海底地下水排泄（SGD）是溶解化学物质由陆地向海洋输送的一个重要的通道，是近海碳循环不容忽视的关键环节，而占据全球海岸线约40%的砂质海岸地下水碳循环过程及其定量化研究十分有限。本项目以广西北海砂质海岸带为研究对象，基于已建有的陆地分层监测竖井附近，增设砂质海岸带采样剖面，通过对陆地井水、海岸带分层地下水、海水等监测和分析，查明不同水文条件下溶解无机碳（DIC）的空间分布变化及其影响因素；借助地球化学和同位素（δ13C-DIC、δ13C-DOC和Δ14C-DIC）手段，探讨地下水DIC的来源及其迁移转化行为；运用碳同位素混合端元模型计算各来源DIC的贡献比例。在此基础上，建立砂质海岸带水文-地化驱动的地下水DIC循环模式，定量评估SGD对研究区近海DIC输送的贡献，为深入理解海岸带SGD对陆架边缘海碳收支平衡的影响提供重要的科学依据。

Submarine groundwater discharge (SGD) is an important channel for the transport of dissolved chemical materials from land to sea, and is a key link that can not be ignored in costal carbon cycle. However, the biogeochemical processes of carbon cycle and quantitative research in groundwater of sandy coasts, which account for about 40% of the global coastline, are very limited. This project takes the sandy coastal zone of the Beihai Sea in Guangxi as the research object. Based on the existing terrestrial stratified monitoring wells, the sandy coastal zone sampling profiles are established. Through monitoring and analysis of well water, stratified groundwater and seawater in the coastal zone, the spatial distribution of dissolved inorganic carbon (DIC) and its influencing factors under different hydrological conditions are identified. Also, geochemistry and isotopes (delta 13C-DIC, Delta 13C-DOC and Δ14C-DIC) are used to identify the source, migration and transformation of DIC in groundwater. By using the end member isotope mixing model, the contribution ratio of DIC from different sources is calculated. On this basis, the groundwater DIC cycle model driven by hydro-geochemistry in the sandy coastal zone is established to quantitatively evaluate the contribution of SGD to the coastal DIC cycles in the study area, which provides an important scientific basis for better understanding the impact of SGD in the coastal zone on the carbon budget balance of the continental shelf system.