[BPT06-P03] Living Polycystine Radiolarian Vertical Distribution in Southern Japan
Keywords:Radiolaria, Vertical Distribution, Kuroshio Current
We have investigated samples collected during the cruise KT08-10 of R/V Tansei-maru and cruise KS15-4 R/V Shinsei-maru in spring 2008 and 2015 respectively. During the KT08-10, plankton tow samples could be collected at five stations in the northern East China Sea (ECS), an area influenced by a branch of the KC the so-called Tsushima Warm Current, while during the KS15-04, plankton tows samples could be collected at three stations in the Kyushu Palao-Ridge, an area influenced by the KC. The deepest samples collected in ECS reach 700 m (near the seafloor of this area), while in the Kyushu Palao Ridge, we could collect samples until 3000 m. In both area, the surface water is characterized by subtropical species such as Tetrapyle circularis group and Didymocyrtis tetrathalamus. However, colonial radiolarians seem to be more abundant is the Kyushu Palao Ridge. The sub-surface of the ECS is characterized by high abundances of Eucecryphalus sp. (200-300 m). However, the abundances of this species are much lower in the Kyushu Paleo Ridge, inferring that a Eucecryphalus sp. likely suggest sub-surface water proper to the ECS. For these water depths (200-300 m), Pterocorys carnitatum dominate the assemblage in Kyushu Paleo Ridge. Pterocorys group is generally associated to the sub-surface of the North Pacific Subtropical Gyre, so we may speculate that in Kyushu Paleo Ridge we have some influence of the Subtropical Gyre. Intermediate to deep-water depths are characterized by relatively high abundances of Cycladophora davisiana in the Kyushu Paleo Ridge, while this species is absent in the ECS. Few factors may be considered such as the depth of the seafloor in the ECS, and provincialism.