Extensive release of methane from Arctic seabed west of Svalbard during summer 2014 does not influence the atmosphere

Myhre, Cathrine Lund; Férré, Bénédicte; Platt, Stephen Matthew; Silyakova, Anna; Hermansen, Ove; Allen, Grant; Pisso, Ignacio; Schmidbauer, Norbert; Stohl, Andreas; Pitt, Joseph; Jansson, Pär; Greinert, Jens; Percival, Carl J.; Fjæraa, Ann Mari; O’Shea, Sebastian; Gallagher, Martin; Breton, Michael Le; Bower, Keith; Bauguitte, Stéphane; Dalsøren, S. B.; Vadakkepuliyambatta, Sunil; Fisher, Rebecca E.; Nisbet, E. G.; Lowry, David; Myhre, Gunnar; Pyle, J. A.; Cain, Michelle; Mienert, Jürgen

doi:10.1002/2016gl068999

Cited by 91 publications

(113 citation statements)

References 45 publications

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“…However, Student t testing found that the fraction of oceans sampled had a consistently large p value across the season (p > 0.05), suggesting that footprint sensitivity in oceans was not correlated with CH 4 . This is consistent with a recent study of summertime sea-air flux of CH 4 around Svalbard, Norway, which measured low boundary layer CH 4 enhancements despite substantial surface ocean concentrations of CH 4 from subsea clathrate deposits in the high Arctic (Myhre et al, 2016). Boltz.-Arrh., Lin.…”

Section: Mountain and Ocean Eco-regionssupporting

confidence: 80%

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

Hartery¹,

Commane

Lindaas

et al. 2018

Atmos. Chem. Phys.

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Abstract. Methane (CH 4 ) is the second most important greenhouse gas but its emissions from northern regions are still poorly constrained. In this study, we analyze a subset of in situ CH 4 aircraft observations made over Alaska during the growing seasons of 2012-2014 as part of the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE). Net surface CH 4 fluxes are estimated using a Lagrangian particle dispersion model which quantitatively links surface emissions from Alaska and the western Yukon with observations of enhanced CH 4 in the mixed layer. We estimate that between May and September, net CH 4 emissions from the region of interest were 2.2 ± 0.5 Tg, 1.9 ± 0.4 Tg, and 2.3 ± 0.6 Tg of CH 4 for 2012, 2013, and 2014, respectively. If emissions are only attributed to two biogenic eco-regions within our domain, then tundra regions were the predominant source, accounting for over half of the overall budget despite only representing 18 % of the total surface area. Boreal regions, which cover a large part of the study region, accounted for the remainder of the emissions. Simple multiple linear regression analysis revealed that, overall, CH 4 fluxes were largely driven by soil temperature and elevation. In regions specifically dominated by wetlands, soil temperature and moisture at 10 cm depth were important explanatory variables while in regions that were not wetlands, soil temperature and moisture at 40 cm depth were more important, suggesting deeper methanogenesis in drier soils. Although similar environmental drivers have been found in the past to control CH 4 emissions at local scales, this study shows that they can be used to generate a statistical model to estimate the regional-scale net CH 4 budget.

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Section: Mountain and Ocean Eco-regionssupporting

confidence: 80%

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

Hartery¹,

Commane

Lindaas

et al. 2018

Atmos. Chem. Phys.

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“…A comprehensive study by Myhre et al (2016) calculated a median methane flux of only 3 µmol m 2 d −1 , which is supported by a median methane flux of 2 µmol m 2 d −1 for the coastal waters of Svalbard (Mau et al, 2017), and this value lies within the previously reported range of 4 to 20 µmol m 2 d −1 ; Table 5). For the North American Arctic Ocean and its shelf seas, rather low methane fluxes of 1.3 µmol m 2 d −1 have been reported (Fenwick et al, 2017).…”

Section: Diffusive Methane Fluxsupporting

confidence: 52%

“…The top-down calculations of methane flux seem to be higher than the bottom-up calculation, at 94 and 200-300 µmol m 2 d −1 , respectively Myhre et al, 2016). Ebullition of methane from the sediment in this area is also reported, resulting in methane fluxes that are 1-2 orders of magnitude higher than the calculated values (Table 5).…”

Section: Diffusive Methane Fluxmentioning

confidence: 77%

“…In contrast to these bottom-up calculations, very few studies have focused on the atmospheric methane concentrations in the study area Shakhova et al, 2014Shakhova et al, , 2010 or in polar regions in general (Myhre et al, 2016). The top-down calculations of methane flux seem to be higher than the bottom-up calculation, at 94 and 200-300 µmol m 2 d −1 , respectively Myhre et al, 2016).…”

Section: Diffusive Methane Fluxmentioning

confidence: 99%

“…When methane leaves the sediment (either by diffusion or by ebullition) at water depths > 200 m, most of it is dissolved into the water below the thermocline and does not reach surface waters or the atmosphere (Gentz et al, 2013;Myhre et al, 2016). However, at shallow water depths, most of the methane released by ebullition does not dissolve in the water but instead is released into the atmosphere.…”

Section: Introductionmentioning

confidence: 99%

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Methane distribution and oxidation around the Lena Delta in summer 2013

et al. 2017

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Abstract. The Lena River is one of the largest Russian rivers draining into the Laptev Sea. The predicted increases in global temperatures are expected to cause the permafrost areas surrounding the Lena Delta to melt at increasing rates. This melting will result in high amounts of methane reaching the waters of the Lena and the adjacent Laptev Sea. The only biological sink that can lower methane concentrations within this system is methane oxidation by methanotrophic bacteria. However, the polar estuary of the Lena River, due to its strong fluctuations in salinity and temperature, is a challenging environment for bacteria. We determined the activity and abundance of aerobic methanotrophic bacteria by a tracer method and by the quantitative polymerase chain reaction. We described the methanotrophic population with a molecular fingerprinting method (monooxygenase intergenic spacer analysis), as well as the methane distribution (via a headspace method) and other abiotic parameters, in the Lena Delta in September 2013.The median methane concentrations were 22 nmol L −1 for riverine water (salinity (S) < 5), 19 nmol L −1 for mixed water (5 < S < 20) and 28 nmol L −1 for polar water (S > 20). The Lena River was not the source of methane in surface water, and the methane concentrations of the bottom water were mainly influenced by the methane concentration in surface sediments. However, the bacterial populations of the riverine and polar waters showed similar methane oxidation rates (0.419 and 0.400 nmol L −1 d −1 ), despite a higher relative abundance of methanotrophs and a higher estimated diversity in the riverine water than in the polar water. The methane turnover times ranged from 167 days in mixed water and 91 days in riverine water to only 36 days in polar water. The environmental parameters influencing the methane oxidation rate and the methanotrophic population also differed between the water masses. We postulate the presence of a riverine methanotrophic population that is limited by sub-optimal temperatures and substrate concentrations and a polar methanotrophic population that is well adapted to the cold and methane-poor polar environment but limited by a lack of nitrogen. The diffusive methane flux into the atmosphere ranged from 4 to 163 µmol m 2 d −1 (median 24). The diffusive methane flux accounted for a loss of 8 % of the total methane inventory of the investigated area, whereas the methanotrophic bacteria consumed only 1 % of this methane inventory. Our results underscore the importance of measuring the methane oxidation activities in polar estuaries, and they indicate a population-level differentiation between riverine and polar water methanotrophs.

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Measurement of the ¹³C isotopic signature of methane emissions from northern European wetlands

Fisher

Lowry

Lanoisellé

et al. 2017

Global Biogeochemical Cycles

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Isotopic data provide powerful constraints on regional and global methane emissions and their source profiles. However, inverse modeling of spatially resolved methane flux is currently constrained by a lack of information on the variability of source isotopic signatures. In this study, isotopic signatures of emissions in the Fennoscandian Arctic have been determined in chambers over wetland, in the air 0.3 to 3 m above the wetland surface and by aircraft sampling from 100 m above wetlands up to the stratosphere. Overall, the methane flux to atmosphere has a coherent δ 13 C isotopic signature of À71 ± 1‰, measured in situ on the ground in wetlands. This is in close agreement with δ 13 C isotopic signatures of local and regional methane increments measured by aircraft campaigns flying through air masses containing elevated methane mole fractions. In contrast, results from wetlands in Canadian boreal forest farther south gave isotopic signatures of À67 ± 1‰. Wetland emissions dominate the local methane source measured over the European Arctic in summer. Chamber measurements demonstrate a highly variable methane flux and isotopic signature, but the results from air sampling within wetland areas show that emissions mix rapidly immediately above the wetland surface and methane emissions reaching the wider atmosphere do indeed have strongly coherent C isotope signatures. The study suggests that for boreal wetlands (>60°N) global and regional modeling can use an isotopic signature of À71‰ to apportion sources more accurately, but there is much need for further measurements over other wetlands regions to verify this.

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Extensive release of methane from Arctic seabed west of Svalbard during summer 2014 does not influence the atmosphere

Cited by 91 publications

References 45 publications

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

Methane distribution and oxidation around the Lena Delta in summer 2013

Measurement of the ¹³C isotopic signature of methane emissions from northern European wetlands

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Extensive release of methane from Arctic seabed west of Svalbard during summer 2014 does not influence the atmosphere

Cited by 91 publications

References 45 publications

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska

Methane distribution and oxidation around the Lena Delta in summer 2013

Measurement of the 13C isotopic signature of methane emissions from northern European wetlands

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Product

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Measurement of the ¹³C isotopic signature of methane emissions from northern European wetlands