HR: 1340h
AN: PP13A-1479    [Abstracts]
TI: Revised Deglacial Chronology of the Laurentide Ice Sheet and Implications for Catastrophic Meltwater Discharge as Triggers for Abrupt Climate Change
AU: * Lowell, T V
EM: Thomas.Lowell@uc.edu
AF: Department of Geology, 500 Geology/Physics University of Cincinnati, Cincinnati, OH 45226 United States
AU: Fisher, T G
EM: Timothy.Fisher@UToledo.Edu
AF: Dept. of Earth, Ecological and Environmental Sciences, University of Toledo, Toledo, OH 43606 United States
AU: Hajdas, I
EM: hajdas@phys.ethz.ch
AF: ETH, ETH Honggerberg, Zurich, CH-8093 Switzerland
AB: A current hypothesis suggests that the Younger Dryas climate change involves the sudden release of stored meltwater from glacial Lake Agassiz. However, such a trigger requires a specific flood chronology and volume. Because the retreat patterns of the Laurentide Ice Sheet control meltwater routing, timing, and volume, it is useful to assess whether the current retreat chronologies support meltwater release from Lake Agassiz immediately preceding the Younger Dryas. Specifically, we reexamine ice margin retreat from proposed outlet areas on the sub-continental divide through which Agassiz meltwater flowed. These outlet areas are the first gates any meltwater must have flowed through before reaching the ocean. In these two gate areas: Fort McMurray, Alberta (proposed northwest outlet), and Thunder Bay, Ontario (proposed eastern outlet), our geomorphic analysis of glacial landforms suggest a more complex deglaciation pattern than previously reconstructed. New radiocarbon analyses indicate that ice recession occurred up to 1000 14C yr later than previously thought. At least four distinct moraine sets around Fort McMurray record downslope ice margin recession that prevented ice-dammed meltwater from draining northward to the Arctic Ocean. These moraines are provisionally assigned ages of 10,460; 9,850; 9,660; and 9,510 14C yr, and the large Clearwater-lower Athabasca spillway cross-cuts the three oldest moraines. This relationship implies that the ice dam held until at least 9,660 14C yr, after which dam failure, lake drainage and any northwest drainage from Lake Agassiz across this divide occurred. Many long linear moraines southwest of Thunder Bay record deglaciation across the uplands of the Gunflint range from 12,000 until 10,550 14C yr. West of Thunder Bay in the lowlands north of the Gunflint range, along which the oldest eastern outlet into the Lake Superior basin is proposed, was not deglaciated until about 10,400 14C yr. Moreover, with continued ice recession, glaciolacustrine sediment records a widespread, ponded water body over the divide region until 10,100 14C yr. These new, younger deglacial chronologies from the proposed northwestern and eastern outlet regions do not support the hypothesis that meltwater from glacial Lake Agassiz triggered the Younger Dryas. Therefore as the evidence for a younger Lake Agassiz concomitant with a younger deglacial chronology continues to mount, it may be prudent to search elsewhere for a cause for the Younger Dryas.
DE: 1620 Climate dynamics (0429, 3309)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4215 Climate and interannual variability (1616, 1635, 3305, 3309, 4513)
DE: 4243 Marginal and semi-enclosed seas
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005