Highly stable active core microbiomes in Greenland cryoconite holes during the bare ice period.

Cryoconite holes host diverse microbiomes on glaciers and ice sheets and are important habitats for supraglacial biogeochemical cycling. Despite reports of relative stability of cryoconite hole community composition on the Greenland Ice Sheet, it is not known how microbial function in cryoconite holes evolves under varying environmental conditions. Here, we address this knowledge gap by quantifying the active community members in five cryoconite holes on the Greenland Ice Sheet over a 3-week period during the 2022 melt season using TotalRNA. Active microbiomes were enriched in cyanobacterial sequences (25%-50%). Spatial variation between cryoconite holes had a greater impact than temporal variation on community composition quantified by rRNA SSUs, suggesting location-distinct and highly stable active microbiomes. In contrast, minor temporal variations in gene expression were identified in the mRNA data (∼1% of quantified transcripts), mostly due to cellular stress responses from washed-in glacier ice algae. Photosynthesis was the dominant active function across all surveyed cryoconite holes and time points, associated with both cyanobacterial taxa and washed-in chlorophyte snow algae. Overall, our data indicate that core cryoconite hole communities stably ensure their ecological roles, such as carbon fixation, regardless of variations in weather, highlighting their resilience and self-sufficiency.