Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 3 2009 10.5194/bg-6-391-2009 http://www.biogeosciences.net/6/391/2009/ http://www.biogeosciences.net/6/391/2009/bg-6-391-2009.html http://www.biogeosciences.net/6/391/2009/bg-6-391-2009.pdf 391 404 2009-03-17 Regulation of phytoplankton carbon to chlorophyll ratio by light, nutrients and temperature in the Equatorial Pacific Ocean: a basin-scale model X. J. Wang wwang@essic.umd.edu M. Behrenfeld R. Le Borgne R. Murtugudde E. Boss University of Maryland, College Park, Maryland, USA Oregon State University, Corvallis, Oregon, USA Institut de Recherche pour le Développement, Nouméa Cédex, New Caledonia, France School of Marine Sciences, University of Maine, Orono, Maine, USA The complex effects of light, nutrients and temperature lead to a variable carbon to chlorophyll (C:Chl) ratio in phytoplankton cells. Using field data collected in the Equatorial Pacific, we derived a new dynamic model with a non-steady C:Chl ratio as a function of irradiance, nitrate, iron, and temperature. The dynamic model is implemented into a basin-scale ocean circulation-biogeochemistry model and tested in the Equatorial Pacific Ocean. The model reproduces well the general features of phytoplankton dynamics in this region. For instance, the simulated deep chlorophyll maximum (DCM) is much deeper in the western warm pool (~100 m) than in the Eastern Equatorial Pacific (~50 m). The model also shows the ability to reproduce chlorophyll, including not only the zonal, meridional and vertical variations, but also the interannual variability. This modeling study demonstrates that combination of nitrate and iron regulates the spatial and temporal variations in the phytoplankton C:Chl ratio in the Equatorial Pacific. 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