Reflection of light from the air/water interface covered with sea-surface microlayers

The sea-surface microlayer as a boundary between the ocean and the atmosphere, where important physicochemical, biological, and photochemical processes take place, plays a major role in the exchange processes of gases, materials, and energy. However, its chemical composition, structure, and involved interactions are very complex and yet not fully understood. Here, we have applied optical/spectroscopic methods and fractal analysis to gain better insight and information regarding composition, structure, and processes in sea-surface microlayer. Regarding the optical properties of sea surface, the material known as chromophoric dissolved organic matter (CDOM) represents the predominant light-absorbing part of dissolved organic material. The enrichment of light-absorbing material in the microlayers has significant effect on transformation processes at the interface and on the properties of interface itself. Original and reconstructed sea-surface microlayer samples have been characterized and visualized by reflection spectroscopy and Brewster angle microscopy (BAM). Due to the presence of chromophores at the air/water interface, the spectrum of reflected light is changed within the spectral range of chromophore absorption, depending on the chromophore density and orientation at the interface. On the other hand, BAM provides information about the homogeneity of the film, existence and formation of domains, phase transitions, and adsorption of material from the aqueous phase to the interface. In this study we have analyzed original and ex-situ reconstructed sea-surface microlayer samples from the middle Adriatic (salt lake Rogoznica) and from Norwegian fjords in the vicinity of Tromso. The reflection spectra and BAM images of microlayers have been taken at different surface pressures. Also, the film formation on initially clean surface was monitored by BAM. It was found that the mechanisms responsible for initial film formation and its later development are diffusion from the bulk and adsorption on the interface followed by subsequent aggregation. Fit of experimental data with theoretical results indicates that the adsorption obeys Frumkin-type isotherm with attractive lateral interaction. Fractal analysis applied to the BAM images detected and identified a second-order phase transition during

[1]  Schwartz,et al.  Growth of a self-assembled monolayer by fractal aggregation. , 1992, Physical review letters.

[2]  J. Meunier,et al.  Microscope at the Brewster angle: Direct observation of first‐order phase transitions in monolayers , 1991 .

[3]  A. Gericke,et al.  Influence of the spreading solvent on the properties of monolayers at the air/water interface , 1993 .

[4]  Benoit B. Mandelbrot,et al.  Fractal Geometry of Nature , 1984 .

[5]  B. Ćosović,et al.  Complex methodological approach to the studies of natural microlayers at the air/water interface , 2003 .

[6]  Gasparovic,et al.  Physicochemical Characterization of Natural and ex-Situ Reconstructed Sea-Surface Microlayers. , 1998, Journal of colloid and interface science.

[7]  S. Pogorzelski,et al.  Static and dynamic properties of surfactant films on natural waters , 2001 .

[8]  P. Santschi,et al.  Dynamics of dissolved organic carbon (DOC) in oceanic environments , 1995 .

[9]  W. Cooper,et al.  Characterization of CDOM in an organic-rich river and surrounding coastal ocean in the South Atlantic Bight , 2003, Aquatic Sciences.

[10]  B. Gašparović,et al.  Surface-active properties of organic matter in the North Adriatic Sea , 2003 .

[11]  Peter Pfeifer,et al.  Chemistry in noninteger dimensions between two and three. I. Fractal theory of heterogeneous surfaces , 1983 .

[12]  E. Ott,et al.  Dimension of Strange Attractors , 1980 .

[13]  Frank E. Hoge,et al.  Satellite observation of Chromophoric Dissolved Organic Matter (CDOM) variability in the wake of hurricanes and typhoons , 2002 .

[14]  D. Crosby,et al.  Aquatic and Surface Photochemistry , 1994 .

[15]  N. Frew,et al.  Scaling of marine microlayer film surface pressure‐area isotherms using chemical attributes , 1992 .

[16]  L. Rampazzo.  Diffusion to a plane with adsorption according to frumkin's isotherm☆ , 1969 .

[17]  D. Risović,et al.  The simple electrochemical method for detection of 3d molecular reorientation in adsorbed layers of organic substances , 2004 .

[18]  B. Ćosović,et al.  Direct determination of surface active substances in natural waters , 1987 .

[19]  L. Mayer,et al.  Enrichment of dissolved phenolic material in the surface microlayer of coastal waters , 1980, Nature.

[20]  Z. Kozarac,et al.  Characterization of aquatic natural microlayers by monolayer techniques and Brewster angle microscopy , 2000 .

[21]  P. Morse,et al.  Methods of theoretical physics , 1955 .

[22]  D. Möbius,et al.  MORPHOLOGY OF PENTADECANOIC ACID MONOLAYERS AT THE AIR-WATER-INTERFACE STUDIED BY BAM , 1992 .

[23]  Michel Orrit,et al.  Reflection and transmission of light by dye monolayers , 1986 .

[24]  E. J. Bock,et al.  Static and dynamic response of natural multicomponent oceanic surface films to compression and dilation: Laboratory and field observations , 1993 .

[25]  D. Möbius,et al.  Enhanced light reflection by dye monolayers at the air–water interface , 1983 .

[26]  J. Essam,et al.  Series expansion study of the pair connectedness in bond percolation models , 1975 .

[27]  B. Ćosović,et al.  Fractionation of surface active substances on the XAD-8 resin Part I. Mixtures of model substances , 1994 .

[28]  L. Kiene,et al.  Fractionation of dissolved organic matter from surface waters using macroporous resins , 1997 .

[29]  B. Gašparović,et al.  Characterization of organic matter in fractionated seawater samples using o-nitrophenol as an electrochemical probe , 1997 .

[30]  S. Pogorzelski.  Structural and thermodynamic characteristics of natural marine films derived from force–area studies , 2001 .

[31]  Sarah A. Green,et al.  Optical absorption and fluorescence properties of chromophoric dissolved organic matter in natural waters , 1994 .

[32]  W. D. Garrett,et al.  COLLECTION OF SLICK‐FORMING MATERIALS FROM THE SEA SURFACE , 1965 .

[33]  Peter S. Liss,et al.  The sea surface and global change , 1997 .

[34]  Dirk Hoenig,et al.  Direct visualization of monolayers at the air-water interface by Brewster angle microscopy , 1991 .