高浊度河流生物地球化学过程对渤海GDGTs指标影响的研究

Recently,a series of molecular proxies based on microbial biomarkers, so-called Glycerol Dialkyl Glycerol Tetraethers (GDGTs) have been proposed and used for the reconstruction of sea(lake) surface temperature, continental air temperature and organic matter sources. These GDGTs-based proxies such as TEX86, MBT/CBT and BIT index have become a hot topic in Paleoceanography, Paleolimnology and Biogeochemistry. In the China continental margins, due to intense influences of large rivers such as Yangtze River, Yellow River and Pearl River，the relationship between the GDGTs-proxies and environmental factors is much more complex than in land and open ocean. Consequently, the global temperature calibration equations of TEX86 and MBT/CBT can not be directly applied in these regions without local calibration. Here, we choose the Yellow River-Bohai Sea as our study area, and examine intact polar GDGTs and core GDGTs in suspended particles, sediments and soils. By combining GDGTs,bulk geochemical parameters and molecular microbiology data, we attempt to evaluate the in-situ production of GDGTs in this high turbid river and its controlling factors, relative stability of isoprenoid and branched GDGTs during long-range transport from the mid-Yellow River to Bohai Sea, as well as the influence of the biogeochemical processes in the Yellow River on the source, composition and proxy reliability of GDGTs in the Bohai Sea. Based on these results, we will analyze GDGTs in sediment cores from certain areas of the Bohai Sea, which are suitable for application of MBT/CBT and TEX86, and reconstruct Holocene variability in sea surface temperature and continental air temperature, thereby understanding the Holocene evolution of East Asian Monsoon in the Yellow River basin.

近年来，基于微生物标志物GDGTs的分子代用指标在重建海洋(湖泊)表层水温度和陆地气温以及指示有机碳来源等方面展现出了巨大的潜力，成为古海洋学、古湖泊学和生物地球化学关注的热点。在我国陆架边缘海，由于受到长江、黄河、珠江等大河的强烈影响，GDGTs指标与环境因子之间的关系远比陆地和大洋复杂，因此有必要研究河流控制陆架边缘海的现代过程，以评估TEX86、MBT/CBT和BIT作为古环境和古气候指标的区域可靠性。本项目拟分析黄河-渤海悬浮颗粒物、沉积物及土壤中的极性和核心GDGTs，结合其他地球化学参数和分子生物学数据，评估高浊度河流中GDGTs的原位生产效应及控制因素，揭示长距离河流搬运中支链和类异戊二烯GDGTs的环境稳定性，并探讨河流生物地球化学过程对渤海GDGTs来源、组成和指标的影响。在此基础上，利用渤海沉积物重建全新世海水温度和陆地气温的变化，揭示黄河流域全新世季风的演化。

项目选择黄河下游-河口-渤海为主要研究区域，采集了颗粒物，水样和沉积物样品，开展了基于微生物标志物 GDGTs 的分子代用指标研究，结合其他地球化学参数，评估了黄河河道摆动、输沙量（浊度）和营养盐变化对渤海有机质埋藏的影响；详细分析了渤海沉积物GDGTs的组成特征，发现支链GDGTs（brGDGTs）化合物在黄河河口、渤海中部和北部具有明显的空间变化，结合文献报道的来自全球1000多个brGDGTs数据，提出了一个可以灵敏判定海洋环境brGDGTs来源的指标，即brGDGT IIIa/IIa比值。当该比值>0.92时表征 brGDGTs来自海洋微生物，< 0.59表征brGDGTs来自陆源输入，而介于0.59~0.92之间时表征brGDGTs具有陆源和海源的混合贡献。该指标不仅有利于快速判定brGDGTs的来源，也可用于评价基于brGDGTs的温度和pH代用指标(即MBT/CBT)的可靠性。在此基础上，项目组还首次报道了一类新型的GDGTs化合物，即7-甲基支链GDGT,并指出该化合物的产生可能与环境pH有关。本项目的实施提升了我们对GDGTs生物标志在高浊度河流影响区的来源、分布和环境指示意义的理解，提供了一个判定复杂环境中brGDGTs来源的新方法，对于准确运用GDGTs古环境代用指标也有积极的意义。