Natural and anthropogenic sources of bromoform and dibromomethane in the oceanographic and biogeochemical regime of the subtropical North East Atlantic

The organic bromine compounds bromoform (CHBr₃) and dibromomethane (CH₂Br₂) influence tropospheric chemistry and stratospheric ozone depletion. Their atmospheric abundance is generally related to a common marine source, which is not well characterized. A cruise between the three Macaroenesian Archipelagos of Cape Verde, the Canaries and Madeira revealed that anthropogenic sources increased oceanic CHBr₃ emissions significantly close to some islands, especially at the Canaries, while heterotrophic processes in the ocean increased the flux of CH₂Br₂ from the sea to the atmosphere in the Cape Verde region. As anthropogenic disinfection processes, which release CHBr₃ in coastal areas increase, and as more CH₂Br₂ may be produced from increased heterotrophy in a warming, deoxygenated ocean, both sources could supply higher fractions of stratospheric bromine in the future, with yet unknown consequences for stratospheric ozone.