South Pacific Water Intrusion Into the Sub‐Thermocline Makassar Strait in the Winter of 2016–2017 Following a Super El Niño

• Published in: Geophysical research letters 2024-09, Vol.51 (18), p.n/a
• Main Authors: Li, Mingting, Yuan, Dongliang, Gordon, Arnold L., Gruenburg, Laura K., Wang, Dongxiao
• Format: Article
• Language: English
• Subjects: Coastal undercurrents; Coastal waters; El Nino; El Nino events; El Nino phenomena; Enthalpy; Equatorial currents; Heat; Heat content; Indonesian Throughflow; Interannual variability; Intrusion; Ocean circulation; Ocean currents; Oceans; Salinity; Salinity effects; South Pacific water; Straits; sub‐thermocline; Summer; super El Nino; Thermocline; Undercurrents; Vertical profiles; Water circulation; Water masses; Water properties; Winter
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL109965

The Makassar Strait throughflow (MST) is the major component of the Indonesian Throughflow (ITF), transferring Pacific water into the Indian Ocean. In our previous study, we identified a new zonal pathway, a. k.a. the North Equatorial Subsurface Current (NESC), which carried equatorial water into the MST sub‐thermocline (>300 m) in the summer 2016 following the 2015/16 El Niño. We now show continued strong southward MST in the sub‐thermocline during the winter of 2016–2017, with salinity higher than that in the summer 2016, due to direct South Pacific water intrusion into the Sulawesi Sea. The origin of the intrusion is identified from the New Guinea Coastal Undercurrent (NGCUC) and from an anomalous westward flow along 3°N in the western equatorial Pacific. The identified interannual variability of the western Pacific Ocean circulation is particularly strong in the winter following super El Niño events. Plain Language Summary The Indonesian Throughflow (ITF) transfers Pacific waters into the eastern Indian Ocean through the complex passages of the Maritime Continent, affecting the water properties and heat content in both oceans. The vertical structure of the ITF plays an important role in modulating the Indo‐Pacific Ocean heat content and climate. Understanding the Pacific water mass sources of the ITF and their variations is essential to understanding interocean heat and salt transports. The sub‐thermocline (>300 m) throughflow within the Indonesian Seas, has waters drawn from the relatively salty South Pacific thermocline. To date, the pathway of the South Pacific water into the ITF is not understood well. Here we present evidence showing a new pathway for high salinity South Pacific water flowing into the sub‐thermocline Makassar Strait directly after strong El Nino events, which may become more common in the future. This study helps to understand the importance of the South Pacific water in the variations of the Great Ocean Conveyer Belt and in biogeochemical processes with ecological impacts downstream of the ITF. Key Points Strong anomalous southward flow with higher salinity in the winter of 2016–2017 was observed in the sub‐thermocline Makassar Strait The high salinity is due to direct intrusion of South Pacific water from the western boundary current and an anomalous flow along 3 °N The identified direct intrusion of South Pacific water into the Makassar Strait appears strong in the winter following a super El Niño