Radiolarian flux at an IMAGES site at the western margin of the subarctic Pacific and its seasonal relationship to the Oyashio Cold and Tsugaru Warm currents

Seasonal changes of radiolarian flux in the far western area of the Western Subarctic Gyre in the Pacific Ocean were examined based on samples from a sediment-trap experiment deployed at a site off the northern Honshu Island of Japan from June 2002 to May 2003. Warm and neritic water species associated with the Tsugaru Warm Current (TGC), originating from the Japan Sea, were dominant, while the cold-water species associated with the Oyashio Cold Current were relatively few, in spite of the location of the site in the subarctic province. R-mode cluster analysis was used to divide species-specific flux patterns into 5 groups of fauna associated with: (1) the TGC forerunner in June 2002, (2) the TGC main flow from September to November 2002, (3) the neritic water in December 2002, (4) the Oyashio Cold Current in May 2003, and (5) surface productivity in the spring of 2002/2003 together with the TGC in summer 2002.