Deglacial Warming in the Gulf of Mexico Preceded Laurentide Ice Sheet Meltwater Input: Implications for Tropical Climate Forcing

As part of the Western Hemisphere Warm Pool (WHWP), the Gulf of Mexico is an important source of heat and moisture to the North American continent and the higher latitudes. Orca Basin on the Louisiana slope in the northern Gulf of Mexico is ideally located to record deglacial WHWP sea-surface temperature (SST) warming in relation to meltwater input from the Laurentide Ice Sheet (LIS). Paired δ¹⁸O and Mg/Ca data on planktic foraminifera (Globigerinoides ruber, white variety) from cores EN32-PC4 and -PC6 are used to separate deglacial changes in SST and δ¹⁸Oseawater due to low-salinity meltwater. In core EN32-PC4, Mg-SST increases from near full-glacial values of about 24°C at ca. 15 ka ¹⁴C to >28°C at ca. 12.8 ka ¹⁴C, including a sharp increase of >3°C from 14.2-13.3 ka ¹⁴C. This warming clearly precedes the peak of meltwater input (minimum Gs. ruber δ¹⁸O) by nearly 2 k.y. Furthermore, Mg-SST and global δ¹⁸Oseawater changes can be subtracted from Gs. ruber δ¹⁸O to isolate the influence of meltwater (ice-volume corrected δ¹⁸Oseawater), which can be interpreted in terms of salinity variations. This exercise indicates a peak in meltwater input at 12 ka ¹⁴C, close to the timing of meltwater pulse 1A. If confirmed in EN32-PC6, these results suggest that (1) subtropical deglacial SST warming preceded LIS decay, and (2) the origin of sea-level rise during mwp-1A was primarily meltwater derived from the LIS. Extending paired Mg-SST and δ¹⁸O data on Gs. ruber into Marine Isotope Stage (MIS) 3 further illuminates the phasing of WHWP changes relative to high-latitude climate variability. Preliminary results indicate significant SST variability that can be correlated to Dansgaard-Oeschger events of the Greenland ice core records. In addition, δ¹⁸O data on Gs. ruber (pink variety) indicate at least one interval of significant meltwater input in mid-MIS 3. Our continuing work will test the hypothesis that the tropical/subtropical Atlantic is an important driver of regional to global climate change.