Methyl bromide and methyl chloride in the Southern Ocean

Air and water concentrations of methyl bromide (CH 3 Br) and methyl chloride (CH 3 Cl) were measured in the Southern Ocean (latitudes 45°–67°S, longitudes 144°–139°E) from late October through mid‐December 2001. CH 3 Br and CH 3 Cl were undersaturated with mean saturation anomalies of −39 ± 11% and −37 ± 11% between 45° and 65°S. The minimum degradation rate constants needed to maintain these saturation anomalies are consistent with the observed total degradation rate constants, suggesting that there is no significant production of these gases in this region. Near the Antarctic coast (south of 65°S) the saturation anomalies for both gases decreased to approximately −80%, although CFC‐11 measurements suggest these extreme anomalies are associated with enhanced vertical mixing rather than with degradation in the surface waters.