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A glacier in northeast Greenland is flowing at an accelerated rate into the North Atlantic Ocean, according to a new report by scientists from the University of California, Irvine (UCI) and published in the current issue of _Science_**.** The glacier, named Zachariae Isstrom (ZI), holds enough water to raise global sea level more than 18 inches if it melts completely.

Jeremie Mouginot and his team reconstructed the shape and movements of the glacier to track how it has changed in geometry due to melting from below caused by warm water intrusion and how much ice it has discharged into the ocean.

The team collected satellite images from international space agencies to measure the speed of the glacier and coupled that with NASA radar, which measured changes in the thickness of the glacier's ice over the last 40 years.

The changes are occurring on multiple fronts, said UCI's Chancellor Professor of Earth System Science Eric Rignot, who also worked on the study.

"Zachariae Isstrom is being hit from above and below," he said. "The top of the glacier is melting away as a result of decades of steadily increasing air temperatures, while its underside is compromised by currents carrying warmer ocean water, and the glacier is now breaking away into bits and pieces and retreating into deeper ground."

The acceleration of ZI's descent into the ocean has tripled and what's left of the ice shelf — the anchor, so to speak, that actually supports the glacier and keeps it from accelerating and discharging more ice into the sea — is melting and thinning at twice its historic rate. And more significant calving events are now occurring, which means large volumes of ice are breaking off into the ocean and contributing to sea level rise.

While scientists have observed changes in the west and south of Greenland, where temperatures are warmer, the fact that a glacier in the north is undergoing such drastic changes is a significant — and worrying — development.

"A glacier in a colder environment, closer to the pole, is starting to react to this change," said Mouginot. "We're really far north in Greenland and seeing this big glacier start to lose mass is actually pretty serious."

ZI is among the first in the north to lose mass. Its neighboring glacier, Nioghalvfjerdsfjorden (NG), is also melting rapidly.

"This glacier may follow the same path as ZI in 10-20 years," Mouginot said.

Together, the two glaciers make up 12 percent of Greenland's ice sheet and, if they both collapse, would contribute more than 39 inches to sea level rise.

ZI and NG encompass one of three major basins grounded on a bed below sea level.

The other basins are also undergoing significant changes. Jakobshavn Isbrae (JI), for example, started changing rapidly in 2002 following the collapse of its ice shelf.

"The glacier is now discharging three times more ice into the ocean than what is needed to keep the basin in equilibrium with snowfall," said Rignot.

The basins that were already emptying into the ocean formed a floating section that acted as a plug, but now, according to Rignot, the plug has disintegrated.

"It's a bit like releasing wine from a bottle, because you took out the cork," he said.