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Arctic ice shelf breaks up
23/09/2003 07:45 - (SA)
Washington - Warming conditions pushing average temperatures above freezing are being blamed for the break-up of an ice shelf at Ellesmere Island in northern Canada.
The break-up of the Ward Hunt ice shelf between 2000 and 2002 was reported on Monday by researchers from Canada and the United States.
Calving of ice shelves into giant icebergs is seen regularly from Antarctica and many scientists believe that is caused by global warming, though research continues to try and verify that.
The similar ice break-up in the Northern Hemisphere was reported by Warwick Vincent and Derek Mueller of Laval University in Quebec City, Quebec, and Martin Jeffries of the University of Alaska, Fairbanks.
Their findings are scheduled to appear in an upcoming issue of Geophysical Research Letters, published by the American Geophysical Union.
The researchers studied the ice both via satellite and through visits to the scene.
They reported that the ice shelves on northern Ellesmere Island had been stable since 1982, but in April 2000 a satellite revealed the first sign of cracking.
By 2002, observations from a helicopter showed that the fracture extended widely, breaking the ice shelf into two major parts and many smaller ones.
In July and August, 2002, the researchers landed to take measurements and found cracks that separated the central part of the shelf into free floating ice blocks. That August, the northern northern edge of the ice shelf broke free, they reported.
Besides freeing the floating ice blocks, the break-up caused the loss of almost all of the freshwater from a lake which had been dammed behind the ice in a fiord.
The scientists measured the temperature on the ice shelf in 2002 and correlated that with readings from Alert, about 172.4 kilometres away.
Using the Alert records, they estimated that the ice shelf had an average annual temperature of 34 degrees Fahrenheit (1 Celsius) since 1967.
Studies in Antarctica have shown a temperature of 32 degrees (0 Celsius) is critical to ice shelves breaking up.
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