At 1:00 PM on May 18, 2021, following a brief maintenance period, the R/V "Shiyan 1" departed from the base wharf of the South China Sea Institute of Oceanology, Chinese Academy of Sciences (hereinafter referred to as "SCSIO") bound for the western South China Sea to execute a scientific expedition cruise mission. This cruise was organized and led by SCSIO, with participating institutions including Xiamen University, Tianjin University of Science and Technology, and other research institutions, involving a total of 19 research personnel in the scientific expedition, with planned operations spanning 17 days. The cruise project leader is Associate Director and Researcher Du Yan from SCSIO, with Associate Researcher Shi Zhen serving as the cruise chief scientist. 

This cruise will utilize various advanced observational equipment including ship-towed vehicles, CTD, ADCP, XCTD, and underwater gliders, employing a combination of large-scale fixed-point observations and underway observations to conduct high-resolution hydrographic and ecological observations of target eddies in the Xisha sea area, investigating the vertical structure of mesoscale eddies and their biogeochemical effects.