Abstract. During the spring of 2009, as part of the OceanAtmosphere-Sea Ice-Snowpack (OASIS) campaign in Barrow, Alaska, USA, we examined the identity, population diversity, freezing nucleation ability of the microbial communities of five different snow types and frost flowers. In addition to the culturing and gene-sequence-based identification approach, we utilized a state-of-the-art genomic next-generation sequencing (NGS) technique to examine the diversity of bacterial communities in Arctic samples. Known phyla or candidate divisions were detected (11-18) with the majority of sequences (12.3-83.1 %) belonging to one of the five major phyla: Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Cyanobacteria. The number of genera detected ranged from, 101-245. The highest number of cultivable bacteria was observed in frost flowers (FFs) and accumulated snow (AS) with 325 ± 35 and 314 ± 142 CFU m L −1 , respectively; and for cultivable fungi 5 ± 1 CFU m L −1 in windpack (WP) and blowing snow (BS). Morphology/elemental composition and ice-nucleating abilities of the identified taxa were obtained using high resolution electron microscopy with energy-dispersive X-ray spectroscopy and ice nucleation cold-plate, respectively. Freezing point temperatures for bacterial isolates ranged from −20.3 ± 1.5 to −15.7 ± 5.6 • C, and for melted snow samples from −9.5 ± 1.0 to −18.4 ± 0.1 • C. An isolate belonging to the genus Bacillus (96 % similarity) had ice nucleation activity of −6.8 ± 0.2 • C. Comparison with Montreal urban snow, revealed that a seemingly diverse community of bacteria exists in the Arctic with some taxa possibly originating from distinct ecological environments. We discuss the potential impact of snow microorganisms in the freezing and melting process of the snowpack in the Arctic.

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Interactive comment on "A next generation sequencing of Arctic bacteria in snow and frost flowers: identification, abundance and freezing nucleation" by R. Mortazavi et al. R. Mortazavi et al. ReplyThanks very much for your detailed comments and suggestions. We have considered all of them, and revised the manuscript accordingly. For your convenience, we put your comments, point-by-point in italic and our replies on regular fonts. Anonymous Referee #1 "Atmospheric Chemistry and Physics Title: A next generation sequencing of Arctic bacteria in snow and frost flowers: identification, abundance and freezing nucleation This paper provides insights into the microbial composition of frost C12418 flowers and other snow sources as well as the ice nucleation capability of culturable bacteria from these samples. This seems to be a novel dataset that is worthy or publication. The paper would greatly benefit from including more details on the methods that were used, particularly with regards to the pyrosequencing and how the samples were prepared and processed in MOTHUR (see specific notes below). The paper would also benefit from being substantially edited and reviewed by a microbial ecologist to improve the flow of language and grammar to more clearly communicate the results and background information (see specific comments below). The paper also mentions more than once the possibility of microbes in snow and ice in contributing to ecological processes in the Arctic but this is not returned to in the discussion of the results with respect to the microbial composition revealed by sequencing. Although this type of discussion requires a bit of speculation, it would be interesting to discuss some hypotheses for future research to build upon."Response: Thank you.Abstract: "Line 1: Seems like there should not be hyphens between "Ocean, Atmospheric Sea Ice Snowpack" Response: Thank you for your comment. Please note that in all their publications, they use hyphens, and thus to assure consistency and respect for the copyrights, we leave it as is.