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https://doi.org/10.5194/egusphere-2025-4461
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-4461
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
09 Oct 2025
| 09 Oct 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).
Measurement report: Isotopic composition of CH4 emitted from gas exploration sites in the Transylvanian Basin, Romania
Abstract. Isotope measurements are increasingly used to constrain the methane budget on various scales, from global to regional. The success of isotope-based source attribution depends to a large degree on the knowledge of the isotope signatures of the various source categories at the point of emission, but this information is in many cases lacking. Here we report the isotopic composition of CH4 emitted from 48 installations in the gas production region of Transylvania, Romania. The isotopic source signatures are quite homogeneous across the basin with average values of δ13C = (-65.6 ± 0.5 ‰) and δD = (-184 ± 1 ‰) confirming the biogenic origin of the Transylvanian gas, produced by hydrogenotrophic CO2 reduction. This is similar to values reported previously from natural seeps in Transylvania, to the natural gas exploited in the Dolj region in Southwestern Romania, and to the natural gas in the distribution grid in Cluj-Napoca. However, is more depleted in heavy isotopes than the oil-associated gas emitted in the Southern Romanian Plain, and gas leakages in the city of Bucharest. In addition, we present a step-by-step derivation of the underlying "Keeling plot" mass balance approach that is used to derive isotope source signatures.
How to cite. Röckmann, T., Menoud, M., van Es, J., van der Veen, C., Maazallahi, H., Jagoda, P., Necki, J. M., Bartyzel, J., Korben, P., Defratyka, S., Schmidt, M., Corbu, M., Iancu, S., Calcan, A., Ardelean, M., Ghemulet, S., Pop, C., Radovici, A., Mereuta, A., Stefanie, H., and Baciu, C.: Measurement report: Isotopic composition of CH4 emitted from gas exploration sites in the Transylvanian Basin, Romania, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-4461, 2025.
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Isotopic composition of methane emitted from gas production sites in Transylvania T. Röckmann et al. https://doi.org/10.18160/4SJW-ST8W
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Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, the Netherlands
Malika Menoud
Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, the Netherlands
now at: International Methane Emissions Observatory (IMEO), UNEP, Paris, France
Jacoline van Es
Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, the Netherlands
Carina van der Veen
Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, the Netherlands
Hossein Maazallahi
Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht University, the Netherlands
now at: Department of Renewable Energies and Environment, College of Interdisciplinary Science and Technologies, University of Tehran, Iran
Pawel Jagoda
Faculty of Physics and Applied Computer Science, AGH - University of Krakow, Poland
Jaroslav M. Necki
Faculty of Physics and Applied Computer Science, AGH - University of Krakow, Poland
Jakub Bartyzel
Faculty of Physics and Applied Computer Science, AGH - University of Krakow, Poland
Piotr Korben
Faculty of Physics and Applied Computer Science, AGH - University of Krakow, Poland
Institute of Environmental Physics, University of Heidelberg, Germany
Sara Defratyka
Faculty of Physics and Applied Computer Science, AGH - University of Krakow, Poland
now at: School of GeoSciences, University of Edinburgh, UK and National Physical Laboratory, Teddington, UK
Martina Schmidt
Institute of Environmental Physics, University of Heidelberg, Germany
Marius Corbu
National Institute for Aerospace Research “Elie Carafoli” – INCAS, Bucharest, Romania
Faculty of Physics, University of Bucharest, Romania
Sebastian Iancu
National Institute for Aerospace Research “Elie Carafoli” – INCAS, Bucharest, Romania
Andreea Calcan
National Institute for Aerospace Research “Elie Carafoli” – INCAS, Bucharest, Romania
now at: International Methane Emissions Observatory (IMEO), UNEP, Paris, France
Magdalena Ardelean
National Institute for Aerospace Research “Elie Carafoli” – INCAS, Bucharest, Romania
Sorin Ghemulet
National Institute for Aerospace Research “Elie Carafoli” – INCAS, Bucharest, Romania
Cristian Pop
Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
Andrei Radovici
National Institute for Aerospace Research “Elie Carafoli” – INCAS, Bucharest, Romania
Alexandru Mereuta
Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
Horatiu Stefanie
Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
Calin Baciu
Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
Short summary
We report the isotopic composition of CH4 emitted from 48 installations in the gas production region of Transylvania, Romania which confirm the biogenic origin of the Transylvanian gas, produced by hydrogenotrophic CO2 reduction. This is similar to values reported previously from natural seeps and natural gas in a major city in the region. However, is more depleted in heavy isotopes than the oil-associated gas emitted in the Southern Romanian Plain, and gas leakages in the city of Bucharest.
We report the isotopic composition of CH4 emitted from 48 installations in the gas production...
This paper presents an important dataset from the Transylvanian Basin gas fields that will improve the quality of the global database on the isotopic signatures of methane from various geological settings. I recommend that it be published after some minor revisions.
The paper would benefit from additional background information, as it is currently difficult for readers unfamiliar with the Transylvanian Basin to fully understand the evolution of biogenic methane in the region. To better place the results in context, I had to conduct an independent literature search to learn about the Transylvanian Basin and gas development within the region. With a little extra work this can become a better self-contained paper.
For each of the 12 sample locations in Figure 1, it would be useful if the authors provided more detail on the regional geology, the nature of the gas traps at each site, the depth to the produced gas, and the current understanding of the local petroleum system. Such information would help readers unfamiliar with the Transylvanian Basin and make this a more valuable dataset, particularly since the gas is biogenic in origin and its formation is of significant scientific interest.
How do these data cluster according to the geological formations mapped by Tiliţă et al. (2013) (Figures 2 and 4 in that paper)? There may exist more detailed geological information, and if the authors are aware of such a source, it could replace or supplement Tiliţă et al. (2013).
It would also be useful to see the data from this paper combined with the dataset shown in Figure 4 of Baciu et al. (2018), along with a discussion of how these results align within that graph. This addition would help readers better understand the context and evolution of the scientific discussion regarding the origin and chemical properties of the methane emitted from this unique gas field.
Overall, this manuscript is a valuable scientific contribution that will enhance the global isotopic methane database once these contextual revisions are addressed.
Minor Concerns
Line 23 - “Isotope measurements are increasingly used to constrain the methane (CH4) budget on various scales, from global to regional.”
As these data are presented as being important for informing the global database, what is the estimated rate of methane emissions from the Transylvanian Basin, and what proportion does that represent of global fossil-fuel methane emissions?
Line 155 - “For example, the “high” outlier at the Dumbraviora gas field may be caused by an interference from combustion emissions.”
What evidence supports this statement? It would be helpful if the authors provided context regarding the proximity and relative magnitude of potential combustion sources.
There is also a typo "Dumbraviora" -> "Dumbravioara"
References
Baciu, C., Ionescu, A., and Etiope, G.: Hydrocarbon seeps in Romania: Gas origin and release to the atmosphere, Mar. Petrol. Geol., 89, 130–143, https://doi.org/10.1016/j.marpetgeo.2017.06.015
Tiliţă, M., Matenco, L., Dinu, C., Ionescu, L., & Cloetingh, S. (2013). Understanding the kinematic evolution and genesis of a back-arc continental “sag” basin: The Neogene evolution of the Transylvanian Basin. Tectonophysics, 602, 237–258. https://doi.org/10.1016/j.tecto.2012.12.029