Surface and Deep Hydrology of the Northern Atlantic Ocean during the past 150 000 Years

The abrupt shifts in foraminiferal $\delta ^{18}$O observed in core ODP 609 (the meltwater signature of the Heinrich events, see Bond et al. 1992b, 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 10$^{6}$ km$^{3}$ 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 degrees N 22 degrees W) and SU 90-08 (43 degrees N 30 degrees 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 $\delta ^{18}$O record corrected for the temperature effect on isotopic fractionation. The density of deep water is directly derived from the benthic $\delta ^{18}$O record, after corrections for the mean global changes in Ocean $\delta ^{18}$O. Results indicate that the North Atlantic Ocean has been repetitively a potential area of deep-water formation during the last glacial period.