Atmospheric constraints on the methane emissions from the East Siberian Shelf

Berchet, Antoine; Bousquet, Philippe; Pison, Isabelle; Locatelli, Robin; Chevallier, F.; Paris, Jean-Daniel; Dlugokencky, E. J.; Laurila, Tuomas; Hatakka, Juha; Viisanen, Y.; Worthy, Doug; Nisbet, E. G.; Fisher, Rebecca E.; Lowry, David; Ivakhov, V.; Hermansen, Ove

doi:10.5194/acp-16-4147-2016

Cited by 80 publications

(71 citation statements)

References 34 publications

(54 reference statements)

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“…A subsequent measurement campaign led by Thornton et al (2016a), though not made during a stormy period, failed to observe the high rates of continuous emissions reported by Shakhova et al (2014), and instead estimated an average flux of 2.9 TgCH 4 yr −1 . Berchet et al (2016) also found that such values were not supported by atmospheric observations, and instead suggested the range of 0.0-4.5 TgCH 4 yr −1 .…”

Section: Introductionmentioning

confidence: 78%

“…Our domain goes from 39 • N to the Pole but it covers all longitudes only above 64 • N, as it is not regular in terms of latitude/longitude. Its regular kilometric resolution of 35 km allows us to avoid numerical issues due to shrunken grid cells near the Pole (Berchet et al, 2016). Twenty-nine vertical levels characterize the troposphere, from the surface to 300 hPa (∼ 9000 m), with an emphasis on the lowest layers.…”

Section: Model Descriptionmentioning

confidence: 99%

“…ESAS emissions are prescribed following Berchet et al (2016), and scaled to 2 TgCH 4 yr −1 . Their temporal variability is underestimated as uniform and constant emissions were applied by emission type (hotspots and background) and period (winter/summer), based on Shakhova et al (2010).…”

Section: Emission Scenariomentioning

confidence: 99%

“…Methane modelling studies that rely on Arctic measurements have been used, for example, to assess the sensitivity of Arctic methane concentrations to uncertainties in its sources, in particular concerning the seasonality of wetland emissions and the intensity of ESAS emissions Berchet et al, 2016). Top-down inversions have also led to methane surface flux estimates and discussions of their variations.…”

Section: Introductionmentioning

confidence: 99%

“…Also, fast horizontal winds more efficiently relate emissions to atmospheric measurements (e.g. Berchet et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

et al. 2017

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Abstract. Understanding the recent evolution of methane emissions in the Arctic is necessary to interpret the global methane cycle. Emissions are affected by significant uncertainties and are sensitive to climate change, leading to potential feedbacks. A polar version of the CHIMERE chemistrytransport model is used to simulate the evolution of tropospheric methane in the Arctic during 2012, including all known regional anthropogenic and natural sources, in particular freshwater emissions which are often overlooked in methane modelling. CHIMERE simulations are compared to atmospheric continuous observations at six measurement sites in the Arctic region. In winter, the Arctic is dominated by anthropogenic emissions; emissions from continental seepages and oceans, including from the East Siberian Arctic Shelf, can contribute significantly in more limited areas. In summer, emissions from wetland and freshwater sources dominate across the whole region. The model is able to reproduce the seasonality and synoptic variations of methane measured at the different sites. We find that all methane sources significantly affect the measurements at all stations at least at the synoptic scale, except for biomass burning. In particular, freshwater systems play a decisive part in summer, representing on average between 11 and 26 % of the simulated Arctic methane signal at the sites. This indicates the relevance of continuous observations to gain a mechanistic understanding of Arctic methane sources. Sensitivity tests reveal that the choice of the land-surface model used to prescribe wetland emissions can be critical in correctly representing methane mixing ratios. The closest agreement with the observations is reached when using the two wetland models which have emissions peaking in AugustSeptember, while all others reach their maximum in JuneJuly. Such phasing provides an interesting constraint on wetland models which still have large uncertainties at present. Also testing different freshwater emission inventories leads to large differences in modelled methane. Attempts to include methane sinks (OH oxidation and soil uptake) reduced the model bias relative to observed atmospheric methane. The study illustrates how multiple sources, having different spatiotemporal dynamics and magnitudes, jointly influencePublished by Copernicus Publications on behalf of the European Geosciences Union. 8372T. Thonat et al.: Detectability of Arctic methane sources the overall Arctic methane budget, and highlights ways towards further improved assessments.

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Section: Introductionmentioning

confidence: 78%

Section: Model Descriptionmentioning

confidence: 99%

Section: Emission Scenariomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Also, fast horizontal winds more efficiently relate emissions to atmospheric measurements (e.g. Berchet et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

et al. 2017

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Rising atmospheric methane: 2007–2014 growth and isotopic shift

Nisbet

Dlugokencky

Manning

et al. 2016

Global Biogeochemical Cycles

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From 2007 to 2013, the globally averaged mole fraction of methane in the atmosphere increased by 5.7 ± 1.2 ppb yr À1. Simultaneously, δ 13 C CH4 (a measure of the 13 C/ 12 C isotope ratio in methane) has shifted to significantly more negative values since 2007. Growth was extreme in 2014, at 12.5 ± 0.4 ppb, with a further shift to more negative values being observed at most latitudes. The isotopic evidence presented here suggests that the methane rise was dominated by significant increases in biogenic methane emissions, particularly in the tropics, for example, from expansion of tropical wetlands in years with strongly positive rainfall anomalies or emissions from increased agricultural sources such as ruminants and rice paddies. Changes in the removal rate of methane by the OH radical have not been seen in other tracers of atmospheric chemistry and do not appear to explain short-term variations in methane. Fossil fuel emissions may also have grown, but the sustained shift to more 13 C-depleted values and its significant interannual variability, and the tropical and Southern Hemisphere loci of post-2007 growth, both indicate that fossil fuel emissions have not been the dominant factor driving the increase. A major cause of increased tropical wetland and tropical agricultural methane emissions, the likely major contributors to growth, may be their responses to meteorological change.

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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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Atmospheric constraints on the methane emissions from the East Siberian Shelf

Cited by 80 publications

References 34 publications

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

Rising atmospheric methane: 2007–2014 growth and isotopic shift

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

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Atmospheric constraints on the methane emissions from the East Siberian Shelf

Cited by 80 publications

References 34 publications

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

Rising atmospheric methane: 2007–2014 growth and isotopic shift

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

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Product

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About

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