DEGLACIAL MELTWATER INPUT TO THE GULF OF MEXICO: A MARINE-BASED RECORD OF LAURENTIDE ICE SHEET RETREAT
Paired G. ruber (white and pink, separately) δ18O and Mg/Ca analyses allow us to use Mg/Ca paleothermometry to remove the temperature component of the δ18O signal, leaving behind a record of seawater δ18O (δ18Osw). After applying a global ice volume correction, the resulting GOM δ18Oivc-sw record is primarily controlled by LIS meltwater input.
Our δ18Oivc-sw records document negative excursions at 19-18.2, 17.5-16.2, 15.3-14.8, and 13.7-13 ka, interpreted as four melting events, followed by the cessation of meltwater at the onset of the Younger Dryas (12.9 ka). Our results provide the first evidence for LIS meltwater contribution to global sea level rise at 19 ka. Additionally, LIS melting at 17.5 ka suggests that enhanced seasonality in the North Atlantic produced mild summers sufficient for ice sheet retreat during the Mystery Interval (17.5-14.5 ka) despite extremely cold winters. Clay mineralogy data from the GOM and 14C-dated glacial moraines provide evidence for ice retreat patterns along the LIS southern margin. Meltwater input at 17.5 ka coincides with an increase in chlorite and illite clays in GOM sediments, suggesting that this meltwater was sourced from the northeast portion of the LIS southern margin, where regional sediments are rich in chlorite/illite. At 15.6 ka, high smectite concentrations in GOM sediments indicate that meltwater may have originated further west, from the Upper Mississippi and Missouri River watersheds. Overall, GOM sediments reveal large variations in the source of meltwater input to the Mississippi River and GOM during the last deglaciation that may reflect high-frequency patterns in LIS retreat linked to changes in northern hemisphere solar insolation, atmospheric temperature, and seasonality.