摘要
近些年,支链甘油二烷基甘油四醚类脂物(brGDGTs)被广泛应用于陆地古气候、古环境重建研究中,并取得了一系列的进展。brGDGTs在海洋沉积物中普遍存在,起初被认为是陆源输入的结果,但越来越受到质疑。在中国东海和黄海区域,brGDGTs的相关研究还相对较少。本文分析了位于南黄海和东海北部的4个站位年龄跨度近百年的柱状岩芯,讨论了brGDGTs相关参数的特点,在此基础上探讨了brGDGTs的来源。结果显示,岩芯沉积物中brGDGTs分布样式与已发表的黄河和长江流域土壤中brGDGTs分布样式存在显著差别,暗示了海洋微生物自生brGDGTs的存在。在假设岩芯沉积物中brGDGTs主要由长江和黄河流域土壤输入和海洋微生物自生三端元贡献的情况下,用四甲基brGDGTs百分含量(%tetra)和四甲基环化指数(#Ring_(tetra))参数计算了三个端元的相对贡献和绝对变化情况。结果表明海洋自生是沉积物中brGDGTs的主要贡献者,在南黄海中北部可达70%以上。从百余年来的沉积序列来看海洋自生brGDGTs的含量有增加的趋势,这种趋势可能与海水的富营养化增强有关,也可能是随沉积深度增加降解加强的结果。
Recently, brGDGTs were widely applied in terrestrial paleo-climatic and paleo-environmental reconstructions. brGDGTs are ubiquitous in marine sediments and are typically considered to be derived from soils, though this assumption is increasingly in doubt. In this work, we analyzed brGDGTs in four sediment cores from the East China and Yellow seas. These cores covered a history of approximately 100 years. BrGDGT compound distributions from these marine sediments are discussed to elucidate their sources. We found that the brGDGT distribution in the studied marine sediments greatly differed from that in the soils from the catchments of the Changjiang and the Yellow rivers, suggesting considerable endogenous production of brGDGTs. Given that brGDGTs in core sediments are derived from three end members, i.e. soils from the Changjiang and Yellow rivers, and in-situ marine production, the relative contributions of the three were calculated based on %tetra and #Ringtetra parameters. The calculated results show that marine in-situ production was the dominant source of the sedimentary brGDGTs, accounting for up to > 70% in the two cores in the central and northern part of the southern Yellow Sea. There is a consistent increasing trend in marine in-situ production over the past 100 years in the four sediment cores, which could have been caused by eutrophication in the marginal seas, or alternatively, associated with enhanced degradation of brGDGTs with sediment depth.
引文
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