| 青藏高原北缘哈拉湖近800年来 湖泊沉积及其环境意义* |
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| 引用本文： | 曹洁,张家武,张成君,陈发虎.青藏高原北缘哈拉湖近800年来 湖泊沉积及其环境意义*[J].第四纪研究,2007,27(1):100-107. |
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| 作者姓名： | 曹洁 张家武 张成君 陈发虎 |
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| 作者单位： | 1. 山东省气候中心,济南,250031;兰州大学西部环境教育部重点实验室中德干旱环境联合研究中心,兰州,730000
2. 兰州大学西部环境教育部重点实验室中德干旱环境联合研究中心,兰州,730000 |
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| 基金项目： | 国家自然科学基金
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国家自然科学基金 |
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| 摘 要： | 文章以青藏高原北缘高山祁连山湖泊——哈拉湖作为研究对象,利用放射性核素210 Pb和137 Cs测年资料,通过对此高海拔湖泊沉积碳酸盐氧碳同位素、碳酸盐含量、总有机碳含量、磁化率等环境代用指标的分析,揭示了这一地区近800年来的气候环境变化过程。分析表明哈拉湖记录的气候环境变化经历了3个阶段:1206~1700A.D.环境较为寒冷、湿润,并有持续变湿的趋势;1700~1920A.D.环境由冷湿的状况趋向温暖干旱,1771年之后,环境保持相对稳定;1920~2002A.D.是自1206年以来最为温暖干旱的阶段。
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| 关 键 词： | 哈拉湖 湖泊沉积 碳酸盐氧碳同位素 环境变化 |
| 文章编号： | 1001-7410（2007）01-100-08 |
| 收稿时间： | 2006-02-10 |
| 修稿时间： | 2006-07-25 |
ENVIRONMENTAL CHANGES DURING THE PAST 800 YEARS RECORDED IN LAKE SEDIMENTS FROM HALA LAKE ON THE NORTHERN TIBETAN PLATEAU |
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| Cao Jie,Zhang Jiawu,Zhang Chengjun,Chen Fahu.ENVIRONMENTAL CHANGES DURING THE PAST 800 YEARS RECORDED IN LAKE SEDIMENTS FROM HALA LAKE ON THE NORTHERN TIBETAN PLATEAU[J].Quaternary Sciences,2007,27(1):100-107. |
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| Authors: | Cao Jie Zhang Jiawu Zhang Chengjun Chen Fahu |
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| Institution: | (Shandong Climate Centre, Jinan250031|Center for Arid Environment &|Paleoclimate Research, Key Laboratory of Western Chinas Environment Systems (Ministry of Education), College of Earth and Environment Sciences, Lanzhou University, Lanzhou730000 |
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| Abstract: | Being surrounded with high mountains, the Hala Lake, is a large salty lake with an altitude of 4078m in the north of the Tibetan Plateau. Due to little human impacts on the lake drainage, the Hala Lake, as a typical inland closed lake located on the Chinese monsoon transition line, can provide sensitive information on the past climatic and natural environmental changes. Plateau area has been reported to be more sensitive in response to global change than the area at lower altitudes. Here we present the result of a short core retrieved form the Hala Lake in the north of Tibetan Plateau. The short core HALA-3B-02, 75cm long, was taken with a weight sampler at water depth of 19.3m in the north-west of Hala Lake (38°20'44.8″N, 97°26'34.3″E) in July, 2002. Sediment samples from the sediment core drilled at the high-altitude Hala Lake were analyzed for a range of palaeoenvironmental indicators, which include stable isotope of oxygen and carbon of carbonates (δ13 C &; δ18 O), total organic carbon content, carbonate content as well as magnetic susceptibility. Chronology of the sediment core was determined using 210 Pb and 137 Cs. However, the 137 Cs dating result shows that the cumulating peak of the year of 1954 is hardly distinguishable due to disintegration with time. In addition, because of its diffusion and transference features, 137 Cs cumulating peak is considered improper for dating. Hala Lake chronology was thus established on dating series from 210 Pb CRS model and linear extrapolating based on bottom deposit rates. Average deposit rate of the profile under 21.5cm (corresponding to the year of 1900) is 0.187cm/a, while that above 21.5cm suddenly rises to 0.199cm/a, which is possibly relevant to more and more intense human activities since the 20th century. The lithology of the profile from bottom to 21.5cm appears to be comparatively conformed, hereby corresponding deposit rate is supposed to be 0.187cm/a. The earliest time was thus extrapolated to be 796 years before 2002A.D. , namely 1206A.D.The average time resolution reaches 11a.Mineral content was analyzed from 5 selected sediment samples by X-ray diffraction. All analyzed samples were mainly composed of authigenous aragonite and calcite. Therefore the carbonates in Hala Lake sediment are mainly authigenous. In terms of the Hala Lake, δ13 C possibly reveals drainage temperature (icebound state due to perennial low temperature) effect on exchange between atmospheric carbon dioxide and aquatic carbon. Total organic carbon content (TOC) in lake sediment stands for the biological primary production in the lake and/or the drainage. Thereby sediment TOC can reveal historical vegetation state, which is unavoidably affected by preservation condition. Carbonate content in lake sediment can indicate aquatic salinity variation and consequently indicate the environmental humidity variation indirectly. Frequency magnetic susceptibility is affected by dynamical factors in lacustrine deposition and also indirectly indicates the environmental humidity variability. Palaeoclimatic proxies show that the δ value of oxygen of carbonate varies from -3.8 ‰ to +1.9 ‰ with an average of -0.7 ‰, while the δ value of carbon is from 1.5 ‰ to 4.9 ‰, and the average is 3.3 ‰. The oxygen and carbon isotope curves change covariantly along the whole profile. The variation range of TOC is from 4.9 ％ to 2.3 ％, and the average is 3.1 ％, which seems to be relatively stable as a whole except some small fluctuations. Carbon content fluctuates between 17.0 ％ and 42.8 ％ with an average of 23.9 ％. The magnetic susceptibility, averaged at the level of 12.1×10-8m3/kg, fluctuates between 9×10-8m3/kg and 19.1×10-8m3/kg. It rises rapidly near the top. Frequency magnetic susceptibility varies with smaller magnitude, from -9.4 ％ to +12.2 ％, averaging at +3.4 ％. A palaeoenvironmental history of ca.800-year of the lake is reconstructed on the basis of multi-proxy analyses. The general environment change is from cool and wet to warm and dry. Three stages can be recognized: 1206~1700A.D. , a cool and wet climate with a gradually cooling and wetting trend. 1700~1920A.D. is a more or less fluctuating period. Coincident fluctuating of oxygen and carbon stable isotopes (δ values) indicates that there was a warming and drying period before 1771A.D. and subsequently a comparatively cool and wet period during 1780~1900A.D. 1920~2002A.D. , the warmest and driest stage. Magnetic susceptibility appears to be fluctuating on a stable level in high frequency before 1970A.D. , but rises rapidly after 1970A.D. with an ascending range of about 54 %, indicating a sharply increased anthropologic gold mining activities since 1970s. The low value of δ18 O and δ13 C as well as carbonate content corresponding to the period of 1653~1718A.D. indicates the lowest temperature and highest efficient humidity in the drainage history. This period was the coldest and wettest in the north of Qinghai-Tibet Plateau in the past ca.800 years. The δ13 C curve variability shows that the environmental state of the north of Qinghai-Tibet Plateau became the warmest and driest in the 20th century, i.e. , 20th century is the hottest 100 years during the past ca.800 years. δ18 O and δ13 C values of carbonate and carbonate content in the profile simultaneously decrease remarkably around 1925A.D. This may reflects the rapid warming occurred in China and the world in the 1920s. |
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| Keywords: | change Hala Lake lake sediment stable isotope of oxygen and carbon of carbonates environmental |
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