The diversity of ice algal communities on the Greenland Ice Sheet revealed by oligotyping

The Artic is being disproportionally affected by climate change and currently experiences unprecedented melt rates. The Greenland Ice Sheet can be regarded as the largest supraglacial ecosystem on Earth and ice algae are the dominant primary producers on bare ice surfaces throughout the course of a melt season. However, only recently have we recognized their importance. The ice-algal-derived pigments cause a darkening of the ice surface, which in turn decreases albedo and increases melt rates. Here we present the first analysis of ice algal communities across a 100 km transect on the GrIS Sheet by high-throughput sequencing and subsequent oligotyping of the most abundant taxa. Our data show that overall algal diversity is extremely low. Ancylonema nordenskiöldii and a Mesotaenium species were by far the dominant taxa in all sites. Yet, an oligotyping approach revealed hidden diversity that could not be detected by conventional clustering of OTUs and taxonomic classification. Oligotypes of the dominant taxa exhibit a site-specific distribution, which may be linked to different stages in the melt season. This will help to better understand the distribution patterns of these algal communities that play a crucial role in the GrIS ecosystem.