This article was written by Dr Arwyn Edwards, Aberystwyth University and UNIS (aye@aber.ac.uk)
Harland-Cox Huset hosts glacier ecologists
Since the turn of the century, NERC Arctic Research Station at Ny-Ålesund has played a foundational role in the discovery that glaciers and ice sheets represent Earth’s largest freshwater ecosystems. The station has hosted three generations of researchers in this new field of Arctic science who have used the range of glaciers accessible by foot or boat to explore the microbial habitats of glacier surfaces. Key advances linked with the station include:
The concept of glacial ecosystems (2008)
Up to 10 tonnes of microbes inhabit each km2 of an ice surface (2008)
Glacier surfaces are globally significant in the carbon cycle (2009)
Each glacier has distinctive microbiomes (2011)
The ice surface accumulates enough microbes to darken the ice (2012)
Hundreds of species of microbe inhabit habitats on glacier surfaces (2012)
Diverse groups of fungi live on glaciers (2013)
Viruses strongly influence the bacteria in glacial melt (2016)
Snow algae influence the melting properties of Arctic glaciers (2016)
“Clouds” of near-identical virus variants infect bacteria on distant glaciers (2020)
Ice loss will disrupt biodiverse microbial habitats on ice surfaces (2023)
Glacier surfaces are ecosystems
Microbes inhabit the critical interface between ice and atmosphere. This means photosynthetic life forms can use sunlight and carbon dioxide for growth, and in turn, subsidize simple food webs comprising of hundreds to thousands of microbial species. These include diverse bacterial groups, fungi, protozoa, and even tardigrades and rotifers. The microbes are plagued by their viruses, but this means that nutrients released from dying microbes burst open by virus infections provide a critical source of nutrients for other microbes in an otherwise nutrient-poor environment.
Why bother about glacier ecosystems?
The importance of glacier surface ecosystems is three-fold. Firstly, in spite of the harsh environment, glaciers host biodiverse and highly active microbial communities at the glacier surface. Within a catchment hosting a glacier, these may be the most abundant pools of carbon, nutrients, and microbes until fully matured soils develop in the glacier forefield. Glacial ecosystems have deeply ancient origins, but as Arctic summers become warmer, the time and space in which melting occurs becomes larger. This means glaciers are becoming heavily colonized with microbes, and their influence becomes more prominent, for a time at least. Secondly, microbes have adaptations to protect themselves from excessive levels of sunlight which cause UV damage to their DNA. These are often in the form of dark pigments, acting as sunscreens. These darken the ice, transferring more solar energy to the ice and hastening its melting rate. This is known as “biological darkening” or “bio-albedo” and is a modest, but highly consequential feedback on the melting rate of glacial ice masses. Thirdly, since many glaciers are expected to be lost in the coming decades, the biodiversity of glaciers is critically endangered. This matters because many of the intricate adaptations to life on ice, and the enigmatic interactions of the diverse microbiota living on ice are still poorly understood. Equally, the same adaptations and interactions can prove valuable for biotechnology, with products ranging from cold-active biological washing powders to potential new antibiotics at stake.
Ice cold hotspots of microbial diversity and activity – cryoconite
Most research on glacier ecology at the NERC Arctic Research Station has focused on cryoconite, which is a dark-brown grainy aggregate of minerals and dust formed by cyanobacteria. Degradation of cyanobacterial pigments forms humic substrates, similar to those found in soil. Grains of cryoconite are dispersed all over the ice surfaces of Svalbard glaciers, darkening the ice. Where enough grains are gathered, their impact on ice darkening is sufficient to form cryoconite holes, by enhancing the melt rate of the ice surface underlying the cryoconite. The holes deepen until the darkening effect is sufficiently weakened to achieve equilibrium with the surface melting rate, resulting in a stable pot-hole like structure with the cryoconite at its bed. This depth is coincident with optimal light level for the photosynthetic cyanobacteria’s capacity to grow, subsidizing the formation of cohesive grains of cryoconite hosting large numbers of diverse microbes. In spite of ambient temperatures which never exceed +1°C, microbes in cryoconite are as active as those in dryland soils, and are as abundant as the microbes in sewage. Measurements of cryoconite holes in the region in 2013 returned an average depth of 11 cm, but the exceptional warmth interspersed with heavy rain of 2024’s melting season means most cryoconite is dispersed across the surface rather than resident in holes. This means that the cryoconite has a strong darkening influence across the ice.
Algae on Arctic glacial surfaces
Two distinctive groups of algae (microscopic eukaryotic cells capable of photosynthesis) are found on the surface of Svalbard’s glaciers. The first are snow algae which are considered “green algae” in evolutionary terms, but often contain other pigments as sunscreens which colour their cells bright red. Snow algae are found in snowpacks (on and off glaciers) across the world, and have been described since antiquity (even Aristotle) but much remains to be understood about their ecology. Researchers have described cells which are green and capable of swimming up and down within the snowpack until they reach an optimum depth, while others describe red spheres reminiscent of red blood cells which rest upon the snowpack. The influence of snow algae are predominantly as the largest primary producers in the ecosystem, creating substantial pools of organic carbon, but where their abundance becomes very high within a snowpack, they are able to colour the snowpack red, creating blooms also known as “blood snow” or “watermelon snow” phenomena. On Svalbard glaciers these blooms are patchy, often associated with remnants of snow left on the banks of stream channels, or near bird cliffs.
The second group of algae are the glacier algae, which in evolutionary terms are near the divide between algae and rudimentary land plants. On Svalbard glaciers the most common species appears to be Ancylonema nordenskioldii which comprises chains of boxcar-like cells. These are coloured dark brown or purple (perhaps depending on the eyewitness!) by a pigment (purpurogallin) chemically similar to the pigments found in black tea. These pigments are found in bags within the cells which are situated above their photosynthetic factories (chloroplasts) to shade them from excessive sunlight. These microscopic parasols are able to rotate within the cells to ensure the chloroplasts are always shaded. Glacier algae are dispersed across the ice surface, and when their abundance is sufficient, they are considered to bloom. Such blooms have the most powerful biological darkening impact, and are visible from space (e.g. the dark zone of the southwestern Greenland Ice Sheet).
Contemporary research on glacier ecology at the NERC Station
Projects recently hosted at the station include NERC Cryo365, which studies year-round microbial activity on glacier surfaces (PI: Arwyn Edwards), with sampling in polar night, light winter and summer. A NERC Arctic Office project is studying the transfer of glacier microbes to downstream habitats (PI: Karen Cameron) Leverhulme iDAPT (PI: Chris Williamson) has studied glacier algae and their evolution. A Human Frontier Science Programme project (PI: James Bradley) is studying the airborne microbial communities deposited on glaciers.
Further reading:
https://www.carbonbrief.org/guest-post-is-glacier-carbon-good-or-bad-for-the-climate/
https://www.antarcticglaciers.org/glacier-processes/glacier-ecosystems/
A view over Svalbard – prominent glacier algae blooms (dark/purple ice surface, easily contrasted with bright ice exposed within crevasses) are apparent. Very little snow is left to nourish the glaciers for the future. 12th August 2024, Arwyn Edwards