| Summary: | A distinction is often drawn between the ice sheets of East and West Antarctica due to marked differences in their geometry. The East Antarctic Ice Sheet (EAIS) rests on ground that is mostly above sea level, and the overlying ice has been considered stable over long time periods (Alley Whillans, 1984) because it is relatively isolated from climatic perturbations. In contrast, the West Antarctic Ice Sheet (WAIS) rests on ground that is predominantly below sea level, and its configuration is considered unstable due to the inland-sloping bedrock geometry, a heightened exposure to oceanic perturbations, and the presence of deformable sediments beneath major outlet glaciers (Alley Whillans, 1991). Here, we determine the volume change of Antarctic outlet glaciers between 1992 and 2003 to characterise the ice sheet mass balance. We conclude that only glaciers of a certain geometry-those seated in submarine basins with no substantial ice shelf barrier-are losing mass today. These glaciers are sited in both East and West Antarctica and, because they are susceptible to changes in climate, we anticipate they will provide a substantial contribution to global sea levels over the twenty-first century should ocean warming continue as projected (Gille, 2002).
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