以分子标志化合物研究珠江口陆源有机碳百年演变特征与环境变化反演

Estuaries are sites of significant land–sea interaction and play a disproportionately important role in the carbon biogeochemical cycles globally. Substantially increased terrestrial matter input into the Pearl River Estuary due to the rapid population growth and increasing human activities, which makes a significant disturbance to the estuarine ecosystems including the carbon bio-geochemical cycle during the past centenary. However, the information on the land vegetation types and environmental change history over the past 100 years is scarce due to the absence of the actual observation records, which restricts the scientific prediction on the environmental changes in the Pearl River estuarine system.. This research is focused on the compositions of molecular biomarkers related to the terrestrial organic carbon and the paleoenvironmental reconstruction in the Pearl River Estuary over the past 100 years. Several aspects will be involved, including: (1) the quantitative and qualitative research of land plant biomarkers in the short sediment cores from the estuary will performed, which could provide the information on the types of the land plants in the past. (2) The composition and distribution of glycerol dialkyl glycerol tetraethers (GDGTs) in the short sediment cores will be investigated, which could provide the information on the sources of GDGTs. GDGT-based indices will be calculated and the relative contribution of the soil would be evaluated. (3) The composition and distribution of lignin phenols in the short sediment cores will be studied and the types of the vegetation will be reconstructed for the same core sediment. (4) All these molecular biomarkers will be studied for the typical soils, land plants and surface sediments collected from the Pearl River systems. (5) The stable isotopes (δD and δ13C) of long-chain n-alkanes will be investigated, which could provide the information on the relative humidity of the climate and the C3/C4 palnts. All these achievements would enable us to elaborate the variations of terrestrial organic carbon and evaluate the relationship between the inputs of the terrestrial organic carbon and the paleoenvironmental change in the Pearl River Estuary since last 100 years.

河口在全球碳的生物地球化学循环中发挥着重要作用。近百年来珠江流域由于人口的快速增长和人类活动的急剧变化，陆源物质输入的增加对珠江口及邻近海域的自然生态过程包括碳循环都产生了重要影响。本项目通过对沉积记录的研究来了解珠江口陆源有机碳百年演变特征，反演区域环境变化，研究结果将有利于对珠江口及邻近海域未来环境演变趋势作出科学预测。项目将通过对珠江口系列柱状沉积物进行高碳数正构烷烃、木质素和甘油二烷基甘油四醚 (GDGTs) 的定性定量研究，结合对珠江流域 (东江、西江、北江) 河流表层沉积物、两岸典型土壤及植被的上述分子标志化合物的定量研究，定量计算珠江口各类陆源有机碳的相对输入贡献，重建珠江流域的大气平均温度, 通过高碳数正构烷烃的δD值重建气候干/湿。在此基础之上探讨珠江口近百年来陆源有机碳的演变特征及与气候/环境变化和人类活动的可能关系，为典型河口地区碳循环研究提供机制上的参考

近百年来珠江流域由于人口的快速增长和人类活动的急剧变化，陆源物质输入的增加对珠江口海域的自然生态过程包括C循环都产生了重要影响。本项目首先通过对珠江主要支流两岸优势植被、堤岸土壤、河流表层沉积物和珠江河口表层沉积物的TOC及其δ13C的研究和对分子标志化合物(高碳数正构烷烃、木质素、地质藿类和GDGTs)的定性定量研究，获取珠江口海域各类陆源有机质输入的特征。项目重点对珠江口海域柱状沉积物进行了与陆源有机碳输入相关的特征分子标志化合物的定性定量研究，对沉积记录的百年陆源有机碳进行了源解析，评估了各类陆源有机碳的相对贡献。对来源于陆地高等植物叶蜡的正构烷烃的δ13C和δ2H进行测试，并利用相关的分子标志物代用指标对珠江口近百年来的气候/环境进行定量化重建。结果现实：自1710年以来，珠江口海域的陆源有机碳经历了4个演化阶段，1710 ̶ 1800年陆源有机碳的比例低，1800 ̶ 1900年陆源有机碳的比例减少，1900 ̶ 1980年陆源有机碳的比例上升，1980 ̶ 2019年陆源有机碳比例快速增加。利用分子标志物指标重建的珠江口地区年均和冬季海表温度在上述4个阶段呈现出升高-降低-升高-升高的变化趋势。相对应，南海 ENSO依次处于厄尔尼诺、拉尼娜、厄尔尼诺和厄尔尼诺相位。这两个温度的差值相应地呈现出低-高-低-低的变化趋势，这主要是由冬季温度的快速升高导致的。人类活动加剧引起的气溶胶导致的暖冬效应与ENSO耦合作用导致了珠江口海域季节性温差的减小。高碳数正构烷烃的δ13C和δ2H的反相位变化揭示出该海域高碳数正构烷烃主要来源于大气颗粒的输入，而且它们反相位变化反映了南海ENSO的厄尔尼诺和拉尼娜相位的变化。人类活动加剧的全球暖化叠加于厄尔尼诺的增强，使得东亚冬季风减弱。减弱的冬季风使得更多的陆源有机质被输送到远离河口的海域埋藏，对全球增温具有一定的负反馈作用。