A seasonal study of methyl bromide concentrations in the North Atlantic (35°–60°N)

Methyl bromide concentrations in and over the North Atlantic were examined during spring, summer, and fall 2003. The results demonstrate that seasonality plays a great role in controlling methyl bromide fluxes from and into the ocean in this area. The North Atlantic acted as a sink of the atmospheric gas during the spring, a source during the summer, and a weak sink during the fall. The annual air-sea flux of methyl bromide from the North Atlantic area between 30°N and 60°N (approximately 15.4 × 106 km2) was estimated to be in the range of −0.3 to −0.6 Gg y−1, with the methyl bromide flux varying between −4.0 × 106 ± 1 × 106 g d−1, 1.6 × 106 ± 0.6 × 106 g d−1, and −0.6 × 106 ± 0.4 × 106 g d−1 in spring, summer, and fall, respectively. Methyl bromide production necessary to balance air-sea exchange with oceanic losses was greater in the southern part than in the northern part of the studied area; no oceanic production was necessary to balance methyl bromide loss from the Arctic waters around 60°N. While the regional contribution to the methyl bromide global oceanic flux is small, it is also complex and dynamic. Our data suggest that in this part of the ocean the flux is not so much dependent on sea surface temperature as it is on other, still unknown environmental variables.