Temporal and spatial variation in methyl bromide flux from a salt marsh

Methyl bromide (CH3Br) is a trace gas involved in stratospheric ozone depletion with both anthropogenic and natural sources. Estimates of natural source strengths are highly uncertain. In this study, >320 highly temporally and spatially resolved measurements of CH3Br emissions from a salt marsh in Scotland (56º00′N, 2º35′W) were made during one year using eight static enclosures. Net emissions showed both strong seasonal and diurnal cycles. Day-to-day maxima in emissions were associated with sunny days. Emissions dropped to zero when vegetation was removed. Mean measured CH3Br emission was 350 ng m-2 h 1, but a few “hot spots” (measured maximum 4000 ng m-2 h-1) dominated integrated emissions. A crude scale-up of the annual mean emission yields an estimate for global CH3Br emission of ~1 (0.5-3 ) Gg y-1 (range uses annual mean from lowest and highest emitting enclosures), ~10% the global salt marsh emission regularly quoted in the literature.