Long-term stability of records of fallout radionuclides in the sediments of Brotherswater, Cumbria (UK)
Long-term stability of records of fallout radionuclides in the sediments of Brotherswater, Cumbria (UK)
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英国坎布里亚郡 Brotherswater 沉积物中放射性核素沉降物记录的长期稳定性
DOI：
10.1007/s10933-018-0055-7
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发表时间：
2018
影响因子：
2.1
通讯作者：
Semertzidou P
中科院分区：
文献类型：
--
作者：
Semertzidou P
最近在坎布里亚郡 Brotherswater 进行的 137 Cs 和 210 Pb 多核研究的结果与 1976/1977 和 1988/1989 年在同一湖进行的两项类似多核研究的结果进行了比较。这项新研究的目的是评估兄弟沃特沉积物中这些放射性核素沉降物记录的长期稳定性及其作为沉积物年代测定工具的可靠性。六个岩心取自该湖的四个不同区域，与早期研究中使用的岩心类似。按照与 1988/1989 年研究中使用的类似方案，通过伽马能谱法分析每个岩心的干燥沉积物样品中的 210 Pb、226 Ra、137 Cs 和 241 Am。 137Cs 结果以图形方式说明了记录 1963 年核武器大气试验最大沉降物浓度峰值的逐渐掩埋，以及随后由于放射性衰变而减少的情况。 1986 年后核心的特征是 1986 年切尔诺贝利事故的第二个峰值记录尘埃的出现和埋藏。 1986 年后岩心中 1963137Cs 峰的识别通过同时存在 241Am 痕迹得到证实，241Am 也是核武器试验放射性尘埃的产物。在 1988/1989 年的研究和本研究中，使用 CRS 模型计算的 210 Pb 日期大部分将 1963 年和 1986 年的深度与根据 137 Cs 记录确定的深度非常相似。该协议在二十多年的时间里得到维持，证明了该湖沉积物记录的可靠性以及用于解释这些记录的模型的有效性。 137C 的记录太模糊，而且 1963 年的时间也太近，无法对 1976/1977 年的核心进行类似的比较。在沉积物记录的 210 Pb 净供应率与大气通量相当的地点，210 Pb 和 137 Cs 日期之间的一致性最好。在 210 Pb 供应率大大超过大气通量的地点观察到小但显着的差异，最可能是由于来自流域的额外的时间依赖性输入，或湖内沉积后沉积物的重新分布。
Results from a recent multi-core study of137Cs and210Pb in Brotherswater, Cumbria, are compared with those from two similar multi-core studies carried out at the same lake in 1976/1977 and 1988/1989. The purpose of this new study was to assess of the long-term stability of fallout records of these radionuclides in the sediments of Brotherswater and their reliability as tools for dating the sediments. Six cores were taken from four different areas of the lake, similar to those used in the earlier studies. Dried sediment samples from each core were analysed by gamma spectrometry for210Pb,226Ra,137Cs and241Am following a similar protocol to that used in the 1988/1989 study. The137Cs results graphically illustrate the progressive burial of a peak in concentrations recording the 1963 fallout maximum from the atmospheric testing of nuclear weapons, and its subsequent reduction due to radioactive decay. The post-1986 cores are characterised by the appearance and burial of a second peak recording fallout from the 1986 Chernobyl accident. Identification of the 1963137Cs peak in post-1986 cores was confirmed by the co-presence of traces of241Am, also a product of nuclear weapons test fallout. In both the 1988/1989 study and the present study,210Pb dates calculated using the CRS model for the most part placed 1963 and 1986 at depths very similar to those determined from the137Cs records. The maintenance of this agreement over a period of more than two decades provides evidence of the reliability of sediment records in this lake and the validity of models used to interpret them. The137Cs records were too indistinct and 1963 too recent to make similar comparisons in the case of the 1976/1977 cores. Agreement between210Pb and137Cs dates was best at sites where the net rate of supply of210Pb to the sediment record was comparable to the atmospheric flux. Small but significant discrepancies were observed at sites where the210Pb supply rate greatly exceeded the atmospheric flux, most probably due to additional time-dependent inputs from the catchment, or post-depositional sediment redistribution within the lake.
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