Preface. Sea ice and life in a river-influenced arctic shelf ecosystem

Preface special issue Sea ice and life in a river-influenced arctic shelf ecosystem. 2 pagesCASES and the operation of CCGS Radisson, Amundsen and Nahidik were funded by the Natural Sciences and Engineering Research Council of Canada (NSERC). ARDEXwas jointly funded by NSERC and the Canada Research Chair program. The Canada Foundation for Innovationprovided the funds for refitting CGGS Amundsen, with additional support from the Canadian Coast Guard. International participants in CASES were funded by agencies in their respective countries, including the Spanish Ministerio de Educacióny Ciencia, the Generalitat de Catalunya, and the US National Science FoundationPeer Reviewe

Prokaryotic community structure and heterotrophic production in a river-influenced coastal arctic ecosystem

14 pages, 3 figures, 5 tablesSpatial patterns in prokaryotic biodiversity and production were assessed in the Mackenzie shelf region of the Beaufort Sea during open-water conditions. The sampling transect extended 350 km northwards, from upstream freshwater sites in the Mackenzie River to coastal and offshore sites, towards the edge of the perennial arctic ice pack. The analyses revealed strong gradients in community structure and prokaryotic cell concentrations, both of which correlated with salinity. Picocyanobacterial abundance was low (102 to 103 cells ml–1), particularly at the offshore stations that were least influenced by the river plume. Analysis by catalyzed reporter deposition for fluorescence in situ hybridization (CARD-FISH) showed that the dominant heterotrophic cell types were β-Proteobacteria at river sites, shifting to dominance by α-Proteobacteria offshore. Cells in the Cytophaga–Flavobacter–Bacteroides and γ-Proteobacteria groups each contributed 10% of counts in the marine samples. Archaea were detected among the surface-water microbiota, contributing on average 1.3% of the total DAPI counts in marine samples, but 6.0% in turbid coastal and riverine waters. 3H-leucine uptake rates were significantly higher at 2 stations influenced by the river (1.5 pmol l–1 h–1) than at other marine stations or in the river itself (≤0.5 pmol–1 h–1). Size-fractionation experiments at 2 coastal sites showed that >65% of heterotrophic production was associated with particles >3 µm. These results indicate the importance of particle-attached prokaryotes, and imply a broad functional diversity of heterotrophic microbes that likely facilitates breakdown of the heterogeneous dissolved and particulate terrestrial materials discharged into arctic seasThis study was made possible with financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canada Research Chair program, Fonds québécois de recherche sur la nature et les technologies (FQRNT) and Indian and Northern Affairs CanadaPeer reviewe

Distribution, phylogeny, and growth of cold-adapted Picoprasinophytes in Arctic Seas

12 pages, 7 figures, 2 tablesOur pigment analyses from a year-long study in the coastal Beaufort Sea in the western Canadian Arctic showed the continuous prevalence of eukaryotic picoplankton in the green algal class Prasinophyceae. Microscopic analyses revealed that the most abundant photosynthetic cell types were Micromonas-like picoprasinophytes that persisted throughout winter darkness and then maintained steady exponential growth from late winter to early summer. A Micromonas (CCMP2099) isolated from an Arctic polynya (North Water Polynya between Ellesmere Island and Greenland), an ice-free section, grew optimally at 61C–81C, with light saturation at or below 10 lmol photons .m-2 . s-1 at 0ºC. The 18S rDNA analyses of this isolate and environmental DNA clone libraries from diverse sites across the Arctic Basin indicate that this single psychrophilic Micromonas ecotype has a pan-Arctic distribution. The 18S rDNA from two other picoprasinophyte genera was also found in our pan-Arctic clone libraries: Bathycoccus and Mantoniella. The Arctic Micromonas differed from genotypes elsewhere in the World Ocean, implying that the Arctic Basin is a marine microbial province containing endemic species, consistent with the biogeography of its macroorganisms. The prevalence of obligate low-temperature, shade-adapted species in the phytoplankton indicates that the lower food web of the Arctic Ocean is vulnerable to ongoing climate change in the regionThis research was supported by the Natural Sciences and Engineering Research Council of Canada; the Strategic Science Fund from Fisheries and Oceans, Canada; the Japan Marine Science and Technology Center, Tokyo, Japan; the Canada Climate Action Fund; ARTIC (REN2001-4909-E/ANT, MCyT) and ESTRAMAR (CTM2004-12631/MAR, MEC) Spain; GENmMar (CTM2004-02586/MAR), European Union; and Fonds québécois de recherche sur la nature et la technologie, Québec, CanadaPeer reviewe

Microbial Communities and Carbon Fluxes

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