Modelling the pelagic nitrogen cycle and vertical particle flux in the Norwegian sea

A 1D Eulerian ecosystem model (Biological Ocean Model) for the Norwegian Se a was developed to investigate the dynamics of pelagic ecosystems. The BIOM combines six biochemical compartments and simulates the annual nitrogen cy cle with specific focus on production, modification and sedimentation of pa rticles in the water column. The external forcing and physical framework is based on a simulated annual cycle of global radiation and an annual mixed- layer cycle derived from field data. The vertical resolution of the model i s given by an exponential grid with 200 depth layers, allowing specific par ameterization of various sinking velocities, breakdown of particles and the remineralization processes. The aim of the numerical experiments is the si mulation of ecosystem dynamics considering the specific biogeochemical prop erties of the Norwegian Sea, for example the life cycle of the dominant cop epod Calanus finmarchicus. The results of the simulations were validated wi th field data. Model results are in good agreement with field data for the lower trophic levels of the food web. With increasing complexity of the org anisms the differences increase between simulated processes and field data. Results of the numerical simulations suggest that BIOM is well adapted to investigate a physically controlled ecosystem. The simulation of grazing co ntrolled pelagic ecosystems, like the Norwegian Sea, requires adaptations o f parameterization to the specific ecosystem features. By using seasonally adaptation of the most sensible processes like utilization of light by phyt oplankton and grazing by zooplankton results were greatly improved. (C) 199 9 Elsevier Science B.V. All rights reserved.