Functional Activity of Phytoplankton and Optical Properties of Suspended Particulate Matter in Onega Bay of the White Sea

The phytoplankton activity was analyzed in June 2015 in Onega Bay of the White Sea. The chlorophyll a concentration, as well as cell abundance and cell biomass, were assessed in natural phytoplankton samples and individually for the picoplankton fraction. These data were compared with the results of additional optical measurements for the same water samples. A strong correlation ( R 2 = 0.82) was found between chlorophyll absorbance (~680 nm, absorbance spectra) and in vivo chlorophyll fluorescence intensity. Мicroalgae had a high level of photosynthetic efficiency ( Fv / Fm > 0.4). The picoplankton fraction was characterized by less efficient photosynthesis, probably due to the presence of cyanobacteria. The picoplankton fraction contributed a few percent to the total biomass, whereas its contribution to the total chlorophyll fluorescence intensity reached up to 40%.