A model of biological production in the euphotic zone of the North Atlantic has been developed by coupling a Nitrate, Phytoplankton, Zooplankton, Detritus (NPZD) nitrogen-based ecosystem model with an eddy-permitting circulation model. The upper ocean physical and biological results are presented for an experiment with monthly climatological forcing. A comparison with satellite ocean color data shows that the model is capable of a realistic description of the main seasonal and regional patterns of surface chlorophyll. Agreement is also good for primary production except in the subtropical gyre where the model produces values more than an order of magnitude smaller than derived from satellite observations. In situ data available at Joint Global Ocean Flux Study (JGOFS) time series and local study sites (Bermuda Atlantic Time-series Study (BATS), 32¿N, 65¿W; North Atlantic Bloom Experiment (NABE), 47¿N, 20¿W; EUMELI oligotrophic, 21¿N, 31¿W) are used for a more detailed analysis of the model's capability to simultaneously reproduce seasonal ecosystem dynamics in different biological provinces of the North Atlantic Ocean. The seasonal cycle of phytoplankton biomass and nitrate is simulated quite realistically at all sites. Main discrepancies between model and observations are a large zooplankton peak, required by the model to end the phytoplankton spring bloom at the 47¿N, 20¿W site, and the underestimation of primary production at EUMELI and under oligotrophic summer conditions at BATS. The former model deficiency can be related to the neglect of phytoplankton aggregation; the latter is caused by too inefficient recycling of nutrients within the euphotic zone. Model improvements are suggested for further steps toward a realistic basin-wide multiprovinces simulation with a single ecosystem model. ¿ 2000 American Geophysical Union