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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Nov 2018

Research article | 26 Nov 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Assessment of the theoretical limit in instrumental detectability of Arctic methane sources using 13C atmospheric signal

Thibaud Thonat1, Marielle Saunois1, Isabelle Pison1, Antoine Berchet1, Thomas Hocking1, Brett Thornton2, Patrick Crill2, and Philippe Bousquet1 Thibaud Thonat et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris- Saclay, F-91191 Gif-sur-Yvette, France
  • 2Department of Geological Sciences and Bolin Centre for Climate Research, Svante Arrhenius väg 8, 106 91, Stockholm, Sweden

Abstract. Despite their modest 4 % magnitude compared to global emissions, Arctic methane sources are key elements in closing the global atmospheric methane budget, due to high uncertainties in their quantification and to their strong climate sensitivity. Recent efforts brought together bottom-up quantification approaches (inventories, process-based models) and regional observations of methane concentrations through inverse modelling to better estimate the Arctic methane sources, but the relatively small number of available observations in Arctic regions leaves gaps in fully understanding the drivers and distributions of the different types of methane sources present in the Arctic. Observations of methane isotope ratios could bring new insights on methane processes with increasingly affordable and accurate instruments. Here, we present the source signal that could be observed from methane isotopic measurements if high-resolution observations were available, and thus what requirements should be fulfilled in future instrument deployments in terms of accuracy in order to constrain different emission categories. This theoretical study uses the regional chemistry-transport model CHIMERE driven by different scenarios of isotopic signatures for each regional methane source mix. It is found that if the current network of methane monitoring sites is equipped with instruments measuring the isotopic signal continuously, only sites that are significantly influenced by emission sources could differentiate regional emissions from the background with a reasonable level of confidence. Nevertheless, we show that the detection of individual Arctic sources requires daily accuracies of < 0.5 ‰, < 0.2 ‰, < 0.15 ‰, and < 0.1 ‰ for wetlands, freshwaters, ESAS, and anthropogenic Arctic emissions, respectively, although these limits vary considerably depending on the observational site.

Thibaud Thonat et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Thibaud Thonat et al.
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Short summary
This paper discusses the methane isotopic signals that could be detected at instrumental sites in the Arctic using a 3D chemistry transport model. Isotopic signal may be used in atmospheric inverse systems to better characterize methane emissions and changes. We show that depending of the source magnitude and the location of the site, detecting isotopic signal of specific individual source may be challenging even for the new generation of methane isotope instruments.
This paper discusses the methane isotopic signals that could be detected at instrumental sites...