Organic carbon dynamics and preservation in deep-sea sediments

Abstract

Three methods of estimating the particulate organic carbon fluxes to the sediment-water interface of the deep Pacific Ocean agree to within the error of the measurements at MANOP sites M, H, and C. Sediment trap experiments, pore water results, and surface sediment organic carbon data suggest that a major fraction of the particulate organic carbon raining to abyssal depths at these locations is degraded within the surface sediments rather than at the sediment-water interface or in the nephloid layer. Organic carbon rain rates at the three sites are similar—within a factor of two; however, the preservation rate of organic carbon and the chemistry of sediment pore waters are very different. A model developed to describe the pore water oxygen and sedimentary carbon distributions indicates model developed to describe the pore water oxygen and sedimentary carbon distributions indicates that changes in the rate constant for organic matter degradation and the bioturbation rate may contribute significantly to the observed differences in character of both pore water and sediment chemistry at these locations. The implication with respect to interpreting the sedimentary record is that cycles of organic carbon and redox sensitive metals (i.e., manganese) are not simply related to particulate organic carbon flux or surface water primary productivity. The residence time of organic carbon with respect to degradation in the surface sediments is on the order of 15 to 150 y.