NOAA/WDS Paleoclimatology - Western Atlantic Deglacial Paired Benthic Mg/Ca and d18O Data

Two new records of paired benthic foraminiferal Mg/Ca and d18O from two low latitude western Atlantic sediment cores - one taken from within the Florida Current and the other from the Little Bahama Bank - provide insights into the spatial distribution of intermediate depth temperature and salinity variability during the deglaciation. During the Younger Dryas cold event, both temperature and salinity increased at the Florida Current site and decreased at the Little Bahama Bank site. The temperature increase within the Florida Current is consistent with a reduction in the strength of the northward-moving surface return flow of the Atlantic meridional overturning circulation; the temperature decrease at the Little Bahama Bank is consistent with a cooling of high latitude North Atlantic surface waters. To test the possibility that a freshening of the surface North Atlantic caused the paleoceanographic changes during the Younger Dryas, the Geophysical Fluid Dynamics Laboratory (GFDL) R30 coupled ocean-atmosphere general circulation model was forced using a North Atlantic freshwater perturbation of 0.1 Sv for a period of 100 years. The freshwater flux causes an overall reduction in the Atlantic overturning from 25 Sv to 13 Sv. However, at ~1,100 m water depth, ventilation increases, causing decreases in both temperature and salinity throughout much of the intermediate depth, open-ocean North Atlantic. At the western boundary, intermediate depth temperatures and salinities increase due to weakened overturning, and also due to an increase in runoff from the Amazon River, which causes a surface stability and a decrease in the upwelling of colder, deeper waters.