Satellite imagery indicates that the floating terminus of Pine Island Glacier has changed little in extent over the past two decades. Data on the velocity and thickness of the glacier reveal that calving of 28 +/- 4 Gt a(-1) accounts for only half of the ice input near the grounding line. The apparently steady configuration implies that the remainder of the Input is lost by basal melting at a mean rate of 12 +/- 3 m a(-1). Ocean circulation in Pine Island Bay transports +1 degrees C waters beneath the glacier and temperatures recorded in melt-laden outflows show that heat loss fi om the ocean is consistent with the requirements of the calculated melt rate. The combination of iceberg calving and basal melting lies at the lower end of estimates for the total accumulation over the catchment basin, drawing into question previous estimates of a significantly positive mass budget for this part of the ice sheet.
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