HR: 11:50h
AN: PP42A-06    [Abstracts]
TI: Tests for causes and consequences of the Younger Dryas in the Laurentian Great Lakes
AU: * Colman, S M
EM: scolman@d.umn.edu
AF: University of Minnesota Duluth, Large Lakes Observatory and Dept. Geological Sciences 2205 E 5th St., Duluth, MN 55812, United States
AB: The cause of the Younger Dryas climate episode is being reexamined with increasing vigor. The conventional explanation has been a switching of meltwater runoff from a large sector of the Laurentide ice sheet from the Mississippi to the St. Lawrence River systems, with a concomitant freshening of the north Atlantic Ocean and a suppression of the Atlantic Meridional Overturning, which transports heat to high northern latitudes. Reexamination of the evidence for both the timing and the location of meltwater routing at the beginning of the Younger Dryas has lead to searches for other causes for this distinctive climate event, including possible extraterrestrial events. Changes in meltwater routing certainly occurred. Cessation of flow down the Mississippi and a major fall in the level of Lake Agassiz are well documented, and the water had to go somewhere. Timing and routing of the meltwater flows are now the questions. Several tests of timing and routing are potentially available from the Laurentian Great Lakes. The unique, but poorly dated Wilmette bed in Lake Michigan was deposited at about the beginning of the of the Younger Dryas. Further analysis of this bed are underway to determine whether it was deposited in association with flows from Lake Agassiz, or whether it contains material indicative of other potential causes of climate change at about that time. In addition, both the purported flood from Lake Agassiz at the beginning of the Younger Dryas and a younger uncontested flood from Lake Agassiz through the Nipigon Basin emptied into the Lake Superior basin. Seismic-reflection surveys are planned to determine if the younger, uncontested flows produced distinctive deposits in the Superior basin, and whether similar deposits of possible Younger Dryas age exist near Thunder Bay or other potential Agassiz outlets. Various explanations for the cause of the Younger Dryas are not necessarily exclusive or independent. For example, an initial event that was largely independent of meltwater routing may have caused changes in the configuration of the Laurentide Ice Sheet, leading to changes in meltwater routing. The changes in meltwater discharge, in turn, could have reinforced or retarded the initial climate forcing.
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4942 Limnology (0458, 1845, 4239)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly