ALBERT

Description: Stable isotopic analyses (18O/16O, 13C/12C) of both benthic and planktonic foraminifers from DSDP Holes 516A and 517 appear to reflect changing paleoclimatic and paleoceanographic conditions in the South Atlantic Ocean during the Pliocene. The d18O records of Cibicides wuellerstorfi and Globigerinoides sacculifer do not vary in phase with one another, indicating that the d18O of C. wuellerstorfi is reflecting changing glacial ice volumes, but the d18O of G. sacculifer is being influenced more by other factors, such as variable sea-surface temperatures and salinities. A net depletion in 18O and a series of very low-amplitude fluctuations characterize the late Pliocene planktonic d18O record. The stability of this section may be related to increasing surface-water temperatures in middle southern latitudes during northern hemisphere glacial ice buildup caused by differences in the phasing of the orbital precessional cycle between the northern and southern hemispheres. Hole 516A is presently located in an area of strong d13C gradients in the water column, and a similar situation probably prevailed during the Pliocene. A record of the difference between the d13C of C. wuellerstorfi and G. sacculifer (d13C) reflects times of increased or decreased similarity in d13C between Circumpolar Water and subtropical surface waters throughout the Pliocene. Periods of increased or decreased d13C may reflect: 1) changes in water mass boundaries because of expansion or contraction of a particular water mass, or 2) changes in the partitioning of 13C within the various components of the global carbon reservoir. These changes may be associated with glacial/interglacial climatic changes, such as the initiation of northern hemisphere glaciation.