Greenhouse gases in the North: from local to regional scale (GHG-Nor)

WP1: Analyse and interpret flux measurements of CO2 at Andøya Carbon flux measurements at the Andøya Eddy covariance flux site were continued throughout 2013 and until 31 August, 2014. Operations were terminated on 1 September because of missing external funding. All data have been analysed with the new algorithm developed in cooperation with Magnus Lund at University of Lund/University of Aarhus in early 2013. In cooperation with the same universities, a publication with the title ?Low impact of dry conditions on the CO2 exchange of a subarctic blanket bog? by Lund et al. was prepared and submitted to Environmental Research Letters. During the remaining period of the project, the flux evaluation algorithm used by Lund et al. to evaluate the measurements is being implemented at NILU to enable future analyses of the complete Eddy covariance and high-resolution meteorological data set. WP2: Measure, analyze and interpret atmospheric observations of CH4, CO2 and N2O, 13CH4, Measurements of isotopic ratios of methane in Arctic requires very high precision (ca 0.05 o/oo). Currently there are no instruments suitable for field observations at a remote location as Zeppelin with this precision, instead we are sampling 5 times per week with appropriate steel canisters, and procedures. The samples are analyzed for 13dCH4 at Royal Holloway University and for D/HCH4, at University of Utrech. Combined information about DCH3 and 13dCH4 is particularly valuable to distinguish emissions from wetlands from hydrates from the ocean/sea floor, and wetlands from fossil sources. We do now have a time series of ca 2 year with these measurements, and we are waiting for the final data for analysis from the collaborating labs to work on the papers. New instrumentation at Zeppelin in 2010 allow for analysis of ethane together with CH4. This has also started last year as enough data is now available. This will provide further information about sources together with the isotopes. Ethane and CH4 has the same fossil sources, with a relatively stable ratio, but only CH4 comes from hydrates or wetlands. We are working on finalizing data analysis to publish this. N2O and CH4 from Zeppelin, with isotopic information serve as central input for WP3, and the model studies.. Furthermore we have established contact with a group in UK (University of East Anglia, School of Environmental Sciences) and assisted and guided them in installation of CH4/CO2 measurements at Kjølnes Lighthouse outside Berlevåg. This will give us access to these data, crucial for constraining model studies of source distribution of CH4 in the Arctic (see WP3). WP3: Quantify greenhouse gas fluxes on a regional scale by inverse modelling An inverse modelling system, FLEXINVERT, for greenhouse gases (GHGs) and other atmospheric species, has been developed based on the work of Stohl et al. (2009). FLEXINVERT is capable of resolving fluxes temporally (e.g. weekly, monthly) and can account for temporal and spatial error correlations in the prior fluxes. These developments were necessary for GHGs that have biosphere fluxes, and considerable temporal variations, such as CO2, CH4 and N2O. Additionally, the background concentration, i.e. the component of the concentration signal that is not accounted for in the period of the Lagrangian backward simulations (typically 10-20 days) can now be estimated by coupling to the output of a global Eulerian model, thus combining the advantages of both the high-resolution, high accuracy Lagrangian model and the Eulerian transport model with the ability to run for many years (at much lower resolution). Inversions using FLEXINVERT have been made for CH4 in Europe (Thompson and Stohl, 2014) and East Asia (Thompson et al, 2014). Methane inversions have also been made for the high northern latitudes for 2007 to 2011 and show higher emissions, relative to the prior, in Canada and Western Siberia, most likely owing to higher wetland emissions (paper in preparation). Atmospheric inversions for N2O have been made globally using the PYVAR inversion framework in collaboration with the Laboratoire des Sciences du Climat et l?Environnement, Gif sur Yvette, France. PYVAR uses the Eulerian global transport model, LMDZ, and its adjoint, thus enabling the fluxes to be optimized at the resolution of the transport model, i.e., 2.5 o × 3.75 o latitude by longitude. The inversion was made for 1999 to 2009 and focused on understanding inter-annual variations in N2O fluxes and how these depend on climate (Thompson et al., 2014b).

The proposed project will improve the knowledge of the emissions of CO2, CH4 and N2O and their budgets on local and regional scale at Northern latitudes, including the Arctic. CO2, CH4 and N2O are central greenhouse gases responsible for around 75% of the man-made greenhouse gas forcing since the year 1750. These gases have both natural and human-related sources, and CH4 has particularly large potential sources in the Arctic region. In the project NILU proposes to develop a method integrating atmospheric greenhouse gas measurements and inverse modelling in order to quantify the regional budgets of particularly atmospheric CH4. Attempt will also be made to quantify the regional budgets of N2O and CO2. The method is based on FLEXPART, combined with measurem ents from Birkenes, Andøya and Zeppelin, in addition to other greenhouse gas measurements from Europe and the Arctic available to NILU. Characterization of the isotopic signature of CH4 at Zeppelin is a part of the project. A synthesis of the sources cont ributing to elevated episodes of greenhouse gases at Zeppelin and Andøya will also be provided. Local CO2 fluxes from a pristine mire at Andøya will be analyzed as a part of the project to improve knowledge of the greenhouse gas emissions from this type o f ecosystem. These flux measurements supplements the source analysis based on inverse modeling method. In GHG-Nor there is also central to develop the institutional competence, and the project strongly supports the recent strategic greenhouse gas observat ional investments at NILU. The project is a collaborative project together with Bioforsk. Also activities strengthening the collaboration with other national and international institutes working on the understanding of the carbon cycle are a part of the p roject.