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Lake Agassiz disgorges its secrets

By Dave Armstrong - 06 Oct 2011 19:28:0 GMT
Lake Agassiz disgorges its secrets

Image: Lake Agassiz Map adapted from John Tester's Minnesota's Natural Heritage. University of Minnesota Press, Minneapolis, 1995, Credit: © Minnesota State University, Mankato

In ancient times a lake the size of Hudson's Bay extended from the borders of North Dakota and Minnesota, into western Ontario and covering almost the whole of Manitoba. Glacial Lake Agassiz was formed from melt-water and Lake Winnipeg, Lake Winnipegosis, Lake Manitoba, and Lake of the Woods are the four main remnants of this great lake. With its huge surface area climatic influence was obvious and Professor Thomas Lowell is now revealing all in Minneapolis to the Geological Society of America. The title of his paper is "Glacial Lake Agassiz-Its History and Influence on North America and on Global Systems: In Honor of James T. Teller."

Prof. Thomas Lowell; Credit: © University of Cincinnati

Lowell's work on abrupt climate change looks at the Younger Dryas cold spell in which the climate cooled down within a 30 year period. Strange low water levels indicate evaporation or drainage at the same time. Theories concerning this freshwater influx into ocean currents have been upheld by scientists for years. Even the St. Lawrence Seaway was thought to have been forged by the force exerted by a new drainage channel.

Lowell's alternative is that the surface area of the lake increased by a factor of 7. This implies much greater evaporation during the Younger Dryas cold period, when there would have been dry and sunny (increased solar radiation) conditions. This adds up to less rain, less melt-water production from glaciers and enhanced evaporation. The Younger Dryas is thought to have "frozen" North America and north-west Europe between 10700 and 9500 BC.

The colours show cooling effects on the climates of North America, Greenland and NW Europe; Credit: Copyright © National Academy of Sciences (The National Academies Press)

The professor's links with Greenland, Alaska, Peru and the rest of Canada give him vast experience of using mineralogy of lake sediments and even Chironomid midge larvae remains to determine temperature in ancient times. Perhaps these methods will finally determine what really happened to the North American and other climates at that time.

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