A silly question? Whilst most people would not fall into the ‘trap’ and suggest that it’s green*, it’s probably a fairly safe bet to say that Greenland is predominantly white. And that’s down to its extensive coverage of glacier/ice sheet [a total area of 1.8 million km² (695 000 square miles) – 14 times the size of England; the ice-free area amounts to 350 000 km² (135 000 square miles) – equivalent to the area of Germany]. However, increasingly this white blanket of ice is darkening. And, apart from how ‘dirty’ and aesthetically unattractive this may make the ice look, it has an important consequence – a darker surface is less reflective of the sun’s rays.
A direct effect of this reduced albedo is that the ice warms and melts. And as the ice gets darker it becomes more sensitive to atmospheric warming, itself in part related to elevated CO2 concentrations from human activities. And melting uncovers previously buried dark-pigmented impurities which further add to the reduced albedo.
This is an example of a positive feedback loop, albeit one with potential global consequences, such as sea level rise. Whilst some of this ‘biological darkening’ is attributed to deposition of black soot from wild fires elsewhere on Earth, it now appears that there is a more direct biotic cause for at least part of this malevolent melanisation. The darkening phenomenon isn’t evenly distributed over the ice surface, but is present as pigmented patches in the pock-marked landscape. Sun-assisted heating-up of aggregations of the wind-blown material – known as cryoconite – cause the ice beneath to melt.
Consequently, the site of what was once surface-situated material is ultimately seen as a dark deposit at the bottom of a water-filled cylindrical melt-hole. But, cryoconite isn’t just ‘dirt’, it contains microbes as well. And work by Jarishma Gokul et al. has begun to unravel the biotic origin of cryoconite.
Investigating material from an icecap in Svalbard (within the Arctic Circle, far north of Norway), they showed that cryoconite formation is driven by photosynthetic cyanobacteria assigned to Leptolyngbya/Phormidesmis pri(e)stleyi that dominate the community and bind together the granular cryoconite**. In that paper they also explore the microbial ecology of cryoconite and reveal a dynamic microbial community – an ecosystem in its own right – in this fascinating material.
So, when it comes to glacial melt, hue’s in charge? But, almost as soon as this complex photoautotroph-created microbial community is revealed it’s made even more complicated by a viral dimension; Sara Rassner et al. suggest that “a delicate interplay of bacterial and viral strategies affects biogeochemical cycling upon glaciers and, ultimately, downstream ecosystems”.
But, and lest those prokaryotic photosynthesisers get all the blame for Arctic ice melt, Stefanie Lutz et al. demonstrate that ice cover by so-called red-pigmented ‘snow algae’ (specifically, eukaryotic taxa such as an ‘uncultured Chlamydomonadaceaen’, Chloromonas polyptera, C. nivalis, C. alpina, and Raphidonema sempervirens) can also reduce albedo (and hence increase ice melt). Arctic algology; colourful work, if a little on the dark side…
* Allegedly, Greenland is so-called because of a smart bit of ancient PR (Public Relations)/marketing by one Erik the Red. Originally, he was banished there from Iceland (which is actually greener than its name might suggest) as a punishment for murder/manslaughter. But, after his period of exile was up he was keen to attract others to that northern land so it could be settled by Europeans. To induce them to make the trip he is said to have described that ice-covered island as a green (and, no doubt, pleasant…) land (and which – in the interests of fairness – does have some green bits).
** Interestingly – and an example of ‘great minds thinking alike’? – Phormidesmis priestleyi was also identified as the likely “key species for primary production and the formation of the granules” of cryoconite on Qaanaaq Glacier (NW Greenland) by Jun Uetake et al..
[Ed. – lest the spectacular natural phenomenon of Greenland’s glaciers soon becomes a memory, treat yourself to these majestic creations as seen through the eyes of an artist, or the photographer’s lens. And, if you’re the slightest bit curious as to how P. priestleyi does so well in the Arctic cold, read Nathan Chrismas et al.’s article.]
Marco Tedesco, Sarah Doherty, Xavier Fettweis, Patrick Alexander, Jeyavinoth Jeyaratnam, Julienne Stroeve, 2016, 'The darkening of the Greenland ice sheet: trends, drivers, and projections (1981–2100)', The Cryosphere, vol. 10, no. 2, pp. 477-496 http://dx.doi.org/10.5194/tc-10-477-2016
Jarishma K. Gokul, Andrew J. Hodson, Eli R. Saetnan, Tristram D. L. Irvine-Fynn, Philippa J. Westall, Andrew P. Detheridge, Nozomu Takeuchi, Jennifer Bussell, Luis A. J. Mur, Arwyn Edwards, 2016, 'Taxon interactions control the distributions of cryoconite bacteria colonizing a High Arctic ice cap', Molecular Ecology, vol. 25, no. 15, pp. 3752-3767 http://dx.doi.org/10.1111/mec.13715
Sara M. E. Rassner, Alexandre M. Anesio, Susan E. Girdwood, Katherina Hell, Jarishma K. Gokul, David E. Whitworth, Arwyn Edwards, 2016, 'Can the Bacterial Community of a High Arctic Glacier Surface Escape Viral Control?', Frontiers in Microbiology, vol. 7 http://dx.doi.org/10.3389/fmicb.2016.00956
Stefanie Lutz, Alexandre M. Anesio, Rob Raiswell, Arwyn Edwards, Rob J. Newton, Fiona Gill, Liane G. Benning, 2016, 'The biogeography of red snow microbiomes and their role in melting arctic glaciers', Nature Communications, vol. 7, p. 11968 http://dx.doi.org/10.1038/ncomms11968
Jun Uetake, Sota Tanaka, Takahiro Segawa, Nozomu Takeuchi, Naoko Nagatsuka, Hideaki Motoyama, Teruo Aoki, 2016, 'Microbial community variation in cryoconite granules on Qaanaaq Glacier, NW Greenland', FEMS Microbiology Ecology, vol. 92, no. 9, p. fiw127 http://dx.doi.org/10.1093/femsec/fiw127
Nathan A. M. Chrismas, Gary Barker, Alexandre M. Anesio, Patricia Sánchez-Baracaldo, 2016, 'Genomic mechanisms for cold tolerance and production of exopolysaccharides in the Arctic cyanobacterium Phormidesmis priestleyi BC1401', BMC Genomics, vol. 17, no. 1 http://dx.doi.org/10.1186/s12864-016-2846-4