Ecosystem modelling across a salinity gradient from the North Sea to the Baltic Sea

Several ecosystem models with different complexity have previously been developed and applied either to the North Sea or the Baltic Sea. However, no attempts have been made to develop and validate a common ecological model covering both areas. In the present study, we applied a modified version of the Baltic Sea ecological model ERGOM (Ecological ReGional Ocean Model) coupled to the 3D circulation model DMI-BSHcmod with a two-way nested fine grid in the Danish straits. ERGOM was adapted to the North Sea by (1) adding silicate, (2) introducing two zooplankton groups and modifying their grazing impact and (3) adjusting light parameterisations. The recalibrated ERGOM model was validated against climatologically surface data of nutrients and measurements from nine monitoring stations in 2004–2006. The validation showed in general a ‘good’ to ‘very good’ agreement with measurements of surface temperature, salinity, DIN, PO4, SiO2 and Chl a and bottom O2 based on cost function values and correlation analysis. However, some deviations were found between model results and observations emphasizing that the descriptions of oxygen dynamics, light attenuation, remineralisation and nutrient loadings in the ecosystem model should be improved in future studies. In conclusion, the modified ecosystem model could reproduce the seasonal and regional patterns in the whole North Sea – Baltic Sea area and can be applied in future studies in these areas.