Arctic permafrost has been the subject of much global warming worry, but not so much detailed research. A new survey of North American Arctic permafrost published in Nature Geoscience this week (subscription required) breaks new ground, literally.
News accounts have focused on the paper’s bottom-line estimate: there is 60% more carbon frozen up there than previously thought. That’s a total of 98.2 billion tonnes of carbon, one-sixth of the amount currently circulating through the atmosphere.
Existing estimates already show more permafrost carbon around the globe than atmospheric carbon. If warming – which is happening faster in the Arctic than anywhere else – releases even a small portion of that store into the atmosphere as carbon dioxide and methane, the results won’t be pretty, especially if the amount frozen in the Asian north is also more than expected. Permafrost has been called a “slow-motion time bomb”, and the effects of its melting are not included in most global climate models.
The new research is by Chien-Lu Ping of the University of Alaska Fairbanks and colleagues. How did they do it?
Well, not with video cameras and pickup trucks. But they did use portable jackhammers. The heavy machinery dug deeper than shovels had previously, which accounts for their finding much more carbon.
Besides digging deeper, Ping et al looked wider than past studies, taking in 117 locations over a variety of landscapes. Christian Beer writes in a News and Views on the paper (subscription required):
The great spatial extent of their dataset, and its coverage of a variety of different landscape
types, including lowlands, uplands, rubblelands and mountainous soils, make their samples more representative of the North American Arctic than any previously available dataset.
And because the authors captured how carbon stocks vary both across landscapes and with depth, their data can be used to get a better idea of how much carbon is stored in distant frosty regions, and to figure out the processes that affect the stocks over time. The Arctic soil is not an inert mass of frozen dirt: organic carbon is stored there in the first place when the thawing, cracking, boiling upper layer sucks biological detritus down to the ice below, where it gets too cold to rot.
This heaving harbor for organic matter behaves differently in the four different landscape types, find Ping et al. According to Beer, we need to better understand such shifts in order to predict future storage and release of carbon – and the Ping et al data is great for testing ideas of how permafrost works.