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

Abstract

[1] 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. 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 Â 10 5 cells mL À1 (July). Integral BP varied from 1 (February) to 80 mg C m À2 d À1 (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.CDOMjChl a = 0.20, p < 0.05, N = 176). Annual BP was estimated as 6 g C m À2 a À1 , implying a total BP of 4.8 Â 10 10 g C a À1 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.

Multiscale control of bacterial production by phytoplankton dynamics and sea ice along the western Antarctic Peninsula: A regional and decadal investigation

“…Indeed, on average, both primary and bacterial production rates 20 were lower in the Ross Sea and Western Arctic Ocean than in other warmer, lower latitude 21 regions reviewed by Kirchman et al (2009b). Kirchman et al (2009a) found significant 22 relationships between BP and temperature both within and across seasons and years (spring-23 summer, 2002, 2004) in the western Arctic Ocean, but Garneau et al (2008), working in nearby 1 Franklin Bay, did not. Simon et al (1999) demonstrated that temperature regulated bacterial 2 activity differently in different water masses in the Southern Ocean.…”

“…together, illustrating the ultimate reliance of bacteria on primary producers in a wide range of 5 aquatic systems (Bird and Kalff, 1984;Cole et al, 1988;Ducklow and Carlson, 1992;Kirchman 6 et al, 2009b;Li et al, 2004). Strong relationships are also commonly observed over full annual 7 cycles, especially in the highly seasonal polar seas, encompassing wide dynamic ranges of 8 bacterial and phytoplankton properties encountered between winter and summer (e.g., Pearce et 9 al., 2007;Garneau et al, 2008). 10…”

Hydrocarbon biodegradation by Arctic sea-ice and sub-ice microbial communities during microcosm experiments, Northwest Passage (Nunavut, Canada)

“…Our results imply that bacteria in these cavities and growing close to the ice-water interface should be capable of biodegradation during winter. Bacteria were shown to be active in the upper water column even in winter, but rates were low at < 0.05 mg C m -3 d -1 (Garneau et al 2008). Assuming the oil reaches the ice-water interface, biodegradation rates could be higher than the ones measured in the microcosms because bottom-ice DOC and EPS concentrations are very low in winter (Riedel et al 2008), as well as the primary producer biomass (< 0.04 mg chl a m -3 ; Garneau et al 2008).…”

Photodegraded dissolved organic matter from peak freshet river discharge as a substrate for bacterial production in a lake-rich great Arctic delta

“…6); however, our estimates in these cases were similar to those found during prior studies. For example, BA in surface water averaged 67 × 10 4 cells mL −1 along a 300 km transect from the Mackenzie River into the Beaufort Sea (Vallières et al 2008), and fluctuated from 10 to 100 × 10 4 cells mL −1 in Franklin Bay (Garneau et al 2008) and on the Mackenzie Shelf (Matsuoka et al 2015).…”

“…Heterotrophic grazers subsequently consume bacteria, which shunts otherwise unavailable carbon, organic matter, and energy back into the aquatic food web via the microbial loop (Azam et al 1983). This is a critical process that mobilizes otherwise unavailable DOM molecules in high-latitude aquatic environments (Cole 1999;Cory et al 2014) via bacteria, contributing to overall food web production in Mackenzie Delta lakes (Spears and Lesack 2006;Tank et al 2011), the Mackenzie River (Vallières et al 2008), and the nearshore Beaufort Sea (Garneau et al 2008;Bell et al 2016). Because DOM is an important component of carbon budgets in aquatic ecosystems, an understanding of how photodegradation alters DOM bioavailability is critical to understand carbon fluxes through the landscape.…”