A model based on transport reaction equations has been developed, introducing a new bacterial kinetic term for the oxidation of organic matter by oxygen. This formulation is known as the Monod rate law. As it depends on both the oxygen and the organic carbon concentrations, it allows in a single model the representation of sediments undergoing totally oxic or oxic plus suboxic diagenesis. It results, however, in a system of coupled nonlinear second-order ordinary differential equations. As the common numerical solutions to such systems are not straightforward, it has infrequently been used in diagnetic modeling. By applying a numerical iterative method which utilizes the previous computation step to solve nonlinearity, the numerical instabilities of the usual methods were avoided. In order to illustrate the wide application field of this model to various diagenetic situations, verifications and sensitivity studies were performed, Rather large variations in bioturbation coefficients and kinetic constants led to small changes in the distribution of oxygen and organic carbon.

On the other hand, small variations in the organic carbon rain rate or bottom water oxygen concentrations resulted in large changes in the calculated depth of the oxic-suboxic boundary. In contrast, the effect of varying sedimentation rate was negligible. Organic carbon preservation was very sensitive to sedimentation rate, the flux of organic carbon, and the bottom water concentration of oxygen. This emphasizes the importance of these three parameters and the key role of their precise determination for the quantification of the organic carbon recycling in the sediments. The effect of near-surface compaction was also estimated in order to asses the influence of physical processes on the early diagenesis of organic carbon and oxygen. The inclusion of this compaction produced a maximum departure of 30% in the oxygen penetration depth and may multiply the carbon preservation by almost a factor of 2 in certain cases. Finally, the effect of varying the kinetics as a function of burial was predicted. It showed that organic carbon might be preserved under oxic diagenetic conditions when an appropriate rate of organic carbon is reached. This addresses the question of the formation and the preservation of refractory carbon in sediments, but more experimental work needs to be done in order to confirm or disprove this hypothesis. ¿ American Geophysical Union 1991