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 infer in situ phytoplankton carbon as a function of chlorophyll a. 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.