Seasonality of Glacial Snow and Ice Microbial Communities

Abstract

Blooms of microalgae on glaciers and ice sheets are amplifying surface ice melting rates, which are already affected by climate change. Most studies on glacial microorganisms (including snow and glacier ice algae) have so far focused on the spring and summer melt season, leading to a temporal bias, and a knowledge gap in our understanding of the variations in microbial diversity, productivity, and physiology on glacier surfaces year-round. Here, we investigated the microbial communities from Icelandic glacier surface snow and bare ice habitats, with sampling spanning two consecutive years and carried out in both winter and two summer seasons. We evaluated the seasonal differences in microbial community composition using Illumina sequencing of the 16S rRNA, 18S rRNA, and ITS marker genes and correlating them with geochemical signals in the snow and ice. During summer, Chloromonas, Chlainomonas, Raphidonema, and Hydrurus dominated surface snow algal communities, while Ancylonema and Mesotaenium dominated the surface bare ice habitats. In winter, algae could not be detected, and the community composition was dominated by bacteria and fungi. The dominant bacterial taxa found in both winter and summer samples were Bacteriodetes, Actinobacteria, Alphaproteobacteria, and Gammaproteobacteria. The winter bacterial communities showed high similarities to airborne and fresh snow bacteria reported in other studies. This points toward the importance of dry and wet deposition as a wintertime source of microorganisms to the glacier surface. Winter samples were also richer in nutrients than summer samples, except for dissolved organic carbon—which was highest in summer snow and ice samples with blooming microalgae, suggesting that nutrients are accumulated during winter but primarily used by the microbial communities in the summer. Overall, our study shows that glacial snow and ice microbial communities are highly variable on a seasonal basis.

DNA/RNA Preservation in Glacial Snow and Ice Samples

“…We attribute the high DNA concentration in IS19-12 to the visibly high amounts of biomass of glacial snow and ice algae within these samples ( Figure 1C ). This sample (IS19-12) also contained high TOC ( Table 2 ; Winkel et al, 2022 ). The only sample to yield RNA concentrations above the detection limit of the Qubit was IS19-12.…”

“…The potential loss of DNA and RNA during RNAlater -preserved sample washing is problematic for low-biomass glacial samples. In contrast to the use of RNAlater, many previous cryosphere studies addressing microbial community compositions froze filtered DNA samples at −20°C in the field ( Larose et al, 2013 ; Christner et al, 2014 ; Maccario et al, 2014 ; Purcell et al, 2014 ; Lutz et al, 2015b , 2016 , 2017 , 2019a , b ; Bergk Pinto et al, 2019 ; Malard et al, 2019 ; Els et al, 2020 ; Ramoneda et al, 2020 ; Winkel et al, 2022 ), while few studies used Zymo -preservation ( Trivedi et al, 2018 , 2020 ; Matys et al, 2019 ; Dillon et al, 2020 ; Lumian et al, 2021 ), and even fewer used RNAlater plus freezing ( Maccario et al, 2019 ). When no flash freezing and preservation of samples in a cryo-shipper exists, our results indicate that Zymo -preservation is a reasonable alternate option, although additional testing should be done to further help narrow the extraction boundary conditions for very low biomass samples as is often the case with snow and ice samples.…”

“…Libraries using poly(A) selection were only generated for site IS19-12 preserved samples, as our detailed microbial ecological analyses of this snow-ice interface sample ( Winkel et al, 2022 ) revealed that the high biomass site was dominated by snow algae. Library concentrations ranged between 0.40 (FieldBL) and 98.4 (12Z) nM ( Table 2 and Figure 3A ).…”

“…Snow and ice samples were collected in August 2019 from two glaciers in Iceland (Snaefellsjökull and Langjökull, respectively, see Figure 1 ) following previously established protocols ( Lutz et al, 2015a ; Winkel et al, 2022 ). For this study, we specifically targeted samples that contained high quantities of visible mineral and microbial particles [equivalent to “dirty snow” and “dirty ice” habitats described in Lutz et al (2014) ].…”

“… Samples are organized by site and with each preservation type and associated short name. Data for filtered volume and TOC content of each sample ( Winkel et al, 2022 ) are shown. The DNA and RNA concentrations are normalized per 100 ml sample volume filtered and reveal that the RNA concentrations were BDL in all but the highest biomass (TOC) IS19-12 sample.…”