Temporal and spatial variation characteristics and influence mechanism of surface cold water in the North Yellow Sea in summer

This study investigates the spatial and temporal evolution characteristics of summer sea surface temperature in the North Yellow Sea using ultra-high-resolution OSTIA SST data from 1982 to 2023, providing quantitative basis for the assessment of regional ecological environment evolution. Results show that SST in the study area increased significantly at a rate of (0.28±0.10) ℃ per decade. Empirical Orthogonal Function (EOF) analysis indicates that the primary mode (81.57% variance) exhibits homogeneous warming across the entire region, while the secondary mode (6.77%) is characterized by an inland-coastal anti-phase oscillation. The summer surface cold water phenomenon in the North Yellow Sea is stably distributed in the West Korea Bay, the Changshan Archipelago, the Chengshanjiao frontal area and Bohai Strait. Among these, the cold water area in West Korea Bay is the most significant, and the statistics based on the temperature threshold method demonstrates a significant interdecadal shrinkage of the cold water area in this region from 1982 to 2023 (−4 497.90±9.59 km²/10 a). Analysis of the driving mechanisms indicates that, alongside the dominant effects of tidal mixing and upwelling, the reduction in summer net heat flux across the North Yellow Sea −4.68 W/(m²·10 a) plays a critical role in driving the contraction of the surface cold water area. In contrast, the declining meridional wind stress component fails to significantly modulate the spatial extent of these cold water features.