The intensity of deep‐ocean mixing critically shapes the global overturning circulation, but the energy cascade participating in the elevated mixing above rough topography remains poorly understood. Using 350‐day moored observations, the energy cascade triggered by eddy‐topography interactions is for the first time revealed in the deep South China Sea. The deep‐ocean observations show bottom‐intensified near‐inertial wave (NIW) pulses during periods of eddy occurrences. Eddy‐induced NIWs appear to catalyze nonlinear wave‐wave interactions, which further cascade energies from NIWs and internal tides to higher‐frequency internal waves (HFIWs) above fk₁ frequency. Corresponding to the HFIW enhancement, the kinetic energy spectrum at 3–9 cycles per day increases by 2–9 times, and the spectral slope becomes ~ −1 rather than ~ −2, as predicted by the Garrett‐Munk oceanic internal wave spectrum. A cascade of internal waves above rough topography potentially promotes extracting energy from eddies and tides and dissipating this energy to mix deep waters.

In the early morning of 21 April 2021 local time, the Indonesian Navy submarine KRI nanggala-402 crashed in the Bali Sea (BS). As internal solitary waves (ISWs) are a great threat to submarine navigation, this paper analyzes the characteristics of ISWs in the BS by surveying satellite remote sensing images collected from 12–21 April 2021. The satellite images revealed active ISWs in the BS near the submarine wreck site with crest lengths approaching 200 km. Originating from the Lombok Strait (LS), the waves travelled northwestward across the BS deep basin, passed through the submarine wreck site, and shoaled onto the continental shelf west of the Kangean Islands, during which process, the propagation speed reached 2.69 m/s in the deep basin and 0.71 m/s in the shallow water. Based on the satellite images, the wave amplitude near the wreck site was reconstructed to be 41 m, and the reconstructed underwater wave structure showed a maximum vertical velocity of 10 cm/s. Satellite images also demonstrated the near-source evidence of ISWs near the Nusa Penida sill of the LS, and their generation were estimated to be related to the southward tidal current troughs.

Water‐mass transports in the vast and seemingly quiescent abyssal ocean, basically along topographically‐guided pathways, play a pivotal role in the Earth's climate. The pulse of abyssal circulations can be taken with observations at topographic choke points. The Yap‐Mariana Junction (YMJ) is the exclusive choke point through which the Lower Circumpolar Deep Water (LCDW) enters the Philippine Sea. Here, we quantify the LCDW transport and its variability based on mooring observations at the YMJ and the Mariana Trench (MT). The LCDW flows northward toward the Philippine Sea as an intensified current on the western side of the YMJ, with maximum mean velocity reaching 7.6 cm/s. The mean LCDW transports through the MT and the YMJ are 2.2 ± 1.0 Sv and 2.1 ± 0.4 Sv, respectively. Reversal flow at autumn in both the YMJ and MT is captured, indicating seasonal variability of the abyssal flow.

Near-inertial waves (NIWs) trapped in a propagating anticyclonic eddy (AE) are investigated along the eddy path at three areas spanning 660 km by using two mooring arrays and a cruise transect. In the upstream area, the reconstructed three-dimensional structure reveals that NIWs are concentrated within the eddy core with wave current amplitudes exceeding 0.2 m s⁻¹; vertically, due to the critical layer effect caused by eddy baroclinicity, NIWs are trapped at depths around 200 and 315 m with frequencies estimated to be ω₁ ≈ 0.918f and ω₂ ≈ 0.985f, respectively. After the AE propagates southwestward for hundreds of kilometers, the NIWs of frequency ω₁ are still detectable inside the AE, while NIWs of frequency ω₂ are absent because of the equatorward migration of the AE on a beta plane. Meanwhile, the wave kinetic energy downstream is trapped closer to the eddy center in radial direction, with the wave amplitude decaying roughly in a Gaussian form along the eddy radius, and becomes more homogeneous in the azimuthal direction, showing a more regular trapping form in the three-dimensional view. Investigation on wind shows that trapped NIWs are likely to be generated by a typhoon but less affected by the wind during the eddy passage time. By an energy analysis, we find that enhanced wave dissipation near the critical layer is roughly balanced by the energy transfer from mean flows, and therefore the trapped wave kinetic energy is largely conserved during the long-distance migration.

The characteristics of the energy flux of internal tides in the northern South China Sea (SCS) were explored by analyzing a fleet of underwater gliders. It was found that the low‐mode diurnal internal tides with ∼300 km wavelength in the middle basin are generated predominantly in the Luzon Strait (LS) and propagate over 1,000 km to the western SCS. However, the semidiurnal internal tides are generated in multiple regions, including the LS in the east part, the continental shelf, and the islands in the west. The energy flux of the mode‐1 diurnal internal tides attenuated rapidly within 450 km of the LS and was less pronounced after that. The estimated dissipation rate based on the mode‐1 energy flux is about 10 ⁻⁸ W/kg, underling the significant role of mode‐1 diurnal internal tides in bolstering far‐field mixing. This study provides a unique view of the spatial pattern, energy flux, and energy sink of the internal tides in the northern SCS, which could supplement the altimetry‐based results and improve the parameterization in ocean models.