南海西南部上升流区浮游有孔虫的季节性/年际变化研究及古海洋学意义

Planktonic foraminiferal fauna and their shell chemical/isotopic composition record the information of the upper-column ocean environment. The investigation of planktonic foraminiferal ecology and the study on the relationship between planktonic foraminifera and ocean environment give the basis of the paleo-environmental reconstruction. In this study, materials from a long-term time-series sediment trap located in the southwestern South China Sea (off the Vietnam coast, an upwelling area driven by the summer Asian monsoon) since 2014, including the planktonic foraminifera flux and composition, stable isotope and Mg/Ca ratios of the individuals, will be analyzed. Based on the comparison with data from other simultaneous sediment traps, this study will disclose the character seasonal and inter-annual changes of planktonic foraminifera and their relationship with the ocean environmental parameters in the upwelling area of the southwestern SCS under different climatic models, such as the El Niño/ La Niña mode or under different monsoon strength, which will benefit the reconstruction of paleo-environment in this region. In addition to the comparison with that of the surface sediment, the exquisite relationship between the planktonic foraminifera and environment will be applied to the late Quaternary core sediment, to disclose the upper-column water property of the southwestern SCS during the glacial-interglacial cycles, with a high-resolution reconstruction over the last glacial-interglacial period, and to understand the mechanism of the paleoceanographic evolution of the South China Sea under the East Asian monsoon system.

浮游有孔虫群落及其壳体化学、同位素组成是上部海洋环境信息的重要载体，对浮游有孔虫生态及其与海洋环境关系认识是重建古环境的基础。研究对南海西南部、西北部和北部同时布设的多年连续沉积物捕获器材料，尤其以西南部越南岸外现代夏季风驱上升流区为研究重点，进行浮游有孔虫群落及其壳体同位素与微量元素等地球化学分析；结合海洋环境参数现代观测数据、表层海水古生产力等资料，通过不同海区的沉积物捕获器浮游有孔虫对比，揭示南海季节性与年际浮游有孔虫群落与季风、El Niño等气候因素影响下的表层和次表层海洋环境结构之间的关系，为古环境重建、区域古海洋学研究提供重要基础。在此基础上，研究将结合夏季风驱上升流区表层沉积物、沉积物柱状样MD05-2901中浮游有孔虫资料，精确重建南海西南部晚第四纪冰期旋回古环境、尤其是末次冰期以来高分辨率古环境变化过程，从而深入理解东亚季风气候系统下的南海古海洋学演化机制。

项目对南海西南部和西北部两个站位沉积物捕获器中的浮游有孔虫进行了系统的微体古生物学鉴定、统计与稳定同位素组成分析研究，结合区域海洋环境资料与海洋上部水体垂直温度、盐度等水文参数，揭示了南海主要浮游有孔虫属种的季节性组成变化与同位素特征。南海西南部于夏季风期间浮游有孔虫总通量及Globigerinoides ruber、Globigerinoides sacculifer 和Neogloboquadrina dutertrei 等分子含量较高，与表层海水温度、营养与季风强度良好对应; Gs. ruber与另一典型热带-亚热带分子Gs. sacculifer不同，在上升流影响下低表层水温环境中该种有较高含量。浮游有孔虫Gs. ruber、Gs. sacculifer和N. dutertrei等属种在南海西北部的钙化深度分别为0-42m、30-65m和75-100m，平均生活温度为 25°C、23.3°C和 20.3°C。与高生产力相对应，南海N. dutertrei含量变化在季风强盛时含量高，反映了N. dutertrei不仅是南海西南部夏季风驱上升流可靠指标之一，同时也是指示南海海洋古生产力的重要标志种。项目研究深入了对南海浮游有孔虫与季风、El Niño等气候因素影响下的表层和次表层环境及海洋垂直结构关系的理解，为南海古环境重建、区域古海洋学研究提供重要基础。