Quantitative interpretation of pore water O 2 and pH distributions in deep-sea sediments

Abstract

A reaction-transport model is used to interpret 13 data sets of in situ O 2 and pH microelectrode profiles measured in deep-sea sediments from five oceanic regions. The model includes a mechanistic description of the major early diagenetic redox transformations, as well as solid and solute transport processes, pore water acid–base equilibria, and calcite dissolution. Four different dependencies of the calcite dissolution rate on the degree of pore water saturation are considered. The results of the systematic and data-driven approach indicate that consideration of two pools of reactive organic carbon is sufficient to reproduce the oxygen data; that the more reactive pool dominates the organic carbon deposition flux; and that suboxic degradation pathways play a non-negligible role at the majority of sites. Estimation of the calcite related parameters, however, yields only nine successful simulations of the pH profiles. The dissolution rate expressions with the higher rate orders tested (2 and 4.5) are generally more successful in reproducing the in situ pH profiles. While the pore water pH profiles cannot constrain the calcite deposition flux, robust estimates of the depth-integrated calcite dissolution rates can be obtained. These correlate positively with the benthic oxygen uptake fluxes, although sites overlain with undersaturated and supersaturated bottom waters exhibit separate trends.