Estimates of dissipation in the ocean mixed layer using a quasi-horizontalmicrostructure profiler

Some recent measurements of the mixed layer in oceans and lakes have indica ted that the rate of the dissipation of turbulent kinetic energy, epsilon, is much higher than expected from a purely shear-driven wall layer. This en hancement has usually been attributed to wave breaking. In this study, meas urements of dissipation in the open-ocean mixed layer on the continental sh elf off Nova Scotia are integrated with air-sea flux estimates and directio nal wave spectra to further study this issue. A microstructure profiler gli ding quasi-horizontally provides estimates of epsilon starting within 2 m o f the ocean surface as it slowly descends through the mixed layer. Dissipat ion rates were found to be enhanced relative to the wind stress production and indicated that similar to6% of the wind energy at 10 m is dissipated in the ocean mixed layer. In addition, results from this experiment demonstra te that the WAVES scaling for epsilon, based on wind and wave parameters, i s valid for the case of a simple windsea in which the swell can be easily s eparated. In more complex wave conditions epsilon remains enhanced relative to the classical wall layer; however, the WAVES scaling does not hold.