南海北部次表层高盐水的季节变化及其与西北太平洋环流的关系

The seasonal variation of subsurface high salinity in the northern South China Sea and its relationship to the northwestern Pacific circulations

次表层高盐水（〉34.68‰）作为北太平洋热带水（NPTW）的示踪, 可用来研究黑潮入侵, 了解南海与太平洋的水体交换.文章利用基于高分辨率混合坐标海洋模式（HYCOM）的海洋再分析资料, 研究了南海北部次表层高盐水的季节变化及其影响因子.模拟结果显示, 南海北部高盐水位于100-200m 水深, 最西可达111°E, 其体积存在明显的季节变化,12 月达到极大值, 6 月达到极小值.进一步的分析表明, 其季节变化主要受低纬度西北太平洋大尺度环流的调制, 与北赤道流分叉点位置的季节变化（1 月到达最北端、6 月到达最南端）呈现很好的相关性.受太平洋大尺度风场的影响, 北赤道流分叉点上半年（下半年）向南（北）移动, 导致黑潮输运增强（减弱）, 通过吕宋海峡进入南海的盐通量减少（增加）, 从而使南海次表层高盐水的盐度降低（升高）.吕宋海峡断面的流速和盐通量分布特征显示, 西太平洋高盐水主要通过吕宋海峡中部（20？~21？18？N）进入南海北部.

Subsurface high salinity （〉34.68‰） is often used as an indicator of the North Pacific Tropical Water （NPTW）. It isalso used as an indicator of the Kuroshio intrusion into the South China Sea （SCS）. It is used here to investigate waterexchange between the SCS and the northwestern Pacific. Using high-resolution hybrid coordinate ocean model （HYCOM）global assimilation data, we investigate seasonal variation of subsurface high salinity water in the northern SCS and theinfluence from the northwestern Pacific. Results show that there exists obviously seasonal variation in the subsurface highsalinity water at about 100-200 m depth, reaching as far west as 111°E in the northern SCS, and the salinity reaches itsmaximum （minimum） in December （June）. Further analysis shows that the seasonal change of high salinity water is stronglyaffected by the seasonal variation of large-scale circulation in the low latitude northwestern Pacific. The volume changes of thehigh salinity water is highly correlated with the bifurcation latitude of the North Equatorial Current （NEC）, which reaches northernmost latitude in January and southernmost latitude in June. Due to the large-scale wind change in the Pacific, the Kuroshio transport strengthens （weakens） when the bifurcation latitude of the NEC shifts to the south （north） during the first （second） half year, the salinity flux diminishes （increases） from upper northwestern Pacific into the SCS through the Luzon Strait, and the intrusion of the subsurface high salinity water in the northern SCS weakens （enhances）. The velocity and salinity flux distribution in the Luzon Strait show that the high salinity water mainly enters the northern SCS between 20？~21°18？N.