Interglacial Collapse of Ice Sheets revealed by Subglacial Drilling of Bedrock

ongoing

The West Antarctic Ice Sheet (WAIS) stores a substantial volume of freshwater on land. It is thought to be inherently unstable and so projections of future sea level rise require robust numerical ice sheet models, fully calibrated against geological data. The WAIS is widely believed to have collapsed in past warm interglacial periods, raising sea level by up to 3.3m, but perhaps surprisingly we do not yet have direct evidence of collapse from Antarctica that can be securely dated. Instead global sea level data have been used to infer that some combination of WAIS, Greenland and the East Antarctic Ice Sheet collapsed in one or more past interglacials, but with substantial uncertainty as to how this mass loss was partitioned between the ice sheets. This matters because it means that models projecting future sea level are calibrated against an assumption of how small the WAIS became during past warm periods. I argue that a fresh approach is needed, one that provides direct evidence of WAIS retreat that can be dated and quantified. INCISED will provide this by rapid drilling to the ice sheet bed to retrieve direct records of past collapse. New modelling of cosmogenic isotope concentrations shows that hypotheses of past WAIS collapses can be tested by analysis of subglacial bedrock from carefully selected sites. INCISED exploits recent engineering advances in ice coring and a new subglacial rock drill to take bedrock samples which will be used to determine past lowering of the ice surface to test for WAIS collapse. Numerical ice sheet modelling will link changes in past ice levels to quantify the range of possible sea level contribution. By determining and quantifying the configuration of WAIS during warm periods I will provide firm targets for ice sheet model calibration and thus more secure future sea level projections. INCISED will deliver a transformative change in modelling of WAIS sea level contributions as well as a significant equipment legacy.