Regional Ocean Conditions Shape Mesoscale Eddy Thermal Responses to ENSO Diversity in the Subtropical Southeastern Indian Ocean

Satellite altimetry, Argo profiles, and ocean reanalysis are used to examine mesoscale eddy thermal responses to eastern-Pacific (EP) and central-Pacific (CP) ENSO in the subtropical southeastern Indian Ocean. Anticyclonic temperature anomalies relative to climatology broadly follow regional background changes. During EP-El Niño, eastern subsurface cooling and central shallow warming coincide with weaker eastern but strong central warm-core anomalies. Leeuwin Current variations suggest that changes in poleward warm-water transport contribute to the eastern temperature response. Cyclonic eddies retain subsurface cold cores under all four ENSO conditions, with pronounced upper-ocean warming producing a warm-over-cold structure during CP-La Niña. Subtracting matched contemporaneous out-of-eddy temperatures preserves these cores and their greater depth in the central sector. The ENSO–shear relationship is stronger for meridional than zonal shear in the eastern Leeuwin Current–Leeuwin Undercurrent system, whereas zonal shear in the central South Indian Countercurrent–South Equatorial Current system is associated with both ENSO indices. These shear changes may affect eddy development through baroclinic instability. Approximately 15–17% of eastern-origin eddies propagate into the central sector and may retain thermal properties acquired upstream. Regional background temperature thus helps explain anticyclonic thermal contrasts, while circulation adjustments and westward propagation may also contribute to subsurface thermal variability.