Morphology of Sea Slicks - Looking on the Sea Surface with the ,,Eye of a Chemist” Frank Hoffmann, Heinrich Hiihnerfuss*, Johannes Simon-Kutscher University of Hamburg, Institute of Organic Chemistry Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany phone: +49-42838 4519 /fax: +49-42838 2893 / e-mail: thoffman@chemie. uni-hamburg.de Werner Alpers Institute of Oceanography, University of Hamburg, D-22529 Hamburg, Germany INTRODUCTION Thus far, different model substances have been used on the open sea, in order to simulate biogenic sea slicks with the aim of studying their influence on various remote sensing signals [1-6]. The choice of these chemicals was largely based on their physiochemical characteristics ancVortheir wave damping potential as inferred from wind wave tunnel investigations. In recent experiments that were performed during the SIR C/X-SAR campaign, it turned out that the spreading procedure, be it fi-omfi-ozenchunks or be it with the help of spreading solvents, may give rise to significantly different distribution patterns (the so-called ,,morphology”) on the sea surface and thus to different influences on remote sensing signals. Morphology effects reflect the phenomenon that the same film-forming compound may be arranged and distri- buted at the air/water interface in the following different manners: ● ● ● The molecules may be spread homogeneously. The molecules may form ‘islands’. So-called domains, of different sizes between microns and several hundred microns [7]. The hydrophobic alkyl chains may be arranged verti- cally with respect to the water surface (i.e., 90°) or at a specific angle of less than 90°. The hydrophobic alkyl chains may exhibit kinks, i.e., the linear arrangement of the alkyl chain is disturbed by irregularities. The head group structure may vary in dependence on the compression status. For more details on these aspects the reader is referred to [3,4,8]. ‘Theobvious correlation between morphology effects and remote sensing signals inspired us to perform systematic laboratory investigations on the influence of the spreading procedure on the surface viscosity, the surface potential and on the morphology. The latter aspect, which will be fiu-therdiscussed in the present paper, is being studied with the help of ‘Brewster Angle Microscopy’ [BAM], while the molecular structure of the system slicldadjacent water layer is being investigated by ‘Intiared Reflection- Absorption Spectroscopy’ [IRRAS]. Both methods allow in situ investigations of the monolayer at the air water interface without disturbing the structure and morphology of the film, though herein we confine ourselves to BAM investigations. Comparison with scatterometer results ob- tained over biogenic and man-made sea slicks during the SIR C/X-SAR campaign will illustrate the morphology aspects and their importance for the simulation of bio- genic sea slicks. METHODS In the present study, the ‘eye of a chemist’ that surveys the water surface is being represented by an optical me- thods, i.e., ‘Brewster Angle Microscopy’ [BAM]. A sche- matic sketch of the BAM setup is shown in Fig. 1a, while the experimental approach is depicted in Fig. lb. lVliniBAM setup (p-mode) laser diode I [ Fig. la: Schematic sketch of the BAM setup o (?s) domain I I Fig. lb: Schematic sketch of the experimental approach 0-7803-5207-6/99/$10.00 (c) 1999 IEEE