Fifteen year time-series of radiolarian fluxes and environmental conditions in the Bering Sea and the central subarctic Pacific, 1990–2005

Abstract

In order to examine radiolarian fluxes and evaluate their relationships to environmental conditions, a fifteen year long time-series observation on radiolarian fluxes was conducted using sediment trap materials collected at the Bering Sea Station AB (53.5°N, 177°W) and the central subarctic Pacific Station SA (49°N, 174°W) during 1990–2005. Encountered radiolarian assemblages include 124 taxa at Station AB and 110 taxa at Station SA. In general, total radiolarian fluxes of the coarse fraction (63μm−1mm) at Station AB (mean: 8.7×103shellsm−2d−1) were greater than those observed at Station SA (mean: 6.5×103shellsm−2d−1), mainly due to the differences in physico-chemical conditions (i.e., mixed layer depth, surface circulation, nutrient concentrations, etc.). Out of >110 taxa, thirty-eight abundant radiolarian taxa were chosen for enumeration and further statistical treatment, including the taxa with >1% annual mean occurrence. As abundant radiolarian species display variable flux patterns during the study period, an R-mode cluster analysis was used to identify eight clusters at Station AB, and eleven clusters at Station SA. Marked changes in the relative contribution of each of the clusters to the total radiolarian assemblages are apparent. Notably high flux maxima of total radiolarians were observed around 1990, 1995, 2000, 2003 and 2004. The observed inter-annual variations in the faunal assemblages in the Bering Sea and the central subarctic Pacific were related to large scale climatic shift such as the Arctic Oscillation (AO). The negative correlation between the radiolarian assemblages including surface to subsurface dwellers and the AO Index may suggest a significant influence by the intensity of surface water mixing and water mass exchanges.