8,200-year-old cooling is analyzed

August 20, 2007

Canadian scientists studying ice core records are questioning current theories about the rapid cooling of the Northern Hemisphere 8,200 years ago.

Many scientists link that event with the final drainage of Lake Agassiz, a large glacial lake that once covered much of central Canada, The drainage is thought to have freshened waters in the northern Atlantic Ocean, slowing the oceanic circulation that helps distribute heat.

Canadian scientists C. Hillaire-Marcel and Anne de Vernal of the University of Quebec and McGill University, along with David Piper of the Geological Survey of Canada, studied oceanic records downstream from Lake Agassiz's flood discharge route.

The researchers found the lake's drainage occurred between 8,500 and 8,350 years ago and that sea-surface and deep-current conditions determined from oceanic sediment cores lack significant concurrent changes in the northern Atlantic.

Instead, the scientists said the data show the 8,200-year-old cooling event was generated by several factors, including melting of North American continental glaciers and a subsequent rapid sea level rise that induced a large-scale reorganization of broad oceanic circulation patterns.

The study appears in the journal Geophysical Research Letters.

Copyright 2007 by United Press International

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