Assessing organic matter mineralization, degradability and mixing rate in an ocean margin sediment (Northeast Atlantic) by diagenetic modeling

We test whether organic matter degradability, mixing activity, and total sediment mineralization can be estimated by inversion of a coupled nonlinear numerical steady-state diagenetic model. We use a single data set comprising oxygen, nitrate, ammonium and organic carbon versus depth profiles from a slope station in the Goban Spur area (1034 m, Northeast Atlantic). Based on an extensive sensitivity analysis, it appears that (1) when using all data, the total mineralization rates can be determined with reasonable precision; bioturbation and degradability are less well constrained and (2) total mineralization rates can be determined based on nitrate and oxygen profiles only; estimates of organic matter mixing rates and degradability are refined when including the solid phase organic carbon profile. The bulk mixing rates obtained for organic carbon are one order of magnitude higher than mixing rates previously estimated from Pb-210 profiles, lending validity to the hypothesis that organic particles are mixed faster than inert particles. The degradability of the organic carbon prior to its incorporation in the sediment is in the order of 10-30 yr(-1), indicating that mineralization in this slope station of the Goban Spur area is fueled mainly by freshly deposited organic matter. [KEYWORDS: Benthic oxygen-demand; deep-sea sediments; marine-sediments; hemipelagic sediments; nutrient diagenesis; equatorial pacific; water interface; carbon; bioturbation; nitrogen]