Simulation analysis of the NW African coastal marine upwelling region

A temporal and spatial marine upwelling system model was developed for analysis of prominent biological and physical system interactions which result in observed nutrient distribution patterns in the northwest African coastal upwelling system near 21° N. latitude. The model is composed of a static physical submodel describing a two-dimensional circulation pattern, and a series of dynamic biological submodels incorporating nutrient uptake, grazing, and nutrient regeneration functions. Model results were qualitatively consistent with nutrient distributions observed during an upwelling event in the 1974 JOINT-I study area. Light was predicted as the primary limiting factor to phytoplankton nutrient uptake, while phosphate was predicted as the nutrient in lowest availability relative to optimal phytoplankton cellular requirements. Simulated silicate distribution patterns suggest that silica dissolution parameter estimates reported for the northwest African region may represent local conditions, but are likely overestimates at a system level of resolution. Sensitivity analysis results identify grazing threshold level as the primary regulator of grazing stress in the model, and suggest that a primarily phytophagous grazing habit for clupeoid fishes is unlikely in the northwest African upwelling area.