Implications of methyl bromide supersaturations in the temperate North Atlantic Ocean

Methyl bromide saturation anomalies measured in the springtime North Atlant ic and summertime North Pacific Oceans during 1998 revealed persistent supe rsaturations in the temperate waters of the northeastern Atlantic but under saturations in tropical waters of both oceans. A comparison of data from th is study with those from a previous cruise to the northeastern Atlantic sug gests that methyl bromide is cycled seasonally in these waters and perhaps in all temperate open-ocean waters. This means that the calculated net flux of methyl bromide into the oceans is slightly less negative than previousl y reported. With these new insights we estimate that the global air-sea flu x of methyl bromide ranges from -11 to -20 Gg yr-l Data combined from this and three previous cruises support a flux dependence upon sea surface tempe rature, as reported recently by Groszko and Moore [1998]. Whereas sea surfa ce temperature can account for 40-70% of the observed variability in methyl bromide globally, it is able to reproduce only a small fraction of the obs erved seasonal cycle in the temperate northeastern Atlantic. The developmen t of reliable predictions of air-sea fluxes of methyl bromide will require information on additional variables as well.