EFFICIENCY OF MIXING IN THE MAIN THERMOCLINE

Estimates of heat flux from direct measurements of vertical velocity-t emperature fluctuation correlations have been obtained from vertical p rofiles through turbulent patches in the main thermocline. These have been compared to more indirect flux estimates derived from dissipation rates of turbulent kinetic energy and temperature variance. Because r ecord lengths are limited by the thickness of observed turbulent patch es, uncertainties are larger than would be expected from relatively lo nger horizontal records. The best estimate of dissipation flux coeffic ient from these data is about 0.15-0.2, but it is characterized by a l arge range of sample values. This implies mixing efficiencies (flux Ri chardson numbers) are about 0.13-0.17. This is within the range of lab oratory estimates but is different from measurements in turbulent tida l fronts.