The oceans: A source or a sink of methyl bromide?

The global ocean/atmosphere flux of methyl bromide has been estimated from shipboard measurements of the saturation anomaly. When such data are extrapolated globally on the basis of constant saturation anomaly, the ocean is a net sink for methyl bromide [Lobert et al., 1995]. The same data can also be extrapolated on the basis of steady-state production rate of methyl bromide in the water column, allowing regional and seasonal variations in temperature to affect the saturation anomaly. We have carried out this type of extrapolation, and we found that the oceans are a strong net source of methyl bromide to the atmosphere. The difference arises mainly due to slow degradation rates ii! water of higher latitudes. A reduction of the applied production rate by more than 35% is needed in order to switch the ocean from a source to a sink of methyl bromide. These results demonstrate the sensitivity of current estimates of oceanic flux to assumptions about methyl bromide production and destruction in the water column.