Pore water profiles and numerical modelling of biogeochemical processes in Peru Basin deep-sea sediments

An extensive set of pore water profiles, including O2, NO3−, NO2−, NH4+, PO43−, Fe2+, Mn2+, SO42−, SiO44−, pH, and alkalinity as well as solid phase data on organic carbon content and porosity, in 18 sediment cores obtained from five areas in the Peru Basin (RV Sonne 106 expedition in 1996) is presented. The pore water profiles indicate that early diagenesis progresses through oxygen respiration, denitrification, and manganese(IV) reduction, while the subsequent redox states, iron(III) reduction, sulphate reduction and methanogenesis, cannot be observed from the dissolved phase in these deep-sea sediments. A numerical diagenetic model was applied to the data in order to derive parameters, such as the depositional flux of metabolizable organic matter or the bioturbation intensity, that control the geochemical conditions in the deep-sea floor and could not be obtained directly by measurements. Moreover, the numerical simulations show that even those pore water NO3− profiles that decline non-linearly to zero concentration are not compatible with a steady state assumption. They can be explained only by transient downward progression of a nitrate front.