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1.
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
2.
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
3.
岱海的"中世纪暖期" 总被引：30，自引：1，他引：29
内蒙古岱海沉积物近2200a来Rb/Sr比值、CaCO3和有机碳含量的变化展现了包括中世纪暖期（MWP）及小冰期（LIA）等典型气候事件在内的环境演化过程,总体表现为暖期的沉积物Rb/Sr比值低,冷期的则高：CaCO3和有机碳含量则相反。这里,以单一流域化学风化记录表明我国北方存在明显的中世纪暖期,发生时间约900－1200aB.P..主要环境特征表现为流域化学风化的显著增强（低Rb/Sr比值）、生物生产力逐步提高（高有机碳）、湖泊水位大幅度抬升的湖泊沉积记录,其间经历的化学风化是近两千年内最强的,并且其发生时间与全球其他地区基本一致。 相似文献
4.
湖泊沉积物中元素相态的连续提取分析—以岱海为例 总被引：7，自引：1，他引：6
如何利用湖泊/海洋沉积物地球化学代用指标有效地指示环境很大程度取决于元素的来源及其在沉积物中赋存形态的确定.对位于半干旱区的内蒙古岱海14个沉积物样品的连续提取实验及18个元素在水可溶态、可交换态、碳酸盐结合态、铁锰氧化物结合态、有机物结合态及残留态等六种赋存相态中含量变化进行了测试和研究,结合沉积物的矿物组成,结果表明在岱海流域内只经历了较弱的化学风化过程,除了Ca和Sr外,其他元素主要赋存于残留态中,只发生了很小程度的活化溶解.受元素亲合性和湖水物理化学状态的制约,出溶的Sr与Ca的赋存相态基本一致,而出溶的Pb、Be、Co、Cu、K、Mn、Fe等元素则与自生碳酸盐、有机质表现出一定的亲合性.元素在不同赋存相态中分布为地球化学环境代用指标的提取和解释提供了机理性的实验依据. 相似文献
5.
湖泊沉积物的磁化率、频率磁化率及其古气候意义—以青海湖、岱海近代沉积为例 总被引：28，自引：9，他引：28
湖泊沉积物的磁性参数是古气候、古环境的重要代用指标。通过对青海湖QI5孔和岱海DH32孔短岩心的磁化率、频率磁化率的研究,并与地球化学参数等其它资料对比,探讨了以上两个湖区历史时期古气候变化规律;论证了用磁化率、频率磁化率作为古气候、古环境指标的可靠性和敏感性;并对其变化机制进行了初步探讨。 相似文献
6.
湖泊沉积物的磁化率、频率磁化率及其古气候意义—以青海湖、岱海近代沉积为例 总被引：15，自引：3，他引：12
湖泊沉积物的磁性参数是古气候、古环境的重要代用指标。通过对青海湖QI_5孔和岱海DH_(32)孔短岩心的磁化率、频率磁化率的研究,并与地球化学参数等其它资料对比,探讨了以上两个湖区历史时期古气候变化规律;论证了用磁化率、频率磁化率作为古气候、古环境指标的可靠性和敏感性;并对其变化机制进行了初步探讨。 相似文献
7.
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
8.
Variations in chemical compositions of the eolian dust in Chinese Loess Plateau over the past 2.5 Ma and chemical weathering in the Asian inland 总被引：5，自引：0，他引：5
Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of
the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase
of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion
of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from
a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters
(such as CIA values, Na/K, Rb/Sr and87Sr/86Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess
deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that
the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change. 相似文献
9.
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
10.
Quantitative measurements on the paleo-weathering intensity of the loess-soil sequences and implication on paleomonsoon 总被引：2，自引：0，他引：2
The loess-soil sequences in northern China provide a near continuous record of Quaternary paleoclimate. The pedogenetic intensity
of the sequences is closely linked with the variations of the East Asian summer monsoon. In this study, 2181 samples from
the Changwu and Xifeng loess sections are analyzed and two high-resolution paleo-weathering timeseries of the last 1.2 Ma
are generated, using the ratio of CBD extractable free Fe2O3 (FeD) versus the total iron (FeT). This new index is compared with micromorphological features, low-frequency magnetic susceptibility,
frequency-dependent magnetic susceptibility, and the Rb/Sr ratio[5,6]. The results suggest that the FeD/FeT ratio is able to better reflect the degree of soil development. Since the chemical
weathering of loess in the Loess Plateau region mainly depends upon the summer precipitation and temperature under modern
climate condition, which are closely associated with strength of summer monsoon, and the chemical weathering intensity of
loess primarily reflects the variations of the summer monsoon circulation. 相似文献
11.
12.
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
13.
湖泊沉积物是记录气候演化信息的重要载体之一,在探讨过去气候变化过程研究中发挥重要作用.然而,沉积物中的许多代用指标对气候的指示意义存在多解性,不同指标所反映的环境信息相互之间有时会存在矛盾.为了能够更准确地解读湖泊沉积物中指标所记录的环境变化信息,开展现代湖泊沉积物指标与环境之间的关系研究,深入探讨各指标对环境变化的响应机制尤为关键.本文选取青藏高原东南部巴松措湖泊表层沉积物作为研究对象,利用210Pb与137Cs比活度检测结果建立年代序列,对沉积物中粒度、磁化率、有机质含量等指标进行分析,揭示巴松措现代沉积过程.结合沉积物粒度端元组分分析结果,并将不同指标变化与林芝气象站所记录的数据资料进行对比,得出以下主要结论：该地区沉积物来源主要包括径流搬运的冰川碎屑物质和来自青藏高原南部、西南部上空悬浮于大气中的风成物质两部分;其中,通过风力搬运的物质输入主要集中在冬半年,受季节性风向及风速变化影响明显;径流受到冰雪融水与夏季降水的补给,因此通过径流搬运的物质输入量受到温度与降水综合影响;湖泊中磁性矿物碎屑的产生和输入主要受区域降水量影响的流域侵蚀速率变化控制,该湖泊沉积物磁化率波动可以有效的指示该地区降水量变化;沉积物中总有机碳含量和总氮含量变化主要反映湖泊自身初级生产力的变化,对区域温度变化的响应显著. 相似文献
14.
Diatom assemblages and quantitative reconstruction for paleosalinity from a sediment core of Chencuo Lake,southern Tibet 总被引：3，自引：0，他引：3
Changing salinity in lakes and especially in closed lakes depends mainly on the balance between precipitation, runoff and evaporation in arid and semi-arid areas, hence influencing lake levels di-rectly[1-4]. Past salinity has been recovered by a vari-ety of environmental indicators from lake sediments such as diatoms, chironomids, ostracoda, isotopes of ostracoda shells, geochemistry, and isotopes of authi-cabonates[3,5—10]. Recently, with extensive data-base study on diatom-salinity transfe… 相似文献
15.
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
16.
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
17.
Jorge Feliciano Ontiveros-Cuadras Ana Carolina Ruiz-Fernández Joan-Albert Sanchez-Cabeza Libia Hascibe Pérez-Bernal Michel Preda Federico Páez-Osuna 《国际泥沙研究》2018,33(2):183-190
Two lead-210 (210Pb) dated sediment cores from Chapala Lake were studied to identify the mineral composition of the sediments and to discuss its relation with trace metals. Minerals and trace metals reflected the domain of volcanic rocks (i.e. basalts, rhyolite and andesite) that characterize Chapala Lake and the Lerma River watershed. Redundancy analyses (RDA) were used to identify the sedimentary variables (magnetic susceptibility, organic matter, sand content, and mineral composition) that could be related to elemental composition. Despite the distance between the two cores (7.3 km) and hydrodynamic circulation the RDA showed that the main mechanism that controls the input of mineral species, and, therefore, element distributions in the lacustrine sediment of Chapala Lake, is related to the weathering of volcanic rocks in the Lerma-Chapala watershed, the consequent runoff and transport of fine grained catchment materials, and later in-lake processes. These findings highlight the importance of controlling watershed erosion to contribute to the improvement of the environmental quality of the lake. 相似文献
18.
Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China 总被引：15，自引：0，他引：15
J. A. Holmes 《中国科学D辑(英文版)》2006,49(12):1280-1290
Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating re- sults. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000―1500 AD, a humid climate during the Little Ice Age (LIA) (c. 1500―1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indi- cate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concen- trations, decreased carbonate content and increased grain size. The humid period during the LIA re- corded by the Bosten Lake sediments is representative of arid central Asia and is supported by nu- merous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipita- tion increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA. 相似文献
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20.
Mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested, metabasaltic Hauver Branch watershed in north‐central Maryland, USA. Previous studies of Hauver Branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering, including biomass. More equations in the mass‐balance matrix were added using existing mineralogic information. The stoichiometry of a deciduous biomass term was determined using multi‐year weekly to biweekly stream‐water chemistry for a nearby watershed, which drains relatively unreactive quartzite bedrock. At Hauver Branch, calcite hosts ~38 mol% of the calcium ion (Ca2+) contained in weathering minerals, but its weathering provides ~90% of the stream water Ca2+. This occurs in a landscape with a regolith residence time of more than several Ka (kiloannum). Previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream Ca2+/Na+ ratios. The relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone. Of the carbon dioxide (CO2) consumed by mineral weathering, calcite is responsible for approximately 27%, with the silicate weathering consumption rate far exceeding that of the global average. The chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles, and therefore, climate, on geological timescales. Based on carbon‐balance calculations, atmospheric‐derived sulfuric acid is responsible for approximately 22% of the mineral weathering occurring in the watershed. Our results suggest that rising air temperatures, driven by global warming and resulting in higher precipitation, will cause the rate of chemical weathering in the Hauver Branch watershed to increase until a threshold temperature is reached. Beyond the threshold temperature, increased recharge would produce a shallower groundwater table and reduced chemical weathering rates. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献