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