Phasing of deglacial warming and laurentide ice sheet meltwater in the Gulf of Mexico

Evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation. However, existing studies show that deglacial warming was asynchronous across the tropical band, complicating the identification of causal mechanisms. The Orca Basin in the northern Gulf of Mexico is ideally located to record subtropical Atlantic sea-surface temperature (SST) warming in relation to mellwater input from the Laurentide Ice Sheet. Paired delta(18)O and Mg/Ca data on the planktonic foraminifer Globigerinoides ruber from core EN32-PC6 are used to separate deglacial changes in SST and delta(18)O of seawater. SST as calculated from Mg/Ca data increased by >3 degreesC from ca. 17.2 to 15.5 ka in association with Heinrich event I and was not in phase with Greenland air temperature. Subtracting temperature effects from delta(18)O values in G. ruber reveals two excursions representing Laurentide meltwater input to the Gulf of Mexico, one of >1.5parts per thousand from ca. 16.1 to 15.6 ka and a second major spike of >2.5parts per thousand from ca. 15.2 to 13.0 ka that encompassed meltwater pulse 1A and peaked ca. 13.8 ka during the Bolling-Allerod. Conversion to salinity through the use of a Laurentide meltwater end member of -25parts per thousand indicates that near-surface salinity decreased by 2parts per thousand-4parts per thousand during these spikes. These results suggest that Gulf of Mexico SST warming preceded peak Laurentide Ice Sheet decay and the Bolling-Allerod interval by >2 k.y. and that heat was retained in the subtropical Atlantic during Heinrich event 1, consistent with modulation of deglaciall climate by thermohaline circulation.