[Distribution pattern of microphytoplankton in the Bering Sea during the summer of 2010]

Based on the analysis of 70 water samples collected by the Chinese icebreaker Xuelong in the areas of 52 degrees 42.29'-65 degrees 30.23' N and 169 degrees 20.85' E-179 degrees 30.37' W in the Bering Sea during the Chinese Arctic Research Expedition on July 10-19, 2010, a total of 143 phytoplankton species were identified, including 95 diatom species belonging to 37 genera, 44 dinoflagellate species belonging to 15 genera, 2 Chlorophyta species belonging to 2 genera, 1 Euglenophyta belonging to 1 genus, and 1 Chrysophyta species belonging to 1 genus. The cluster analysis revealed that the phytoplankton in the study areas could be divided as oceanic and shallow water groups. The oceanic group found in the western North Pacific Ocean and the Bering Basin was dominated by the boreal oceanic species such as Neodenticula seminae and Chaetoceros atlanticus and the cosmopolitan species such as Thalassionema nitzschioides and Chaetoceros compressus, with the characteristics of low abundance and high evenness of diversified species. The shallow water group found in the continental shelf and slope of Bering Sea was mostly composed of the pan-arctic neritic species such as Thalassiosira nordenskioldi and Chaetoceros furcellatus and the cosmopolitan species such as Leptocylindrus danicus and Chaetoceros curvisetus, with the characteristics of low species diversity and evenness index due to the high abundance in certain species. The phytoplankton abundance in the surface water layer distributed unevenly among the stations, ranging from 950 to 192400 cells x L(-1) and with an average of 58722 cells x L(-1). Horizontally, the abundance distribution trend was decreased in the order of the Bering Sea shelf, the Bering Sea slope, the Bering Sea basin, and the western North Pacific Ocean. Vertically, the abundance was lower in surface layer and maximized in the thermocline, suggesting that the phytoplankton abundance in vertical distribution varied with the regional thermocline.