TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 54 (No. 5), pp. 545-552, 1998

Photosynthesis-Irradiance Relationship of Phytoplankton and Primary Production in the Vicinity of Kuroshio Warm Core Ring in Spring

Ken Furuya1, Osamu Hasegawa1, Takashi Yoshikawa1 and Satoru Taguchi2

1Department of Aquatic Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan
2Faculty of Engineering, Soka University, Tangi, Hachioji, Tokyo 192-0003, Japan

(Received 31 March 1998; in revised form 18 June 1998; accepted 22 June 1998)

Abstract: The light-saturated maximum value (PBmax) and initial slope (a) of the photosynthesis-irradiance (P-E) curve were examined in a warm streamer, a cold streamer and a warm core ring off the Sanriku area in the subarctic western North Pacific Ocean during an ADEOS/OCTS Sanriku field campaign in early May 1997. Both PBmax and a were within the ranges of temperate populations. A regional difference was apparent in PBmax: populations in the warm streamer tended to show higher value ranging between 1.92 and 4.74 mgC (mgChl a)-1h-1 than those in the cold streamer and the warm core ring (1.35-2.87 mgC (mgChl a)-1h-1). A depth variation was also observed in a in both the warm streamer and the warm core ring: shallow populations tended to have lower a than deep populations. The depth variations in both PBmax and a resulted in a lower light intensity of the light saturation in a deeper population than that of a shallower one. These depth-related variations in the P-E parameters were likely a manifestation of "shade-adaptation" of photosynthesis. Photoinhibition was not observed over in situ surface light intensity varying below ca 1600 mmol photon m-2s-1. Water-column primary productivity was bio-optically estimated to be 233 to 949 mgC m-2d-1using vertical distributions of the P-E parameters, chlorophyll a, phytoplankton light absorption and underwater irradiance. Applicability of surface data sets for estimation of water-column productivity is discussed.

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