The Xiamen Symposium on Marine Environmental Sciences (XMAS 2027)

The Indian Ocean Shallow Meridional Overturning Circulation (SMOC) significantly influences the Indian monsoon and global climate change by regulating heat balance. Using two reanalysis datasets and a series of ocean model experiments conducted at both high (eddy-resolving) and low resolutions, this study investigates how mesoscale eddies affect the strength of the Indian Subtropical Cell (STC), a key/major branch of the SMOC. The subtropical southern Indian Ocean (SSIO; 70°E-110°E, 35°S-20°S) serves as a significant subduction zone, characterized by high eddy kinetic energy, with its subduction rate closely linked to the intensity of the STC. In eddy-resolving models, the improved representation of mesoscale eddies enhances subduction rates, ultimately strengthening the simulation of STC strength through the northward spreading of subducted water masses. Eddy subduction contributes approximately 48.0% of the total subduction in eddy-resolving models, particularly in the subtropical southeast Indian Ocean (SEIO; 90°E–110°E, 35°S–20°S), where more eddies are present. Eddies accelerate changes in the mixed layer depth, resulting in a more pronounced mixed layer depth tendency term, thereby enhancing the subduction rate. This study enhances understanding of the impact of mesoscale processes on STC strength, shedding light on the mechanisms of tropical Indian Ocean circulation and its material-energy balance.