Antarctic ice sheet was unstable at end of last ice age

Researchers have found that the Antarctic ice sheet started melting about 5,000 years earlier than previously believed while coming out of the last ice age and it's shrinkage accelerated during eight distinct episodes, causing rapid sea level rise.

Researchers at University of Cologne, Oregon State University, the Alfred-Wegener-Institute, University of Hawaii at Manoa, University of Lapland, University of New South Wales, and University of Bonn, examined two sediment cores from the Scotia Sea between Antarctica and South America that contained "iceberg-rafted debris" that had been scraped off Antarctica by moving ice and deposited via icebergs into the sea.

As the icebergs melted, they dropped the minerals into the seafloor sediments, giving scientists a glimpse at the past behavior of the Antarctic Ice Sheet.

Periods of rapid increases in iceberg-rafted debris suggest that more icebergs were being released by the Antarctic Ice Sheet. The researchers discovered increased amounts of debris during eight separate episodes beginning as early as 20,000 years ago, and continuing until 9,000 years ago.

The melting of the Antarctic Ice Sheet wasn't thought to have started, however, until 14,000 years ago.

"Conventional thinking based on past research is that the Antarctic Ice Sheet has been relatively stable since the last ice age, that it began to melt relatively late during the deglaciation process, and that its decline was slow and steady until it reached its present size," said lead author Michael Weber, a scientist from the University of Cologne in Germany.

"The sediment record suggests a different pattern - one that is more episodic and suggests that parts of the ice sheet repeatedly became unstable during the last deglaciation," Weber added.

According to co-author Axel Timmermann, a climate researcher at the University of Hawaii at Manoa, the researchers suspect that a feedback mechanism may have accelerated the melting, possibly by changing ocean circulation that brought warmer water to the Antarctic subsurface.

The study has been published in the journal Nature.