Production of surfactants by plankton agitation in the wakes of surface ships

Grant Winners

Dean

Abstract

Surface-active materials, or surfactants, play an important role in oceanic processes. Under appropriate weather conditions, the concentration as little as 1 mg/m2 of surfactant is enough to produce a slick – an area covered by monomolecular film with greatly reduced surface roughness. This effect is responsible for the visibility of ship wakes (as well as eddies, internal waves, fronts, and other oceanic features) in satellite-based optical and radar images.

Surfactants are naturally present in seawater mainly due to marine life activity. There are evidences that sea storm events stimulate plankton to produce more surfactant. Our hypothesis is that the passage of surface vessels and the associated effects such as wave-breaking, noise, cavitation, and turbulence may have the same stimulating effect on surfactant release by marine plankton as a storm event. The additional amount of surfactants released in a ship wake can make it visible for long time – an effect extremely important for ship traffic monitoring, maritime security, and pollution control.

Our goal is to test the above hypothesis. We plan to study the effect of turbulence, cavitation, and noise on the production of surfactants by the marine plankton in laboratory conditions. Some field measurements in real ship wakes may be required to support and validate the laboratory observations; however, laboratory settings allow us to study the role of each individual factor. The presence of surfactants will be detected in two ways: by change of damping properties of induced capillary waves and by change of the plankton biomass composition. In this way we avoid direct measurements of tiny amounts of surfactants that has always been a challenge to experiments in this area.

If successful, this experiment will contribute to theory of far wakes of ships and will suggest an explanation of the high variability in the observed ship wake's features.