The northern coast of Ellesmere Island in the Canadian High Arctic is undergoing amplified warming that parallels the rapid decline in Arctic Ocean sea ice extent, and many lakes in this region have already shown changes in response to warming. However, biogeochemical data from High Arctic freshwaters are limited, and mostly restricted to the short, ice-free period. We sampled four coastal lakes in Stuckberry Valley (82° 54’ N, 66° 56’ W) before the onset of spring melting in 2017, 2018 and 2019, to assess biogeochemical gradients in their water columns and characteristics of their surface sediments. Despite their proximity, there were large differences in limnological properties. The two shallower lakes closer to the ocean were oxygen deficient while the two deeper, more distant lakes were more oxygenated. There were pronounced vertical gradients in major ions, metals and nutrients that suggested large differences in the extent of anaerobic microbial processes among the lakes. Morphometry and dissolved oxygen were the overriding determinants of biogeochemical differences rather than position along this short ocean-inland gradient. The diversity of limnological conditions, and the sensitivity of these characteristics to changes in ice cover, underlines the need for further study of under-ice processes in extreme northern lakes.

Arctic lakes are experiencing increasingly shorter periods of ice cover due to accelerated warming at northern high latitudes. Given the control of ice cover thickness and duration over many limnological processes, these changes will have pervasive effects. However, due to their remote and extreme locations even first-order data on lake ecology is lacking for many ecosystems. The aim of this study was to characterize and compare the microbial communities of four closely spaced lakes in Stuckberry Valley (northern Ellesmere Island, Canadian Arctic Archipelago), in the coastal margin zone of the Last Ice Area, that differed in their physicochemical, morphological and catchment characteristics. We performed high-throughput amplicon sequencing of the V4 16S rRNA gene to provide inter- and intra-lake comparisons. Two deep (>25 m) and mostly oxygenated lakes showed highly similar community assemblages that were distinct from those of two shallower lakes (<10 m) with anoxic bottom waters. Proteobacteria, Verrucomicrobia, and Planctomycetes were the major phyla present in the four water bodies. One deep lake contained elevated proportions of Cyanobacteria and Thaumarchaeota that distinguished it from the others, while the shallow lakes had abundant communities of predatory bacteria, as well as microbes in their bottom waters that contribute to sulfur and methane cycles. Despite their proximity, our data suggest that local habitat filtering is the primary determinant of microbial diversity in these systems. This study provides the first detailed examination of the microbial assemblages of the Stuckberry lakes system, resulting in new insights into the microbial ecology of the High Arctic.

We isolated two closely related strains that belong to the Myoviridae family and infect cyanobacteria in a shallow subarctic rock basin lake. Their host was identified as a member of the Synechococcus-Cyanobium complex. Sequenced genomes of the two phages were 244,930 bp and 243,633 bp. We describe their annotation and highlight some noteworthy features.C yanobacteria often dominate picophytoplankton biovolume in high-latitude freshwater systems (1). The genomes of phages infecting these cyanobacteria are expected to give insight into top-down control of this group.We isolated cyanophage strains by using a viral concentrate obtained by collecting water from the surface and bottom of a small rock basin lake in Nunavik, Canada (55°16=N, 77°44=W) and prefiltering it sequentially at 20, 0.45, and 0.22 m. This concentrate was used to inoculate a mixture of 24 cultures from the Polar Cyanobacteria Culture Collection at the Centre for Northern Studies (Université Laval, Québec, Canada). A process of filtration at 0.45 m to obtain the viral lysate, reinoculation, and incubation under continuous light at 15°C was repeated three times and yielded two cyanophage strains capable of producing cell lysis in cyanobacterial cultures P-101 and O-120. Transmission electron microscopy revealed an icosahedral capsid and contractile tail typical of members of the family Myoviridae (Fig. 1A through C). Analysis of the 16S rRNA gene of cultures P-101 and O-120 located the host in the Synechococcus-Cyanobium complex.Viral DNA was extracted using precipitation with NaCl and polyethylene glycol 8000, followed by the use of a MasterPure complete DNA and RNA purification kit (Epicentre). DNA was fragmented in a Covaris sonicator and purified using magnetic beads (Axygen), and libraries were prepared using a NEBNext Ultra II kit for Illumina (New England Biolabs). DNA was sequenced using a MiSeq reagent kit v.2 (Illumina) at the Plateforme d'Analyses Gé nomiques de l'IBIS (Université Laval).The total number of paired-end sequenced reads was 2,723,694, with an average length of 300 bp. All analyses were performed using default parameters, unless otherwise stated. Raw reads were filtered using Trimmomatic v.0.36 (2) to remove low-quality regions and Illumina adaptors. Reads were resampled using seqtk v.1.0-r31 (3) to reduce the assembly coverage to 100-fold (114,251 reads), and genomes were assembled de novo using SPAdes v.3.9.0 (4). We designed two primers, circ_B3 and circ_B23, to check the circularity of the genomes. PCRs were carried out in a 25-l reaction mixture containing Platinum Taq polymerase (2 U; Thermo Fisher Scientific), PCR buffer with MgCl 2 , 0.2 mM deoxynucleoside triphosphates (dNTPs), and 0.4 M each primer. Thermal cycling consisted of an initial step at 94°C for 2 min followed by 29 cycles of denaturation at 94°C for 15 s, hybridization at 50°C for 15 s, and elongation at 72°C for 1 min, with a final elongation step at 72°C for 5 min (7 min for circ_B23). Products were of the expected sizes (ϳ500 bp [B3] and 350 bp [B23]),...