Radionuclides as markers of a new time: the anthropocene

On May 2019, the members of the Anthropocene Working Group completed a binding vote to affirm some of the key questions that have been agreed in 2016: the Anthropocene should be considered as a formal chronostratigraphic unit, defined by a Global Boundary Stratotype Section and Point (GSSP), using one of the stratigraphic signals around the mid-twentieth century of the Common Era. The fallout from nuclear weapons testing appears as the most suitable GSSP. In this article, the main anthropogenic markers are discussed as well as the sources or human-made radiation and the signature of nuclear weapons testing. The appearance of 239+240Pu in the early 1950s and the clear peak, in 1963, makes a good marker. High resolution archives include layers of sedimentary rocks, lacustrine and marine sediments and corals and polar ice cores. A coupled application of other radioactive isotopes, as 137Cs, 14C and 241Am, may be useful to categorize distinct fallout signatures. A site to define the Anthropocene (golden spike) would ideally be located between 30º and 60º north of the equator. Nevertheless, results obtained in sediments on the Brazilian coast showed that both 239+240Pu and 137Cs signatures could be detected and quantified as markers of this “atomic age”.

2019年5月，人类世工作组（Anthropocene Working Group）成员完成具有约束力的投票，确认了2016年已达成共识的若干核心议题：人类世应被认定为正式的年代地层单位，需以全球界线层型剖面和点位（Global Boundary Stratotype Section and Point，GSSP）定义，选用公元20世纪中叶前后的某一地层信号作为判定依据。其中，核武器试验沉降物被视为最适宜的GSSP候选。
本文探讨了主要的人为地层标志物，同时分析了人为辐射来源与核武器试验沉降的特征。1950年代初出现的239+240钚（239+240Pu）以及1963年出现的清晰峰值，是优质的地层标志物。高分辨率沉积载体包括沉积岩层、湖相与海相沉积物、珊瑚及极地冰芯。联合使用137铯（137Cs）、14碳（14C）与241镅（241Am）等放射性同位素，或可用于区分不同的沉降信号特征。
理想情况下，用于划定人类世的金钉子（golden spike）点位应坐落于赤道以北30°至60°的区域。不过，巴西海岸沉积物的研究结果显示，239+240Pu与137Cs的信号均可被检测并量化，可作为这一"原子时代"的地层标志物。