Phasing of deglacial warming and Laurentide Ice Sheet meltwater in the Gulf of Mexico

Abstract

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 asyn- chronous 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 meltwater input from the Laurentide Ice Sheet. Paired d 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 d 18 O of sea- water. SST as calculated from Mg/Ca data increased by .3 8C from ca. 17.2 to 15.5 ka in association with Heinrich event 1 and was not in phase with Greenland air temperature. Subtracting tem- perature effects from d 18 O values in G. ruber reveals two excur- sions representing Laurentide meltwater input to the Gulf of Mex- ico, one of .1.5‰ from ca. 16.1 to 15.6 ka and a second major spike of .2.5‰ from ca. 15.2 to 13.0 ka that encompassed melt- water 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 225‰ indicates that near-surface salinity de- creased by 2‰-4‰ 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 deglacial climate by thermohaline circulation.