Selective Ocean–Atmosphere Bacterial Flux Through the Pacific Sea Surface Microlayer

Marine–atmosphere microbial exchange is essential for nutrient cycling and ecosystem dynamics, though mechanisms are poorly understood. The role of the sea surface microlayer (SML) in mediating these exchanges was investigated. Samples were collected across a latitude gradient in the Pacific Ocean, and 16S rRNA gene and transcript sequences from surface seawater (SW), SML, and atmospheric samples were analyzed. The genomic signature varied diurnally and spatially, with the SW community being the most consistent and the air community the most variable. The SML displayed genomic characteristics intermediate between SW and air. The 16S rRNA transcript signature, a proxy for active microbial communities, showed tight clustering in the air and SML, suggesting selective control compared to SW. The transcriptional community composition in the air clustered between the SML and SW, pointing to viable non-SML-mediated exchange. Furthermore, taxa from air- and marine-associated communities showed a gradient of presence through all three environments, suggesting an exchange of key species through the SML. Additionally, certain volatile organic compounds in the atmosphere demonstrated a noteworthy relationship with specific bacterial taxa in the SML. This study improves our understanding of the role of the SML in ocean–atmosphere exchanges of marine bacteria and highlights how microbial communities travel and best utilize their environment.