Distribution of living radiolarians in spring in the South China Sea and its responses to environmental factors

Using a planktonic net(62-?m mesh) and a Rose-Bengal staining method, we studied the spatial distribution of living radiolarians in spring along two sections of the South China Sea(SCS) in spring and discussed the responses of living radiolarian distribution to tropical environmental factors. Generally, the highest abundance of living radiolarians occurred at the depth range of 25–75 m, where the chlorophyll-a maximum and the highest primary productivity were. In contrast, the maximum living abundance occurred in the top 25 m in cold eddies in the open seas and the abundance decreased with depth. We found that the inhibition effect of changing salinity(due to runoffs) on living radiolarians was much stronger than the promotion effect of mesoscale cold eddies. We observed that large variation of temperature was unfavorable for living radiolarians. The dominant species composition consisted of tropical-subtropical warm species. We identified some indicator species for tropical environments. Living Didymocyrtis tetrathalamus tetrathalamus could be an indicator for tropical surface water or mixed-layer water, and even for tropical oligotrophic water. Living Tetrapyle octacantha could be used to indicate tropical thermocline and eutrophic environment. Living Acanthodesmia vinculata could indicate tropical surface and subsurface waters. T. octacantha and A. vinculata should only be used as indicators for upwelling in the open seas, i.e., far away from river mouths. Living Siphonosphaera polysiphonia preferred to form colonies, which might be related to the effect of warm eddies. Living Cyrtopera laguncula and living Cornutella profunda occurred in the tropical upper layer, even in the surface layer, which suggests that they should not be used as indicators for intermediate and deep waters.

Radiolarian biostratigraphy in the Southern Bering Sea since Pliocene

Detailed radiolarian biostratigraphy in the Plio-Pleistocene was analyzed by using samples from IODP Site U1340 that was drilled to a core depth of 604 m in the southern Bering Sea.A total of 227 species belonging to 102 genera were identified.Based on the distributions of the radiolarian index species at Site U1340,five radiolarian zones since the Pliocene were established in the southern Bering Sea for the first time,and 25 radiolarian bioevents were recognized.Their ages were estimated on the basis of the age-depth plot that was constructed by the synthetical datum of the effective biostratigraphic and magnetostratigraphic events.The radiolarian zones at Site U1340 were systematically compared with those in its adjacent regions since the late Early Pliocene,which further improved and interpreted the biostratigraphic datum as well as their correlations in the middle-high latitude of the North Pacific.In addition,the comparative results of radiolarian zones show that Botryostrobus aquilonaris Zone emended in this paper is equivalent to the upper part of the same zone defined by Hays,1970,and Druppatractus irregularis-Dorydruppa bensoni Zone as well as Spongodiscus sp.Zone,newly proposed in this paper,are well correlated with Cycladophora sakaii Zone and Stylatractus universus Zone in the subarctic North Pacific,respectively.