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

Abstract

Abstract. Glaciers and ice sheets possess layers of basal ice characterized by high amounts of entrained debris that can serve as sources of nutrients and organic matter, providing habitat for microorganisms adapted to the frozen conditions. Basal ice forms through various mechanisms and is classified based on its 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 ratios of amplified sequences for 16S rRNA relative to that for 16S rRNA genes implicated certain bacterial taxa (e.g., Paenisporosarcina, Desulfocapsa, Syntrophus, Desulfosporosinus) as being potentially active, with ice temperature appearing to be an important predictor for the diversity of taxa inferred to be active. Compared to those of other sympagic environments, these microbiomes often resembled those found in permafrost or perennial cave ice rather than other glacial ice environments. In contrast, debris-poor basal ices harbored microbiomes more like those found in oligotrophic englacial ice. Collectively, these results suggest that different basal ice types contain distinct microbiomes that are actively structured by the diagenesis of their habitat.

Biolocomotion and Premelting in Ice

“…For example, recently a 30,000 year old giant virus Pithovirus sibericum was found in permafrost along with microbes and nematodes, and viable bacteria have been found in 750,000 year old glacial ice. Basal ice often contains subglacial debris and sediment, which serve as a source of nutrients and organic matter, providing a habitat for micro-organisms adapted to subfreezing conditions [8,9]. Additionally, the microbiomes of sediment rich basal ices are distinct from those found in glacial ice and are equivalent to those found in permafrost [8], expanding the nature of subfreezing habitats.…”

“…Basal ice often contains subglacial debris and sediment, which serve as a source of nutrients and organic matter, providing a habitat for micro-organisms adapted to subfreezing conditions [8,9]. Additionally, the microbiomes of sediment rich basal ices are distinct from those found in glacial ice and are equivalent to those found in permafrost [8], expanding the nature of subfreezing habitats.…”