Field measurements of turbulent mixing south of the Lombok Strait, Indonesia.

The Indonesian seas, with their complex passages and vigorous mixing, constitute the only route and are critical in regulating Pacific-Indian Ocean interchange, air-sea interaction, and global climate events. Previous research employing remote sensing and numerical simulations strongly suggested that this mixing is tidally driven and localized in narrow channels and straits, with only a few direct observations to validate it. The current study offers the first comprehensive temporal microstructure observations in the south of Lombok Strait with a radius of 0.05° and centered on 115.54^oE and 9.02^oS. Fifteen days of tidal mixing observations measured potential temperature and density, salinity, and turbulent energy dissipation rate. The results revealed significant mixing and verified the remotely sensed technique. The south Lombok temporal and depth averaged of the turbulent kinetic energy dissipation rate, and the diapycnal diffusivity from 20 to 250 m are $\epsilon$  = 4.15 ± 15.9) × 10^-6 W kg^-1 and $K\rho$ = (1.44 ± 10.7) × 10^-2 m²s^-1, respectively. This $K\rho$ is up to 10⁴ times larger than the Banda Sea [ $K\rho$  = (9.2 ± 0.55) × 10^-6 m²s^-1] (Alford et al. Geophys Res Lett 26:2741-2744, 1999) or the "open ocean" $K\rho$ = 0.03 × 10^-4 m²s^-1 within 2° of the equator to (0.4-0.5) × 10^-4 m²s^-1 at 50°-70° (Kunze et al. J Phys Oceanogr 36:1553-1576, 2006). Therefore, nonlinear interactions between internal tides, tidally induced mixing, and ITF plays a critical role regulating water mass transformation and have strong implications to longer-term variations and change of Pacific-Indian Ocean water circulation and climate.

Supplementary information: The online version contains supplementary material available at 10.1186/s40562-024-00349-3.