William D. Garrett

The organic chemical composition of the ocean surface

Abstract Samples were collected under various oceanographic conditions from the Atlantic and Pacific oceans, the Gulf of Lower California, the Gulf of Mexico, and the Bay of Panama to determine the surface-active chloroform-soluble components present in the sea surface. The chloroform-soluble organic constituents were isolated from these samples and were analyzed by various gas chromatographic techniques. The major chloroform-soluble organic constituents of the sea are fatty esters, free fatty acids, fatty alcohols, and hydrocarbons. A fraction of the isolated components may be products of the biological organisms contained in the sampled sea water. The chemical classes found are general to all areas sampled, but specific differences within these classes exist from one location to another. Thus, the distribution of fatty acids and alcohols varies according to meteorological and oceanographic conditions prevalent at a articular location. A competition for adsorption sites exists at the surface between the various chemical species. The higher molecular weight and less water-soluble fatty acids and alcohols are the most surface-active and likely to be found adsorbed at the surface while the more water-soluble or less surface-active entities are forced out of the surface by the fatty material when competitive adsorptive processes occur.

Surface chemical properties of banded sea slicks

Abstract Surface concentrations and film pressures of slick-forming organic constituents were measured in situ and on surface water samples from the Pacific Ocean, west of San Diego. The surface tension data, accurate to ±0·6 dyne/cm, indicated that film pressures ranged as low as a few dyne/cm in the banded slicks associated with internal waves. This observation is consistent with previously reported data which show that water-insoluble surface films damp capillary waves strongly at film pressures as low as 0·5–1·0 dyne/cm. Some surface-active material was present in all samples, whether from ‘clean’ rippled water or from visible slicks. Film pressures were measured as a function of the surface concentration of film-forming constituents. These data indicated that concentrations in many of the slicked zones were just sufficient to damp or resist the formation of ripples. This observation was also corroborated by the in situ surface tension data. It was estimated that a four-fold compression of the surface layer by horizontal convergent forces was required to create visible slicks at this location.

Stabilization of air bubbles at the air-sea interface by surface-active material

Abstract The longevity of air bubbles at the air-water interface is a function of the surface-chemical activity of the water and the chemical condition of the water surface. In the absence of a sea surface film, the lifetime of an air bubble is determined by the surface-active material adsorbed during its passage upwards through the ocean. The presence of a compressed monomolecular layer (sea slick) at the sea surface will significantly reduce bubble stability and act as an antifoaming agent even though the underlying water may be rich in bubble-stabilizing substances. Single bubbles are stabilized by a surface tension gradient flow, but their lifetimes may be decreased by resistance to flow caused by intermolecular cohesional forces within the monolayer at higher film pressures. Bubble stability studies on pure compounds provide useful qualitative information about molecular interactions and orientations within the stabilizing film.

EFFECTS OF AN ARTIFICIAL SEA SLICK UPON THE ATMOSPHERE AND THE OCEAN

Abstract Vertical mean wind profiles, hot-film data, and wave height data measured during the passage of an artificial sea slick are compared with similar measurements without a sea slick. The effects of the slick are modifications of profile roughness length z0, and a possible increase in mean wind speed. Power spectral density plots of wave records obtained before, during and after the slick show wave energy modifications for wavelengths up to 10 m. Coherence values computed from a cross-spectral density of the wind field and simultaneously measured wave field both during and after the slick demonstrate the importance of small waves to air-sea interaction processes. Phase angles indicate the maximum horizontal velocity occurs over the wave trough for all spectral components, some of which are above and some below the wind-wave “matched layer.” During a stick, however, the horizontal velocity maximum occurs over the wave crest for those waves remaining coherent with the wind field.

The effect of monomolecular surface films on the microwave brightness temperature of the sea surface

Abstract Airborne microwave radiometer measurements at 1·43 and 2·65 GHz over a sea surface covered with a monomolecular oleyl alcohol surface film and over adjacent slick sea surfaces are presented. The measurements show that at 2·65 GHz the brightness temperature T B is not affected by the slick, while at 1·43 GHz it drops from 93 K to a minimum value of almost O K. This implies that at 1·43 GHz the emissivity of the slick-covered sea surface is extremely small, similar to a metallic layer, and that this resonant-type phenomenon is confined to a narrow frequency band of width δƒ/ ƒ<0·6. The theoretical implications of these experimental findings are discussed in the framework of the Debye relaxation theory of polar liquids. It is conjectured that a thin layer of water molecules polarized by the surface film gives rise to an anomalous dispersion, which causes the large decrease in brightness temperature at 1·43 GHz. The modulus of the relative dielectric constant e∗ is estimated to be ≥ 5·2 × 10−4 and th...

Effects of organic surface films on evaporation and thermal structure of water in free and forced convection

Abstract Surface-active, film-forming compounds of the type which reduce evaporation (1-heptadecanol) and compounds which are not expected to affect evaporation (oleyl alcohol) were introduced on the surface of a 50 cm deep tank of water. Changes in heat flux and near-surface temperature structure were measured in 20°C and 28°C water with room temperature of 22°C and 30% relative humidity. Comparison with an earlier study by Jarvis indicates that the turbulence and surface renewal associated with deep water convection are important in mitigating the effects of surface-active compounds. A weak air flow (1 m s−1)over the open tank resulted in dramatic changes in the frequency and amplitude of temperature fluctuations below the interface.

The impact of organic material on cloud and fog processes

Airborne surface-active organic substances can form adsorbed films at air-water and air-solid interfaces in the atmosphere. On the basis of considerable laboratory research, it has been suggested that these films can modify the microphysical processes of clouds and fog. The possible alterations of physical processes include retardation of the rate of growth and evaporation of water drops, passivation of cloud condensation nuclei, modification of drop coalescence efficiency, and the promotion of drop instability. The chemical structure of the film-forming compounds and the physical properties of the adsorbed films determine the degree to which the physical processes are modified. Upon consideration of the actual organic composition of the atmosphere, it was concluded that natural surface films will not greatly influence drop growth and evaporation. In addition, there is no definitive evidence from field experiments that other processes are influenced by natural organic films. The potential for useful weather modification through the intentional introduction of film-forming organic substances into the atmosphere was critically evaluated. Although numerous approaches have been suggested by laboratory studies, only the stabilization of airborne drops against evaporation has been unequivocally demonstrated in field experiments.

The discrimination between crude-oil spills and monomolecular sea slicks by an airborne lidar

Abstract Airborne lidar measurements were performed over a deployed mono-molecular oleyl alcohol surface film (‘slick’), the physicochemical characteristics of which are known to be similar to biogenic organic compounds secreted by plankton and fish, and adjacent ‘clean’ sea surfaces in the North Sea. In the presence of the slick,the suppression of the Raman backscatter at 381 nmand of two spectral bands indicative of water column fluorescent organic material at 414 and 482 nm were observed. This effect is explained by two possible mechanisms giving rise to a modification of the transmission or coupling of the laser beam into the water column: (i) the damping of capillary and short gravity water waves by the oleyl alcohol slick, and (ii) the modification of the uppermost water layer by the oleyl alcohol film. The results obtained in the presenceof a slick are compared with data measured over a Murban crude-oil spill with the same lidar system off the coast of the U.S.A. The consequences of the lidar-monom...