Large-amplitude internal waves transport energy from the open ocean toward continental slopes and shelves, where shoaling and instability can enhance turbulent mixing and alter upper-ocean structure. However, direct observations linking nearshore internal-wave activity to mixed-layer evolution remain limited. This study investigates a large-amplitude internal-wave event observed over the nearshore slope of the southern Taiwan Strait using coordinated shipboard, satellite, and model-based observations. Shipboard acoustic Doppler current profiler measurements, sea-surface photographs, and satellite imagery revealed pronounced velocity anomalies and surface signatures consistent with a shoreward-propagating internal wave. Microstructure observations collected before and after the wave passage showed substantial changes in the upper-ocean density structure, including mixed-layer deepening and downward displacement of the pycnocline. The observed mixed-layer variation was considerably larger than the low-frequency background variability represented by regional model fields. Enhanced turbulent dissipation, increased Thorpe overturning, elevated buoyancy Reynolds numbers, and more frequent low Richardson numbers were observed near the mixed-layer base and upper pycnocline following the wave passage. Temperature-salinity characteristics did not indicate the arrival of a distinct new water mass, suggesting that the hydrographic changes were more consistent with enhanced local vertical mixing than with strong lateral water-mass replacement. An event-scale energy comparison further showed that the enhanced turbulence was energetically consistent with the observed mixed-layer deepening. These results provide observational evidence that the shoaling of large-amplitude internal waves over nearshore slopes can be accompanied by intensified turbulence and rapid reorganization of the upper-ocean mixed layer. Such intermittent processes may contribute importantly to coastal and marginal-sea mixing but remain difficult to resolve in regional models and reanalysis products.
 

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