Part of the East Antarctic ice sheet repeatedly retreated hundreds of kilometres inland during periods of global warmth 5 to 2.5 million years ago, reports a paper published online this week in Nature Geoscience. The findings suggest that the East Antarctic ice sheet was more sensitive to warming than previously thought.
Carys Cook and colleagues assessed the geochemical composition of marine sediments deposited offshore of East Antarctica during the Pliocene epoch 5.3 to 2.5 million years ago. The Pliocene was characterized by atmospheric carbon dioxide concentrations of 350 to 450 ppmv, similar to levels seen today. The team found that during the warmest intervals, the sediments were derived from rocks located several hundred kilometres inland, a region presently covered by the East Antarctic ice sheet. They suggest that for the sediments to have been generated, the margin of the ice sheet must have retreated inland as temperatures in the high southern latitudes rose.
In an accompanying News and Views article, Claus-Dieter Hillenbrand writes that “the constraints on Pliocene ice-sheet extent on East Antarctica provided by Cook et al. imply that subglacial basins in East Antarctica may represent an ‘Achilles heel’, where substantial ice-sheet retreat can occur under warm climatic conditions.”