Abstract
Time-series sediment traps were deployed in the subtropical (Station WCT-1) and transitional (Station WCT-2) areas in the northwestern Pacific for one year from 1997 to 1998. Radiolarians were counted and categorized into families to study seasonal and regional changes in radiolarian productivity and faunal composition. The polycystine annual mean flux was 10,406 shells m−2day−1 at WCT-2, which was higher than that at WCT-1 (3,901 shells m−2day−1). The phaeodarian annual mean flux was low (1,583 shells m−2day−1) at WCT-2 and extremely low (7 shells m−2day−1) at WCT-1. These indicate that radiolarian productivity is generally higher in the transitional area than in the subtropical area. Temporal fluxes of polycystines at the transitional site showed variations associated with high flux during the spring and low flux during the summer, while polycystine fluxes at the subtropical site did not show apparent seasonal variations. Family-level percentage composition and statistical testing did not show significant seasonal changes at either site. This seasonal stability in faunal composition was a quite unexpected result, since there were seasonal changes in the sea surface temperature in the studied areas. This stability indicates lack of response of polycystine radiolarians to oceanic seasonality in the subtropical and transitional regions. There was a difference in the annual polycystine composition between the two sites, probably corresponding to differences in oceanic water masses. Comparing the polycystine annual composition and flux between the two sites, three families, Collosphaeridae, Coccodiscidae and Pterocorythidae, are more abundant elements in the subtropical region, whereas dominance of Plagiacanthidae characterizes the transitional region.
