2006 Philadelphia Annual Meeting (22–25 October 2006)

Paper No. 5
Presentation Time: 9:10 AM


CRONIN, Thomas M.1, MANLEY, Pat2 and RAYBURN, John1, (1)Earth Surface Processes, USGS, 12201 Sunrise Valley Drive, Reston, VA 20192, (2)Deparment of Geology, Middlebury College, McCardell Bicentennial Hall, Middlebury, VT 05753, tcronin@usgs.gov

One postulated cause of abrupt climate change, such as the Younger Dryas, invokes catastrophic discharges from North American glacial lakes that led to reductions in North Atlantic salinity and meridional overturning circulation. Despite geomorphological evidence for discharges, the timing, duration, and direction of meltwater events is insufficiently known to establish causality. The Champlain Valley lies at a critical location to understand Laurentide Ice Sheet retreat and glacial lake discharge between ~ 14 and 10 kyrBP (calendar years) because, unlike large lakes in the Great Plains and Great Lakes region, the isostatically depressed Champlain Valley was inundated by marine water of the Champlain Sea immediately following glacial lake drainage.

We present benthic foraminiferal and marine and freshwater ostracode data from radiocarbon dated post-glacial lake and marine sediments and reconstruct the history of lacustrine and marine conditions with emphasis on paleosalinity. Cores from New York and offshore in southern Lake Champlain show a complex faunal sequence during the transition from Lake Vermont to the Champlain Sea (~13-12.5 kyrBP) involving a shift from the ostracode Candona to the benthic foraminifera Cassidulina reniforme, a second Candona zone, and a series of benthic foraminiferal assemblages. In addition, a shift from Elphidium excavatum clavata to E. cf. incertum occurred ~12-11.8 kyrBP in the deep basin of the Champlain Sea. Multiple factors might have caused changes in salinity during the Champlain Sea episode: ice-sheet readvance and accelerated melting, freshwater inflow from western lakes into the Champlain-St. Lawrence, isostatic uplift. Our results suggest at least three major lake discharge events occurred, two at the inception of and one during the Younger Dryas. If confirmed by additional proxies under investigation (stable isotopes, trace elements, dinoflagellates), the Champlain record supports the hypothesis that large freshwater discharges catalyzed rapid climate change.