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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-597
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Jul 2018

Research article | 05 Jul 2018

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

Methane at Svalbard and over the European Arctic Ocean

Stephen M. Platt1, Sabine Eckhardt1, Benedicte Ferré2, Rebecca E. Fisher3, Ove Hermansen1, Pär Jansson2, David Lowry3, Euan G. Nisbet3, Ignacio Pisso1, Norbert Schmidbauer1, Anna Silyakova2, Andreas Stohl1, Tove M. Svendby1, Sunil Vadakkepuliyambatta2, Jürgen Mienert2, and Cathrine Lund Myhre1 Stephen M. Platt et al.
  • 1NILU – Norwegian Institute for Air Research, PO Box 100, 2027 Kjeller, Norway
  • 2CAGE-Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT The Arctic University of Norway, 9037 Tromsø, Norway
  • 3Department of Earth Sciences, Royal Holloway, University of London, Egham, UK

Abstract. Methane (CH4) is a powerful greenhouse gas and atmospheric mixing ratios have been increasing since 2005. Therefore, quantification of CH4 sources is essential for effective climate change mitigation. Here we report observations of the CH4 mixing ratios measured at Zeppelin Observatory (Svalbard) in the Arctic and aboard the Research Vessel (RV) Helmer Hanssen over the Arctic Ocean from June 2014 to December 2016, as well as the long-term CH4 trend measured at the Zeppelin Observatory (Svalbard) from 2001–2017. We investigated areas over the European Arctic Ocean to identify possible hot spot regions emitting CH4 from the ocean to the atmosphere, and used state-of-the-art modelling (FLEXPART) combined with updated emissions inventories to identify CH4 sources. Furthermore, we collected air samples in the region as well as samples of gas hydrates, obtained from the sea floor using a new technique developed as part of this work. Using this new methodology, we evaluated the suitability of ethane and isotopic signatures (δ13C in CH4) as tracers for ocean-to-atmosphere CH4 emission. We show that the mean atmospheric CH4 mixing ratio in the Arctic increased by 5.9±0.38 parts per billion by volume (ppb) per year (yr−1) from 2001–2017. Meanwhile most large excursions from the baseline CH4 mixing ratio over the European Arctic Ocean are due to long-range transport from land-based sources, lending confidence to the present inventories for high latitude CH4 emissions. However, we also identify a potential hot spot region with ocean-atmosphere CH4 flux North of Svalbard (80.4°N, 12.8°E) of up to 26nmolm−2s−1 from a large mixing ratio increase at the location of 30ppb. Since this flux is highly consistent with previous constraints (both spatially and temporally), there is no evidence that the area of interest North of Svalbard is unique in the context of the wider Arctic. Rather, that the meteorology at the time of the observation was unique in the context of the measurement time series, i.e. we obtained, over the short course of the episode, measurements highly sensitive to emissions over an active seep site, without sensitivity to land based emissions.

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We measured atmospheric mixing ratios of methane over the Arctic Ocean around Svalbard and compared observed variations to inventories for anthropogenic, wetland, and biomass burning methane emissions and an atmospheric transport model. With knowledge of where variations were expected due to the aforementioned land based emissions, we were able to identify and quantify a methane source from the ocean North of Svalbard, likely from sub sea hydrocarbon seeps and/or gas hydrate decomposition.
We measured atmospheric mixing ratios of methane over the Arctic Ocean around Svalbard and ...
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