8th International Nannoplankton Association Conference


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Alexandra Zeltner, Ralf Schiebel, Christoph Hemleben:
A comparison of coccolith fluxes from the western, central, and eastern Arabian Sea

The coccolith export production of three mooring arrays in the western (WAST-13), central (CAST-12), and eastern (EAST-13) Arabian Sea was investigated. Traps were deployed in ~3000m water-depth. Sampling in the C Arabian Sea was carried out from November, 1995 through April, 1997, while the W and E traps were sampled between June, 1997 and February, 1998.

Fluxes of coccoliths in all three deep moorings were relatively uniform in contrast to diatoms which strongly prevailed in the W Arabian Sea. Mean coccolith fluxes increased slightly from the W to E Arabian Sea. However, highest coccolith fluxes were observed at WAST during July/August, 1997. The fluxes in the deeper traps ranged between 1.85x108 and 1.44x109 coccoliths m-2d-1 at WAST-13, between 2.12x108 and 8.68x108 coccoliths m-2d-1 at CAST-12, and between 3.73x108 and 1.03x109 coccoliths m-2d-1 at EAST-13. The increase towards the eastern sites seems to be due to a greater ability of the coccolithophores to adapt to varying nutrient concentrations in contrast to diatoms, and/or due to lateral advection. In general, highest coccolith fluxes were observed during the SW monsoon. At the western trap, the highest fluxes were observed during mid-August, while at CAST-12 and EAST-13 the highest fluxes occurred in late September. Coccolithophore diversity was lowest when highest coccolith fluxes occurred. The dominant species was Gephyrocapsa oceanica. The relative proportions of this species increased during the SW monsoon, indicating the maximum intensity of upwelling. Most favourable conditions of this species seem to exist at Site CAST-12, where floral proportions ranged between 50 and 70%. In addition, Calcidiscus leptoporus types A and B, Oolithotus antillarum, Umbilicosphaera sibogae var. foliosa and var. sibogae, Umbellosphaera irregularis and Florisphaera profunda, showed high absolute abundances. An average annual coccolith calcite flux of 4gm-2 is assumed for the deep traps while planktonic foraminifers contributed 7.15gm-2y-1.


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

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