Long-lasting Marine Heatwaves in the East Korea Bay in the East/Japan Sea: Characteristics and drivers

The East Korea Bay (EKB), located in the northwestern the East/Japan Sea (EJS), experiences the most intense and prolonged marine heatwaves within the EJS. In this study, we examine characteristics of the MHWs in the EKB from 1982 to 2018 and explore possible physical mechanisms for long-lasting MHWs using satellite data and reanalysis products. Over the 37 years, MHWs in the EKB lasted 32% longer (17±24 days) than the long-term average of the whole EJS. Notably, two exceptionally prolonged MHWs were observed, primarily during cooling seasons (fall and winter): one lasting 161 days in 2008/9 and another for 126 days in 2017/8. During these two MHWs, ocean surface cooling, predominantly driven by latent cooling, was intensified while solar heating remained near normal, suggesting that ocean processes play a crucial role in maintaining these extended MHWs. Spatiotemporal distributions of sea surface height indicate that intensified, persistent anticyclonic eddies significantly contribute to maintaining the long-lasting MHWs. A heat budget analysis further supports that the anticyclonic eddies are the primary drivers of these extended MHWs. Our findings underscore the critical role of ocean processes, including eddies and currents, in driving extremely long-lasting MHWs in the EKB within the EJS, particularly during cooling seasons.