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Reconstruction of Paleoenvironmental Changes using Radionuclides:Uranium and Thorium Isotopes in the Lake Sediments

利用放射性核素重建古环境变化：湖泊沉积物中的铀和钍同位素

基本信息

批准号：
18510008
负责人：
YAMAMOTO Masayoshi
金额：
$ 2.63万
依托单位：
Kanazawa University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

项目摘要

Investigation on polar ice-sheet and lake sediments of mide-latitude area have made studies on past climatic and environmental conditions in continental areas very important to obtain a more information cu mechanisms of Quaternary environmental changes. In Lake Baikal in southeastern Siberia, the dear signal of changing paleoclimate in the sediments has been found in depth distributions of the diatom frustule numbers, water content and organic carbon content in sediments. Furthermore, microelements, especially, uranium have been also noticed as one of the most important chemical index. Thus, the U (and Th) isotopes in lacustrine sediments serve as good proxies for not only chronology but also indicator of climatic changes. Jake Hovsgol, the largest fresh water lake in Mongolia, promiePa the sensitive response to environmental changes in surrounding catchments. In this study, an attempt was made to get a detail feature of U and Th isotopes distribution in the sediment core of Lake Hovsgol. The obtained data were discussed laying stress on dating using 238U-234U-230Th-232Th system, and compared with those obtained previously in sediments core fit Lake Baikal The final purpose of this study was to elucidate the changes in the depth distribution of U and Th isotopes and their ratios in the sediments ad to obtain insight into their implication for paleoclimatic variation.1. Depth profiles of U and Th isotopes in a 81 m length sediment core (HDP-04) of Lake Hovsgol were measured in details, and U-series isochron techniques were successfully applied to the dating for some layers.2. The depth distribution of authigenic U well correlated with that of bio-marker of primary products, suggesting that the fluctuation of authigenic U well correlates with glacial-interglacial cycle at least about IMa.3. A similar pattern of u depth profiles in sediments was observed in the dated depth from 24 m to surface in Lake Hovsgol and lake Baikal with quite different water qualities.

中纬度地区极地冰盖和湖泊沉积物的调查，使得研究大陆地区过去的气候和环境条件对于进一步了解第四纪环境变化的机制具有重要意义。在西伯利亚东南部的贝加尔湖，沉积物中硅藻孔数、沉积物含水量和有机碳含量的深度分布是古气候变化的重要信号。此外，微量元素，特别是铀，也被认为是最重要的化学指标之一。因此，湖泊沉积物中的U（和Th）同位素不仅可以作为年代学的良好指标，而且还可以作为气候变化的指标。Jake Hovsgol是蒙古最大的淡水湖，它对周围集水区的环境变化做出了敏感的反应。本研究试图获得Hovsgol湖沉积物岩心中U、Th同位素分布的详细特征。以238U-234U-230Th-232Th体系定年为重点进行了讨论，并与贝加尔湖拟合沉积物岩心的测年结果进行了对比。本研究的最终目的是阐明沉积物中U和Th同位素的深度分布及其比值的变化，并探讨其对古气候变化的意义。详细测量了Hovsgol湖81 m沉积物岩心（HDP-04）的U和Th同位素深度剖面，并成功地将U系列等时线技术应用于部分层的定年。自生U的深度分布与原生产物生物标记物的深度分布具有较好的相关性，表明自生U的波动至少在IMa.3前后与冰期-间冰期旋回有较好的相关性。在水质差异较大的霍夫斯戈尔湖和贝加尔湖，从24 m到地表的沉积物u深度剖面具有相似的分布规律。