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1. Assessing the response of sea ice, ocean circulation, and climate to projected increases in Antarctic Ice Sheet melt

   Rogstad, S. (December 2018, AGU Fall Meeting)

   Observational evidence indicates that the West Antarctic Ice Sheet is losing mass at an accelerated rate while ice sheet models highlight the potential for a significant ice collapse in the next century. The impacts of this large fresh water forcing on sea-ice formation, ocean circulation and climate could be significant, but to-date they have not been investigated using complex numerical models with realistic fresh water forcing and dynamical ice sheet models. Here, we present results from several climate model simulations performed under IPCC future climate scenarios RCP 4.5 and 8.5 with a high-resolution, fully coupled, ocean-atmosphere model (CESM 1.2). In each experiment, runoff from Antarctica is prescribed from a regional dynamic/thermodynamic ice sheet/shelf model. Our results highlight a significant rise in subsurface ocean temperatures (>1C) at the ice sheet grounding line that may accelerate rates of ice melt beyond those currently projected. In contrast, the increased runoff creates a cold surface layer that allows Antarctic sea ice to continue to expand through the end of the current century. It is vital that these processes are accounted for in the next generation of climate and ice sheet models. 

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2. Response of Water Isotopes in Precipitation to a Collapse of the West Antarctic Ice Sheet in High-Resolution Simulations with the Weather Research and Forecasting Model

   https://doi.org/10.1175/JCLI-D-22-0647.1  

   Dütsch, Marina; Steig, Eric J.; Blossey, Peter N.; Pauling, Andrew G. (August 2023, Journal of Climate)

   Abstract The West Antarctic Ice Sheet (WAIS) may have collapsed during the last interglacial period, between 132 000 and 116 000 years ago. The changes in topography resulting from WAIS collapse would be accompanied by significant changes in Antarctic surface climate, atmospheric circulation, and ocean conditions. Evidence of these changes may be recorded in water-isotope ratios in precipitation archived in the ice. We conduct high-resolution simulations with an isotope-enabled version of the Weather Research and Forecasting Model over Antarctica, with boundary conditions provided by climate model simulations with both present-day and lowered WAIS topography. The results show that while there is significant spatial variability, WAIS collapse would cause detectable isotopic changes at several locations where ice-core records have been obtained or could be obtained in the future. The most robust signals include elevatedδ¹⁸O at SkyTrain Ice Rise in West Antarctica and elevated deuterium excess andδ¹⁸O at Hercules Dome in East Antarctica. A combination of records from multiple sites would provide constraints on the timing, rate, and magnitude of past WAIS collapse. 

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3. ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century

   https://doi.org/10.5194/tc-14-3033-2020  

   Seroussi, Hélène; Nowicki, Sophie; Payne, Antony J.; Goelzer, Heiko; Lipscomb, William H.; Abe-Ouchi, Ayako; Agosta, Cécile; Albrecht, Torsten; Asay-Davis, Xylar; Barthel, Alice; et al (January 2020, The Cryosphere)

   null (Ed.)

   Abstract. Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution inresponse to different climate scenarios and assess the mass loss that would contribute tofuture sea level rise. However, there is currently no consensus on estimates of the future massbalance of the ice sheet, primarily because of differences in the representation of physicalprocesses, forcings employed and initial states of ice sheet models. This study presentsresults from ice flow model simulations from 13 international groups focusing on the evolutionof the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet ModelIntercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from theCoupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climatemodel results. Simulations of the Antarctic ice sheet contribution to sea level rise in responseto increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent(SLE) under Representative ConcentrationPathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment withconstant climate conditions and should therefore be added to the mass loss contribution underclimate conditions similar to present-day conditions over the same period. The simulated evolution of theWest 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 and8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighingthe increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelfcollapse, here assumed to be caused by large amounts of liquid water ponding at the surface ofice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without iceshelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, thecalibration of these melt rates based on oceanic conditions taken outside of ice shelf cavitiesand the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario basedon two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared tosimulations done under present-day conditions for the two CMIP5 forcings used and displaylimited mass gain in East Antarctica. 

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4. Linearity of the Climate System Response to Raising and Lowering West Antarctic and Coastal Antarctic Topography

   https://doi.org/10.1175/JCLI-D-22-0416.1  

   Pauling, Andrew G.; Bitz, Cecilia M.; Steig, Eric J. (September 2023, Journal of Climate)

   Abstract A hierarchy of general circulation models (GCMs) is used to investigate the linearity of the response of the climate system to changes in Antarctic topography. Experiments were conducted with a GCM with either a slab ocean or fixed SSTs and sea ice, in which the West Antarctic ice sheet (WAIS) and coastal Antarctic topography were either lowered or raised in an idealized way. Additional experiments were conducted with a fully coupled GCM with topographic perturbations based on an ice-sheet model in which the WAIS collapses. The response over the continent is the same in all model configurations and is mostly linear. In contrast, the response has substantial nonlinear elements over the Southern Ocean that depend on the model configuration and are due to feedbacks with sea ice, ocean, and clouds. The atmosphere warms near the surface over much of the Southern Ocean and cools in the stratosphere over Antarctica, whether topography is raised or lowered. When topography is lowered, the Southern Ocean surface warming is due to strengthened southward atmospheric heat transport and associated enhanced storminess over the WAIS and the high latitudes of the Southern Ocean. When topography is raised, Southern Ocean warming is more limited and is associated with circulation anomalies. The response in the fully coupled experiments is generally consistent with the more idealized experiments, but the full-depth ocean warms throughout the water column whether topography is raised or lowered. These results indicate that ice sheet–climate system feedbacks differ depending on whether the Antarctic ice sheet is gaining or losing mass. Significance StatementThroughout Earth’s history, the Antarctic ice sheet was at times taller or shorter than it is today. The purpose of this study is to investigate how the atmosphere, sea ice, and ocean around Antarctica respond to changes in ice sheet height. We find that the response to lowering the ice sheet is not the opposite of the response to raising it, and that in either case the ocean surface near the continent warms. When the ice sheet is raised, the ocean warming is related to circulation changes; when the ice sheet is lowered, the ocean warming is from an increase in southward atmospheric heat transport. These results are important for understanding how the ice sheet height and local climate evolve together through time. 

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5. Competing climate feedbacks of ice sheet freshwater discharge in a warming world

   https://doi.org/10.1038/s41467-024-49604-3  

   Li, Dawei; DeConto, Robert M; Pollard, David; Hu, Yongyun (June 2024, Nature Communications)

   Abstract Freshwater discharge from ice sheets induces surface atmospheric cooling and subsurface ocean warming, which are associated with negative and positive feedbacks respectively. However, uncertainties persist regarding these feedbacks’ relative strength and combined effect. Here we assess associated feedbacks in a coupled ice sheet-climate model, and show that for the Antarctic Ice Sheet the positive feedback dominates in moderate future warming scenarios and in the early stage of ice sheet retreat, but is overwhelmed by the negative feedback in intensive warming scenarios when the West Antarctic Ice Sheet undergoes catastrophic collapse. The Atlantic Meridional Overturning Circulation is affected by freshwater discharge from both the Greenland and the Antarctic ice sheets and, as an interhemispheric teleconnection bridge, exacerbates the opposing ice sheet’s retreat via the Bipolar Seesaw. These results highlight the crucial role of ice sheet-climate interactions via freshwater flux in future ice sheet retreat and associated sea-level rise. 

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