RECONSTRUCTING THE STABLE-ISOTOPE GEOCHEMISTRY AND PALEOTEMPERATURES OF THE EQUATORIAL ATLANTIC DURING THE LAST 150,000 YEARS - RESULTS FROM INDIVIDUAL FORAMINIFERA

This study represents an attempt to extract paleoclimatic data from th e deep-sea record by analyzing foraminiferal shells individually. Usin g the oxygen (delta(18)O) and carbon (delta(13)C) isotopic composition of individual Orbulina universa and Neogloboquadrina dutertrei, we pr esent an approach to reconstruct the delta(18)O of seawater (delta(18) O(w)), the delta(13)C of Sigma CO2, and seasonal maximum sea surface t emperatures (SST) in the western and eastern equatorial Atlantic. We e xamine the glacial and interglacial extremes of the last 150,000 years (isotope stages 1, 2, 5e, and 6). Comparison of recent water column h ydrography with reconstructions from core top assemblages shows that O . universa and N. dutertrei delta(18)O and delta(13)O values accuratel y record hydrographic conditions in the mixed layer and upper thermocl ine at both sites. By analyzing shells individually, we can evaluate t he effect of bioturbation on the range of delta(18)O and delta(13)C va lues in each interval and take it into consideration in our data inter pretations. Downcore results show that N. dutertrei delta(18)O values in the western equatorial Atlantic reflect glacial to interglacial cha nges in delta(18)O(w) due to continental ice formation (Delta delta(18 )O = 1.30 parts per thousand). We use changes in N. dutertrei delta(18 )O values between core intervals to estimate the ice-volume effect in paleotemperature calculations for the mixed layer. To validate the use of O. universa for mixed layer reconstructions, we have added individ ual Globigerinoides sacculifer data for stages 1 and 2 at both sites. Paleotemperature reconstructions from O. universa delta(18)O values in dicate that maximum seasonal mixed layer temperatures in the equatoria l Atlantic decreased by at most 2.6 degrees C between isotope stages 1 and 2 and by no more than 3.4 degrees C between stages 1 and 6. Indiv idual shell data from G. sacculifer yield similar results indicating t hat maximum O. universa delta(18)O values reflect the mixed layer envi ronment. In agreement with Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) [1981] SST reconstructions for stage 2, these data indicate little change between glacial and interglacial paleotem peratures in the equatorial Atlantic.