DEGLACIAL MELTWATER INPUT TO THE GULF OF MEXICO: A MARINE-BASED RECORD OF LAURENTIDE ICE SHEET CHRONOLOGY

Laurentide Ice Sheet (LIS) dynamics have been resolved in numerous proxy records including glacial moraines, proglacial lakes, coral-derived sea level reconstructions, and deep-sea sediments. While terrestrial data sets often suffer from sediment reworking and limited age control, marine-based records have the ability to provide a continuous and uninterrupted time series of ice sheet melting. LIS meltwater has been previously documented in Gulf of Mexico (GOM) sediments using foraminiferal δ¹⁸O throughout the last deglaciation. However, existing records lack temporal resolution and age control to assess millennial-scale melting chronology.

We present two records of LIS melting history from Orca Basin located 300 km from the modern Mississippi River delta that span the entire deglacial sequence from ca. 24.5-7.0 ka. High sedimentation rates (40 cm/1000 years) and 52 ¹⁴C dates provide the necessary resolution to capture high-frequency melting events resolved by planktic foraminifera (G. ruber) δ¹⁸O. To further isolate the meltwater signal, characterized by highly negative δ¹⁸O values, we use paired Mg/Ca measurements to remove the isotopic effect of sea-surface temperature from foraminiferal δ¹⁸O values. After an ice-volume correction is applied, the resulting δ¹⁸O seawater record (termed δ¹⁸O_GOM) is primarily controlled by deglacial meltwater input and salinity variability.

Our δ¹⁸O_GOM results reveal large negative excursions centered at ca. 23.4 ka, 21.2 ka, 16.6 ka, 15.1 ka and 13.4 ka, that confirm at least five melting episodes followed by a cessation of meltwater at the onset of the Younger Dryas (ca. 12.9). Comparison to clay mineralogy data from nearby cores suggests the Great Lakes region may have been origin to a significant melting event (ca. 16.9-16.2 ka) followed by a northwest shift to the Mississippi and Missouri River watersheds at ca. 15.5 ka. Moreover, many melting events appear to follow significant glacial advances suggesting a correlation between meltwater production and glacial recession possibly driven by mild summers and enhanced seasonality postulated for the North Atlantic region. We speculate that the LIS was highly sensitive to small changes in northern hemisphere insolation and seasonal air temperature, which may be relevant to modern mid-latitude ice sheet melting.