Much stronger tundra methane emissions during autumn freeze than spring thaw

• Published in: Global Change Biology
• Main Authors: Bao, Tao, Xu, Xiyan, Jia, Gensuo, Billesbach, David P., Sullivan, Ryan C.
• Other Authors: U.S. Department of Energy
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Arctic; Tundra
• Online Access: http://dx.doi.org/10.1111/gcb.15421; https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.15421; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/gcb.15421; https://onlinelibrary.wiley.com/doi/am-pdf/10.1111/gcb.15421

Abstract Warming in the Arctic has been more apparent in the non‐growing season than in the typical growing season. In this context, methane (CH 4 ) emissions in the non‐growing season, particularly in the shoulder seasons, account for a substantial proportion of the annual budget. However, CH 4 emissions in spring and autumn shoulders are often underestimated by land models and measurements due to limited data availability and unknown mechanisms. This study investigates CH 4 emissions during spring thaw and autumn freeze using eddy covariance CH 4 measurements from three Arctic sites with multi‐year observations. We find that the shoulder seasons contribute to about a quarter (25.6 ± 2.3%, mean ± SD ) of annual total CH 4 emissions. Our study highlights the three to four times higher contribution of autumn freeze CH 4 emission to total annual emission than that of spring thaw. Autumn freeze exhibits significantly higher CH 4 flux (0.88 ± 0.03 mg m −2 hr −1 ) than spring thaw (0.48 ± 0.04 mg m −2 hr −1 ). The mean duration of autumn freeze (58.94 ± 26.39 days) is significantly longer than that of spring thaw (20.94 ± 7.79 days), which predominates the much higher cumulative CH 4 emission during autumn freeze (1,212.31 ± 280.39 mg m −2 year −1 ) than that during spring thaw (307.39 ± 46.11 mg m −2 year −1 ). Near‐surface soil temperatures cannot completely reflect the freeze–thaw processes in deeper soil layers and appears to have a hysteresis effect on CH 4 emissions from early spring thaw to late autumn freeze. Therefore, it is necessary to consider commonalities and differences in CH 4 emissions during spring thaw versus autumn freeze to accurately estimate CH 4 source from tundra ecosystems for evaluating carbon‐climate feedback in Arctic.