Methane Production in the Arctic: Under-recognized Cold Season and Upland Tundra - Arctic Methane Sources-UAMS

在这个项目中，我们将使用最先进的方法和知识来更好地了解北极向大气释放甲烷（CH4）的当前模式和控制措施，并改进主要模型，以更好地模拟随着地球变暖，北极未来释放的CH4。大气中的甲烷（CH4）是第二重要的温室气体（仅次于二氧化碳），具有强烈的人为来源。北纬高纬度陆地生态系统约占热带外生物源湿地排放的50%。更重要的是，未来北极的甲烷排放量可能会急剧增加。北极土壤顶部3米的巨大有机碳储量（约1,300 GtC）以及北极地区经历和预测的快速气候变化，导致本世纪极有可能从这些土壤中释放出大量生物源性CH4。尽管来自北极的CH4通量很重要，但现在和将来，人们对生物源和天然CH4排放总量的了解很少，建模也很差（Fisher et al., 2014）。2013年，我们更新了阿拉斯加北极地区的5个涡动相关（EC）塔，使其能够全年可靠地运行并测量CH4通量。最初的测量产生了两个意想不到且非常重要的发现：1)寒冷季节的CH4排放量占年排放量的50%；2)干燥的高地冻原比潮湿的淹没冻原排放更多的CH4 （Zona et al . 2016 PNAS）。这些观测和过程目前尚未纳入用于计算当前和预测未来北极甲烷排放的主要全球陆地表面/碳循环模型。验证这一新的认识，并将其纳入英国和其他地方使用的模式，将彻底改变我们准确计算和模拟陆地甲烷通量的能力。这些结果，如果得到本项目产出的支持，对于验证当前的基线排放，检测变化的基线，以及有信心地预测未来北极生物源性甲烷排放至关重要。该项目有两个总体目标：(1)确定寒冷季节和高地冻土带在北极CH4排放中的模式、控制和重要性；(2)将这一认识纳入JULES、LPJ和TCF，从而显著提高我们估计当前和预测未来北极CH4通量的能力。预计这项工作将通过新的信息和模式开发影响政策，这些信息和模式将通过会议和出版物进行报告，并在即将发布的IPCC报告中加以引用。在该项目中，我们将继续全年观测甲烷向大气的释放，以及与这些通量相对应的大气和土壤环境。我们将开展新的实验和观测，以了解控制观测到的CH4通量的过程和条件，包括一个新的测量CO2、CH4和222Rn浓度的系统，该系统允许根据土壤深度和雪层自主地全年测定CH4的产生、消耗和通量。我们将全年测量[CH4]， d13CH4将有助于确定不同地点和季节表层土壤中甲烷氧化的重要性。我们将确定GPP在控制CH4生成速率中的作用。我们还将确定维管植物的重要性，为深层产生的甲烷提供管道，通过氧化表面层逃逸到大气中。这一新信息将为北极社区使用的模型的开发和改进提供信息。这些模型的性能将使用模型开发中未使用的唯一数据集进行验证。因此，我们希望UAMS能够对社区在不断变化的世界中计算当前和充满信心地预测未来北极CH4排放量的能力产生重大影响，从而更好地为政策决策提供信息。

In this project, we will use state of the art approaches and knowledge to better understand the current patterns of and controls on methane (CH4) release from the Arctic to the atmosphere and to improve major models to better simulate future releases of CH4 from the Arctic as the planet warms. Atmospheric methane (CH4) is the second most important greenhouse gas (after CO2) that has strong anthropogenic origins. High northern latitude terrestrial ecosystems account for ca. 50% of extra-tropical biogenic wetland emissions. More importantly methane emissions from the Arctic could increase dramatically in the future. The very large organic carbon stocks (>1,300 GtC) in the top 3 m of Arctic soils and the rapid climate change experienced and predicted in the Arctic, results in a very real possibility of large biogenic CH4 release from these soils in this century. Despite the importance of CH4 fluxes from the Arctic, now and in the future, biogenic and total natural CH4 emissions are poorly understood and very poorly modelled (Fisher et al., 2014).In 2013, we updated five eddy covariance (EC) towers in Arctic Alaska to operate reliably year-round and measure CH4 fluxes. Initial measurements yielded two unexpected and highly significant findings: 1) cold season CH4 emissions account for >50% of annual emissions and 2) drier upland tundra are larger emitters of CH4 than wetter inundated tundra (Zona et al 2016 PNAS). These observations and processes are not now incorporated in leading global land-surface/carbon-cycle models used to calculate current and predict future CH4 emissions from the Arctic. Verifying this new understanding and incorporating this understanding into models used in the UK and elsewhere will revolutionize our ability to accurately calculate and model terrestrial CH4 fluxes. These results, if supported by the outputs of this project, are critical to verifying current baseline emissions, detecting a changing baseline, and for predicting, with confidence, biogenic CH4 emissions from the Arctic in the future. This project has two overarching objectives: (1) determining the patterns of, controls on, and importance of cold season and upland tundra in Arctic CH4 emissions; (2) incorporating this understanding into JULES, LPJ and TCF, thus significantly improving our ability to estimate current and predict future CH4 fluxes in the Arctic. This work is expected to impact policy through new information and model development, reported through conferences and publications and referenced in upcoming IPCC reports. In the project, we will continue year-round observation of methane release to the atmosphere, and the atmospheric and soil environment that corresponds to these fluxes. We will initiate new experiments and observations to understand the processes and conditions controlling the observed CH4 fluxes including a new system of measurement of CO2, CH4, and 222Rn concentrations that allow autonomous, year-round, determination of CH4 production, consumption, and flux by soil depth and snow layer. We will measure year-round [CH4] and d13CH4 will help identify the importance of methane oxidation in surface soil layers at different locations and seasons. And we will determine the role of GPP in controlling rates of CH4 production. We will also determine the importance of vascular plants in providing a conduit for CH4 produced at depth, to escape to the atmosphere past an oxidizing surface layer. This new information will inform model development and improvement of models used by the Arctic community. Performance of these models will verified with unique data sets not used in model development. As a result, we intend UAMS to have a major impact on the communities' ability to calculate current and to predict with confidence future Arctic CH4 emissions in a changing world and thereby better inform policy decisions.