Planktonic Foraminiferal Sea Surface Temperature Variations in the Southeast Atlantic Ocean: A High-Resolution Record MD962085 of the Past 400,000 Years from the IMAGES II-NAUSICAA Cruise

Abstract

A high-resolution (~4-5 cm/kyr) giant piston core record (MD962085) retrieved during an IMAGES II ¡V NAUSICAA cruise form the continental slope of the southeast Atlantic Ocean reveal striking variations in planktonic foraminifer faunal abundances and sea-surface temperatures (SST) during the past 400,000 years. The location and high-quality sedimentary record of the core provide a good opportunity to assess changes in the intensity and position of the Benguela Current System and the Subtropical Convergence, two key features of the ocean-climate system in the south Atlantic. This record can be also used to evaluate the possible influence of Agulhas Current from the throughflow of the Indian Ocean into the South Atlantic. The planktonic foraminifer faunal abundances of the core are dominated by three assemblages: (1) N. pachyderma (right coiling) + N. dutertrei, (2) G. bulloides, and (3) G.inflata. The assemblage of N.pachyderma (right coiling) + N. dutertrei shows distinctive abundance changes which are nearly in-phase with glacial-interglacial variations. High abundances of this assemblage are associated with major glacial conditions, possibly representing low SST/high nutrient level conditions in the southwestern Africa margin. In contrast, the assemblages of G. bulloides and G. inflate show more high-frequency abundance change patterns, which are not well-parallel to glacial-interglacial changes. These patterns may indicate rapid oceanic frontal movements from the south, and a rapid change in the intensity of Benguela upwelling system from the east. A winter-season SST estimate using transfer function techniques for this record shows primarily glacial-interglacial variations. The SST reaches maxima during the transitions from the major glacial to interglacial stages (Termination II, III, IV), and is associated with the abundance maxima of a warm water species indicator G. rubber. The relationship shown by the SST and planktonic foraminifer a18O implies that the SST maxima lead the a18O minima by approximately3-5 kyr.

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