2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 3
Presentation Time: 1:30 PM-5:30 PM


MA, Lin, Department of Geological Sciences, Univ of Michigan, 425 East University Ave, 2534 C. C. Little Bldg, Ann Arbor, MI 48109, CASTRO, Maria Clara, Geological Sciences, Univ of Michigan, 2534 C.C. Little Building, 425 E. University Ave, Ann Arbor, MI 48109 and HALL, Chris M., Geological Sciences, Univ of Michigan, 4534 CC Little Building, Ann Arbor, MI 48109-1063, linma@umich.edu

A ~17kyr paleoclimatic reconstruction using noble gas concentrations and 14C derived ages was carried out in the Marshall aquifer in southern Michigan, a region that experienced ice-sheet covering during the Last Glacial Maximum (LGM) and early deglaciation periods. At ~17kyrs BP, results reveal a ground temperature of ~1 °C, 5.1 °C cooler than today, suggesting that glacial melt water recharged the aquifer under high hydraulic pressures induced by overlying glaciers.

In addition to the general warming trend observed between the LGM and present time, the noble gas temperature (NGT) record indicates an abrupt warming event between ~12.8 and 11.1kyrs BP, correlative to the Bolling-Allerod (BOA) warm phases. Such abrupt warming is followed by a climate reversal, possibly the Younger Dryas. Ice-sheet-linked changes in freshwater delivery to the North Atlantic, as well as changes in the North Atlantic Deep Water (NADW) circulation are possibly at the origin of such abrupt climate shifts in northeastern US.

Our NGT record reveals a ~3 °C temperature difference within the last millennium. Unfortunately, lack of age resolution through 14C does not allow for a detailed paleoclimatic reconstruction within this period.

Analysis of δ18O and δD reveal, for most samples, a lack of correlation with NGTs and thus, with local precipitation temperatures. Importantly, Pleistocene waters with the coldest recharge temperatures present the most positive δ18O and δD values, suggesting a dominant latitude effect over local precipitation temperatures, and thus, an atmospheric circulation pattern distinct from present time during the early deglaciation periods, with a stronger moisture component from the Gulf of Mexico.