Indian Ocean Dipole‐Induced Decoupling of Sea Surface pCO ₂ and Temperature in the Northern Bay of Bengal

Abstract The partial pressure of carbon dioxide at the sea surface (pCO 2sea ) is a key component in the ocean carbon cycle, jointly influenced by the thermodynamic, dynamical, and biological processes. Among these, thermodynamic control generally induces a pronounced positive covariation between pCO 2sea and sea surface temperature (SST). However, using multiple observations, reanalysis data sets, and BIO‐ROMS model simulations, this study reveals an anomalous decoupling between pCO 2sea and SST in the northern Bay of Bengal (BoB) during Indian Ocean dipole (IOD) events, highlighting the importance of non‐thermal mechanisms in determining pCO 2sea interannual variability. During positive IOD events, anomalies in dissolved inorganic carbon (DIC) and sea surface salinity (SSS) jointly exert positive influences on pCO 2sea , though partially offset by the opposite SST effects. Specifically, IOD‐related negative SST anomalies in the equatorial eastern Indian Ocean trigger the Matsuno‐Gill atmospheric response, enhancing evaporation and suppressing precipitation over the northern BoB. This leads to positive freshwater flux anomalies that elevate both DIC and SSS, contributing to increased pCO 2sea . Simultaneously, positive wind stress curl anomalies in the northwestern BoB enhance cyclonic eddy and upwelling, bringing the colder, DIC‐rich subsurface water into the mixed layer. Overall, these processes result in surface cooling while further enriched DIC. Moreover, anomalous southerly wind in the southwestern BoB weakens the East India Coastal Current, facilitating anomalous transport of saline water that enhances positive SSS anomalies, thereby increasing pCO 2sea anomalies. Our findings underscore the complex interplay between thermodynamic and dynamical processes in shaping BoB carbon cycle variability under IOD influence.