| Summary: | International audience Human-‐induced environmental changes are affecting cold ecosystems and predicted impacts include rapid warming, increased nitrogen and pollutant deposition, yet the effect of these on microbial communities and nutrient cycling is poorly understood. Much of the research concerning Arctic microbial community structure and function stems from soil and permafrost studies, however relatively little is known about the snowpack. Seasonal snow cover extends over a third of the Earth's land surface, covering up to 47 million km2 and is also an important feature of the Arctic. Snow cover can be considered as a dynamic habitat of limited duration that acts as a medium and a mediator by transmitting and modifying interactions among microorganisms, plants, animals, nutrients, the atmosphere and soil. A growing body of evidence suggests that microbial communities play key roles in biogeochemical cycling in the snowpack, but little is known about the processes controlling their biogeographic distributions. We used metagenomic tools such as phylogenetic microarrays and high throughput sequencing to explore microbial community structure in samples collected from various Arctic snowpacks (North Pole, Greenland and Ny-‐Alesund) at different seasons (spring, summer, winter) and compared these to publicly available data from other ecosystems to evaluate the roles of niche-‐based processes vs spatial processes in explaining variations in community structure. The biogeography of Arctic microbial communities appears to be influenced by environmental factors, such as snow physics and chemistry relative to geographic distance. The results from this study offer insights into the mechanisms that generate and maintain diversity, such as speciation, extinction, dispersal and species interactions.
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