High bacterial production, uptake and concentrations of dissolved organic matter in the Central Arctic Ocean

Recent studies have indicated that biological activity is higher in the central Arctic Ocean than once thought. To assess the contribution of heterotrophic processes, we examined bacterial production and the uptake of specific components of the dissolved organic matter (DOM) pool during a trans-Arctic expedition. Bacterial production generally covaried with phytoplankton production and bacterial numbers; the highest values of all three parameters were in the more open waters of the Chukchi Sea and they were generally lower at the other stations which were covered by ice. Although bacterial production correlated with phytoplankton production, the ratio of bacterial to phytoplankton production (BP:PP) varied substantially. It was lowest (BP:PP<0.1) at stations with some open water and highest at ice-covered stations, sometimes exceeding 1, depending on how bacterial production was measured. These high BP:PP ratios imply that bacterial respiration and DOM fluxes are large. This bacterial activity could be accounted for by the uptake of dissolved free amino acids (DFAA) and glucose. Uptake of these DOM components was high because of rapid turnover and high concentrations, especially of DFAA. Concentrations of dissolved combined neutral carbohydrates (e.g. polysaccharides) were often also high compared to other environments. These data indicate that heterotrophic bacteria and the rest of the microbial loop are large and active components of the biological community in the Arctic Ocean in spite of perennially low temperatures.