DCO Project Summary

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Project Title
Reduced Carbon Associated with Altered Oceanic Crust
Start DateEnd Date
2011-04-01
NameRoleInstitutionDCO ID
Related GrantsDCO ID
11121/3515-2688-3796-9573-CC
Description
Serpentinization produces H2-rich fluids, which may promote the formation of abiotic organic compounds and/or sustain deep subsurface microbial communities in ultramafic rocks. We are studying organic compounds in serpentinized peridotite from the Mid-Atlantic Ridge, Southwest Indian Ridge, ophiolitic complexes from the Apenines, Italy, and California, USA, hydrothermal chimneys from Prony, New Caledonia, and altered basalt from ODP Site 801B in order to track their distribution and behaviors with respect to H2 production.
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Reporting Year 2012 Click to expand


  • RY2012-1 - submitted on Jan 01, 2012

    Update Details:

    [2012-00-01] Generation of reduced carbon may be limited to young and possibly hot crust.
  • RY2012-2 - submitted on Feb 01, 2012

    Update Details:

    [2012-00-02] Indication of organomineralizing processes that imply the presence of microbial filaments and may drive chimney edification at the hyperalkaline hydrothermal field of Prony Bay.
  • RY2012-3 - submitted on Mar 01, 2012

    Update Details:

    [2012-00-03] In situ evidence of tryptophan formation and stabilization at the olivine-serpentine interface in the hot hydrating mantle.
  • RY2012-4 - submitted on Apr 01, 2012

    Update Details:

    [2012-00-04] Direct evidence for the presence of hydrothermal oil of biological origin in various portions of the hydrated oceanic lithosphere.
  • RY2012-5 - submitted on May 01, 2012

    Update Details:

    [2012-00-05] Discovery of deep microbial niches, based on the energy of hydrogen that mediate elemental fluxes in hydrated oceanic mantle.

Reporting Year 2014 Click to expand


  • RY2014-1 - submitted on Oct 01, 2013

    Update Details:

    10-1-2013

     

     IPGP (Magali Ader Lead)   In order to quantify the potential of H2 derived from serpentinization to promote the formation of abiotic organic compounds at both low and high temperatures and/or sustain deep subsurface microbial communities in (ultra)mafic rocks, we investigated drilled and dredged oceanic samples (both altered basalts and hydrated peridotites) collected along the Mid Atlantic-Ridge, the South West Indian Ridge or in ophiolitic complexes (Appenins, Italy; California, USA). We also beneficiated from the opportunity of sampling chimneys from the hyperalkaline hydrothermal field of Prony (New Caledonia), a close analog of the well-known Lost City hydrothermal field that constitutes an open window to serpentinization processes. On one hand, we deployed a combination of high-resolution techniques (i.e. coupled CLSM/Raman spectroscopy with aspecific or specific staining (i.e. FISH), SEM, TEM, synchrotron-based deep UV and FTIR µimaging, Scanning X-ray Transmission Microscopy, ToF-SIMS) to track organic compounds at the pore level, image in situ their nature and spatial distribution while characterizing concomitantly their microhabitats/mineralogical environment along with past interactions. On the other hand, a set of 15-20 basaltic samples from hole 801B (Jurassic age) have been analyzed for carbon content and isotope composition of total and reduced carbon, as well as carbonate. The comparison of these results to those obtained previously on younger crust (Hole 1256D, 15 Ma, Shilobreeva et al., 2011) provides constraints on the variations with time of C storage in the oceanic crust (carbonation vs. organic synthesis). Moreover, in order to characterize the processes of C reduction in the presence of serpentinite, we also studied an exhumed serpentinite– sediment contact in Alpine Corsica, France, using carbon stable isotopes and Raman spectroscopy.

    Discovery of deep microbial niches, based on the serpentinization byproducts that mediate elemental fluxes in the hydrated oceanic mantle. These correspond to microhydrogarnets that may have constituted a prebiotic environment of prime interest for studying the emergence of the first microbial cells on Earth (Ménez et al., 2012, Nature Geoscience). Hydrogarnets were found to be widespread in the oceanic crust, affecting both the serpentinized mantle and the crystalline basalts thus allowing to suspect a widespread and long-lasting existence of such occurrences (Ménez et al., 2013, Mineralogical Magazine)

    Direct evidence for the presence of hydrothermal oil of biological origin in various portions of the hydrated oceanic lithosphere. This confirms that thermogenic (± oxidized) organic compounds generated at depth can significantly contribute to the organic carbon balance at peridotite-hosted hydrothermal fields, likely obscuring by mixing the isotopic signatures of the organic compounds collected at hydrothermal vents (Pasini et al., 2013, Lithos)

    Clues for massive organomineralizing processes implying heterotrophic microbial filaments that drive chimney edification at the hyperalkaline hydrothermal field of the Prony Bay (New Caledonia). Microimaging techniques (i.e. FISH/Raman and electronic microscopy) demonstrated that the chimneys-hosted communities initiate brucite and carbonate formation in active vents (Pisapia et al., to be submitted).

    The addition of reduced carbon seems to be limited to the young and possibly “hot” crust. Comparison between young (1256D) and old crust (801B) show that during aging samples are mostly enriched in carbonates; whereas the reduced fraction remains almost constant both in concentration (0.2 wt%) and in isotopic composition (13C =-25‰), suggesting an abiotic origin occurring during FTT types reactions close to ridge-axis.

    In Corsica samples, we find that serpentinite promoted the reduction of close calcite into highly crystalline graphite during subduction metamorphism.

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