Toward a parameterization of global‐scale organic carbon mineralization kinetics in surface marine sediments

Abstract

AbstractAn empirical function is derived for predicting the rate‐depth profile of particulate organic carbon (POC) degradation in surface marine sediments including the bioturbated layer. The rate takes the form of a power law analogous to the Middelburg function. The functional parameters were optimized by simulating measured benthic O2 and NO3− fluxes at 185 stations worldwide using a diagenetic model. The novelty of this work rests with the finding that the vertically resolved POC degradation rate in the bioturbated zone can be determined using a simple function where the POC rain rate is the governing variable. Although imperfect, the model is able to fit 71% of paired O2 and NO3− fluxes to within 50% of measured values. It further provides realistic geochemical concentration‐depth profiles, NO3− penetration depths, and apparent first‐order POC mineralization rate constants. The model performs less well on the continental shelf due to the high sediment heterogeneity there. When applied to globally resolved maps of rain rate, the model predicts a global denitrification rate of 182 ± 88 Tg yr−1 of N and a POC burial rate of 107 ± 52 Tg yr−1 of C with a mean carbon burial efficiency of 6.1%. These results are in very good agreement with published values. Our proposed function is conceptually simple, requires less parameterization than multi‐G‐type models, and is suitable for nonsteady state applications. It provides a basis for more accurately simulating benthic nutrient fluxes and carbonate dissolution rates in Earth system models.