Implications of methyl bromide supersaturations in the temperate North Atlantic Ocean

Methyl bromide saturation anomalies measured in the springtime North Atlantic and summertime North Pacific Oceans during 1998 revealed persistent supersaturations in the temperate waters of the northeastern Atlantic but undersaturations in tropical waters of both oceans. A comparison of data from this study with those from a previous cruise to the northeastern Atlantic suggests 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 previously reported. With these new insights we estimate that the global air-sea flux 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 temperature, as reported recently by Groszko and Moore [1998]. Whereas sea surface 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 observed seasonal cycle in the temperate northeastern Atlantic. The development of reliable predictions of air-sea fluxes of methyl bromide will require information on additional variables as well.