Remote sensing and in situ observations of marine slicks associated with inhomogeneous coastal currents

Field observations co-located and simultaneous with satellite radar imagery of biogenic slick bands on the sea surface aimed to study relation between slicks and marine stream currents were carried out in the coastal zone of the Black Sea. Measurements of the current velocities at different depths were performed using an acoustic Doppler current profiler (ADCP) and surface floats. Samples of surfactant films inside/ outside slick bands were collected from the water surface with nets. The sampled films were reconstructed in laboratory conditions and measurements of the damping coefficient of gravity-capillary waves and the surface tension were carried out using an original parametric wave method. It is obtained that the banded slicks are characterized by enhanced concentration of surfactants due to their compression by convergent current components. The slicks are revealed to be oriented along the stream currents and are located in the zones of current shears. Small convergent transverse velocity components are observed near slick boundaries and are responsible for slick formation in stream shear currents. Different examples of slicks formed by stream shear current are described. Results of a case study of two streams of different directions merging and forming a banded slick in a shear zone with convergent transverse current components are presented. Another case study is when a flow below a thermocline coming to the shore meets a bottom slope and a vertical current occurs resulting in horizontal divergence and convergence on the surface.