The impact of spatially varying wetland source signatures on the atmospheric variability of δd-CH 4

Abstract

We present the first spatially resolved distribution of the δD-CH4 signature of wetland methane emissions and assess its impact on atmospheric δD-CH4. The δD-CH4 signature map is derived by relating δD-H2O of precipitation to measured δD-CH4 of methane wetland emissions at a variety of wetland types and locations. This results in strong latitudinal variation in the wetland δD-CH4 source signature. When δD-CH4 is simulated in a global atmospheric model, little difference is found in global mean, inter-hemispheric difference and seasonal cycle if the spatially varying δD-CH4 source signature distribution is used instead of a globally uniform value. This is because atmospheric δD-CH4 is largely controlled by OH fractionation. However, we show that despite these small differences, using atmospheric records of δD-CH4 to infer changes in the wetland emissions distribution requires the use of the more accurate spatially varying δD-CH4 source signature. We find that models will only be sensitive to changes in emissions distribution if spatial information can be exploited through the spatially resolved source signatures. In addition, we also find that on a regional scale, at sites measuring excursions of δD-CH4 from background levels, substantial differences are simulated in atmospheric δD-CH4 if using spatially varying or uniform source signatures. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'.