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.
The Indonesian Throughflow (ITF) transfers large amount of Pacific waters into the eastern Indian Ocean through the complex passages of the Maritime Continent (Figure 1a), impacting on the water properties and heat content in both oceans (Gordon, 1986;Sprintall et al., 2019). The heat transport of the ITF is sensitive to the vertical profile of the velocities Potemra et al., 2003;Song & Gordon, 2004), which is forced by both local and remote forcing. High frequency (intraseasonal to seasonal) variations of the ITF vertical structure are associated with local forcing, propagating downward quickly into the sub-thermocline (
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