The microbiome of glaciers and ice sheets

Abstract

Glaciers and ice sheets, like other biomes, occupy a significant area of the planet and harbour biological communities with distinct interactions and feedbacks with their physical and chemical environment. In the case of the glacial biome, the biological processes are dominated almost exclusively by microbial communities. Habitats on glaciers and ice sheets with enough liquid water to sustain microbial activity include snow, surface ice, cryoconite holes, englacial systems and the interface between ice and overridden rock/soil. There is a remarkable similarity between the different specific glacial habitats across glaciers and ice sheets worldwide, particularly regarding their main primary producers and ecosystem engineers. At the surface, cyanobacteria dominate the carbon production in aquatic/sediment systems such as cryoconite holes, while eukaryotic Zygnematales and Chlamydomonadales dominate ice surfaces and snow dynamics, respectively. Microbially driven chemolithotrophic processes associated with sulphur and iron cycle and C transformations in subglacial ecosystems provide the basis for chemical transformations at the rock interface under the ice that underpin an important mechanism for the delivery of nutrients to downstream ecosystems. In this review, we focus on the main ecosystem engineers of glaciers and ice sheets and how they interact with their chemical and physical environment. We then discuss the implications of this microbial activity on the icy microbiome to the biogeochemistry of downstream ecosystems.

Fig. 1

The different shades of colours and the glacial biome habitats. a Landscape scale view of the west side of the Greenland ice sheet (GrIS) showing the extent of impurities and colonisation of algae at the ice surface; b Photo of a section of the Mittivakkat glacier in the southeast coast of Greenland showing a variety of different surface habitats, from clean snow to “dirty” ice; c a small crevasse on the GrIS. Features like this provide opportunities for transport of material from the ice surface to the englacial system; d runoff from Leveret glacier (west Greenland—Kangerlussuaq) containing a large signature of subglacial water (sediment rich); e 3D visualisation of the canyon under the GrIS (Photo by J. Bamber based on ref. 135). The amount of water stored under the ice is unknown

Fig. 2

a Schematic figure of the different glacial habitats for biological colonisation and activity with a closer view of the surface ecosystem. The significance of microbial activity in englacial and subglacial systems is still largely unknown; b white snow at the beginning of the melt season; c, d green snow with its dominant main primary producer (Chlamydomonadales) collected from a Svalbard glacier; e, f red snow with its dominant main primary producer (Chlamydomonadales) collected from a Svalbard glacier, g, h “dirty” ice with one of its dominant main primary producer (a Zygnematales); i, j an example of a cryoconite hole in the GrIS and one of its main primary producers (Phormidesmis priestleyi)

Fig. 3

Pathway for microbial adaptation to glacial conditions. Time, size and spatial distance are all likely to contribute to patterns in microbial communities found in glaciers and ice sheets. Horizontal/diagonal arrows represent selection of microbial communities from glacial margins that are increasingly adapted to glacial survival at the interior of the ice. Vertical arrows represent potential links between different glaciers at different spatial and time scales