COCCOLITHOPHORID RESPONSE TO AN UPWELLING HYDROGRAPHIC SYSTEM: EXAMPLE FROM OFFSHORE SOMALIA
Patrizia Ziveri (1), Simona Giunta(2), & Gerald Ganssen(1)
Alexandra Broerse (1) , Markus Geisen(3), Jeremy Young(3)
1 Faculty of Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
2 Earth Science and Environmental Geology, University of Bologna, Italy
3 Palaeontology Department, The Natural History Museum, Cromwell Road, London
The comparison of coccolithophorid export production at different water depths can improve our ability to use sedimentary coccolith records as a paleoclimatic proxy. These data can be used to reconstruct particulate inorganic carbon fluxes over time-scales ranging from seasons to millenia and in different climate regimes.
We will present here results from a sediment trap study at 1032 and 3050m depth (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 seafloor 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 (<32microns) 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 (non 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 re-stratification 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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