Long term analysis of the North Sea light climate, using remotely sensed sediment data in a 3D coupled ecosystem mode

Recent studies have indicated changes in the light climate of the North Sea. While an overall reduction of clarity over the 20^th century could be observed in in situ measurements, more recent analysis of satellite data suggests reductions in clarity in some regions, and increases in others, as well as shifts in ocean colour. The strongest influences on both clarity and colour are inorganic sediment, dissolved organic matter and chlorophyll. To determine their impact on the changes in the light climate, a long term analysis of the North Sea ecosystem is performed over twenty years using a 3D coupled hydrodynamical and biological model. The influences of temporal, as well as lateral variability in downwelling attenuation are being analysed in a sensitivity study. Modifications are made to the light attenuation scheme in the Carbon Silicon and Nitrogen Ecosystem model (CoSiNE), so that effects of inorganic suspended particulate matter (SPM) and coloured dissolved organic matter (CDOM) can be accounted for. By utilising satellite measurements for SPM and an inverse relation with salinity for CDOM, we can isolate the influence of SPM changes on the primary production in the North Sea and simulate a realistic light climate. We relate our findings to observed trends in water clarity and colour.