Contrasting Sea Surface Cooling and Chlorophyll‐a Responses to Typhoon Hinnamnor (2022) Modulated by Oceanic Background Conditions

Abstract

This study investigates the physical and biological responses of the Yellow Sea (YS) and East China Sea (ECS) to Typhoon Hinnamnor (2022), with an extensive 34‐kt wind radius of approximately 430 km, using satellite‐derived sea surface temperature and ocean color data, in situ observations, and ocean analysis data. Three adjacent regions exhibited contrasting sea surface cooling (SSC) and chlorophyll‐a (Chl‐a) responses: the southeastern YS (left‐hand side of the typhoon track) showed pronounced SSC without a Chl‐a bloom, the northern ECS (center) exhibited both strong SSC and enhanced Chl‐a, and the southwestern Kyushu region (right‐hand side) showed minimal surface and biological responses. Although subsurface cold water facilitated significant SSC in the southeastern YS, strong pre‐typhoon stratification limited nutrient entrainment, thereby suppressing Chl‐a enhancement. In contrast, the northern ECS experienced intense mixing and Ekman suction‐induced upwelling, transporting nutrients from depths >40 m to the surface. In southwestern Kyushu, a thick layer of warm oligotrophic Kuroshio‐origin water buffered the thermal response and Chl‐a enhancement. These results demonstrate that typhoon‐induced responses in continental shelf seas are not solely determined by wind forcing but are significantly modulated by regional hydrographic factors, including stratification, subsurface thermal structures, and nutrient availability.