青海湖湖泊沉积物木质素AMS-^(14)C测年

AMS-^(14)C dating of lignin phenols extracted from the lacustrine sediments from Qinghai Lake

对青海湖1A钻孔0—4 m不同深度共10个沉积物样品提取木质素,并进行AMS-^(14)C测年。结果显示,木质素的AMS-^(14)C年龄-深度曲线呈良好的线性关系,大于10μg碳量的木质素单体^(14)C年龄比1F孔同深度基于总有机碳(TOC)获得的^(14)C年龄平均偏年轻约110年,接近采用平均值概念分段线性回归确定的1F孔4.99 m以上碳库效应估算(126年)。这表明沉积物木质素AMS-^(14)C测年可有效减少老碳效应的影响;同时,1A与1F两个平行钻孔不同材料测年结果之间的良好对比,也佐证了基于沉积物TOC的^(14)C测年并采用平均值概念进行分段线性回归建立的青海湖湖泊沉积物年代框架的可靠性。

Background, aim, and scope The establishment of reliable framework is an important part of paleoclimate research. Selecting reliable dating material is the most important part of the chronology research. Qinghai Lake is located in the northeastern margin of Qinghai-Tibet Plateau, influenced by the monsoon climate and drought climate, and sensitive to climate and global environmental change. It is an excellent location for the research of environmental change in the western China, the Qinghai-Tibet Plateau uplift process, environment effect and their associated with global changes. The lakes in the arid-semiarid areas are influenced widespread by reservoir effect and brings much inconvenience in establishing the chronology framework of lacustrine sediments. In order to establish a reliable chronological framework of Qinghai Lake lacustrine sediment core, we tried the AMS-14C dating of lignin phenols. Materials and methods The Qinghai Lake 1A core was from the southeast lake bay. The lignin phenols were extracted from 12 lacustrine sediment samples from above 4 m Qinghai Lake 1A core, defined by GC-FID, and then separated by HPLC in the University of Washington. The measurement of lignin phenols AMS-lOc dating was finished in the University of California, Irvine. Results Finally 10 effective AMS-^14C ages （3550 a BP, 1470 a BP, 2800 a BP, 2390 a BP, 3920 a BP, 3520 a BP, 6390 a BP, 5900 a BP, 7050 a BP, 7150 a BP on the depth of 4.87 cm, 19.18 cm, 26.15 cm, 107.40 cm, 140.19 cm, 196.94 cm, 257.38 cm, 300.24 cm, 342.10 cm, 398.68 cm respectively） were obtained except 2 samples with lignin phenols too little （〈2 pg） to be measured on AMS. ^14C ages were calibrated by CALIB 6.0. Discussion Overall the 10 lignin AMS- ^14C ages were linear well. The lignin ^14C ages （pure carbon 〉10 μg） were younger than TOC ^14C ages average in 110 a, which is more close to reservoir age （126 a） of 1F core above 4.99 m determined by a piecewise linear regression using ＂mean value concept＂ method （Cheng, 2008）. Conclusions This not only explained that the lignin AMS-^14C dating can effectively avoid the reservoir effect, but also corroborated the reliability of Qinghai Lake sediments chronological framework established by TOC-^14C dating and piecewise linear regression using the ＂mean value concept＂ method. Recommendations and perspectives The lignin AMS-^14C dating can effectively avoid the reservoir effect of Qinghai Lake and help to establish a reliable chronological framework of Qinghai Lake lacustrine sediment core. The lignin phenols extracted from sediments can be used as reliable dating material based on the perfect chemical extraction, precise chromatography and mass spectrometry technology in the future research.