Antarctic mass balance and sea level change

The Antarctic ice, remote as it is, has the potential to affect coastal communities and habitats around the world, because any change in its mass will directly affect mean sea level. Despite all the study of the ice sheet in the last several decades, however, it is still uncertain whether the ice sheet is growing, shrinking, or unchanging in mass. The most recent studies are contradictory—glaciological evidence from the continent suggests that the ice sheet is slowly growing, oceanographic evidence around the continent suggests that it is shrinking, and indirect satellite evidence relating to changes in mass distribution over the surface of the globe suggests that changes of either sign must be small. The glaciological evidence has most recently been summarized by Bentley and Giovinetto [1991]. By analyzing all available measurements on the rate of snow accumulation on the ice sheet (the mass input) and the mass flux across the boundary between the land-based and floating margins of the ice sheet (the mass output), they came to the conclusion that there is a net gain of about 200 Gt yr−1, that is, a sea-level lowering of about 0.5 mm yr−1. The data cover the large drainage systems that encompass the vast interior plateaus where the mass input rates are small. Much less is known about more limited coastal systems characterized by higher specific mass input rates. Nevertheless, it seems unlikely that these smaller regions could be losing mass rapidly enough to make up for the mass gain over the majority of the continent.