Microbial communities and ecological functions shift with glacier retreat in the Canadian High Arctic

Glaciers are rapidly retreating under climate warming, raising concerns about the loss of unique microbial ecosystems in both glacier ice and forelands. However, the changes in microbial diversity, community structure, and functional traits across the glacier ice-foreland transition remain poorly understood. In this study, we investigated how glacier retreat shapes bacterial and fungal communities along an ice-foreland chronosequence at the Arklio Glacier on Ellesmere Island, Nunavut, in the High Arctic of Canada. Using 16S and ITS amplicon sequencing, both the bacterial and fungal communities on the glacier ice contrasted markedly with those in the glacier foreland sediments, suggesting limited microbial connectivity and strong environmental filtering between these habitats. On the glacier ice, bacterial diversity increased toward the terminus, whereas fungal diversity declined. In the glacier foreland, bacterial diversity peaked at ~ 100 m from the glacier terminus (~ 20 years post-retreat), whereas fungal diversity peaked at 30 m, suggesting different successional responses following deglaciation. Taxonomy-based functional predictions indicated contrasting metabolic profiles, characterized by phototrophy on the glacier ice and predominantly chemoheterotrophy in the glacier foreland. Together, these results demonstrate that glacier retreat restructures microbial communities in habitat- and taxon-specific ways, and they underscore how glaciers are vulnerable reservoirs of microbial biodiversity.