Radiolarians from the western North Pacific Ocean: a latitudinal study of their distributions and fluxes

Abstract

Free-drifting sediment traps were deployed individually to make day-long collections of settling particulates at seven stations in the western North Pacific Ocean. Samples were taken between 70 and 2200 m along a longitudinal section between 16 and 50°N latitude. Radiolarian skeletons were mechanically isolated under a reflected light microscope. Subsequent gravimetrically determined radiolarian silica fluxes range from 0 to 4.43 mg m-2 day-1 and show significant and consistent increases at all depths with increasing latitude. Radiolarians also were counted and categorized into each of their three suborders: Nassellaria, Spumellaria and Phaeodaria. An inverse relationship is evident between the proportions of phaeodarians and polycystines (nassellarians plus spumellarians), with the phaeodarins increasing relative to the polycystines with increasing latitude. Although the absolute numbers of phaeodarians in the northern samples may not exceed the numbers of their polycystine counterparts in the south, the comparatively large and heavy phaeodarian skeletons contribute significantly to the increased silica fluxes noted in the north. This contribution, combined with a high susceptibility to dissolution, may signify that phaeodarians are important for the recycling of silica in the northern North Pacific. Spectrophotometric analyses of seven phaeodarian species and one species of colonial spumellarian show that silica constituted between 86 and 99% of the phaeodarians' skeletons and 75% of the spumellarians' skeletons. Non-radiolarian amorphous silica was mobilized by a selective chemical leach and quantified spectrophotometrically. Significant and consistent increases in the flux of this diatomaceous silica fraction (ranging from 0.14 to 47.0 mg m-2 day-1) are noted with increasing latitude. In almost all cases, diatomaceous silica fluxes are greater than those of the radiolarians. With the exception of some anomalously high percentages, radiolarian-derived silica ranges from 0 (only one sample) to 24% of the total amorphous silica flux. © 1990.