According to a team of scientists from the United States, Finland, Australia and Germany, the Antarctic Ice Sheet began melting about 5,000 years earlier than previously believed.
An iceberg. Image credit: Doug Knuth / CC BY-SA 2.0.
The team 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 8 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 Dr Michael Weber from the University of Cologne in Germany, the lead author of the study published in the journal Nature.
“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.”
“The research also provides the first solid evidence that the Antarctic 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,” added study co-author Prof Peter Clark of Oregon State University.
The largest of the eight episodic pulses outlined in this study coincides with meltwater pulse 1A.
“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,” Prof Clark said.
“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.”
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M. E. Weber et al. Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation. Nature, published online May 28, 2014; doi: 10.1038/nature13397
