Biologically Induced Changes in the Partitioning of Submicron Particulates Between Bulk Seawater and the Sea Surface Microlayer

Studies over the last two decades have shown that submicron particulates (SMPs) can be transferred from the seawater into sea spray aerosol (SSA), potentially impacting SSA cloud seeding ability. This work reports the first concurrent bulk and sea surface microlayer (SSML) SMP (0.4–1.0 μm) measurements, made during two mesocosm phytoplankton blooms in a region devoid of active wave breaking and bubble formation, providing insight into how biological and physicochemical processes influence seawater SMP distributions. Modal analyses of the SMP size distributions revealed contributions from multiple, biologically related particulate populations that were controlled by the microbial loop. With negligible bubble scavenging occurring, SSML enrichment of SMPs remained low throughout both experiments, suggesting scavenging is vital for SMP enrichment in the SSML. Our findings are discussed in the context of SMP transfer into SSA and its potential importance for SSA cloud seeding ability.