An ecosystem model for the North Pacific embedded in a general circulation model: Part I: Model description and characteristics of spatial distributions of biological variables

An ecosystem model is embedded in an ocean general circulation model (OGCM) and the ecosystem–physical combined model is applied to the North Pacific. The OGCM yields realistic physical environments concerning the mixed layer depth (MLD) and vertical flow except for MLD off Sanriku coast, Japan, and on both sides of the equator. The modeled nitrate, chlorophyll zooplankton, net primary production, and total organic nitrogen are within the order of magnitude of the observations. The biological activities are low in the subtropical region and high in the subpolar and the equatorial region as observations show. The modeled primary production rate shows a local maximum along the subpolar front, which seems to have a counterpart in the observation. There, the temperature and the nutrient condition are best combined for photosynthesis. The modeled concentrations differ from the observations in some respects: chlorophyll concentration is low in the subpolar region and high in the subtropical and the equatorial region compared with the Coastal Zone Color Scanner observation; the equatorial net primary production rate is higher than the observed. Part of the disagreement may be ascribed to the photoadaptation process, which is not included in the model and/or the simple extrapolation of the temperature dependence of photosynthesis.