Characteristics of the ice surface over the Gamburtsev Mountains, Antarctica from airborne laser altimetry

Airborne laser altimetry was used to map the ice surface over Dome A region in East Antarctica during the AGAP project in 2008-09. The instrument used was a Riegl scanning laser altimeter mounted on an aircraft flying 250-500 m above the surface. The study was conducted over an area of 250 × 750 km with the ice thickness varying between 1500 and 3000 m. Here we present the surface characteristics of ice as it flows across the underlying Gamburtsev Mountains. The study includes the flow patterns of ice over areas where radar images indicate accretion of ice at the base of the ice sheet. The initiation points of the accretion areas are usually marked by mounds on the surface and troughs on the down slope. The elevations of the mounds are ~ 15-30 m above the surface and the troughs are around 1-2 km wide and ~ 50 m in depth. Radar images show the layers close to the base of the ice sheet being pushed up by the accreting ice sometimes as high as 500 m towards the surface. However, we do not see such an elevation change being transferred one to one to the surface. We predict that the excess mass is being redistributed within the ice sheet by flow mechanisms over steep bed topography, changes in ice dynamics influenced by the accretion or by ablation processes on the surface by the prevailing katabatic winds. In order to understand whether the accretion mounds on the surface are being eroded by the winds, a surface roughness parameter was calculated using two levels- near surface wind speeds from an Automatic Weather Station near Dome A. The surface roughness parameter thus estimated shows that the erosion over the surface due to wind shear is a slow process with the activity peaking during the summer months. This study contributes to the understanding of subglacial processes as they relate to the surface of the ice sheet.