Wind speed dependent accumulation patterns of organic matter in the sea surface microlayer: Results from the 2014 AEOLOTRON experiment

The sea surface microlayer (SML) is the uppermost layer of the water-column and the interface between ocean and atmosphere. We investigated how SML formation, composition and stability are related to biogeochemistry, microbial activity and physical factors, such as wind speed and air bubbling, during an experiment conducted with natural seawater at the large annular wind-wave facility AEOLOTRON in 2014. Our data suggest that heterotrophic as well as autotrophic microbial activity provide organic matter for SML formation. Accumulation of particulate components like transparent exopolymer particles (TEP), amino acids and bacteria in the SML were found to be related to wind speed, while dissolved organic matter concentrations rather reflected the underlying seawater regime and partially increased in the SML after the entrainment of bubbles. Wind speeds ＞8m s^-1 significantly altered the particle size distribution (PSD) of TEP in the 2-60 μm size range, whereas PSD of CSP remained unaffected. The presentation provides insight to the relationship between physical forcing and organic matter enrichment in the SML, and discusses the potential role of different organic matter sources for air-sea exchange processes.