南海北部有孔虫、放射虫的现代过程研究及其古环境应用

The modern process of foraminifera and radiolarian is very important for their implications in marine paleoenvironmental changes study. Few studies on the calibrations, validations and applicability of these foraminiferal- and radiolarian- based paleoenvironmental proxies were carried out in the South China Sea (SCS). Through a trinitarian modern process investigation strategy, which combine plankton tow, sediment trap, sea surface sediment sampling and in-situ observations of marine environmental parameters together, with two areas, the southwestern region off Dongsha Island and the Xisha Trough as the key areas, we aims to build a series of paleoenvironmental proxies based on foraminifera and radiolarian for the whole water column (from the intermediate water to the subsurface and then to the surface water) in the northern SCS, by means of modern process studies of planktonic foraminifera, benthic foraminifera and radiolarian. We try to uncover the regional distribution pattern, depth habitation and seasonal faunal variations of planktonic foraminifera and radiolarian in the northern SCS using plankton tow and sediment trap sampling method, and to disclose the faunal composition of radiolarian living in the intermediate water, and to discuss the relationship of their distributions with marine environments. Through stable isotope analyses and Mg/Ca ratio measurements of dominant planktonic foraminifera species from the tow, trap to the surface sediment samples, combined with foraminiferal dissolution experiment, we try to evaluate the affecting factors (such as vital effect, and partial dissolution) on these proxies during the whole process of the information carrier (planktonic foraminifera) undergone, from the upper ocean to the sea bottom, to validate the specific environmental significance and applicability of these proxies in the northern SCS. Through living benthic foraminifera analysis, including faunal composition and shell geochemistry (stable isotope and Mg/Ca), we try to build a relationship of benthic foraminifera with the intermediate water mass. At last, we apply these validated proxies to 6-7 sediment cores from three key slope regions in the northern SCS, to reconstruct the evolution history of the intermediate water, the subsurface water and the surface water since the last glacial, and further to discuss the affecting mechanism of these paleoenvironmental changes in the northern SCS.

有孔虫、放射虫现代过程研究是其古环境正确解释应用的重要基础。本申请拟通过南海北部上层水体浮游拖网、中层沉积物捕获器和底部表层沉积物“三位一体”结合的调查方法，以东沙西南和西沙海槽区为重点研究区域，结合现代海洋环境要素观测，揭示浮游有孔虫、放射虫的区域分布、深度习性及其季节性变化特征，查明放射虫中层水属种组成与西北太平洋中层水的关联，探讨微体群落组成与中上层海洋环境之间的关系；对主要浮游有孔虫的氧碳同位素和Mg/Ca比进行立体时空追踪测试，结合碳酸盐溶解实验，分析沉积保存过程中生命效应和溶解作用对指标的影响，核实环境替代指标指示意义及适用范围；对底层活体底栖有孔虫进行群落组成及壳体同位素与Mg/Ca比等分析，探讨其对中层水的指示作用。构建出南海北部全水柱（从表层到次表层到中层水）的环境替代指标体系。应用于三个重点陆坡区的沉积柱样分析，探讨末次冰期以来南海北部中上层水体的演变历史及其影响机制。

项目通过浮游拖网、沉积物捕获器和沉积物“三位一体”结合的研究方法，对南海北部浮游有孔虫、放射虫的现代生态沉积过程、孢粉和粘土矿物的物质来源输运指示方面进行了系统研究。发现南海北部浮游有孔虫通量为单峰态季节变化，与南海南部和中部的双峰态不同，认为南海浮游有孔虫群落主要受控于季风影响下的上层水体混合与生产力变化。揭示了主要浮游有孔虫属种的栖息深度季节性变化。发现南海活体放射虫生态空间分布与中尺度涡旋关系密切，放射虫深度分布受海流横向输运影响，提出径向翻转流能把中深层放射虫带到中上层水体。揭示了现代表层水体中的孢粉分布与洋流密切相关，而季风和洋流则是沉积物中的孢粉输运的主要影响因素。发现南海北部沉积物捕获器中粘土矿物组成无明显季节变化，提出南海北部深水底流能把台湾源物质从东往西搬运，此外黑潮对东部沉积输运也有明显影响。指出了G.ruber的两个模态种有明显的环境指示差异，提出在南海北部用150-250微米粒级的G. ruber S.S作为表层海水环境替代指标更可靠。建立了G.ruber的区域Mg/Ca温度校正方程。提出了G. bulloides可用作南海北部冬季表层水替代指标，而Globorotalia inflata可作为南海北部中层水替代指标。应用这些指标进行古环境重建开展了末次冰期以来南海北部上中层水体的演化研究。发现近2万年来该区表层海水温度和盐度呈明显的阶段性变化，认为热带低纬度海洋的变化可通过南海黑潮分支的传输对南海的沉积环境起明显影响；全新世南海北部表层水团演化有明显的东西区域差异；揭示了南海全新世冬季风记录在7-8ka最强，其后逐渐减弱；南海中层水在17.7-8.3ka主要受南源AAIW水的影响，而在冰期和晚全新世NPIW的影响更强。本项目对南海北部已有古海洋研究指标进行了检验和校正，并提出了若干新指标，对于深入了解区域古海洋环境演化有重要的科学意义。