Relative contributions of photophysiology and chlorophyll-a abundance to phytoplankton group-specific primary production in the Kuroshio region as inferred by satellite ocean color remote sensing

The primary production by diatoms, haptophytes and cyanobacteria in the Kuroshio region was evaluated using satellite ocean color remote sensing. We developed a method that estimates bio-optical properties such as the photosynthetic quantum yield index and chlorophyll- a -specific optical absorption coefficient of phytoplankton to derive the group-specific production. In contrast with the previous efforts that assume bio-optical properties to derive the production, our method relaxes the assumption by integrating an image processing of bulk satellite data into bio-optical modeling. Especially, our bio-optical model uses a universal bio-optical principle that we found: i.e., the absorption coefficient of phytoplankton at the wavelength of 510 nm can represent their spectral average. Climatological average of the group-specific primary production in the Kuroshio region showed 134, 72 and 40 mg C m –2 day –1 for diatoms, haptophytes and cyanobacteria, respectively. The quantum yield index of each phytoplankton group varied spatially, resulting in a latitudinal gradient, and diatoms had a higher quantum yield than those of cyanobacteria and haptophytes. Analysis of seasonal variability in the group-specific primary production in the Kuroshio region suggested that the primary production due to diatoms was mainly driven by variability in their chlorophyll-a abundance, whereas that due to cyanobacteria by variability in their quantum yield index or photophysiology. The production due to haptophytes was shown seasonally regulated by variability in both chlorophyll- a abundance and photophysiology.