Profiles of currents, density, and microstructure were obtained in the Pacific Ocean on and near the equator at 140 ¿W in late 1984 as part of the Tropic Heat program. During a 4 1/2-day time series on the equator, the shear zone above the core of the undercurrent had very low mean Richardson numbers, Ri, between 1/4 and 1/2. Average turbulent dissipation rates, &egr;, were high in this zone, ≈10-7 W kg-1, and varied by a factor of 100 between minima in the early afternoon and maxima at night. The signal reached to 90 m, well into the stratified zone. Eddy coefficients, K, were low at high Ri, and gradually increased as Ri decreased, until they rose dramatically near Ri=1/4. The observed K(Ri) relations are specific to time, location, and temporal and spatial resolution of the data. ¿ American Geophysical Union 1988