Stable carbon isotopic composition of methane from some natural and anthropogenic sources

The results of δ 13 C measurements of several types of major sources of atmospheric methane are as follows: rice paddies, −67‰; the peat bogs of the Lake Agassiz region of northern Minnesota, −67±5‰; swamps of the Florida Everglades, −55±3‰ and biomass burning, −24 to −32‰. In addition, results are presented of a study of the δ 13 C of CH 4 released from a slough, compared to the CH 4 in the bottom sediment. These isotopic values are used, together with previously published data, to make up a tentative budget of the fluxes of the major sources for atmospheric methane with an average isotopic composition matching the measured value for atmospheric CH 4 , taking into account the fractionation effect of the sink processes. This budget requires the existence of a significant flux from an anthropogenic source of heavy CH 4 , calculated to be 45±15 Tg yr −1 if attributed to CH 4 from biomass burning, with δC = −25‰.