A High-Resolution Record of Meltwater Discharge and Deglacial Warming in the Gulf of Mexico

Sea surface temperature (SST) and δ18Osw records from the Gulf of Mexico (GOM) during the last deglaciation will help distinguish different mechanisms for abrupt climate change. Orca Basin is an ideal location to study climate changes in the GOM and to record the timing of meltwater discharge events through the Mississippi River; the anoxic hypersaline bottom water prevents bioturbation and results in finely laminated sediments. We sampled core MD 02-2550 at 0.5 cm resolution which, given sedimentation rates of greater than 30 cm/ka, corresponds to ~20 yr resolution. We analyzed Mg/Ca ratios on Globigerinoides ruber (white) to generate a SST record using the calibration of Anand et al. (2003). The record presented here extends from ca. 13 to 10.4 ka BP. The average temperatures at the beginning of the record from 13 to 12.5 ka BP are 26.3°C, with a variability of 1.0°C (1 σ). A major SST decrease of 3.0°C is recorded in two steps at 12.5 ka and 12.2 that lasts ca. 500 years. Within this transition, a more rapid cooling of ~2.0°C in less than 100 years is observed starting at ca. 12.2 ka. A reciprocal warming is observed in three stages from 12.0 to 11.0 ka: first a warming of 1.3°C over 300 years, relatively constant temperatures for 400 years, and a final warming of 1.7°C over 300 years returning to the same average SST as before the cold period. These cooler temperatures persisted for ca. 1500 yrs and likely corresponds to the Younger Dryas stadial. The annual SST in the GOM today is the same as the average temperature preceding and following the cold period. These trends represent the most detailed Mg/Ca SST records of the B/A Younger Dryas oscillation observed in the GOM. Paired with the Mg/Ca-derived SST, δ18O data will be generated to produce a δ18Osw record. This will enable us to ascertain the timing and precise phasing of deglacial warming relative to Laurentide ice sheet meltwater input into the GOM.