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How the Impact of ENSO Events on the Indonesian Throughflow and Interannual Variability of Circulation in the Halmahera Sea
(2026-09-01)
Lubis, Muhammad Zainuddin
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Dwinovantyo, Angga
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Batara, B.
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Kausarian, Husnul
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Hidayat, Syarief
This study investigates the influence of El Niño–Southern Oscillation (ENSO) on the Indonesian Throughflow (ITF) in the Halmahera Sea (HS) during 2013–2023. Although ITF variability has been widely studied, the response of the HS to different ENSO phases remains insufficiently understood. Using a validated CROCO model, we quantified changes in HS throughflow and associated oceanographic conditions under El Niño and La Niña events. EOF analysis of sea surface height (SSH), meridional velocity, and salinity revealed dominant modes explaining more than 50% of the total variance and exhibiting clear ENSO-related variability. During El Niño events, ITF transport weakened substantially, with volume transport becoming less negative from − 4.0 ± 2.0 Sv to − 1.5 ± 1.5 Sv in the upper layer (0–100 m) and from − 5.0 ± 2.5 Sv to − 2.0 ± 2.0 Sv in the intermediate layer (0–400 m). These conditions were associated with a shallower thermocline, lower sea surface temperatures (25.5–26.0°C), and reduced surface salinity (34.74 PSU). In contrast, La Niña events strengthened the ITF, with transport reaching −7.0 ± 1.5 Sv in the upper layer and −7.0 ± 2.0 Sv in the intermediate layer, accompanied by a deeper thermocline and higher SSTs (29.8–30.42°C). The results suggest that ENSO-related variability in the HS is associated with coupled changes in thermocline structure, SSH gradients, and salinity, highlighting the importance of the HS in regulating ITF transport variability.
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How the interannual and seasonal variability in connectivity to ITF and its relation to ENSO events in the Halmahera Sea: A modeling approach and observation
(2026-02-01)
Lubis, Muhammad Zainuddin
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Hu, Song
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Simanjuntak, Andrean V.H.
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Dwinovantyo, Angga
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Arnold, Ekoué Ewane Blaise
Understanding circulation dynamics in the Halmahera Sea (HS) is essential for clarifying the interactions between El Niño and La Niña events and ITF variability, which significantly impacts the global climate. Despite studies on air-sea interactions in the HS, gaps remain regarding interannual and seasonal variability, leading to uncertainties in understanding ocean circulation and throughflow dynamics. Specifically, there is a lack of understanding of how seasonal temperature and salinity shifts influence the strength and direction of ocean currents in the HS region. This study investigated how temperature and salinity variations during interannual and different seasons affect ocean current patterns in the HS. We used the CROCO model from 2019 to 2023 and observed it in September 2021. Our findings indicate distinct interannual patterns in SST, with the northwest monsoon SST ranging from approximately 28.3–29.8°C and the southeast monsoon SST ranging from approximately 26.8–29.0°C. The SSS varied between approximately 34.1 and 34.6 PSU, with the maximum mean water mass transport in the subsurface recorded at −0.5479 ± 0.6583 Sv at 0.5°S, indicating transport toward the Banda Sea. The SSH ranged from ∼0.69 to ∼0.73 m in the northwest and ∼0.66 to ∼0.69 m in the southeast monsoon. The densities at the surface, subsurface, and intermediate layers were 22.5, 25.5, and 26.5 σ<inf>ѳ</inf>. This research advances our understanding of the factors affecting HS circulation dynamics and their responses to El Niño and La Niña events, paving the way for Indo-Pacific water exchange studies.
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Indonesian Throughflow, spatial–temporal variability, and its relationship to ENSO events in the Lombok Strait
(2025-03-01)
Lubis, Muhammad Zainuddin
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Situmorang, Edriyan
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Simanjuntak, Andrean V.H.
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Riama, Nelly F.
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Pasma, Gumilang R.
Understanding the interactions between ocean currents and climate variability is crucial for predicting future oceanic and climatic shifts in the Lombok Strait and beyond. Our study examines the Lombok Strait from 2013 to 2018, focusing on the impact of interannual and seasonal variability driven by climatic events such as the El Niño-Southern Oscillation. Our findings reveal significant fluctuations in oceanographic parameters, including temperature, salinity, and ocean currents. The lowest recorded temperature was ∼27.2 °C, and the minimum salinity was ∼32.3 psu, linked to the strong El Niño event in 2015, which altered local rainfall and evaporation patterns. Analysis of meridional and zonal velocities showed enhanced water flow, with maximum meridional velocities reaching around ∼0.04 m/s and zonal velocities peaking at ∼0.18 m/s in early 2018. Seasonal variations in sea surface height show higher values during warmer months, reflecting the influence of ENSO phenomena. The vertical distribution of salinity indicated stratification, with values ranging from ∼27.5 psu to ∼34.0 psu across different depths, corresponding to water density ranging from 22.50 σ<inf>θ</inf> to 24.0 σ<inf>θ</inf>, highlighting the interaction between Pacific and Indian Ocean waters. Water mass transport averages at 100 m and 200 m show values of −1.21 ± 0.97 Sv and −1.350 ± 1.069 Sv, with the lowest transport occurring during the summer at −1.97 Sv with a depth range of 0–100 m, suggesting robust outflow. Our findings underscore the critical role of the ITF in shaping regional oceanographic conditions and their implications for global climate dynamics.

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