海洋浅层经圈环流的次表层分支是副热带海洋信号影响热带海区的重要“海洋桥”，对于海洋水团的时空变化、热量交换、以及碳、氧等化学要素的吸收和释放都具有重要的调控作用。本项目将采用现场实测和卫星遥感数据，结合数值模拟和同化产品，特别是OFAM3高分辨率全球环流模型的结果，研究南印度洋浅层经圈环流次表层分支的年代际变化特征与机理。具体而言，我们将结合数据分析与拉格朗日轨迹追踪方法，刻画关键海区次表层环流和水团的年代际变化，认识水体来源及其移动路径。重点关注副热带海区的潜沉过程和印尼贯穿流的平流输运对次表层水体年代际变化的各自贡献。通过水团潜沉过程诊断和多变量统计分析方法，阐明海面动力和热力强迫、环流调整、涡旋活动等因素对次表层水体生成和运移的调控作用。进而计算次表层的热盐输运过程，量化评估环流和水团的年代际演变对热带南印度洋层结变化的不同影响。上述研究有助于进一步理解印度洋的环流演变及其气候效应。

Subsurface branch of the shallow overturning cell is an important "oceanic bridge" conveying the subtropical signals to tropical regions. It plays important roles in the spatiotemporal variations of water masses, the heat and salt exchanges, and the uptake/release of chemical elements (e.g. Carbon, Oxygen). Based on the in-situ and satellite observations, and some numerical modeling or assimilating products （particularly the OFAM3 high-resolution model results）, this proposal will illustrate the decadal variability of subsurface branch within the southern Indian Ocean (IO) shallow overturning cell. With the synergy of data analysis and Lagrangian particle tracking, we intend to investigate the decadal changes of the subsurface circulation and water masses, and then understand the origins and pathways of typical waters. Attention will be paid to clarifying the respective contributions of water subduction in the subtropical region and the advection of Indonesian Throughflow to the formation of T/S anomalies. Then the subduction rate estimations and multi-variable statistical analyses will be applied to evaluate the potential impacts of air-sea fluxes, large-scale circulation and eddy activities on the formation and migration of subsurface water. Furthermore, the heat and salt transports in the subsurface layer will be quantified for assessing the relative importance of decadal variations on the circulation and water property to the tropical IO stratifications. The above results should be helpful in better understanding the IO circulation changes and their climate impacts.