Methane at Svalbard and over the European Arctic Ocean

Abstract

<p><strong>Abstract.</strong> Methane (CH<sub>4</sub>) is a powerful greenhouse gas and atmospheric mixing ratios have been increasing since 2005. Therefore, quantification of CH<sub>4</sub> sources is essential for effective climate change mitigation. Here we report observations of the CH<sub>4</sub> 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 CH<sub>4</sub> 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 CH<sub>4</sub> from the ocean to the atmosphere, and used state-of-the-art modelling (FLEXPART) combined with updated emissions inventories to identify CH<sub>4</sub> 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 (<i>δ</i><sup>13</sup>C in CH<sub>4</sub>) as tracers for ocean-to-atmosphere CH<sub>4</sub> 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<sup>−1</sup>) from 2001–2017. Meanwhile most large excursions from the baseline CH<sub>4</sub> 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 CH<sub>4</sub> emissions. However, we also identify a potential hot spot region with ocean-atmosphere CH<sub>4</sub> flux North of Svalbard (80.4° N, 12.8° E) of up to 26 nmol m<sup>−2</sup> s<sup>−1</sup> from a large mixing ratio increase at the location of 30 ppb. 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.</p>

Atmospheric composition in the European Arctic and 30 years of the Zeppelin Observatory, Ny-Ålesund

“…The CH 4 mixing ratio is also clearly increasing over time. After a brief pause, since 2005 daily mean CH 4 mixing ratios at Zeppelin have increased by an average 5.9 ± 0.3 ppb yr −1 (Platt et al, 2018) and by 14 ppb for 2018 to 2019, reaching a record level of 1952.9 ppb. For comparison, the global mean CH 4 mixing ratio in 2019 was 1869 ppb (WMO, 2020), reflecting considerable latitudinal variation in CH 4 due to the uneven spatial distribution of sink strength and sources and its relatively short lifetime (approximately 11 years).…”

Physical controls of dynamics of methane venting from a shallow seep area west of Svalbard

“…Ship-mounted meteorological instruments continuously recorded air temperature, atmospheric pressure, wind speed and direction. Furthermore, atmospheric methane mixing ratios were recorded continuously with a Cavity Ring-Down Spectrometer (CRDS, PICARRO G2401) with an air intake at 22.4 m above sea level (Platt et al, 2018).…”

Overview: Recent advances in the understanding of the northern Eurasian environments and of the urban air quality in China – a Pan-Eurasian Experiment (PEEX) programme perspective

“…All estimates are in the lower range of values reported earlier (Pisso et al, 2016). Platt et al (2018) reported a potential region with high oceanatmosphere CH 4 fluxes located north of Svalbard but addressed how at the time of the measurements the meteorological conditions were unique, including a short episode of the highly sensitive emissions over an active seep site without a sensitivity to land-based emissions.…”