Sea surface warming suppresses primary sea spray aerosol number production

Sea spray aerosol (SSA) influences climate through direct and indirect interactions with radiation. However, the magnitudes of these interactions remain poorly constrained, in part due to a lack of understanding of the influences of sea surface temperature (SST) on SSA production. There is no agreed-upon dependence of SSA production on SST despite numerous field, laboratory, and modelling investigations. In this study, we describe a simple theoretical framework relating the interfacial processes and contextualizing previous work. Next, we characterize the connection between SST, bubble concentrations, SSA number concentrations, and SSA emission fluxes using measurements in the Scripps Ocean-Atmosphere Research Simulator (SOARS). This isolated ocean-atmosphere interaction system incorporates wind, waves, and SST controls to produce wave breaking under realistic and controlled conditions. Increasing SST from 2 to 23 °C suppressed total subsurface bubble concentrations (between 6.17 and 830 µm) by a factor of 1.5, SSA number concentrations (between 0.008 and 20 µm) by a factor of 3, and SSA number flux by a factor of 3. Importantly, we identify size-resolved differences including a non-monotonic SST dependence of supermicron number and mass emissions. Using these trends, we derive SST-dependent number and mass emission flux correction factors for SSA source functions in climate models. These controlled wind-wave-SST experiments demonstrate that increasing SST overall suppresses SSA production. Resolving this SST dependence is critical, as it directly alters marine aerosol burdens, cloud condensation nuclei, and radiative forcing, and provides a needed constraint missing from current parameterizations.