We incorporate multinutrient and size-structured ecosystem dynamics into a three-dimensional ocean general circulation model for the North Atlantic. The model reproduces the magnitude and general spatial and temporal patterns in nutrients, chlorophyll and primary production seen in in situ (BATS, NABE, and OWSI) and satellite (SeaWiFS) data, showing substantial improvements over prior basin-scale simulations. Model skill is evaluated quantitatively against SeaWiFS data using a Taylor diagram approach. Model-data correlation R for the overall surface chlorophyll time-space distribution is ~0.6, with comparable model and observed total variability. The agreement relative to satellite-based primary production is somewhat weaker (0.2 < R < 0.5). The simulations capture observed ecological characteristics, e.g., the dominance of picoplankton and episodic diatom blooms in the subtropics, nutrient-controlled plankton succession at higher latitudes, and associated seasonal/depth changes in new and regenerated production and particle export. In a sensitivity experiment that mimics behavior of simpler single-species models, removal of diatom silica limitation leads to major shifts in community structure and export and larger model-data errors similar to previous model studies. Model results also suggest that episodic diatom blooms at BATS may be related to interannual variations in the southward transport of nutrients, mainly SiO3, and plankton cells.