FESOM2.1-REcoM3-MEDUSA2: an ocean-sea ice-biogeochemistry model coupled to a sediment model

This study describes the coupling of the process-based Model of Early Diagenesis in the Upper Sediment (MEDUSA version 2) to an existing ocean biogeochemistry model consisting of the Finite-volumE Sea ice-Ocean Model (FESOM version 2.1) and the Regulated Ecosystem Model (REcoM version 3). Atmospheric CO2 in the model is a prognostic variable which is determined by the carbonate chemistry in the surface ocean. The model setup and its application to a pre-industrial control climate state is described in detail. In the coupled model 400 PgC are stored in equilibrium in the top 10 cm of the bioturbated sediment, mainly as calcite, but also to 5 % as organic matter. Simulated atmospheric CO2 is in equilibrium at 286 ppm in the coupled simulation, which is close to the initially assumed value of the pre-industrial CO2 level. Sediment burial of carbon, alkalinity and nutrients in the coupled simulation is set to be partly compensated by riverine input. The spatial distribution of biological production is altered depending on the location of riverine input and the strength of local nutrient limitation, while the global productivity is not affected substantially.