HR: 11:05h
AN: PP12A-04 INVITED     [Abstracts]
TI: Continued Support for a St. Lawrence Routing Event as the Cause for the Younger Dryas
AU: * Clark, P U
EM: clarkp@onid.orst.edu
AF: Dept. Geosciences, Oregon State University, Corvallis, OR 97331
AU: Carlson, A
EM: carlsand@geo.oregonstate.edu
AF: Dept. Geosciences, Oregon State University, Corvallis, OR 97331
AU: Meissner, K
EM: katrinm@ocean.seos.uvic.ca
AF: School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8W 3P6
AB: Proxies of deepwater formation show that a large reduction in the Atlantic meridional overturning circulation (AMOC) occurred at the start of the Younger Dryas event, suggesting that the attendant loss of ocean heat transport caused Younger Dryas cooling in the North Atlantic region. The trigger of this ocean response remains unclear, however, with the leading mechanism, involving the routing of continental runoff to the St. Lawrence River, now questioned on the basis of marine and terrestrial evidence, and modeling. Here we capitalize on the well-known relation between river geochemistry and underlying bedrock lithology to use changes in 87Sr/86Sr, U/Ca, and Mg/Ca measured in planktonic foraminifera tests as tracers of routing of continental runoff derived from distinct geological terranes. These data, supported by changes in planktonic „13C and „18O, confirm that routing of runoff from western Canada to the St. Lawrence River occurred at the start of the Younger Dryas. Changes in these tracers indicate that freshwater flux through the St. Lawrence River increased by 0.08 +/- 0.03 Sv, which is sufficient to induce a large decrease in the meridional overturning circulation. Using the UVic Earth System Model, we also evaluate the AMOC response to a large 1-2 year lake-discharge event relative to a sustained routing event of continental runoff, and find little difference between the combined effects and just a routing event.
DE: 1620 Climate dynamics (0429, 3309)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005