Stable carbon isotope signatures of methane from a Finnish subarctic wetland

Methane emissions from Lompolojänkkä, a Finnish aapa mire within the Arctic Circle, were studied by non-intrusive Keeling plot methods, to place better constraints on the seasonal variations in isotopic signature of methane (δ¹³C_CH4) emitted from Arctic wetland. Air samples were collected in Tedlar bags over the wetland at heights of 42 and 280 cm between May and October 2009 and in August 2008. The mixing ratio and δ¹³C of the methane in the samples were incorporated into Keeling plot analyses to derive bulk δ¹³C_CH4 signatures for the methane inputs to the air above the wetland. The results show an unexpected consistence in δ¹³C_CH4 from early to late summer, clustered around −68.5±0.7‰, but during spring thaw and autumnal freezing, δ¹³C_CH4 is enriched by approximately 2 and 4‰, respectively. The techniques reported in this paper are simple and economical to employ, and give a bulk source signature for the methane inputs to the air above the entire wetland that can be extrapolated to a larger regional area.