On the sediment age estimated by ^(210)Pb dating: probably misleading “prolonging” and multiple-factor-caused “loss”

作     者：JIA Jianjun YANG Yang CAI Tinglu GAO Jianhua XIA Xiaoming LI Yan GAO Shu 

作者机构：State Key Laboratory of Estuarine and Coastal Research East China Normal University Key Laboratory of Coast and Island Development of MOE Nanjing University State Research Centre for Island Exploitation and Management Second Institute of Oceanography State Oceanic Administration College of the Environment and Ecology Xiamen University 

出 版 物：《Acta Oceanologica Sinica》 (海洋学报（英文版）)

年 卷 期：2018年第37卷第6期

页      面：30-39页

核心收录：

学科分类：0710[理学-生物学] 070704[理学-海洋地质] 07[理学] 0908[农学-水产] 0707[理学-海洋科学] 

基　　金：The National Natural Science Foundation of China under contract Nos 41376068 and 41776068 

主　　题：^210Pb dating sedimentation rate sediment flux 

摘      要：The radionuclide ^（210） Pb is suitable for century-scale dating and has been used to calculate the sedimentation rate in a variety of environments. However, two common ways to apply 210 Pb dating techniques may give misleading results. One is ＂prolonging of age＂, i.e., using the calculated sedimentation rate to date back to 200 or 300 years.This practice must be treated with caution because the 210 Pb dating techniques do not guarantee direct dating for ages much older than 100 years. Another is ＂loss of age＂, i.e., the calculated time span between the topmost layer and the 210 Pb background layer in cores is less than 100 years when an apparent sedimentation rate is used in the calculation. Here, we propose that based on the principle of 210 Pb dating, the upper limit of age suitable for direct210 Pb dating is between 110 and 155 years. The ＂prolonging＂ application is acceptable only if the sedimentary environment in the past several hundred years was stable and the sedimentation rate was generally constant, and verification with independent evidence（such as historical records or biomarker methodology） is needed.Furthermore, after analyzing many published and collected data, we found four possible reasons for the ＂loss of age＂. First, the compaction effect of sediment should be corrected in laboratory analysis or else the calculated age will be underestimated. Second, the accuracy and uncertainty of 210 Pb activity measurement affect the judgment of the background. To be cautious, researchers are apt to choose a background activity with a younger age. Third,use of a slightly smaller value of supported 210 Pb activity in a calculation will lead to considerable underestimation of the time span. Finally, later-stage erosion and migration are common for sedimentation, which lead to loss of sedimentary records and are often reflected as a ＂loss of age＂ in cores. We believe that proper use of 210 Pb dating data may provide helpful information on our understanding of sediment records and recent environmental changes.