长江口外赤潮多发区近几十年来的古生产力记录及环境意义

选取长江口外赤潮多发区沉积物柱状样,在高分辨率测年基础上,通过有机碳、有机碳同位素(δ13C)、生物硅、绿素等多项指标的分析获得了调查海区古生产力的变化信息。并结合近几十年来营养盐浓度及组成结构的变化探讨了海洋浮游藻类组成结构的变化在海洋古环境中的记录。柱状样年代可追溯到20世纪40年代初。δ13C值在柱中的分布为-26.15×10-3~-19.5×10-3,表明有机碳为陆源与海生的混合。生物标志物在柱状样中的分布可大致分为三个阶段,50年代以前含量均较低;50年代至80年代含量均增加,表明海洋浮游藻类活动强烈且以硅藻为主,与此阶段长江口营养盐浓度迅速增加相对应;80年代以后,生物硅的含量下降至整个柱中最低水平,绿素有所降低,但高于50年代前的水平,而有机碳含量增加,表明在该时段硅藻生物量降低,其他藻类生物量有所增加,这与长江口营养盐氮盐持续增加而硅酸盐逐年降低、氮与磷的含量比值、磷与硅的含量比值迅速增大有关。沉积记录还表明此阶段陆源有机碳的贡献增强。

Variations of paleoproductivity in the past decades and the environmental implications in the Changjiang Estuary in China

Stable organic carbon isotope, biogenic silicate and chlor in were studied from a sediment core for discussing the variation of paleoproductivity and environmental implications in the past decades in the Changjiang Estuary.The shifting of structures of phytoplankton community in the past decades were disscused using the records of these biomarkers with the long-term variations of nutrient concentrations and their ratios.The results show that δ13C values range from - 26.15×10-3 to - 19.5×10-3, suggesting the mixing of organic carbon sources of riverine with marine or ganisms.The biogenic proxies present three stages of paleoproductivity changes: before the 1950s with low production; the 1950s——the 1980s with increasing production dominated by diatoms, consistent with increasing of nutrient concentrations; shallower before the 1980s with decreasing production.In this stage, the diatom production decreased while the production of other phytoplankton communities increased affected by high nutrients inputs and high content ratios of nitrogen to phosphorus and phosphorus to silicon in the Changjiang Estuary.The sedimentation records also indicated that the riverine organic carbon increased after the 1980s.