Explore the vast range of titles available.

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 CO 2 storages significantly. Here the authors use in situ mooring data in the Maluku Channel and the Lifamatola Passage of the Indonesian seas to show that a western boundary current transports Antarctic water from the South Pacific to the Indian Ocean.

The currents and water mass properties at the Pacific entrance of the Indonesian seas are studied using measurements of three subsurface moorings deployed between the Talaud and Halmahera Islands. The moored current meter data show northeastward mean currents toward the Pacific Ocean in the upper 400 m during the nearly 2-yr mooring period, with the maximum velocity in the northern part of the channel. The mean transport between 60- and 300-m depths is estimated to be 10.1–13.2 Sv (1 Sv ≡ 10 6 m 3 s −1 ) during 2016–17, when all three moorings have measurements. The variability of the along-channel velocity is dominated by low-frequency signals (periods > 150 days), with northeastward variations in boreal winter and southwestward variations in summer in the superposition of the annual and semiannual harmonics. The current variations evidence the seasonal movement of the Mindanao Current retroflection, which is supported by satellite sea level and ocean color data, showing a cyclonic intrusion into the northern Maluku Sea in boreal winter whereas a leaping path occurs north of the Talaud Islands in summer. During Apri–July, the moored CTDs near 200 m show southwestward currents carrying the salty South Pacific Tropical Water into the Maluku Sea.

The mean circulation and volume budgets in the upper 1200 m of the Maluku Sea are studied using multiyear current meter measurements of four moorings in the Maluku Channel and of one synchronous mooring in the Lifamatola Passage. The measurements show that the mean current in the depth range of 60–450 m is northward toward the Pacific Ocean with a mean transport of 2.07–2.60 Sv (1 Sv ≡ 10 6 m 3 s −1 ). In the depth range of 450–1200 m, a mean western boundary current (WBC) flows southward through the western Maluku Sea and connects with the southward flow in the Lifamatola Passage. The mean currents in the central-eastern Maluku Channel are found to flow northward at this depth range, suggesting an anticlockwise western intensified gyre circulation in the middle layer of the Maluku Sea. Budget analyses suggest that the mean transport of the intermediate WBC is 1.83–2.25 Sv, which is balanced by three transports: 1) 0.62–0.93 Sv southward transport into the Seram–Banda Seas through the Lifamatola Passage, 2) 0.97–1.01 Sv returning to the western Pacific Ocean through the central-eastern Maluku Channel, and 3) a residual transport surplus, suggested to upwell to the upper layer joining the northward transport into the Pacific Ocean. The dynamics of the intermediate gyre circulation are explained by the potential vorticity (PV) integral constraint of a semienclosed basin.

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 Kρ= (1.44 ± 10.7) × 10–2 m2s–1, respectively. This Kρ is up to 104 times larger than the Banda Sea [Kρ = (9.2 ± 0.55) × 10–6 m2s–1] (Alford et al. Geophys Res Lett 26:2741–2744, 1999) or the “open ocean” Kρ= 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.

Mooring observations in the Halmahera Sea during September 2018 through October 2020 show a mean transport of 0.37–0.76 Sv through the Gebe Strait into the Indonesian seas. This estimate, together with mooring measurements in the Makassar Strait, the Maluku Channel, and the Jailolo Strait of the Halmahera Sea, suggests the total mean transport of the Indonesian Throughflow (ITF) to be 16.8 Sv ± 1.0 Sv (1 Sv = 106 m3 s−1), larger than the 15 Sv mean transport previously measured at the exit straits. Mooring data in the Maluku and Halmahera Seas, combined with Lagrangian tracking of the Makassar Strait throughflow using reanalysis velocity, show that 40% of the total ITF transport comes directly from the South Pacific Ocean. The above findings have revised the traditional concept that the ITF comes mainly from the North Pacific. One Sentence Summary The direct South Pacific to Indian Ocean transfer into the Great Ocean Conveyor is revealed.

The Indonesian Seas and Surroundings (ISS) play an important role in global ocean circulation by connecting the Pacific and Indian Oceans via the global thermohaline circulation. This region regulates the exchange of water mass, heat, salinity, and biogeochemical elements, further influencing the global climate and carbon cycle. Consequently, in this region, extensive observations and surveys, particularly the in-situ measurements, have been conducted in this region over the past two centuries. This study analyzed over 461 865 oceanographic casts from multiple international repositories, with 360 409 casts, or 21.97 % rejection, after rigorous quality control. The results show that data collection was sparse and temporally limited before the early 19th century, with a marked increase beginning in the mid-20th century. Spatially, observations are heavily concentrated along major international shipping routes, including the Makassar Strait, Malacca Strait, and South China Seas, while vast areas, such as the Halmahera Sea, Timor Sea, Java Sea, and Sulawesi Sea, remain poorly detected. Temperature and salinity are the most collected data, whereas deep-sea observations, particularly below 800 m, are critically lacking, with limited measurements of essential ocean variables such as dissolved oxygen, nutrients, and currents. Additionally, coastal regions exhibit substantial data deficiencies. Given the region's complex ocean-atmosphere interactions and unique topographic features, the current observational coverage remains insufficient to resolve the uncertainties in Indonesian Throughflow (ITF) variability, ocean heat transport, and monsoon forecasting. This study proposes to address the gaps by deploying autonomous monitoring technologies (Argo floats, gliders, moored buoys) in deep-sea and coastal regions, expanding regional observational networks, and enhancing executable data-sharing mechanisms. The raw datasets can be accessed freely from the website provided in the text, and processed datasets are preserved in data repositories with a corresponding assigned DOI. Final datasets and the computed cast per half-degree grid square with Python syntax are freely available on Mendeley repository. The data were in the TXT file format, and we used Ocean Data View Software (ODV Ver. 5.7.2), Python, and QGIS Software to process, visualize, and analyze the data (https://doi.org/10.17632/nm5txj3fps.1, Purba et al., 2025b.