The work of the Halocarbon group aims at the identification of the main driving factors for the regional and temporal variability of marine halocarbon distributions and emissions and their impact in the troposphere and stratosphere. The tropical oceans are of special significance, as most tropospheric trace gases, including the oceanic emissions of the short-lived halocarbons, enter the stratosphere in the tropics. They are transported towards the winter pole by large-scale circulation in the stratosphere, finally descending to the troposphere at mid and high latitudes again. Hence, tropical processes impact the chemical composition of the entire atmosphere. In the projects SOPRAN, TRANSBROM, SHIVA, ROMIC-THREAT, OASIS, and Astra- OMZ, oceanic halocarbon distributions, sources, their air-sea exchange, transport through the atmosphere and impact on the stratosphere are investigated. The interdisciplinary cooperation with atmospheric chemists and physicists, biologists and biogeochemical modelers, currently further investigates ” Threats to Ozone Recovery from Anthropogenic Emissions of ‘Very Short-lived’ Halocarbons” and the “Biological control of climate-active trace gases in the surface ocean”.