The gelatinous nature of the sea-surface microlayer

The sea-surface microlayer (SML) represents the interfacial layer between the ocean and atmosphere and covers about 70% of the worldʹs surface. Gel-like transparent exopolymer particles (TEP) in the SML were studied in oceanic and estuarine SML and subsurface water samples from South East Asia. The TEP enrichment factor, determined as the ratio of the TEP concentration in the SML to that in the corresponding subsurface water, was in the range of 0.39 to 2.43 (1.31 ± 0.52 mean ± standard deviation) and 0.29 to 9.72 (1.77 ± 3.03) in the oceanic and estuarine samples, respectively. Sulfate half-ester groups in the TEP showed a higher enrichment (3.29 ± 2.36) than the less strongly binding carboxyl groups (1.12 ± 0.71). Enrichment processes of TEP to the SML are discussed including diffusion to the SML, bubble scavenging and higher production rates of TEP in the SML than in subsurface waters. The results of a general enrichment of gel particles support the concept of a hydrated gelatinous interfacial layer with a complex matrix of dissolved organic matter rather than a more classical model of organized layers of “wet” and “dry” surfactants.