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ArticleA Maluku Sea intermediate western boundary current connecting Pacific Ocean circulation to the Indonesian Throughflow(Nature Research, 2022-04-19) Yuan, Dongliang ; Yin, Xueli ; Li, Xiang ; Corvianawatie, Corry ; Wang, Zheng ; Li, Yao ; Yang, Ya ; Hu, Xiaoyue ; Wang, Jing ; Tan, Shuwen ; Surinati, Dewi ; Purwandana, Adi ; Wardana, Adhitya Kusuma ; Ismail, Mochamad Furqon Azis ; Budiman, Asep S. ; Bayhaqi, Ahmad ; Avianto, Praditya ; Santoso, Priyadi Dwi ; Kusmanto, Edi ; Dirhamsyah, Dirham ; Arifin, Zainal ; Pratt, Lawrence J.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.
ArticleHydraulics and mixing of the deep overflow in the Lifamatola Passage of the Indonesian Seas(American Meteorological Society, 2020-09-01) Tan, Shuwen ; Pratt, Lawrence J. ; Yuan, Dongliang ; Li, Xiang ; Wang, Zheng ; Li, Yao ; Corvianawatie, Corry ; Surinati, Dewi ; Budiman, Asep S. ; Bayhaqi, AhmadHydrographic measurements recently acquired along the thalweg of the Lifamatola Passage combined with historical moored velocity measurements immediately downstream of the sill are used to study the hydraulics, transport, mixing, and entrainment in the dense overflow. The observations suggest that the mean overflow is nearly critical at the mooring site, suggesting that a weir formula may be appropriate for estimating the overflow transport. Our assessment suggests that the weir formulas corresponding to a rectangular, triangular, or parabolic cross section all result in transports very close to the observation, suggesting their potential usage in long-term monitoring of the overflow transport or parameterizing the transport in numerical models. Analyses also suggest that deep signals within the overflow layer are blocked by the shear flow from propagating upstream, whereas the shallow wave modes of the full-depth continuously stratified flow are able to propagate upstream from the Banda Sea into the Maluku Sea. Strong mixing is found immediately downstream of the sill crest, with Thorpe-scale-based estimates of the mean dissipation rate within the overflow up to 1.1 × 10−7 W kg−1 and the region-averaged diapycnal diffusivity within the downstream overflow in the range of 2.3 × 10−3 to 10.1 × 10−3 m2 s−1. Mixing in the Lifamatola Passage results in 0.6–1.2-Sv (1 Sv ≡ 106 m3 s−1) entrainment transport added to the overflow, enhancing the deep-water renewal in the Banda Sea. A bulk diffusivity coefficient estimated in the deep Banda Sea yields 1.6 × 10−3 ± 5 × 10−4 m2 s−1, with an associated downward turbulent heat flux of 9 W m−2.