东海周边河流沉积物源汇体系的关键过程：沉积地球化学约束

The East China Sea, as a typical river-dominated marginal sea with a broad shelf, receives huge terrigenous sediments from the large river (Changjiang) and small mountainous rivers (e.g. Zhuoshui R.) in Taiwan, which makes it an ideal site for the study of river source-to-sink transport system (S2S) and land-sea interaction on multiple spatiotemporal scales. Following the strategy of land-sea connection and focus on temporal evolution, this project will investigate the key elements of sediment routing systems of the Changjiang and Zhuoshui rivers since the last glacial maximum (LGM), which include the provenance signal propagation and the time scale of environment response. We plan to collect time-series sediment samples from the lower sections of modern Changjiang and Zhuoshui rivers, and measure the sediment characters, mineral, element geochemistry and meteoric Be-10, Nd and Li isotopes. The weathering and erosion patterns and their relationship with sedimentary recycling in two river catchments will be discussed, and furthermore, the influence of extreme climate events on sedimentary geochemical heterogeneity will be evaluated. Based on the sedimentary geochemical records in several cores recovered from the shelf and Okinawa Trough, we investigate the propagation and preservation of monsoon climate signals and weathering-erosion processes in these two river catchments and marine sediments, and anthropogenic perturbation on natural riverine S2S process. By comparing with the typical S2S case studies in the world, we will highlight the importance of Changjiang-East China Sea S2S study, and advance the research progress of East Asian continental margin sedimentology.

东海作为典型的河控型宽陆架边缘海，接收世界大河长江和台湾山溪性小河（如浊水溪）的巨量入海物质，是全球开展河流源汇过程和多时空尺度陆海相互作用研究的理想地区。本课题拟剖析末次冰盛期以来两类河流沉积物源汇体系的关键要素（源区信号传递、保存与环境响应的时间尺度），回答国际源汇研究的关键问题。采集长江与浊水溪河口代表性观测断面的时序样品，在沉积矿物学和元素组成分析基础上，发展大气成因Be-10与Nd-Li多同位素示踪体系，揭示两类河流源区不同的风化剥蚀过程与沉积物旋回的关系，及入海端元组成对极端气候事件响应的敏感性；通过东海典型岩芯中河流源汇信息提取，揭示LGM以来季风气候变化和大陆-岛屿风化信号在流域到边缘海的传递与保存机制，及人类活动对自然源汇过程的干预影响。与国际大陆边缘源汇研究的典型案例比较，提升长江/台湾河流−东海源汇沉积体系的特色和全球参照意义，推进东亚大陆边缘沉积学研究进展。

项目开展了十多次长江全流域、台湾和东南沿海的典型山溪小流域野外考察，组织两次长江口-东海陆架多学科交叉航次，系统采集400多个各类水体和沉积物样品，完成750多个各类水体（河水、海水、孔隙水等）、沉积物（悬浮颗粒物、表层和浅岩芯沉积物）样品的综合分析。.项目研究揭示世界大河长江和台湾（及东南沿海）山地小河风化物质从源到汇的关键过程，和对自然环境变迁与人类活动的响应差异。（1）通过剖析经典的硅酸盐风化程度指标（CIA, WIP等）的指示意义及沉积动力过程和旋回性的控制影响，建立提取当前旋回风化信号的量化研究方法；提出大陆硅酸盐风化的温度主控机制，及东亚和东南亚大陆风化对晚新生代变冷的不同响应；（2）提出快速转换的沉积物搬运模式是台湾小河流呈现极强组成不均一性和物源信号传递复杂的主要原因；大气10Be新方法揭示台湾流域风化剥蚀过程中的岩性控制，及降水引发随机山体滑坡侵蚀机理；阐明矿物差异风化控制花岗闪长岩风化过程中Sr稳定同位素行为，粘土粒级Li同位素组成指示长江流域硅酸盐风化响应末次冰消期快速气候变化，长江口水体混合过程Li同位素呈现保守行为；（3）流域大坝建设通过改变长江中下游泥沙源汇过程而显著影响入海河流沉积物组成，进而影响流域风化信号的传递、保存和解读。在构造、季风气候和海平面因素控制下，晚中新世-上新世以来长江三角洲沉积从局地物源演变成现代长江大河源汇系统，主导了黄东海典型沉积体系形成；海平面变化和黑潮入侵是台湾源物质主导南海北部陆坡碎屑沉积物源汇过程的关键因素。.项目在NC, GCA, EPSL, QSR等知名刊物发表SCI论文42篇，培养毕业研究生20位和出站博士后6位，组织召集十多次国内外学术大会专题，开展各类科普讲座活动十多次；项目成果深化了大陆边缘源汇过程和环境响应研究认识，推动了我国大陆边缘沉积学研究进展，将我国从源到汇过程研究推向国际最前沿。