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Modern and past processes of ocean-atmosphere-climate interactions in the low-latitude western Pacific and Indian Ocean
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Variations in coccolithophore productivity off South Africa over the last five glacial cycles
Wednesday 9th @ 1350-1410, Conference Room 1
Deborah Tangunan* , MARUM Center for Marine Environmental Sciences, University of Bremen
Karl-Heinz Baumann, Department of Geosciences, University of Bremen
Christina Fink, Department of Geosciences, University of Bremen
Presenter Email: tangunan@uni-bremen.de |
| Here we present a 500-kyr coccolithophore productivity record off the South African continent from assemblage composition and geochemical-based coccolithophore proxies from sediment cores obtained from the southwestern Indian Ocean (MD96-2077) and the eastern South Atlantic Ocean (ODP Sites 1264/1266). Our multiproxy reconstruction highlights how hydrodynamic and astronomical processes controlled variations in the coccolithophore productivity record. We interpreted the productivity changes to be driven by the migration of the subtropical front (STF) and the strength of the prevailing westerlies. Fluctuations in the records also show prominent glacial/interglacial variations at 100-kyr orbital periodicity. Here two assemblage groups are recognized: cooler water dominated by Gephyrocapsa muellerae suggestive of the northward shift of the STF and warm water taxa, including Syracosphaera pulchra, Rhabdosphaera clavigera, Umbilicosphaera foliosa, U. sibogae, Calciosolenia spp., Oolithotus fragilis, Umbellosphaera tenuis and Calcidiscus leptoporus, indicative of the Agulhas Current warm water transport to the South Atlantic. We propose that the frontal shifts have modulated the Agulhas Current in the Indian Ocean and the Benguela Current upwelling in the South Atlantic, and played a key role in the water column physico-chemical characteristics of these regions. The equatorward migration of the STF during glacial periods resulted in a reduced intensity of the Agulhas Current and a stronger Benguela Current upwelling, as revealed by similar long-term productivity patterns between the Natal Valley (MD96-2077) and off Namibia (ODP Site 1082), showing enhanced surface water productivity during the glacial periods. By contrast, productivity in the Walvis Ridge (ODP Site 1266), shows opposite patterns, i.e., enhanced productivity during the interglacial periods indicating that the nutrient-rich upwelled waters off Namibia could be transported via seaward lateral advection during the weakening of the upwelling process in the coastal region or by the entrance of cold nutrient-rich southern sourced water. |
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