Abstract

The cryosphere has a significant influence on global climate; sea ice is an important amplifier in the climate system and meltwater from polar ice sheets influences ocean circulation and the associated sea level rise directly affects coastal populations. However, future model projections of Antarctic Ice Sheet and sea ice change are highly uncertain. Our understanding of the long term (i.e. beyond the satellite era) interplay between ice sheets, sea ice and the climate system can be improved by examining how these systems responded during a range of past climates. In particular, the last interglacial (LIG; 130,000 to 115,000 years ago) allows investigation of the ice sheet and sea ice response to warmer than present conditions – similar to those projected for coming centuries.

This talk will demonstrate the combined use of climate model simulations and Antarctic ice core and marine core data to better interpret past climate change. Novel methods of data-model comparison, focussing on the LIG Antarctic climate optimum (~128,000 years ago), are used to assess the stability of the West Antarctic Ice Sheet (WAIS) and Southern Hemisphere sea ice. We show that an early collapse of the WAIS is not consistent with Antarctic ice core data. Instead, a major retreat of Southern Hemisphere sea ice best explains the ice and marine core data. By optimizing the model-data agreement, we suggest that sea ice retreat was greatest in the Atlantic sector of the Southern Ocean and weakest in the Pacific sector. Further model investigation indicates that changes in global heat transport, in response to melting Northern Hemisphere ice sheets during the proceeding deglaciation, likely caused heat build-up in the South Atlantic, leading to sea ice retreat and substantial Antarctic warming. These conditions may have led to a collapse of the WAIS and sea ice build-up later during the LIG .