Abstract: Diatoms collected from the top 1 cm of the surface sediment layer at seven Bering Sea stations during the Fourth Chinese National Arctic Research Expedition (4th CHINARE-Arctic) in 2010 were studied. In total, 101 taxa belonging to 38 genera were found. The species were divided into four groups: eurythermal species, boreal-temperate species, polar species, and sea-ice species. The diatom assemblages at the stations in the southwestern basin area were primarily composed of boreal-temperate species, such as Neodenticula seminae, Thalassiosira trifulta, Rhizosolenia hebetata f. hiemalis, and Actinocyclus curvatulus. The northeastern shelf stations were dominated by polar species, including Fragilariopsis oceanica, Thalassiosira antarctica spora, Thalassiosira nordenskioeldii, and Thalassiosira hyalina. The overall abundance was highest at the basin stations with 3.7 ×106 cells?g-1 of wet sediment, whereas the eastern shelf stations had the lowest abundance of 0.7×106 cells?g-1 of wet sediment (excluding the resting spores of Chaetoceros spp.). The relationship between the distribution of the surface sediment diatom assemblages and the environment is discussed.

Key words: Bering Sea, surface sediment, diatom, species composition, distribution