Characterization of radiolarian assemblages in the surface sediments of the Antarctic Ocean

The purpose of this study is to synthesize the radiolarian assemblages in the sediment samples south of 60°S in the Southern Ocean in terms of their taxonomic composition and paleoceanographic distribution. The radiolarian assemblages were examined from the core top sediment samples at 146 sites in six areas around Antarctica: the Victoria Land/Ross Sea area, the Wilkes Land sea area, the Enderby Land sea area, the Queen Maud Land/Weddell Sea area, the sea area surrounding the Antarctic Peninsula, and the Amundsen/Bellingshausen Sea area. All of the examined samples are correlated with the Antarctissa denticulata Zone (Omega Zone) except sample PC401 from the Wilkes Land sea area, which is correlated with the Stylatractus universus Zone (Psi Zone). The radiolarian assemblages are composed of both typical Antarctic pelagic and coastal assemblages. The coastal radiolarian assemblage is well defined in the Victoria Land/Ross Sea area and the sea area surrounding the Antarctic Peninsula; the latter area is distinguished from the other sea areas in the Antarctic Ocean by the fact that the species are highly diversified and found in samples deeper than 3000 m. The peri-Antarctic Peninsula area has the widest distribution of the main component species of the Antarctic radiolarian coastal assemblage, including Rhizoplegma boreale (Cleve) and Phormacantha hystrix (Cleve)/Plectacantha oikiskos (Jorgensen) group in the Southern Ocean, and the radiolarian assemblages in this area were intermingled by various ages or environments, as previously reported (Nishimura et al., 1997). It is found that the relative abundance of spumellarians tends to be greater than that of nassellarians in the typical Antarctic pelagic assemblage, whereas the relative abundance of nassellarians is greater than that of spumellarians in the coastal water assemblage.