Carbon-to-chlorophyll ratio and growth rate of phytoplankton in the sea

Observations from offshore regions (NW Atlantic and Arabian Sea) and from a semi-enclosed bay (Tokyo Bay) were used to study the relationships between chlorophyll and particulate carbon in the sea. A simple conceptual model was then developed to inferin situphytoplankton carbon as a function of chlorophylla. This allowed indirect estimates of the carbon-to-chlorophyll ratio of phytoplankton in the sea. Using data from high-performance liquid chromatography, field samples dominated by diatoms, dinoflagellates, green algae, prymnesiophytes and cyanobacteria were identified, and their carbon-to-chlorophyll ratios were established. The computations yielded conservative estimates for the ratio (15 to 176 weight:weight). The results were applied to satellite data to map the carbon-to-chlorophyll ratios in the NW Atlantic. Since methods were already in place to estimate photosynthesis–irradiance parameters for the region by remote sensing (Platt et al. 2008), we showed that it was possible, using remote sensing, to compute carbon-based phytoplankton growth rates by making use of the existing information on photosynthesis–irradiance parameters and carbon-to-chlorophyll ratios. The method makes it possible to compute primary production by using either carbon-based growth models or photosynthesis–irradiance models in ways that are fully comparable with each other.