CAICE Studies: Insights from a Decade of Ocean–Atmosphere Experiments in the Laboratory

Ocean-atmosphere interactions control the composition of the atmosphere, hydrological cycle, and temperature of our planet and affect human and ecosystem health. Our understanding of the impact of ocean emissions on atmospheric chemistry and climate is limited relative to terrestrial systems, despite the fact that oceans cover the majority (71%) of the Earth. As a result, the impact of marine aerosols on clouds represents one of the largest uncertainties in our understanding of climate, which is limiting our ability to accurately predict the future temperatures of our planet. The emission of gases and particles from the ocean surface constitutes an important chemical link between the ocean and atmosphere and is mediated by marine biological, physical, and chemical processes. It is challenging to isolate the role of biological ocean processes on atmospheric chemistry in the real world, which contains a mixture of terrestrial and anthropogenic emissions. One decade ago, the NSF Center for Aerosol Impacts on Chemistry of the Environment (CAICE) took a unique ocean-in-the-laboratory approach to study the factors controlling the chemical composition of marine aerosols and their effects on clouds and climate. CAICE studies have demonstrated that the complex interplay of phytoplankton, bacteria, and viruses exerts significant control over sea spray aerosol composition and the production of volatile organic compounds. In addition, CAICE experiments have explored the physical production mechanisms and their impact on the properties of marine cloud condensation nuclei and ice nucleating particles, thus shedding light on connections between the oceans and cloud formation. As these ocean-in-the-laboratory experiments become more sophisticated, they allow for further exploration of the complexity of the processes that control atmospheric emissions from the ocean, as well as incorporating the effects of atmospheric aging and secondary oxidation processes. In the face of unprecedented global climate change, these results provide key insights into how our oceans and atmosphere are responding to human-induced changes to our planet.This Account presents results from a decade of research by chemists in the NSF Center for Aerosol Impacts on Chemistry of the Environment. The mission of CAICE involves taking a multidisciplinary approach to transform the ability to accurately predict the impact of marine aerosols on our environment by bringing the full real-world chemical complexity of the ocean and atmosphere into the laboratory. Toward this end, CAICE has successfully advanced the study of the ocean-atmosphere system under controlled laboratory settings through the stepwise simulation of physical production mechanisms and incorporation of marine microorganisms, building to systems that replicate real-world chemical complexity. This powerful approach has already made substantial progress in advancing our understanding of how ocean biology and physical processes affect the composition of nascent sea spray aerosol (SSA), as well as yielded insights that help explain longstanding discrepancies in field observations in the marine environment. CAICE research is now using laboratory studies to assess how real-world complexity, such as warming temperatures, ocean acidification, wind speed, biology, and anthropogenic perturbations, impacts the evolution of sea spray aerosol properties, as well as shapes the composition of the marine atmosphere.