A late Pleistocene-Holocene noble gas paleotemperature record in southern Michigan

Abstract

Noble gas temperatures (NGTs) and 14C derived ages in groundwaters of the Michigan Basin reveal a ground temperature of ∼1°C toward the end of the Last Glacial Maximum (LGM) suggesting that groundwater recharge occurred under the Laurentide Ice Sheet (LIS) cover. In addition to the general warming observed since the LGM, the NGT record indicates an abrupt warming event between ∼12.8 and 11.1kyrs BP, correlative to the Bølling-Allerød (BOA) warm phases. Ice-sheet-linked changes in freshwater delivery to the North Atlantic, together with changes in the North Atlantic Deep Water (NADW) circulation are possible causes of such abrupt climate shifts in northeastern US. Pleistocene waters yielding the lowest NGTs have the highest δ18O and δD values, suggesting an atmospheric circulation pattern distinct from today, with a stronger moisture component from the Gulf of Mexico, possibly due to the presence of the LIS which weakened the Pacific westerly flow. Copyright 2004 by the American Geophysical Union.