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Sédimentation organique profonde sur la marge continentale namibienne (Lüderitz, Atlantique Sud-Est) : impacts des variations climatiques sur la paléoproductivité

Abstract : The goal of this multi-proxy study is to allow a better understanding of the local role played by the Benguela upwelling system regarding carbon sequestration over the last 2 climatic cycles.
Outstandingly high organic matter (OM) accumulation occurs on the Namibian slope albeit sedimentary processes are exclusively hemipelagic. First, we investigate organic matter preservation mechanisms that have acted at the sediment as well as in the water column, and their effectiveness and distribution over the organic-rich slope off Lüderitz (25°6S). Pyrolysis results as well as petrographic, spectroscopic and molecular analyses reveal that OM burial was more effective during glacial periods due to higher OM fluxes to the sediment, which promoted sulphurization processes. In addition, organo-mineral association presumably protected OM during sinking in the water column and ensured its accumulation on the lower slope.
Organic carbon contents of the sediment show climatic-related variations. We thus examine the effects of glacial-interglacial changes on paleoproductivity and export fluxes by deciphering the d15N signals, dust grain-size records, biogenic and terrigenous contents of three cores distributed from the upper to the lower slope (from 1000 to 3600m). We suggest that nitratesustained paleoproductivity is only partly controlled by wind-strength. Angola and Indian water mass advection in the Benguela region as well as nutrient utilization in the Souhern Ocean both affect nitrate and silica supplies to the upwellings and hence, the attendant productivity and its rain ratio over climatic cycles.
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https://tel.archives-ouvertes.fr/tel-00110119
Contributor : Nathalie Pothier <>
Submitted on : Thursday, October 26, 2006 - 3:02:33 PM
Last modification on : Friday, September 18, 2020 - 2:34:08 PM
Long-term archiving on: : Tuesday, April 6, 2010 - 9:04:46 PM

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Laetitia Pichevin. Sédimentation organique profonde sur la marge continentale namibienne (Lüderitz, Atlantique Sud-Est) : impacts des variations climatiques sur la paléoproductivité. Océan, Atmosphère. Université Sciences et Technologies - Bordeaux I, 2004. Français. ⟨tel-00110119⟩

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