Role of Indonesian throughflow on Indian Ocean warming pattern formation during the recent global warming hiatus in CMIP6 models

Despite the slowdown in global surface temperature rise, the early twenty-first century global warming hiatus (2000-2013) was characterized by accelerated warming in the south Indian Ocean (IO), highlighting the role of inter-basin interactions in modulating regional ocean warming trends. This study investigates the thermodynamics of the IO in two groups of CMIP6 historical simulations, categorized based on contrasting trends in Indonesian Throughflow (ITF) volume and heat transport during the hiatus period. The CMIP6 models show large spread in ITF volume transport trends, leading to the construction of strong and weak ITF composite groups. The predominance of La Nina events in the strong group and El Nino events in the weak group contributes to these contrasting ITF trends. The estimated heat transport through the ITF in the strong group is -1 TW/yr, while the weak group shows a weakening trend of 0.7 TW/yr. This stronger heat transport from the Pacific to the IO results in thermocline deepening in the southeastern Indian Ocean (SEIO), which further intensifies the eastward warming compared to the west by triggering strong westerly winds through the Bjerknes feedback process. A similar mechanism warms the western half of the IO in the weak group composite through the intensification of southeasterly winds over the equatorial region. Reduced ITF heat transport and the shoaling of the thermocline, associated with upwelling favorable winds, cool the SEIO in the weak composite models. The study highlights the role of ITF strength in shaping zonally contrasting sea surface temperature (SST) warming patterns in CMIP6 models.