Mass balance measurements on King George Island ice cap in 2007 and 2008

The Antarctic Peninsula has been identified as a region of rapid on-going climate change with impacts on the cryosphere. The knowledge of glacial changes and freshwater budgets resulting from intensified glacier melt is an important boundary condition for many biological and integrated earth system science approaches. We provide a case study on glacier and mass balance changes for the ice cap of King George Island. The area loss between 2000 and 2008 amounted to about 20 km**2 (about 1.6% of the island area) and compares to glacier retreat rates observed in previous years. Measured net accumulation rates for two years (2007 and 2008) show a strong interannual variability with maximum net accumulation rates of 4950 mm w.e./a and 3184 mm w.e./a, respectively. These net accumulation rates are at least 4 times higher than reported mean values (1926-95) from an ice core. An elevation dependent precipitation rate of 343 mm w.e./a (2007) and 432 mm w.e./a (2008) per 100 m elevation increase was observed. Despite these rather high net accumulation rates on the main ice cap, consistent surface lowering was observed at elevations below 270 m above ellipsoid over an 11-year period. These DGPS records reveal a linear dependence of surface lowering with altitude with a maximum annual surface lowering rate of 1.44 m/a at 40 m and -0.20 m/a at 270 m above ellipsoid. These results fit well to observations by other authors and surface lowering rates derived from the ICESat laser altimeter. Assuming that climate conditions of the past 11 years continue, the small ice cap of Bellingshausen Dome will disappear in about 285 years.

Present-day King George Island ice cap geometry measured by ground penetrating radar in 2008/09

We present a consistent data set for the ice thickness, the bedrock topography and the ice surface topography of the King George Island ice cap (Arctowski Icefield and the adjacent central part). The data set is composed of groundbased and airborne Ground Penetrating Radar (GPR) and differential GPS (DGPS) measurements, obtained during several field campaigns. The data set incorporates groundbased measurements in the safely accessible inner parts and airborne measurements in the heavily crevassed coastal areas of the ice cap. In particular, the inclusion of airborne GPR measurements with the 30MHz BGR-P30-System developed at the Institute of Geophysics (University of Münster) completes the picture of the ice geometry substantially. The compiled digital elevation model of the bedrock shows a rough, highly variable topography with pronounced valleys, ridges, and troughs. The mean ice thickness is approx. 238m, with a maximum value of approx. 400m in the surveyed area. Noticeable are bounded areas in the bedrock topography below sea level where marine based ice exists.