Biogenic sources and sinks of bromocarbon in different marine environments

Oceanic bromocarbons are highly reactive volatile organic compounds and may contribute up to 40% of stratospheric ozone depletion in mid latitudes. High sea-air fluxes of bromocarbons in the tropical regions have been related to biological cycling in the surface ocean, mainly to phytoplankton and bacteria, but the underlying processes and magnitude of the biogenic sources and sinks are poorly known. Recently, it has been suggested that reactive halogen species in seawater halogenate dissolved organic matter (DOM) releasing halogenated trace gases. In order to understand temporal and spatial fluctuations of oceanic bromocarbon emissions, we studied microbial production and removal processes in the surface ocean during research cruises in low, temperate and high latitudes. Water samples were incubated with ¹³C-labelled bromoform (CHBr₃) and deuteraded dibromomethane (CD₂Br₂) substrate to determine bromocarbons consumption rates. ¹²C/¹³C-bromocarbon concentrations as well as bacterial abundance and organic matter concentrations were monitored to estimate the microbial activity and turn over. Experimental data are compared to measured depth profiles of microbial biomass, bromocarbon and organic matter concentrations.