Geometry and thermal regime of the King George Island ice cap, Antarctica, from GPR and GPS

King George Island is the largest of the South Shetland Islands, close to the tip of the Antarctic Peninsula. The annual mean temperature on the island has increased by 1 degrees C during the past three decades, and the ice cap that covers the majority of the island is sensitive to climatic change. We present data from two field campaigns (1997 and 2007): 700 km of global positioning system (GPS) and ground-penetrating radar (GPR) profiles were collected on Arctowski Icefield and on the adjacent central part. The data were analysed to determine the surface and bed topography and the thermal regime of the ice. Average ice thickness is 250m and maximum thickness is 420m. The GPR profiles show isochrones throughout the ice cap which depict the uparching of Raymond bumps beneath or close to the ice divides. A water table from percolation of meltwater in the snowpack shows the urn ice boundary at similar to 35 m depth. The firn layer may be temperate due to the release of latent heat. In the area below 400 m a.s.I., backscatter by water inclusions is abundant for ice depths below the water table. We interpret this as evidence for temperate ice. Scatter decreases significantly above 400m. Ice temperatures below the water table in this part of the ice cap are subject to further field and modelling investigations.