Phytoplankton productivity in the western subarctic gyre of the North Pacific in early summer 2006
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We deployed a profiling buoy system incorporating a fast repetition rate fluorometer in the western subarctic Pacific and carried out time-series observations of phytoplankton productivity from 9 June to 15 July 2006. The chlorophyll a (Chl a) biomass integrated over the euphotic layer was as high as 45–50 mg Chl a m−2 in the middle of June and remained in the 30–40 mg Chl a m−2 range during the rest of observation period; day-to-day variation in Chl a biomass was relatively small. The daily net primary productivity integrated over the euphotic layer ranged from 144 to 919 mg C m−2 day−1 and varied greatly, depending more on insolation rather than Chl a biomass. In addition, we found that part of primary production was exported to a 150-m depth within 2 days, indicating that the variations in primary productivity quickly influenced the organic carbon flux from the upper ocean. Our results suggest that the short-term variability in primary productivity is one of the key factors controlling the carbon cycle in the surface ocean in the western subarctic Pacific.
KeywordsOrganic carbon flux Phytoplankton Primary production Profiling buoy system Western subarctic Pacific
We are grateful to the captain and crew of the R/V Mirai for their support during the cruise, to the staff of Marine Works Japan Ltd. and Global Ocean Development Inc. for their on-board analysis and deck work, and to T. Nakamura (Nichiyu Giken Kogyo) for design of an underwater profiling buoy system. We also thank M.C. Honda and H. Kawakami (JAMSTEC) for sediment trap data and their interpretation of this data. The development of the profiling buoy system was supported by the SORST (Solution Oriented Research for Science and Technology) programs of the Japan Science and Technology Agency.
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