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Background: Arctic snowpack microbial communities are continually subject to dynamic chemical and microbial input from the atmosphere. As such, the factors that contribute to structuring their microbial communities are complex and have yet to be completely resolved. These snowpack communities can be used to evaluate whether they fit niche-based or neutral assembly theories., Methods: We sampled snow from 22 glacier sites on 7 glaciers across Svalbard in April during the maximum snow accumulation period and prior to the melt period to evaluate the factors that drive snowpack metataxonomy. These snowpacks were seasonal, accumulating in early winter on bare ice and firn and completely melting out in autumn. Using a Bayesian fitting strategy to evaluate Hubbell's Unified Neutral Theory of Biodiversity at multiple sites, we tested for neutrality and defined immigration rates at different taxonomic levels. Bacterial abundance and diversity were measured and the amount of potential ice-nucleating bacteria was calculated. The chemical composition (anions, cations, organic acids) and particulate impurity load (elemental and organic carbon) of the winter and spring snowpack were also characterized. We used these data in addition to geographical information to assess possible niche-based effects on snow microbial communities using multivariate and variable partitioning analysis., Results: While certain taxonomic signals were found to fit the neutral assembly model, clear evidence of niche-based selection was observed at most sites. Inorganic chemistry was not linked directly to diversity, but helped to identify predominant colonization sources and predict microbial abundance, which was tightly linked to sea spray. Organic acids were the most significant predictors of microbial diversity. At low organic acid concentrations, the snow microbial structure represented the seeding community closely, and evolved away from it at higher organic acid concentrations, with concomitant increases in bacterial numbers., Conclusions: These results indicate that environmental selection plays a significant role in structuring snow microbial communities and that future studies should focus on activity and growth. Video Abstract., (© 2023. The Author(s).)

Fe(II) is more soluble and bioavailable than Fe(III) species, therefore the investigation of their relative abundance and redox processes is relevant to better assess the supply of bioavailable iron to the ocean and its impact on marine productivity. In this context, we present a discrete chemiluminescence-based method for the determination of Fe(II) in firn matrices. The method was applied on discrete samples from a snow pit collected at Dome C (DC, Antarctica) and on a shallow firn core from the Holtedahlfonna glacier (HDF, Svalbard), providing the first Fe(II) record from both Antarctica and Svalbard. The method showed low detection limits (0.006 ng g -1 for DC and 0.003 ng g -1 for the HDF) and a precision ranging from 3% to 20% RSD. Fe(II) concentrations ranged between the LoD and 0.077 ng g -1 and between the LoD and 0.300 ng g -1 for the Antarctic and Arctic samples, respectively. The Fe(II) contribution with respect to the total dissolved Fe was comparable in both sites accounting, on average, for 5% and 3%, respectively. We found that Fe(II) correctly identified the Pinatubo/Cerro Hudson eruption in the DC record, demonstrating its reliability as volcanic tracer, while, on the HDF core, we provided the first preliminary insight on the processes that might influence Fe speciation in firn matrices (i.e. organic ligands and pH influences)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The role of oceanic primary production on climate variability has long been debated. Defining changes in past oceanic primary production can help understanding of the important role that marine algae have in climate variability. In ice core research methanesulfonic acid is the chemical marker commonly used for assessing changes in past primary production. However, other organic compounds such as amino acids, can be produced and emitted into the atmosphere during a phytoplankton bloom. These species can be transported and deposited onto the ice cap in polar regions. Here we investigate the correlation between the concentration of chlorophyll-a, marker of marine primary production, and amino acids present in an ice core. For the first time, free l- and d-amino acids in Arctic snow and firn samples were determined by a sensitive and selective analytical method based on liquid chromatography coupled with tandem mass spectrometry. The new method for the determination of free amino acids concentrations was applied to firn core samples collected on April 2015 from the summit of the Holtedahlfonna glacier, Svalbard (N 79'08.424, E 13'23.639, 1120m a.s.l.). The main results of this work are summarized as follows: (1) glycine, alanine and proline, were detected and quantified in the firn core samples; (2) their concentration profiles, compared with that of the stable isotope δ 18 O ratio, show a seasonal cycling with the highest concentrations during the spring and summer time; (3) back-trajectories and Greenland Sea chlorophyll-a concentrations obtained by satellite measurements were compared with the amino acids profile obtained from ice core samples, this provided further insights into the present results. This study suggests that the amino acid concentrations in the ice samples collected from the Holtedahlfonna glaciers could reflect changes in oceanic phytoplankton abundance., (Copyright © 2017 Elsevier B.V. All rights reserved.)