Seasonal dynamics of bacterial biomass and production in a coastal arctic ecosystem: Franklin Bay, western Canadian Arctic

The Canadian Arctic Shelf Exchange Study (CASES) included the overwintering deployment of a research platform in Franklin Bay (70°N, 126°W) and provided a unique seasonal record of bacterial dynamics in a coastal region of the Arctic Ocean. Our objectives were (1) to relate seasonal bacterial abundance (BA) and production (BP) to physico‐chemical characteristics and (2) to quantify the annual bacterial carbon flux. BA was estimated by epifluorescence microscopy and BP was estimated from 3 H‐leucine and 3 H‐thymidine assays. Mean BA values for the water column ranged from 1.0 (December) to 6.8 × 10 5 cells mL −1 (July). Integral BP varied from 1 (February) to 80 mg C m −2 d −1 (July). During winter‐spring, BP was uncorrelated with chlorophyll a (Chl a ), but these variables were significantly correlated during summer‐autumn ( r s = 0.68, p < 0.001, N = 38), suggesting that BP was subject to bottom‐up control by carbon supply. Integrated BP data showed three distinct periods: fall‐winter, late winter–late spring, and summer. A baseline level of BB and BP was maintained throughout late winter–late spring despite the persistent cold and darkness, with irregular fluctuations that may be related to hydrodynamic events. During this period, BP rates were correlated with colored dissolved organic matter (CDOM) but not Chl a ( r s BP.CDOM∣Chl a = 0.20, p < 0.05, N = 176). Annual BP was estimated as 6 g C m −2 a −1 , implying a total BP of 4.8 × 10 10 g C a −1 for the Franklin Bay region. These results show that bacterial processes continue throughout all seasons and make a large contribution to the total biological carbon flux in this coastal arctic ecosystem.