The bubble transport of natural surfactant materials from seawater to the air‐water interface and to the air is investigated experimentally by a radiotracer test system. We have studied the rates at which four lipid materials of differing molecular structure are scavenged from artificial seawater and ejected into the atmosphere by air bubbles of various size distributions at differing airflow rates and bubbling times. We have found that the bubble transport to the air for all materials studied is linearly proportional to the quantity of material transported to the surface microlayer, and the constant of proportionality appears to be independent of the type of material but is a function of the airflow rate and bubble size. Small bubbles were found generally to be more effective in transporting surface‐active organic compounds from seawater to the air.

The motion of sound ray trajectories in deep ocean environments, including internal wave induced scattering, is considered. Using the empirical Garrett–Munk internal wave spectrum and results from the study of stochastic differential equations, a framework for studying and modeling stochastic ray motion is developed. It is argued that terms in the ray equations involving internal wave induced sound speed perturbations δc can be neglected, but those involving ∂δc/∂z cannot. It is then shown in that the (Markov) approximation that spatial variations of ∂δc/∂z are delta correlated is remarkably good. These results lead naturally to an extremely simple system of coupled stochastic ray equations (in ray depth z, ray slowness p and travel time T) in which stochasticity enters the system only through the equation for p. Solutions to the stochastic ray equations—or the corresponding Fokker–Planck equation—describe approximately the density of acoustic energy in range, depth, angle and time. Two dimensionless parameters are introduced: (1) an acoustic Péclet number which is a measure of the ratio of the strength of deterministic ray refraction to that of stochastic scattering induced ray diffusion; and (2) a measure of the ratio of the strength of scattering induced ray diffusion to that of wave diffraction. Numerical solutions to the stochastic ray equations are compared to full wave simulations. These results show that, even in the weak scattering regime (large acoustic Péclet number), the inclusion of internal wave induced scattering may lead to important qualitative corrections to predictions of distributions of acoustic energy.

We have examined microbubble scavenging of four different types of lipid materials (oleic acid, stearic acid, triolein, and cholesterol) from seawater. These experiments have covered a range of bubble diameters (approximately 200 to 750 μm), bubble Reynolds numbers (approximately 10 to 150), and bubble void fractions (approximately 0.08% to 1.3%). We present here a model which synthesizes the experimental results. The model is based on turbulent diffusion to a single bubble coupled with experimentally determined adsorption kinetics. We have also introduced into the model a factor to account for the dependency of the scavenging observations on bubble void fraction. The introduction of this factor can be anticipated, because the flow hydrodynamics of single bubbles and bubble plumes are quite different. However, these differences are not well enough understood at this time to permit a thorough theoretical explanation of the void fraction factor.

Surface slicks at sea arc characterized hy the occurence of capillary wave-damping materials at the air-water interface. Physical mechanisms causing such slicks are believed to include internal waves, Langmuir circulations, and other phenomena involving vertical or horizontal transport and compression of surfactants. We report the rates of transport and deposition of four naturally occurring surface-active organic materials to the scawatcrvair interface by an ascending current field. Our results indicate that the susceptibility of thcsc materials to transport bv current follows the same relative order as thcir susceptibility to transport by bubbles (although the latter ratc is dramatically greater). The current transport results obtained can be explained by standard surface adsorption kinetics. Our data also indicate that subtle variations in the chemical structure and polarity of different materials may he major determining factors influencing their transport to the sea surface by currents.

The modal description of sound propagation in deep ocean environments is considered. Recently published inversion algorithms have assumed that modal group time delays can be measured. Such a measurement is straightforward to make if either: ͑1͒ the modal group arrival of interest is resolved in time; or ͑2͒ the wave field is sampled on a dense vertical array which spans much of the water column, thereby enabling the orthogonality of the modes to be exploited. In order to temporally resolve modal group arrivals using measurements made on a single hydrophone, the frequency bandwidth must: ͑a͒ be sufficiently broad that the temporal separation between successive modal arrivals exceeds the reciprocal bandwidth; and ͑b͒ be sufficiently narrow that, across the band, the group slownesses of neighboring mode numbers do not overlap. To satisfy both conditions ͓͑a͒ and ͑b͔͒ the ratio of the range to the center frequency must be large. Unlike ray arrivals, modal group arrivals broaden as range increases due to dispersive spreading. To minimize dispersive spreading so that accurate group delay time estimates can be obtained, the ratio of range to center frequency should be kept small. Thus the requirements for temporally resolving modal group arrivals conflict with the conditions that minimize dispersive spreading. Numerical results are presented which give quantitative estimates of which combinations of range, center frequency, bandwidth, and mode number produce conditions which are favorable for temporally resolving modal group arrivals in six regions of the deep ocean at mid and low latitudes. These results suggest that it is extremely difficult to find conditions which allow modal group arrivals to be temporally resolved and simultaneously allow group delay times to be measured with sufficient accuracy to be useful for tomography. The situation is further complicated by internal waves which appear to cause mode coupling and significant broadening of modal group arrivals at frequencies above approximately 50 Hz. The combined effects of dispersive spreading and internal wave-induced mode coupling suggest that, without employing mode filtering techniques, modal group time delay-based inversion schemes in the deep ocean do not appear to be promising.