Signature paléoenvironnementale des séquences holocènes en Rade de Brest : forçages climatiques et anthropiques

Abstract : This PhD study aims at understanding mechanisms and regional responses of the Holocene climatic variability, targeting the Bay of Brest and the Bay of Douarnenez. In coastal environments, the vulnerability of human societies to climate hazards is particularly high and anthropogenic pressures on ecosystems are increasing. In this context, the respective part of natural forcings from those related to human activities can be discussed thanks to paleoenvironmental Holocene reconstructions carried out on sediment archives.Several sedimentary sequences allowed us to focus on different key periods across the last 10,000 years BP.Multiproxy studies mainly based on palynological analyzes (pollen and dinoflagellate cysts) allowed discussing continental and marine signals in parallel, and thus to better understand forcing mechanisms.Pollen studies are used to characterize terrestrial landscape evolutions while dinocysts, counted from the same palynological slides as pollen grains and spores, make it possible to discuss surface palaeohydrological conditions. In addition, in order to complete the understanding of our Holocene palynomorph records conducted on Bay of Brest marine sediments, Bay of Brest surface sediments were investigated so as to deliver a current palynological message.This work has demonstrated the robustness of palynological studies conducted at a regional scale and in a macro-estuarian environment, and also the relevance of our tools to highlight the intertwining of human and natural influences. This work therefore represents a regional contribution to the study of Holocene environmental variability in Brittany, providing high resolution palynological records over the last 150 years (resolution of 1 to 4 years) as well as over the last 9,500 years BP (averaged resolution of 30 years) characterized by the growing influence of human societies in relation to increased deforestation and agropastoral practices on watersheds.
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Clément Lambert. Signature paléoenvironnementale des séquences holocènes en Rade de Brest : forçages climatiques et anthropiques. Sciences de la Terre. Université de Bretagne occidentale - Brest, 2017. Français. ⟨NNT : 2017BRES0112⟩. ⟨tel-01783962⟩

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