A LATE PLEISTOCENE-HOLOCENE NOBLE GAS PALEOTEMPERATURE RECORD IN SOUTHERN MICHIGAN

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.