长江口及其邻近海区环流和温、盐结构动力学研究Ⅳ盐度结构

DYNAMICS OF CIRCULATION AND TEMPERATURE-SALINITY STRUCTURES IN CHANGJIANG RIVER MOUTH AND ITS ADJACENT SEA Ⅳ.THE SALINITY STRUCTURE

盐度的数值模拟结果表明:一年四季长江口及其邻近海区的盐度分布均为近岸低,外海高,近岸与外海盐差大。冬季近岸和外海的上层盐度呈垂直均匀分布,陡坡及外海的底层出现层化;近岸特别是长江口及其以南近岸盐度的水平变化显著,外海变化缓慢。春季在长江口以北,近岸至外海的表层至近底层盐度呈垂直均匀分布,近岸至外海的底层存在一个向北延伸的盐舌;长江口及其以南近岸和外海的表层至次表层盐度呈垂直均匀分布,在近岸稍远的表层至次表层形成盐跃层,其强度自近岸至外海和自表层至底层逐渐减弱;在陡坡区的底层盐度几乎呈均匀分布,并保持高盐特征。夏季除长江口及其以南近岸浅水区盐度呈垂直均匀分布外,其它区域盐度均出现剧烈分层,在长江冲淡水区形成强盐跃层,其强度自表层至底层迅速减弱,陡坡至外海的底层盐度大致呈均匀分布且保持高盐特征。秋季长江口以北近岸浅水区表层盐度低且出现层化,表层以下盐度高且呈垂直均匀分布;近岸以远自表层至底层呈垂直均匀分布,在外海上层盐度低且呈垂直均匀分布,而底层盐度高并出现分层;长江口及其以南近岸浅水区盐度呈垂直均匀分布,陡坡区出现层化,其盐度为表层低,底层高;层化自表层至底层逐渐增强,并随陡坡至外海的减弱,上层又逐渐变为垂直均匀分布。

We simulated the seasonal salinity distribution in the Changjiang River mouth and its adjacent sea. Result of simulation displays that salinity is low near shore and high in the open sea, with a big difference in between. In winter, salinity is uniform vertically in all upper layers of near shore and the open sea. Stratification occurs in steep slope and the bottom layer of the open sea. Horizontal salinity change is severe in near shore of the mouth and southward and then gradually evens out to the open sea. In spring, salinity is uniform vertically from surface layer to bottom layer in open sea north of the mouth, and a northward salinity tongue forms in bottom layer off the coast to open sea. Salinity is uniform vertically in near shore area and in surface-subsurface layer of the open sea in the river mouth and southward. A halocline forms in surface-subsurface layer off the coast, and it weakens gradually in surface layer to bottom layer. Salinity is almost uniform vertically in the bottom layer of steep slope and characterized by high salinity. In summer, salinity is uniform vertically in near shore shallow area of the river mouth and southward, whereas in other areas severe stratification occurs. A stronger halocline forms in the Changjiang River Diluted Water area, and then weakens rapidly from surface layer to bottom layer. Salinity is almost uniform in deep bottom layer of steep slope to open sea and characterized by high salinity. In autumn, salinity is low in surface layer of shallow near shore area in north of the Changjiang River mouth and stratified, which is high below surface layer and uniform vertically off the coast. Salinity is low in upper layer of the open sea and uniform vertically, high in the bottom layer and stratified. Salinity is uniform vertically in shallow near shore area of the river mouth and southward. Stratification occurs in steep slope, strengthens gradually from surface to bottom layer, and weakens from steep slope to the open sea.