Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis

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Abstract

Pore water profiles of total-CO2, pH, PO3−4, NO3 plus NO2, SO2−4, S2−, Fe2+ and Mn2+ have been obtained in cores from pelagic sediments of the eastern equatorial Atlantic under waters of moderate to high productivity. These profiles reveal that oxidants are consumed in order of decreasing energy production per mole of organic carbon oxidized (O2 > manganese oxides ~ nitrate > iron oxides > sulfate). Total CO2 concentrations reflect organic regeneration and calcite dissolution. Phosphate profiles are consistent with organic regeneration and with the effects of release and uptake during inorganic reactions. Nitrate profiles reflect organic regeneration and nitrate reduction, while dissolved iron and manganese profiles suggest reduction of the solid oxide phases, upward fluxes of dissolved metals and subsequent entrapment in the sediment column. Sulfate values are constant and sulfide is absent, reflecting the absence of strongly anoxic conditions.

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    Present address: Dept of Oceanography, Florida State University Tallahassee, FL 32306, U.S.A.

    Present address: School of Oceanography, Oregon State University, Corvalis, OR 97330, U.S.A.

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