Calculation of diffusive fluxes across the sediment-water wnterface

The calculation of diffusive flux rates across the sediment-water interface is subject to two considerations that have not previously been dealt with. The first consideration is that the concentration of a dissolved species at the sediment-water interface is not necessarily the generally assumed concentration of the overlying ‘bulk’ water owing to the possible existence of a stagnant benthic boundary layer. The second consideration is that any function fit to the change in concentration with depth in the sediment must, upon integration over an interval, yield the measured average concentration of the interval. A simple model is applied to measurements of dissolved silica in a core from the North American basin. The calculated range of possible silica flux rates agrees with experimentally measured values of Fanning and Pilson (1974). The maximum possible thickness of the stagnant benthic boundary layer (1 cm) is within the limit of the calculations of Wimbush (1970) for the South Pacific.