现代台风风暴沉积层序的探测与高分辨率研究

Being one of the strongest air-sea interacting processes in changing marine environment, the typhoons affect the continental shelf topography and marine sedimentary sequences drastically through intensive mixing, resuspension and transport of particles during a relatively short time period. The mud depo-area off the Zhejiang-Fujian coast (MDZFC) acts as a sink for Changjiang River particles and accounts for the primary mud deposits on the East China Sea inner shelf, containing an abundance of marine environment and geological information. At the same time, located in the mostly frequently typhoon-affected region in China, the MDZFC is an ideal location to study the typhoon sedimentary processes and seabed topography evolution. This project plans to carry out the high-resolution sedimentologic study on the modern typhoon-induced sedimentary sequence in the MDZFC, based on a combination of geophysical exploration technology, radioisotope geochemistry, marine sedimentary hydrodynamics, and marine sedimentary geochemical method. Specifically, the study objectives include 1) detecting the modern process of typhoon impacts on seabed topography and sedimentary sequence; 2) evaluating the impacting degree and revealing the impact mechanism; 3) analyzing the sedimentary geological records within the mud depo-area and 4) exploring the specific marker indicating the typhoon storm modern sedimentary sequence (index system). These researches are of importance on understanding marine material exchange, marine sedimentation and sedimentary strata under the influence of typhoon storms.

台风是天气尺度上对海洋环境影响最大的海气相互作用过程之一，对海底地形地貌和海洋沉积层序有不可忽视的影响。闽浙沿岸泥质区是我国陆架海泥质沉积体系的组成部分之一，蕴含了丰富的海洋环境和地质信息。同时，泥质区是我国受台风影响最频繁的区域之一，是研究台风过程对海底地形地貌和海洋沉积层序影响的理想海域。本项目拟在闽浙沿岸泥质沉积区利用海洋地球物理探测技术和放射性同位素地球化学、海洋沉积动力学、海洋沉积地球化学等相结合的方法开展高分辨率的现代台风风暴沉积层序研究，探讨现代台风风暴过程对海底地形地貌和沉积地层的影响和改造，评价影响程度，分析影响机制；探索指示现代台风风暴沉积层序的特异性指标（指标体系），探讨风暴沉积的地质记录。研究成果对台风风暴影响下的海洋物质交换、沉积动力过程、沉积地质记录等研究都有重要意义。

根据项目的研究内容和目标，结合台湾海峡及其周边海域台风过程的实际路径及其影响范围，对2008～2019年间的10次台风（热带风暴）过程开展了多次野外调查和数据资料收集，获得了大量的海洋环境数据和样品。对这些数据和样品进行了综合分析，取得了如下认识：1）台风过程引起了海底沉积物的再分配。在沙波分布区，台风导致的沙波移动距离可达数十米，并显著改变了海底地形地貌；在泥质沉积区，台风导致近岸沉积物向外海输运，形成10~30 cm厚的风暴沉积层。沉积物7Be含量呈现近岸低远岸高的特征，新形成沉积层向外海延伸至水深70 m的泥质沉积区边缘。数值模拟台风期间风场结果显示，台风的强风动力是导致沉积物运移的主要动力机制；2）台风过程显著影响了海水-悬浮颗粒物-底质沉积物体系，导致水体结构、颗粒物组成与粒级分配以及沉积物粒度、地球化学及其物质组成（包括硅藻种群）等发生显著变化，其中沉积物中硅藻种属、有机碳氮同位素及生源硅等可以作为台风风暴沉积的标志物；3）台风过程引起了入海物质通量增加和海湾内物质的再分配，导致了海湾沉积物重金属的“二次污染”和碳循环的变化；4）台风强动力过程打破了“平常态”海洋（沉积）动力场，显著改变了海洋动力环境，对沉积物输运以及流场结构（包括上升流体系）等造成了“事件性”影响，其对影响海域的物质传输、沉积格局和海洋（生态）环境产生不可忽视的影响。.在此基础上撰写论文十余篇（其中发表SCI论文11篇，核心期刊论文3篇），在国内外学术会议上多次做报告交流。较好地完成了课题的任务，达到了预期目标。