methyl bromide loss rate constants in the north Pacific Ocean

The degradation rate constant of CH 3 Br in the North Pacific Ocean was measured in surface seawater between September and October 1999, using a stable isotope ( 13 CH 3 Br) incubation technique. Total degradation rate constants ranged from 0.02 to 0.43 d −1 , decreasing in colder waters as a result of the temperature‐dependence of chemical losses. Biological rate constants ranged from 0.01 to 0.20 d −1 . In subtropical waters (13‐20°N), biological loss rate constants were small compared to chemical loss rate constants. North of Hawaii, biological processes played an increasingly significant role in CH 3 Br degradation. In subpolar waters (40‐58°N), biological losses dominated the removal of methyl bromide. Comparison of the measured loss rate constants with surface water CH 3 Br concentrations suggest that the CH 3 Br production rate is higher in warm, low latitude waters than in cold subpolar waters at this time of year. Diel studies revealed a midday maximum in biological degradation of methyl bromide.