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Figure F5. Model for relative rates of organic carbon (OC) oxidation and radiolytic H2 oxidation with depth. Dotted pink line indicates maximum depth below seafloor cored curing KNOX-02RR survey. Radiolytic H2 may provide more than half of the electron donors at some proposed sites (D’Hondt et al., 2009). Because OC is oxidized at highest rates in the youngest sediment, at some depth below seafloor (dashed blue line) microbial oxidation of radiolytic H2 may exceed oxidation of buried organic carbon. At still greater depth (solid green line), reactive organic matter may be depleted and radiolytic H2 may be the sole electron donor. These predictions can only be tested by drilling the entire sediment column.

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