Modeling the effect of eddies and advection on the lower trophic ecosystem in the northeast tropical Pacific

A medium complexity, nitrogen-based ecosystem model is developed in order to simulate the ecosystem in the northeast tropical Pacific. Several physical processes have major impact on the ecosystem in this region, most importantly local wind jets and upwelling at the Costa Rica Dome (CRD). The ecosystem model is run "offline", using a subdomain of the global Navy Coastal Ocean Model (NCOM) as input. The NCOM is a hybrid sigma-z level model with data assimilation. The model forced by daily heat and momentum fluxes and it therefore captures short-term variability. The ecosystem model is validated using satellite data and ship-based observations, and the model analyses is focused on the years 2000--2002.; At the Gulf of Tehuantepec, the Tehuantepec jet is responsible for upwelling nutrient rich water. The jet also occasionally produces large anti-cyclonic eddies that detach from the coast. Calculations of cross-shelf fluxes show that there is high offshore export of organic material during fall and winter. The highest export is of order of 10 Mg C per meter of coastline per day and happens during eddy events. During these events, there is a comparable onshore flux to the south of the gulf. The model estimated transport away from the coast at the Gulf of Tehuantepec is 167 Tg C/year, and the onshore transport to the south of the gulf is 704 Tg C/year.; The second subject of interest is the CRD. A mass-balance budget is calculated at the CRD, and the horizontal and vertical fluxes are related to the abundance of plankton at the dome. There is upwelling (7.2 x 10-2 Sv) at the dome throughout the year, but the upwelling is largest during winter. Further west, nitrate input from deeper layers is larger in the fall and summer. The results suggest that about 80% of the nitrate that is supplied to the dome in the summer is actually brought up to the west of the dome and transported eastward by the North Equatorial Counter Current.