The morphology and dynamics of the lower Lambert Glacier and Amery Ice Shelf system

The Lambert Glacier and Amery Ice Shelf system is one of the major east Antarctic drainage basins and is the subject of long term and on-going investigation as part of the Australian Antarctic program. In the region of the grounding zone between the glacier stream and the floating ice shelf, snow which accumulated over tens of thousands of square kilometres of the interior ice sheet is funnelled through a relatively narrow area. The way in which the ice in this region flows is influenced by subglacial topography, ice thickness, internal ice flow properties and the nature of the source area of the ice. The primary aim of this study is to use all available data to describe the morphology and dynamic regime of the lower Lambert Glacier and Amery Ice Shelf, and to provide the best estimate of the present mass balance and spatial distribution of the grounding zone. The available data include radio echo soundings of ice thickness, surface elevation data, ice velocity and surface mass balance measurements from Australian field projects in 1968-1970 and in 1988-1990, satellite imagery, derived products from satellite altimetry and Russian geophysical surveys. The main region being studied is located between 70° to 72°S and 68° to 72°E. Within this area, five transecting profiles have identified the Lambert Glacier ice stream from both eastern and western plateau ice that also flows into the Lambert graben before entering Prydz Bay via the Amery Ice Shelf. Two of these profiles are situated north of T4 at 71 ° 13'S 69°28'E (Budd etal., 1992), the remaining three are south of T4. The Lambert Glacier ice stream broadens from an average width of 34km to 421cm in the area between the profiles south of T4 and the profiles north of T4. Two longitudinal profiles incorporating the eastern and western edges of the drainage system have added to the conclusion that previously determined grounding zone parameters for the Lambert Glacier need to be redefined. The grounding zone is estimated to cover a distance of 220km from an area near T4 (71°39'S) to the Lambert Glacier hinge line near 73°19'S. Total mass flux through the lower Lambert Glacier averages 9.6Gt in the grounding zone and increases marginally to 9.8Gt on the Amery Ice Shelf proper. These figures are comparable with the earlier calculations of Budd et al. (1982).