N chemical species concentrations (μmol l<sup>−1</sup>) throughout the field season

<p><strong>Figure 2.</strong> N chemical species concentrations (μmol l<sup>−1</sup>) throughout the field season. Surface concentrations are shown with diamonds while basal snow concentrations are circles. The black line represents the date that snowpack became isothermal.</p> <p><strong>Abstract</strong></p> <p>Arctic snowpacks are often considered as chemical reactors for a variety of chemicals deposited through wet and dry events, but are overlooked as potential sites for microbial metabolism of reactive nitrogen species. The fate of deposited species is critical since warming leads to the transfer of contaminants to snowmelt-fed ecosystems. Here, we examined the role of microorganisms and the potential pathways involved in nitrogen cycling in the snow. Next generation sequencing data were used to follow functional gene abundances and a 16S rRNA (ribosomal ribonucleic acid) gene microarray was used to follow shifts in microbial community structure during a two-month spring-time field study at a high Arctic site, Svalbard, Norway (79° N). We showed that despite the low temperatures and limited water supply, microbial communities inhabiting the snow cover demonstrated dynamic shifts in their functional potential to follow several different pathways of the nitrogen cycle. In addition, microbial specific phylogenetic probes tracked different nitrogen species over time. For example, probes for <em>Roseomonas</em> tracked nitrate concentrations closely and probes for <em>Caulobacter</em> tracked ammonium concentrations after a delay of one week. Nitrogen cycling was also shown to be a dominant process at the base of the snowpack.</p>