A model of plankton dynamics for the coastal upwelling system of Monterey Bay, California

A seven-box plankton model for the mixed layer of the open ocean (Fasham et al., 1990, Journal of Marine Research 48, 591-639) was modified and applie d to the coastal upwelling ecosystem of Monterey Bay, California. Upwelling velocities, photosynthetically active radiation and changes in mixed-layer depth drove the model. The observed long-term mean (1989-1995) seasonal cy cles of nitrate concentration, primary production and phytoplankton concent ration within the mixed layer were reproduced. Bacteria and zooplankton bio mass, and ammonium concentration were within the same order of magnitude as observations. Modeled dissolved organic nitrogen (labile) values were an o rder of magnitude lower than observations (total). New production estimates were high, leading to an annual f-ratio of 0.84, typical of productive coa stal upwelling systems. Export production was much lower, and horizontal ex port by upwelling-induced advection was the dominant loss term for phytopla nkton primary production. It exceeded sinking and gratings and the flux of zooplankton-derived detritus throughout most of the year. The model suggest s that a large proportion of the daily phytoplankton growth is ungrazed in the mixed layer, and is advected downstream and offshore of the production site. (C) 2000 Elsevier Science Ltd. All rights reserved.