Methane at svalbard and over the european arctic ocean

Autor(en): Stephen Platt, Sabine Eckhardt, Benedicte Ferré, Rebecca Fisher, Ove Hermansen, Par Jansson, David Lowry, Euan Nisbet, Ignacio Pisso, Norbert Schmidbauer, Anna Silyakova, Andreas Stohl, Tove Svendby, Sunil Vadakkepuliyambatta, Jurgen Mienert, Cathrine Lund Myhre
Abstrakt: Methane ( classCombining double low line"inline-formula">CH4) is a powerful greenhouse gas. Its atmospheric mixing ratios have been increasing since 2005. Therefore, quantification of classCombining double low line"inline-formula">CH4 sources is essential for effective climate change mitigation. Here we report observations of the classCombining double low line"inline-formula">CH4 mixing ratios measured at the 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 classCombining double low line"inline-formula">CH4 trend measured at the Zeppelin Observatory from 2001 to 2017. We investigated areas over the European Arctic Ocean to identify possible hotspot regions emitting classCombining double low line"inline-formula">CH4 from the ocean to the atmosphere, and used state-of-the-art modelling (FLEXPART) combined with updated emission inventories to identify classCombining double low line"inline-formula">CH4 sources. Furthermore, we collected air samples in the region as well as samples of gas hydrates, obtained from the sea floor, which we analysed using a new technique whereby hydrate gases are sampled directly into evacuated canisters. Using this new methodology, we evaluated the suitability of ethane and isotopic signatures ( classCombining double low line"inline-formula">δ13C in classCombining double low line"inline-formula">CH4) as tracers for ocean-to-atmosphere classCombining double low line"inline-formula">CH4 emission. We found that the average methane / light hydrocarbon (ethane and propane) ratio is an order of magnitude higher for the same sediment samples using our new methodology compared to previously reported values, 2379.95 vs. 460.06, respectively. Meanwhile, we show that the mean atmospheric classCombining double low line"inline-formula">CH4 mixing ratio in the Arctic increased by classCombining double low line"inline-formula">5.9±0.38 parts per billion by volume (ppb) per year (yr classCombining double low line"inline-formula">ĝ'1) from 2001 to 2017 and classCombining double low line"inline-formula">ĝ1/48 pbb yr classCombining double low line"inline-formula">ĝ'1 since 2008, similar to the global trend of classCombining double low line"inline-formula">ĝ1/4 7-8 ppb yr classCombining double low line"inline-formula">ĝ'1. Most large excursions from the baseline classCombining double low line"inline-formula">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 classCombining double low line"inline-formula">CH4 emissions. However, we also identify a potential hotspot region with ocean-atmosphere classCombining double low line"inline-formula">CH4 flux north of Svalbard (80.4 classCombining double low line"inline-formula">ĝ N, 12.8 classCombining double low line"inline-formula">ĝ E) of up to 26 nmol m classCombining double low line"inline-formula">ĝ'2 s classCombining double low line"inline-formula">ĝ'1 from a large mixing ratio increase at the location of 30 ppb. Since this flux is 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, because the meteorology at the time of the observation was unique in the context of the measurement time series, 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.
Organisation(en): Institut für Meteorologie und Geophysik
Externe Organisation(en): Norwegian Institute for Air Research, University of Tromsø - The Arctic University of Norway, University of London
Journal: Atmospheric Chemistry and Physics
Band: 18
Seiten: 17207-17224
Anzahl der Seiten: 18
ISSN: 1680-7316
DOI: https://doi.org/10.5194/acp-18-17207-2018
Publikationsdatum: 2018
Peer-reviewed: Ja
ÖFOS 2012: 105206 Meteorologie
ASJC Scopus Sachgebiete: Atmospheric Science
Sustainable Development Goals: SDG 13 – Maßnahmen zum Klimaschutz
Link zum Portal: https://ucrisportal.univie.ac.at/de/publications/99123b5d-d780-4161-b0ac-763b5e5e702a

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