The primary production module in the marine ecosystem model ERSEM II, with emphasis on the light forcing

New elements in the primary production module of ERSEM II relative to ERSEM I are described. The main changes are the inclusion of picoalgae and dinoflagellates as additional functional groups, the decoupling of carbon- and nutrient-uptake kinetics and the refining of the light dependency of the primary producers, with emphasis on the last. The results of a reference run are compared with measurements. The consequences of using production-irradiance (pI) relations assuming a different degree of photoinhibition in calculating net annual primary production are shown in a sensitivity analysis, and it is concluded that a pI relation with a high degree of photoinhibition leads to clear underestimates of primary production in turbid coastal waters.