气候变化领域集成服务门户(CCPortal): Evidence for methane isotopic bond re-ordering in gas reservoirs sourcing cold seeps from the Sea of Marmara

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DOI	10.1016/j.epsl.2020.116619
	Evidence for methane isotopic bond re-ordering in gas reservoirs sourcing cold seeps from the Sea of Marmara
	Giunta T.; Labidi J.; Kohl I.E.; Ruffine L.; Donval J.P.; Géli L.; Çağatay M.N.; Lu H.; Young E.D.
发表日期	2021
ISSN	0012821X
卷号	553
英文摘要	The measurement of methane clumped isotopologues (Δ13CH3D and Δ12CH2D2) allows exploring isotope bond ordering within methane molecules, and may reveal equilibrium temperatures. Whether such temperature reflects the formation or re-equilibration temperature of the methane is not well understood, but would have critical implications for the use of methane clumped isotopologues as geo-thermometers. Here we investigate gas bubbles from vigorous emissions at cold seeps (n = 14) in the Sea of Marmara, Turkey. These cold seeps are sourced from deeper sedimentary reservoirs. Conventional geochemical tracers such as carbon and hydrogen bulk isotopic ratios (13C/12C and D/H) or n-alkane molecular ratios, suggest these gases reflect various degrees of mixing between thermogenic and microbial sources. Some samples would generally be considered purely microbial in origin (C1/C2+>1500; δ13C<−60‰). We report measurements of Δ13CH3D and Δ12CH2D2 showing that a fraction of those gases are in internal thermodynamic equilibrium, with the abundances of the two mass-18 isotopologues indicating concordant temperatures of ∼90 °C and ∼130 °C. These concordant temperatures are recorded by gases of putative microbial and thermogenic origin; the temperatures of equilibration are irrespective of the formation mechanism of the gases. We conclude that the two high-temperatures recorded by Δ13CH3D and Δ12CH2D2 are best explained by non-enzymatic re-equilibration at two local subsurface temperatures. First principles suggest that unequal rates of exchange are possible. Disequilibrium signatures where the two isotopologues yield discordant apparent temperatures are exhibited by other samples. In those cases the data define a trend of variable Δ13CH3D at nearly constant Δ12CH2D2. These signatures are enigmatic, and we investigate and reject multiple possible explanations including mixing, diffusion or Anaerobic Oxidation of Methane. Different rates of re-equilibration between the two rare isotopologues are implied, although lacks experimental foundation at present. In general, all of these data point towards re-equilibration of the mass-18 methane isotopologues as an important process. © 2020 Elsevier B.V.
关键词	bond-ordering clumped isotopologues cold seeps methane
英文关键词	Gas emissions; Isotopes; Methane; Mixing; Offshore gas fields; Paraffins; Petroleum reservoirs; Anaerobic oxidation of methanes; Apparent temperature; Carbon and hydrogens; Equilibrium temperatures; Formation mechanism; Sedimentary reservoirs; Subsurface temperature; Thermodynamic equilibria; Temperature; chemical bonding; equilibrium; gas seepage; geothermometry; isotopic composition; methane; temperature; Sea of Marmara; Turkey
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/203102
作者单位	IFREMER, Unité des Géosciences Marines, Plouzané, 29280, France; Université de Bretagne Occidentale, Laboratoire Géosciences Océan, Plouzané, 29280, France; Université de Paris, Institut de Physique du Globe de Paris, CNRS, Paris, F-75005, France; University of California Los Angeles, Department of Earth, Planetary and Space Sciences, Los Angeles, CA 90095, United States; Istanbul Teknik University, Faculty of Mines, Department of Geological Engineering, Istanbul, TR-34469, Turkey; Peking University, Department of Energy & Sciences, College of Engineering, Beijing, 100871, China
推荐引用方式 GB/T 7714	Giunta T.,Labidi J.,Kohl I.E.,et al. Evidence for methane isotopic bond re-ordering in gas reservoirs sourcing cold seeps from the Sea of Marmara[J],2021,553.
APA	Giunta T..,Labidi J..,Kohl I.E..,Ruffine L..,Donval J.P..,...&Young E.D..(2021).Evidence for methane isotopic bond re-ordering in gas reservoirs sourcing cold seeps from the Sea of Marmara.Earth and Planetary Science Letters,553.
MLA	Giunta T.,et al."Evidence for methane isotopic bond re-ordering in gas reservoirs sourcing cold seeps from the Sea of Marmara".Earth and Planetary Science Letters 553(2021).