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Influence of Amur River discharge on phytoplankton photophysiology in the Sea of Okhotsk during late summer
Author(s) -
Isada Tomonori,
Iida Takahiro,
Liu Hongbin,
Saitoh SeiIchi,
Nishioka Jun,
Nakatsuka Takeshi,
Suzuki Koji
Publication year - 2013
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/jgrc.20159
Subject(s) - phytoplankton , photosynthesis , environmental science , chlorophyll a , oceanography , photic zone , photosynthetically active radiation , pelagic zone , nitrate , nutrient , biology , botany , geology , ecology
We investigated the photosynthetic parameters of phytoplankton in the Sea of Okhotsk during the late summer of 2006 to characterize their spatiotemporal variability and to test the hypothesis that discharge from the Amur River could influence the algal photophysiology. The highest maximum quantum yield of carbon fixation in photosynthesis (Φ cmax ; 0.098 mol C mol photons ‐1 ) was found near the Amur River mouth, where nitrate was depleted. However, none of the photosynthetic parameters, including primary productivity ( PP ) at the surface, were correlated with temperature, daily photosynthetically available radiation (PAR), or ambient nutrient concentrations. Variations in Φ cmax depended on the variations in not only the mean chlorophyll a specific absorption coefficient of phytoplankton ( ā * ph ) but also the slope index of the absorption coefficient of phytoplankton ( a ph slope), an indicator for the ratio of nonphotosynthetic carotenoids to photosynthetic carotenoids. These results indicated that the phytoplankton assemblages acclimated to the ambient light conditions by regulating their cellular pigments. Additionally, ā * ph and euphotic depth ( Z eu ) were significantly correlated with salinity, suggesting that photoacclimation of the phytoplankton assemblages observed in this study could be induced by discharge of Amur River. Because spatiotemporal variations in PP were concomitant with Φ cmax , ā * ph , and the chlorophyll a concentration, PP models based on inherent optical property (IOP) were suitable for estimating PP in the Sea of Okhotsk. This study is the first to investigate the factors controlling phytoplankton photophysiology in the Sea of Okhotsk, one of the highest primary production areas in the world.