Laurentide Ice Sheet Meltwater and the Atlantic Meridional Overturning Circulation During the Last Glacial Cycle: A View From the Gulf of Mexico

Abstract

0GM001016-RA-Flower.3 Pro of Meltwater input from the Laurentide Ice Sheet (LIS) has often been invoked as a cause of proximal sea surface temperature (SST) and salinity change in the North Atlantic and of regional to global climate change via its influence on the Atlantic meridional overturning circulation (AMOC). Here we review the evidence for meltwater inflow to the Gulf of Mexico and its reduction relative to the onset of the Younger Dryas, compare inferred meltwater inflow during marine isotope stage 3 (MIS 3), and thereby assess the role of LIS meltwater routing as a trigger of abrupt climate change. We present published and new Mg/Ca and δO data on the planktic foraminifer Globigerinoides ruber from four northern Gulf of Mexico sediment cores that provide detailed records of SST and δO of seawater (δOsw) for most of the last glacial cycle (48–8 ka). These results generally support models that suggest meltwater rerouting away from the Gulf of Mexico and directly to the North Atlantic may have caused Younger Dryas cooling via AMOC reduction. Alternatively, southern meltwater input may simply have been reduced during the Younger Dryas. Indeed, Dansgaard-Oeschger cooling events must have had a different cause because southern meltwater input during MIS 3 does not match their number or timing. Furthermore, the relationships between Gulf of Mexico meltwater input, Heinrich events, Antarctic warm events, and AMOC variability suggest bipolar warming and enhanced seasonality during meltwater episodes. We formulate a “meltwater capacitor” hypothesis for understanding enhanced seasonality during abrupt climate change in the North Atlantic region.