Bacterial communities in sediments of the Caiwei Seamount, a typical guyot located in the northwest Pacific Ocean, were investigated. A total of 727,879 16S ribosomal RNA gene sequences were retrieved from eight sediment samples of the top (mean depth = 1,407 m) and the base (mean depth = 5,525 m) of the guyot through pyrosequencing of V6 hypervariable region and clustered into 32,844 operational taxonomic units. Abundant‐weighted UniFrac metric partitioned bacterial assemblies into two categories (the top community and the base community) by principal coordinates analysis, consisting with the grouping of sampling stations by environmental variables. Differences in depth and physicochemical properties of the surrounding environment (e.g., concentrations of dissolved oxygen and geochemical elements) between the top and the base of the guyot may cause this partition of bacterial communities, whereas the typical fluid flow around the guyot may potentially contribute to the bacterial dispersal and environmental homogeneity along the same layer, resulting in the similarity of bacterial community structure within the same region (the top or the base). The surface sediment on the top of the guyot harbored the bacterial communities with greater diversity and evenness, represented by Gamma‐ and Deltaproteobacteria involved in sulfur cycling. At the base of the guyot, Gammaproteobacteria related to sulfur‐oxidizing and Chloroflexi functioning in the decomposition of refractory organic matter dominated, suggesting that the redox condition at the interface of the sediment and the water can influence bacteria‐mediated elemental cycling, eventually shaping the physicochemical and geological characteristics of a guyot.

was estimated to account for 2.4-51% (19 ± 14%) and 2.7-59% (24 ± 20%) of bacterial carbon and nitrogen demand, respectively, and putrescine uptake contributed 4.4-100% (27 ± 33%) and 13-293% (80 ± 96%), respectively. Spatial variation in uptake rates indicated that biogeochemical cycling of DFAAs was distinct from that of DFPAs. Redundancy analysis and metagenomes demonstrated that environmental variables and distinction in bacterial assembleges using DFAAs and DFPAs could both affect their dynamics in the northern slope water of the SCS.

We used molecular biomarkers (brassicasterol, dinosterol and C37 alkenones) measured from the surface sediments of the Bering Sea, the Chukchi Sea and the western Arctic Ocean in years of 1999 and 2010 to represent the groups of phytoplankton (diatoms, dinoflagellates and coccolithophores) and reconstruct the phytoplankton composition structure and biomass. The distribution of concentrations of three biomarkers were compatible to previous studies on measured phytoplankton, which showed that the phytoplankton biomass was most abundant in the Chukchi Sea, followed by the Bering Sea and the western Arctic Ocean, and diatoms were the dominant group. It suggests that molecular biomarkers are the suitable indicators of phytoplankton composition, structure and abundance. A record of biomarkers in a sediment core (NB01) collected at the Bering Sea in 2010 presented that the biomass of three phytoplankton groups increased in past 107 years, and their variation patterns were consistent. The synchronous increase of concentrations of phytoplankton biomarkers and cholesterol, a proxy of zooplankton biomass, implied that the primary production increased intensely in the last hundreds of years, corresponding to the trend of sea-ice melting as a result of global warming. Moreover, our results suggested that the combined effect of the anormal interannual changes of the El Niño-Southern Oscillation (ENSO) and the Arctic Oscillations (AO) played a key role in regulating the interannual and decadal variations of phytoplankton biomass and community composition, giving us an insight into the impact of atmospheric circulation on phytoplankton production and carbon flux in the Arctic seas.