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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Aug 2019

Submitted as: research article | 28 Aug 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Using ship-borne observations of methane isotopic ratio in the Arctic Ocean to understand methane sources in the Arctic

Antoine Berchet1, Isabelle Pison1, Patrick M. Crill2, Brett Thornton2, Philippe Bousquet1, Thibaud Thonat1, Thomas Hocking1, Joël Thanwerdas1, Jean-Daniel Paris1, and Marielle Saunois1 Antoine Berchet et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, CEA-CNRS-UVSQ, IPSL, Gif-sur-Yvette, France
  • 2Department of Geological Sciences, Stockholm University, SE-10691 Stockholm, Sweden

Abstract. Due to the large variety and heterogeneity of sources in remote areas hard to document, the Arctic regional methane budget remain very uncertain. In situ campaigns provide valuable data sets to reduce these uncertainties. Here we analyse data from the SWERUS-C3 campaign, on-board the icebreaker Oden, that took place during summer 2014 in the Arctic Ocean along the Northern Siberian and Alaskan shores. Total concentrations of methane, as well as isotopic ratios were measured continuously during this campaign for 35 days in July and August 2014. Using a chemistry-transport model, we link observed concentrations and isotopic ratios to regional emissions and hemispheric transport structures. A simple inversion system helped constraining source signatures from wetlands in Siberia and Alaska and oceanic sources, as well as the isotopic composition of lower stratosphere air masses. The variation in the signature of low stratosphere air masses, due to strongly fractionating chemical reactions in the stratosphere, was suggested to explain a large share of the observed variability in isotopic ratios. These points at required efforts to better simulate large scale transport and chemistry patterns to use isotopic data in remote areas. It is found that constant and homogeneous source signatures for each type of emission in the region (mostly wetlands and oil and gas industry) is not compatible with the strong synoptic isotopic signal observed in the Arctic. A regional gradient in source signatures is highlighted between Siberian and Alaskan wetlands, the later ones having a lighter signatures than the first ones. Arctic continental shelf sources are suggested to be a mixture of methane from a dominant thermogenic origin and a secondary biogenic one, consistent with previous in-situ isotopic analysis of seepage along the Siberian shores.

Antoine Berchet et al.
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Antoine Berchet et al.
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Short summary
Methane isotopes in the atmosphere can help us differentiate between emission processes. A large variety of natural and anthropogenic emission types are active in the Arctic and are unsatisfactorily understood and documented up to know. A ship-based campaign was carried out in summer 2014 providing a unique dataset of isotopic measurements in the Arctic ocean. Using a chemistry-transport model, we link these measurements to circum polar emissions and retrieve information about their signature.
Methane isotopes in the atmosphere can help us differentiate between emission processes. A large...