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

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Abstract
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.