鸭绿江口^(137)Cs的沉积记录及其意义

Deposition records and the significance of ^(137)Cs in Yalu River estuary

根据2013、2014、2018年鸭绿江口16个柱状样的^(137)Cs沉积记录,分析了其垂向分布特征,划分了^(137)Cs的4种沉积类型.根据柱状样^(137)Cs蓄积量较高、沉积连续、沉积过程清楚、最大蓄积峰对应1963年的特征初步确定了适合河口不同沉积状态的4个“参考”剖面,并与理想状态的大气沉降曲线进行了对比分析,显示鸭绿江口参考剖面的^(137)Cs沉积记录与大气沉降量(输入函数)曲线基本吻合. 1963年的主计年时标涵盖大部分柱状样,层位清楚、容易识别、可以信赖.鸭绿江口存在疑似1975年和1986年^(137)Cs的计年时标,但用于计年时需谨慎. 1986年以后大多数沉积记录显示了^(137)Cs沉积迅速降低的趋势,其他少部分柱状样的^(137)Cs蓄积峰是动力过程混合或扩散作用的结果,也不排除陆源输送.表层沉积物大多数站位检测不出^(137)Cs,说明近期陆源^(137)Cs的输送量微乎其微,个别站位表层中较多的^(137)Cs来源有待进一步研究.

Based on the^(137)Cs deposition records of 16 cores collected in Yalu River estuary, their characteristics of the vertical distribution were analyzed, and 4 sedimentary types of^(137)Cs were found out. 4 reference sections available for different depositional states in the estuary were preliminarily determined, according to the^(137)Cs sedimentary characteristics including the high accumulation, the continuous deposition, the definite deposition process and the maximum accumulation peak corresponding to 1963. Then these reference sections were compared with the ideal atmospheric deposition curve. The results indicated that the^(137)Cs depositional records of the reference section in Yalu River estuary were in almost agreement with the atmospheric settlement(input function) curve.The 1963 key dating markers were reliable, because they were easily found in the most cores with the clear location. The suspected^(137)Cs dating markers of 1975 and 1986 existed in the deposit records in the Yalu River estuary, but they needed to be used cautiously when dating. The most deposition records after 1986 showed a rapidly decreasing trend of^(137)Cs specific activity, while the few^(137)Cs accumulation peaks in the others after 1986 might be the result of the perturbation, mixing or diffusion in the dynamic process, but the land-source transport could not be ruled out. No^(137)Cs in the surface sediments in Yalu River estuary was detected in most sampling points. It indicated that little^(137)Cs was transported by the river dynamics. The source of^(137)Cs in the surface sediments from the particular sampling points needs further studied.