Do Climate Feedbacks in the Tropical East Pacific Impact Emissions of Biogenic Halocarbons?

Natural emissions of marine halogenated compounds (halocarbons) are of large interest since they strongly influence the oxidative capacity of the troposphere, are involved in aerosol and ultrafine particle formation, and take part in tropospheric ozone depletion. In regions of strong tropical deep convection they can even be transported into the stratosphere, where the released halogens take also part in ozone destruction. Recent studies identified oceanic upwelling systems, where cold, nutrient rich deep waters foster enhanced biological activity in the surface, as important source regions for brominated compounds such as bromoform and dibromomethane, as well as the iodinated compounds such as methyl iodide, chloroiodomethane and diiodomethane.

The tropical Pacific is subject to strong variations in atmospheric and oceanographic conditions known as the El Niño – Southern Oscillation (ENSO). During regular conditions, a strong upwelling band is observed at the western coast of South America especially close to Peru. In contrast, the upwelling ceases during the anomalous warm phase known as El Niño with severe consequences for biogeochemical cycles in the tropical East Pacific. We identified the Peruvian upwelling as a strong source for iodinated and only as a moderate source for brominated halocarbons during the M91 cruise in December 2012 during regular ENSO conditions. We demonstrate that the organoiodine emissions contribute most of the tropospheric iodine found during this season. During the onset of the ENSO-warm phase, the biological activity and thus the emissions may change drastically. Such changes and their impact on tropospheric halogen budgets are investigated for the ASTRA-OMZ SONNE cruise taking place in the same region in October 2015 as M91 but during a strong El Niño event.