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| 美国西部Owens湖地球化学记录及其古气候意义 | |
| 引用本文： | 李红春,朱照宇.美国西部Owens湖地球化学记录及其古气候意义[J].第四纪研究,2002,22(6):578-588. |
| 作者姓名： | 李红春 朱照宇 |
| 作者单位： | 1. 美国南加州大学地球科学系,洛杉矶,CA90089 2. 中国科学院广州地球化学研究所,广州,510640 |
| 基金项目： | 美国国家科学基金 (批准号 :ATM - 96 15 875 )，王宽诚科研教育基金资助项目 |
| 摘 要： | 美国加州中部Owens湖的稳定同位素、稀酸可溶相锂元素浓度及其它地球化学指标揭示本区0.155MaB.P.～62500aB.P.间的气候变化。在0.155～0.140MaB.P.,0.122～0.114MaB.P.,91000～83000aB.P.和72000～62500aB.P.期间,气候冷湿,对应于深海氧同位素(MIS)6,5d,5b和4阶段。这些期间内湖泊开放,δ18 O和δ13 C无协变性,Li和有机碳浓度很低。在0.140～0.122MaB.P.,0.114MaB.P.～91000aB.P.和83000～72000aB.P.期间,气候干热,对应于MIS5e,5c和5a阶段。湖泊在这些期间内封闭,δ18 O和δ13 C有很好的协变性,封闭湖δ18 O的变化代表了湖水体积的变化。来自湖中自生镁硅酸盐的锂元素浓度的变化反映了盐度和温度的变化。Owens湖的记录与DevilsHole洞穴流石记录和格陵兰冰芯记录有很好的对比,进一步证实了终结期Ⅱ在海相记录中的年龄滞后。本文讨论了冰期与间冰期之间,美国西部和中国黄土地区气候模式的差异及其互动机制。 |
| 关 键 词： | 稳定同位素 稀酸可溶相锂 Owens湖 古气候 |
| 收稿时间： | 2002-06-26 |
| 修稿时间： | 2002年6月26日 |
GEOCHEMICAL RECORDS AND THEIR PALEOCLIMATE SIGNIFICANCE IN OWENS LAKE, WESTERN USA |
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| Institution: | 1. Department of Earth Sciences, University of Southern California, Los Angeles CA90089; 2. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 |
| Abstract: | Owens Lake is located in eastern central California within the rainshadow of the Eastern Sierra Nevada, western United States. As a closed basin lake, its hydrological and geochemical budgets were strongly influenced by climatic changes before it became a playa as a result of human activities in the 20th century. A 330 m long sediment core, OL 92, was retrieved from the depocenter of the playa by USGS in 1992. The δ18 O, δ13 C, total organic carbon (TOC), total inorganic carbon (TIC), and concentrations of 17 acid leachable elements on 443 samples from 32 to 82.45 m depth of the core exhibit climatic and hydrological condition spanning from 0 155 MaB.P. to 62 500aB.P ., with a resolution of～200 yr. In general, the rate of change in δ18 O represents the rate of change in lake volume due to climatic fluctuations, whereas variation in δ13 C reflects mainly the variations in biological productivity, nutrient supply and dissolved carbonate in the lake. For a closed basin lake, a rapidly declining lake will have its δ18 O and δ13 C both elevated, giving rise to strong δ18 O δ13 C covariance. During rapid lake level transgression, both δ18 O and δ13 C values move toward lighter values, and the lake exhibits good δ18 O δ13 C covariance. When the lake becomes an overflowed/open lake, both δ18 O and δ13 C are relatively constant, with δ18 O being close to the input δ18 O and the δ13 C being 1‰～3‰. There should be very poor δ18 O δ13 C covariance. In this case, the δ18 O gives little information on lake level change, but water temperature (hence air temperature) and δ18 O of moisture. Therefore, we can use stable isotope records to decipher lake hydrologic change hence paleoclimate. Among the 17 elements we analyzed in the acid leachable fractions of 443 salt free samples, lithium (Li), which comes chiefly from authigenic Mg hydroxy silicates, was found to have concentration variations reflecting lake salinity and climatic changes during the past. The lithium concentration is correlated well with the Greenland ice core record, indicating the effect of air temperature change on the lake salinity and silicate productivity. All proxies show that Owens Lake was overflowed (cold/wet) during marine isotope stages (MIS) 6, 5b and 4, and closed (warm/dry) during MIS 5e, 5c and 5a. The lake was partially overflowed during MIS 5d. According to the Owens Lake records, the MIS 5/6 boundary (Termination II) is around 0.140 MaB.P., supporting the Devils Hole record. The age discrepancy of Termination II between marine records and continental records indicates that a time leg may exist in the marine record in response the climatic driving force. Thus, when using marine record as a time scale to determine the chronology of a regional record, one should be aware the age discrepancy. Furthermore, the opposite precipitation regimes between the Great Basin (cold/wet) and eastern China (cold/dry) on Milankovich time scales imply a climatic teleconnection. The opposite wetness in two continents may be attributed to the extension of high latitude ice sheet pushing the summer monsoon frontal zone in China and polar jet stream in North America southward. This kind of teleconnection also appears on short time scales driving by other forces. Understanding of these teleconnection and driving force will provide us the guide lines for future climate prediction. $$$$ |
| Keywords: | stable isotopes acid leachable Li Owens Lake paleoclimate |
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