How biogenic polymers control surfactant dynamics in the surface microlayer: insights from a coastal Baltic Sea study

[摘要] Surfactants can hamper gas exchange by up to 50 % incoastal seas; however, their small-scale temporal and spatial dynamics arepoorly constrained. This study investigated possible biogenic sources ofsurfactants in the sea surface microlayer (SML) and the underlying water ata coastal Baltic Sea site. To relate surfactant dynamics to biogenicproduction, we conducted two field studies (June and September 2018) andfocused on amino acids and carbohydrates as the main components of organicmatter derived from phytoplankton. Furthermore the composition of the biochemicalsprovided insights into microbial degradation dynamics and wascomplemented by flow-cytometry-based community analysis. In total, 76samples were collected within an area of approximately 50 km 2 , allowingfor high spatial resolution. Moreover, morning and afternoon samplingenabled us to investigate diel cycles. Our results reveal thatsurfactant concentrations were tightly coupled to the abundance ofnano-phytoplankton and generally higher in September than in June, with cellabundance 3 times higher. Surfactant concentration in June was bestexplained by the combined effect of the particulate fraction of thenon-essential amino acid serine, the concentration of particulate combinedcarbohydrates (PCHO), and dissolved organic carbon (DOC). Surfactant andPCHO concentrations were significantly enriched in the SML and followed apronounced diel cycle, possibly linked to microbial processing and/orphoto-processing. In contrast to June, the surfactant pool in Septembercorrelated to a diverse mixture of semi-labile organic matter components,represented best by dissolved glucose and the essential amino acidisoleucine. We conclude that the surfactant pool in surface seawater ismainly composed of organic matter components that resist rapid microbialdegradation. Elevated surfactant concentrations are triggered by the releaseof fresh organic matter. While the effect of the resistant but lesssurface-active stock is potentially longer-lasting, the additive effect oflabile, highly surface-active agents on gas exchange may diminish on shorttimescales.

[学科分类] 大气科学