Air-sea ammonia fluxes in the Southern Ocean: Quantifying sources and sinks from surface waters to penguins.

NH₃ drives nutrient cycling in the surface ocean and contributes to new particle formation in the marine atmospheric boundary layer. Surface ocean NH₃/Ammonium(NH₄⁺) is a vital component of the recycled nutrient pool, and NH₃ air-sea fluxes influence its redistribution. There are significant uncertainties in global NH₃ flux estimates due to a lack of concurrent air-sea measurements and ambiguity surrounding NH₃ sources.  Southern Ocean, a major driver of global climate, is experiencing rapid warming, altering the exchange of climate-relevant aerosols and precursor gases such as NH₃. Models systematically underpredict cloud droplet number concentrations and aerosol production in this region, a bias that arises from poorly captured aerosol precursor sources and lack of detailed microphysical cloud processes. We present atmospheric and seawater NH₃ measurements, along with NH₃ air-sea flux estimates, across the Southern Ocean during November and December 2024. Our study focuses on 1) identifying key NH₃ sources and sinks in the marine polar environment, and 2) quantifying how NH₃ fluxes vary across distinct emission hotspots. Preliminary observations show penguin colonies and volcanic activity drive distinct, localised NH₃ emission hotspots. The open ocean is generally thought to be a source of NH₃, but our data show that the open waters of the Southern Ocean is a sink of NH₃. By quantifying these fluxes, we reveal the variability across NH₃  source/sink regions and their potential to influence regional ocean-atmosphere biogeochemical processes.  

Our findings are crucial for improving the representation of clouds and aerosols in climate models, offering deeper insight into poorly understood aerosol-cloud interactions in this region. Improving these mechanisms will help reduce persistent Southern Ocean biases in model simulations of surface radiation and sea surface temperature and enhance our capacity to model regional and global climate.