Glacial Isostatic Adjustment over Antarctica from combined ICESat and GRACE satellite data

The glacial history of Antarctica during the most recent Milankovitch cycles is poorly constrained relative to the Northern Hemisphere. As a consequence, the contribution of mass changes in the Antarctic ice sheet to global sea-level change and the prediction of its future evolution remain uncertain. The process of Glacial Isostatic Adjustment (GIA) represents the ongoing response of the solid Earth to the Late-Pleistocene deglaciation and, therefore, provides information about Antarctic glacial history. Moreover, insufficient knowledge of GIA hampers the determination of present-day changes in the Antarctic mass balance through satellite gravity measurements. Previous studies have laid the theoretical foundation for distinguishing between signals of ongoing GIA and contemporary ice mass change through the combination of satellite gravimetry and satellite altimetry. This distinction is made possible by the fact the GIA-induced changes (involving relatively dense rock) will produce a different combination of topography and gravity change than those produced by variations in ice or firn thickness (due to the lower density of these materials); however, no conclusive results have been produced to date. Here we show that, by combining laser altimetry and gravity data from the ICESat and GRACE satellite missions over the period March 2003-March 2008, the GIA contribution can indeed be isolated. The inferred GIA signal over the Antarctic continent, which represents the first result derived from direct observations by satellite techniques, strongly supports Late-Pleistocene ice models derived from glacio-geologic studies. The GIA impact on GRACE-derived estimates of mass balance is found to be 100 ± 67 Gt/yr.