INA8

INA8
8^th International Nannoplankton Association Conference

ABSTRACTS

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Patrizia Ziveri, Simona Giunta, Alexandra Broerse, Jeremy R. Young, Gerald Ganssen:
Coccolithophorid response to an upwelling hydrographic system: example from offshore Somalia
(Talk)

The comparison of coccolithophorid export production at different water-depths can improve our ability to use sedimentary coccolith records as a palaeoclimatic proxy. These data can be used to reconstruct particulate inorganic carbon fluxes over time-scales ranging from seasons to millennia in different climate regimes.

We will present here results from a sediment trap study at 1032 and 3050m depths (sea-floor depth 4047m) off Somalia, from June, 1992 to February, 1993, in order to document coccolithophorid flux response to the SW and NE monsoons. The main objective was to determine how the coccolithophorid response to an upwelling hydrographic system is recorded during sinking to the sea-floor, and at the sea-floor, in surface-sediment along a transect perpendicular to the coast of Somalia from 459 to 4035m water-depth.

At 3050m water-depth, the fine-fraction (<32µm) sediment flux contributes 63% to the total sediment flux. Carbonate was a major component of the biogeochemical fluxes, forming 58% of the total sediment flux. The fine-fraction carbonate formed 51% of the total carbonate flux.

Maximum coccosphere and coccolith fluxes were recorded during the upwelling (SW monsoon) and at the beginning of the upwelling relaxation (intermonsoon). The lowest fluxes were recorded during the end of the intermonsoon phase, and during the NE monsoon (not the upwelling season).

Gephyrocapsa oceanica had high flux during the SW monsoon. Umbilicosphaera sibogae var. foliosa had maximum fluxes during the height of the upwelling, and at the beginning of water-column restratification in the intermonsoon period.

The mean annual coccolithophorid CaCO₃ flux (obtained by the transformation of coccolith flux number per coccolith specific weight of CaCO₃) is 35% of the fine-fraction carbonate flux, and 18% of the total carbonate flux.

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

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Tania Hildebrand-Habel (hiha@micropal.uni-bremen.de)