Spatially resolved isotopic source signatures of wetland methane emissions

We present the first spatially resolved wetland δ¹³C(CH₄) source signature map based on data characterizing wetland ecosystems and demonstrate good agreement with wetland signatures derived from atmospheric observations. The source signature map resolves a latitudinal difference of ~10‰ between northern high‐latitude (mean −67.8‰) and tropical (mean −56.7‰) wetlands and shows significant regional variations on top of the latitudinal gradient. We assess the errors in inverse modeling studies aiming to separate CH₄ sources and sinks by comparing atmospheric δ¹³C(CH₄) derived using our spatially resolved map against the common assumption of globally uniform wetland δ¹³C(CH₄) signature. We find a larger interhemispheric gradient, a larger high‐latitude seasonal cycle, and smaller trend over the period 2000–2012. The implication is that erroneous CH₄ fluxes would be derived to compensate for the biases imposed by not utilizing spatially resolved signatures for the largest source of CH₄ emissions. These biases are significant when compared to the size of observed signals.