HR: 11:20h
AN: PP12A-05    [Abstracts]
TI: The 8.4 ka lake Agassiz drainage event: its deep-sea sedimentary record and impact on the Atlantic Meridional Overturning
AU: Hillaire-Marcel, C
EM: chenv@uqam.ca
AF: GEOTOP - UQAM & McGill, POB 8888, Montreal, Qc H3C 3P8 Canada
AU: de Vernal, A
EM: devernal.anne@uqam.ca
AF: GEOTOP - UQAM & McGill, POB 8888, Montreal, Qc H3C 3P8 Canada
AU: Piper, D J
EM: DPiper@nrcan.gc.ca
AF: Geological Survey of Canada, POB 1006, Dartmouth, NS B2Y 4A2 Canada
AU: * St-Onge, G
EM: guillaume_st-onge@UQAR.QC.CA
AF: GEOTOP - UQAM & McGill, POB 8888, Montreal, Qc H3C 3P8 Canada
AU: * St-Onge, G
EM: guillaume_st-onge@UQAR.QC.CA
AF: ISMER - UQAR, 310, All‚e des Ursulines, Rimouski, Qc G5L 3A1
AB: Many papers have linked the ca. 8.4 ka drainage of the Laurentide Ice Sheet pro-glacial Lake Agassiz (Barber et al, 2002, Nature 400, 344-348) to a significant reduction in the Atlantic Meridional Overturning (AMO) and to climate excursions of variable age and duration in the 8.5-8 ka time frame, with reference to the so-called "8.2 ka event" (see refs. in Rohling and P„like, 2004, Nature 434, 975-979) based on the Greenland ice core chronology. Unfortunately, none of these papers provide direct marine evidence for a collapse or significant reduction in the AMO, neither for a widespread change in sea-surface conditions over the northern North Atlantic. Moreover, model experiments made with reference to this event lack critical evaluation based on data. Here, we present paleoceanographical records near the source area in the northwest North Atlantic with chronological resolution as high as 15 years per sample in some instances. They provide evidence for two short duration, local sedimentological events (possibly each of one year duration according to Clarke et al., 2003, Science 301, 922-923), but indicate the absence of significant change in sea-surface conditions as well as in the outflow of the deep Western Boundary Under Current, at the resolvable time scale. We conclude that there is no evidence for a significant change in the AMO linked to the drainage event that lasted more than a few tens of years, if at all. Nonetheless, all marine records indicate that the 8.5 to 7.5 ka time interval does correspond to a major large scale re-organisation both of land drainage in NE America and of the North Atlantic climate-ocean system (cf. St-Onge et al., 2003, EPSL 209, 113-130; Keigwin et al., 2005, Paleoceanography, 20, 10.1029/2004PA001074), notably marked by a reduction in the North East North Atlantic Water outflow, an increasing Denmark Strait Overflow and the inception of Labrador Sea Water formation.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4900 PALEOCEANOGRAPHY (0473, 3344)
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005