南印度洋副热带高盐水团的形成和变异机制及输运路径研究

There are sea surface salinity (SSS) maximum regions in the major oceans corresponding to the subtropical maxima of evaporation minus precipitation (E-P). These SSS maximum water extend to subsurface through subduction and form salty water masses, which are usually referred to as Subtropical Underwater (STUW). Surface temperature and salinity anomalies can be transported to other areas by these water masses and thus impact regional stratification and climate changes. Therefore, these STUWs have great research significance. So far, the STUWs in the Atlantic and Pacific ocean have already been fully studied, but there is still a lack of study about the South Indian Ocean STUW. The special pattern of wind and circulation in the Indian Ocean suggest that South Indian Ocean STUW has distinct variability and transport pathways. So this project is going to study this water mass using Argo data, as well as other observation data and model outputs. Firstly, we are going to evaluate the variability of South Indian Ocean STUW and analyze its variation mechanisms. Secondly, we are going to study the annual variability of its subduction rate and variation mechanism. Thirdly, we are going to evaluate the fate and transport pathways of this water mass. This project will help us to have a better knowledge of the salinity’s effects on ocean dynamic processes and climate changes, and also facilitate our understanding about the pattern of circulation in Indian Ocean and regional climate changes.

大洋中的副热带海域是强蒸发区。形成于此的表层高盐水在潜沉至次表层后，形成具有高盐特性的副热带高盐水团（Subtropical Underwater, STUW）。这些水团能够将海表温、盐异常信号通过密度跃层输送至其他海域，继而对相关海域的密度层结以及区域甚至全球性气候变化产生一定影响，因此这些水团具有重要的研究意义。目前，物理海洋学者已对太平洋及大西洋中的STUW展开了相关研究，针对南印度洋STUW的研究却十分匮乏。印度洋中特殊的风场和环流结构决定了南印度洋STUW具有与众不同的变异特征和输运通道。本项目将基于Argo浮标数据，结合其他观测资料和模式结果，进行南印度洋STUW的时空变化特征及变异机制、水团潜沉率年际变化信号及变化机制以及水团的输运路径和归宿的研究。研究结果将有助于进一步掌握盐度在海洋动力过程及气候变化中的作用，并加深对印度洋环流结构和气候变化过程的理解。

南印度洋副热带高盐水团为南印度洋主要的盐度来源，其低频变化对局地环流结构及海表高度异常均具有显著影响。但过去针对该水团的研究较为稀少，对其基本特征及变化机制缺少基本的认识。因此本项目基于最近二十余年间积累的Argo浮标观测资料，对该水团展开了相关研究并获得以下几点主要科学认识：（1）结合更加严格的判据和经过优化的方法，对南印度洋副热带高盐水团的温度、盐度、密度、深度等基本物理量的空间分布及变化范围给出了相对以往研究更加精准的描述；（2）计算了南印度洋副热带高盐水团潜沉率的多年平均值，并揭示了其年际变化与南半球环状模（SAM）之间的密切关联和内在动力机制；（3）揭示了南印度洋副热带高盐水团盐度的年代际变率，以及来自厄尔尼诺-南方涛动（ENSO）对该信号的显著影响，并讨论了作用机理；（4）揭示了中尺度涡旋在南印度洋副热带高盐水团潜沉区，即南印度洋副热带海表盐度极大值区对盐度的显著耗散作用。这些研究成果回答了众多以往关于南印度洋副热带高盐水团的疑问，弥补了关于其盐度及潜沉率变化特征的研究空白，证实了关于活跃的中尺度涡旋是导致该水团盐度偏低的原因之一的理论猜想，提升了对于南印度洋上层盐度结构认知，为进一步研究南印度洋海域环境气候变化打下了基础。