Primary Productivity Studies in February-March in the Northwestern Pacific off Japan

Abstract

Primary productivity studies were carried out in February and March 1966 at 15 stations in the northwestern Pacific off Japan. Estimated depth of the photosynthetic zone (or euphotic zone) ranged from 48 to 80 m. Chlorophyll a concentration in water varied from 0.026 to 0.621 mg/m³, of which small values less than 0.1mg/m³ were usually obtained in deeper layers far below the euphotic zone. Total amount of chlorophyll a in the euphotic zone was 8.2-28.8mg/m². The vertical chlorophyll profiles indicated no distinct pattern, and a considerable amount of chlorophyll with high photosynthetic ability was found in the deeper layers. Photosynthetic rates of phytoplankton measured at 14 klux ranged from 0.024 to 23.0 mgC/mg. chl. a/h, normally from 1 to 8mgC/mg. chl. a/h. At two stations the photosynthetic rates of phytoplankton from various depths were measured at various temperatures and compared with each other. The estimated primary gross production is 0.3-0.8gC/m²/day, indicating that a fairly high level of primary productivity is maintained in the present area in February and March. Annual gross production was estimated to be 100-150gC/m² in the Kuroshio area and 200-250gC/m² in the Oyashio area.