【摘要】 通过分析1981—2010年的SODA2.2.4(Simple Ocean Data Assimilation)温盐数据,发现南极中层水在这个时期表现出了盐度减小的变化趋势,包括垂向盐度极小值处与沿27.2kg/m~3等密度面的盐度。但是这个淡化过程并不是渐进的,而是先在1996—2000年间达到了一个盐度异常的最大值,然后才进入快速减小阶段。盐度最小值处(27.2kg/m~3等密度面)盐度的EOF分解表明,南非以南海域以及东南大西洋海域的盐度减小幅度显著大于太平洋与印度洋水体,这隐含了厄加勒斯流系统对大西洋-印度洋通道上中层水体性质变化的重要影响。在形成机制上,本文从两个海气相互作用过程解释了上述的结果。南半球纬向风应力的EOF结果表明,亚南极锋以南的西风带在1979—2014年间是一个增强的变化趋势,由此产生的低盐南极表层水向北输送导致了上述的多年南极中层水淡化现象。这其中1998年风应力的极大值应当对应一个盐度异常的极小值,但在这里表现出的是盐度异常的最大值产生了一个矛盾的因果关系。进一步的分析表明,这个盐度异常最大值是海表面淡水输入量(降雨-蒸发)在相应时期大幅度减小的结果。更多还原

【Abstract】 The Antarctic Intermediate Water had experienced freshened during period 1981-2010,after analyzing the salinity dataof SODA2.2.4(Simple Ocean Data Assimilation).The above freshening was revealed both in the vertical salinity minimum and on the 27.2 kg/m~3 potential density surface.The salinity anomaly first reached to a maximum in 1996-2000,and then decreased drastically.The pattern of EOF1(salinity in vertical salinity minimum and on 27.2 kg/m~3 potential density surface)shows that,the freshening south of South Africa and southeast of Atlantic was distinctly larger than that in the Pacific Ocean and the Indian Ocean.This implied the great influence of Agulhas Current System on the intermediate water between the Atlantic Ocean and the Indian Ocean.The mechanical analysis revealed that the freshening was caused by two contributor of sea-air interaction.The EOF1 pattern of zonal wind stress displayed that the westerlies south of Subantarctic Front had strengthened during 1979-2014,which facilitate the lower salinity of Antarctic Surface Water being transported northward.As a result,the salinity of Antarctic Intermediate Water had reduced.According to the relationship between westerlies and salinity of Antarctic Intermediate Water,it should be a minimum of salinity anomaly corresponding to the maximum of wind stress.However,there was the maximum of salinity anomaly along with the maximum of wind stress in 1998,which was a contradictory result.The analysis of fresh water input(precipitation minus evaporation)at sea surface further revealed that,the maximum of salinity anomaly around 1998 was caused by a large decrease of fresh water input during that period.更多还原