Antarctic Ice Collapse Began End of Ice Age?

Stefan Lovgren
for National Geographic News

March 17, 2003

The melting of an enormous Antarctic ice sheet 14,000 years ago
triggered climatic changes in Europe and North America that ultimately
led to the end of the last ice age, according to a new study.

Using super computers to simulate the melting of part of the Antarctic, scientists analyzed what effect the dumping of huge amounts of freshwater into the southern oceans would have on the climate in the rest of the world.

"The last gasp of the ice age was punctuated by a series of dramatic events," said Jerry Mitrovica, a professor of geophysics at the University of Toronto in Canada and one of the study's co-authors. "These events were linked together like falling dominoes, and it all began with the collapse of the Antarctic ice.

Rising Waters

The new study builds on research published last year. Studying sea level changes in corals and organic materials from Vietnam and Barbados, scientists concluded that an influx of freshwater from the Antarctic 14,000 years ago increased sea levels by an average of 66 feet (20 meters) over 200 years, about 100 times faster than today. There is evidence that debris was coming off the Antarctic as a result of the melting of the ice sheet.

The theory countered a common belief that the melting ice came from North America. "There are many reasons why a North American source does not make sense," said Peter Clark, a geologist at the University of Oregon, who co-authored both the 2002 and 2003 studies. "If [North America] had been the source, one-third to one-half of the ice sheet would have had to disappear. That didn't happen."

Supercomputers

But the 2002 study focused on the melting of the Antarctic, an event known as meltwater pulse 1A (mwp-1A). The new study answers the question: If the Antarctic was the source, what happened next?

To answer that question, scientists at the University of Victoria in British Columbia built a complex computer model to simulate the effect of mwp-1A, taking into account things like the deformation of the Earth and the gravitational attraction between ice sheets and oceans.

What they found was that a catastrophic collapse of an Antarctic ice sheet dumped roughly one million cubic liters per second of freshwater into the southern oceans and caused a great water current that dramatically influenced climate.

By transporting warmer water to Europe and the North Atlantic, the region's climate was significantly heated, leading to a 1,000-year-long climatic shift known as the Bølling-Allerød warm interval. Once the process of warming the North started, the main deglaciation began and the ice age ended.

The model also predicts the significant cooling of the south, known as the Antarctic Cold Reversal, which coincided with the warming of the North.

"The connection of the major climatic events is beautifully reproduced in the computer model," said Andrew Weaver, a numerical climate modeler and geophysicist at the University of Victoria.

Lessons Learned

The new study not only sheds light on the last throes of the ice age, explaining how the Earth got from a deep freeze to its current climate, it also proves that Earth's climate is strongly linked together.

"Change one thing, like ice sheet mass at one of the poles, and it can trigger a sequence of other global scale events," said Mitrovica.

Until now, the end of the ice age has fixated on North America, leaving the Southern Hemisphere "woefully understudied," said Weaver.

According to a study last year, the Antarctic is the only continent in the world that is currently growing cooler. Researchers discovered that temperatures on the icy continent actually decreased by 0.7° Celsius (1.8° Fahrenheit) per decade in the last 35 years.

That study sparked a controversy because it suggested the Antarctic is not doing what most scientists expect it to do: grow warmer. That may be good news. As the new findings suggest, even the partial melting of the Antarctic would have potentially devastating consequences on the climate of the rest of the world.