AbstractThe East Asian marginal seas (EAMS) are one of the fastestโwarming ocean regions globally. This study presents the longโterm trends (1982โ2020) of extreme ocean warming events called โmarine heatwavesโ over the EAMS and examines the relationships between marine heatwave trends and mean SST warming trends. We focus on five subregions with different influences from atmospheric perturbation and ocean currents: the northern East Sea (NโES), southern East Sea, Yellow Sea, Korea Strait (KS), and East China Sea (ECS). During the past four decades, marine heatwave duration and intensity in the EAMS have increased to approximately +4 days and +0.3ยฐC per decade on average, respectively. In summer, the positive trend of marine heatwaves is the highest in the ECS, primarily due to the rapidly increasing mean sea surface temperature (SST). In winter, the NโES reveals remarkably rapid increases in marine heatwave properties in the last two decades, with increasing rates of approximately 6.2 (4.9) times longer total duration (stronger intensity) than the global average changes. Beyond the impact of the rapid increase in mean SST, the NโES marine heatwaves can be further extended due to the northward shift of the East Korea Warm Current. In general, mean SST changes are critical to the increasing trend in marine heatwave duration and intensity. This study further emphasizes that the changes in ocean circulation may expedite more rapid changes in extreme ocean events, which can produce more vulnerability in some places, such as the NโES, to marine heatwaves under continued global warming.