Coccolithophore response to oceanographic changes in the equatorial Atlantic during the last 200,000 years

A deep-sea core from the eastern equatorial Atlantic (Meteor core 16772, 1 degrees 21'S, 11 degrees 58'W) revealed strong primary productivity variati ons (70-230 gC/m(2)/year) based on the relative abundance (%) of the deep l iving coccolithophore Florisphaera profunda with productivity maxima follow ing temperature minima during the last 200,000 years. The response of the c occolithophore flora was investigated by relative and absolute abundance re cords of coccoliths. The wind strength and the resulting equatorial upwelli ng intensity are thought to comprise the most important control of coccolit h abundance and species composition, which reflects the different abundance of coccolithophores living in the upper or lower photic zone. Relative abu ndances of the different species varies widely throughout the core. Althoug h a wide range of species were present in the different samples. three diff erent taxa dominated the assemblage. The lower photic zone species F, profu nda was the most abundant, with a mean relative abundance of 49.4% througho ut the core. The upper photic zone flora were divided into three groups. Em iliania huxleyi together with small Gephyrocapsa (<3 mu m) was the second m ost abundant species group (mean 20.8%). Gephyrocapsa oceanica was the thir d most important species in the core and had a mean relative abundance of 1 6.8%. All other species together represented a mean of 13%. Highest absolut e abundance of coccoliths (number/gram sediment) occurs in sediments deposi ted during periods of high SST: mainly in warm isotope stages 1 and 5. The accumulation rates of coccoliths (number/cm(2)/ky) show peaks in isotope st ages I and 5, but also in some parts of cool isotope stages 4 and 6, High r elative and absolute abundance of F. profunda were found in warm isotope st ages, which suggests that a deep nutricline existed and that primary produc tivity was low. Absolute and relative abundance records of E. huxleyi and s mall Gephyrocapsa (<3 mu m) mainly showed higher values in sediments from w arm periods. The other upper photic zone coccolith species were generally m ore abundant during periods of low SST, particularly in isotope stages 2, 4 , and 6, which were times of high primary productivity and a shallow nutric line. This suggest that E. huxleyi and small Gephyrocapsa probably were abl e to live deeper in the water column than most other species during periods of low nutrient supply to the upper photic zone. In summary, the compositi on of the coccolith flora can be explained by the nutricline depth level wi th three different assemblages being recognized, a deep photic zone assembl age consisting of F. pi profunda, a middle-upper photic zone assemblage of E, huxleyi and small Gephyrocapsa and an upper photic zone assemblage consi sting of all other species. (C) 2000 Elsevier Science B.V. All rights reser ved.