Origin of floating Sargassum in the Yellow and East China Sea

Abstract

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 Sargassum blooms were generally found on spring in the YS and ECS. The Sargassum blooms was proceeded in 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 Sargassum blooms were build-up in the middle of the ECS and pile-up in the coast of Korea from March to May. Recently, the Sargassum blooms were temporally expanded from to May from 2019 to 2022 and spatially raised in the YS and ECS. From the annual pattern maps of the golden tide blooms, we suggested two origins with tracing the temporal and spatial distribution and development. The first blooms were onset on fall around the Bohai Bay and/or Shandong Peninsula and southward controlled by the local wind and sea surface temperature condition on winter. The second blooms were initiated on winter near the Zhejiang Province, China and east- and northward affected by the local current and wind condition.