Tuesday, July 29, 2008

Giant chunks break off Canadian ice shelf

Tue Jul 29, 2008 1:17pm EDT

By David Ljunggren

OTTAWA, July 29 (Reuters) - Giant sheets of ice totaling almost eight square miles (20 square km) broke off an ice shelf in the Canadian Arctic last week and more could follow later this year, scientists said on Tuesday.

Temperatures in large parts of the Arctic have risen far faster than the global average in recent decades, a development that experts say is linked to global warming.

The ice broke away from the shelf on Ward Hunt Island, an small island just off giant Ellesmere Island in one of the northernmost parts of Canada.

It was the largest fracture of its kind since the nearby Ayles ice shelf -- which measured 25 square miles -- broke away in 2005.

Scientists had already identified deep cracks in the Ward Hunt shelf, which measures around 155 square miles. The shelf is one of five along Ellesmere Island in the northern Arctic.

"Because the break-off occurred between two large parallel cracks they're thinking more could go this summer before the freeze sets in," said Trudy Wohlleben of the Canadian Ice Service.

Asked to be more specific, she told Reuters: "More could be a piece as large as the Ayles ice shelf."

Ellesmere Island was once home to a single enormous ice shelf totaling around 3,500 square miles. All that is left of that shelf today are five much smaller shelves that together cover just under 400 square miles.

"The break-off is consistent with other changes we've seen in the area, such as the reduction in the amount of sea ice, the retreat of the glaciers and the break-up of other ice shelves," Wohlleben said.

She said a likely reason for the shelf breaking away was a strong wind from the south.

Warwick Vincent, director of the Centre for Northern Studies at Laval University in Quebec, said much of the remaining Ward Hunt ice shelf is now in a vulnerable state.

"It underscores the fact that each year we're now crossing new thresholds in environmental change in the High Arctic, and of course our concern in the longer term is that these may signal the onset of serious change at all latitudes, much further to the south, for example," he told Reuters.

Derek Mueller, an Arctic ice shelf specialist at Trent University in Ontario, said he was concerned by the rapidity of changes in the High Arctic over the last few years.

"It's a bit of a wake-up call for those people who aren't yet affected by climate change that there are places on earth that are, and the same could be true for them (these people) if you fast-forward a decade or two or three," he said.

Mueller initially estimated that 1.5 square miles of ice had broken off the shelf but increased that figure to eight square miles after studying the data more closely.

"Whatever has kept this ice shelf in balance for 3,000 years is no longer keeping it in balance," he told Reuters, saying he too would not be surprised to see more ice breaking away from the Ward Hunt shelf this year.

Wohlleben said the ice shelves, which contained unique ecosystems that had yet to be studied, would not be replaced because they took so long to form.

"Once they've broken off they're gone," she said. (Reporting by David Ljunggren; Editing by Peter Galloway)

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