Meltwater input into the Gulf of Mexico and 8.2 kyr BP cool event in Greenland

Investigators: Jenna M. LoDico, Benjamin P. Flower, and Terrence M. Quinn

Introduction: Determining the past record of sea surface temperatures and salinities is fundamental for understanding past changes in climate. Oceanographic processes in the Gulf of Mexico have an affect on North American climate. It is part of the Western Hemisphere Warm Pool which provides a source of heat and moisture to the North American continent and Northern high latitudes. Establishing the history of Holocene SSTs from Mg/Ca and d18O of sea water in the Gulf of Mexico will provide insight into the role of tropical climate system on global climate.

French research vessel Marion Dufresne

In July 2002, core MD02-2550 was taken by the French RV Marion Dufresne (Figure 1); 9.09 m of sediment was recovered from Orca Basin situated in the northern Gulf of Mexico (figure 2) at a depth of 2248 m. Orca Basin is advantageous for high-resolution paleoclimatology because of very high sedimentation rates greater than 50 cm/1000 yr and a brine layer overlying the sediment that preserves sedimentary laminations (Leventer et al., 1983). The presence of pteropods assures that dissolution of carbonates is minimal. The planktonic foraminifera G. ruber was chosen due to their preference for inhabiting surface waters.

8.2 kyr BP Cool Event: Records in Greenland revealed that around 8.2 kyr BP ago temperatures cooled abruptly for a period of about 300-400 years. It has been proposed that this climatic event was caused by a shut down of the thermohaline circulation (THC) in the North Atlantic. Around 8.2 kyr BP a collapse took place of the last dome of the Laurentide Icesheet that covered the Hudson Bay (North America). This collapse would have considerably increased the influx of freshwater into the North Atlantic, causing a freshwater pulse that could possibly have lowered the surface water density, and slowing or shutting down the formation of deepwater and weakening the THC (Barber et al., 1999).

SST calculations: Mg/Ca(mmol/mol)=0.38exp[0.09*SST]
(Dekens et al., 2002)


d18O sea water calculations:
T °C=14.9-4.8*(dcarbonate-dseawater)
(Bemis et al., 1998)

d18O (‰ PDB) and Mg/Ca
(mmol/mol) values vs. Depth (cm). 99 %
Replicate analysis was completed for Mg/Ca
values.