| 137Cs湖泊沉积年代学方法应用的局限——以Crawford湖为例 |
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| 引用本文： | 项亮.137Cs湖泊沉积年代学方法应用的局限——以Crawford湖为例[J].湖泊科学,1995,7(4):307-313. |
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| 作者姓名： | 项亮 |
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| 作者单位： | 中国科学院南京地理与湖泊研究所湖泊沉积与环境开放研究实验室 南京 |
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| 基金项目： | 国家自然科学基金资助项目(编号:49401011) |
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| 摘 要： | ＾１３７Ｃｓ湖泊沉积年代学方法是测定现代湖泊沉积物沉积年代和沉积速率的重要同位素年代学方法之一。对加拿大Ｃｒａｗｆｏｒｄ湖采集的沉积孔柱内＾１３７Ｃｓ垂直分布的研究发现，该方法给出时的标有明显偏差。比较＾２１０Ｐｂ和纹层等年代方法的结果，其１９６３年时标蓄积峰值所在位置明显移向表层，而作为１９５４年时标的该核素出现蓄积的层位则远早于该年沉积物蓄积层位。研究还表明，孔柱中较高的间隙水含量、缺少足以吸
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| 关 键 词： | 湖泊 沉积年代 钯同位素 沉积速率 |
| 收稿时间： | 1994/7/10 0:00:00 |
| 修稿时间： | 1994/11/2 0:00:00 |
Limitations of the application of 137Cs limnochronology:a case study of 137Cs profile in crawford lake sediment |
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| Xiang Liang.Limitations of the application of 137Cs limnochronology:a case study of 137Cs profile in crawford lake sediment[J].Journal of Lake Science,1995,7(4):307-313. |
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| Authors: | Xiang Liang |
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| Institution: | Lake Sediment and Baviroament Lab., Nanjing Institute of Geography & Limnology, CAS, Nanjing 210008 |
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| Abstract: | Over the last three decades, artificial radionuclide, 137Cs, has been introduced into the paleolimnologicai study for interpreting the geochronology of recent sedimentary deposits. The main source of 137Cs was fallout from the atmospheric testing of nuclear weapons. Where this isotope is strongly adsorbed onto sediments i the variation of its activity with depth in a core should reflect the fallout history, in which the onset of fallout in 1954 and peak fallout in 1963 provide two distinct chronological markers. However, in the lake sediment core which was studied in this paper, the two time markers deviate greatly from expectations based on 210Pb and varve chronology. 137Cs is distributed more deeply in the sediment that has been dated decades older than the beginning of 137Cs fallout and the profile of it has its maxima nearer to the sediment surface than expectations. In the lake there is no evidence of physical mixing, disturbance and time lag in the sediment of catchment material. We argue that the high interstitial water content of these sediments provides a possibility of 137Cs redistribution in cores by molecular diffusion and could transport it downward. So, the occurrence of 137Cs at pre-fallout sediment depths is due mostly to net downward molecular diffusion and scarcity of clay minerals for adsorption. On the other hand, the presence of high organic matter content suggests some redistribution of the isotope within the sediments and will tend to enrich the upper sediment layers. Because more of this nuclide is accumulated in organic matter than in inorganic mineralsi the mobility of this nuclide in the sediment may begin with release of it into interstitial water by decomposition of organic matter. Thus more 137Cs which has been released by organic decomposition would tend to be re-adsorbed by upper part sediments which have high organic matter content than lower part sediments and the peak of the 137Cs profile would remove from lower sediment layer to the upper one. The 137Cs profile in the lake core is believed to be the result of a combination of diffusion, biological concentration from sediment. Under these circumstances, 137Cs dating is not useful, but 210Pb dating can be valid because it differs from 137Cs in physical and chemical characteristics. |
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| Keywords: | 137Cs dating Limnochronology Crawford Lake |
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