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New Arctic feedback: vicious peat circles

peatcircles.jpgResearchers have discovered new hot spots for emissions of the greenhouse gas nitrous oxide: barren patches of peat dotted across northern tundra. And warming in the Arctic – just as it threatens to multiply emissions of carbon dioxide and methane from thawing permafrost and drying bogs – could accelerate the output of this lesser-known climate change culprit, according to a study in Nature Geoscience this week (subscription).

Nitrous oxide is the other other greenhouse gas. In the new paper, Pertii Martikainen of the University of Kuopio in Finland and colleagues call it third most important behind carbon dioxide and methane, noting that it contributes a reported 6% to global warming. It’s not been considered a player at all in the Arctic, where the few scientists who’ve looked for the gas have found negligible emissions. But that’s because they’ve been looking in the wrong places, say Martikainen’s team.

To get nitrous oxide you need to deliver plenty of nitrogen to microbes that release the gas as waste. Most Arctic ecosystems have little nitrogen available, with plants taking up much of it. But in some permafrosted peatlands, the churning of surface soil by repeated freezes and thaws, known as cryoturbation, creates ‘peat circles’ – bare spots where no plants grow. The heaving ground also speeds decay and the release of carbon dioxide, leading to a low carbon/nitrogen ratio that favours nitrous oxide production.

In the peat circles the authors studied in Northern Russia, the result is emissions worthy of the world’s most nitrogen-rich environments. They report that these peat patches during the growing season release as much nitrous oxide per square metre as tilled and fertilized croplands do in summer, and at least as much as tropical forests do year-round.

Extrapolating their measurements around the globe, they estimate that the greenhouse effect of nitrous oxide emissions from peat circles today is about 4% of that from methane now seeping out of Arctic lands. But there’s evidence that northern warming will boost cryoturbation and make more peat circles crop up. “Even a small increase in the abundance of these N2O emitting surfaces with global warming would result in significantly enhanced N2O emissions from the Arctic,” the group warns. The carbon dioxide let loose by cryoturbation goes unmentioned at this point in the paper, but presumably it could be subject to the same enhancement. So we may be looking at an greenhouse gas-peat circle feedback loop – on top of the region’s other, less literal vicious circles. The researchers conclude:

not only carbon, but also nitrogen stored in permafrost soils, has to be considered when predicting the atmospheric impact of Arctic tundra in a changing climate.

Anna Barnett

Image: Peat circles; Credit: Maija Repo


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