Huge ice chunks break away from Antarctic shelf

[April 30, 2009]  BERLIN (AP) -- Massive ice chunks are crumbling away from a shelf in the western Antarctic Peninsula, researchers said Wednesday, warning that 1,300 square miles of ice -- an area larger than Rhode Island -- was in danger of breaking off in coming weeks.

The Wilkins Ice Shelf had been stable for most of the last century, but began retreating in the 1990s. Researchers believe it was held in place by an ice bridge linking Charcot Island to the Antarctic mainland.

But the 127-square-mile (330-square-kilometer) bridge lost two large chunks last year and then shattered completely on April 5.

"As a consequence of the collapse, the rifts, which had already featured along the northern ice front, widened and new cracks formed as the ice adjusted," the European Space Agency said in a statement Wednesday on its Web site, citing new satellite images.

The first icebergs broke away on Friday, and since then some 270 square miles (700 square kilometers) of ice have dropped into the sea, according to the satellite data.

"There is little doubt that these changes are the result of atmospheric warming," said David Vaughan of the British Antarctic Survey.

The falling away of Antarctic ice shelves does not, in itself, raise sea levels, since the ice was already floating in the sea. But such coastal tables of ice usually hold back glaciers, and when they disintegrate, that land ice will often flow more quickly into the sea, contributing to sea-level rise.

Researchers said the quality and frequency of the ESA satellite images have allowed them to analyze the Wilkins shelf breakup far more effectively than any previous event.

"For the first time, I think, we can really begin to see the processes that have brought about the demise of the ice shelf," Vaughan said.

He said eight ice shelves along the Antarctic Peninsula have shown signs of retreat over the last few decades.

"The retreat of Wilkins Ice Shelf is the latest and the largest of its kind," he said.

The Wilkins shelf, which is the size of Jamaica, lost 14 percent of its mass last year, according to scientists who are looking at whether global warming is the cause of its breakup.

Average temperatures in the Antarctic Peninsula have risen by 3.8 degrees Fahrenheit (2.5 Celsius) over the past 50 years -- higher than the average global rise, according to studies.

Over the next several weeks, scientists estimate the Wilkins shelf will lose some 1,300 square miles (3,370 square kilometers) -- a piece larger than the state of Rhode Island, or two-thirds the size of Luxembourg.

One researcher said, however, that it was unclear how the situation would evolve.

"We are not sure if a new stable ice front will now form between Latady Island, Petrie Ice Rises and Dorsey Island," said Angelika Humbert of Germany's Muenster University Institute of Geophysics.

But even more ice could break off "if the connection to Latady Island is lost," she said, "though we have no indication that this will happen in the near future."

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On the Net:

ESA's "'Webcam' from Space":
http://www.esa.int/esaEO/
SEMWZS5DHNF_index_0.html

[Associated Press; By DAVID RISING]

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