New Study Finds Antarctic Ice Sheet Unstable at End of Last Ice Age
A new study, funded in part by the National Science Foundation, has found that the 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 is particularly important coming on the heels of recent studies that suggest destabilization of part of the West Antarctic Ice Sheet has begun.
Results of this latest study were published May 2014 in Nature. It was conducted by 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. 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 minerals into 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. 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. 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. 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,” says lead author Michael Weber, a scientist from Germany’s University of Cologne.
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, according to Peter Clark, an Oregon State University paleoclimatologist and co-author on the study. The largest of the eight episodic pulses outlined in the new Nature study coincides with meltwater pulse 1A.
“During that time, sea level on a global basis rose about 50 feet in just 350 years – or about 20 times faster than sea level rise throughout the last century,” notes Clark, a professor in Oregon State’s College of Earth, Ocean and Atmospheric Sciences. “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.”
Researchers suspect that a feedback mechanism may have accelerated the melting, possibly by changing ocean circulation that brought warmer water to the Antarctic subsurface, according to co-author Axel Timmermann, a climate researcher at the University of Hawaii at Manoa.
Today, the annual calving of icebergs from Antarctic represents more than one-half of the annual loss of mass of the Antarctic Ice Sheet – an estimated 1,300 to 2,000 gigatons (a gigaton is a billion tons). Some of these giant icebergs are longer than 18 kilometers.
Oregon State University College of Earth, Ocean and Atmospheric Sciences (CEOAS) is internationally recognized for its faculty, research and facilities, including state-of-the-art computing infrastructure to support earth/ocean/atmosphere observation and prediction. The college is a leader in the study of the Earth as an integrated system, providing scientific understanding to complex environmental challenges.