SURFICIAL GLACIOLOGY OF JAKOBSHAVNS ISBRAE, WEST GREENLAND .2. ABLATION, ACCUMULATION AND TEMPERATURE

Accumulation studies along the lower most 100 km of Jakobshavns Isbrae show that the local net balance above the equilibrium line (1210 m elevation in 1986) is significantly less than that measured along the EGIG line about 100 km further north. This indicates the presence of a precipitation low in this region which will affect any global mass-balance assessment for the Jakobshavns Isbrae drainage basin. Comparison of the estimated calving and ablation fluxes shows that calving removes about twice as much mass from this drainage basin as does melting. Basal melting over the entire basin accounts for about 20% of the total ice loss by ablation. Temperature measurements at 12 m depth along the same section of the isbrae show the warming effects of refreezing meltwater and cooling effects of severe crevassing. In addition, there is a significant variation in temperature across the fast-moving ice stream which is probably caused by deformation heating in the shear margins which delineate the ice stream within the ice sheet. This lateral temperature gradient could be important in ice stream dynamics through its effects on ice rheology. Detailed measurements within the percolation facies show that surface melt can penetrate up to 3 m by piping in cold firn, and, upon refreezing, can cause significant warming at these depths.