南海18°N 断面中层水的年代际变化

摘要

Decadal change characteristics of the intermediate water at 18°N in the South China Sea during 1965 and 2012 were investigated using the historical temperature and salinity profile data from SCSIO (South China Sea In-stitute of Oceanology)and WOD09 (World Ocean Database 2009).This study revealed the significant decadal changes of the intermediate water based on the analysis of its decadal averaged salinity.The salinity was 34.432 on average in the period of 1965 to 1977 and increased to 34.440 in the 1980s,followed by an evident decrease after the 1990s.Modulated by the decadal scale changes,the salinity variation presented different trends in different pe-riods.There was a significant decrease trend from 1967 to 1977,followed by a further decrease from 34.450 to 34.414 during 1990 and 1997.Thereafter there appeared a significant increase.Meanwhile,the temperature pres-ented the same changing trends.Both temperature and salinity decreased in the 21st century with smaller amplitude of variation compared those in 1990s.The decadal changes of the intermediate water at 18°N were found to present different characteristics than those of Indian Ocean and the Pacific Ocean .In addition,the significant decadal chan-ges of the intermediate water have greater amplitudes than those of the decadal scale variations.In addition,it is found that the salinity was closely related with ENSO that it reached its minimum in El Nio years.%利用中国科学院南海海洋研究所历史温盐剖面观测资料和 WOD09（World Ocean Database 2009）中的 CTD、OSD、PFL 温盐剖面资料，分析了1965-2012年间南海18°N 跨海盆断面中层水的变化特征。研究结果表明：中层水平均盐度呈现显著的年代际变化，20世纪60年代中期至70年代末，中层水平均盐度约为34．432，80年代盐度增加至34．440，90年代之后至今盐度明显降低；在年代际尺度变异调制下，不同年代中层水盐度变化有不同的变化趋势，1967-1977年呈现显著的下降趋势，1990-1997年中层水盐度从34．450迅速降为34．414，而在1997年之后表现出明显上升趋势，与此同时，中层水温度有着相似的变化特征，与90年代之前相比，21世纪以来温度与盐度同步下降，并且变化幅度变小。与大洋的中层水团年代际变异相比，南海18°N 断面中层水呈现出与大洋不同的特征。另外，中层水盐度有着十分显著的年际变化，其振幅远大于年代际尺度变异，并且与 ENSO 密切相关，在厄尔尼诺年达到极小值。