Organic matter oxidation in deep-sea sediments: Distribution in the sediment column and implications for calcite dissolution

Abstract

This study uses pore water profiles of NO3− and O2 from 34 deep-sea study sites from five oceanic regions encompassing broad ranges of sediment composition and organic matter oxidation rate to analyze the depth distribution of organic matter oxidation within the sediment column. While the results are consistent with those of Hammond et al. (1996) and Hales (2003), the broader range of environmental variables considered in this study allows us to show that the depth of oxidation varies systematically with the integrated sedimentary organic matter oxidation rate. The scale length for oxidation varies from large values of about 4 cm when the organic matter oxidation rate is 5 μmol/cm2/y to about 0.35 cm at oxidation rates above 20 μmol/cm2/y. We have included this variability of organic matter oxidation depth in models of calcite dissolution. Our results show that variations in oxidation depth at a constant degree of supersaturation may result in changes in metabolic dissolution efficiency that are similar in magnitude to those resulting from basin-wide variations in the degree of supersaturation with respect to calcite. The model shows that, when the ratio of sedimentary organic matter oxidation rate to calcite rain rate is held fixed at 0.8 mol/mol, metabolic dissolution is likely to be significant at all bottom-water saturation levels and may result in dissolution of up to 50% of the calcite rain at the calcite saturation horizon.