by
Günther Radach and Johannes Pätsch
Institut für Meereskunde der Universität Hamburg
Troplowitzstraße 7, 22529 Hamburg, Germany

Abstract

A large amount of nutrient and chlorophyll data from the North Sea were compiled and organized in a research data base to produce annual cycles on a relatively fine spatial resolution of 1° in each horizontal direction. The data originate from many different sources and were partly provided by the ECOMOD data base of the Institut für Meereskunde in Hamburg and partly by ICES in Copenhagen to cover the time range from 1950 to 1994. While the annual cycles of nutrients and chlorophyll derived for the continental coastal zone are representative for the decade 1984 - 1993 only, those for the remaining parts of the North Sea may be considered as climatological annual cycles based on data from more than four decades. The composite data set of climatological annual cycles of medians and their climatological ranges is suited to serve for validational and forcing purposes for ecosystem models of the North Sea, which have a resolution larger than or equal to 1° in both longitudinal and latitudinal directions. The annual cycles of the macronutrients and chlorophyll presented here for 1° by 1° squares in the North Sea show especially that sufficient observational data exist to provide initial, forcing and validational data for the simulations with the 130-box setup (ND130) of the ecosystem model ERSEM. The annual cycles presented give a clear picture for the whole of the North Sea. The highest concentrations occur at the continental coasts as result of continued river input, which is added to the ongoing atmospheric input over the North Sea. Also from the Atlantic Ocean water with relatively high nutrient concentrations enters the North Sea via the northern boundary. In the productive areas on and around the Dogger Bank nutrient concentrations are lower than in the other parts of the North Sea even in winter. The areas with seasonal stratification have very different annual cycles in the upper layer (0 - 30 m) and lower layer (30 m - bottom). The shallow boxes are fully mixed and exhibit a relatively fast increase of nutrient concentrations caused by summer regeneration of nutrients.