Meltdown Blamed
For Big Freeze

By Gary Wisby
Environment Reporter
Chicago Sun-Times
Talk about a climate change: A University of Illinois at Chicago professor says he has found new evidence that a massive meltdown of polar ice 8,200 years ago put North America into a deep freeze for a century.
The "most dramatic climate change in the last 10,000 years" followed a flood of fresh water from a glacial reservoir into the salty water of the Gulf Stream, which controls our continent's weather. That led to a 43-degree temperature drop, said UIC's Torbjorn Tornqvist.
His report on earth core samples that indicate an abrupt jump in sea levels caused by the colossal flood will appear Saturday in an online issue of Geophysical Research Letters. Scientists believe the flood's source was a glacial reservoir called Lake Agassiz, holding twice the volume of the Caspian Sea in Eurasia, the world's largest inland sea.
According to this theory, all that fresh water gushed into the North Atlantic. There it mixed with the salty waters of the Gulf Stream.
Now less salty and less buoyant, the warm surface water sank, cooling the stream that ordinarily carries tropical waters to this continent.
The result? A temperature plunge of 43 degrees Fahrenheit that may have lasted 100 years or more.
At a time when scientists are focused on global warming, the "take-home message" is that climate change is a complicated phenomenon featuring abrupt swings toward both ends of the thermometer.
Tornqvist and his students found evidence of the millennia-old freshwater deluge while taking core samples of earth in the Mississippi Delta. "We were studying the loss of coastal wetlands but found something much more interesting," he said.
His team discovered deep core samples of peat that radiocarbon dating pegged at around 8,200 years, when the so-called "8.2 Event" occurred. Made up of decayed plant material in soggy ground, peat forms as sea levels rise.
His findings establish the first sea-level record corresponding to the big flood.
"The $64 million question is how much fresh water was released," the professor said. "My suspicion is that the only way is looking at sea levels."
Could the 8.2 Event happen again, as in the disaster movie "The Day After Tomorrow"?
"We don't have a Lake Agassiz now," Tornqvist said. But in Greenland, where the first evidence of the great flood was found, the ice sheet is melting at an accelerating rate. And global warming puts more moisture into the air, producing more rain and, in turn, fresher ocean water.
"It depends on how sensitive the North Atlantic is to that kind of process," Tornqvist said. "One possibility is that global warming could lead to this type of surprise but only affect part of the world."
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