Meltwater and Abrupt Climate Change in the Gulf of Mexico During the Last Glacial Termination

During the Last Glacial Termination from 18,000-8,000 cal. yrs B.P., meltwater routing of the Laurentide Ice Sheet (LIS) may have been linked to abrupt climatic events, such as the Younger Dryas. Previous studies show episodic meltwater input from the LIS, via the Mississippi River to the Gulf of Mexico (GOM) several thousand years before the onset of the Younger Dryas until approximately 13,000 cal yrs B.P., when meltwater routing may have switched to a more northern spillway, causing an abrupt change in thermohaline circulation (THC). The exact timing and magnitude of this meltwater input to the GOM is poorly constrained due to the lack of high-resolution data. Also unknown are the detailed relationships between GOM sea surface temperature, sea surface salinity and ice volume, relative to Northern and Southern Hemisphere climate from Greenland and Antarctica ice core records. High sedimentation rates (~40 cm/kyr) from laminated, anoxic Orca Basin core MD02-2550 provide the necessary resolution to assess GOM paleoceanography. Paired Mg/Ca and δ18O values from planktonic Foraminifera species Globigerinoides ruber (pink and white varieties) provide the relative timing of meltwater input and temperature change in the GOM with nearly decadal resolution. δ18Ocalcite results show multiple cool and/or high salinity periods with isotopic excursions of at least 2‰ that coincide with abrupt climatic events in Greenland ice core records, including the Oldest Dryas from 16,200-15,000 cal. yrs B.P. and the Intra-Allerod Cold Period at 13,860-13,560 cal. yrs B.P. Meltwater input to the GOM is seen for several thousand years before the onset of the Younger Dryas with white G. ruber δ18Ocalcite values as low as -4‰. Thirty-three AMS radiocarbon dates and high-resolution δ18O results provide excellent temporal constraints on deglacial climate events, including an abrupt (<200 yrs) cessation of meltwater in the GOM centered at 10,970± 40 radiocarbon yrs B.P., with a δ18O increase of 3.5‰. The δ18Ocalcite of white G. ruber shows a clearly defined Younger Dryas interval (δ18Ocalcite ~ -0.5‰) after the Cessation Event from 13,000-11,700 cal yrs B.P. Pink G. ruber displays a similar cessation of meltwater, yet exhibits a much small isotopic range (4‰ vs. 6‰ for pink and white varieties, respectively) without a fully defined Younger Dryas period. The radiocarbon age of the Cessation Event in the GOM (10,970± 40) coincides with large changes in Δ14C, a proxy for THC strength, as well as the radiocarbon onset of the Younger Dryas in European lake sediments. These results suggest that the onset of the Younger Dryas and other abrupt climate events during the Last Glacial Termination may be linked to a decrease in THC due to a change in meltwater routing of the LIS.