New contributions of measurements in Europe to the global inventory of the stable isotopic composition of methane

Abstract

Abstract. Recent climate change mitigation strategies rely on the reduction of methane (CH4) emissions. Carbon and hydrogen isotope ratio (δ13CCH4 and δ2HCH4) measurements can be used to distinguish sources and thus to understand the CH4 budget better. The CH4 emission estimates by models are sensitive to the isotopic signatures assigned to each source category, so it is important to provide representative estimates of the different CH4 source isotopic signatures worldwide. We present new measurements of isotope signatures of various, mainly anthropogenic, CH4 sources in Europe, which represent a substantial contribution to the global dataset of source isotopic measurements from the literature, especially for δ2HCH4. They improve the definition of δ13CCH4 from waste sources, and demonstrate the use of δ2HCH4 for fossil fuel source attribution. We combined our new measurements with the last published database of CH4 isotopic signatures and with additional literature, and present a new global database. We found that microbial sources are generally well characterised. The large variability in fossil fuel isotopic compositions requires particular care in the choice of weighting criteria for the calculation of a representative global value. The global dataset could be further improved by measurements from African, South American, and Asian countries, and more measurements from pyrogenic sources. We improved the source characterisation of CH4 emissions using stable isotopes and associated uncertainty, to be used in top-down studies. We emphasise that an appropriate use of the database requires the analysis of specific parameters in relation to source type and the region of interest. The final version of the European CH4 isotope database coupled with a global inventory of fossil and non-fossil δ13CCH4 and δ2HCH4 source signature measurements is available at https://doi.org/10.24416/UU01-YP43IN (Menoud et al., 2022a).

Stable Carbon Isotope Signature of Methane Released From Phytoplankton

“…Global CH 4 monitoring is usually based on measurements of CH 4 mixing ratios, that is, quantification of CH 4 emissions, while a growing number of studies include measurements of δ 13 C-CH 4 values in order to better constrain the strengths of different sources in context of total emissions (e.g., Allen, 2016;Dlugokencky et al, 2011;Fletcher & Schaefer, 2019;Houweling et al, 2017;Menoud et al, 2022;Nisbet & Weiss, 2010). Ranges of measured δ 13 C-CH 4 values have been reported for conventional sources which might be classified into thermogenic (from geological processes), pyrogenic (from biomass burning) and biogenic (from methanogenic archaea) origin (Saunois et al, 2020).…”

Stable Carbon Isotope Signature of Methane Released from Phytoplankton

“…The data is provided in the Supporting Information (Figure S3; Text S6) and are considered in the discussion section below. Global CH 4 monitoring is usually based on measurements of CH 4 mixing ratios, i.e., quantification of CH 4 emissions, while a growing number of studies include measurements of δ 13 C-CH 4 values in order to better constrain the strengths of different sources in context of total emissions (e.g., Allen, 2016;Dlugokencky et al, 2011;Fletcher & Schaefer, 2019;Houweling et al, 2017;Menoud et al, 2022;Nisbet & Weiss, 2010). Ranges of measured δ 13 C-CH 4 values have been reported for conventional sources which might be classified into thermogenic (from geological processes), pyrogenic (from biomass burning) and biogenic (from methanogenic archaea) origin (Saunois et al, 2020).…”

Atmospheric methane isotopes identify inventory knowledge gaps in the Surat Basin, Australia, coal seam gas and agricultural regions

“…Different CH 4 formation processes result in each CH 4 source having different δ 13 C CH 4 population statistics for both the range and distribution shape (Whiticar, 1999;Sherwood et al, 2017Sherwood et al, , 2020Menoud et al, 2022a). Thus, the isotopic composition of air samples can be used to identify inputs from similar sources, the extent of mixing of two or more sources, and samples that are offset to the isotopic composition expected from the BU inventory Subsets of samples were collated based on altitude (Fig.…”

“…There is another biological source of CH 4 in the grazing cattle and mixed cropping districts that could be a contributor, upwind of IFAA samples 1604 and 1906. There are three sources of CH 4 listed in Sherwood et al (2017Sherwood et al ( , 2020 and Menoud et al (2022a) with δ 13 C CH 4(s) signatures of −80 ‰: wetlands, waste, and termites. Of these three sources termites are the most likely, as termite mounds were observed during the field campaign in many of the forested and dryland farming regions.…”

“…For CH 4 emission studies both carbon (δ 13 C) and hydrogen (δD) isotopic composition can help with determining CH 4 sources and the extent of the mixing of various sources (Lowry et al, 2020;Menoud et al, 2020Menoud et al, , 2021Röckmann et al, 2016;Townsend-Small et al, 2015), but in this study only δ 13 C is used. Due to the population range of δ 13 C CH 4 values for each source, δ 13 C CH 4 may or may not be useful for source attribution (Lan et al, 2021;Lu et al, 2021;Milkov and Etiope, 2018;Menoud et al, 2022a;Quay et al, 1999;Sherwood et al, 2017Sherwood et al, , 2020. Thus, the interpretation of IFAA sample δ 13 C CH 4(a) must be examined critically in the context of likely sources documented in the BU inventory upwind of a sample collection point.…”