基于南海北部开放航次观测的2004-2005年次表层盐度异常特征与形成机制

摘要

Observation in the northern South China Sea (NSCS) Open Cruises during 2004 to 2013 revealed abnormal subsurface salinity in the NSCS that increased by 0.1-0.14 in 2004 and 2005 after compared with the Simple Ocean Data Assimilation (SODA) data.The temperature-salinity (T-S) profiles show that the phenomenon occurred mostly at 150 m below surface.The net freshwater fluxes in 2004 and 2005 were higher than the climatological mean values,and they were not responsible for the salty events.In 2004,the net freshwater flux was slightly greater than the climatological mean value,while the salinity at the subsurface water that came from the Luzon Strait (LS) was significant higher than the climatological value.Therefore,we believe that salt content transported through the LS was the main reason for the abnormal high salinity at the subsurface.In addition,the salinity of the LS in 2005 was slightly lower than that in 2004,while that of the subsurface water in the NSCS was enhanced in the 18°N Transection,for which meridional salt advection should be responsible.%基于2004-2013年的南海北部开放航次数据和1980-2010年Simple Ocean Data Assimilation (SODA)数据,发现南海北部次表层水体盐度在2004-2005年间盐度显著增大,相比于气候态均值分别增加了0.1和0.14,而且温盐特征曲线显示盐度增大的现象主要发生在150m以浅.2004年净淡水通量仅略低于气候态均值,2005年净淡水通量则明显高于气候态均值,因此净淡水通量不会是导致此高盐事件的有利因素.我们进一步通过块体简化盐度收支方程,定量评估盐度收支方程里中平流输运项(包括跨海盆经吕宋海峡的平流输运项和南海海盆内部南北海盆之间的平流输运项)的贡献.发现在2004年,通过吕宋海峡进入南海北部的盐含量输运显著大于气候态均值,是导致南海北部上层水体盐度迅速增大的主要原因.为探究2005年南海北部盐度持续增强的原因,我们进一步比较2004年和2005年的平流项演变,发现相对于2004年,虽然2005年吕宋海峡盐含量输运略低于气候态均值,但南海内部南海南北海盆间(通过18°N断面进入南海北部)的盐含量输运增强,即在2005年,海盆内部经向平流盐输运的贡献是促使南海北部上层盐度继续增强的关键因素.