南海典型区域放射虫群落的季节与年际特征及其古环境意义

A good understanding of the relationship between the sedimentary proxy and environmental condition is a necessary precondition for reconstructing paleoceanographic and paleoclimatic history. Radiolarian is a reliable proxy indicator for the environment, and its modern process as well as depositional behavior plays a key role in studies on regional environment and global change. This project is aimed to analyze time series samples from 3 sets of sediment traps in typical areas of the South China Sea (SCS), to reveal the seasonal and interannual changes in radiolarian flux pattern and assemblage composition in the SCS, and then to discuss their relations to sea currents, water masses, monsoon climate, and terrigenous input based on the combined data including clay minerals, geochemical elements, biogenic opal and in-situ observations of marine environmental parameters(such as sea surface temperature, sanility, and primary productivity). In addition, we will further compare radiolarian records from the traps to those from the surface sediments, to evaluate the depositional behavior and preservation characteristics of the radiolarian and their influence factors during the whole process from the upper ocean to the sea bottom. Results from this study will add new proxies on the East Asian monsoon and the marine environment in the SCS, and provide scientific evidence for further revealing the paleoceanographic and paleomonsoon history of this region during the formation and evolution of the SCS.

建立和验证有效的沉积替代指标是揭示南海古海洋与古气候变化规律的必要前提，放射虫作为可靠的生态环境指示物，了解其现代过程与沉积效应将在区域与全球变化研究中发挥关键作用。本课题拟利用位于南海北部西边界流区、越南上升流区和南沙海区的3套沉积物捕获器多年连续样品及相关区域的海底表层样品，结合实测的海水温度、盐度和初级生产力等资料，详细分析水体中放射虫群落与通量的季节和年际变化特征及其与相关海流、水团、季风气候和陆源输入的关系，同时开展粘土矿物、生物硅和地化元素等指标的相关与佐证分析；进而对比海底表层沉积物中的放射虫记录，探讨和阐明放射虫在区域环境中的生态、沉降与保存特征及影响因素，为利用沉积物中放射虫指标重建古环境演变提供重要的基础资料和科学依据。研究成果将为南海的古环境替代指标增添新的信息和证据，对进一步揭示全球变化的区域响应、以及南海形成演变过程中的环境与资源效应有着重要的科学意义与应用价值。

建立和验证有效的沉积替代指标是揭示南海古海洋与古气候变化规律的必要前提，放射虫作为可靠的生态环境指示物，了解其现代过程与沉积效应将在区域与全球变化研究中发挥关键作用。本研究主要利用南海北部西沙海槽及南部永署礁附近的沉积物捕获器(布放深度均约1500m)样品及相关海区典型区域的海底表层样品，重点研究了南海放射虫群落季节与年际的变化特征，结合水文资料以及主要环境参数等，探讨了南海放射虫群落对季风气候、El Niño事件及表层水体温度等的响应特征及规律，进而通过对比表层沉积物样品的放射虫记录，探讨了南海区域环境对放射虫沉降过程的影响，以及西北太平洋不同边缘海沉积物中放射虫群落特征与差异变化及其与大洋环流的关系。取得的主要成果有：1) 揭示了南海南、北部典型区域放射虫群落组成和通量的季节性与年际变化特征；2) 讨论了南海放射虫通量及群落对季风气候及El Niño (La Niña)事件的响应特征与规律，提取了表层水体温度及初级生产力的放射虫替代指标；3) 分析了水体与表层沉积物放射虫群落的异同，初步探讨了放射虫保存特征与环境的关系；4) 阐明了南海与西太平洋各边缘海表层沉积物中的放射虫生物地理特征，探讨了其主要环境控制因素及其与北太平洋环流之间的关系。相关成果为南海的古环境替代指标增添了新的信息和证据，对进一步揭示全球变化的区域响应以及深入探讨放射虫的古环境意义、生物地层及其合理解释具有重要的科学意义和应用价值。