HR: 09:45h
AN: PP11C-08    [Abstracts]
TI: The Expression of the 8.2 ka and Younger Dryas Events in the Eastern Canadian Arctic
AU: * Miller, G H
EM: gmiller@colorado.edu
AF: INSTAAR and Geol. Sci., University of Colorado, Boulder, CO 80309-0450 United States
AU: Wolfe, A P
EM: awolfe@ualberta.ca
AF: Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AL AB T6G 2E Canada
AU: Briner, J P
EM: jason.briner@colorado.edu
AF: INSTAAR and Geol. Sci., University of Colorado, Boulder, CO 80309-0450 United States
AU: Nesje, A
EM: atle.nesje@geo.uib.no
AF: Dept. of Earth Science, University of Bergen All‚gaten 41, Bergen, 5007 Norway
AB: The two largest climate coolings following the end of the last glaciation are the Younger Dryas and the 8.2 ka events. Evidence for these cold excursions is widespread around the North Atlantic and in more distant regions. Both events are well expressed in Greenland ice cores; glacier readvances occurred across much of NW Europe during the Younger Dryas and cold surface waters returned to the North Atlantic, with depressed summer temperatures in eastern North America. The 8.2 ka event has a similar pattern, but the magnitude is substantially lower, with a much shorter duration. However, surprisingly little evidence has been presented for either event from the North Atlantic Arctic. Recently acquired lake sediment records from the Eastern Canadian Arctic contain evidence for both excursions. The 8.2 ka event is recorded at two sites as a significant glacier readvance of cirque and outlet glaciers of local ice caps at 8.2ñ0.1 ka. In some non-glacially-dominated lakes, a reduction in primary productivity is apparent at the same time. These records suggest colder summers without a dramatic reduction in precipitation, producing positive mass balances and glacier readvances. For most local glaciers, this was the last significant readvance before they receded behind their Little Ice Age margins. Only a few lakes contain records that extend through the Younger Dryas chron. The best-dated lake record, Donard Lake, extends back to 15 ka. Lacustrine sedimentation is currently dominated by a meltwater from an outlet glacier that terminates a few hundred meters from the lake. The glacier has been within the drainage basin of the lake for the past 5.5 ka, although the contribution of glacial sediment has been larger since about 2.5 ka. Prior to 5.5 ka, there is no evidence of a glacier in the catchment of Donard Lake, suggesting that throughout the entire Neoglacial period, the local glacier has been more advanced than at any time since 15 ka. During the Younger Dryas chron, lacustrine primary productivity was greatly reduced, whether measured as the flux of organic carbon to the lake floor or as the percentage of organic matter in lake sediment. We interpret this change to reflect a substantial reduction in summer temperatures for more than 1 ka. However, this temperature drop was not accompanied by a significant glacier readvance, suggesting precipitation must have been very low. This differs from the 8.2 ka event when precipitation must have remained relatively high. These records indicate that in the Eastern Canadian Arctic, summers during the Younger Dryas were much colder than present, but precipitation was dramatically lower too, so glaciers did not advance, whereas during the briefer, and less severe summer cooling associated with the 8.2 ka event, precipitation was not dramatically reduced and glaciers readvanced.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting