Antarctica Ocean that is sensitive to climatic influence plays a profound role in regulating global carbon cycle. Amundsen Sea Polynya (ASP) in western Antarctic is undergoing rapid response to climate change and is among the most productive coastal polynyas with the highest primary productivity (PP) in water column. Despite of high PP in the water column, relatively low organic carbon (OC) contents were detected in the ASP sediments, and OC oxidation rate was reported higher that the non-polynyas sediments. We collected sediment core samples up to ~ 15 cm depth at 1-2 cm interval within polynyas (Stations 10 & 17), surrounding ice shelf (Station 19) and sea-ice zone (Station 83) to elucidate microbial communities related to nutrient cycles including carbon and nitrogen in the ASP sediment.
Unconstrained ordination (NMDS) showed very distinct depth profile of microbial community compositions as well as sediment geochemical properties per each station. Entire microbial communities, archaeal communities and bacterial communities were all very distinct (P < 0.001 by PERMANOVA and ANOSIM). NMDS ordination plot also indicated clear vertical representation of sediment microbial communities per station as well as greater similarity among microbial communities of surface samples than deeper samples. Redundancy analysis (RDA) generated statistical models between microbial communities and geochemical properties at each station. Exceptional predominant Planctomycetes in the ASP polynya sediments (up to 68% of the total 16S rRNA gene sequences) were associated with particulate organic carbon (POC) content and nitrate-nitrite (NO3--NO2-), which may suggest that members of Planctomycetes are an important carbon oxidizing microbial group in the polynya sediments. Additionally, Granger causality test identified POC and NO3--NO2- had significant casual relationship with Planctomycetes. Whereas Thaumarchaeota, that is a dominant microbial phylum in the extremely oligotrophic non-polynyas sediments (up to 67% of the total 16S rRNA gene sequences), is considered as a significant chemolithotroph. Overall statistical analyses showed that microbial communities in the sediments of polynyas and non-polynyas could be clearly distinguished by correlations with environmental parameters related to organic carbon oxidation process. Our results imply that changes of vertical OC fluxes by climate change will lead to changes of Antarctic benthic microbial communities, furthermore it will affect to the biogeochemical cycles.