Tracing the golden tide outbreak in the Yellow Sea and East China Sea over a 15-year period using multi-satellite sensor data

The Yellow Sea (YS) and East China Sea (ECS) have the world’s largest supply of floating algae. The golden tides (Sargassum horneri) appear mainly in the YS and ECS, but become entangled as they drift. The floating harmful macroalgae blooms (HMBs) obstructs navigation and is a huge socioeconomic problem in the vicinity of coastal areas. To determine the origin and movement trend of the golden tide in the YS and ECS, the multi-satellite sensor data (e.g. Sentinel-2 and GOCI) was used to detect the floating macroalgae which was determined by the Alternative Floating Algae Index (AFAI, Wang and Hu, 2016) and mapped over the study area using a 15-year data. 

The occurrence period of the golden tide from 2008 to 2019 determined that they were found between January and March in the China coast, and the patches of floating macroalgae in Jeju Island and the west coast of Korea were observed between March and May. The macroalgae was detached from the waters near the Yangtze River and Zhejiang Province, China and then floating into the east and north-east ward influenced by the Tsushima warm current or Kuroshio. The build-up of the gold tide was occurred in the middle of the ECS and pile-up of them was in the coast of Korea from March to May. Recently, changes have begun to appear in movement trend of the golden tide. During 2020 and 2021, the golden tide was found in the western coast of Korea on January and in the northern waters of Jeju Island, Korea on February, and at the same time, another large-scale patch was found in the waters near the mouth of the Yangtze River and Zhejiang Province, China. From the results, the golden tide outbreak occurred that first flowed in west coast of Korea and northern Jeju Island in the winter, and then another outbreak occurred in southern Jeju Island in spring. It was analyzed that the movement trend of the golden tide has changed in recent years that the golden tide presented in the YS and ECS have different origins such as Bohai Bay and near the Yangtze River and Zhejiang Province, China.