HR: 10:20h
AN: PP12A-01 INVITED     [Abstracts]
TI: Late Glacial Outbursts From Lake Agassiz: the Marine Record on the Labrador, Newfoundland, and Scotian Shelves
AU: * Teller, J T
EM: tellerjt@ms.umanitoba.ca
AF: Department of Geological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2 Canada
AU: Miller, A A
PP12A-01 AF: Marine Geos, Apt.1, 1003 Peter St., New Minas, NS B4N 3L7 Canada
AU: Lewis, C M
PP12A-01 AF: Geological Survey of Canada Atlantic, Natural Resources Canada, Bedford Institute of Oceanography, Box 1006, Dartmouth, NS B2Y 4A2 Canada
AU: Lewis, C M
PP12A-01 AF: Graduate School of Oceanography University of Rhode Island, University of Rhode Island, Narragansett, RI 02882 United States
AU: Levac, E
PP12A-01 AF: Department of Environmental Studies and Geography, Bishop's University, Lennoxville, QC J1M 1Z7 Canada
AU: Sonnichsen, G V
PP12A-01 AF: Geological Survey of Canada Atlantic, Natural Resources Canada, Bedford Institute of Oceanography, Box 1006, Dartmouth, NS B2Y 4A2 Canada
AU: Piper, D J
PP12A-01 AF: Geological Survey of Canada Atlantic, Natural Resources Canada, Bedford Institute of Oceanography, Box 1006, Dartmouth, NS B2Y 4A2 Canada
AB: Lake Agassiz formed along the Laurentide Ice Sheet (LIS) between ~13.7-8.4 cal ka, and periodically released large (1.6 to 160 x 103 km³) bursts of water into different oceans as ice retreated past critical topographic thresholds. Differential isostatic rebound, reconstructions of the LIS margin, and dated lake levels are used to identify the routing taken by these outbursts. The two largest outbursts (0.3 and 5.2 Sv) occurred at ~12.9 cal ka and ~8.4 cal ka, which are near the start of the Younger Dryas (YD) and the 8.2 cal ka cooling, respectively. There is a distinct lack of evidence in the western North Atlantic Ocean (e.g. Labrador Sea) for the largest outburst from Lake Agassiz when it drained out of Hudson Strait at 8.4 ka. However, new data and re-evaluation of previously published results from cores collected on the Labrador, Newfoundland and Scotian continental shelves show the presence of a calcite-rich detrital carbonate (DC) layer, around 8.4 ka, indicating plume transport of sediments from Hudson Bay in the Labrador Current. Changes in dinocyst assemblages and shifts to lighter delta ¹⁸O values indicate reduced ocean sea-surface temperatures and salinities in this flow. Significant changes in benthic foraminiferal faunas at some sites indicate water-mass shifts, and reduced salinities and temperatures, at the sea floor, all of which correlate to the flux of waters from the final Agassiz drawdown. Through mixing with offshore branches of the Labrador Current, some of these waters may have been incorporated in the North Atlantic Current east of Grand Bank, or into the Gulf Stream south of Grand Bank, and transported to northern North Atlantic areas of convection, confirming the potential role of Lake Agassiz freshwaters in triggering the 8.2 ka cooling event by impacting thermohaline circulation (THC). The presence of a YD-dated DC layer, with a strong dolomite component, on Northeast Newfoundland Shelf is possibly a consequence of a northwestern outburst from Lake Agassiz at the start of the YD, routed via the Arctic Ocean, through Fram Strait, then into the East, then West, Greenland currents, to the Labrador Current, rather than through the Great Lakes-St. Lawrence drainage system. The same benthic foraminiferal changes observed on Northeast Newfoundland Shelf in the 8.2 ka DC layer also occurred during YD DC deposition, suggesting water mass changes and flux were of similar magnitude in the YD as during the 8.2 ka event, and much more significant than previously recognized. Some of these waters may also have coalesced with the Gulf Stream and North Atlantic Current, for transport back to the Norwegian and Greenland seas, where in combination with the Arctic outflow they inhibited THC. The final 163,000 km³ drainage of Lake Agassiz at 8.4 ka may also have been responsible for triggering a tsunami in the Labrador Sea, and for rapid marine transgressions along gently-sloping continental shelves of the world.
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 3025 Marine seismics (0935, 7294)
DE: 3030 Micropaleontology (0459, 4944)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4942 Limnology (0458, 1845, 4239)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005