利用^(210)Pb、^(137)Cs和^(241)Am计年法测算云南抚仙湖现代沉积速率

Radionuclide dating (^(210)Pb,^(137)Cs,^(241)Am) and modern sedimentation rate in Lake Fuxian

通过对云南抚仙湖沉积物柱芯样品的^(210)Pb、^(137)Cs和^(241)Am测试表明,柱芯剖面上有明显的1963年和1986年^(137)Cs蓄积峰,验证了1975年次级蓄积峰存在的可能性,这些峰形完好的蓄积峰对抚仙湖的现代沉积环境有明显的时标意义。利用^(137)Cs计年法得到抚仙湖沉积物自1963年、1975年及1986年以来到2007年的平均沉积速率分别为0.063g/(cm^2·a)、0.052g/(cm^2·a)和0.039g/(cm^2·a),说明了过去近五十年抚仙湖沉积速率整体上经历了一个由快到慢的过程。借助于^(241)Am的1963年蓄积峰可以提高^(137)Cs计年的准确性。根据^(210)Pb CRS计年模式,计算出每个样品深度所对应的年代,与^(137)Cs计年法比较存在一定的偏差,分析了两种计年方法存在差异性的原因。通过质量深度和年代分析,抚仙湖的沉积速率变化幅度比较大,表明抚仙湖近129年来的沉积环境不稳定,可能与相应历史时期的人类活动有密切的关系。

^210pb, ^137Cs and ^241 Am were used to analyze the sediment core of Lake Fuxian. In the core, there were obvious peaks corresponding to 1963 and 1986, verifying the existence of peak recorded in 1975, which was important age mark for the Lake Fuxian sediment. The sedimentation rate of the Lake Fuxian was 0. 063g/（ cm^2 ·a） by 137 Cs time marker （1963）, 0.052g/（ cm^2 ·a） by 137Cs time marker （1975） and 0. 039g/（ cm^2 ·a） by ^137Cs time marker （ 1986）, which indicated a slower process in the past 50 years. 241 Am dating can improve the accuracy of peak in 1963. ^210Pb （CRS） dating showed a little deviation from ^137Cs dating, explaining the reasons in different views. The limit mass depth was 7. 366g/cm^2 , which corresponded to the age of 1878. The average sedimentation rate from 1878 to 2007 was 0. 057g/（ cm^2·a）, which was changeable in the Lake Fuxian by analyzing the mass depth and ages, which showed that the sedimentation environment was related to human disturbance in the past 129 years.