Heat content increase of the tropical Indian Ocean induced by extreme positive Indian Ocean Dipole

Ocean heat content (OHC) changes in the tropical Indian Ocean (TIO) broadly affect the monsoon, tropical cyclogenesis, regional sea level, and marine heatwaves. While El Niño is known to induce basin-wide TIO warming, the OHC response to the Indian Ocean Dipole (IOD), the dominant climate mode in the Indian Ocean, remains unclear. Our analysis of the observational data reveals that extreme positive IOD (pIOD) events also drive a substantial increase in TIO OHC, with pronounced warming in the western basin. During the record‑breaking 2019 pIOD event, the 0-2000 m TIO OHC rose by ~8.2 ZJ (1 ZJ = 1021 Joules), comparable to signatures of strong El Niño events. Ocean model experiments and heat budget analysis diagnostics indicate that ∼80% of this gain is attributable to pIOD‑related surface wind changes, whereas the Indonesian Throughflow plays a minor role. Specifically, extreme pIOD-induced wind anomalies, dominated by northwesterlies south of 10°S, equatorial easterlies, and northeasterlies over the western Arabian Sea, drive basin-scale heat redistribution, suppressing heat export to the subtropical southern Indian Ocean and increasing TIO OHC. These results highlight the pivotal role of extreme pIOD events in regulating TIO heat content, with significant climatic implications under projected increases in such events due to anthropogenic forcing.