Tibetan Plateau’s freshwater bridge shifts the Indian Ocean Dipole to a high-frequency regime

Abstract The Tibetan Plateau (TP) exerts a profound influence on global climate, yet its impact on the Indian Ocean (IO) subsurface structure remains poorly understood. Using Earth system model simulations, we uncover a fundamental physical cascade linking the TP to the intermediate ocean. By intensifying the Asian monsoon, the presence of TP alters wind fields and, more critically, reorganizes precipitation and freshwater flux over the IO. This freshwater anomaly drives a dipolar shift in vertical stratification—weakening in the upper ocean while substantially strengthening at intermediate depths. The resulting “stratification shield” suppresses vertical heat exchange, locking in a persistent “upper-warm, lower-cold” thermal dipole that extends to ~1000 m. This previously unrecognized, monsoon-driven freshwater–stratification mechanism shifts the paradigm beyond wind-driven surface processes and establishes topography as a key driver of the intermediate ocean’s mean state. Importantly, this physical cascade fundamentally reshapes regional climate dynamics, most notably by modulating the stability of the coupled system and shifting the Indian Ocean Dipole (IOD) variability towards a high-frequency regime.