The amount of ice lost to the sea from Antarctica has increased by 75 percent in the last 10 years. This is the result of an increase in glacial flow. It had previously been thought, and perhas was the case, that Greenland ice loss outpaced the Antarctica. This is no longer the case.

An article coming out in the next issue of Nature Geoscience, by Rignot et al (“Recent Antarctic ice mass loss from radar interferometry and regional climate modelling”) is the most detailed study of this phenomenon to date.

There are two factors that affect the flow of ice into the sea at the edge of the southern continent. One is the amount of snow that falls across the continent, which might increase the total amount of water trapped in glacial ice, or might increase the speed of glacial movement towards the sea. The other is how rapidly the glaciers slide into the sea at the glaciers’ “grounding sites,”

Global warming may have increased the amount of precipitation in Antarctica, which could increase the total volume of water trapped in this mass of ice. This would partially offset sea level rise caused by glacial melting in the Arctic and in mountain glaciers. However, warmer seas surrounding Antarctica and warmer air temperatures can cause the melting edge of the glaciers to mlt faster. When the grounding edge of the glaciers falls apart due to warm air or water, the mass of the glacier behind this leading edge moves more quickly to the sea.

There have always been an insufficient number of data collection points across the continent to accurately estimate snow fall accumulations, and it is hard to measure glacial edge melting as well along the 18 thousand kilometers of coast line.,

The present study uses 15 years of satellite radar data from the European Earth Remote Sensing satellites, the Japanese Advanced Land Observing satellites, and the Canadian Radarsat satellite, to observe and measure ice loss at the seaward edges of the glaciers. The snowfall estimates were derived from a regional atmospheric model cover the last 25 years.

This study indicates that outflow of ice changed about 112 gigatonnes per year in 1996 to about 196 gigatonnes per year in 2006. That is a very large difference. According to study author Eric Rignot:

Our new results emphasize the vital importance of continuing to monitor Antarctica using a variety of remote sensing techniques to determine how this trend will continue and, in particular, of conducting more frequent and systematic surveys of changes in glacier flow using satellite radar interferometry … Large uncertainties remain in predicting Antarctica’s future contribution to sea level rise. Ice sheets are responding faster to climate warming than anticipated.

The study also found that the amount of net loss differed across the continent. In the following map from the study, Red circles indicate mass loss and blue circles indicate gain in large basins around the continent.

The study concludes:

Our results provide a nearly complete assessment of the spatial pattern in mass flux and mass change along the coast of Antarctica, glacier by glacier, with lower error bounds than in previous incomplete surveys, and a delineation of areas of changes versus areas of near stability. Over the time period of our survey, the ice sheet as a whole was certainly losing mass, and the mass loss increased by 75% in 10 years. Most of the mass loss is from Pine Island Bay sector of West Antarctica and the northern tip of the Peninsula where it is driven by ongoing, pronounced glacier acceleration. In East Antarctica, the loss is near zero, but the thinning of its potentially unstable marine sectors calls for attention. In contrast to major increases in ice discharge, snowfall integrated over Antarctica did not change in 1980-2004 (ref. 27) and even slightly increased in areas of large loss17. We conclude that the Antarctic ice sheet mass budget is more complex than indicated by the temporal evolution of its surface mass balance. Changes in glacier dynamics are significant and may in fact dominate the ice sheet mass budget.

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Rignot, E., Bamber, J.L., van den Broeke, M.R., Davis, C., Li, Y., van de Berg, W.J., van Meijgaard, E. (2008). Recent Antarctic ice mass loss from radar interferometry and regional climate modelling. Nature Geoscience DOI: 10.1038/ngeo102