Abstract
Two plankton model formulations (a single-species and a multi-species) are presented and analyzed. They are subsequently incorporated into a three-dimensional general circulation model to investigate the effects of ocean circulation and mesoscale variability on the distribution and dynamics of plankton in oligotrophic oceans.Despite their simplicity, the ecosystem models respond realistically to physical forcing and reproduce the main biological processes and structures. In high energy unstable oligotrophic environments (such as, western boundary currents) upward advection, caused by growing instabilities in the currents and mesoscale activity (meanders and eddies), is the main source of nitrogen to the phytoplankton, and new production accounts for a large portion of total primary production. Conversely, in low energy stable oligotrophic areas (such as, subtropical gyres), phytoplankton growth is in approximate balance with zooplankton grazing and primary production is mostly regenerated, except near the nutricline, where intermittent inputs of nitrogen from below maintain moderate levels of new production.In the case of the multi-species ecosystem, physical processes control the overall temporal and spatial patterns of biological production (upwelling areas and mesoscale eddies), but biological processes are the main factors controlling species' relative abundances and community structure. The variation in photosynthetic efficiencies and half-saturation constants between phytoplankton species, and the enhanced recycling through the microbial loop in the multi-species model, result in higher primary and secondary production than in the single-species model. The multi-species ecosystem model is capable of simulating a realistic deep chlorophyll maximum and true oligotrophic surface conditions.