Bacterioplankton and picophytoplankton abundance, biomass, and distribution in the Western Canada Basin during summer 2008

During the R/V Xuelong Arctic cruise in summer 2008, we investigated bacterioplankton and picophytoplankton abundance, biomass, spatial distribution, and these variables' relationship with environmental variables in the Western Canada Basin. The bacterioplankton and picophytoplankton abundances in the upper 200 m of the water column were 0.17–8.38×105 cells ml−1 and 0.01–17.71×106 cells L−1, respectively. The average integrated bacterioplankton and picophytoplankton biomasses in the upper 100 m of the water column were 413.3 and 118.8 mg C m−2, respectively. Microbial biomass was comparable with previous reports and distributed mainly in the upper 50 m of the water column.The bacterioplankton and picophytoplankton biomasses decreased with increasing latitude. Compared with eastern transects, which were strongly influenced by an influx of Pacific water, the western transects had relatively low temperature, high salinity, high nutrients, and high biomass. No significant relationships were detected between assemblages and water temperature or salinity, expect for one between bacterioplankton and salinity in the latitudinal transects. However, a significant negative correlation between picophytoplankton and nutrients and a significant positive correlation between bacterioplankton and picophytoplankton were observed. We suggest that this was mainly caused by the relatively low picophytoplankton biomass, occurrence of heavy stratification (nutricline), and the subsurface chlorophyll maxima (SCM) in study area. Heavy melting of sea ice in summer increases the stratification, which obstructs nutrient supplementation from deep waters, and this might increase the role of microbial assemblages in the upper water column in the Arctic basin area.