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Restitution de la variabilité climatique le long de la marge sud chilienne depuis le Dernier Maximum Glaciaire : approche sédimentologique et nouvelles applications en téphrochronologie

Abstract : The south-chilean margin is the one continental mass to intercept the entire Westerly Winds cell (SWW), closely linked to the oceanic circulation. It constitutes a strategic area for paleoclimatic reconstructions and represents a peculiar interest since the last decades. In the southern high latitude chilean margin setting, the main objectives of this thesis were focused on (1) the establishment of a precise chronology based on radiocarbon dates and tephrochronology and (2) to restore the north-Patagonian icefield dynamic strongly linked to the rainfall features, temperatures and/or internal glaciers dynamic over the last 22 ka BP from a High-resolution and High sedimentation rate deep-sea core collected offshore the Taitao peninsula (~46°S). Based on robust age model by radiocarbon dates and tephrochronology study, the marine record MD07-3088 allows a large time-span since the Last Glacial Maximum, the deglaciation and the Holocene. Several proxies (clay mineralogy, grain-size and inorganic geochemistry) were used to restore the variability in continental source inputs and north-patagonian icefield fluctuations. Coupled to SST estimations and palynological dataset, this study allows to reconstruct rainfall changes and interconnections between oceanic and atmospheric features. Results show that during the LGM (22-18 ka BP), the globally colder temperatures play a major role in the detrital supplies from Coastal Range and glacier dynamic. During the deglaciation (18-11,5 ka BP), warmer conditions mark a drastic change in the terrigenous source with a dominance of Andean Cordillera influence. This interval is punctuated by 3 colder events, in particularly the ACR event (14,3-12,7 ka BP) during which a renewed glacial activity is recorded as shown by the expansion of Magellanes moorlands, typical of colder and more humid climate as a result of the northward migration of the Westerly Winds. The Early Holocene (11,5-8 ka BP) is marked by climatic conditions similar to those of the deglaciation with only the presence of one colder event resulting either by slightly temperatures decreasing (~2°C) or the internal glacier dynamic contribution. The Middle Holocene (8-3 ka BP) is illustrated by the settlement of the Neoglaciation phase resulting from the northward displacement of the SWW cell favouring more intense rainfalls in the study site even Tough any significant temperature variations are observed. Finally, the low SST variability and the slight increase of rainfalls recorded during the Upper Holocene (3 ka BP to present) give clues about the return of the SWW to modern location.
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Submitted on : Monday, September 2, 2013 - 1:13:54 AM
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Mélanie Carel. Restitution de la variabilité climatique le long de la marge sud chilienne depuis le Dernier Maximum Glaciaire : approche sédimentologique et nouvelles applications en téphrochronologie. Sciences de la Terre. Université Paris Sud - Paris XI, 2012. Français. ⟨NNT : 2012PA112352⟩. ⟨tel-00856588⟩



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