High frequency acoustic observations of Mediterranean flow into the Black Sea

Abstract

The physical behavior of Mediterranean flow entering the Black Sea through the Strat of Istanbul is described using a variety of high frequency acoustic systems. Because of the density difference between salty Meditermnean and fresh Black Sea water, a two layer exchange is formed which is confined within a canyon in the Black Sea exit region of the stmit. A 120 kHz high resolution echo sounder is used to visualize the two layer dynamics which has a strong acoustic scattering strength. A 600 kHz bmd band acoustic Doppler current profiler shows that the Mediterranean flow exhibits tempoml variability associated with blockage. But during a time of maximum flow a balance offriction, Coriolis and pressure gradient forces give rise to Ekman current spirals and thus strong turbulence levels. A 307 kHz acoustical scintillation system over a 300 m path describes the turbulent boundary layer characteristics of the Mediterranean flow. The dominant component of the observed acoustic scintillation is from turbulent velocity mther than tempemture variability. An assumption of isotropic and homogeneous turbulence leads to estimates of the turbulent kinetic energy dissipation rate, shear stress and bottom drag coefficient.