer in the future. The CMIP5 multimodel mean (MMM) projection suggests up to 5 degrees C of warming under an RCP85 scenario by 2100. Previous studies employed Sverdrup balance to associate a trend in basin wide zonally integrated wind stress curl (resulting from the multidecadal poleward intensification in the westerly winds over the Southern Ocean) with enhanced transport in the EAC extension. Possible regional drivers are yet to be considered. Here we introduce the NEMO-OASIS-WRF coupled regional climate model as a framework to improve our understanding of CMIP5 projections. We analyze a hierarchy of simulations in which the regional atmosphere and ocean circulations are allowed to freely evolve subject to boundary conditions that represent present-day and CMIP5 RCP8.5 climate change anomalies. Evaluation of the historical simulation shows an EAC extension that is stronger than similar ocean-only models and observations. This bias is not explained by a linear response to differences in wind stress. The climate change simulations show that regional atmospheric CMIP5 MMM anomalies drive 73% of the projected 12 Sv increase in EAC extension transport whereas the remote ocean boundary conditions and regional radiative forcing (greenhouse gases within the domain) play a smaller role. The importance of regional changes in wind stress curl in driving the enhanced EAC extension is consistent with linear theory where the NEMO-OASIS-WRF response is closer to linear transport estimates compared to the CMIP5 MMM.
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Cornford, S., Seroussi, H., Asay-Davis, X., Gudmundsson, G., Arthern, R., Borstad, C., et al. (2020). Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP plus ). Cryosphere, 14(7), 2283–2301.
Abstract: We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods – taking a secondary role.
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Davaze, L., Rabatel, A., Dufour, A., Hugonnet, R., & Arnaud, Y. (2020). Region-Wide Annual Glacier Surface Mass Balance for the European Alps From 2000 to 2016. Frontiers In Earth Science, 8.
Abstract: Studying glacier mass changes at regional scale provides critical insights into the impact of climate change on glacierized regions, but is impractical usingin situestimates alone due to logistical and human constraints. We present annual mass-balance time series for 239 glaciers in the European Alps, using optical satellite images for the period of 2000 to 2016. Our approach, called the SLA-method, is based on the estimation of the glacier snowline altitude (SLA) for each year combined with the geodetic mass balance over the study period to derive the annual mass balance.In situannual mass-balances from 23 glaciers were used to validate our approach and underline its robustness to generate annual mass-balance time series. Such temporally-resolved observations provide a unique potential to investigate the behavior of glaciers in regions where few or no data are available. At the European Alps scale, our geodetic estimate was performed for 361 glaciers (75% of the glacierized area) and indicates a mean annual mass loss of -0.74 +/- 0.20 m w.e. yr(-1)from 2000 to 2016. The spatial variability in the average glacier mass loss is significantly correlated to three morpho-topographic variables (mean glacier slope, median, and maximum altitudes), altogether explaining 36% of the observed variance. Comparing the mass losses fromin situand SLA-method estimates and taking into account the glacier slope and maximum elevation, we show that steeper glaciers and glaciers with higher maximum elevation experienced less mass loss. Because steeper glaciers (>20 degrees) are poorly represented byin situestimates, we suggest that region-wide extrapolation of field measurements could be improved by including a morpho-topographic dependency. The analysis of the annual mass changes with regard to a global atmospheric dataset (ERA5) showed that: (i) extreme climate events are registered by all glaciers across the European Alps, and we identified opposite weather regimes favorable or detrimental to the mass change; (ii) the interannual variability of glacier mass balances in the “central European Alps” is lower; and (iii) current strong imbalance of glaciers in the European Alps is likely mainly the consequence of the multi-decadal increasing trend in atmospheric temperature, clearly documented from ERA5 data.
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Derkacheva, A., Mouginot, J., Millan, R., Maier, N., & Gillet-Chaulet, F. (2020). Data Reduction Using Statistical and Regression Approaches for Ice Velocity Derived by Landsat-8, Sentinel-1 and Sentinel-2. Remote Sensing, 12(12).
Abstract: During the last decade, the number of available satellite observations has increased significantly, allowing for far more frequent measurements of the glacier speed. Appropriate methods of post-processing need to be developed to efficiently deal with the large volumes of data generated and relatively large intrinsic errors associated with the measurements. Here, we process and combine together measurements of ice velocity of Russell Gletscher in Greenland from three satellites-Sentinel-1, Sentinel-2, and Landsat-8, creating a multi-year velocity database with high temporal and spatial resolution. We then investigate post-processing methodologies with the aim of generating corrected, ordered, and simplified time series. We tested rolling mean and median, cubic spline regression, and linear non-parametric local regression (LOWESS) smoothing algorithms to reduce data noise, evaluated the results against ground-based GPS in one location, and compared the results between two locations with different characteristics. We found that LOWESS provides the best solution for noisy measurements that are unevenly distributed in time. Using this methodology with these sensors, we can robustly derive time series with temporal resolution of 2-3 weeks and improve the accuracy on the ice velocity to about 10 m/yr, or a factor of three compared to the initial measurements. The presented methodology could be applied to the entire Greenland ice sheet with an aim of reconstructing comprehensive sub-seasonal ice flow dynamics and mass balance.
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Dunn, R., Alexander, L., Donat, M., Zhang, X., Bador, M., Herold, N., et al. (2020). Development of an Updated Global Land In Situ-Based Data Set of Temperature and Precipitation Extremes: HadEX3. Journal Of Geophysical Research-Atmospheres, 125(16).
Abstract: We present the second update to a data set of gridded land-based temperature and precipitation extremes indices: HadEX3. This consists of 17 temperature and 12 precipitation indices derived from daily, in situ observations and recommended by the World Meteorological Organization (WMO) Expert Team on Climate Change Detection and Indices (ETCCDI). These indices have been calculated at around 7,000 locations for temperature and 17,000 for precipitation. The annual (and monthly) indices have been interpolated on a1.875 degrees x1.25 degrees longitude-latitude grid, covering 1901-2018. We show changes in these indices by examining “global”-average time series in comparison with previous observational data sets and also estimating the uncertainty resulting from the nonuniform distribution of meteorological stations. Both the short and long time scale behavior of HadEX3 agrees well with existing products. Changes in the temperature indices are widespread and consistent with global-scale warming. The extremes related to daily minimum temperatures are changing faster than the maximum. Spatial changes in the linear trends of precipitation indices over 1950-2018 are less spatially coherent than those for temperature indices. Globally, there are more heavy precipitation events that are also more intense and contribute a greater fraction to the total. Some of the indices use a reference period for calculating exceedance thresholds. We present a comparison between using 1961-1990 and 1981-2010. The differences between the time series of the temperature indices observed over longer time scales are shown to be the result of the interaction of the reference period with a warming climate. The gridded netCDF files and, where possible, underlying station indices are available from and .
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Dussaillant, I., Berthier, E., Brun, F., Masiokas, M., Hugonnet, R., Favier, V., et al. (2020). Two decades of glacier mass loss along the Andes. Nature Geoscience, 13(9), 802–+.
Abstract: Andean glaciers are among the fastest shrinking and largest contributors to sea level rise on Earth. They also represent crucial water resources in many tropical and semi-arid mountain catchments. Yet the magnitude of the recent ice loss is still debated. Here we present Andean glacier mass changes (from 10 degrees N to 56 degrees S) between 2000 and 2018 using time series of digital elevation models derived from ASTER stereo images. The total mass change over this period was -22.9 +/- 5.9 Gt yr(-1) (-0.72 +/- 0.22 m w.e. yr(-1) (m w.e., metres of water equivalent)), with the most negative mass balances in the Patagonian Andes (-0.78 +/- 0.25 m w.e. yr(-1)) and the Tropical Andes (-0.42 +/- 0.24 m w.e. yr(-1)), compared to relatively moderate losses (-0.28 +/- 0.18 m w.e. yr(-1)) in the Dry Andes. Subperiod analysis (2000-2009 versus 2009-2018) revealed a steady mass loss in the tropics and south of 45 degrees S. Conversely, a shift from a slightly positive to a strongly negative mass balance was measured between 26 and 45 degrees S. In the latter region, the drastic glacier loss in recent years coincides with the extremely dry conditions since 2010 and partially helped to mitigate the negative hydrological impacts of this severe and sustained drought. These results provide a comprehensive, high-resolution and multidecadal data set of recent Andes-wide glacier mass changes that constitutes a relevant basis for the calibration and validation of hydrological and glaciological models intended to project future glacier changes and their hydrological impacts.
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Dutheil, C., Lengaigne, M., Bador, M., Vialard, J., Lefevre, J., Jourdain, N., et al. (2020). Impact of projected sea surface temperature biases on tropical cyclones projections in the South Pacific. Scientific Reports, 10(1).
Abstract: Climate model projections generally indicate fewer but more intense tropical cyclones (TCs) in response to increasing anthropogenic emissions. However these simulations suffer from long-standing biases in their Sea Surface Temperature (SST). While most studies investigating future changes in TC activity using high-resolution atmospheric models correct for the present-day SST bias, they do not consider the reliability of the projected SST changes from global climate models. The present study illustrates that future South Pacific TC activity changes are strongly sensitive to correcting the projected SST changes using an emergent constraint method. This additional correction indeed leads to a strong reduction of the cyclogenesis (-55%) over the South Pacific basin, while no statistically significant change arises in the uncorrected simulations. Cyclogenesis indices suggest that this strong reduction in the corrected experiment is caused by stronger vertical wind shear in response to a South Pacific Convergence Zone equatorward shift. We thus find that uncertainty in the projected SST patterns could strongly hamper the reliability of South Pacific TC projections. The strong sensitivity found in the current study will need to be investigated with other models, observational constraint methods and in other TC basins in order to assess the reliability of regional TC projections.
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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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Gavrikov, A., Gulev, S., Markina, M., Tilinina, N., Verezemskaya, P., Barnier, B., et al. (2020). RAS-NAAD: 40-yr High-Resolution North Atlantic Atmospheric Hindcast for Multipurpose Applications (New Dataset for the Regional Mesoscale Studies in the Atmosphere and the Ocean). Journal Of Applied Meteorology And Climatology, 59(5), 793–817.
Abstract: We present in this paper the results of the Russian Academy of Sciences North Atlantic Atmospheric Downscaling (RAS-NAAD) project, which provides a 40-yr 3D hindcast of the North Atlantic (10 degrees-80 degrees N) atmosphere at 14-km spatial resolution with 50 levels in the vertical direction (up to 50 hPa), performed with a regional setting of theWRF-ARW3.8.1model for the period 1979-2018 and forced by ERA-Interim as a lateral boundary condition. The dataset provides a variety of surface and free-atmosphere parameters at sigma model levels and meets many demands of meteorologists, climate scientists, and oceanographers working in both research and operational domains. Three-dimensional model output at 3-hourly time resolution is freely available to the users. Our evaluation demonstrates a realistic representation of most characteristics in both datasets and also identifies biases mostly in the ice-covered regions. High-resolution and nonhydrostatic model settings in NAAD resolve mesoscale dynamics first of all in the subpolar latitudes. NAAD also provides a new view of the North Atlantic extratropical cyclone activity with a much larger number of cyclones as compared with most reanalyses. It also effectively captures highly localized mechanisms of atmospheric moisture transports. Applications of NAAD to ocean circulation and wave modeling are demonstrated.
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Hausmann, U., Sallee, J., Jourdain, N., Mathiot, P., Rousset, C., Madec, G., et al. (2020). The Role of Tides in Ocean-Ice Shelf Interactions in the Southwestern Weddell Sea. Journal Of Geophysical Research-Oceans, 125(6).
Abstract: To investigate the role of tides in Weddell Sea ocean-ice shelf melt interactions, and resulting consequences for ocean properties and sea ice interactions, we develop a regional ocean-sea ice model configuration, with time-varying ocean boundary and atmospheric forcing, including the deep open ocean (at 2.5-4 km horizontal resolution), the southwestern continental shelf (approximate to 2.5 km), and the adjacent cavities of eastern Weddell, Larsen, and Filchner-Ronne ice shelves (FRIS, 1.5-2.5 km). Simulated circulation, water mass, and ice shelf melt properties compare overall well with available open ocean and cavity observational knowledge. Tides are shown to enhance the kinetic energy of the time-varying flow in contact with the ice shelves, thereby increasing melt. This dynamically driven impact of tides on net melting is to almost 90% compensated by cooling through the meltwater that is produced but not quickly exported from regions of melting in the Weddell Sea cold-cavity regime. The resulting systematic tide-driven enhancement of both produced meltwater and its refreezing on ascending branches of, especially the FRIS, cavity circulation acts to increase net ice shelf melting (by 50% in respect to the state without tides, approximate to 50 Gt yr(-1)). In addition, tides also increase the melt-induced FRIS cavity circulation, and the meltwater export by the FRIS outflow. Simulations suggest attendant changes on the open-ocean southwestern continental shelf, characterized by overall freshening and small year-round sea ice thickening, as well as in the deep southwestern Weddell Sea in the form of a marked freshening of newly formed bottom waters.
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Helanow, C., Iverson, N., Zoet, L., & Gagliardini, O. (2020). Sliding Relations for Glacier Slip With Cavities Over Three-Dimensional Beds. Geophysical Research Letters, 47(3).
Abstract: Results of glacier flow models and associated estimates of future sea level rise depend sensitively on the prescribed relation between shear stress and slip velocity at the glacier bed. Using a fully three-dimensional numerical model of ice flow, we compute steady-state sliding relations for where ice slips over a rock bed with three-dimensional, periodic topography. In agreement with studies of two-dimensional beds, water-filled cavities that form down-glacier from bedforms cause basal shear stress to peak at a threshold slip velocity and decrease at higher velocities (i.e., rate-weakening drag). However, the shear stress magnitude and extent of rate-weakening drag depend systematically on lateral topographic variations not considered previously. Moreover, steep up-glacier-facing slopes of bedforms can result in shear stress that increases monotonically over a wide range of slip velocity, helping to stabilize slip. These results highlight the potential variability of sliding relations and their likely sensitivity to the morphological diversity of glacier beds. Plain Language Summary Parts of ice sheets that flow into the oceans and affect sea level can flow unusually fast by slipping over their beds. We use a computer to solve for the first time in three dimensions the equations that describe the flow of ice as it slips over a bumpy rock bed. We include the important tendency for glaciers to separate from rock and form water-filled cavities down-glacier from bumps. These calculations indicate that resistance to slip depends sensitively on the bump shape and spacing. Cavities can cause the bed to become more slippery the faster the ice slides, with this destabilizing effect being more severe for bumps that are laterally narrow and widely spaced. However, bumps with steeply sloping up-glacier sides can reverse this effect and cause resistance to slip to increase over a wide range of increasing slip velocity. This diverse behavior highlights the need for estimates of glacier slip velocity to incorporate the actual topography of glacier beds.
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Jourdain, N., Asay-Davis, X., Hattermann, T., Straneo, F., Seroussi, H., Little, C., et al. (2020). A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections. Cryosphere, 14(9), 3111–3134.
Abstract: Climate model projections have previously been used to compute ice shelf basal melt rates in ice sheet models, but the strategies employed – e.g., ocean input, parameterization, calibration technique, and corrections – have varied widely and are often ad hoc. Here, a methodology is proposed for the calculation of circum-Antarctic basal melt rates for floating ice, based on climate models, that is suitable for ISMIP6, the Ice Sheet Model Intercomparison Project for CMIP6 (6th Coupled Model Intercomparison Project). The past and future evolution of ocean temperature and salinity is derived from a climate model by estimating anomalies with respect to the modern day, which are added to a present-day climatology constructed from existing observational datasets. Temperature and salinity are extrapolated to any position potentially occupied by a simulated ice shelf. A simple formulation is proposed for a basal melt parameterization in ISMIP6, constrained by the observed temperature climatology, with a quadratic dependency on either the nonlocal or local thermal forcing. Two calibration methods are proposed: (1) based on the mean Antarctic melt rate (MeanAnt) and (2) based on melt rates near Pine Island's deep grounding line (PIGL). Future Antarctic mean melt rates are an order of magnitude greater in PIGL than in MeanAnt. The PIGL calibration and the local parameterization result in more realistic melt rates near grounding lines. PIGL is also more consistent with observations of interannual melt rate variability underneath Pine Island and Dotson ice shelves. This work stresses the need for more physics and less calibration in the parameterizations and for more observations of hydrographic properties and melt rates at interannual and decadal timescales.
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Kane, E., Rignot, E., Mouginot, J., Millan, R., Li, X., Scheuchl, B., et al. (2020). Impact of Calving Dynamics on Kangilernata Sermia, Greenland. Geophysical Research Letters, 47(20).
Abstract: Iceberg calving is a major component of glacier mass ablation that is not well understood due to a lack of detailed temporal and spatial observations. Here, we measure glacier speed and surface elevation at 3 min intervals using a portable radar interferometer at Kangilernata Sermia, West Greenland, for a period of 2 weeks in July 2016. We detect a 20% diurnal variation in glacier speed in phase with tidal height propagating kilometers inland. We find no speedup from ice shedding off the calving face or the detachment of floating ice blocks but a 30% speedup within a few hundred meters of the ice front that persists for days when calving removes full-thickness grounded ice blocks. Within one ice thickness from the calving front, we detect maximum strain rates 2 to 3 times larger than observable from satellite data, which has implications for studying iceberg calving as a fracturing process.
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Khan, S., Bjork, A., Bamber, J., Morlighem, M., Bevis, M., Kjor, K., et al. (2020). Centennial response of Greenland's three largest outlet glaciers. Nature Communications, 11(1).
Abstract: The Greenland Ice Sheet is the largest land ice contributor to sea level rise. This will continue in the future but at an uncertain rate and observational estimates are limited to the last few decades. Understanding the long-term glacier response to external forcing is key to improving projections. Here we use historical photographs to calculate ice loss from 1880-2012 for Jakobshavn, Helheim, and Kangerlussuaq glacier. We estimate ice loss corresponding to a sea level rise of 8.11.1 millimetres from these three glaciers. Projections of mass loss for these glaciers, using the worst-case scenario, Representative Concentration Pathways 8.5, suggest a sea level contribution of 9.1-14.9mm by 2100. RCP8.5 implies an additional global temperature increase of 3.7 degrees C by 2100, approximately four times larger than that which has taken place since 1880. We infer that projections forced by RCP8.5 underestimate glacier mass loss which could exceed this worst-case scenario. The Greenland Ice Sheet is the largest land ice contributor to sea level rise and understanding the long-term glacier response to external forcing is key to improved projections. Here the authors show Greenland's three largest outlet glaciers will likely exceed current worst-case scenario
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Li, Y., Sen Gupta, A., Taschetto, A., Jourdain, N., Di Luca, A., Done, J., et al. (2020). Assessing the role of the ocean-atmosphere coupling frequency in the western Maritime Continent rainfall. Climate Dynamics, .
Abstract: High-frequency interactions between the ocean and atmosphere have the potential to affect lower frequency or mean state climate in various regions. Here we examine the importance of sub-daily air-sea interactions over the Maritime Continent region to the rectification of longer timescale variation. In order to determine the importance of these high-frequency interactions, we conducted two regional ocean-atmosphere coupled simulations over the Maritime Continent where exchanges between the oceanic and atmospheric components are performed either every hour (i.e. resolving diurnal changes) or every day. We find that coupling frequency has a significant influence on mean sea surface temperature (SST) and the mean state and diurnal cycle of rainfall over certain regions of the western Maritime Continent where air-sea interactions are strong during the Asian monsoon season, with little effect in other regions or seasons. Without sub-daily air-sea interactions, the mean SST along the southwest off Sumatra is similar to 2 degrees C warmer during the period from June to October as a result of a deepening of thermocline along the coast. This deepening is linked to anomalous downwelling equatorial eastward propagating Kelvin waves triggered by westerly anomalies in the eastern equatorial Indian Ocean. In addition, the mean rainfall in the vicinity of ocean warming increases, thereby producing an enhanced barrier layer that also provides a positive warming feedback. Although the coupling frequency has little impact on the timing of the rainfall diurnal cycle, suppression of sub-daily coupling significantly changes the diurnal rainfall amplitude causing a relative decrease (increase) in amplitude over the coast of Northwestern (Southwestern) Sumatra during the South Asian monsoon season.
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Masiokas, M., Rabatel, A., Rivera, A., Ruiz, L., Pitte, P., Ceballos, J., et al. (2020). A Review of the Current State and Recent Changes of the Andean Cryosphere. Frontiers In Earth Science, 8.
Abstract: The Andes Cordillera contains the most diverse cryosphere on Earth, including extensive areas covered by seasonal snow, numerous tropical and extratropical glaciers, and many mountain permafrost landforms. Here, we review some recent advances in the study of the main components of the cryosphere in the Andes, and discuss the changes observed in the seasonal snow and permanent ice masses of this region over the past decades. The open access and increasing availability of remote sensing products has produced a substantial improvement in our understanding of the current state and recent changes of the Andean cryosphere, allowing an unprecedented detail in their identification and monitoring at local and regional scales. Analyses of snow cover maps has allowed the identification of seasonal patterns and long term trends in snow accumulation for most of the Andes, with some sectors in central Chile and central-western Argentina showing a clear decline in snowfall and snow persistence since 2010. This recent shortage of mountain snow has caused an extended, severe drought that is unprecedented in the hydrological and climatological records from this region. Together with data from global glacier inventories, detailed inventories at local/regional scales are now also freely available, providing important new information for glaciological, hydrological, and climatological assessments in different sectors of the Andes. Numerous studies largely based on field measurements and/or remote sensing techniques have documented the recent glacier shrinkage throughout the Andes. This observed ice mass loss has put Andean glaciers among the highest contributors to sea level rise per unit area. Other recent studies have focused on rock glaciers, showing that in extensive semi-arid sectors of the Andes these mountain permafrost features contain large reserves of freshwater and may play a crucial role as future climate becomes warmer and drier in this region. Many relevant issues remain to be investigated, however, including an improved estimation of ice volumes at local scales, and detailed assessments of the hydrological significance of the different components of the cryosphere in Andean river basins. The impacts of future climate changes on the Andean cryosphere also need to be studied in more detail, considering the contrasting climatic scenarios projected for each region. The sustained work of various monitoring programs in the different Andean countries is promising and will provide much needed field observations to validate and improve the analyses made from remote sensors and modeling techniques. In this sense, the development of a well-coordinated network of high-elevation hydro-meteorological stations appears as a much needed priority to complement and improve the many glaciological and hydro-climatological assessments that are being conducted across the Andes.
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Menegoz, M., Valla, E., Jourdain, N., Blanchet, J., Beaumet, J., Wilhelm, B., et al. (2020). Contrasting seasonal changes in total and intense precipitation in the European Alps from 1903 to 2010. Hydrology And Earth System Sciences, 24(11), 5355–5377.
Abstract: Changes in precipitation over the European Alps are investigated with the regional climate model MAR (Modele Atmospherique Regional) applied with a 7 km resolution over the period 1903-2010 using the reanalysis ERA-20C as forcing. A comparison with several observational datasets demonstrates that the model is able to reproduce the climatology as well as both the interannual variability and the seasonal cycle of precipitation over the European Alps. The relatively high resolution allows us to estimate precipitation at high elevations. The vertical gradient of precipitation simulated by MAR over the European Alps reaches 33% km(-1) (1.21mm d(-1) km(-1)) in summer and 38% km(-1) (1.15 mm d(-1) km(-1)) in winter, on average, over 1971-2008 and shows a large spatial variability. A significant (p value < 0.05) increase in mean winter precipitation is simulated in the northwestern Alps over 1903-2010, with changes typically reaching 20% to 40% per century. This increase is mainly explained by a stronger simple daily intensity index (SDII) and is associated with less-frequent but longer wet spells. A general drying is found in summer over the same period, exceeding 20% to 30% per century in the western plains and 40% to 50% per century in the southern plains surrounding the Alps but remaining much smaller (< 10 %) and not significant above 1500 ma.s.l. Below this level, the summer drying is explained by a reduction in the number of wet days, reaching 20% per century over the northwestern part of the Alps and 30% to 50% per century in the southern part of the Alps. It is associated with shorter but more-frequent wet spells. The centennial trends are modulated over the last decades, with the drying occurring in the plains in winter also affecting high-altitude areas during this season and with a positive trend of autumn precipitation occurring only over the last decades all over the Alps. Maximum daily precipitation index (Rx1day) takes its highest values in autumn in both the western and the eastern parts of the southern Alps, locally reaching 50 to 70 mm d(-1) on average over 1903-2010. Centennial maxima up to 250 to 300 mm d(-1) are simulated in the southern Alps, in France and Italy, as well as in the Ticino valley in Switzerland. Over 1903-2010, seasonal Rx1day shows a general and significant increase at the annual timescale and also during the four seasons, reaching local values between 20% and 40% per century over large parts of the Alps and the Apennines. Trends of Rx1day are significant (p value < 0.05) only when considering long time series, typically 50 to 80 years depending on the area considered. Some of these trends are nonetheless significant when computed over 1970-2010, suggesting a recent acceleration of the increase in extreme precipitation, whereas earlier periods with strong precipitation also occurred, in particular during the 1950s and 1960s.
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Millan, R., St-Laurent, P., Rignot, E., Morlighem, M., Mouginot, J., & Scheuchl, B. (2020). Constraining an Ocean Model Under Getz Ice Shelf, Antarctica, Using A Gravity-Derived Bathymetry. Geophysical Research Letters, 47(13).
Abstract: Getz Ice Shelf, the largest producer of ice shelf meltwater in Antarctica, buttresses glaciers that hold enough ice to raise sea level by 22 cm. We present a new bathymetry of its sub-ice shelf cavity using a three-dimensional inversion of airborne gravity data constrained by multibeam bathymetry at sea and a reconstruction of the bedrock from mass conservation on land. The new bathymetry is deeper than previously estimated with differences exceeding 500 m in a number of regions. When incorporated into an ocean model, it yields a better description of the spatial distribution of ice shelf melt, specifically along glacier grounding lines. While the melt intensity is overestimated because of a positive bias in ocean thermal forcing, the study reveals the main pathways along which warm oceanic water enters the cavity and corroborates the observed rapid retreat of Berry Glacier along a deep channel with a retrograde bed slope.
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Montagnat, M., Chambon, G., Gaume, J., Hagenmuller, P., & Sandells, M. (2020). Editorial: About the Relevance of Snow Microstructure Study in Cryospheric Sciences. Frontiers In Earth Science, 8.
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Montagnat, M., Lowe, H., Calonne, N., Schneebeli, M., Matzl, M., & Jaggi, M. (2020). On the Birth of Structural and Crystallographic Fabric Signals in Polar Snow: A Case Study From the EastGRIP Snowpack. Frontiers In Earth Science, 8.
Abstract: The role of near-surface snow processes for the formation of climate signals through densification into deep polar firn is still barely understood. To this end we have analyzed a shallow snow pit (0-3 meters) from EastGRIP (Greenland) and derived high-resolution profiles of different types of mechanically relevant fabric tensors. The structural fabric, which characterizes the anisotropic geometry of ice matrix and pore space, was obtained by X-ray tomography. The crystallographic fabric, which characterizes the anisotropic distribution of thec-axis (or optical axis) orientations of snow crystals, was obtained from automatic analysis of thin sections. The structural fabric profile unambiguously reveals the seasonal cycles at EastGRIP, as a consequence of temperature gradient metamorphism, and in contrast to featureless signals of parameters like density or specific surface area. The crystallographic fabric profile unambiguously reveals a signal of cluster-type texture already at shallow depth. We make use of order of magnitude estimates for the formation time of both fabric signals and discuss potential coupling effects in the context of snow and firn densification.
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Nanni, U., Gimbert, F., Vincent, C., Graff, D., Walter, F., Piard, L., et al. (2020). Quantification of seasonal and diurnal dynamics of subglacial channels using seismic observations on an Alpine glacier. Cryosphere, 14(5), 1475–1496.
Abstract: Water flowing below glaciers exerts a major control on glacier basal sliding. However, our knowledge of the physics of subglacial hydrology and its link with sliding is limited because of lacking observations. Here we use a 2-year-long dataset made of on-ice-measured seismic and in situ-measured glacier basal sliding speed on Glacier d'Argentiere (French Alps) to investigate the physics of subglacial channels and its potential link with glacier basal sliding. Using dedicated theory and concomitant measurements of water discharge, we quantify temporal changes in channels' hydraulic radius and hydraulic pressure gradient. At seasonal timescales we find that hydraulic radius and hydraulic pressure gradient respectively exhibit a 2- and 6-fold increase from spring to summer, followed by comparable decrease towards autumn. At low discharge during the early and late melt season channels respond to changes in discharge mainly through changes in hydraulic radius, a regime that is consistent with predictions of channels' behaviour at equilibrium. In contrast, at high discharge and high short-term water-supply variability (summertime), channels undergo strong changes in hydraulic pressure gradient, a behaviour that is consistent with channels behaving out of equilibrium. This out-of-equilibrium regime is further supported by observations at the diurnal scale, which prove that channels pressurize in the morning and depressurize in the afternoon. During summer we also observe high and sustained basal sliding speed, which supports that the widespread in-efficient drainage system (cavities) is likely pressurized concomitantly with the channel system. We propose that pressurized channels help sustain high pressure in cavities (and therefore high glacier sliding speed) through an efficient hydraulic connection between the two systems. The present findings provide an essential basis for testing the physics represented in subglacial hydrology and glacier sliding models.
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Nowicki, S., Goelzer, H., Seroussi, H., Payne, A., Lipscomb, W., Abe-Ouchi, A., et al. (2020). Experimental protocol for sea level projections from ISMIP6 stand-alone ice sheet models. Cryosphere, 14(7), 2331–2368.
Abstract: Projection of the contribution of ice sheets to sea level change as part of the Coupled Model Intercomparison Project Phase 6 (CMIP6) takes the form of simulations from coupled ice sheet-climate models and stand-alone ice sheet models, overseen by the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). This paper describes the experimental setup for process-based sea level change projections to be performed with stand-alone Greenland and Antarctic ice sheet models in the context of ISMIP6. The ISMIP6 protocol relies on a suite of polar atmospheric and oceanic CMIP-based forcing for ice sheet models, in order to explore the uncertainty in projected sea level change due to future emissions scenarios, CMIP models, ice sheet models, and parameterizations for ice-ocean interactions. We describe here the approach taken for defining the suite of ISMIP6 stand-alone ice sheet simulations, document the experimental framework and implementation, and present an overview of the ISMIP6 forcing to be used by participating ice sheet modeling groups.
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Paul, F., Rastner, P., Azzoni, R., Diolaiuti, G., Fugazza, D., Le Bris, R., et al. (2020). Glacier shrinkage in the Alps continues unabated as revealed by a new glacier inventory from Sentinel-2. Earth System Science Data, 12(3), 1805–1821.
Abstract: The ongoing glacier shrinkage in the Alps requires frequent updates of glacier outlines to provide an accurate database for monitoring, modelling purposes (e.g. determination of run-off, mass balance, or future glacier extent), and other applications. With the launch of the first Sentinel-2 (S2) satellite in 2015, it became possible to create a consistent, Alpine-wide glacier inventory with an unprecedented spatial resolution of 10 m. The first S2 images from August 2015 already provided excellent mapping conditions for most glacierized regions in the Alps and were used as a base for the compilation of a new Alpine-wide glacier inventory in a collaborative team effort. In all countries, glacier outlines from the latest national inventories have been used as a guide to compile an update consistent with the respective previous interpretation. The automated mapping of clean glacier ice was straightforward using the band ratio method, but the numerous debris-covered glaciers required intense manual editing. Cloud cover over many glaciers in Italy required also including S2 scenes from 2016. The outline uncertainty was determined with digitizing of 14 glaciers several times by all participants. Topographic information for all glaciers was obtained from the ALOS AW3D30 digital elevation model (DEM). Overall, we derived a total glacier area of 1806 +/- 60 km(2) when considering 4395 glaciers > 0.01 km(2). This is 14% (-1.2% a(-1)) less than the 2100 km(2) derived from Landsat in 2003 and indicates an unabated continuation of glacier shrinkage in the Alps since the mid-1980s. It is a lower-bound estimate, as due to the higher spatial resolution of S2 many small glaciers were additionally mapped or increased in size compared to 2003. Median elevations peak around 3000ma.s.l., with a high variability that depends on location and aspect. The uncertainty assessment revealed locally strong differences in interpretation of debris-covered glaciers, resulting in limitations for change assessment when using glacier extents digitized by different analysts. The inventory is available at https.//doi.org/10.1594/PANGAEA.909133 (Paul et al., 2019).
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Peyaud, V., Bouchayer, C., Gagliardini, O., Vincent, C., Gillet-Chaulet, F., Six, D., et al. (2020). Numerical modeling of the dynamics of the Mer de Glace glacier, French Alps: comparison with past observations and forecasting of near-future evolution. Cryosphere, 14(11), 3979–3994.
Abstract: Alpine glaciers are shrinking and rapidly loosing mass in a warming climate. Glacier modeling is required to assess the future consequences of these retreats on water resources, the hydropower industry and risk management. However, the performance of such ice flow modeling is generally difficult to evaluate because of the lack of long-term glaciological observations. Here, we assess the performance of the Elmer/Ice full Stokes ice flow model using the long dataset of mass balance, thickness change, ice flow velocity and snout fluctuation measurements obtained between 1979 and 2015 on the Mer de Glace glacier, France. Ice flow modeling results are compared in detail to comprehensive glaciological observations over 4 decades including both a period of glacier expansion preceding a long period of decay. To our knowledge, a comparison to data at this detail is unprecedented. We found that the model accurately reconstructs the velocity, elevation and length variations of this glacier despite some discrepancies that remain unexplained. The calibrated and validated model was then applied to simulate the future evolution of Mer de Glace from 2015 to 2050 using 26 different climate scenarios. Depending on the climate scenarios, the largest glacier in France, with a length of 20 km, could retreat by 2 to 6 km over the next 3 decades.
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Rees, W., Golubeva, E., Tutubalina, O., Zimin, M., & Derkacheva, A. (2020). Relation between leaf area index and NDVI for subarctic deciduous vegetation. International Journal Of Remote Sensing, 41(22), 8573–8589.
Abstract: We consider the relationship between leaf area index (LAI) and normalized difference vegetation index (NDVI) for green-leaf vegetation from a subarctic study site, specifically to test whether relationships optimized for lower-latitude vegetation can be assumed to hold at higher latitudes. We focus attention particularly on dwarf-shrub vegetation, which has received little previous investigation. We have collected hyperspectral measurements of the optical properties (reflectance and absorptance) of single leaves from dwarf shrub and tree species common to northern European Russia, and have developed a simple physical model of the properties of assemblages ('leaf stacks') of these leaves. The model is shown to provide a satisfactory explanation of the effect of varying the number of leaves in a stack on its NDVI, and can be easily adapted to make simple measurements using relatively inexpensive equipment. Our results show that the LAI-NDVI relationship for a vegetation canopy will saturate (approach within 10% of its limiting value) when the LAI reaches a value of around 2 to 3. Values this low are not uncommon in subarctic vegetation. It is also shown that dwarf shrub vegetation may show lower NDVI than trees for the same LAI.
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Robinson, A., Alvarez-Solas, J., Montoya, M., Goelzer, H., Greve, R., & Ritz, C. (2020). Description and validation of the ice-sheet model Yelmo (version 1.0). Geoscientific Model Development, 13(6), 2805–2823.
Abstract: We describe the physics and features of the ice-sheet model Yelmo, an open-source project intended for collaborative development. Yelmo is a thermomechanical model, solving for the coupled velocity and temperature solutions of an ice sheet simultaneously. The ice dynamics are currently treated via a “hybrid” approach combining the shallow-ice and shallow-shelf/shelfy-stream approximations, which makes Yelmo an apt choice for studying a wide variety of problems. Yelmo's main innovations lie in its flexible and user-friendly infrastructure, which promotes portability and facilitates long-term development. In particular, all physics subroutines have been designed to be self-contained, so that they can be easily ported from Yelmo to other models, or easily replaced by improved or alternate methods in the future. Furthermore, hard-coded model choices are eschewed, replaced instead with convenient parameter options that allow the model to be adapted easily to different contexts. We show results for different ice-sheet benchmark tests, and we illustrate Yelmo's performance for the Antarctic ice sheet.
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Seroussi, H., Nowicki, S., Payne, A., Goelzer, H., Lipscomb, W., Abe-Ouchi, A., et al. (2020). ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century. Cryosphere, 14(9), 3033–3070.
Abstract: Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015-2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between 7:8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between 6 :1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.
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Sun, S., Pattyn, F., Simon, E., Albrecht, T., Cornford, S., Calov, R., et al. (2020). Antarctic ice sheet response to sudden and sustained ice-shelf collapse (ABUMIP). Journal Of Glaciology, 66(260), 891–904.
Abstract: Antarctica's ice shelves modulate the grounded ice flow, and weakening of ice shelves due to climate forcing will decrease their 'buttressing' effect, causing a response in the grounded ice. While the processes governing ice-shelf weakening are complex, uncertainties in the response of the grounded ice sheet are also difficult to assess. The Antarctic BUttressing Model Intercomparison Project (ABUMIP) compares ice-sheet model responses to decrease in buttressing by investigating the 'end-member' scenario of total and sustained loss of ice shelves. Although unrealistic, this scenario enables gauging the sensitivity of an ensemble of 15 ice-sheet models to a total loss of buttressing, hence exhibiting the full potential of marine ice-sheet instability. All models predict that this scenario leads to multi-metre (1-12 m) sea-level rise over 500 years from present day. West Antarctic ice sheet collapse alone leads to a 1.91-5.08 m sea-level rise due to the marine ice-sheet instability. Mass loss rates are a strong function of the sliding/friction law, with plastic laws cause a further destabilization of the Aurora and Wilkes Subglacial Basins, East Antarctica. Improvements to marine ice-sheet models have greatly reduced variability between modelled ice-sheet responses to extreme ice-shelf loss, e.g. compared to the SeaRISE assessments.
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Swingedouw, D., Speranza, C., Bartsch, A., Durand, G., Jamet, C., Beaugrand, G., et al. (2020). Early Warning from Space for a Few Key Tipping Points in Physical, Biological, and Social-Ecological Systems. Surveys In Geophysics, .
Abstract: In this review paper, we explore latest results concerning a few key tipping elements of the Earth system in the ocean, cryosphere, and land realms, namely the Atlantic overturning circulation and the subpolar gyre system, the marine ecosystems, the permafrost, the Greenland and Antarctic ice sheets, and in terrestrial resource use systems. All these different tipping elements share common characteristics related to their nonlinear nature. They can also interact with each other leading to synergies that can lead to cascading tipping points. Even if the probability of each tipping event is low, they can happen relatively rapidly, involve multiple variables, and have large societal impacts. Therefore, adaptation measures and management in general should extend their focus beyond slow and continuous changes, into abrupt, nonlinear, possibly cascading, high impact phenomena. Remote sensing observations are found to be decisive in the understanding and determination of early warning signals of many tipping elements. Nevertheless, considerable research still remains to properly incorporate these data in the current generation of coupled Earth system models. This is a key prerequisite to correctly develop robust decadal prediction systems that may help to assess the risk of crossing thresholds potentially crucial for society. The prediction of tipping points remains difficult, notably due to stochastic resonance, i.e. the interaction between natural variability and anthropogenic forcing, asking for large ensembles of predictions to correctly assess the risks. Furthermore, evaluating the proximity to crucial thresholds using process-based understanding of each system remains a key aspect to be developed for an improved assessment of such risks. This paper finally proposes a few research avenues concerning the use of remote sensing data and the need for combining different sources of data, and having long and precise-enough time series of the key variables needed to monitor Earth system tipping elements.
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Talalay, P., Li, Y., Augustin, L., Clow, G., Hong, J., Lefebvre, E., et al. (2020). Geothermal heat flux from measured temperature profiles in deep ice boreholes in Antarctica. Cryosphere, 14(11), 4021–4037.
Abstract: The temperature at the Antarctic Ice Sheet bed and the temperature gradient in subglacial rocks have been directly measured only a few times, although extensive thermodynamic modeling has been used to estimate the geothermal heat flux (GHF) under the ice sheet. During the last 5 decades, deep ice-core drilling projects at six sites – Byrd, WAIS Divide, Dome C, Kohnen, Dome F, and Vostok – have succeeded in reaching or nearly reaching the bed at inland locations in Antarctica. When temperature profiles in these boreholes and steady-state heat flow modeling are combined with estimates of vertical velocity, the heat flow at the ice-sheet base is translated to a geothermal heat flux of 57.9 +/- 6.4mW m(-2) at Dome C, 78.9 +/- 5.0mW m(-2) at Dome F, and 86.9 +/- 16.6mW m(-2) at Kohnen, all higher than the predicted values at these sites. This warm base under the East Antarctic Ice Sheet (EAIS) could be caused by radiogenic heat effects or hydrothermal circulation not accounted for by the models. The GHF at the base of the ice sheet at Vostok has a negative value of -3.6 +/- 5.3mW m(-2), indicating that water from Lake Vostok is freezing onto the ice-sheet base. Correlation analyses between modeled and measured depth-age scales at the EAIS sites indicate that all of them can be adequately approximated by a steady-state model. Horizontal velocities and their variation over ice-age cycles are much greater for the West Antarctic Ice Sheet than for the interior EAIS sites; a steady-state model cannot precisely describe the temperature distribution here. Even if the correlation factors for the best fitting age-depth curve are only moderate for the West Antarctic sites, the GHF values estimated here of 88.4 +/- 7.6mW m(-2) at Byrd and 113.3 +/- 16.9mW m(-2) at WAIS Divide can be used as references before more precise estimates are made on the subject.
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Velicogna, I., Mohajerani, Y., Geruo, A., Landerer, F., Mouginot, J., Noel, B., et al. (2020). Continuity of Ice Sheet Mass Loss in Greenland and Antarctica From the GRACE and GRACE Follow-On Missions. Geophysical Research Letters, 47(8).
Abstract: We examine data continuity between the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (FO) missions over Greenland and Antarctica using independent data from the mass budget method, which calculates the difference between ice sheet surface mass balance and ice discharge at the periphery. For both ice sheets, we find consistent GRACE/GRACE-FO time series across the data gap, at the continental and regional scales, and the data gap is confidently filled with mass budget method data. In Greenland, the GRACE-FO data reveal an exceptional summer loss of 600 Gt in 2019 following two cold summers. In Antarctica, ongoing high mass losses in the Amundsen Sea Embayment of West Antarctica, the Antarctic Peninsula, and Wilkes Land in East Antarctica cumulate to 2130, 560, and 370 Gt, respectively, since 2002. A cumulative mass gain of 980 Gt in Queen Maud Land since 2009, however, led to a pause in the acceleration in mass loss from Antarctica after 2016.
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