Processes supplying nitrogen to phytoplankton,thus sustaining primary production,over the oligotrophic subtropical North Atlantic gyre are assessed using a coupled physical/biogeochemical model.The three dimensional ocean circulation model developed by the French Mercator project for operational oceanography is used with a horizontal grid spacing of 1/3 rd of a degree.This eddy-permitting physical model,coupled with a simple nitrogen-based ecosystem model (Nutrients,Phytoplankton,Zooplankton,Detritus and Dissolved Organic Matter) is integrated for the SeaWiFS years 1997 to 1999 in order to simulate chlorophyll concentration and primary production.