Summer dynamics of microbial diversity on a mountain glacier

Under climate change, glaciers are rapidly receding worldwide. A melting cryosphere will dramatically alter global sea levels, carbon cycling, and water resource availability. Glaciers also host rich biotic communities that are dominated by microbial diversity and this biodiversity can impact surface albedo, thereby driving a feedback loop between biodiversity and cryosphere melt. However, the microbial diversity of glacier ecosystems remains largely unknown outside of major ice sheets, particularly from a temporal perspective. Here, we characterized temporal dynamics of bacteria, eukaryotes, and algae on the Paradise Glacier, Mount Rainier, USA, over the summer melt season. During our study, the glacier surface steadily darkened as seasonal snow melted and darkening agents accumulated until new snow fell in late September. From a community-wide perspective, the bacterial community remained generally constant and eukaryotes exhibited a clear temporal progression of community change while fungal diversity was intermediate. Individual taxonomic groups, however, exhibited considerable stochasticity. We found little support for our a priori prediction that autotroph abundance would peak before heterotrophs. Notably, two different trends in snow algae emerged--an abundant early-and late-season OTU with a different mid-summer OTU that peaked in August. Overall, our results highlight the need for temporal sampling to clarify microbial diversity on glaciers and that caution should be exercised when interpreting results from single or few timepoints.