Antarctic ice shelf retreats happened before

The retreat of Antarctic ice shelves is not new according to research published this week (24 Feb) in the journal Geology by scientists from Universities of Durham, Edinburgh and British Antarctic Survey (BAS).

A study of George VI Ice Shelf on the Antarctic Peninsula is the first to show that this currently 'healthy' ice shelf experienced an extensive retreat about 9500 years ago, more than anything seen in recent years. The retreat coincided with a shift in ocean currents that occurred after a long period of warmth. Whilst rising air temperatures are believed to be the primary cause of recent dramatic disintegration of ice shelves like Larsen B, the new study suggests that the ocean may play a more significant role in destroying them than previously thought.

The University of Durham's, Dr Mike Bentley, one of the leaders of the project said, 'We know that rising air temperatures can break up ice shelves but there has been a suspicion for some time that the role of the ocean may have been underestimated. This is some of the first evidence that a shift in ocean currents can actually destroy ice shelves. In this case it's possible that a preceding warm period may have primed the ice shelf to disintegrate when the ocean currents shifted.'

The scientists analysed sediments from the bottom of a freshwater lake close to the edge of the present George VI Ice Shelf. The results revealed that about 9500 years ago the ice shelf retreated, allowing the sea to flood into the lake. The ice shelf didn't reform until 1500 years later, and has been present ever since.

The findings are particularly relevant for other studies on the West Antarctic Ice Sheet where scientists have found that a relatively warm current, Circumpolar Deep Water, is causing high melt rates on the underside of an ice shelf in Pine Island Bay*. The gradual removal of this ice shelf may be causing the glaciers inland to flow faster, which could lead to enhanced drainage of part of the West Antarctic Ice Sheet, and a consequent rise in sea level.

Source : British Antarctic Survey