Antarctic Ice Sheet Began Melting 5,000 Years Earlier Than Previously Assumed

An international study reveals that the melting of the Antarctic Ice Sheet started thousands of years earlier and is more unstable than previously assumed.

In a collaborative study, researchers found that it was nearly 5000 years earlier than previously thought that the Antarctic Ice Sheet began melting and the shrinkage of the ice sheet increased between 20,000 and 9,000 years ago triggering a rapid rise in the sea level.

The study included researchers from the University of Cologne, Oregon State University, Alfred Wegener Instituite, University of Lapland, University of New South Wales and University of Bonn.

This finding is crucial as studies conducted recently highlighted that destabilization of a portion of the West Antartic Ice Sheet has already begun and is irreversible.

The finding is based on the examination of two sediment cores taken from Scotia Sea located between Antarctica and South America that had the 'iceberg rafted debris' that was taken off Antartica by the flowing ice and deposited by the icebergs into the sea. Minerals were deposited into the seafloor sediments as the icebergs melted and this gave scientists a peek into the past behavior of the Antarctic Ice Sheet.

The rapid increase in iceberg-rafted debris reveals that a greater amount of icebergs were released by the Antartic Ice Sheet. This increased amount of debris during eight separate episodes started nearly 20,000 years ago and remained the same until 9,000 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. "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."

This finding provides strong evidence that the Antarctic Ice Sheet played a major role in contributing to the meltwater pulse 1A, the period when there was a rapid rise in sea levels and started some 14,500 years ago.

During this period, worlwide there was a dramatic rise in sea levels to about 50 feet in 350 years. The scientists remain clueless on what really caused the eight pulses. They assume that since the melting of the ice sheet began it was further amplified by various physical processes.

Co-author Axel Timmermann, a climate researcher at the University of Hawaii at Manoa suggests that it was a feedback mechanism that increased the melting. And it was 9,000 years ago that the episodic pulses of melting stopped.

"Just as we are unsure of what triggered these eight pulses," Clark said, "we don't know why they stopped. Perhaps the sheet ran out of ice that was vulnerable to the physical changes that were taking place. However, our new results suggest that the Antarctic Ice Sheet is more unstable than previously considered."

The finding was published in the journal Nature.