Étude de la variabilité des conditions océanographiques et climatiques en Antarctique de l'Est (Terre Adélie-Georges V) au cours de l'Holocène tardif et de la période instrumentale

摘要

Antarctic sea ice has large impacts on the heat and gas transfers between the ocean andthe atmosphere, on the global oceanic circulation, on the Earth albedo and on theprimary productivity of the Southern Ocean. However, because of its remote and icecoveredlocation, the climate of the Antarctic continent and of the Southern Ocean isstill poorly studied and constitutes a challenge for climate model predictions. Recentobservations highlighted opposite patterns of climate variability between Western andEastern Antarctica, but poorly resolved the mechanisms and forcing involved.Reconstructions of temperature signals indicate that regional disparities have persistedover the Holocene period. The Late Holocene period includes the recent climate change(so-called modern global warming) as well as preceding rapid climate variabilitiesthough of lower amplitude. Achieving paleoenvironmental reconstructions in theAntarctic region at high temporal resolution over this period therefore offers theopportunity to improve the understanding of climate changes in response to bothnatural and anthropogenic forcing. While paleoenvironmental records obtained from icecores provide robust information on the past atmospheric conditions over Antarctica,the paleoceanography of the nearby ocean is constrained by a limited set of rather lowresolution, discontinuous records from sediment cores. Our study focuses on themarginal zone of the Adélie-Georges V Land, East Antarctica, a region which has beenpoorly studied so far, despite the presence of thick and laminated sedimentary depositsthat allow accurate and high resolution paleoclimate reconstructions. Our work is basedon several marine sedimentary records, made of diatom oozes and covering theinstrumental period to the last 2,000 years. Our results show that diatom assemblages,diatom specific biomarkers (HBI) and elemental geochemistry in the sedimenteffectively testify of local but also regional oceanographic and climatic variations atdecadal to centennial scales. Coupled atmospheric and oceanic dynamics linked to majorclimate modes of the Southern Hemisphere, along with glacial dynamics constitutemajor forcing mechanisms of ice covered changes during the late Holocene.