Sauvage Justine

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Sauvage
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Justine
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  • Article
    The contribution of water radiolysis to marine sedimentary life
    (Nature Research, 2021-02-26) Sauvage, Justine ; Flinders, Ashton F. ; Spivack, Arthur J. ; Pockalny, Robert ; Dunlea, Ann G. ; Anderson, Chloe H. ; Smith, David C. ; Murray, Richard W. ; D'Hondt, Steven
    Water radiolysis continuously produces H2 and oxidized chemicals in wet sediment and rock. Radiolytic H2 has been identified as the primary electron donor (food) for microorganisms in continental aquifers kilometers below Earth’s surface. Radiolytic products may also be significant for sustaining life in subseafloor sediment and subsurface environments of other planets. However, the extent to which most subsurface ecosystems rely on radiolytic products has been poorly constrained, due to incomplete understanding of radiolytic chemical yields in natural environments. Here we show that all common marine sediment types catalyse radiolytic H2 production, amplifying yields by up to 27X relative to pure water. In electron equivalents, the global rate of radiolytic H2 production in marine sediment appears to be 1-2% of the global organic flux to the seafloor. However, most organic matter is consumed at or near the seafloor, whereas radiolytic H2 is produced at all sediment depths. Comparison of radiolytic H2 consumption rates to organic oxidation rates suggests that water radiolysis is the principal source of biologically accessible energy for microbial communities in marine sediment older than a few million years. Where water permeates similarly catalytic material on other worlds, life may also be sustained by water radiolysis.
  • Article
    Relationship of bacterial richness to organic degradation rate and sediment age in subseafloor sediment
    (American Society for Microbiology, 2016-06-10) Walsh, Emily A. ; Kirkpatrick, John B. ; Pockalny, Robert ; Sauvage, Justine ; Spivack, Arthur J. ; Murray, Richard W. ; Sogin, Mitchell L. ; D'Hondt, Steven
    Subseafloor sediment hosts a large, taxonomically rich and metabolically diverse microbial ecosystem. However, the factors that control microbial diversity in subseafloor sediment have rarely been explored. Here we show that bacterial richness varies with organic degradation rate and sediment age. At three open-ocean sites (in the Bering Sea and equatorial Pacific) and one continental margin site (Indian Ocean), richness decreases exponentially with increasing sediment depth. The rate of decrease in richness with depth varies from site to site. The vertical succession of predominant terminal electron acceptors correlates to abundance-weighted community composition, but does not drive the vertical decrease in richness. Vertical patterns of richness at the open-ocean sites closely match organic degradation rates; both properties are highest near the seafloor and decline together as sediment depth increases. This relationship suggests that (i) total catabolic activity and/or electron donor diversity exerts a primary influence on bacterial richness in marine sediment, and (ii) many bacterial taxa that are poorly adapted for subseafloor sedimentary conditions are degraded in the geologically young sediment where respiration rates are high. Richness consistently takes a few hundred thousand years to decline from near-seafloor values to much lower values in deep anoxic subseafloor sediment, regardless of sedimentation rate, predominant terminal electron acceptor, or oceanographic context.