Arctic marine microbes are affected by environmental changes that may ultimately influence their functions in carbon cycling. Here, we investigated in concert the structure and enzymatic activities of pelagic, particle-associated and benthic bacterial communities in the central Arctic Ocean, and used these data to evaluate microbial structure–function relationships. Our findings showed influences of hydrographic conditions and particle association on community composition, and sharp pelagic-benthic contrasts. In addition to community compositional differences, regional and depth-related patterns in enzymatic activities were observed. Peptide hydrolysis rates were highest in surface waters, especially at ice-free and first year ice-covered regions, and decreased with depth. While the range of hydrolysed polysaccharides showed varying geographic patterns, particles often showed a wider spectrum of polysaccharide hydrolase activities. Summed benthic peptidase rates differed across stations but showed similar proportions of individual enzyme activities. Analysing for potential linkages between structure and function after subtracting the effect of environmental conditions revealed no direct link, indicating functional redundancy to carry out peptide hydrolysis among pelagic microbes. Thus, while community composition and activities are influenced by environmental conditions, bacterial functional redundancy suggests that compositional shifts – in response to the changing Arctic – may have complex and less predictable functional consequences than previously anticipated
