(CNN) The sea ice off the coast of northern Greenland is normally some of the thickest in the entire Arctic, with ridges of ice piled as high as 70 feet in some places.

And despite the rapid retreat of sea ice across the region due to climate change, this harsh corner of the globe was expected to be the last to retain year-round sea ice cover.

But recent satellite imagery shows that some of the Arctic's oldest ice has been replaced by miles of open water for the first time on record, surprising scientists and ice monitors.

"This was the area that was seen as the last bastion, where we'd see these changes come last, but they've arrived," said Walt Meier, a senior research scientist with the National Snow and Ice Data Center.

How the breakup happened

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