ISMIP6 projections of ocean-forced Antarctic Ice Sheet evolution using the Community Ice Sheet Model

• Main Authors: Lipscomb, William H., Leguy, Gunter R., Jourdain, Nicolas C., Asay-Davis, Xylar S., Seroussi, Hélène, Nowicki, Sophie
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarctic; East Antarctica; The Antarctic; West Antarctic Ice Sheet; Antarc*; Antarctica; Ice Sheet; Ice Shelf
• Online Access: https://doi.org/10.5194/tc-2019-334; https://tc.copernicus.org/preprints/tc-2019-334/

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, ISMIP6 projections of ocean-forced Antarctic Ice Sheet evolution are illustrated using the Community Ice Sheet Model (CISM). 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 nudge the ice thickness toward observed values. The model is then run forward for 500 years, 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, including the Amundsen, Filchner-Ronne, and Ross Basins. Mass loss accelerates late in the 21st century and rises steadily over the next several centuries without leveling off. The resulting ocean-forced SLR at year 2500 varies from about 10 cm to nearly 2 m, depending on the melt scheme and model forcing. Relatively little ice loss is simulated in East Antarctica. Large uncertainties remain, as a result of parameterized basal melt rates, missing ocean and ice sheet physics, and the lack of ice–ocean coupling.