MIXING EFFICIENCIES IN TURBULENT TIDAL FRONTS - RESULTS FROM DIRECT AND INDIRECT MEASUREMENTS OF DENSITY FLUX

The authors report direct measurements of density flux at a single dep th in a turbulent tidal flow, made by towing a Ctd beside the vertical beam of a modified acoustic Doppler current profiler. The direct flux estimates are compared with indirect estimates of density flux based on simultaneous microscale profiler measurements of epsilon and chi, d issipation rates of turbulent kinetic energy and of temperature varian ce, respectively. Two mixing efficiency estimates are made using Gamma (d) from the ratios of indirect flux estimates and Gamma(O) from the r atio of direct to epsilon flux estimates. The analysis indicates that Gamma(d) is no different from that determined in other open ocean expe riments and is independent of the sign of the flux Gamma(d) < /Gamma(0 )/, regardless of the sign of the flux Gamma(0) (flux > 0) < /Gamma 0/ (flux < 0). The consequences for interpretation of ocean microstructu re flux estimates are discussed.