Observed vertical fine-structure and mixing in the western equatorial Pacific Ocean

Abstract

Hydrographic observation including high vertical resolution velocity using 6oo kHz Lowering Acoustic Doppler Current Profilers and turbulence using a Microstructure profiler (MSP) along a TRION line at 156E was conducted in June 2011. Small-vertical-scale features in the vertical shear(SVSs) appear in the thermocline depth but less clear than previous observations reported in Richards et al(2012). Turbulent kinetic energy dissipation rate, ε estimated from MSP data reveal patches of high ε in the thermocline suggesting mixing associated with SVSs. It is indicated that enhanced thermocline mixing is also related to the meridional interleaving structure of water masses. Four-day time series data at 0.5N,156E reveal that the flow field varies strongly with semi diurnal frequency. An about 30 m thick vertical band of high energy dissipation rate appears in the depth range associated with strong vertical velocity shear in the thermocline throughout the time of the measurements.