ORIGINAL PAPER Respiration and bacterial carbon dynamics in Arctic sea ice Dan Nguyen • Roxane Maranger Received: 28 September 2010 / Revised: 18 May 2011 / Accepted: 20 May 2011 / Published online: 28 June 2011 Ó Springer-Verlag 2011 Abstract Bacterial carbon demand, an important com- ponent of ecosystem dynamics in polar waters and sea ice, is a function of both bacterial production (BP) and respi- ration (BR). BP has been found to be generally higher in sea ice than underlying waters, but rates of BR and bac- terial growth efficiency (BGE) are poorly characterized in sea ice. Using melted ice core incubations, community respiration (CR), BP, and bacterial abundance (BA) were studied in sea ice and at the ice–water interface (IWI) in the Western Canadian Arctic during the spring and summer 2008. CR was converted to BR empirically. BP increased over the season and was on average 22 times higher in sea ice as compared with the IWI. Rates in ice samples were highly variable ranging from 0.2 to 18.3 lgCl -1 d -1 . BR was also higher in ice and on average *10 times higher than BP but was less variable ranging from 2.39 to 22.5 lgCl -1 d -1 . Given the high variability in BP and the relatively more stable rates of BR, BP was the main driver of estimated BGE (r 2 = 0.97, P \ 0.0001). We conclude that microbial respiration can consume a signifi- cant proportion of primary production in sea ice and may play an important role in biogenic CO 2 fluxes between the sea ice and atmosphere. Keywords Arctic Ocean Á Sea ice Á Respiration Á Bacterial production Á BGE Á C cycling Introduction Estimating rates of major biogeochemical cycles is a great challenge in the Arctic environment and for sea ice in particular. Annual polar sea ice is a dynamic habitat characterized by steep physical and chemical gradients that permit the establishment of a diverse microfauna critical to sustaining polar food webs (Michel et al. 1996; Lizotte 2001). The expulsion of salts and nutrients from the ice through brine channels creates nutrient-rich con- ditions at the growing ice front (Bunch and Harland 1990), supporting dense autotrophic and heterotrophic communities (Thomas and Dieckmann 2010). Auto- trophic production in sea ice during the spring has been the topic of several studies because of the high rates of ice algal primary production and impressive biomass accumulation (Gosselin et al. 1986; Riedel et al. 2006; Arrigo et al. 2010). Indeed, ice algal production can contribute up to one-third of the total primary production (PP) in the Arctic (Legendre et al. 1992) and therefore plays an important functional role in ecosystem dynamics of polar seas. The increase in solar radiation during spring rapidly induces blooms in the bottom ice resulting in the release of dissolved organic compounds by ice algae, producing critical substrates that support heterotrophic microbial communities (Smith et al. 1997; Riedel et al. 2006). Bacterial abundance (BA) and bacterial production (BP) in sea ice typically follow increasing algal production and biomass during the spring bloom (Kottmeier et al. 1987; Smith et al. 1989; Bunch and Harland 1990; Kuparinen et al. 2007). The ratio of BP to PP ranges from 10 to 30% in the literature (Cole et al. 1988; Ducklow 2000). However, Garneau et al. (2008) observed a higher ratio in the Franklin Bay of Amundsen Gulf, with BP accounting for 37% This article belongs to the special issue ‘‘Circumpolar Flaw Lead Study (CFL)’’, coordinated by J. Deming and L. Fortier. D. Nguyen Á R. Maranger (&) De ´partement des sciences biologiques, Groupe de Recherche Interuniversitaire en Limnologie (GRIL-UdeM), Universite ´ de Montre ´al, CP 6128, Succ. Centre-ville, Montre ´al, QC H3C 3J7, Canada e-mail: r.maranger@umontreal.ca 123 Polar Biol (2011) 34:1843–1855 DOI 10.1007/s00300-011-1040-z