from glacial Lake Agassiz during the Younger Dryas cold interval

Julian Murton

The Younger Dryas cold interval - an abrupt cooling in Northern Hemisphere temperatures that resulted in much harsher winters for around 1,400 years - began, ironically, at the end of the last Ice Age, about 12,900 years ago.  Scientists have been trying to work out why such a sudden and dramatic cooling event in the Northern Hemisphere would have taken place at that time, and how it happened.

Before now, the most recent thinking was that the climate cooling was caused by vast volumes of icy water bursting out of a giant Ice Age lake in Canada - glacial Lake Agassiz - and directly into the North Atlantic Ocean, shutting down the ocean circulation there. However, this research has identified gravels near the Mackenzie Delta that suggest that the huge glacial outburst flood swept into the Arctic Ocean, along the northwest route. Geological dating of a regional erosion surface and flood gravel deposit at the mouth of the Mackenzie River indicate a major flood event just after 13,000 years ago, near the start of the Younger Dryas.

Based on new dates at the downstream end of the Mackenzie River drainage basin, combined with modelling of the topography of the Agassiz region, radiocarbon dating, and beach elevations in the Fort McMurray area, this research concludes that Lake Agassiz released a catastrophic overflow of glacial meltwater through its northwest outlet at the start of the Younger Dryas, which flowed to the Arctic Ocean. 

Dryas flower

This discovery demonstrates that many elements of the earth’s climate system are strongly linked. Changes in one part can have an impact on others. In this case, the discharge of ice melt water into the Arctic Ocean had a significant effect on Europe’s climate.

The Mackenzie Delta research was funded by the Royal Society, the Quaternary Research Association, the British Society for Geomorphology and the Geological Survey of Canada and was carried out by; Julian B. Murton (University of Sussex⁾, Mark D. Bateman (University of Sheffield), Scott R. Dallimore (Geological Survey of Canada), James T. Teller  & Zhirong Yang (University of Manitoba)