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

[1] The Canadian Arctic Shelf Exchange Study ( CASES) included the overwintering deployment of a research platform in Franklin Bay ( 70 degrees N, 126 degrees 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. BAwas 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 ( rs = 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 ( rs BP. CDOMjChl 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 x 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.