Is the Arctic Methane Budget Changing?

甲烷（CH4）是第二重要的温室气体（仅次于二氧化碳）。对大气中甲烷的来源，包括自然的和人为的，已经进行了深入的研究，现在已经得到了很好的确定；然而，他们的全球和区域估计仍然存在很大的不确定性。从这个角度来看，北极圈以上的区域非常重要，因为它有一个独特的组合，既有现在活跃的CH4排放源，如湿地和森林火灾，也有由于区域气候变化而可能在未来变得活跃的CH4排放源。未来潜在的重要来源包括融化的永久冻土和富含ch4的海洋沉积物（笼状物）。由于北极的变暖速度比世界其他地区快得多，这可能会引发活跃CH4源以及代表大量碳库（永久冻土）或气态CH4（包合物）的源的各种变化。因此，拟议项目的目标是定位和量化北极向大气排放甲烷的主要来源，并有助于了解这些排放如何随着区域气候进一步变暖而变化。目前，北极CH4测量的数量根本不足以对区域CH4源作出可靠的估计，也不足以了解大气CH4浓度的近期趋势。除了稀缺的测量之外，大多数北极CH4研究都得到了基于运动的对导致CH4排放的当地过程的观测的支持，这些观测主要是在该地区最容易到达的夏季进行的。但是，由于大多数CH4源排放的偶然性，在某些情况下是季节性的，与零星的基于运动的采样相对应，不可能对不同的北极CH4源产生可靠的排放估计。为了解决这个问题，我们建议建立全年连续测量环境空气中CH4浓度和同位素组成，并将基于运动的研究与CH4源排放的预期季节性和位置同步。由于不同来源排放的甲烷具有不同的同位素“特征”，因此有可能将观测到的排放归因于特定来源。这种方法需要对气团轨迹进行回顾性分析，以根据观测到的同位素特征确定空气的起源。更具体地说，我们建议在俄罗斯Teriberka （69.2N, 35.1E；俄罗斯西北北极海岸）建立连续的CH4测量，这将为欧亚大陆中部的北极过程提供新的见解。此外，我们计划对欧洲和俄罗斯北极地区几个地点的环境空气进行详细的同位素研究。这些数据将与到达英国的巴拉（苏格兰）和韦伯恩（诺福克）测量站的北极空气记录进行比较。将我们的数据集与我们的国际同事的少数其他北极站的数据集相结合，我们将确定北极区域气候的持续变化是否导致甲烷排放增加。具体来说，我们将使用这些浓度和同位素数据与p-TOMCAT化学运输和气象局NAME模型来定位北极CH4源并量化排放的任何年际变化。除了这些主要目标之外，我们还计划定期测量从几个北极地点收集的玻璃瓶中其他气体（CO2、CO、N2O、SF6、H2、O2/N2和Ar/N2）的大气浓度。由于这些测量将与CH4测量同时进行，因此不需要额外的收集或成本，从而提高了成本效率。对其他气体种类的测量将有助于评估相关的北极过程和这些气体在陆地和海上的源排放，例如火灾排放（CO增加）、海洋变暖、海洋“死亡区”的扩大（由于溶解的O2量减少）以及永久冻土和湿地的融化。

Methane (CH4) is the second (after CO2) most important greenhouse gas. Sources of CH4 to the atmosphere, both natural and human-driven, have been intensively studied and are now well established; however, their global and regional estimates still suffer from large uncertainties. The region above the Arctic Circle is very important from this perspective because of a unique combination of CH4 emission sources which are active now, e.g. wetlands and forest fires, and those which may become active in the future owing to regional climate change. Potentially important future sources include thawing permafrost soils and CH4-rich oceanic sediments (clathrates). Since the Arctic has been warming much faster compared to the rest of the world, this may trigger various changes in the active CH4 sources as well as those that represent large pools of carbon (permafrost soil) or gaseous CH4 (clathrates). The goal of the proposed project is thus to locate and quantify major sources of Arctic CH4 emissions to the atmosphere and contribute to understanding how these emissions may change with further regional climate warming. At present, the number of Arctic CH4 measurements is simply not sufficient to either make reliable estimates of regional CH4 sources or to understand recent trends in atmospheric CH4 concentrations. In addition to scarce measurements, most Arctic CH4 studies have been supported by campaign-based observations of the local processes responsible for CH4 emissions, mostly in summer when the region is most accessible. But owing to the episodic, and in some instances seasonal, nature of most CH4 source emissions paired against sporadic campaign-based sampling, it has not been possible to produce reliable emission estimates of different Arctic CH4 sources. To address this problem, we propose to establish year-round continuous measurements of CH4 concentration and isotopic composition in ambient air, and to synchronise campaign-based studies with the expected seasonality and location of the CH4 source emissions. Since CH4 emitted from different sources has distinct isotopic 'signatures', it is possible to attribute the observed emissions to the particular sources. This approach requires a retrospective analysis of the air mass trajectories to establish the origin of air with the observed isotopic signature. To be more specific, we propose to establish continuous CH4 measurements at Teriberka, Russia (69.2N, 35.1E; NW Russian Arctic coast), which will provide new insight into central Eurasian Arctic processes. In addition, we plan to carry out detailed isotopic studies of ambient air from several locations in the European and Russian Arctic. These will be compared with records of Arctic air reaching the UK at measurement stations at Barra (Scotland) and Weybourne (Norfolk). Combining our datasets with those from the small number of other Arctic stations of our international colleagues, we will determine whether ongoing changes in the Arctic regional climate are resulting in increased CH4 emissions. Specifically, we will use these concentration and isotopic data with the p-TOMCAT chemical transport and Met Office NAME models to locate Arctic CH4 sources and quantify any interannual changes in emissions. In addition to these main objectives, we plan to make regular measurements of atmospheric concentrations of other gases (CO2, CO, N2O, SF6, H2, O2/N2 and Ar/N2) from glass bottles collected at several Arctic locations. Such measurements will not require additional collections or costs as they will be made in parallel to the CH4 measurements, improving cost efficiency. Measurement of other gas species will help to assess the linked Arctic processes and source emissions of these gases, both on land and at sea, e.g. fire emissions (increased CO), ocean warming, expansion of oceanic 'dead zone' (due to decreased amounts of dissolved O2) and thawing permafrost soils and wetlands.