Radiolarian Flux Research Articles

Fluxes of living radiolarians and their skeletons along a northeast Pacific transect from coastal upwelling to open ocean waters

Sinking fluxes of living polycystine and phaeodarian radiolarians and their intact empty skeletons were measured from surface waters to 2000 m using free-floating particle interceptor traps at three sites ranging from highly productive coastal upwelling to oligotrophic central gyre waters in the northeast Pacific Ocean. Total radiolarian fluxes and living pheodarian fluxes were generally highest at the coastal site throughout the water column. There was no consistent site-specific pattern for fluxes of living polycystines, polycystine empty skeletons, and phaeodarian empty skeletons. Living phaeodarians were the only group that showed the same rank order of sites with respect to flux at both the base of the euphotic zone and at 2000 m. Thus different short-term processes occurring in the water column (e.g. destructive and non-destructive predation and midwater addition of living radiolarians) altered radiolarian fluxes. Neither radiolarian fluxes at the base of the euphotic zone nor fluxes at 2000 m showed a simple correspondence with primary production, indicating that short-term measurements did not reveal long-term patterns. At most depths at all sites, fluxes of living, skeleton-bearing phaeodarians outnumbered fluxes of empty phaeodarian skeletons. In contrast, at most depths at all sites, fluxes of empty polycystine skeletons outnumbered fluxes of living, skeleton-bearing polycystines. Relatively large, living skeleton-less phaeodarians were the numerically dominant radiolarian in the uppermost traps at the oceanic and coastal sites. These phaeodarians agglutinate siliceous skeletons of other plankton and contributed 5% of the silicoflagellate flux, 16% of the polycystine flux, and 2% of the centric diatom flux at these depths. The resemblance of skeleton-less phaeodarians to fecal pellets may cause them to be misidentified as fecal material when trap contents are dried for processing.

El Niño in Santa Barbara Basin: Diatom, radiolarian and foraminiferan responses to the “1983 El Niño” event

Santa Barbara Basin box cores collected in August of 1985 were sub-sampled and processed in search of microfossil evidence of the “1983 El Niño”. Microplankton and microbenthos indicate the presence of that El Niño bounded by non-El Niño conditions. Specifically the event is recognized by: an increase in diatom diversity, and the presence of several warm water taxa (e.g., Coscinodiscus plicatoides, Hemidiscus cuneiformis, Nitzschia kolaczekii, Pseudoeunotia doliolus, Thalassiosira lineata, Thalassiosira nodulolineata); an increase in polycystine radiolarian flux, and the presence of the eastern tropical Pacific species Spongaster pentas; an increase in the diversity of planktonic foraminifera, and the occurrence of the warm water species Globoturborotalita rubescens. There is also evidence for an oxygenation of the basin during the 1983 El Niño as suggested by the increase in the abundance of the benthic foraminifera Bolivina vaughani and by the decrease in the preservation of phaeodarian radiolarian spines which are best preserved under anoxic conditions. A new onboard procedure for sampling of box cores and freezing of subcores is described.

Radiolarian flux and seasonality: Climatic and El Nino response in the subarctic Pacific, 1982–1984

Seasonal flux distributions of numerically dominant radiolarian species were studied using Particle Flux (PARFLUX) 1982‐1984 high‐resolution, time series sediment trap samples recovered from the eastern subarctic Pacific Station Papa (water depth: 4,200 m) in the Gulf of Alaska. Flux patterns of several major radiolarian species showed more temporally restricted seasonal maxima than those of siliceous phytoplankton groups, suggesting more confined seasonal flux signals than those of siliceous phytoplankton. These species showed significant flux reduction from year 1 to year 2 associated with an El Nino event, as did siliceous phytoplankton. On the other hand, fluxes of three major radiolarian subgroups and some other radiolarian species showed little change in timing or amplitude of seasonal flux patterns from year 1 to year 2 except for the presence/absence of summer maxima. This type of radiolarian flux signal is a reflection of recurring large changes in seasonal environmental conditions and, to a lesser extent, of response to the deviations of interannual amplitudes. Two generic pairs of radiolarian fluxes showed temporal niches which may have evolved due to dietary preferences. Biological competition may take place among species from different genera but not within a genus. Fluxes of juvenile and adult forms of two Pterocanium species were compared in order to understand their reproductive cycles. Reproduction appears to occur sporadically throughout most of the year and nonsynchronously among population members. The longevity of Pterocanium species was estimated to be several weeks. There are two separate radiolarian sinking processes; accelerated sinking via aggregates and discrete sinking. Smaller‐sized species tend to sink faster due to aggregate incorporation than larger ones. Radiolarians are considered a good measure of productivity. The contribution of phaeodarians can be as high as 10% or more in total opal flux. Large‐sized phaeodarian specimens are involved in this high percentage and play a significant role in silica redistribution within the water column since they dissolve quickly.

Radiolarian and silicoflagellate response to oceanographic changes associated with the 1983 El Niño

Strong seasonal signals in fluxes and composition of siliceous microfossils have been recorded in sediment traps from two sites in the equatorial Pacific, deployed from December 1982 to March 1984. During the early part of the sampling period, the 1982–83 El Nino event had a profound effect on the radiolaria and silico-flagellates within these two areas. During the El Nino, the radio-larian trap assemblages at Site C (1° N, 139° W) most resembled faunal assemblages in western equatorial Pacific sediments, whereas the trap assemblages resembled equatorial divergence sediments in the latter half of the period. At Site S (11° N, 140° W), the radiolaria and silicoflagellate species can be correlated with organic carbon fluxes. In general, silicoflagellate shell fluxes are correlated to total opal fluxes where radiolarian fluxes do not exhibit this relationship. Approximately 20–25% of the total count of radiolaria in traps are not present in underlying sediments with a significant loss of the weakly silicified forms. However, the comparison of trap sample assemblages with underlying sediments reported here shows that dissolution does not alter relative abundances of the fossil species used in palaeoclimatic reconstructions. A significant difference is observed between the silicoflagellate trap assemblage and the underlying sediment assemblage.