Recent Acceleration of Arabian Sea Warming Induced by the Atlantic-Western Pacific Trans-basin Multidecadal Variability

Arabian Sea (AS) warming has been significantly accelerated since the 1990s, in particular in the spring season. Here we link the AS warming changes to the Atlantic multidecadal oscillation (AMO). A set of Atlantic pacemaker experiments with a slab mixed-layer ocean model successfully reproduces the AS spring multidecadal variability and its connection with the AMO. An atmospheric teleconnection from the Atlantic to the AS in the preceding winter and associated thermodynamic air-sea feedback is found to be important. The teleconnection can be reestablished by the atmospheric model when the AMO sea surface temperature (SST) and its trans-basin footprint over the western Pacific are prescribed simultaneously. The western Pacific SST warming associated with the AMO positive phase induces a Gill-type Rossby wave over the AS, showing anomalously low pressures and converging southerlies that weaken winter northerlies. Thus, the wind-evaporation-SST feedback results in and maintains the AS warm SST anomalies to the subsequent spring. Plain Language Summary The rapid warming of the Arabian Sea (AS) since the 1990s not only has significant impacts on the monsoon climate change and extreme weather events (flood, heat wave, and cyclone) in Arabian Peninsula and Indian subcontinent but also poses increasingly severe risks of damage to the coastal and marine ecosystems. However, the cause of this recent acceleration of AS warming remains unclear. Here using observations and atmosphere-ocean coupled models, we link the observed AS warming changes to the Atlantic multidecadal oscillation (AMO) and show that more than 70% of AS multidecadal variability can be explained by the AMO. This Atlantic-AS teleconnection involves atmosphere-ocean interactions across multiple ocean basins, with a contribution from the western Pacific (WP). The SST footprint of theAMO over the WPacts as a relay for the effect of theAMO on the AS by exciting an atmospheric teleconnection and subsequently thermodynamic feedbacks over the AS. The concurrent cold-to-warm phase shift of theAMO and its WPSST footprint since the 1990s contribute constructively to the rapid warming of the AS. Our results highlight an unexpected multiple-basin interaction at decadal timescales, which plays a key role in the attribution of historical regional SST warming.