The Maluku Channel is a major opening of the eastern Indonesian Seas to the western Pacific Ocean, the upper-ocean currents of which have rarely been observed historically. During December 2012–November 2016, long time series of the upper Maluku Channel transport are measured successfully for the first time using subsurface oceanic moorings. The measurements show significant intraseasonal-to-interannual variability of over 14 Sv (1 Sv ≡ 106 m3 s−1) in the upper 300 m or so, with a mean transport of 1.04–1.31 Sv northward and a significant southward interannual change of over 3.5 Sv in the spring of 2014. Coincident with the interannual transport change is the Mindanao Current, choked at the entrance of the Indonesian Seas, which is significantly different from its climatological retroflection in fall–winter. A high-resolution numerical simulation suggests that the variations of the Maluku Channel currents are associated with the shifting of the Mindanao Current retroflection. It is suggested that the shifting of the Mindanao Current outside the Sulawesi Sea in the spring of 2014 elevates the sea level at the entrance of the Indonesian Seas, which drives the anomalous transport through the Maluku Channel. The results suggest the importance of the western boundary current nonlinearity in driving the transport variability of 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.

Hydrodynamical condition of Java sea as a part of Indian-Pacific throughflow system which is influenced by monsoon will affect the condition of Banten bay such tidal current. Bordered by Java sea makes Banten bay preoccupied with fisheries and shipping activities, so the information of current pattern e.g. tidal current is very necessary. This study aims to simulate the tidal current pattern using flow model fm as a numerical approach. Two-dimensional hydrodynamic model was employed to perform the simulation of tidal current. Model was validated by using current and tidal observation data which was taken on September 2015 and April 2016. The result shows that the current moved southwestern toward the land during high neap and high spring tidal conditions which ranged 0 – 0.142 m/s at the first transitional monsoon and 0-0.153 m/s at second transitional monsoon. During low spring tidal condition for both transitional monsoon, the current flowed northwestward on west side and northeastward on east side within the bay which ranged 0 – 0.137 m/s and 0 – 0.127 m/s respectively. The hydrodynamic conditions of Banten Bay are severe different between 2 transitional seasons, especially for the current speed and direction. It induces a different transport mechanism, resulting the unstable accretion and abrasion along Banten Bay coast.

The regional INDESO model configured in the Indonesian seas from 2008 to 2016 is used to study the mechanisms responsible for the variability of the currents in the Sulawesi Sea of the Indonesian seas. The model simulation compares reasonably with the seasonal to interannual variability of the moored current meter observations in the upper 350 m or so of the Maluku Channel during 2015 and 2016. The interannual variability of the currents in the eastern Sulawesi Sea in the model is found to be associated with both the Pacific and Indian Ocean remote forcing. Lag correlation analysis and a theoretical linear wave model simulation suggest that both the equatorial Kelvin waves from the Indian Ocean and the coastally trapped Kelvin waves from the western Pacific along the Philippine coast can propagate through the Indonesian seas and arrive at the Maluku Channel. In particular, from mid‐2015 to 2016 the Indian Ocean Kelvin waves are found to significantly impact the sea level anomaly variability in the Maluku Channel. The results indicate the importance of Indo‐Pacific planetary waves to the interannual variability of the currents in the Sulawesi Sea at the entrance of the Indonesian seas.

SOUTH JAVA CURRENT. Indian Ocean is influenced by the monsoon cycle. Monsoon cycle that occurs in the Indian Ocean influences the current patterns. Since a very strong westerlies occurs in The Tropical Convergence Zone (TCZ) at the equator, wyrtki jet is formed in the 40° - 80° W Indian Ocean on a transitional season. Its branchs are possibly formed when the wyrtki jet is in the equatorial west coast of Sumatra to the north and south along the western coast of Sumatra which eventually creates South Java Current (SJC). SJC flows southeastward during December–April and northwestward during June–October, when it is associated with coastal upwelling. SJC develop upwelling on a seasonal basis.