Observed velocity fluctuations on a major Antarctic ice stream

Abstract

Most of the Antarctic ice sheet is drained by systems comprising an area of slow sheet flow which converges into a much faster valley glacier or ice stream. On reaching the coast, this ice then either enters an ice shelf confined by embayments and ice rises, or calves off into the ocean. The higher speed of ice streams enables them to respond to changes in their environment faster than the slower ice sheet. In the West Antarctic, where the ice sheet moves across bedrock well below sea level, the ice streams have the potential to rapidly increase or decrease the ice discharge into the sea¹. The timescale for these changes has been placed at a few hundred years. If this is true, then changes should be detectable by careful measurements on a decadal timescale. By comparing recent ice velocity measurements with those collected ten years ago, we establish that the ice in the mouth of Ice Stream B has decelerated by ∼20%. We discuss the possible causes of this deceleration on the basis of our knowledge of the current regional dynamics, and the possible ramifications of this deceleration on future ice stream behaviour.