Surface and deep hydrology of the Northern Atlantic Ocean during the past 150000 years

The abrupt shifts in foraminiferal δ18O observed in core ODP 609 (the meltwater signature of the Heinrich events, see Bond et al. 1992 b,1993) are seen in ten North Atlantic high sedimentation rate cores; the decreasing south-west to north-east gradient is well pronounced. This confirms that the Heinrich events are associated with major surges of the Laurentide ice sheet, when it is believed approximately 106 km3 of ice are liberated during each event. A tentative reconstruction of the changes in surface and deep-water density, based upon the study of cores SU 90-39 (53° N 22° W) and SU 90-08 (43° N 30° W), is presented. To calculate the density of surface water, sea surface temperature is obtained using a foraminiferal transfer function (see CLIMAP 1981) and salinity is estimated using the foraminiferal δ18O record corrected for the temperature effect on isotopic fractionation. The density of deep water is directly derived from the benthic δ18O record, after corrections for the mean global changes in Ocean δ18O. Results indicate that the North Atlantic Ocean has been repetitively a potential area of deep-water formation during the last glacial period.