01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-04-0347 |
| Title of Abstract | Observed characteristics and interannual variability of Indonesian Throughflow Water in the southwestern Indian Ocean |
| Authors | Hyungbo Kim*, Suyun Noh, SungHyun Nam, Dong-Jin Kang, TaeKeun Rho |
| Organisation | Seoul National University/KIOST |
| Address | 145, Bunpo-ro, Nam-gu Busan, Busan, Korea, Rep. Pincode: 48515 E-mail: hbkim1017@gmail.com |
| Country | Korea, Rep. |
| Presentation | Poster |
| Abstract | The Indonesian Throughflow (ITF) transports low-salinity, oxygen-depleted, and silicate-rich waters from the Pacific to the Indian Ocean, playing a crucial role in global ocean circulation and regional climate dynamics. While modification of Indonesian Throughflow Water (ITW) during its westward advection has been hypothesized, direct observations of ITW at thermocline depths in the Southwestern Indian Ocean (SWIO) are limited. This study investigates the persistence and variability of ITW in the SWIO (61°⿿67°E, 5°N⿿27°S ) . Using CTD (Conductivity-Temperature Depth) profiles and discrete water samples collected during six research cruises from 2017-2025, we analyzed temperature, salinity, dissolved oxygen, and silicate along with spiciness anomalies to identify and track the presence of ITW . We identified a distinct ITW layer between 100⿿300 m depth, characterized by absolute salinity of 35.25 ± 0.08 g/kg, conservative temperature of 15.13 ± 0.36 °C, dissolved oxygen of 101.52 ± 10.90 μmol/kg, and silicate of 19.05 ± 2.61 μmol/kg. ITW was distributed between 15°S⿿8°S within the South Equatorial Current, showing slight interannual variations in its position and extent. During 2018⿿2019, we observed a remarkable northward shift of the entire ITW structure by ~3° latitude (from 15⿿11°S to 8⿿10°S), concurrent with a similar northward shift of Indian Ocean Subtropical Underwater (IOSTUW) boundaries. This northward shift of ITW and IOSTUW was coincident with anomalously high IOSTUW subduction rates reported in recent studies. These findings demonstrate that ITW, though modified by mixing during westward transport, retains its distinctive water mass signatures far into the western Indian Ocean and responds sensitively to large-scale climate forcing through thermocline-scale water mass interactions. These results have important implications for understanding circulation at thermocline depths, tropical-subtropical exchange processes, and subsurface indicators of basin-scale climate variability in the Indian Ocean. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Indonesian Throughflow (ITF), Indonesian Throughflow Water (ITW), Seychelles-Chagos Thermocline Ridge (SCTR), Indian Ocean Subtropical Underwater (IOSTUW), thermocline, ocean circulation |
| For Awards | no |