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Abstract

The report is intended to introduce the reader to the model structure of the oceanic biogeochemical model HAMOCC5, and to assist in setting-up and running HAMOCC5 driven by the ocean general circulation model MPI-OM. First, an overview over the simulated biogeochemical processes is given. Second, the modules that compute biogeochemistry are described in detail. Third, the interface to MPI-OM and the coupling between the ocean physics and the biogeochemical tracer model are described. Finally, the input and output files are described and an appendix provides some tablesand cross references for the usage of the model code. HAMOCC5 simulates biogeochemical tracers in the oceanic water column and in the sediment. The model can be used with any Ocean General Circulation Model (OGCM). Here, it is set up as a subroutine of the Ocean Model of the Max-Planck-Institute for Meteorology, MPI-OM (Marsland et al., 2003). HAMOCC5 is driven by the same radiation as the OGCM to compute photosynthesis. Temperature and salinity from MPI-OM are used to calculate chemical transformation rates and constants e.g., for solubility of carbon dioxide. The flux of carbon dioxide between atmosphere and ocean is computed depending on the local concentrations and the rates for air-sea gas exchange. With only few modifications any field of atmospheric trace gases or wind stress can be used to drive the fluxes. The biogeochemistry of HAMOCC5 is based on that of HAMOCC3.1 (Six and Maier-Reimer, 1996). Modifications have been made to account for tracers in addition to phosphorous, namely nitrogen, nitrous oxide, DMS, dissolved iron and dust. Additional simulated processes are denitrification and N-fixation, formation of calcium carbonate and opaline shells by phytoplankton, aggregation and size dependent sinking of detritus and marine snow, DMS production, uptake and release of dissolved iron by biogenic particles, and dust deposition and sinking. Biological production is now co-limited by phosphorous, nitrogen, and iron. For IPCC-type experiments additional tracers, anthropogenic DIC and alkalinity have been introduced. The model now also features a sediment module based on Heinze and Maier-Reimer (1999) and Heinze et al. (1999). The sediment model basically calculates the same tracers as the water column model.