engleski

Surface signatures of natural sea surface films: Application of force-area quantification approach

The sea surface microlayer (ML) forms the interface between the atmosphere and oceans covering about 71% of the Earth’s surface. An improved knowledge of the MLs distributions under different forcing conditions, its chemical composition and rheological characteristics are of crucial importance for better insight into the structural changes and mechanisms of ML formation as well as for modelling the phenomena and processes at the air-sea interface. An understanding of the processes and physical mechanisms governing the exchange of gases between air and sea is essential when considering coupled models of atmosphere-ocean interactions and global climate, the interactions which are of particular concern as they may affect or be affected by global changes. The chemical composition of natural films is largely undefined, although significant enrichment of many specific classes of compounds in the ML has been demonstrated. Instead of analysing the chemical composition, it should be possible to scale the MLs π-A isotherms in terms of structural parameters, reflecting the natural film morphology, and resulting from the generalized physical formalisms adopted to multicomponent films of surface active substances (SAS) (Pogorzelski and Kogut, 2003). In particular, a set of the structural film parameters appears to be a sensitive and quantitative measure of the film physicochemical composition (molecular mass Mw, specific limiting area Alim and elasticity modulus Eisoth), surface concentration (πmax, SAS), and the miscibility (y) of its film-forming components. This concept has been tested for marine coastal waters of the Adriatic Sea during longer period time. The MLs were studied by using monolayer technique and structural state scaling approach of -A isotherms as original samples and as ex-situ reconstructed films. In order to address the problem of solvent polarity effect on the surface structural parameters of ex-situ reconstructed films, the surface isotherms obtained from the material extracted from original ML with different solvents (n-hexane and dichloromethane) spread onto water surface were also analyzed by means of the novel scaling approach. The parameters can be novel indicators of surface-active source-specific organic matter production, migration and degradation status tracing physicochemical characterization of the surface active organic matter of the ML with the emphasis to the role of the source-specific lipids as film-forming components or end-members which may dominate the static surface properties of the ML. The normalization of the film structural parameters, based on the physical states similarity theory, provides a universal measure of surface properties evolution, applicable to a wide variety of the original and different ex-situ recovered films met in nature, giving an insight to the additional organic matter characterization of the natural films.

Adriatic Sea; sea surface microlayer; surfactants; isotherms; surface rheology; organic matter

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