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La sédimentation organique associée à deux systèmes d'upwelling en Amérique du Sud tropicale : implications paléocéanographiques et paléoclimatiques au cours de l'Holocène

Abstract : South American climate is strongly affected by ocean-atmosphere interactions, especially those coming from Pacific and Atlantic oceans. This work is under the scope of a broad scientific cooperation project CLIMPAST (IRD - CNPq), and is financially supported by Brazil (CAPES, UFF), Peru (IMARPE) and France (IRD, CNRS, Université d'Orléans). The objectives of this thesis are to reconstructe the climatic evolution of South America during the Holocene (12 000 - 800 ans cal BP). It is based on a high temporal resolution study of several organic sedimentary proxies from high productivity zones of eastern and western continental shelves of South America. Two sedimentary cores were studied, the first was sampled in the Cabo Frio (Brazil) seasonal upwelling system and the last was sampled from Humbold Current in front of Peru, the latter was from a permanent upwelling system. The organic matter was analysed by bulk elementary, Rock-Eval pyrolysis, palynofacies and molecular geochemical methods, as well as a very high resolution stratigraphy (X ray imaging and 14C based chronological models). Based on our results we have reconstructed the climatic changes in different time scales (millennium to decadal time intervals), mainly linked to the displacements of Intertropical and South Atlantic Convergence Zones. Last sea level rising is accompanied by moister conditions on the continent. Middle Holocene represents the strongest upwelling records in the Atlantic side. Eroded traces are found in the Pacific side during the same period. While the Upper Holocene shows higher frequency (El Niño type) and then changed to more low frequency during the Medieval Climate Optimum, guided by a La Niña type record.
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Submitted on : Friday, October 24, 2008 - 2:38:03 PM
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  • HAL Id : tel-00334019, version 1

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Marcio Gurgel. La sédimentation organique associée à deux systèmes d'upwelling en Amérique du Sud tropicale : implications paléocéanographiques et paléoclimatiques au cours de l'Holocène. Géochimie. Université d'Orléans, 2008. Français. ⟨tel-00334019⟩

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