A Net Sink for Atmospheric CH 3 Br in the East Pacific Ocean

Abstract

Surface waters along a cruise track in the East Pacific Ocean were undersaturated in methyl bromide (CH₃Br) in most areas except for coastal and upwelling regions, with saturation anomalies ranging from + 100 percent in coastal waters to –50 percent in open ocean areas, representing a regionally weighted mean of –16 (–13 to –20) percent. The partial lifetime of atmospheric CH₃Br with respect to calculated oceanic degradation along this cruise track is 3.0 (2.9 to 3.6) years. The global, mean dry mole fraction of CH3Br in the atmosphere was 9.8 ± 0.6 parts per trillion, with an interhemispheric ratio of 1.31 ± 0.08. These data indicate that ∼8 percent (0.2 parts per trillion) of the observed interhemispheric difference in atmospheric CH3Br could be attributed to an uneven global distribution of oceanic sources and sinks.