(Appendix) Planktonic foraminifera abundances in ODP Site 138-847B

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Sediments from Site 847 in the eastern equatorial Pacific Ocean provide a record of the variability of the equatorial divergence and associated upwelling. We interpret the variation in foraminifer assemblages in the context of regional Oceanographic change. Our record is composed of three time slices selected from the last 0.9 Ma. A Q-mode analysis of foraminifer abundance data results in a four-factor model that was used to quantify the faunal changes and to characterize paleoceanographic variability. The species of foraminifers with high factor scores for each factor suggested a specific set of Oceanographic conditions. The timing of the high loadings for each factor appears to be associated with a particular part of a glacial cycle. Thus, we interpreted our findings in the context of the glacial/interglacial cycle proposed by Imbrie et. al. (1992). This idealized cycle consists of four stages that are defined by characteristic changes in specific elements of the climate system. We evaluated how such changes in the climate system might affect the Oceanographic conditions at Site 847. Our results suggest that upwelling remains a dominant process in both glacial and interglacial stages, but decreases significantly on most deglacials. Subantarctic mode water formation and equatorial upwelling appear to form a linked system that determines the specific characteristics of the water forming a major part of the Equatorial Undercurrent as well as the transport volume of the undercurrent. In conjunction with changes in upwelling at Site 847, this variation in the undercurrent results in changes in mixed layer depth, sea-surface temperature, and oxygen and nutrient levels at the site.

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