Use of hydrogen isotopes of methane to distinguish between biogenic and thermogenic sources: examples from several regions and comparisons to ethane and carbon-13
Abstract
Scientists investigating rising CH4 concentrations regionally and globally have relied on a variety of approaches to estimate sources of excess methane, including inventories of sources, carbon isotopes of CH4, and methane:ethane ratios. This presentation will focus on several studies that have measured the hydrogen stable isotopic composition (δD) of CH4 in both sources (i.e., at the "bottom up" level) and in well mixed air masses (for "top down" source apportionment). This tracer has advantages and disadvantages as compared to the other more commonly used methods. Advantages include 1), apparently consistent δD ratios of CH4 within oil and gas basins as compared to δ13C and CH4:C2H6; 2), most sources have a distinct δD-CH4 from atmospheric background, which makes it easier to distinguish small enhancements in CH4, unlike δ13C, where some oil and gas sources have similar signatures to background air; and 3), the ability to use a two-endmember mixing model for source apportionment rather than a one-endmember mixing model, which is the case with CH4:C2H6 (because biogenic sources do not have C2H6). Some disadvantages of using this tracer over the others include 1), there are no in situ instruments available for measuring dD, as there are for δ13C and C2H6, and 2), currently there are somewhat larger sample volume requirements for δD than δ13C, although still much smaller than in the recent past.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A51D..05T
- Keywords:
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- 0315 Biosphere/atmosphere interactions;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 1605 Abrupt/rapid climate change;
- GLOBAL CHANGEDE: 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGE