Application and problems of <sup>210</sup>Pb and <sup>137</sup>Cs dating techniques in lake sediments

湖泊沉积记录研究对了解流域侵蚀、揭示区域气候环境变化及人类活动影响、建立外生地球化学循环模式等均具有重要意义.放射性同位素210Pb和137Cs组合定年法是百年尺度湖泊沉积记录研究的首选方法，在过去几十年中得到了广泛应用，大力推动了湖泊沉积记录的高分辨率气候环境变化研究的开展.然而，如何理解和选择适用的计算模式来尽可能地提高定年准确度目前仍存在争议，这在一定程度上限制了该方法的应用.鉴于上述问题，本文基于本实验室近年来从青藏高原获取的若干支代表性湖芯的定年结果，从样品前处理、仪器及测试、数据分析及计算等全过程对210Pb、137Cs定年原理和方法进行了较为系统的阐述；在此基础上，提出了210Pb定年样品封装原则，探讨了高纯锗γ谱仪在放射性活度测量中的影响因素，并建立了准确有效的比活度校正方法；明确指出了恒定初始浓度模式（constant initial concentration，CIC）可用于计算沉积物每层的年龄，而不是部分研究中认为的平均沉积速率，这对于深刻理解该定年模式并提供准确的定年结果具有重要的参考意义.同时，通过对比两种放射性核素的分布特征发现，相对于210Pb而言，137Cs更容易发生垂向迁移进而影响其时标准确性，这需引起研究者的充分重视，因此，当二者定年结果出现明显差异时，建议以210Pb定年结果为准.;The study of lacustrine sedimentary records is great significance for understanding basin erosion, revealing regional climatic and environmental changes the influence human activities, establishing exogenous geochemical cycle patterns. The combined dating method 210Pb 137Cs preferred centennial-scale lake records. It has been widely used in past decades, which greatly promotes high-resolution climate However, it still controversial how to understand select applicable calculation model improve accuracy as much possible, limits application this a certain extent. Because above problems, based on results several representative cores obtained from Tibetan Plateau by our laboratory recent years, principles methods with were systematically expounded whole process sample pretreatment, instrument measurement, data analysis calculation. On basis, packing principle samples was proposed, influencing factors High-purity germanium Gamma-Ray Spectrometer radioactive activity measurement discussed, an accurate effective specific correction established. pointed out that constant concentration (CIC) could be calculate age each layer sediments, rather than average deposition rate some studies, providing results. Meanwhile, comparing distribution characteristics two radioisotopes, found more likely have vertical migration compared 210Pb, thus affected accuracy, should paid attention researchers. Therefore, case obvious difference between results, suggested prevail.