渤海盐度年代际变异对环流结构的影响

The Effect of Decadal Salinity Variations on Circulation in the Bohai Sea

收集并利用1950年代～1990年代后共5个年代的渤海盐度统计资料,诊断计算了不同时期的渤海密度流分布及其变化.通过对比分析,揭示了冬、夏两季渤海盐度的年代际变异特征及其对环流结构的影响.结果显示,自1980年代以来,渤海的盐度格局发生了显著的变化,盐度的水平梯度减小,渤海内部盐度由明显低于海峡区向普遍高于海峡区转变.渤海密度流在冬季较弱,对总环流的贡献较小,而在夏季较强,并在总环流中占优.夏季,渤海密度流随盐度变异有所改变,在1990年代后环流系统在海区中部、渤海湾以及莱州湾呈现出局部的差异,原有流动明显减弱.夏季渤海重要断面的密度流流量和盐通量值整体上呈减小趋势,渤海与外海间的平均水及盐交换量由1950年代的7.85×10^4 m^3/s、2.49×10^6kg/s降至1990年代后的7.09×10^4 m^3/s、2.27×10^6 kg/s.

By using the 10-year-averaged salinity fields in five decades （from 1950s to present）,a three-dimensional ROMS model is established to diagnostically calculate the density currents in the Bohai Sea during the different periods.Through the comparison and analysis of the results,the decadal variations of the salinity fields and its impact on circulation are discussed.It is shown that since the 1980s,the salinity distribution in the Bohai Sea has changed a lot in summer and winter,and its horizontal gradient has been decreasing.Salinity value in the interior zone of the Bohai Sea is relatively higher than that in the Bohai Strait recently,which is a completely opposite situation to the past.Density currents of the Bohai Sea are stronger in summer than that in winter,and they contribute a lot to general circulation during summertime.In summer,the variations of salinity has led to a little of difference on currents.After the 1990s,local changes of currents can be found in the central area,Bohai Bay and Laizhou Bay,the main form of which is the decrease of flow velocity.Volumetric flux and salinity flux induced by density currents through some representative sections show a generally dropping trend in summer as time goes by.The exchange values of the Bohai Strait have decreased from 7.85 × 10^4 m^3/s and 2.49 × 10^6 kg/s in the 1950s to 7.09×10^4 m^3/s and 2.27×10^6kg/s after the 1990s.