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.]