Edited by Susan E. Trumbore, Max Planck Institute for Biogeochemistry, Jena, Germany, and approved May 1, 2017 (received for review February 20, 2017)
The Arctic is warming rapidly, causing permafrost soils to thaw. Vast stocks of nitrogen (>67 billion tons) in the permafrost, accumulated thousands of years ago, could now become available for decomposition, leading to the release of nitrous oxide (N2O) to the atmosphere. N2O is a strong greenhouse gas, almost 300 times more powerful than CO2 for warming the climate. Although carbon dynamics in the Arctic are well studied, the fact that Arctic soils store enormous amounts of nitrogen has received little attention so far. We report that the Arctic may become a substantial source of N2O when the permafrost thaws, and that N2O emissions could occur from surfaces covering almost one-fourth of the entire Arctic.
Permafrost in the Arctic is thawing, exposing large carbon and nitrogen stocks for decomposition. Gaseous carbon release from Arctic soils due to permafrost thawing is known to be substantial, but growing evidence suggests that Arctic soils may also be relevant sources of nitrous oxide (N2O). Here we show that N2O emissions from subarctic peatlands increase as the permafrost thaws. In our study, the highest postthaw emissions occurred from bare peat surfaces, a typical landform in permafrost peatlands, where permafrost thaw caused a fivefold increase in emissions (0.56 ± 0.11 vs. 2.81 ± 0.6 mg N2O m−2 d−1). These emission rates match those from tropical forest soils, the world’s largest natural terrestrial N2O source. The presence of vegetation, known to limit N2O emissions in tundra, did decrease (by ∼90%) but did not prevent thaw-induced N2O release, whereas waterlogged conditions suppressed the emissions. We show that regions with high probability for N2O emissions cover one-fourth of the Arctic. Our results imply that the Arctic N2O budget will depend strongly on moisture changes, and that a gradual deepening of the active layer will create a strong noncarbon climate change feedback.
Author contributions: C.V., M.E.M., M.J.-K., M.M., T.R.C., P.J.M., and C.B. designed research; C.V., M.E.M., R.E.L., M.J.-K., A.L., L.G., and T.T. performed research; L.G. contributed new reagents/analytic tools; C.V. analyzed data; and C.V., M.E.M., P.J.M., and C.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
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