Prolonged marine heatwaves in the East Korea Bay in the East Sea: characteristics and mechanisms

Abstract

Marine heatwaves (MHWs)—prolonged extremely high ocean temperature events—have become more intense, frequent, and longer in recent years, destructively impacting marine ecosystems and subsequent socio-economic consequences. The East Korea Bay (EKB) in the northwestern East/Japan Sea (EJS) has experienced 32% longer MHWs (16.8±24.0 days/event) compared to those of the whole EJS (12.6±11.5 days/event), especially with two extremely long-lasting MHWs of more than three months (161 and 126 days). In this study, we investigate the distinct characteristics of the long-lasting MHWs in the EKB for 37 years (1982–2018) and their possible physical mechanism using satellite and reanalysis products. During the long-lasting MHWs (top 20% duration, >18 days) in the EKB, an enhanced ocean surface cooling dominated by latent heat flux anomaly (-51 W/m^2) and the weak positive solar radiation anomaly (3.6 W/m^2 ) suggest a predominant role of oceanic processes. The spatiotemporal distribution of sea level anomalies shows that the long and strong anticyclonic eddies with higher amplitude seem to be associated with extremely longlasting MHWs. There is a significant positive correlation between the MHWs duration and the eddy intensity in the EKB (r= 0.32; p<0.05), especially during the long-lasting or consecutive MHWs in the EKB. A heat budget analysis further supports the dominant role of advection by the anticyclonic eddies for maintaining long-lasting MHWs. Our findings suggest that the ocean processes including eddies can contribute to driving extremely long-lasting MHWs in the EKB in the EJS.