Big chunk of ice shelf breaks off

Scientists say it's another dramatic sign of how the polar frontier is being changed by warmer temperatures.

They say a chunk of ice shelf -- nearly the size of Manhattan -- has broken away from Ellesmere Island in Canada's northern Arctic.

An ice shelf specialist at Trent University in Ontario says the Markham Ice Shelf, which is 4,500 years old, separated in early August, and that the 19-square-mile piece is now adrift in the Arctic Ocean.

Derek Mueller says another ice shelf lost two large sections, and that a third one continues to break up.

Ice shelves are large platforms of thick, ancient sea ice that float on the ocean's surface, but are connected to land.

Scientists say the loss of the ice shelves means that the rare ecosystems that depend on them are threatened with extinction.

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