Possible ocean-forced East Antarctic Ice Sheet instability and sea level change at the Last Interglacial
Abstract:The contribution of the Antarctic ice sheets to global sea levels under projected future warming remains uncertain. The Last Interglacial (135,000-116,000 years ago) provides an analogue for future scenarios, with global temperatures some 2°C above present, but with sea level estimated to be 6.6 to 9.4m higher. Previous studies suggest that this high stand in sea level resulted from collapse of the marine-based West Antarctic Ice Sheet and Greenland, combined with thermal expansion of the oceans; with little, if any sea level rise attributed to the East Antarctic Ice Sheet (EAIS). However, Last Interglacial model simulations, cannot fully account for the magnitude of sea level rise suggested by geologic records.
Here we report a series of model simulations that explore the impact of migrating Southern Hemisphere westerly winds on Last Interglacial ocean circulation and Antarctic ice-sheet dynamics. Our simulations suggest that a poleward shift in the westerlies could have had a significant impact on the Southern Ocean polar gyres, inducing pervasive warming (0.2-0.8°C in the upper 1,200m) adjacent to three regions of the East Antarctic Ice Sheet: the Weddell Sea, Ross Sea and Prydz Bay. Ice-sheet modeling indicates the adjacent sectors of the EAIS are highly sensitive to ocean forcing due to their geometries and connectivity to the Southern Ocean, and may have contributed to the ‘missing’ component of high Last Interglacial sea level. Furthermore, 21st century projections indicate that circum-Antarctic warming may be pervasive, suggesting an EAIS response may be anticipated, with important implications for future sea level projections.