Sensitivity of Methane Emissions to Later Soil Freezing in Arctic Tundra Ecosystems
Sensitivity of Methane Emissions to Later Soil Freezing in Arctic Tundra Ecosystems
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DOI：
10.1029/2019jg005242
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发表时间：
2019-08-01
影响因子：
3.7
通讯作者：
Zona, Donatella
中科院分区：
文献类型：
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作者：
Arndt, Kyle A.;Oechel, Walter C.;Zona, Donatella
大气中甲烷（CH 4）浓度是一种强有力的温室气体，再次上升，因此了解CH 4排放的控制至关重要。在北极苔原生态系统中，甲烷排放量的很大一部分来自寒冷季节，特别是在“零幕”期间，土壤在0摄氏度左右保持不冻。由于目前可获得的数据很少，对控制冷季CH 4排放的了解很少。本研究探讨了秋季ZC和CH 4排放量之间的关系，使用长期的土壤温度测量和CH 4通量从四个涡度相关（EC）塔在北方阿拉斯加。为了确定EC结果的大规模影响，我们调查了2001年至2017年美国国家海洋和大气管理局位于AK Utqiagvik的监测站陆地CH 4增强的时间变化及其与ZC的关联。我们发现，ZC延长到冬季（2001年至2017年为2.6 - 0.5天/年），陆地秋季CH 4增强与后期土壤冻结（0.79 - 0.18-ppb CH 4天（-1）未冻土）。ZC条件与测量期间（2013-2017年）所有EC塔的CH 4通量一致高于土壤冻结后。未冻土壤持续后，空气温度远低于0摄氏度，这表明空气温度对CH 4通量相对于土壤温度的预测能力较差。这些结果表明，土壤冻结后期会增加CH 4的损失，土壤温度应该用来模拟秋季CH 4的排放。简明扼要的语言摘要甲烷（CH 4）是一种强大的温室气体，每分子吸收的热量比二氧化碳（CO2）多。虽然甲烷在大气中的浓度较低，但它是仅次于二氧化碳的第二大温室气体。北极苔原生态系统是CH 4的潜在主要来源，因为土壤碳储量大，而且通常条件潮湿，有利于CH 4的产生。这项研究调查了冻土的持久性是否与北极地区较高的甲烷排放量有关。我们结合了长期的土壤温度测量，陆地CH 4增强从美国国家海洋和大气管理局监测站在Utqiagvik，AK，和CH 4排放量从北极苔原生态系统在阿拉斯加北坡的四个站。我们的研究结果表明，从2001年到2017年，土壤冻结较晚，较晚的土壤冻结与较高的秋季CH 4增强有关。鉴于未冻土壤与较高的甲烷排放量有关，较晚的土壤冻结可能有助于观察到的区域大气甲烷增加。在气温远低于0摄氏度之后，未冻土层仍然存在，这表明气温不能正确预测甲烷排放对气候变暖的敏感性。
The atmospheric methane (CH4) concentration, a potent greenhouse gas, is on the rise once again, making it critical to understand the controls on CH4 emissions. In Arctic tundra ecosystems, a substantial part of the CH4 budget originates from the cold season, particularly during the "zero curtain" (ZC), when soil remains unfrozen around 0 degrees C. Due to the sparse data available at this time, the controls on cold season CH4 emissions are poorly understood. This study investigates the relationship between the fall ZC and CH4 emissions using long-term soil temperature measurements and CH4 fluxes from four eddy covariance (EC) towers in northern Alaska. To identify the large-scale implication of the EC results, we investigated the temporal change of terrestrial CH4 enhancements from the National Oceanic and Atmospheric Administration monitoring station in Utqiagvik, AK, from 2001 to 2017 and their association with the ZC. We found that the ZC is extending later into winter (2.6 0.5 days/year from 2001 to 2017) and that terrestrial fall CH4 enhancements are correlated with later soil freezing (0.79 0.18-ppb CH4 day(-1) unfrozen soil). ZC conditions were associated with consistently higher CH4 fluxes than after soil freezing across all EC towers during the measuring period (2013-2017). Unfrozen soil persisted after air temperature was well below 0 degrees C suggesting that air temperature has poor predictive power on CH4 fluxes relative to soil temperature. These results imply that later soil freezing can increase CH4 loss and that soil temperature should be used to model CH4 emissions during the fall.Plain Language Summary Methane (CH4) is a powerful greenhouse gas, capturing more heat per molecule than carbon dioxide (CO2). Although CH4 is less concentrated in the atmosphere, it is the second most important greenhouse gas with respect to climate change after CO2. Arctic tundra ecosystems are potentially major sources of CH4, given large soil carbon storage and generally wet conditions, favorable to CH4 production. This study investigates if the persistence of unfrozen soils is associated with higher CH4 emissions from the Arctic. We combined long-term soil temperature measurements, terrestrial CH4 enhancements from the National Oceanic and Atmospheric Administration monitoring station in Utqiagvik, AK, and CH4 emissions from Arctic tundra ecosystems across four stations in the North Slope of Alaska. Our results show that from 2001 to 2017 the soil is freezing later and that later soil freezing is associated with higher fall CH4 enhancements. Given that unfrozen soils are related to higher CH4 emissions, a later soil freezing could contribute to the observed increase in the regional atmospheric CH4 enhancement. Unfrozen soil layers persisted after the air temperature was well below 0 degrees C, suggesting that air temperature does not properly predict the sensitivity of CH4 emissions to climate warming.