Oregon State University

College of Earth, Ocean, and Atmospheric Sciences

Meltwater and rapid cooling

ice sheet

New study shows freshwater input route from melting ice led to rapid cooling

By Mark Floyd, OSU News and Research Communications

Posted January 24, 2018

CORVALLIS, Ore. – Scientists have long known that a reduction in Atlantic Ocean currents bringing warm water to the Northern Hemisphere from the tropics created abrupt cooling known as the Younger Dryas cold period nearly 13,000 years ago, but the cause of this phenomenon has not been proved.

Now a team of scientists from the United States and Canada think they have the answer – input of fresh water from the Laurentide Ice Sheet retreating from the Lake Superior basin, creating a river through the lower Great Lakes to the Gulf of St. Lawrence and the North Atlantic.

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The findings are important because it could happen again, a result of both the Greenland Ice Sheet melting and a significant rise in fresh water from the Arctic through increased rain and snow. The study also highlights how sensitive the Atlantic current is to changes in the input of fresh water.

Results of the study have been published online in Geology, a publication of The Geological Society of America.

“It has been well-documented that the Atlantic meridional overturning circulation, or AMOC, slowed because of fresh water, but there has been little agreement as to how,” noted Anders Carlson, an Oregon State University geologist and co-author on the study. “Some scientists have argued for years that it has been this freshwater path, but others say the region was still iced in when the cooling period begun.

“Some people have even speculated that a comet caused the cooling period. We found convincing evidence, however, that it was fresh water – a river the size of the Mississippi that flowed into the North Atlantic.”

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