THE DETAILED NET MASS-BALANCE OF THE ICE PLAIN ON ICE STREAM-B, ANTARCTICA - A GEOGRAPHIC INFORMATION-SYSTEM APPROACH

Field data of ice thickness, velocity and accumulation of the ice plain region of Ice Stream B, Antarctica, are organized into a geographic information system (GIS) and used to calculate the spatial pattern of net mass balance. Overall, the ice plain is thickening at a rate of 0.13 +/- 0.05 m a-1. Large uncertainties of the high-resolution calculations are reduced by spatial averaging, revealing a number of areas significantly out of balance. Ice in the broad diverging flow field is mostly thinning but a thinner region of the ice plain which includes ice raft ''a'' is thickening. Thickening is also indicated farther downstream on the ice plain, matching the thickening already calculated to be occurring upstream of Crary Ice Rise. The patterns of net mass balance for the two major tributaries of Ice Stream B are asymmetric, demonstrating a real difference in the current dynamics of these two tributaries.