New production in the equatorial Pacific: a coupled dynamical–biogeochemical model

A simple 3-D biogeochemical model is coupled to a dynamical model forced by weekly winds deduced from ERS1 scatterometer data, to simulate new production in the equation Pacific from April 1992 to June 1995. The biogeochemistry is modelled as a nitrate sink modulated by chlorophyll, using nitrate/chlorophyll regressions derived from field data. The first simulation was carried out assuming that remineralization below the euphotic layer is totally controlled by sinking particles. In the second simulation, it is shown that the simulation of nitrate and new production by the biogeochemical model is improved, in comparison with field data, by adding an explicit dissolved organic nitrogen compartment. In the equatorial band, the model simulates a nitrate-poor region (low new production) in the fresh warm pool separated from richer waters of the upwelling region by a salinity front. The zonal displacement of this salinity/nitrate front is associated with the El Niño–Southern Oscillation (ENSO). The modelled new production and physics, both in good agreement with the field data, represent useful tools for the study of skipjack tuna ( Katsuwonus pelamis ) forage distribution in the Pacific.