Younger Dryas paleotopographic modeling of the Northwestern Outlet of glacial Lake Agassiz
Abstract
Overflow from glacial Lake Agassiz has been implicated in altering thermohaline circulation in the North Atlantic Ocean, and in bringing about widespread cooling at several times, namely during the Younger Dryas, the PreBoreal Oscillation, and the 8.2 ka event. The eastward routing of overflow from Lake Agassiz into the Great Lakes-St. Lawrence during the Younger Dryas has been questioned recently, and a NW overflow route through the Athabasca-Mackenzie River basin to the Arctic Ocean has been proposed. Our DEM paleotopographic reconstructions of the region around the NW outlet, near Fort McMurray, Alberta, adjusted for differential isostatic rebound, show that topography at the start of the Younger Dryas would have allowed overflow from Lake Agassiz into the Athabasca-Mackenzie route to the Arctic Ocean, if the Laurentide Ice Sheet had retreated from that area. Radiocarbon dates indicated that that region was deglaciated by then. Furthermore, when beaches of Younger Dryas age in the Lake Agassiz basin are projected northwest into the Athabasca Valley near Fort McMurray, they coincide with mapped beaches there, indicating that the lake extended far north of its currently accepted limits, to the edge of the Laurentide Ice Sheet. Therefore, based on paleotopographic modeling, dating, and beach elevations, combined with new OSL dates of ~13 cal ka associated with flood gravels at the mouth of the Mackenzie River, we conclude that Lake Agassiz overflowed to the northwest around the LIS margin in the Athabasca-Mackenzie valley to the Arctic ocean during the Younger Dryas. Ocean-atmosphere models should consider the implications of this routing in assessing the role of Lake Agassiz in global change.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP21A1331T
- Keywords:
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- 4901 PALEOCEANOGRAPHY / Abrupt/rapid climate change