The impact of spatially varying wetland source signatures on the atmospheric variability of dD-CH4

We present the first spatially varying map of the δD-CH4 signature of wetland methane emissions and model its impact on atmospheric δD-CH4. The δD-CH4 signature map is derived by relating the δD-H2O of precipitation to the measured δD-CH4 of methane wetland emissions at a variety of wetland types and locations. Since the δD-H2O of precipitation is highly latitude-dependent, including this spatial variation has the potential to have a large impact on the distribution of δD-CH4 observed in the atmosphere. This latitude-dependence means that wetland emissions at different latitudes can have very different impacts on atmospheric δD-CH4, which could provide a useful way to constrain the location of wetland methane emissions in future inverse modelling studies. Here, we assess the implications for model studies on the differences that arise by treating δD-CH4 wetland source signatures as globally uniform rather than accounting for the large spatial variation. We also assess the potential for δD-CH4 to provide an independent constraint on wetland emissions over the more abundant and widely measured δ13C-CH4.