In the southeastern Yellow Sea, the summer intrusion of bottom cold water induces temperature fluctuations in the coastal bottom layer, which are closely linked to regional fisheries productivity. Therefore, it is important to analyze the physical factors driving the onshore intrusion of bottom cold water. This study utilizes the Finite Volume Community Ocean Model (FVCOM) to analyze the relationship between summer freshwater discharge from major rivers along the Korean west coast, including the Han, Geum, and Yeongsan Rivers, and the onshore intrusion of bottom cold water over the period 2019–2023. Among the study years, the two years with the highest freshwater discharge were designated as high-discharge periods (2020, 2023), and the two years with the lowest discharge were designated as low-discharge periods (2019, 2021). Model results indicate that during high-discharge periods, the horizontal density gradient in the direction from the estuary toward the open sea increases compared to low-discharge periods. This enhanced density gradient drives an onshore bottom flow through density-induced circulation, where the offshore surface plume is compensated by the onshore flow at depth. Flux analysis shows that onshore bottom velocity and volume flux increase during high-discharge periods relative to low-discharge periods, serving as the primary mechanism for accelerated onshore transport of bottom cold water. Consequently, bottom cold water intrudes further onshore during high-discharge periods compared to low-discharge periods, resulting in a decrease in coastal bottom water temperatures. However, the extent of this bottom cold water intrusion may be reinforced or suppressed depending on wind direction and intensity, suggesting that the combined effects of freshwater discharge and wind stress need to be considered together. In conclusion, this study demonstrates that freshwater discharge from rivers along the Korean west coast is an important physical factor regulating coastal bottom water temperature variability in the southeastern Yellow Sea, and may serve as foundational data for understanding future variability in the coastal fisheries environment.

This research was a part of the project titled 'BEACON for Future Marine Workforce : Integrating Spatial and Resource Utilization(RS-2025-02220608)', funded by the Ministry of Oceans and Fisheries, Korea.
 

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