海底地下水排放（SGD）能显著降低受排海域的溶解氧（DO）含量，是近岸、河口海域季节性低氧现象的潜在成因机制。本项目拟以长江口外低氧区为研究区域，利用天然镭、氡等多核素示踪技术，定量评估SGD对低氧形成的“直接贡献”。首先，阐明长江口外低氧水团的分布特征、空间结构及其在多时间尺度上的变化规律；其次，利用多核素示踪技术确定SGD的显著区域，剖析其与低氧区的对应关系；最终借助同位素模型量化低氧区中不同时间尺度上的SGD通量，并评估由其携带入海的DO对低氧形成的“直接贡献”。本项目聚焦SGD与低氧现象的内在耦合关系，研究结果将为全面认识长江口外低氧现象的形成及变动机制提供新的视角。

Submarine Groundwater Discharge (SGD) could significantly reduce the concentration of dissolved oxygen (DO), which is a possible mechanism of seasonal hypoxia formation in coastal and estuarine oceans. In this study, we are proposing to use multi-isotope technique to quantitatively assess how SGD directly contributes the formation of hypoxia off the Yangtze River Estuary (YRE). We will firstly portray the distributions, structure and variation patterns of low DO water mass on different timescales. Multi-isotopes distributions are then used to locate the significant SGD area, to see if it matches with the hypoxia area. By using the mass balance model of multi-isotopes, SGD fluxes on both seasonal and daily timescales could be calculated. Based on the SGD derived DO fluxes, one can easily estimate the direct contribution of SGD to hypoxia formation. In this project, we will mainly focus on the linkage between SGD and hypoxia phenomenon. Results obtained here will be helpful to open a brand new perspective to better understand the formation and variation of hypoxia off the YRE.