The North Sea Light Climate: Analysis of Observations and Numerical Simulations


Recent studies have indicated changes in the light climate of the North Sea. An overall reduction of water clarity over the twentieth century could be observed in measurements, and more recent analysis suggests that these trends continue. Inorganic sediment is often named one of the driving factors in these changes and it has been shown to locally increase. With 20 years' worth of satellite-derived sediment data, we were able to conduct basin wide investigations of the temporal dynamics of the biogeochemical state of the North Sea. To identify the impact of inter-annual and seasonal changes in sediment, we fed from two different remote sensing sources (GlobColour & IFREMER) into a 3D coupled hydrodynamic and biological model. The light scheme in the Carbon Silicon Nitrogen Ecosystem model (CoSiNE) was modified to account for sediment specific attenuation. We performed a total of five numerical experiments for the period of 2000–2017. The main two experiments were conducted using monthly averaged data. Additionally, as controls, one experiment with annually averaged and one with a 20 years average of sediment, as well as a fifth one without sediment were performed. Our model showed a clear relation between changes in sediment and water clarity. Phytoplankton biomass was reduced only in areas with high nutrient availability.
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