Measurement of temperature in a margin of Ice Stream B, Antarctica: implications for margin migration and lateral drag

Ice temperature was measured in and around the chaotically crevassed south margin of Ice Stream B, Antarctica., from 1992 to 1994. The temperatures at 30 m depth in the chaotic zone are about 12 K lower than in the adjacent uncrevassed ice, due to the pending of cold winter air. At depths greater than 150 m, there is clear evidence of internal heating of the ice due to the large shear deformation rate in the marginal zone. Analysis of the depth of cooling below the crevasses and of the internal heating git es two pieces of information. First, over the last half century the lateral shear stress averaged 2.0 x 10(5) Pa in the top third of the margin and, second, the margin moved outward at an average rate of 7.3 m a(-1). These values do not involve any assumptions about the flow law of ice. The uncertainties are roughly 20%. The value of lateral shear stress indicates that the most of the drag on the ice stream is along its sides.