Oceanographic conditions influencing silicoflagellate flux assemblages in the Bering Sea and subarctic Pacific Ocean during 1990–1994

Abstract

To determine the influence of oceanographic conditions on silicoflagellate assemblages, sinking fluxes and composition of silicoflagellates were studied from August 1990 to July 1994 at two long-term monitoring sites: Station AB in the Bering Sea (53.5°N, 177°W) and Station SA in the northern subarctic Pacific Ocean (49°N, 174°W). Total silicoflagellate flux (TSF) increased annually in spring and/or fall at both stations. Interannual variation in the timing of the spring TSF increase was probably related to the depth of the mixed layer during winter and to the starting time of stratification. Composition of the silicoflagellate assemblage differed between the two stations. The assemblage at Station AB was composed almost entirely of Distephanus speculum, similar to the assemblage in the Western Subarctic Gyre. The temperate-subtropical genus, Dictyocha, occurred only sporadically. The assemblage at Station SA was more variable, reflecting changes in the climate–ocean relationships indicated by the Pacific Decadal Oscillation Index (PDOI). Dictyocha increased during the positive phase of the PDOI, due to intensification of the Alaskan Stream. In colder water, Distephanus with heptagonal skeletons were more abundant than hexagonal Distephanus. These results will be useful for paleoceanography studies of the area.