With the oceans covering 71% of the Earth, sea spray aerosol (SSA) particles profoundly impact climate through their ability to scatter solar radiation and serve as seeds for cloud formation. The climate properties can change when sea salt particles become mixed with insoluble organic material formed in ocean regions with phytoplankton blooms. Currently, the extent to which SSA chemical composition and climate properties are altered by biological processes in the ocean is uncertain. To better understand the factors controlling SSA composition, we carried out a mesocosm study in an isolated ocean-atmosphere facility containing 3,400 gallons of natural seawater. Over the course of the study, two successive phytoplankton blooms resulted in SSA with vastly different composition and properties. During the first bloom, aliphatic-rich organics were enhanced in submicron SSA and tracked the abundance of phytoplankton as indicated by chlorophyll-a concentrations. In contrast, the second bloom showed no enhancement of organic species in submicron particles. A concurrent increase in ice nucleating SSAparticles was also observed only during the first bloom. Analysisof the temporal variability in the concentration of aliphatic-richorganic species, using a kinetic model, suggests that the observedenhancement in SSA organic content is set by a delicate balance betweenthe rate of phytoplankton primary production of labile lipids andenzymatic induced degradation. This study establishes a mechanisticframework indicating that biological processes in the ocean and SSAchemical composition are coupled not simply by ocean chlorophyll-aconcentrations, but are modulated by microbial degradation processes.This work provides unique insight into the biological, chemical, andphysical processes that control SSA chemical composition, that whenproperly accounted for may explain the observed differences in SSAcomposition between field studies.
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