Indonesian throughflow water and its circulation in the Maluku Sea: An evaluation using the CROCO model

A high-resolution (1/36 degrees) regional ocean circulation simulation was conducted for 2018-2022 using the CROCO model to examine Indonesian Throughflow (ITF) water distribution and circulation mechanisms. The results indicate that the model effectively reproduces CTD data collected from Argo floats as well as from the BUDEE 2022 Cruise carried out in September 2022. Results reveal that ITF water in the Maluku Sea (MS) has distinct layers: near-surface fresh water (<23 sigma(theta)), maximum salinity thermocline water from North Pacific (NP) Subtropical Water (23.5-26.0 sigma(theta)), salinity minimum subthermocline water from NP Intermediate Water and South Pacific Subtropical Water (25.5-27.0 sigma(theta)), and less saline Antarctic Intermediate Water (AAIW) (similar to 27.2 sigma(theta)). The model's detailed spatial-temporal depiction of water mass distribution expands on previous studies. It indicates that thermocline water (S_max) and intermediate water (S_min) originate primarily from NP, transported southward by the Mindanao Current along the western boundary. Saline thermocline water also enters MS from the Halmahera Sea through the Obi Strait, while South Pacific Subtropical Water reaches MS along the same path. AAIW flows into MS via the northern passage. This ITF water distribution reflects southeast monsoon conditions (September 2022), which may differ during the northwest monsoon, warranting further study for a comprehensive understanding of seasonal variability in the eastern region.