The vertical distribution of radiolarians was investigated by using a closing-type net with 63 μm mesh in the Okhotsk Sea (Station NU'2, near Bussol' Strait) down to 1000 m depth and in the northwestern North Pacific (Oyashio region, Station X) down to 500 m depth. Both stations were sampled in September 1995. Radiolarian standing stocks were high between 50 and 200 m at both stations, and generally decreased with depth. The depth-integrated living total radiolarian standing stock from 0 to 500 m at Station NU'2 was more than three times higher than that at Station X. The maximum standing stocks of polycystine radiolarians occurred in the 50-100 m depth interval, but there were also significant abundance peaks of phaeodarian radiolarians in the 100-200 m interval at both stations. The radiolarian production is likely to be associated with not only phytoplankton production in upper waters, but also with microbial production in intermediate waters. A total of 79 taxa were encountered: 25 Spumellaria, 41 Nassellaria, and 13 Phaeodaria. Five radiolarian groups were obtained based on R-mode cluster analysis: Group A: lower intermediate water dwellers (300-1000 m), Group B: taxa with different distributions in the Okhotsk Sea (300-1000 m) and in the Oyashio region (0-100 m), Group C: upper intermediate water dwellers (200-500 m), Group D: surface-subsurface water dwellers (0-200 m), and Group E: taxa with pronounced 200 m.
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