Interannual variability of the North Sea primary production: comparison from two model studies

The North Sea is known to be a very productive area. Several models and in situ measurements have been used to quantify the primary production and its spatial variability, but large uncertainties still exist. Except for gener al statements about the level of production, very little is known about the interannual variability of it. In this paper two state of the art ecologic al models have been run with realistic forcing for 10 different years to in vestigate this interannual variability. The focus has been on differences d ue to changing wind fields, and differences due to changes in river dischar ges. Separated into ERSEM boxes, both spatial and temporal variability is d iscussed. The models suggest that the interannual variability in the North Sea primary production is around 15%, and that the variability locally is h igher than this, thus an increase in one area is often compensated by a dec rease somewhere else. The impact of the river nutrient inputs is estimated to be less than 10% of the total production. The modelled variation in prim ary production, can in both models be related to, and explained from, actua l variability found in the modeled physics. The large variability in primar y production found due to these changes in the underlying physical fields, suggests that a realistic three-dimensional circulation model is essential for this kind of modelling. (C) 2000 Elsevier Science Ltd All rights reserv ed.