Cyclisation degree of tetramethylated brGDGTs in marine environments and its implication for source identification
Cyclisation degree of tetramethylated brGDGTs in marine environments and its implication for source identification
复制标题
海洋环境中四甲基化brGDGT的环化程度及其对来源识别的意义
DOI：
10.1016/j.gloplacha.2019.103043
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发表时间：
2019
影响因子：
3.9
通讯作者：
Jia Guodong
中科院分区：
文献类型：
--
作者：
Zhang Jie;Yu Zhigang;Jia Guodong
支化甘油二烷基甘油四醚（brGDGT）在海洋环境中普遍存在。然而，目前还不清楚这些brGDGT是否来自陆地土壤或原位产生。最近，有人提出，四甲基化brGDGT，#Ringstetra，环戊烷部分的加权平均数，可用于确定来源的沉积brGDGT在海洋环境中。然而，人们对#Ringstetrain海水知之甚少。在这项研究中，我们报告了#Ringstetradata悬浮颗粒物（SPM）在表层陆架沃茨的中国东海（ECS）和中国南海（SCS）沿岸，以及在核心顶部沉积物的深层南海（SCS）。根据一个两端成员模型，#Ringstetra值在SPM海上增加从0.48到0.86在ECS和从0.39到0.83在SCS，这表明增加海洋产生的brGDGT。在ECS和SCS的陆架表层沉积物中也观察到#Ringstetrais的近海增加趋势，表明海洋产生的brGDGT的贡献增加。然而，南海岩芯顶部沉积物的近海增加趋势在水深约1000m处停止。100 m，在深度超过780 m的地点，#Ringstetra值始终较低（0.3 ± 0.1），在329 m处的过渡值为0.58。而不是解释的低#Ringstetravalues在深海沉积物中的陆地来源的brGDGT的贡献增加的结果，我们建议，在深海沉积物中的brGDGT原位产生。深海底层水和沉积物孔隙水的pH值低于海水柱中的pH值可能是造成低#林斯特拉值的原因。我们进一步提出，深海沉积物岩心的pH重建（例如，水深>1000米），受陆地影响最小，应反映海底环境的pH值变化。
Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are ubiquitous in marine environments. Nevertheless, it is unclear whether these brGDGTs are derived from terrestrial soils or produced in situ. Recently, it was proposed that the weighted average number of cyclopentane moieties of tetramethylated brGDGTs, #Ringstetra, could be used to identify sources of sedimentary brGDGTs in marine environments. However, little is known about #Ringstetrain seawater. In this study, we report #Ringstetradata in suspended particulate materials (SPM) in the surface shelf waters of the East China Sea (ECS) and coastal South China Sea (SCS), as well as in core-top sediments of the deep SCS. According to a two-end member model, #Ringstetravalues in SPM increase offshore from 0.48 to 0.86 in the ECS and from 0.39 to 0.83 in the SCS, suggesting increasing marine-produced brGDGTs. An offshore increasing trend of #Ringstetrais also observed in the shelf surface sediments of the ECS and SCS, suggesting increased contributions of marine-produced brGDGTs. However, the offshore increasing trend in core-top sediments of the SCS ceases at a water depth ca. 100 m, with constantly low #Ringstetravalues (0.3 ± 0.1) at sites deeper than 780 m and a transition value of 0.58 at 329 m. Instead of interpreting the low #Ringstetravalues in deep-sea sediments as the result of increased contributions of terrestrial-derived brGDGTs, we propose that brGDGTs in deep-sea sediments are produced in situ. The lower pH in the deep-sea bottom water and sediment porewater than in the seawater column could be the reason for the low #Ringstetravalues. We further propose that pH reconstructions of deep-sea sediment cores (e.g., >1000 m water depth) with the least terrestrial influence should reflect pH changes in marine bottom environments.