Marine Heatwaves in Korean waters: Seasonal and regional differences

Abstract

Marine heatwaves (MHWs) are phenomena in which the sea surface temperature (SST) extremely increases over thousands of kilometers for days to months. MHWs can cause substantial socio-economic damages along with the impacts in marine ecosystem such as a decrease in catch production and species diversity, and also contribute to increases in the occurrences of mass mortality of farming fishes and harmful algae blooms. Korean waters are regions where MHWs occur due to a combination of various factors such as atmospheric phenomena and ocean influences, and each sea area has different characteristics and seasonal fluctuations. In this study, we aim to investigate the characteristics of MHWs in the Korean waters focusing on their seasonal and regional differences, using OISST (Optimum Interpolation Sea Surface Temperature) data for the recent 37 years (1982-2018). The MHWs in the East Sea was generally 1.5 times stronger than in the Yellow Sea and the East China Sea; but exceptionally, in spring, the MHW in the Yellow Sea was the strongest. In summer, MHWs were as strong as about 3℃ throughout the East/Japan Sea, but in fall and winter, distributions of MHWs intensity(>3℃) were relatively concentrated on the polar front in the East/Japan Sea. In particular, in the fall, the influence of ocean current is dominant on the occurrence of MHWs in the East/Japan Sea. Our findings suggest that MHWs over Korean waters are different depending on the season and region, and also ocean variability could have a larger contribution than atmosphere for initiation of extensive MHWs. We will also present return level and return period of MHWs calculated by extreme value analysis.