Variation in bacterial composition, diversity, and activity across different subglacial basal ice types

Abstract

Abstract. Glaciers and ice sheets possess basal ice layers characterized by high amounts of entrained debris that can serve as sources of nutrients and organic matter, providing a habitat for microorganisms adapted to the frozen conditions. Basal ice forms through various mechanisms and is classified based on ice and debris content; however, little is known about variation in microbial composition, diversity, and activity across different basal ice types. We investigated these parameters in four different types of basal ice from a cold-based and temperate glacier and used a meta-analysis to compare our findings with microbiome studies from other frozen environments. We found basal ice environments harbor a diverse range of microbiomes whose composition and activity can vary significantly between basal ice types, even within adjacent facies from the same glacier. In some debris-rich basal ices, elevated ATP concentrations, isotopic gas signatures, and high 16S rRNA/rDNA amplicon ratios implicated certain bacterial taxa (e.g., Paenisporosarcina, Desulfocapsa, Syntrophus, and Desulfosporosinus) as being potentially active, with ice temperature appearing to be an important predictor for the diversity of inferred active taxa. Compared to those of other sympagic environments, the basal ice microbiomes more closely resemble those found in permafrost or perennial cave ice than glacial ice. In contrast, debris-poor basal ices harbored microbiomes more like those found in englacial ice. Collectively, these results suggest that different basal ice types contain distinct microbiomes that are actively structured by physicochemical properties of their habitat.