Bacterial communities along stratified water columns at the Chukchi Borderland in the western Arctic Ocean

An expedition of the IBRV ARAON took place in the Arctic Ocean during the summer of 2010. To investigate the hydrographic features and bacterial variations in water columns, we categorized 16 water samples collected from distinct water masses at the Chukchi Borderland in the western Arctic Ocean. Bacterial diversity, relative abundance, and community composition were determined based on a pyrosequencing approach, and their relationship with water mass properties was considered. Alphaproteobacteria (43.2%), Gammaproteobacteria (16.7%), Flavobacteria (13.7%), and Deltaproteobacteria (12.0%) were the most common bacteria found in all samples, and the relative abundance of these predominant taxa represent the population dynamics of bacterial communities in different water masses (from the euphotic to the sub-euphotic zone) in the Arctic Ocean. Furthermore, the relative abundance of Alphaproteobacteria and its subgroup, SAR11 group I, were significantly related to depth change in water columns, suggesting that environmental heterogeneity caused by changes in depth may play an important role in bacterial population dynamics. In this study, bacterial communities in the Arctic Ocean exhibit biogeographic patterns according to the type of water mass. The halocline layer between the Pacific winter water and Atlantic water exhibits a variation in the composition of bacterial communities, which may be influenced by mixing of Pacific winter water and Atlantic water.