Pore water of marine sediments recovered from two stations of the continental slope off southwest Africa were investigated. We present computer simulations of in situ and laboratory concentration profiles of oxygen as well as laboratory concentration profiles of nitrate, calcium, pH and alkalinity. The simulations were carried out with help of a numerical model (CoTAM) to describe the transport and the reaction of dissolved species in sediments. CoTAM is based on an operator-splitting approach comprising the independent calculation of transport and chemical reaction. The consumption rates of oxygen and nitrate were determined by optimal fits to the measured pore water profiles of these species. It could be shown that measured concentrations of nitrate in pore water correspond to a decomposition of organic matter with ratios between 3 and 3.7. However, artificially increased subsurface nitrate concentrations due to core recovery cannot be excluded, but our results show much greater deviations from expected concentrations (assuming Redfield stoichiometry) than previously reported from comparative studies (i.e. [Martin and Sayles, 1996]). Oxygen consumption in situ was shown to be distinctively lower than measured in multicorer cores after recovery. Simulations with varying denitrification rates indicate reduced diffusive nitrate release into the bottom water by up to 50% compared to shipboard results. Effects of nitrification and denitrification on pore water pH, carbonate alkalinity and calcium concentrations were simulated by recalculating concentrations of these species with regard to calcite equilibrium. For these calculations we used the standard software PHREEQE as a subroutine of CoTAM. Calcium and carbonate alkalinity increase due to solid phase calcite dissolution. ΔpH was calculated to be an order of magnitude lower within the zone of oxygen depletion than indicated by shipboard results. This difference is mainly related to non-equilibrium conditions during pH measurements.