Gridded maps of geological methane emissions and their isotopic signature

• Published in: Earth System Science Data
• Main Authors: Etiope, Giuseppe, Ciotoli, Giancarlo, Schwietzke, Stefan, Schoell, Martin
• Other Authors: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione Roma2, Roma, Italia, #PLACEHOLDER_PARENT_METADATA_VALUE#
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: Arctic
• Online Access: http://hdl.handle.net/2122/12092; https://doi.org/10.5194/essd-11-1-2019

Methane (CH4) is a powerful greenhouse gas, whose natural and anthropogenic emissions contribute 20% to global radiative forcing. Its atmospheric budget (sources and sinks), however, has large uncertainties. Inverse modelling, using atmospheric CH4 trends, spatial gradients and isotopic source signatures, has recently improved the major source estimates and their spatial–temporal variation. Nevertheless, isotopic data lack CH4 source representativeness for many sources, and their isotopic signatures are affected by incomplete knowledge of the spatial distribution of some sources, especially those related to fossil (radiocarbon-free) and microbial gas. This gap is particularly wide for geological CH4 (geo-CH4) seepage, i.e. the natural degassing of hydrocarbons from the Earth’s crust. While geological seepage is widely considered a major source of atmospheric CH4, it has been largely neglected in 3-D inverse CH4 budget studies given the lack of detailed a priori gridded emission maps. Here, we report for the first time global gridded maps of geological CH4 sources, including emission and isotopic data. The 1 1 maps include the four main categories of natural geo-CH4 emission: (a) onshore hydrocarbon macro-seeps, including mud volcanoes, (b) submarine (offshore) seeps, (c) diffuse microseepage and (d) geothermal manifestations. An inventory of point sources and area sources was developed for each category, defining areal distribution (activity), CH4 fluxes (emission factors) and its stable C isotope composition ( 13C-CH4). These parameters were determined considering geological factors that control methane origin and seepage (e.g. petroleum fields, sedimentary basins, high heat flow regions, faults, seismicity). The global geosource map reveals that the regions with the highest CH4 emissions are all located in the Northern Hemisphere, in North America, in the Caspian region, in Europe and in the East Siberian Arctic Shelf. The globally gridded CH4 emission estimate (37 Tg yr????1 exclusively based on data and ...