Bacteria could be speeding up the darkening of Greenland's ice
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Version 0 of 1. A single species of bacteria could be about to accelerate the melting of Greenland. A photosynthesising microbe from a genus called Phormidesmis has been identified as the guilty party behind the darkening of Greenland. It glues soot and dust together to form a grainy substance known as cryoconite. As the surface darkens, the Greenland ice becomes less reflective, more likely to absorb summer sunlight and more likely to melt. And, Dr Arwyn Edwards, a biologist at Aberystwyth University tells the Microbiology Society’s annual conference in Liverpool today, cryoconite holes now pockmark 200,000 square kilometres of the Greenland ice sheet. “I think this is going to contribute to the overall picture of Greenland melting. Greenland holds about seven metres of sea level rise,” said Edwards. “There is considerable uncertainty over the rates and timings of that melt. However it seems more likely that we will commit to a longer-term melting of the ice sheet within our century. The question is: how much are these bacterial processes contributing?” Two things keep the Arctic ice sheets stable: one is the temperature, the other the albedo, or reflectivity of the ice. Clean polar ice bounces two-thirds of sunlight back into space. But the Arctic region is the fastest warming on the planet and the cryoconite effect has reduced the albedo of the ice sheet dramatically: where the microbes have been at work, four-fifths of the radiation is now absorbed, and the ice is melting faster. Scientists have known about the cryoconite phenomenon for more than a century – the word was coined during an expedition to Greenland by Nils Adolf Erik Nordenskiöld in 1870 – but not the identity of the culprit. Britain’s Natural Environment Research Council has now put £2.4m into such research and working in Svalbard, Edwards and colleagues identified the species that triggers the process of microbial change on the ice sheet. They confirmed its presence in western Greenland and on the Petermann Glacier in north-west Greenland. “If we recognize ice species as a living landscape we can see that the microbes themselves are able to change the glacial surface,” Edwards said. “It’s only recently that we’ve begun to understand that these cryoconite holes are dynamic, changing in size and shape. Microbes are capable of ecosystem engineering and respond to changes in their environment all the time.” Researchers have repeatedly confirmed an acceleration of glacial melting rates on the biggest body of ice in the northern hemisphere. They have also identified a pattern of darkening. What the new study reveals is the important role of one microbial species among many that have adapted to snow and ice. The researchers cannot yet put a measure to the microbial contribution. However, they now have evidence that one member of the cyanobacteria family is working in the dust and soot to form granules which darken the ice, cause it to melt into holes maximized to catch sunlight, to fill with water, to release nutrients frozen in the ice, and create conditions for other microbes to join in the process. The culprit might be microscopic, but the impact is visible. And not just visible. “It is very difficult to walk around on the ice surface without tripping into one of these cryoconite holes. I have done that myself. These are not small entities we are talking about, they are pothole size to dinner plate size to bin lid size. They are literally pockmarking the ice surface itself,” Dr Edwards said. |