Regulation of phytoplankton carbon to chlorophyll ratio by light, nutrients and temperature in the Equatorial Pacific Ocean: a basin-scale model

摘要

The complex effects of light, nutrients and temperature lead to a variablecarbon to chlorophyll (C:Chl) ratio in phytoplankton cells. Using field datacollected in the Equatorial Pacific, we derived a new dynamic model with anon-steady C:Chl ratio as a function of irradiance, nitrate, iron, andtemperature. The dynamic model is implemented into a basin-scale oceancirculation-biogeochemistry model and tested in the Equatorial Pacific Ocean.The model reproduces well the general features of phytoplankton dynamics inthis region. For instance, the simulated deep chlorophyll maximum (DCM) ismuch deeper in the western warm pool (~100 m) than in the EasternEquatorial Pacific (~50 m). The model also shows the ability toreproduce chlorophyll, including not only the zonal, meridional and verticalvariations, but also the interannual variability. This modeling studydemonstrates that combination of nitrate and iron regulates the spatial andtemporal variations in the phytoplankton C:Chl ratio in the EquatorialPacific. Sensitivity simulations suggest that nitrate is mainly responsiblefor the high C:Chl ratio in the western warm pool while iron is responsiblefor the frontal features in the C:Chl ratio between the warm pool and theupwelling region. In addition, iron plays a dominant role in regulating thespatial and temporal variations of the C:Chl ratio in the Central and EasternEquatorial Pacific. While temperature has a relatively small effect on theC:Chl ratio, light is primarily responsible for the vertical decrease ofphytoplankton C:Chl ratio in the euphotic zone.