三原黄土中支链甘油单烷基甘油四醚类化合物的检出及其环境指示意义

THE OCCURRENCE AND ENVIRONMENTAL SIGNIFICANCE OF BRANCHED GLYCEROL MONOALKYL GLYCEROL TETRAETHERS IN LOESS DEPOSITS FROM SANYUAN COUNTY,XIANYANG CITY,SHAANXI PROVINCE IN THE SOUTH-CENTRAL PART OF THE CHINESE LOESS PLATEAU

来源于古菌和细菌的甘油二烷基甘油四醚(GDGTs)是重建古环境的重要指标。近年来,在培养菌、海洋、河流、湖泊和泥炭中检出了甘油单烷基甘油四醚类化合物(GMGTs或H-GDGTs),其中,支链甘油单烷基甘油四醚类化合物(brGMGTs或H-brGDGTs)的存在被认为与高温环境有关。目前,brGMGTs在黄土中的分布特征和环境指示意义还不明确。三原黄土剖面(34.70°N,109.04°E)位于黄土高原中南部,剖面深度为17.1 m,年龄跨度为0~219 ka,涵盖S_(0)、L_(1)、S_(1)、L_(2)和S_(2-1)等地层单元。三原黄土剖面地层连续性好、分辨率高,是开展brGMGTs研究的理想材料。本研究选取了三原黄土剖面中72个黄土和古土壤样品,通过高效液相色谱-大气压化学电离-质谱/质谱,确认了黄土高原的黄土中存在brGMGT-1020、brGMGT-1034和brGMGT-1048这3种brGMGTs;brGMGTs的含量与GDGTs中的Ⅰa、Ⅱa和Ⅲa相关,这表明brGMGT-1020、brGMGT-1034和brGMGT-1048可能分别是由Ⅰa、Ⅱa和Ⅲa在微生物的作用下转化而来。三原黄土剖面中的brGMGTs相对含量与剖面深度/样品年龄正相关,这种关系可能是沉积后的物理化学过程导致的。在沉积年龄小于40 ka的黄土和古土壤中,brGMGTs相对含量的变化可以在一定程度上反映气候环境特征,较高的brGMGTs相对含量可能对应温度较高的时段。brGMGTs有潜力成为指示古增温事件的生物标志物。

Glycerol Dialkyl Glycerol Tetraethers(GDGTs)derived from archaea and bacteria are important indicators for reconstructing paleoenvironment.In recent years,Glycerol Monoalkyl Glycerol Tetraethers(GMGTs,or H-GDGTs)have been detected in cultured archaea,oceans,rivers,lakes and peat.The presence of branched Glycerol Monoalkyl Glycerol Tetraethers(brGMGTs,or H-brGDGTs)is thought to be associated with high-temperature environments.At present,the distribution characteristics and environmental significance of brGMGTs in loess remain unclear.The Sanyuan loess section(34.70°N,109.04°E)is located in the south-central part of the Chinese Loess Plateau,with a depth of 17.1 m and an age span of 0 to 219 ka,covering strata units such as S_(0),L_(1),S_(1),L2,and S_(2-1).The Sanyuan Loess section has good stratigraphic continuity and high resolution,which is an ideal material for brGMGTs research.In this study,72 loess and paleosols samples from the Sanyuan loess section were analyzed.Using high performance liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry,brGMGT-1020,brGMGT-1034,and brGMGT-1048 were identified in the Chinese Loess Plateau.The relative content of brGMGTs was correlated with that ofⅠa,Ⅱa andⅢa,indicating that brGMGT-1020,brGMGT-1034 and brGMGT-1048 may be transformed fromⅠa,Ⅱa andⅢa,respectively,under microbial influence.The relative content of brGMGTs in the Sanyuan loess section was positively correlated with depth or age,which may be caused by the physical and chemical processes after deposition.In loess and paleosols samples with deposition age less than 40 ka,the fluctuation trend of brGMGTs relative content can partly reflect climatic and environmental characteristics,i.e.,higher brGMGTs relative content may indicate warmer climatic conditions.Therefore,brGMGTs provide a new potential biomarker for identifying past warming events.