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Large Antarctic ice shelf disintegrating

Ice break-up
About two-thirds of the 12,000-square-kilometer Larsen B Ice Shelf is now threatening to break off  
April 17, 1998
Web posted at: 7:37 p.m. EDT (2337 GMT)

By Environmental News Network staff

(ENN) -- A large section of an ice shelf on the Antarctic Peninsula has broken away -- a possible result of global warming, say scientists at the University of Colorado-based National Snow and Ice Data Center.

Recent satellite images show that a section about 40 kilometers long and five kilometers wide broke off, according to Ted Scambos, a research associate at the Cooperative Institute for Research in Environmental Sciences, a joint institute of CU-Boulder and the National Oceanic and Atmospheric Administration.

NSIDC researchers spotted the event within a few days of its occurrence in late February after analyzing images obtained with a radiometer aboard a polar-orbiting NOAA satellite.

A second image from March 23 confirmed the disintegrated area of ice, about 200 square kilometers in size, on a shelf known as the Larsen B Ice Shelf.

"The February 26 image shows that much of the ice was already gone," said Scambos. "The March 23 image made it crystal clear that a significant portion of the ice shelf had broken off."

In rapid retreat

The satellite pictures appear to confirm earlier studies by the British Antarctic Survey that predicted the 12,000-square-kilometer ice shelf was nearing its stability limit. Researchers believe it has retreated too far to be able to brace itself against the rocky peninsulas and islands that flank it.

If the model is correct, the ice shelf will continue to crumble rapidly beginning early next year, said Scambos. Although no more reduction is expected until summer begins again in Antarctica in late December, "This may be the beginning of the end for the Larsen Ice Shelf," said Scambos.

Antarctic Peninsula ice shelves have been in rapid retreat for the last few decades, apparently in response to a regional climate warming of 4.5 degrees F since the 1940s. Although the rate of warming is several times that of the global average, the exact cause of the warming is not known.

"The warming trend appears to be related to a reduction in sea ice," said Scambos. "The question now is what is causing the reduction. At this point we do not have enough evidence to find a smoking gun."

About two-thirds of the 12,000-square-kilometer ice sheet is now threatening to break off, he said. The other one-third is nestled in bays that are expected to protect it from breaking off.

"This is the biggest ice shelf yet to be threatened," Scambos said. "The total size of the Larsen B Ice Shelf is more than all the previous ice that has been lost from Antarctic ice sheets in the past two decades."

'Speed of the final breakup was unprecedented'

Chasm on the ice shelf  

In early 1995, a smaller ice shelf area, called the Larsen A, completely disintegrated during a single storm after years of gradually shrinking. "The speed of the final breakup was unprecedented, and followed several of the warmest summers on record for this portion of the Antarctic." he said.

A much smaller ice shelf, the Wordie, disappeared in the late 1980s. Currently the Larsen B is the northernmost ice shelf in Antarctica, and therefore "on the front line of the warming trend," said Scambos.

Ice shelves, thick plates of floating ice surrounding portions of Greenland and Antarctica, are fed by glaciers and snowfall. Reaching up to 800 meters in thickness in some cases, the largest ice shelf is the Ross Ice Shelf, which is larger than the state of Texas. The Larsen Ice Shelf is roughly the size of Connecticut.

Copyright 1998, Environmental News Network, All Rights Reserved

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