01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-02-0067 |
| Title of Abstract | Influence of climate-driven thermocline variability on vertical distribution of mesozooplankton in the western Indian Ocean |
| Authors | Hyeon Kim*, Minju Kim, Sun-Hee Lee, Dong-Jin Kang, Jung-Hoon Kang |
| Organisation | Korea Institute of Ocean Science and Technology |
| Address | 203ho, 2dong, 15, Tapgok-ro 4-gil Geoje-si, Gyeonsangnamdo, Korea, Rep. Pincode: 53304 E-mail: kh8515@kiost.ac.kr |
| Country | Korea, Rep. |
| Presentation | Oral |
| Abstract | The Seychelles-Chagos Thermocline Ridge (SCTR) in the western Indian Ocean is a major open-ocean upwelling region with notable interannual variability. To understand annual differences in mesozooplankton vertical distribution around the SCTR, we collected mesozooplankton at five discrete depths (from surface to 1,000 m) at the inner (08°S, 65°E) and outer (02°S, 65°E) stations of the SCTR during May-June 2023 and June 2024. Hydro-climate parameters, including the Indian Ocean Dipole (IOD) index and thermocline depth (20⿿ isotherm depth, D20), were evaluated as proxies for physical forcing. Mesozooplankton communities were mostly concentrated within the surface mixed layer and thermocline depth. Integrated abundances (0-1,000 m) at the inner station of the SCTR declined sharply from 2,072 inds./m3 in 2023 to 158 inds./m3 in 2024 (13.1-fold), and those at the outer station of the SCTR also decreased from 975 inds./m3 to 665 inds./m3 (1.5-fold). Mesozooplankton communities were categorized into five vertical distribution types: (1) surface dwellers, (2) surface-thermocline migrants, (3) thermocline dwellers, (4) sub-thermocline dwellers, and (5) diel vertical migrants. At the inner station of the SCTR, the proportion of surface dwellers decreased (2023: 84%, 2024: 18%), but that of surface-thermocline migrants (2023: 12%, 2024: 40%) and thermocline dwellers increased (2023: 3%, 2024: 40%), as D20 deepened from 48 to 72 m, coinciding with the transition of the IOD index from negative (-0.6 to -0.1) in 2023 to positive (+0.5 to +0.7) in 2024. At the outer station of the SCTR in 2024, the proportion of surface dwellers (2023: 29%, 2024: 52%) and surface-thermocline migrants increased (2023: 20%, 2024: 37%), but that of thermocline dwellers declined (2023: 48%, 2024: 9%) compared with 2023. Overall, the differences in the thermocline depth, the related changes in vertical distribution of mesozooplankton communities and the shift from negative to positive IOD phases between the inner and outer stations of the SCTR imply that climate-driven variability may influence the significant interannual shift in the depth-related characteristics of mesozooplankton communities in the western Indian Ocean. |
| Are you part of IIOE-2 endorsed project | yes |
| Endorsed Project Number | IIOE2-EP51 |
| Keywords | mesozooplankton, seychelles-chagos thermocline ridge, cilmate variability |
| For Awards | no |