engleski

Characterization of Sea-Surface Microlayers and Phytoplankton Culture Samples by Brewster Angle Microscopy

The sea-surface microlayer has been defined as the top 1 to 1000m of the sea surface. It is an important boundary, as an area of exchange of matter and energy, that either affects or is affected by global change. Sea surface layer is generally enriched in organic substances, particularly those which are surface active, metal ions, bacteria and other microorganisms, relative to subsurface water. Organic substances found in the microlayer originate from the in-situ production or from different sources and have been brought there by different transport mechanisms from the seawater bulk, atmosphere or land. Adsorbed organic substances change the physical and optical properties, depending on the nature of organics, i.e. the nature of polar groups, architecture of the hydrophobic chain, and ionic strength, pH and temperature Brewster angle microscopy (BAM) was developed as a powerful method for optical characterization of monolayers at the air/water interface providing information about the homogeneity of the film, existence and formation of domains, phase transition and adsorption of material from the aqueous phase. Although BAM has been used very successfully to investigate the morphology of lipid and fatty acid monolayers, as well as in studies of protein adsorption and crystallization processes at the air-water interface, to our knowledge no study of natural sea surface microlayer samples has been reported till now (except of ours). In this work we report about the studies of lipid monolayers spread on phytoplankton culture samples and of natural samples of sea-surface microlayer previously extracted by organic solvent and then reconstructed on the water surface by using BAM. BAM images of monolayers of dipalmitoyl phosphatidylcholine (DPPC), dimyristoyl-phosphatidic acid (DMPA) and dioctadecyldimethyl ammonium bromide (DOMA) spread on an aqueous subphase containing a sample of phytoplankton culture show that surface active substances released by phytoplankton culture influence the molecular organization as well as domain morphology of the lipid monolayers. There seems to exist a dependence between the primary phytoplankton production in the natural waters and the morphology of natural films. Samples taken in period of high production gave the BAM images with granular structures of liquid condensed domains in liquid expanded phase, while samples taken in period of low primary production showed only homogeneous and continuous feature in BAM images. BAM is proved to be very efficient analytical tool for a physico-chemical characterization of natural films and phytoplankton culture samples. It can be used for the investigations of interfacial layers in the real aquatic systems in order to improve our understanding of the mechanisms and physicochemical processes at natural phase boundaries which play an important role in the marine environmental protection and global change. References: 1. The sea-surface microlayer and its role in global change, 1995. Gesamp Report and Studies Series b No. 59., WMO, Geneva, 76 p. 2. Z. Kozarac, D. Möbius and D.B.Spohn, Croat. Chem. Acta, 71 (1998) 285-301 3. B. Gašparović, Z. Kozarac, A. Saliot, B. Ćosović and D. Möbius, J. Colloid Interface Sci., in press.

sea-surface microlayers; Phytoplankton cultura samples; BAM

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