Atmospheric Sciences Research Spotlight

What’s the Average Methane Isotope Signature in Arctic Wetlands?

Aircraft measurements confirm that methane emissions from northern European wetlands exhibit a uniform regional carbon isotopic signature, despite considerable ground-level heterogeneity.

Source: Global Biogeochemical Cycles

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Although methane (CH4) is a potent greenhouse gas, the relative contributions of its various sources to the global budget are still poorly constrained. In wetlands, different metabolic and transport processes, as well as the variety and extent of vegetation, affect the rate at which methane is emitted as well as its isotopic composition. Although these processes are known to produce varied isotopic signatures on local scales, it is uncertain whether wetland emissions that reach the broader atmosphere have a more coherent signature.

To determine whether a uniform methane isotopic signature can be identified from specific wetlands, Fisher et al. analyzed hundreds of samples collected in and above five Arctic wetlands in northern Norway, Sweden, and Finland. Using three separate collection methods, the team compared the isotopic compositions of samples gathered at the wetland-air interface; at 30 centimeters and 3 meters above the wetland surface; and, using aircraft, from 100 meters to 9 kilometers above the wetlands.

The results confirm that wetlands are the primary source of summer methane emissions over Fennoscandia. Although measurements at the wetland-air interface displayed considerable heterogeneity, the air samples show that the methane emissions rapidly mix just above the surface, creating a uniform regional carbon-13 isotopic signature of −71‰ ± 1‰. This signature is more depleted in carbon-13 than results obtained from wetland samples in Canadian boreal forests, which are located farther south.

A research aircraft takes measurements over Sodankylä wetland in northern Finland. Aircraft measurements above northern European wetlands can be used to quickly characterize the regional isotopic signature of their methane emissions. Credit: Rebecca Fisher

The authors conclude that aircraft measurements can be used to quickly characterize the isotopic signature of methane emissions on a regional scale and that these broad signatures can then be incorporated into regional and global models to discriminate the sources of methane emissions. Because the isotopic signatures measured in the study are lower than the values typically entered into global climate change models, the results of this study suggest the models may be underestimating the change to atmospheric carbon-13 for each simulated emissions scenario. (Global Biogeochemical Cycles, https://doi.org/10.1002/2016GB005504, 2017)

—Terri Cook, Freelance Writer

Citation: Cook, T. (2017), What’s the average methane isotope signature in Arctic wetlands?, Eos, 98, https://doi.org/10.1029/2017EO072973. Published on 04 May 2017.
© 2017. The authors. CC BY-NC-ND 3.0
  • patrick.hogan

    Other than a research thesis, given the concern humans ‘should’ have regarding a condition that is rapidly going terminal, any specific source of methane will represent all sources of methane at similar ecosystems and latitude. Spitting hairs as to which wetland in particular, seems akin to figuring out which blend of herbs we poison ourselves with. Of more interest is knowing the rate of poisoning and not so much any particular source. The common origin of which is simply planetary warming on an unprecedented scale (in terms of acceleration). Humble apologies please, this is not meant to criticize the tremendous science going into this research! Especially if it can help move us to better behaviour, that of total renewable energy now. It would seem more informative to know where we are with regard to the methane monster being conjured by a heartless drive to profiteer a few rather than pacify, appreciate and indulge such a sweetly beautiful world.
    Shakespeare’s Romeo last words to his darling Juliet. . .
    Eyes, look your last.

    Arms, take your last embrace. And, lips, O you

    The doors of breath, seal with a righteous kiss

    A dateless bargain to engrossing death.