Isotopic constraints on the Arctic methane budget

点击翻译按钮获取中文摘要

This project is designed to determine the active methane sources in the Arctic by measurement of d13C(CH4) at several key sites, and by trajectory modelling studies to identify the location, nature and seasonality of inputs. Understanding the sources of Arctic methane is essential, given the risk of positive-feedback responses to greenhouse warming. Examples include clathrate release, enhanced wetland output and sharply increased fire emissions. The danger of sudden runaway methane release is arguably among the greatest unknowns in global warming: here lies a significant potential risk of abrupt, rather than gradual climate change. The best tool to understand sources is isotopic fingerprinting, identifying them by their d13C(CH4) isotopic signature in winds, traced back to source by back-trajectory analysis. The intentions in this project are: 1. To collect samples of ambient air at chosen key locations and analyse them for CH4 mixing ratio and d13C(CH4). 2. To study a variety of Arctic CH4 sources, especially wetlands, but also fires, gas deposits and clathrates, to assess timing of emissions, isotopic character, and distribution. 3. To use back-trajectory analysis, compared to regional background, to locate sources and their isotopic character and seasonality. The project has several components: 1: d13C measurements of ambient air. In the High Arctic, at Ny Alesund (Spitsbergen, Svalbard), regular bag samples will be collected at Zeppelin mountain station, sampling air both from the westerly Atlantic background and also easterly Arctic (Siberian) air from varied sources (especially gas in winter; wetland in summer). At Pallas station in Arctic Finland, just above the Arctic circle, a similar sampling program will be implemented to sample westerly air from less northerly Atlantic, and easterly air from Russia. Flasks will also be collected for mixing ratio analysis only (St. Petersburg lab) at Teriberka (Russian Kola) and in the Ob River estuary (gasfields). At Weybourne, incursions of Arctic air arrive at the N. Sea coast. Tanks of air will be collected for high precision analysis of d13C(CH4). Finally, at Mace Head, Ireland, or an alternative North Atlantic site, the d13C(CH4) seasonality in background Atlantic air will be sampled, for distant inputs of fire or wetland methane from Canada and the high Arctic. 2 Source studies.will include wetland and forest studies at Pallas, to observe d13C(CH4) in ambient air (i.e. after release) in a set of field campaigns in several seasons. Measurements and sample collection will be made above wetlands and forests (tower), including diurnal air sampling and chamber experiments. Other source studies will include fire sampling (Canada), and gas sampling. 3. Back-trajectory modelling will use the data to identify regional methane emissions. Single-trajectory studies of air arriving at the collection stations will be used, compared against regional and seasonal background air, to locate individual sources. This study will characterise emissions by isotopic signature and hence suggest source type, and will watch these change over the seasons as emission strength varies. Multiple trajectory studies wil use sector analysis, to identify major regions of Arctic input. The Arctic is now and is in future likely to be the fastest-warming region of the planet. Potentially it could become a very major source of methane, and hence a source of strong positive feedback into greenhouse warming. This is one of the most dangerous regions of the planet in terms of 'warming feeding the warming'. The work will provide a UK contribution both to International Polar studies in the aftermath of IPY, and to the UN's Global Atmosphere Watch, under the aegis of the World Meteorological Organisation and (for isotopes) the International Atomic Energy Agency. More widely, the results will be important to the global understanding of the carbon budget and the Kyoto process.