A Multi-proxy Approach to Distinguish Between Changes in SST and Meltwater Input in the Gulf of Mexico Back to MIS 3.

The Gulf of Mexico (GOM) is part of the Western Hemisphere Warm Pool providing a source of heat and moisture to the North American continent and Northern high latitudes. Paleoclimatic records from the GOM can test the hypothesis that the tropical climate system is an important driver of past global climate change. In July 2002, core MD02-2551 was taken by the French research vessel Marion Dufresne at 26°56.78 N 91°21.75 W and recovered 31.79 m of sediment from Orca Basin situated in the northern GOM 290 km south of the present Louisiana coast. The basin is advantageous for high-resolution paleoclimatology because of a brine layer overlying the sediment that preserves sedimentary laminations and high sedimentation rates estimated at greater than 50 cm/1000 yr. A multi-proxy approach using Mg/Ca and δ18O from foraminiferal calcite will isolate past sea surface temperature (SST) and δ18O of sea water (controlled by salinity, and ice volume). Separation of these parameters will help establish the relationship between changing GOM SSTs and meltwater input from the Laurentide Ice Sheet. The chronology of the core is being established using AMS C14 dating. Both white and pink species of the planktonic foraminifera Globigerinoides ruber were analyzed for δ18O and will be analyzed for Mg/Ca. Coarse resolution data from white G. ruber show a mean value of about -1.5 per mil during the Holocene (low variability of <0.5 per mil) and a mean value of about 0.0 per mil at the Last Glacial Maximum (low variability of <0.5 per mil). Marine Isotope Stage Three (MIS 3) indicates a mean value of about -0.75 per mil (high variability of >0.5 per mil). Sea surface temperature and sea surface salinity have distinctly higher variability during MIS 3 in comparison to the Holocene. Foraminiferal Mg data will add an additional constraint for SST. Phasing between GOM SSTs and high latitude temperatures will help assess the role of the tropical climate system on global climate change.