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Using Postglacial Eolian Dune Depositional Ages from Northeast Alberta, Canada to Assess the Likelihood of Northwestward Routing of Lake Agassiz Overflow at the Onset of the Younger Dryas Cold Event
  • Ken Munyikwa
Ken Munyikwa
Athabasca University

Corresponding Author:[email protected]

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The release of freshwater into the North Atlantic by glacial Lake Agassiz towards the end of the last glacial period is hypothesized to have triggered the Younger Dryas (Y.D.) cold event of 12.9 -11.7 ka ago. It is thought that the influx of freshwater into the Atlantic weakened meridional overturning circulation, impeding heat transport to the northern latitudes. A subject of debate at present is how the freshwater released from Lake Agassiz was routed to the ocean. One suggestion is that the retreat of the Laurentide Ice Sheet (LIS) from the Lake Superior Basin allowed water from Lake Agassiz, which was flowing south to the Gulf of Mexico, to be redirected eastward via the St Lawrence River to reach the Atlantic. Reported surface exposure ages indicate that the St Lawrence River route became available between 13.0 and 12.7 ka ago, timing that is coincident with the onset of the Y.D. event. An alternative route for the drainage from Lake Agassiz is that it flowed northwestwards to the Arctic Ocean via the Mackenzie River in northwest Canada. This suggestion has been affirmed by some modeling studies that found that meridional overturning in the North Atlantic would have been weakened more significantly if freshwater was introduced via the Arctic. A flow path, and deposits that have been identified on the Canadian Arctic Coastal Plain have yielded luminescence ages indicating that a major flood event occurred sometime between 13.0 and 11.7 ka ago. From that age range, however, it is not possible to ascertain if the flood triggered the Y.D. Thus, in this study, in order to determine a more precise timeline for the northwestward drainage of Lake Agassiz, we collected postglacial eolian dune sands from northeast Alberta, Canada, an area through which water from Lake Agassiz would have had to pass in order to reach the Arctic Ocean. The dune sands were sourced by wind from sediments left behind following the drainage of glacial Lake McConnell which had also been dammed in the region by the LIS. Preliminary luminescence ages obtained from the eolian sands suggest that northeast Alberta was free of both ice and glacial lakes by 13.5-12.5 ka ago. This indicates that flow from Lake Agassiz via the Mackenzie River cannot be excluded as a trigger for the Y.D. since the northwestward drainage path appears to have also been available at the start of the event.