Mapping and tracing Sargassum distribution and origin in the Yellow Sea and East China Sea using Sentinel-2 and GOCI data

Abstract

Macroalgal blooming or seaweed tide has determined effects on coastal ecosystem and local economy. ‘Golden tide’ caused by Sargassum occurred globally. Sargassum horneri is only a species causing outbreaks in northwestern Pacific and largest supply of floating patches are introduced into the Yellow Sea (YS) and East China Sea (EC). The annual pattern of Sargassum bloom is not well known due to changing air-sea interaction conditions. To determine the spatio-temporal distribution and variation 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 patch using the Alternative Floating Algae Index and mapped over the study area using a 15-year data. The floating patches detected by both satellite data were overlapped to make the annual pattern maps. 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.