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1.
小冰期弱化学风化的湖泊沉积记录 总被引：38，自引：3，他引：38
封闭湖泊沉积物的低Sr含量、低磁化率和高Rb/Sr比记录了单一湖泊流域在以冷干为特征的小冰期气候环境下经历的弱化学风化过程. 由于Rb, Sr在表生环境下不同的地球化学行为, 内陆湖泊沉积物中Rb/Sr比值是沉积记录中具有明确气候意义的有效指标. 与热带气候和现代温湿环境下化学风化受降水控制不同, 湖泊沉积岩芯的磁化率、Sr含量与冰芯δ18O一致的变化趋势揭示了小冰期最盛期极弱的化学风化过程是受气温控制的. 而随着气温的升高, 化学风化强度逐渐受降水的制约. 相似文献
2.
XRF岩芯扫描技术是古气候研究中的重要工具,其中所获得的基于湖泊岩芯的Rb/Sr比值在古气候研究中被广泛用于表征流域化学风化的强度.然而在不同的地质背景下,影响Rb/Sr比值变化的因素不同,使得其古气候解释意义较为复杂.本研究选取青藏高原东部若尔盖盆地的湖泊沉积物岩芯,获取了高分辨率的XRF岩芯扫描Rb/Sr比值、传统XRF测试Rb/Sr比值、化学蚀变指数CIA以及其他古气候替代指标,开展了不同指标间的对比分析.研究结果显示:(1)在细粒物质为主的沉积段,岩芯扫描Rb/Sr和CIA可作为指示化学风化强度的可靠指标;(2)岩芯扫描Rb/Sr和CIA的低值对应于总有机碳含量、乔木花粉含量、碳酸盐含量和C/N比值的高值,综合分析各古气候代用指标的指示意义,认为岩芯扫描Rb/Sr可指示亚洲夏季风强度的变化;(3)受"粒度效应"和测试精度限制,若尔盖岩芯25~0.3和56~47m沉积段的扫描Rb/Sr数据不适用于化学风化强度的重建,在今后若尔盖盆地古气候演化历史的重建工作中应加以注意.本研究指出,当涉及XRF岩芯扫描Rb/Sr在其他研究区古气候分析中的应用时,应通过多指标间的相互验证来明确其特有的古气候指示意义. 相似文献
3.
近1800年来云南洱海流域气候变化与人类活动的湖泊沉积记录 总被引：12，自引：3，他引：9
对云南洱海湖泊岩芯沉积物进行了多环境指标（年代学、色素、硅藻、有机碳稳定同位素、磁化率、化学元素）的分析,建立了近１８００年来云南洱海流域气候与环境变化的序列,气候演化具有暖干、冷湿交替的组合呈些特征气候阶段如中世纪温暖期、小冰期气候特征在洱海源泊沉积记录中均有反映,洱海湖泊上沉积记录的气候暖干－冷湿交替变化规律,反映了西南委风影响下的气候演化特征,湖泊沉积记录中包含丰富的人类以的信息,磁化率,元 相似文献
4.
花岗岩化学风化过程中的Sr同位素演化——矿物相对风化速率的影响 总被引：9，自引：2，他引：9
对江西南部黑云母花岗岩和花岗斑岩风化剖面中Sr同位素体系的研究结果显示,花岗岩化学风化过程中,Rb,Sr之间发生明显分异,风化早期释放出的Sr/Si,Sr/Ca比值大于母岩值,Sr的淋失速率大于Si,Ca,K,Rb等营养离子.主要含Sr(和Rb)矿物相对风化速率的动态变化,导致花岗岩风化壳及其释放出Sr的87Sr/86Sr比值随时间波动变化黑云母、斜长石和钾长石的先后风化,导致风化残余物的87Sr/86Sr比值历经下降-升高-下降的波动变化,最终趋于稳定.这进一步说明,当用锶同位素示踪流域和全球范围的生物地球化学过程时,必须慎重考虑Sr从溶解固相中的优先释放以及含Sr矿物相对风化速率的变化导致的87Sr/86Sr比值的波动. 相似文献
5.
最近800ka洛川黄土剖面中Rb/Sr分布和古季风变迁 总被引：63，自引：4，他引：59
对洛川剖面中Rb和Sr分布规律的研究表明不同时代的黄土和古土壤中Rb和Sr分布特征存在明显差别 ,按Rb/Sr比值可以清晰地区别出剖面中的黄土层和古土壤层 ;在风化成壤过程中Rb是稳定组分 ,Sr是活动性组分 ,Rb/Sr比值的变化反映了风化成壤作用的强度 ,因而实际上记录了夏季风环流强度的大小 ;剖面中最近 80 0kaRb/Sr比值时间序列与SPECMAP十分吻合 ,揭示了全球冰量大小可能是控制夏季风环流强度变化的主要动力学因素 . 相似文献
6.
2008年5月12日里氏7.9级汶川大地震引发了超过56000多个山体滑坡，在龙门山地区产生巨量的碎屑物质，极大地影响了流域的地表过程.然而，地震对河流碎屑物质组成及沉积过程的改变却知之甚少.紫坪铺水库超高沉积速率（平均74 cm/a）的沉积物完整记录了汶川地震前后的沉积过程，为研究2008年汶川地震对流域地表物质搬运及沉积物组成的影响提供了宝贵的素材.本研究测试了汶川地震前后紫坪铺水库沉积物的Sr同位素以及元素组成，结果表明其在地震之后均发生了显著变化.震后沉积物87Sr/86Sr与Rb/Sr比值同步降低，并且和沉积物化学蚀变指数（CIA）呈正相关性，反映了地震滑坡导致的新鲜物质对沉积物的贡献，特别是地震后强径流的2010—2011年.地震前后沉积物组成的差异性，为利用沉积物反演水文气候和构造事件及其环境效应提供了基础和潜在指标. 相似文献
7.
南四湖沉积剖面中色素与有机碳同位素特征的古环境意义 总被引：7，自引：1，他引：6
湖泊沉积物中的色素含量与种类是研究湖泊初始生产力和湖泊环境的有效手段之一．而有机碳同位素比值反映了沉积有机物来源信息．本文在对南四湖沉积剖面中总有机碳含量分析的基础上,测定了有机碳的同位素比值,同时通过剖面中色素指标的分析,揭示该湖泊环境演化历史．研究表明,南四湖成湖时代为2．45kaB．P,成期水体主要来自黄河泛滥;其次,南四湖东西沉积环境差异较大,西部（微山湖）主要受黄河泛滥影响,东部（独山湖）则为山麓碎屑沉积;近代南四湖中蓝藻大量繁盛,湖泊具有逐步向富营养化发展的趋势． 相似文献
8.
为明确长江中游地区湖泊沉积物中多环芳烃（PAHs）的分布特征、来源及其生态风险，于2018年7月采集了该地区12个湖泊的表层沉积物样品.采用气相色谱-质谱联用仪（GC-MS）测定了沉积物中16种PAHs的含量.结果表明：12个湖泊沉积物中均检测出16种优控PAHs，PAHs的总含量在572.7~1766.2 ng/g （dw）之间（均值为976.5±285.0 ng/g （dw））.武汉市东湖沉积物中PAHs含量最高，达到1634.8±111.4 ng/g （dw）.与国内外其他地区湖泊沉积物相比，长江中游地区湖泊沉积物中PAHs含量高于国内偏远地区的抚仙湖、青海湖及博斯腾湖，低于东部地区的巢湖、太湖及美国经济工业发达地区的湖泊.根据单体PAH的聚类分析结果，12个湖泊可以分成3种类型，类型1主要以低环为主，占比为64.04%±7.02%，类型2低环和中高环分布相对平均，分别为50.76%±5.17%和49.24%±5.17%，类型3低、中、高环分布相对平均，占比分别为35.35%±3.56%、26.17%±0.45%和38.48%±3.84%.综合该区域PAHs的分布特征及异构体比值法与主成分分析法的结果表明，类型1湖泊沉积物中PAHs主要来源为煤炭、木材等生物质的燃烧源；类型2和类型3湖泊沉积物中PAHs主要来源为煤炭、木材等生物质的低温燃烧以及机动车等燃烧汽油、柴油的尾气排放和工业炼焦等化石燃料的高温燃烧源.沉积物中PAHs与总有机碳（TOC）之间显著的相关性表明，沉积物中TOC含量是影响长江中游湖泊沉积物中PAHs归趋分布的主要因素.长江中游流域湖泊沉积物中PAHs的RQNCs值均小于800，且RQMPCs值大于1的风险商值法生态风险评价结果表明，长江中游流域湖泊表层沉积物中PAHs整体呈中等风险水平. 相似文献
9.
10.
悬浮颗粒物和沉积物是湖泊有机污染物的主要承载物质,其稳定同位素研究对有效识别有机质污染导致的湖泊富营养化具有重要意义.本研究选取乌梁素海为研究区,于2019年4月（融冰期）、7月（夏灌期）和10月（秋灌期）对湖区及入湖渠道的表层沉积物和悬浮颗粒物中有机碳的δ13C、C/N比及总有机碳（TOC、POC）和总氮（TON、PON）含量进行测定分析,联合采用δ13C、C/N及同位素多元混合模型研究湖泊有机碳来源及其贡献率.结果表明,乌梁素海悬浮颗粒物有机碳δ13CPOC的变化范围为-23.29‰~-29.75‰,呈现10月>4月>7月、入湖渠道>湖区的趋势,悬浮颗粒物POC/PON比变化范围为4.10~21.35,呈现出4月<7月<10月的时间变化,悬浮颗粒有机质主要来源于浮游植物（51.59%）、入湖渠道泥沙（34.60%）和大型水生植物（13.76%）.沉积物有机碳δ13CTOC变化范围为-27.58‰~-22.68‰,呈现4月<10月<7月的变化,沉积物TOC/TON比变化范围为3.06~23.77,时空变化明显,沉积物有机质则主要源于入湖渠道挟带的泥沙,贡献达72.79%以上,而浮游植物与大型水生植物的贡献率相差较小,分别为11.85%和15.36%.本研究可以初步判定受入湖渠道影响的富营养化湖泊中悬浮颗粒物和沉积物有机碳来源,为改善湖泊有机污染和研究有机碳来源提供更多理解. 相似文献
11.
Variation in the rubidium to strontium (Rb/Sr) ratio of the loess–palaeosol sequences has been proposed to reflect the degree of pedogenesis and weathering in the northwestern region of China. To characterize the Rb/Sr ratio of the dissolved loads of a single catchment, we analysed a 12·08 m sediment core from Daihai Lake in Inner Mongolia, north China. Dating control was provided by 210Pb, 137Cs and AMS‐14C. Sequential extraction experiments were conducted to investigate the concentrations of Rb and Sr on various chemical fractions in the lake sediments. Down‐core variation in the Rb/Sr ratios provides a record of Holocene weathering history. From 9 to 3·5 ka bp , accelerated chemical weathering was experienced throughout the Daihai catchment under mainly warm and humid conditions, and this reached a maximum at c. 5 ka bp . However, weathering was reduced between c. 8·25 and 7·90 ka bp , which may reflect the global 8·2 ka cooling event. After c. 2·5 ka bp , increased Rb/Sr ratios with higher frequency of fluctuations indicate reduced weathering within the Daihai catchment. The highest Rb/Sr ratios in the Little Ice Age lake sediments indicate the weakest phase of Holocene chemical weathering, resulting from a marked reduction in Sr flux into the basin. The Rb/Sr record also shows an enhancement of chemical weathering under today's climate, but its intensity is less than that of the Medieval Warm Period. Increased Rb/Sr in lake sediment corresponding to reduced catchment weathering is in striking contrast to Rb/Sr decrease in the glacial loess layers in the loess–palaeosol sequence. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
12.
Lakes in arid zone are sensitive to climatic changes. The lacustrine sediment sequence in Sogo Nur has well and truly recorded climatic events such as the Sui-Tang Dynasty Warm Period, the Song-Liao Dynasty Cold Period, the Medieval Warm Period, the Little Ice Age and the 20th Century Warm Period. Commonly, the climate in warm Periods was relatively humid, accordingly the lake area extended and water level rose, and vice versa. Apart from climatic change, human activity is also an important factor of influencing lake vicissitude, and they played the dominant role alternatively during different periods; the factor of climatic change predominated in historical period, while since the beginning of the 20th century the utilization of water resources by human has became decisive. 相似文献
13.
Lakes in arid zone are sensitive to climatic changes. The lacustrine sediment sequence in Sogo Nur has well and truly recorded climatic events such as the Sui-Tang Dynasty Warm Period, the Song-Liao Dynasty Cold Period, the Medieval Warm Period, the Little Ice Age and the 20th Century Warm Period. Commonly, the climate in warm Periods was relatively humid,accordingly the lake area extended and water level rose, and vice versa. Apart from climatic change, human activity is also an important factor of influencing lake vicissitude, and they played the dominant role alternatively during different periods; the factor of climatic change predominated in historical period, while since the beginning of the 20th century the utilization of water resources by human has became decisive. 相似文献
14.
The X-ray fluorescence(XRF)core-scanned Rb/Sr ratios of lake sediments have been widely used as a proxy for chemical weathering intensity and past climate change.However,some factors could affect Rb/Sr ratios,causing misinterpretation and limiting its application.In this study,we present a high-resolution XRF core-scanned Rb/Sr record of core ZB13-C1 from the Zoige Basin in the eastern Tibetan Plateau.To validate its application,we correlated this record with the chemical index of alteration(CIA)and other paleoclimatic proxies.Our results showed that(1)the core-scanned Rb/Sr ratios and CIA were reliable proxies of chemical weathering intensity in fine-grained sedimentary sequences;(2)the low values of corescanned Rb/Sr ratios and CIA were significantly correlated with high total organic carbon content,arboreal pollen content,carbonate content,and C/N ratios,confirming its reliability as a proxy for the Asian summer monsoon intensity;(3)the corescanned Rb/Sr ratios at core depths of 25–0.3 and 56–47 m were unable to reliably reflect chemical weathering intensity due to both the grain-size effect and the low test accuracy.Our study highlights the need for mutual verification of multiple indicators before accurately applying Rb/Sr as a paleoclimatic proxy in other similar study areas. 相似文献
15.
Low magnetic susceptibility, low Sr content and hence high Rb/Sr ratio in the lake sediment sequence indicate a weak chemical
weathering process under arid and cold climate of the Little Ice Age in a single closed lake watershed. According to different
geochemical behavior between rubidium and strontium in earth surface processes, variation of Rb/Sr ratios in the lake sediment
sequence can be used as an effective geochemical proxy with definite climatic significance of chemical weathering in watershed.
Unlike chemical weathering process in tropic zone and modern temperate-humid climate, concordant changes in both Sr content
and magnetic susceptibility with δ18O values of Dunde ice core suggest that the weak chemical weathering was controlled by air temperature during the Little Ice
Age maximum. After the Little Ice Age, chemical weathering intensity was controlled also gradually by precipitation with increasing
in temperature. 相似文献
16.
Zhangdong Jin Sumin Wang Ji Shen Enlou Zhang Fuchun Li Junfeng Ji Xinwei Lu 《地球表面变化过程与地形》2001,26(7):775-782
Because of the different geochemical behaviour of rubidium and strontium in earth surface processes, variations of the Rb/Sr ratios in lake sediments were used as a geochemical proxy of chemical weathering and past climate in a single watershed. Low magnetic susceptibility, low CaCO3, low Sr concentration and, hence, high Rb/Sr ratio in the lake sediments indicate weak chemical weathering under a cold but wet climate during the Little Ice Age (LIA) in the closed Daihai Lake watershed. The concordant change in both Sr and CaCO3 concentrations with δ18O values in the Dunde ice core suggests that weak chemical weathering during the wet LIA was controlled by air temperature. After the LIA, however, precipitation played a dominant role in chemical weathering. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
17.
Distribution of Rb and Sr in the Luochuan loess- paleosol sequence of China during the last 800 ka 总被引：4，自引：0，他引：4
The concentrations of Rb and Sr, and magnetic susceptibility in loess and paleosol samples from the Luochum profile have been
measured. The loess units deposited in different geological periods display a very similar pattern of Rb and Sr distribution
while paleosol units exhibit a dramatic increase in the Rb/Sr ratio, ranging from 20% to 120% in increase amplitude. Owing
to different geochemical behavior of the two elements, Rb appears to be immobile while Sr appears to be mobile in the processes
of weathering and pedogenesis. So variations of the Rb/Sr ratio in the loess-paleosol sequences could reflect intensities
of weathering and pedogenesis, thus recording the relative wind strength of the East Asian summer monsoon circulation. This
could be supported by the high degree of cornlation between the Rb/Sr ratio and the magnetic susceptibility. A continuous
record of the Rb/Sr ratio in the Luochuan profile over the last 800 ka bears a striking resemblance to the δ18 O curve of the deep sea sediments and is in accordance with the SPECMAP chronology. Such similarity between the terrestrial
and the deep sea records suggests that variability in global ice volume is a primary dynamic factor controlling long-term
changes of the East Asian summer monsoon intensity.
Project supported by the National Natural Science Foundation of China (Grant No. 49725307). 相似文献
18.
19.
Optically stimulated luminescence dating of aeolian sand in the Otindag dune field and Holocene climate change 总被引：3，自引：0，他引：3
YaLi Zhou HuaYu Lu Mason Joseph XiaoDong Miao Swinehart James Goble Ronald 《中国科学D辑(英文版)》2008,51(6):837-847
The dune system in Otindag sand field of northern China is sensitive to climate change, where effective moisture and related vegetation cover play a controlling role for dune activity and stability. Therefore, aeolian deposits may be an archive of past environmental changes, possibly at the millennial scale, but previous studies on this topic have rarely been reported. In this study, thirty-five optically stimulated luminescence (OSL) ages of ten representative sand-paleosol profiles in Otindag sand field are ob-tained, and these ages provide a relatively complete and well-dated chronology for wet and dry varia-tions in Holocene. The results indicate that widespread dune mobilization occurred from 9.9 to 8.2 ka, suggesting a dry early Holocene climate. The dunes were mainly stabilized between 8.0 and 2.7 ka, implying a relatively wet climate, although there were short-term penetrations of dune activity during this wet period. After ~2.3 ka, the region became dry again, as inferred from widespread dune activity. The "8.2 ka" cold event and the Little Ice Age climatic deterioration are detected on the basis of the dune records and OSL ages. During the Medieval Warm Period and the Sui-Tang Warm Period (570-770 AD), climate in Otindag sand field was relatively humid and the vegetation was denser, and the sand dunes were stabilized again. These aeolian records may indicate climate changes at millennial time scale during Holocene, and these climatic changes may be the teleconnection to the climate changes elsewhere in the world. 相似文献
20.
Beatriz Ortega Margarita Caballero Socorro Lozano Gloria Vilaclara Alejandro Rodríguez 《Earth and Planetary Science Letters》2006,250(3-4):444-458
Magnetic and non-magnetic mineral analyses were conducted on a lacustrine sequence from Lago Verde in the tropical coast along the Gulf of Mexico that covers the last 2000 years. The site witnessed the transformation of the environment since the early Olmec societies until forest clearance in the last century. Through these analyses we investigated the processes that affected the magnetic mineralogy in order to construct a model of past environmental changes, and compare this model with the archeological record and inferred climatic changes in the northern hemisphere of tropical America. Volcanic activity has played a major influence on sediment magnetic properties, as a purveyor of Ti-magnetites/Ti-maghemites, and as a factor of instability in the environment. Anoxic reductive conditions are evident in most of Lago Verde's sedimentary record.
Direct observations of magnetic minerals and ratios of geochemical (Fe, Ti), and ferrimagnetic (χf) and paramagnetic (χp) susceptibility (χ) data, are used as parameters for magnetite dissolution (χp/χ, Fe/χf), and precipitation (χf/Ti) of magnetic minerals. Intense volcanic activity and anoxia are recorded before A.D. 20, leading to the formation of framboidal pyrite. Increased erosion, higher evaporation rates, lower lake levels, anoxia and reductive diagenesis in non-sulphidic conditions are inferred for laminated sediments between A.D. 20–850. This deposit matches the period of historical crisis and multiyear droughts that contributed to the collapse of the Maya civilization. Dissolution of magnetite, a high organic content and framboidal pyrite point to anoxic, sulphidic conditions and higher lake levels after A.D. 850. Higher lake levels in Lago Verde broadly coincide with the increased precipitation documented during the Medieval Warm Period (A.D. 950–1350) in the northern tropical and subtropical regions of the American continent. For the Little Ice Age (A.D. 1400–1800), the relatively moist conditions inferred are in concordance with the glacial advances recorded in central Mexico. Higher erosion rates reflect destruction of the rainforest over the last 40 years. 相似文献