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Felix Heidersdorf, Karl-Heinz Baumann:
Late Quaternary coccolith assemblages in the equatorial Atlantic: palaeoenvironmental information and coccolith carbonate production
(Poster)

Downcore analyses of coccolith assemblages in two sediment cores (GeoB 2204, 8°32'S, 34° 01'W, 2072m; GeoB 2908, 0°06'S, 23°20'W, 3809m) were used to assess temporal and spatial changes in surface-water conditions and productivity in the western equatorial Atlantic for the last 150ky. Besides absolute assemblage counts, morphometric data of key taxa were used to quantify the CaCO₃ contribution of the coccoliths to the total carbonate accumulation.

Pronounced differences in surface-water conditions and productivity between the equatorial divergence zone (GeoB 2908) and the low-productivity western tropical Atlantic (GeoB 2204) are indicated both by the coccolith numbers and the assemblage compositions. Generally, assemblages are dominated by small placoliths (Emiliania huxleyi and Gephyrocapsa spp.) and varying, but high, amounts of the deep-dwelling Florisphaera profunda. Enhanced production of coccoliths in the equatorial divergence zone can be correlated to periods of increased productivity, probably related to a lateral extension of the equatorial upwelling area and increased advection of cool and nutrient-rich water-masses. In contrast, fluctuations in coccolith numbers in the western equatorial Atlantic remain low, but variations are detectable and fit well into previously-reported palaeoenvironmental reconstructions of this area.

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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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