Clean-up of accidents like the 2010 Deepwater Horizon oil spill can be complicated by what goes on beneath the ocean surface. Variations in temperature and salinity in seawater create stratification, stacked layers of water with differing densities. When less dense layers are on top, the fluid is said to be stably stratified. Since oil is less dense than water, one might assume that buoyancy should make an oil plume should rise straight to the ocean surface. But the presence of additives or surfactants in the oil mixture plume can prevent that. With surfactants present, an oil mixture tends to emulsify, breaking into tiny droplets like a well-mixed salad dressing. Even if the density of the emulsion is smaller than the surrounding fluids, such a plume can get trapped at a density boundary, as seen in the photo above. Researchers report a critical escape height, which depending on the plume’s characteristics and stratification boundary, determines whether a plume escapes or becomes trapped. (Image credit: R. Camassa et al.)
Plume Stratification
