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Icebergs drift at sea.
Photo Credit: Janice O'Reilly/Antarctic Photo Library
Icebergs drift off the Antarctic Peninsula. A new study found that the West Antarctic Ice Sheet began melting about 5,000 years earlier than previously thought based on debris released by icebergs that was found in sediment cores from the seafloor.

Unstable

Study: Antarctic ice sheet shrinkage began earlier than previously estimated

A new study has found that the West Antarctic Ice Sheet began melting about 5,000 years earlier than previously thought coming out of the last ice age – and that shrinkage of the vast ice sheet accelerated during eight distinct episodes, causing rapid sea level rise.

The international study, funded in part by the National Science Foundation (NSF) External U.S. government site, is particularly important coming on the heels of recent studies that suggest destabilization of part of the West Antarctic Ice Sheet has begun. [See previous article — Unstoppable: Two high-profile studies: Collapse of parts of West Antarctic Ice Sheet inevitable.]

Results of this latest study were published last month in the journal Nature. It was conducted by researchers at University of Cologne External Non-U.S. government site, Oregon State University External Non-U.S. government site, the Alfred-Wegener-Institute External Non-U.S. government site, University of Hawaii at Manoa External Non-U.S. government site, University of Lapland External Non-U.S. government site, University of New South Wales External Non-U.S. government site, and University of Bonn External Non-U.S. government site.

The researchers 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 ice sheet.

Several sediment cores stacked side by side.
Photo Credit: Peter West/Antarctic Photo Library
Sediment cores –these are from an unrelated project – were used to find iceberg-rafted debris that implied the West Antarctic Ice Sheet had calved frequently at the end of the last ice age.

Periods of rapid increases in iceberg-rafted debris suggest that more icebergs were being released by the 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 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.

The research also provides the first solid evidence that the ice sheet contributed to what is known as meltwater pulse 1A, a period of very rapid sea level rise that began some 14,500 years ago, according to Peter Clark External Non-U.S. government site, an Oregon State University paleoclimatologist and co-author on the study whose work was supported by NSF.

“During that time, the sea level on a global basis rose about 50 feet in just 350 years – or about 20 times faster than sea level rise over the last century,” Clark said in a press release External Non-U.S. government site. “We don’t yet know what triggered these eight episodes or pulses, but it appears that once the melting of the ice sheet began it was amplified by physical processes.”

To help determine what might have brought about such huge ice sheet collapses in Antarctica, the team conducted a series of climate modeling experiments.

“An unusually strong flow of warm water towards Antarctica may have triggered these events,” explained co-author Axel Timmermann, professor at the International Pacific Research Center External Non-U.S. government site of the University of Hawaii, whose work was also supported by NSF.

“Our model experiments reveal further that the associated melting in turn increased the warm water flow, thus providing a positive feedback," Timmermann said in a press release External Non-U.S. government site. "This is a perfect recipe for rapid sea level rise.”

NSF-funded research in this story: Peter Clark, Oregon State University, Award No. 1043517 External U.S. government site; and Axel Timmermann and Oliver Elison Timm, University of Hawaii, Award No. 1341311 External U.S. government site.

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Curator: Peter Rejcek, Antarctic Support Contract | NSF Official: Winifred Reuning, Division of Polar Programs