Subsurface cooling trend in the Southern Tropical Indian Ocean (1958–2023) linked with global warming and the Interdecadal Pacific Oscillation

Abstract Over the past 66 years, the upper ocean heat content (OHC, 0–400 m) in the Southern tropical Indian Ocean (TIO) has not increased despite ongoing global warming and rapid local sea surface temperature rises. Here we show that the decrease in OHC is primarily due to the local subsurface cooling at depths of approximately 60–400 m. The increasing cyclonic surface wind stress in the TIO has intensified Ekman pumping locally, thereby enhancing vertical cold advection through upwelling processes. We further show that while the Interdecadal Pacific Oscillation can drive similar changes in OHC and patterns of subsurface temperature through changes in surface wind stress, its effect is confined to decadal timescales and therefore does not leave evident imprints on this long-term trend. This study highlights the crucial role of local air–sea interactions and related oceanic dynamical processes in shaping the regional climate change response.