WESTERN NORTH-ATLANTIC EVIDENCE FOR MILLENNIAL-SCALE CHANGES IN OCEAN CIRCULATION AND CLIMATE

Two late Quaternary series of high resolution percent carbonate data from western North Atlantic sediment drifts (Bermuda Rise and Bahama Outer Ridge) show millennial-scale oscillations superimposed on the familiar, longer-period oscillations of orbital origin. The dominant high-frequency oscillation in these records has a quasi-period of about 4000 years. These percent CaCO3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern Canada, the resuspension of continental margin sediment by deep eddy kinetic energy, and carbonate dissolution. Sediment is transported to the Bermuda Rise by deep recirculating gyres and to the Bahama Outer Ridge by the deep western boundary current system. Stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent CaCO3. Oxygen isotope ratios of planktonic foraminifera suggest large variations in near-surface temperature and/or salinity, and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of North Atlantic Deep Water (NADW). These data support models which couple surface ocean conditions in the North Atlantic, production of NADW, North Atlantic heat flux, and evidence for temperature oscillations in ice cores.