Radiolarian Assemblages In The Surface Sediments Of The Western North Pacifc And Their Ecological Indication Of Environmental Conditions

Radiolarians,being important subject of marine micropaleontology,are unicellular marine planktonic protists that have wide distribution and high diversity.This study was based on the sea surface sediments collected from the northwest Pacific,including the shallow-water shelf area of the Yellow Sea and the East China Sea,the deep-water marginal seas of the northwest Pacific,and the western equatorial Pacific.Combined with the annual average data derived from online environmental database,the radiolarians in the study area were investigated to explore the relationships between radiolarian assemblages in the surface sediments and environmental conditions.The main results are as follows:1.The radiolarian assemblages of 59 surface sediment samples were analyzed in the shelf area of the marginal seas in the northwest Pacific,including the Yellow Sea and the East China Sea.The derivative branches of the Kuroshio Current had an important influence on the radiolarians composition and distribution pattern in the study area.The abundance of radiolarians in the Yellow Sea was quite low,and no radiolarians were detected in 15 stations of the Yellow Sea.Based on the results of cluster analysis,radiolarians in the shelf area of the East China Sea can be divided into three regional groups: the East China Sea north region group,the East China Sea middle region group,and the East China Sea south region group.The results of the redundancy analysis indicated that sea surface temperature,sea surface salinity and silt percentage were the main sedimental and hydrological variables that explained the structure of radiolarian assemblages(p < 0.05).2.In the marginal seas of the northwest Pacific,including the South China Sea,the East China Sea,and the Philippine Sea,radiolarians of 45 surface sediment samples were examined to explore the correlations between radiolarian assemblages and the surface hydrography.According to the results of Q-mode cluster analysis,radiolarian assemblages in the study region can be divided into four major assemblages,i.e.the North Equatorial Current assemblage,the North Equatorial Current Bifurcation assemblage,the Kuroshio-South China Sea assemblage,and the Kuroshio-East China Sea assemblage.Winter sea surface temperature,winter sea surface salinity and annual silicate concentration were the most important environmental parameters determining the species composition,among which winter sea surface temperature displayed the strongest relation with the radiolarian composition.The remarkable influences of winter sea surface temperature and winter sea surface salinity indicated that the seasonal variation of the North Equatorial Current-Kuroshio Current system had a great influence on the abundance and distribution pattern of the radiolarians.3.In the equatorial western Pacific,92 surface sediment samples were collected to study radiolarians in the Western Pacific Warm Pool.The results of Q-mode cluster analysis showed that three main radiolarian faunas were obtained: the north fauna,the south fauna,and the Ethmodiscus-rich fauna.The co-existences of excessively abundant radiolarian skeletons and diatom fragments of Ethmodiscus were observed in the Ethmodiscus-rich fauna.Net primary production,sea surface temperature,and phosphate,were important environmental variables that explained the radiolarian composition in the western equatorial Pacific with oligotrophic warm conditions.Main innovation points of this work are as follows: in the surface sediments of the northwest Pacific,based on rigorous statistical methods and detailed environmental databases,the influences of the derivative branches of the Kuroshio Current on the distribution patterns of radiolarians were discussed for the first time in the shallow-water shelf area of the Yellow Sea and the East China Sea.The relationships between radiolarians composition and the North Equatorial Current-Kuroshio Current system were firstly explained in the marginal seas of the northwest Pacific.It is first presented that primary production was the crucial determinant of radiolarian composition in the western Western Pacific Warm Pool.