南海北部溶解态铝的分布、影响因素及其对陆源物质输送的示踪

The study of marine biogeochemical cycles of trace elements and their isotopes is the key research areas of the international research project GEOTRACES. Aluminum (Al) is one of the GEOTRACES key trace metals and is expected to be measured on all GEOTRACES ocean section cruises. Dissolved Al is often used to estimate the atmospheric deposition into the open ocean and is often applied as a sensitive tracer for water mass mixing and terrestrial transport into the ocean. The biogeochemical cycles of Al in the large rivers and their estuaries and the marginal seas of China (YS and ECS) have been investigated in our country. However, relevant study in the South China Sea is just started and need to be strengthened in the near future. In present study, the distribution and seasonal variation of dissolved Al in the Zhujiang (Pearl River) Estuary and northern South China Sea (NSCS) and its influencing factors will be studied detailedly. Box model for dissolved Al will be established by quantitative estimation of fluxes through riverine input, atmospheric deposition and sediment-water interface. Water mass mixing and cross shelf transport of terrestrial material will be studied by using dissolved Al as a tracer. Lateral transport pattern of terrestrial material at the subsurface layer and its function on the primary production in the NSCS will be discussed. The results of this study will fill in the data blanks of dissolved Al in the NSCS and also provide useful tool and foundation for understanding the role of marginal seas to the northwest Pacific.

痕量元素及其同位素的海洋生物地化学研究是国际海洋科学研究计划GEOTRACES关注的重点研究领域。铝（Al）作为GEOTRACES科学计划规定的关键参数之一，可以估算大洋中大气沉降通量、示踪水团混合和陆源物质向大洋的输送，其海洋生物地球化学循环引起人们的广泛关注。我国关于Al的海洋生物地球化学研究主要集中在大河河口和黄、东海，对南海的研究尚属起步。本课题拟对珠江口和南海北部溶解态Al的海洋生物地球化学行为进行研究，认识珠江口及南海北部溶解态Al的分布、季节变化及影响因素，定量估算通过河流、大气、沉积物-水界面向南海北部的输送通量，探讨以溶解态Al为示踪因子研究南海水团混合及陆源物质跨陆架输送的可行性，认识陆源物质在次表层的水平输送格局及其对南海初级生产的支持功能。该研究将填补南海北部溶解态Al海洋生物地球化学研究的空白，为认识陆架边缘海对西北太平洋的影响提供研究思路和科学基础。

项目执行期间通过搭载国家自然科学基金季共享航次计划，探讨珠江口邻近海域及南海北部溶解态Al、Mn的生物地球化学行为及其影响因素。以溶解态Al、Mn为示踪因子，认识源自珠江口的陆源营养物质跨陆架输送途径及对南海中部寡营养海域初级生产的支持功能，探讨夏季黑潮次表层水入侵南海的路径及年际变化。研究结果表明，南海北部陆架次表层水体中溶解态Al、Mn与盐度线性相关，其行为主要受水团混合影响。在等密度面21.6-22.2 kg/m³的次表层水体，夏、秋季均存在源自珠江口近底层水体向北部陆坡区延伸的跨陆架输送途径，证明南海北部陆架是南海中部微量营养物质的重要来源。综合2015年至2018年三个夏季航次的观测结果，通过对比24.5和25.0 kg/m3等密度面盐度和溶解态Al的分布，发现高盐度的黑潮次表层水通过吕宋海峡进入南海以后主要分为两个分支，一支向西北沿北部陆坡入侵南海北部，另一支则转向西南达到吕宋岛西侧海域。2017年夏季黑潮次表层水入侵南海的强度显著强于2018年夏季，存在显著的年际变化。测定了南海北部夏季气溶胶中12种微量金属元素的含量、溶解度及溶解动力学曲线。以微量营养元素Fe为例，估算出气溶胶颗粒中可溶出态Fe向混合层的输送通量约为21.4-150 nmol/m2，是夏季南海寡营养海域微量营养物质的重要来源。本项目的研究成果证明了次表层水体微量营养元素可以在陆架泵的作用下跨陆架输送并支持南海的初级生产，揭示了夏季黑潮入侵南海的路径及其对水团结构的影响，为物理海洋学的模式研究提供证据。采集西太平洋痕量元素样品，分析黑潮源头及黑潮延伸体区域不同水团溶解态Al、Mn浓度的改变，为认识陆架边缘海对西北太平洋的影响提供数据支撑。已发表科研论文11篇，其中SCI论文5篇，已接收论文2篇，较圆满地完成了项目的预期目标。