Water Mass Variations in the Maluku Channel of the Indonesian Seas During the Winter of 2018-2019

An autonomous underwater glider was deployed in the Maluku Channel during 1 December 2018 through 21 February 2019 to measure temperature and salinity profiles of the upper similar to 1,000 m continuously. The measurements suggest intraseasonal variations of the Pacific water mass intrusions into the Maluku Channel, which has not been reported before. The North Pacific Tropical and Intermediate Waters are found to intrude episodically into the eastern Maluku Channel at the depths of 130-180 m and 250-300 m, respectively, during January through February of 2019, each lasting for a few days to a week. The Antarctic Intermediate Water was present in the middle and western Maluku Channel between 600 and 800 m with intraseasonal variability. The South Pacific Subsurface Water was only found to intrude into the eastern Maluku Channel between 250 and 300 m during the first two transections in early December of 2018. Concurrent meter data from three moorings in the Maluku and Talaud-Halmahera Channels are used to verify the water mass movement. The subsurface and intermediate water mass variations here are found to be closely related to the swing of the Mindanao Current near the Maluku Channel. These intraseasonal water mass intrusions are important aspects of water exchange between the western Pacific Ocean and the Indonesian seas. Indonesian Throughflow (ITF) carries a large amount of mass, heat and salt from the Pacific to the Indian Ocean, playing an important role in global ocean circulation and climate. The Maluku Channel is one of the main passages of the eastern Indonesian seas, the ocean circulation of which has been poorly observed in history. The water exchange between the Pacific and Indian Ocean through the eastern Indonesian seas is not clear so far. An autonomous underwater glider was used to collect salinity and temperature profiles of the upper 1,000 m in the Maluku Channel for nearly 3 months in the winter of 2018-2019. Three moorings were also deployed to measure the movement of the water masses. These measurements have shown for the first time that the North Pacific Intermediate Water, the Antarctic Intermediate Water, and the South Pacific Subsurface Water have intruded into the Maluku Channel, sometimes episodically. The presence of the Pacific water masses in the Indonesian seas has shed light on the pathway of the ITF, the importance of which is profound on global ocean circulation and climate change.