Stable carbon isotope signatures of methane from a Finnish subarctic wetland

Abstract

Methane emissions from Lompolojankka, 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 (delta C-13(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 delta C-13 of the methane in the samples were incorporated into Keeling plot analyses to derive bulk delta C-13(CH4) signatures for the methane inputs to the air above the wetland. The results show an unexpected consistence in delta C-13(CH4) from early to late summer, clustered around -68.5 +/- 0.7 parts per thousand, but during spring thaw and autumnal freezing, delta C-13(CH4) is enriched by approximately 2 and 4 parts per thousand, 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.