|Xiang Liang,Wu Ruijin,Ji Lei.137Cs and 241Am profiles and dating of sediments from two lakes in Yunnan Province, China. J. Lake Sci.1996,8(1):27-34. DOI:10.18307/1996.0104
|关键词: 137Cs 241Am 时标 湖泊沉积 滇池 剑湖
|137Cs and 241Am profiles and dating of sediments from two lakes in Yunnan Province, China
Xiang Liang, Wu Ruijin, Ji Lei
Lake Sediment and Environment Lab., Nanjing Institute of Geography & Limnology, CAS, Nanjing 210008
|Atmospheric nuclear weapons testing produced global radioactive fallout that has been widely studied for dating recent lacustrine sediments over the past 20 years.This paper describes the use of 137Cs and 241Am radioactivity measurements to determine the accumulation rates of sediments from two lake cores, one is Core DC9301 from Dianchi Lake, the other is Core JL9301 from Jianhu Lake, in Yunnan Province, China.The vertical distributions of 137Cs and 241Am in the sediment cores are markedly similar to the expectations based on estimated and measured temporal variation of the two radioisotopes fallout in this area.The variation of the 137Cs activity with depth in cores provides four distinct chronological markers with the onset of fallout in 1954,the peak fallouts from the atmospheric testing of nuclear weapons in 1963 and two lower peaks occurred in 1974 by nuclear tests and in 1986 from Chernobyl accident.The variation of Am proves two chronological markers from the atmospheric resting of nuclear weapons in 1963 and 1974.According to the 137Cs and 241Am results, the dry mass accumulation rates of Core DC9301 and JL9301 are 42.2 and 28.7mg/(cm2·a), respectively..Because of the post-depositional mobility of in iake sediments, tht 137C.s chronologi-cal marker results of 1954 for these two cores were of no chronological value.Although the Am activities are extremely lower than those of ia,Cs in these two cores, the former is significantly less mobile in Iake sediments and longer half-iife rhan the latter.So 241Am is likely to play an increasingly important role in dating recent lacustrine sediments.
|Key words: 137Cs 241Am chronological marker sediment Dianchi Lake Jianhu Lake