Gridded abundance product representing chlorophyll-a values in the Dutch North Sea from 1976 till 2014. Chlorophyll –a can be interpreted as a proxy for phytoplankton. The resulting values vary seasonally. The winter concentrations are lower because low light and temperature are not optimal for phytoplankton growth. In spring we observe the highest concentrations occurring in near coastal waters where nutrients from rivers are most abundant. Phytoplankton organisms are responsible for about 45% of annual global photosynthesis. They are as such vital for the functioning of marine food webs (considered in MSFD descriptor 4) and are the main drivers of the global biogeochemical cycles. This product was developed with DIVA (Data-Interpolating Variational Analysis) and the scale is log-transformed abundance (in µg per liter). Data was provided by Rijkswaterstaat (RWS).