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 115.54oE and 9.02oS. 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 ε  = 4.15 ± 15.9) × 10-6 W kg-1 and K ρ = (1.44 ± 10.7) × 10-2 m2s-1, respectively. This K ρ is up to 104 times larger than the Banda Sea [ K ρ  = (9.2 ± 0.55) × 10-6 m2s-1] (Alford et al. Geophys Res Lett 26:2741-2744, 1999) or the "open ocean" K ρ = 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.

A Maluku Sea intermediate western boundary current connecting Pacific Ocean circulation to the Indonesian Throughflow.

The Indonesian Throughflow plays an important role in the global ocean circulation and climate. Existing studies of the Indonesian Throughflow have focused on the Makassar Strait and the exit straits, where the upper thermocline currents carry North Pacific waters to the Indian Ocean. Here we show, using mooring observations, that a previous unknown intermediate western boundary current (with the core at ~1000 m depth) exists in the Maluku Sea, which transports intermediate waters (primarily the Antarctic Intermediate Water) from the Pacific into the Seram-Banda Seas through the Lifamatola Passage above the bottom overflow. Our results suggest the importance of the western boundary current in global ocean intermediate circulation and overturn. We anticipate that our study is the beginning of more extensive investigations of the intermediate circulation of the Indo-Pacific ocean in global overturn, which shall improve our understanding of ocean heat and CO2 storages significantly.