Changes in Deep Ocean Conditions of the Last 450 Thousand Years Based on Paired Measurements of Benthic Foraminiferal d18O and Mg/Ca: Evidence from the Eastern Equatorial Pacific

Most continuous records of sea level change are based on benthic foraminiferal δ18O, which is a measure of both the δ18O of sea water and temperature. The relationship between the Mg/Ca ratio of benthic foraminiferal calcite and bottom water temperature provides a means to identify the contribution of bottom water temperature to changes in the δ18O of the calcite through time. We measured the δ18O of the benthic foraminifer species, Cibicidoides wuellerstorfi, in the upper 5 meters of Eastern Equatorial Pacific piston core TR163-14 (5°54.1'N, 87°14.2'W; 2365 m) and our data indicates that the record extends back to ~450 thousand years (MIS 1-12). We also measured the Mg/Ca ratio of C. wuellerstorfi and estimated bottom water temperatures using an unpublished Mg/Ca - temperature equation for this species. Preliminary results suggest that bottom waters in this region change by 1.5-2.5 °C between glacial and interglacial periods, which accounts for 0.33-0.55‰ of the total δ18O changes (1.3-2.1‰) associated with the glacial-interglacial transitions during this time period.