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1.
Magnetostratigraphy and palaeoclimate of Red Clay sequences from Chinese Loess Plateau 总被引:5,自引:0,他引:5
Two Red Clay profiles near Xi’an and Xifeng were investigated in an attempt to determine magnetostratigraphic and palaeoclimatic
records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma,
and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic
history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5–2.5 Ma. Stepwise
increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the
Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global
ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences
from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan
Plateau, solar radiation, global ice volume, etc.
Project supported by the National Natural Science Foundation of China and the Foundation of Xi’an Laboratory of Loess and
Quaternary Geology, Chinese Academy of Sciences. 相似文献
2.
石笋氧同位素和微量元素记录的陕南地区4200~2000a B.P.高分辨率季风降雨变化 总被引:2,自引:0,他引:2
基于陕南祥龙洞石笋XL2的19个230Th年龄、218个氧同位素分析以及896个Sr/Ca分析数据,高分辨率重建了4200~1972a B.P.期间陕南地区季风降雨变化.重建结果显示陕南地区这一时期季风降雨有显著的127~105a和57a周期,可能分别受控于太阳活动、PDO和/或AMO的变化.重建时段有3次百年尺度的干旱事件,分别发生于2200~2100a B.P.,2900~2700a B.P.和3600~3400a B.P.,其中2900~2700a B.P.干旱事件对应于北大西洋地区2.8ka冷事件.对比研究显示,尽管祥龙洞石笋和董哥洞石笋δ18O记录整体一致,但除了2900~ 2700aB.P.干旱事件之外,其他两次干旱事件在董哥洞石笋记录中并不明显.而尽管总体上祥龙洞和和尚洞石笋δ18O记录的差异要大,但XL2的3次干旱事件在和尚洞记录都有明显体现.有精确年代控制的祥龙洞、董哥洞及和尚洞石笋氧同位素记录的差异,揭示晚全新世我国季风降雨在十一百年尺度存在区域差异. 相似文献
3.
4.
Identification of Greigite in the Pliocene Sediments of Qinghai Lake and Its Geological Significance
正Objective The Qinghai Lake in North China is the largest interior plateau lake in Central Asia,and is sensitive to climate change and the environmental effects of Tibetan Plateau uplift.An almost continuous 626 m long sediment core was drilled in an in-filled part of the southern lake basin in the Scientific Drilling at Qinghai Lake.Previous 相似文献
5.
Yajie Zhang Yao Li Jing Ge Gaopeng Li Zhisheng Yu Haishan Niu 《Environmental Earth Sciences》2018,77(12):462
Drought monitoring is a key topic in environmental monitoring and assessment although there is still a need to determine the correlation between drought monitoring indices and remote sensing products. We analyzed the correlation between the self-calibrating Palmer Drought Severity Index (sc_PDSI), the Standardized Precipitation Index and the Standardized Precipitation Evapotranspiration Index (SPEI) and terrestrial water storage monitored through the Gravity Recovery and Climate Experiment (GRACE) on a monthly timescale from 2002 to 2015 in China. As a consequence of anomalies in the soil water budget, the highly significant correlation between the sc_PDSI and the GRACE satellite-observed terrestrial water storage suggested that these two datasets are the most suitable for use in monitoring droughts. In comparing the three drought indices, the sc_PDSI was introduced as a means of drought monitoring in the Yangtze, Pearl, Huaihe, Southeast and Songhua River Basins, whereas the SPEI was found to be more applicable to other major river basins, such as the Inland River Basin. These diverse spatial behaviors are caused by the differences between the hydrological droughts characterized by these three drought indices. 相似文献
6.
结合T-Matrix方法和雨滴谱仪数据反演双偏振参量,设计了一种雨滴谱反演评估方法(雨滴谱法),利用其反演结果可对双偏振天气雷达数据进行评估。将此方法应用于不同类型降水过程的雷达偏振参量数据质量评估,结果表明:满足微雨条件时,雨滴谱法与传统的微雨滴法均能有效监测由雷达系统误差导致的观测偏差,且评估结果十分接近;不满足微雨条件时,雨滴谱法评估的不同类型降水过程的雷达数据质量与满足微雨条件下的评估结果十分接近,客观证明了系统调整后雷达运行良好、数据质量稳定;不同雨强(R)情况下,雨滴谱法的评估结果具有一致性。10 mm·h-1≤R<20 mm·h-1时,雷达观测的数据质量最为稳定。该雨滴谱法适用范围广,可动态评估双偏振雷达偏振参量质量,有助于雷达调整和数据校正。 相似文献
7.
Jule Xiao Yoshio Inouchi Hisao Kumai Shusaku Yoshikawa Yoichi Kondo Tungsheng Liu Zhisheng An 《Quaternary Research》1997,47(3):277-283
The record of the biogenic silica flux (BSF, g cm−2(103yr)−1) in Lake Biwa reflects changes in diatom productivity in the lake and provides information regarding changes in paleoclimatic conditions. The BSF record of Lake Biwa demonstrates five periods over the past ca. 145,000 yr when the BSF values were significantly greater than 7.5 g cm−2(103yr)−1, and five intervals when they were lower. The data imply that paleoclimatic conditions were warmer and wetter from ca. 123,000 to 115,000, 103,000 to 95,000, 88,000 to 72,000, 57,000 to 32,000 yr B.P., and around ca. 6000 yr B.P. when the BSF values were greater, and relatively dry and cold from ca. 141,000 to 123,000 yr B.P. and during intervals between two of the five warm and wet episodes when the BSF values were lower. Time series of the BSF record can be correlated with the record of biogenic silica content in Lake Baikal and the marine oxygen isotope stages 1 through 6. Furthermore, the BSF values varied with much higher amplitude during the last interglaciation than during the last glaciation, probably implying that the diatom productivity in Lake Biwa was likewise more variable and had a larger range under interglacial conditions than under glacial conditions. 相似文献
8.
关于晚新生代准1.2Ma周期构造气候旋回 总被引:6,自引:2,他引:6
构造气候旋回的理论要点是构造作用驱动气候变化,因而不同于Milankovitch冰期气候旋回,但两者又都是受地球轨道要素控制的。本文主要根据青藏高原和黄土高原的晚新生代地质记录,以磁性地层为时间标尺,以黄道倾斜(ε)最大变幅位置为模式年龄,划分最近8Ma的准1.2Ma周期构造气候旋回的主旋回层,即MTC7、MTC6、MTC5、MTC4、MTC3、MTC2、MTC1、MTC0,它们的界线年龄分别为7.3、6.1、4.9、3.7、2.5、1.3和0.2MaBP。在此基础上,分析了青藏高原构造隆升和黄土高原风尘沉积各自显示的准1.2Ma周期的演变特征,表明它们之间具有构造驱动气候的因果关系。文中还探讨了最近7.3MaBP的古环境变迁,获得了有关晚新生代东亚季风形成演变和环境分异是在轨道气候旋回背景下受构造气候旋回控制的新认识。 相似文献
9.
The alkenone unsaturation index UK′37 has been applied to reconstruct past temperature changes in both marine and lacustrine systems. However, few studies have addressed whether the relative abundance of the C37:4 alkenone to the total C37 production (%C37:4) can reflect surface salinity changes in lacustrine systems. Here we present long-chain C37 alkenone distribution patterns in surface sediments from Lake Qinghai, China. Surface sediments were sampled over a large range of surface salinity changes (1.7-25 g/l) within Lake Qinghai and its surrounding lakes, while temperature differences at these sampling locations should be relatively small. We have found that %C37:4 varies from 15% to 49% as surface salinity decreases. We tentatively describe this %C37:4-salinity link with a general linear regression: %C37:4 = 53.4 (±7.8) − 1.73 (±0.45) × S (n = 28, r2 = 0.62), although step-wise %C37:4 changes in response to salinity variation may exist. UK′37 values vary between 0.10 and 0.16 at these sites and the inferred range of lake water temperature changes is ∼2-3 °C, suggesting that UK′37 largely reflects temperature signal across a large salinity range, consistent with previous findings that UK′37 can indicate temperature changes over a large diversity of environmental settings. We have also found that UK′37 values are correlated with salinity changes (r2 = 0.4), and thus cannot exclude potential temperature effect on %C37:4 and salinity effect on UK′37 in this study. However, even extreme estimates of temperature differences within the lake are still unable to explain the observed %C37:4 changes. We therefore suggest that %C37:4 could be used to infer past lake salinity changes at a regional scale. 相似文献
10.
不同氧化度碱性水钠锰矿氧化As(Ⅲ)和Cr(Ⅲ) 的动力学特性 总被引:1,自引:0,他引:1
用批量法研究了Mn平均氧化度分别为4.02、3.85和3.70的碱性水钠锰矿对As(Ⅲ)和Cr(Ⅲ)氧化的动力学特性。结果表明,碱性水钠锰矿氧化As(Ⅲ)和Cr(Ⅲ)先经历准一级动力学反应阶段,随后表观速率常数(kobs)逐渐减小至趋近零,达到反应平衡,kobs逐渐减小除了逆反应影响外,还与产物在矿物表面不断积累,钝化反应位点有关。初始反应阶段kobs随氧化度增加而增大,氧化As(Ⅲ)的kobs分别为: 0.095 1、0.039 6和0.007 1 min-1;氧化Cr(Ⅲ)的kobs分别为0.034 2、0.017 8和0.014 8 min-1。氧化As(Ⅲ)的初始反应阶段生成的Mn(Ⅱ)基本保留在矿物表面,对反应位点钝化大,使kobs减小速度快。而Cr(Ⅲ) 氧化初始阶段,Mn(Ⅱ)释放明显滞后于Cr(Ⅵ)释放,但随反应进行逐渐增加,与Cr(Ⅵ)释放量比值接近于反应计量比。故Cr(Ⅲ) 氧化生成Mn(Ⅱ)对位点的钝化远小于As(Ⅲ)氧化,其初始反应阶段后kobs减小速度较慢,且氧化度越高,保持一级动力学的初始反应阶段越长,kobs减小越慢。因此,水钠锰矿的Mn氧化度越高,氧化As(Ⅲ)和Cr(Ⅲ)的反应速率越快,As(Ⅲ)和Cr(Ⅲ)在碱性水钠锰矿表面氧化产物的释放行为是影响其反应动力学特性的重要因素。 相似文献