Antarctic Ice Sheet Less Stable than Assumed, Researchers Say

Antarctic ice sheet is less stable than it was previously believed to be, according to an international team of researchers.

The study, which was conducted by researchers from the University of Hawaii at Manoa and colleagues, was based on analysis of new, long deep-sea sediment cores. Researchers found that abrupt calving in the ice sheet occurred some 19,000 to 9,000 years ago.

"One of the iceberg events in our data that is of particular interest took place 14,600 years ago and coincided with a huge ice-sheet melt, the famous Meltwater Pulse 1A, which according to previous studies led to a global sea level rise of about 4 meters within 100 years," said Michael Weber of the University of Cologne in Germany, lead author of the study, according to a news release.

"This is the first direct evidence that shows that instabilities of the Antarctic ice sheet caused rapid sea level rise during the last glacial termination," said co-author Peter Clark, professor at the Oregon State University.

The sediments examined in the study came from the region between the Falkland Islands and the Antarctic Peninsula. The sediments are important because they were deposited by ancient icebergs that drifted from the Antarctic ice sheet.

The level of the sediments gives researchers an idea about the rate of ice-sheet melting in the past. In the present study, researchers found that debris deposited by melting icebergs peaked at least eight times in the past. Some of this rapid melting occurred as early as 20,000 years ago and continued until 9,000 years ago.

This finding is important because currently most climate scientists assume that Antarctic ice sheet hadn't melted until 14,000 years ago.

According to Michael Weber, Antarctic ice sheet was considered to be relatively stable and that its decline was uniform.

However, the current study changes that thinking.

"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 in a news release.

But, why did the ice calving stop 9,000 years ago?

Researchers said that they have no idea. One reason might be that Antarctica ran out of the ice that was vulnerable to climate change at that time, according to Clark.

The study is published in the journal Nature and is funded by the National Science Foundation.