An eddy-permitting coupled physical-biological model of the North Atlantic2. Ecosystem dynamics and comparison with satellite and JGOFS local studies data

A model of biological production in the euphotic zone of the North Atlantic has been developed by coupling a Nitrate, Phytoplankton, Zooplankton, Detr itus (NPZD) nitrogen-based ecosystem model with an eddy-permitting circulat ion model. The upper ocean physical and biological results are presented fo r an experiment with monthly climatological forcing. A comparison with sate llite ocean color data shows that the model is capable of a realistic descr iption of the main seasonal and regional patterns of surface chlorophyll. A greement is also good for primary production except in the subtropical gyre where the model produces values more than an order of magnitude smaller th an derived from satellite observations. In situ data available at Joint Glo bal Ocean Flux Study (JGOFS) time series and local study sites (Bermuda Atl antic Time-series Study (BATS), 32 degrees N, 65 degrees W; North Atlantic Bloom Experiment (NABE), 47 degrees N, 20 degrees W; EUMELI oligotrophic, 2 1 degrees N, 31 degrees W) are used for a more detailed analysis of the mod el's capability to simultaneously reproduce seasonal ecosystem dynamics in different biological provinces of the North Atlantic Ocean. The seasonal cy cle of phytoplankton biomass and nitrate is simulated quite realistically a t all sites. Main discrepancies between model and observations are a large zooplankton peak, required by the model to end the phytoplankton spring blo om at the 47 degrees N, 20 degrees W site, and the underestimation of prima ry production at EUMELI and under oligotrophic summer conditions at BATS. T he former model deficiency can be related to the neglect of phytoplankton a ggregation; the latter is caused by too inefficient recycling of nutrients within the euphotic zone. Model improvements are suggested for further step s toward a realistic basin-wide multiprovinces simulation with a single eco system model.