Investigations of an "ice plain" in the mouth of Pine Island Glacier, Antarctica

We present newly acquired airborne radar data showing ice thickness and sur face elevation for Pine Island Glacier, Antarctica. These data, when combin ed with earlier measurements, suggest the presence of a lightly grounded ar ea immediately above the grounding line of Pine Island Glacier. We identify this region as an "ice plains" It lies close to the centre line of the gla cier, has an elevation above buoyancy of < 50 m and extends inland for > 28 km. The upstream edge of the ice plain is defined by a "coupling line". Th e configuration of the ice plain implies that nearby thinning of the ice st ream would result in substantial grounding-line retreat. We suggest that th e grounding-line retreat of Pine Island Glacier, observed between 1992 and 1996, probably commenced sometime after 1981.