Journal
NATURE COMMUNICATIONS
Volume 13, Issue 1, Pages -Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41467-022-30421-5
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Funding
- CNRS
- Region Ile de France
- Ministere delegue a l'Enseignement superieur et a la Recherche
- Museum National d'Histoire Naturelle
- Italian program MIUR PRIN [2017ZE49E7_002]
- University of Milan
- European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme [864045]
- SEED (Grant RV_PSR_SOE_2020_AVILL)
- European Research Council (ERC) [864045] Funding Source: European Research Council (ERC)
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Ocean sediments mainly consist of calcium carbonate and organic matter. When subducted, some carbon is released as CO2 in arc magmas. This study challenges the assumption that the isotopic signature of CO2 reflects the organic/inorganic carbon fraction, and demonstrates that it is mainly controlled by the ratio of CO2 to CaCO3.
Ocean sediments consist mainly of calcium carbonate and organic matter (phytoplankton debris). Once subducted, some carbon is removed from the slab and returns to the atmosphere as CO2 in arc magmas. Its isotopic signature is thought to reflect the bulk fraction of inorganic (carbonate) and organic (graphitic) carbon in the sedimentary source. Here we challenge this assumption by experimentally investigating model sediments composed of C-13-CaCO3 + C-12-graphite interacting with water at pressure, temperature and redox conditions of an average slab-mantle interface beneath arcs. We show that oxidative dissolution of graphite is the main process controlling the production of CO2, and its isotopic composition reflects the CO2/CaCO3 rather than the bulk graphite/CaCO3 (i.e., organic/inorganic carbon) fraction. We provide a mathematical model to relate the arc CO2 isotopic signature with the fluid-rock ratios and the redox state in force in its subarc source. The carbon isotopic signature of CO2 released from marine sediments subducted beneath volcanic arcs does not reflect their organic/inorganic fraction, but instead the fluid-rock ratios and the redox conditions in force at the top of the slab.
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