近二十年南海表层海水的盐度淡化及其机制

The freshening trend of surface salinity in the South China Sea in recent two decades and its mechanism

南海北部航次观测资料显示南海北部表层盐度在2004—2012年期间缓慢降低,2012年盐度达到最低。客观分析数据EN4(the UK Met Office EN.4.0.2 objective analyses)以及OFES(ocean general circulation model for the Earth Simulator)模式结果都显示南海表层海水盐度在1993—2014年有淡化趋势,最显著区域位于吕宋岛以西和南海南部。盐度收支分析表明淡水强迫在吕宋岛以西海域起主要贡献,而水平平流输运主导南海西部的表层盐度变化。吕宋岛以西表层盐度的降低与近年来沃克环流加强引起的夏季强降雨增加有关。

In situ hydrographic data of sea surface salinity(SSS)revealed a freshening trend in the northern South China Sea(SCS)during2004-2012,which was the freshest in2012.Such freshening was also found in the UK Met Office EN4objective analysis product and the ocean general circulation model for the Earth Simulator(OFES)output during1993-2014,particularly west of Luzon Island and in the southeastern SCS.The salinity budget analysis in the upper layer indicated that the fresh water forcing and horizontal salinity advection contributed to the trends of SSS west of Luzon Island and in the western SCS,respectively.The excessive precipitation in summer accounted for the decrease of SSS to a great extent west of Luzon Island,which was associated with the strengthening trend of the Walker Circulation.