Is the Arctic methane budget changing?

甲烷(CH4)是仅次于二氧化碳的第二大温室气体。对大气中甲烷的自然来源和人为来源进行了深入研究，现已确立；然而，其全球和区域估计仍然存在很大的不确定性。从这一角度来看，北极圈上方的区域非常重要，因为现在活跃的甲烷排放源的独特组合，例如湿地和森林火灾，以及未来可能因区域气候变化而活跃的排放源。未来潜在的重要来源包括融化的永久冻土和富含甲烷的海洋沉积物(笼状物)。由于北极变暖的速度比世界其他地区快得多，这可能会引发活跃的CH4来源以及代表大量碳库(永久冻土)或气态CH4(笼状化合物)的各种变化。因此，拟议项目的目标是确定和量化北极甲烷排放到大气的主要来源，并有助于了解这些排放可能如何随着区域气候进一步变暖而变化。目前，北极甲烷测量的数量根本不足以对区域甲烷来源作出可靠估计，也不足以了解大气中甲烷浓度的最新趋势。除了稀缺的测量之外，大多数北极CH4研究都得到了对造成CH4排放的当地过程的运动观测的支持，这些过程大多在该地区最容易进入的夏季进行。但是，由于大多数甲烷源排放的间歇性，在某些情况下是季节性的，与零星的基于活动的采样相结合，无法对北极不同的CH4源产生可靠的排放估计。为了解决这一问题，我们建议建立全年连续测量环境空气中甲烷浓度和同位素组成的方法，并将以运动为基础的研究与预期的甲烷源排放的季节性和地点同步进行。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。这种方法需要对空气质量轨迹进行回顾分析，以确定具有观测到的同位素特征的空气的来源。更具体地说，我们建议在俄罗斯Teriberka(北纬69.2N，东经35.1度；俄罗斯北极海岸西北部)建立CH4连续测量，这将为中欧亚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的几个地点的环境空气进行详细的同位素研究。这些数据将与巴拉(苏格兰)和韦伯恩(诺福克)测量站的北极空气到达英国的记录进行比较。将我们的数据集与我们的国际同行的少数北极其他站的数据集结合起来，我们将确定北极区域气候的持续变化是否导致CH4排放增加。具体地说，我们将使用这些浓度和同位素数据以及p-TOMCAT化学传输和气象局名称模型来定位北极甲烷的来源，并量化排放的任何年际变化。除了这些主要目标外，我们计划定期测量在北极几个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。这种测量将不需要额外的收集或费用，因为它们将与CH4测量并行进行，从而提高成本效益。对其他气体种类的测量将有助于评估陆地和海洋上相关的北极过程和这些气体的来源排放，例如火灾排放(CO增加)、海洋变暖、海洋“死区”的扩大(由于溶解的O2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.