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Arctic permafrost set for faster carbon leak

July 18, 2018, by Tim Radford

Permafrost near the study site in northern Sweden. Image: By Caitlin Singleton

Researchers now know more about the intricate mechanisms of change in the thawing Arctic permafrost. And what they know is ominous.

LONDON, 18 July, 2018 – The Arctic permafrost – a frozen store of at least half the planet’s organic carbon – could be about to release more carbon in the form of greenhouse gases than it absorbs in the growing season.

A 42-year study of atmospheric carbon dioxide over the north slope of Alaska reveals that the “cycling time” – that is, the time a quantity of carbon is locked away in the frozen subsurface of the tundra regions – has been reduced by more than 13% over four decades.

This means that in response to global warming, the world’s greatest single store of ancient sunshine in the form of peat and other preserved vegetation is about to surrender yet more carbon dioxide and methane, and accelerate the process.

And a second study delivers better understanding of the mechanisms that will get to work as the permafrost thaws.

All decay from foliage and wood is achieved by soil microbes – and researchers have now taken more than 200 samples from a stretch of once-frozen bog and fen in northern Sweden to identify the genomic mix of fungi, bacteria and archaeo-bacteria ready and waiting to turn old vegetation back into atmospheric carbon.

“Large amounts of carbon sequestered in perennially frozen permafrost are becoming available for microbial degradation”

The first study is published in the journal Science Advances: Korean, US and Chinese scientists went to the data archives of the US National Oceanic and Atmospheric Administration to analyse the variations in carbon dioxide over Barrow, Alaska between 1974 and 2015.

Levels vary naturally from season to season as plants flower, bloom and die back in the brief polar summer. But over the 42-year span of the study, the scientists also found a pattern of change.

Respiration during the early cold season was, under the warming of the last four decades, beginning to outpace the take-up of carbon during the growing season, as the tundra dwindled, and the boreal woodlands began to march northwards.

And, they warn, by 2100 this potentially means an increase in atmospheric concentrations of greenhouse gases, an increase of from 50 billion tonnes of carbon to 200 billion tonnes.

More accurate prediction

Swedish and US researchers, led by Australian microbiologists, report in the journal Nature that they used new software to identify the DNA of 1,500 microbe samples, all new to science, and all little cogs in the complex machinery of decay, found in the thawed, partially thawed, and frozen first three metres of northern Swedish permafrost.

With luck and patience, the extra understanding of the biochemistry of change in the permafrost should lead to more accurate predictions of global warming.

“As global temperatures rise, large amounts of carbon sequestered in perennially frozen permafrost are becoming available for microbial degradation,” said Ben Woodcroft, of the Australian Centre for Ecogenomics at the University of Queensland, who led the research.

“Until now, accurate prediction of greenhouse gas emissions produced from thawing permafrost has been limited by our understanding of permafrost microbial communities and their carbon metabolisms.” – Climate News Network

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