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West Antarctic ice streams draining into the Ross Ice Shelf: Configuration and mass balance

Authors

  • Sion Shabtaie,

  • Charles R. Bentley


Abstract

Extensive airborne radar soundings, closely tied to accurately located ground stations made over a portion of the West Antarctic inland ice sheet and the Ross Ice Shelf, have enabled us to map the boundaries of the ice streams and their flow bands on the Ross Ice Shelf. The surfaces of the active ice streams, A and B, are heavily crevassed, but there are no visible crevasses on ice stream C. However, the existence of numerous crevasses at a depth of about 35 m implies that ice stream C ceased to be active about 250 years ago. There is a complex zone at the head of ice stream B that suggests that ice stream B is currently widening and advancing toward the interior of the ice sheet. The grounding lines between the inland ice and the ice shelf were mapped from the surface elevations using the requirement of hydrostatic balance, and the character of the radar echoes. The inland ice is more extensive than previously mapped, and includes a large, weakly grounded area downstream of ice streams A and B, where the surface elevations are barely above hydrostatic equilibrium. Crary Ice Rise extends 70 km upstream of the previously mapped position. To relate surface elevation data from satellite observations to sea level, three geoidal models were tested. We conclude that the GEM 10C model is the best of the three for this section of Antarctica. A new map of surface elevation shows deep marginal troughs and longitudinal ridges along ice streams A and B, but not on ice stream C, whose surface contours show signs of stagnation. Ice stream C shows a strongly positive and ice stream B a significantly negative net balance rate. Ice streams A and D also show a significantly negative net flux, whereas ice streams E and F do not. The overall net balance of this part of the West Antarctic inland ice is suggestively negative (−23 ± 15 km3 yr−1). From the measured flux into the Ross Ice Shelf and previous measurements we calculate an average basal melt rate from beneath the ice shelf of 0.12 ± 0.03 m yr−1.

Ancillary