Temporal and spatial flux changes of radiolarians in the northwestern Pacific Ocean during 1997–2000

In order to examine the radiolarian fluxes and evaluate their relationship to the physical and biological environments, time-series sediment traps were deployed at three stations (Stations 50N, KNOT, and 40N) in the northwestern North Pacific from 1997 to 2000. Station 50N (50°N, 165°E, 3260 m) is located in the center of Western Subarctic Gyre (WSAG); Station KNOT (44°N, 155°E, 2957 m) is located toward the margin of WSAG; and Station 40N (40°N, 165°E, 2986 m) is located in the Subarctic Boundary. Total radiolaria fluxes at Station 40N showed higher values than those at the other two stations, and were mainly attributed to the influence of relatively high-temperature and high-salinity subtropical gyre waters. Correlation coefficients between total mass fluxes (mainly composed of diatoms) and radiolarian fluxes at three stations were relatively low. This is primarily because of the wide vertical distribution of radiolarians and various trophic patterns corresponding to their niche. Radiolarian species were classified according to their geographic water mass and vertical distributions based on previous studies using sediment samples. As a result, seasonal changes of radiolarian fluxes in each water mass showed patterns corresponding to particular controlling factors such as physical hydrography and food conditions. Among these patterns, temporal changes in radiolarian taxonomic composition in the upper layer (0–100 m) seemed to reflect well the sea-surface temperature anomaly (SSTA) changes, affected by El Niño and La Niña events, at Station 40N. Therefore, radiolarian assemblages can be used to reconstruct past SSTA changes and to understand the past El Niño and La Niña teleconnection in the Kuroshio-Oyashio Extension region.