Growing season methyl bromide and methyl chloride fluxes at a sub‐arctic wetland in Sweden

Methyl bromide and methyl chloride fluxes were measured at several sites in a sub‐arctic wetland near Abisko, Sweden (68°28′N 18°49′E) throughout the 2008 growing season. Averaged over 92 flux measurements the sub‐arctic wetland was found to be a small net sink for CH 3 Br, with mean (±1 sd) uptake of −25 (±20) ng m −2 h −1 , but a small net source of CH 3 Cl with mean emissions of 400 (±1600) ng m −2 h −1 . Seasonal trends were observed in both CH 3 Br and CH 3 Cl net fluxes, but diurnal trends for CH 3 Cl only, with peak emissions observed during the afternoon. CH 3 Cl fluxes differed significantly with hydrological status of measurement locations; however, no other substantial correlations were observed between fluxes and external parameters (air and soil temperature and PAR). This study shows that the single previous estimated sink flux for CH 3 Cl in tundra globally (derived from measurements in Alaska) requires revision, although not that for CH 3 Br.