Uranium isotope composition of Eocene marine sediments: does organic matter ?

• Main Authors: Bagard, Marie-Laure, Dickson, A.J., Disnar, Jean-Robert, Jacob, Jérémy, Le Milbeau, Claude, Davies, M.K., Cohen, A.S.
• Other Authors: School of Environment, Earth and Ecosystem Sciences Milton Keynes, Faculty of Science, Technology, Engineering and Mathematics Milton Keynes, The Open University Milton Keynes (OU)-The Open University Milton Keynes (OU), Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Biogéosystèmes Continentaux - UMR7327, Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Department of Earth Sciences Oxford, University of Oxford, School of Geography, Earth and Environmental Sciences Plymouth (SoGEES), Plymouth University
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2017
• Subjects: [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; [CHIM.ANAL]Chemical Sciences/Analytical chemistry; [CHIM.ORGA]Chemical Sciences/Organic chemistry; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Arctic; Arctic Ocean
• Online Access: https://insu.hal.science/insu-03547436

International audience Oxygen in seawater is a key parameter for the development oflife; changes in dissolved O2 concentrations throughout thePhanerozoic have played a major role in the evolution of marineecosystem s through com plex interactions with dissolvednutrients. However, the precise timing and magnitude of@uctuations in global ocean oxygenation in the past remainpoorly constrained. U stable isotope compositions recorded in marine anoxicsedim ents m ay be used to reconstruct the global extent of m arineanoxia due to their sensitivity to the rem oval @ux of reducedU(IV) from seawater. Nonetheless, it is critical to understandlocal sedim entary processes and their im pact on U isotopefractionation before any global redox inform ation can be inferredfrom A238U variations in the sediments. In particular, previousstudies have suggested that U isotopes could be fractionated byorganic matter in the water column, and that this process mightaCect the isotope value recorded in the sedim ent [1,2]. In this w ork, w e explore the im pact of organic m atter onA238U values measured in Arctic Ocean sediments (IODPExpedition 302) deposited during the Early to Middle Eocene(~56–46 M a), a period characterised by strong hydrographicrestriction and high productivity in the A rctic basin.[1] Holmden, Amini & François (2015), Geochimica etCosmochimica Acta153, 202-215. [2] Hinojosa, Stirling, Reid,Moy & Wilson (2016), Geochimica et Cosmochimica Acta179,89-109