| 摘要: |
| 人类核事件形成的137Cs蓄积峰作为一种重要的时标，被广泛应用于湖泊沉积物计年。在云南地区湖泊沉积剖面中，除1963年137Cs主蓄积峰外，“1975”年和“1986”年次蓄积峰存在与否，其成因及时标意义一直存在争议。本文选取滇西腾冲青海湖为研究对象，通过构建137Cs沉积模型，利用重建的区域137Cs大气沉降数据拟合出137Cs的沉积分布曲线，结合210Pbex年代、Pu同位素分析结果及前人对区域其他湖泊研究结果，对沉积物剖面中137Cs主次蓄积峰的年代、成因及其影响因素进行深入解析，进而识别其对应的时标特征。结果表明，腾冲青海湖沉积剖面中的1963年和1986年137Cs峰主要由大气沉降的137Cs蓄积形成，大气沉降量的贡献比例为77~80%和51~62%，分别对应于1963年的全球大气沉降高峰和1986年的切尔诺贝利核事故沉降峰，具有明确的时标特征。其中，1986年137Cs峰层位的137Cs/239+240Pu活度比值明显高于全球大气沉降值，进一步证实存在切尔诺贝利核事故来源137Cs的额外贡献。腾冲青海湖沉积剖面中1975年137Cs峰则主要由流域输入的137Cs蓄积形成，流域输入量的贡献比例高达80~88%；但流域输入成因的“1975年”137Cs蓄积峰不具有时标特征，不能作为时标应用。在云南地区，1963年137Cs主蓄积峰的时标特征明显，是湖泊沉积物计年的可靠时标；1986年次蓄积峰的时标特征可识别，可作为计年的辅助时标。 |
| 关键词: 137Cs 沉积模型 239+240Pu 1986年时标 切尔诺贝利核事故 |
| DOI： |
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| 基金项目:国家自然科学基金项目（面上项目，重点项目，重大项目）,国家重点基础研究发展计划（973计划） |
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| The distribution characteristics and genesis analysis of 137Cs accumulation peaks in the sediment cores of Lake Tengchongqinghai in Western Yunnan*Guo Haiting1, Wu Mengmeng1, Pan Shaoming1**, Xu Yihong2**, Li Qifan3, Kang Du3 |
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Guo Haiting,Wu Mengmeng,Pan Shaoming,Xu Yihong,Li Qifan,Kang Du
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School of Geography and Ocean Science, Nanjing University
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| Abstract: |
| The 137Cs accumulation peaks, resulting from human nuclear activities, serve as crucial time markers and extensively used in contemporary sediment dating. In addition to the main 137Cs accumulation peak in 1963, secondary peaks observed in “1975” and “1986” in the sedimentary profiles of Yunnan lakes have been a subject of debate regarding their origins, causes, and chronological significance. This study focuses on Lake Tengchongqinghai, a natural volcanic lake located in Western Yunnan. By constructing a sedimentation model and utilizing reconstructed regional atmospheric deposition data to fit the 137Cs deposition distribution curves, combined with 210Pbex dating, Pu isotope analysis results, and previous studies on other lakes in the region, this paper provides an extended analysis of the age, genesis, and influencing factors of these 137Cs accumulation peaks, thereby identifying their corresponding time-marker characteristics.The results indicate that the 137Cs peaks in 1963 and 1986 are predominantly the result of atmospheric deposition. The two peaks are attributed to global atmospheric nuclear testing and the 1986 Chernobyl nuclear accident, with contribution rates of 77-80% and 51-62%, respectively. Notably, the activity ratio of 137Cs/239+240Pu in 1986 sedimentary layer is significantly higher than the global atmospheric deposition value, further confirming an additional contribution from the Chernobyl nuclear accident. However,? the 137Cs accumulation peak in 1975 is primarily attributed to input from the catchment area, with contributions ranging from 80-88%. This suggests that the peak does not serve as a time marker resulting from direct atmospheric fallout from nuclear events. Synthesizing results from other Yunnan lakes, the 137Cs accumulation peak in 1963 exhibits clear time-marker characteristics, making it a reliable marker for sediment dating in the region; the 1986 peak, with recognizable chronological features, can serve as an auxiliary time marker. |
| Key words: 137Cs sedimentation model 239+240Pu 1986 time-marker Chernobyl accident |
