for National Geographic News
An epic gush of fresh water into the North Atlantic slowed a deep ocean current and triggered a century-long chill in Europe and North America some 8,200 years ago, according to a new study.
The finding confirms scenarios suggested by previous models of the ancient climate and should raise confidence in predictions made about how the oceans will respond to Greenland's rapidly melting glaciers, an outside expert said.
Some scientists are concerned that Greenland's fast-melting ice could again slow the deep current, sparking changes in weather around the world ranging from reduced rainfall to a new mini ice age.
The current, called the North Atlantic Deep Water, helps keep Europe's climate mild. It shuttles cold, dense waters from the northern seas to the tropics, allowing the warm surface waters of the Gulf Stream to flow north. (Learn more about weather patterns.)
Since fresh water is less dense than cold salt water, climate models suggest a flood of fresh water into the North Atlantic should force the current to slow or shut down.
Scientists suspect the sudden draining of North America's ancient glacial lake Agassiz—which was seven times larger than all of the Great Lakes combined—caused a well-studied cold snap about 8,200 years ago. But evidence that the deep-water current slowed was lacking.
Now, a team of European scientists has found the evidence in the contents of a 39-foot (12-meter) plug of seabed mud pulled from some 11,200 feet (3,400 meters) deep in the northwest Atlantic.
"We show that there's a sudden disruption in the deep circulation which takes place just at the time of the flood outburst," said Helga Kleiven, a paleoclimate expert at the Bjerknes Center for Climate Research in Bergen, Norway.
She and her colleagues report the finding in tomorrow's issue of the journal Science.
Evidence Found in Ancient, Tiny Bugs
Kleiven and her colleagues drilled the core off the southern tip of Greenland, where sediment-rich deep waters slow down and deposit their loads.
"The sedimentation rate is 10 to 15 times higher at these drift sites than they are in the rest of the North Atlantic," Kleiven said.
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