Luzon Strait heat transport and mesoscale eddies’ enhancement effect on boreal winter subsurface marine heatwaves in the South China Sea

Marine heatwaves (MHWs) in the South China Sea (SCS) significantly impact marine ecosystems, yet boreal winter subsurface events remain underexplored. This study investigates the spatiotemporal characteristics, vertical structure, and driving mechanisms of winter subsurface MHWs in the SCS from 1994 to 2023 using high-resolution ocean reanalysis data. Winter MHWs exhibit distinct spatial patterns, with surface events concentrated along northern coasts and subsurface events peaking in the northeastern SCS west of the Luzon Strait. Intensity peaks at ∼130 m, with high-intensity zones shifting from the southwest to the northeast with depth. The Luzon Strait region shows deeper, more intense, and more frequent MHWs compared to SCS-wide averages. Key drivers include Kuroshio-branch heat influx and mesoscale eddies, with positive heat influx anomalies strongly correlated with MHW intensity at 250–300 m and negative vorticity (anticyclonic eddies) enhancing frequency at 70–200 m. Heat budget analysis reveals advection dominance: vertical advection provides stable heating, while horizontal advection offsets surface cooling, with anomalous anticyclonic eddies (negative vorticity) promoting downwelling and subsurface warming in peak MHW years. These findings highlight the northeastern SCS as a winter MHW hotspot and provide a basis for assessing ecological risks to vulnerable marine ecosystems. 海洋热浪对南海海洋生态系统产生显著影响, 然而南海冬季次表层海洋热浪事件的特征仍缺乏深入研究.本文基于1994—2023年高分辨率海洋再分析资料, 系统分析了南海冬季次表层海洋热浪的时空分布特征,垂直结构及其驱动机制.结果表明, 南海冬季海洋热浪呈现显著的空间差异性:表层事件主要集中于北部近岸海域, 而次表层事件强度峰值位于吕宋海峡以西的南海东北部;热浪强度在约130米深度达到最大, 高强度区随深度增加从西南向东北方向迁移.吕宋海峡区域的海洋热浪相对于南海整体平均表现出更深,更强且更频繁的特征.主要驱动因子包括黑潮分支的热量输入和中尺度涡旋.正热量输入异常与250–300米深度的热浪强度呈显著正相关;负涡度(即反气旋涡)显著提升70–200米深度范围内的热浪发生频率.热收支分析显示, 平流过程主导热浪维持:垂直平流提供稳定的加热, 水平平流有效抵消表层冷却;在热浪峰值年份, 反常的反气旋涡(负涡度)通过促进下沉运动显著加强次表层增温.研究结果凸显南海东北部为冬季海洋热浪的重要热点区域, 为评估脆弱海洋生态系统的生态风险提供了科学依据.