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

Abstract : 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
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Submitted on : Friday, January 28, 2022 - 3:15:07 PM
Last modification on : Wednesday, August 3, 2022 - 4:05:54 AM

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  • HAL Id : insu-03547436, version 1

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Marie-Laure Bagard, A.J. Dickson, Jean-Robert Disnar, Jérémy Jacob, Claude Le Milbeau, et al.. Uranium isotope composition of Eocene marine sediments: does organic matter ?. Goldschmidt 2017, Aug 2017, Paris, France. ⟨insu-03547436⟩

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