共查询到17条相似文献，搜索用时 109 毫秒
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若尔盖盆地RH孔近80万年来δ13Corg气候特征的频谱分析 总被引：2，自引：3，他引：2
运用最大熵谱方法，对若尔盖深钻８００ｋａＢ．Ｐ．以来有机碳同位素序列进行了频谱分析，结果表明；１）０－８００ｋａＢ．Ｐ该地区存在有准８０ｋａ，６０ｋａ，４１ｋａ和２０ｋａ的周期，其中４１ｋａ和２０ｋａ的周期来米氏计算的地倾角及岁差周期较一致；２）０－４８０ｋａＢ．Ｐ，以１００ｋａ周期为主，其次为４１ｋａ和２０ｋａ，与米氏计算的各天文周期相一致；３）４８０－８００ｋａＢ．Ｐ．出现有１１５ｋａ，３３ｋ 相似文献
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云南鹤庆盆地中更新世以来的孢粉记录及其植被与气候变化 总被引：5，自引：0，他引：5
通过对“中国大陆环境钻探计划”首钻——云南鹤庆深钻前155 m约800 ka以来的岩芯进行孢粉研究,探讨了云南鹤庆盆地中更新世以来的植被演替与古气候变迁．研究表明鹤庆盆地周围山地的植被在约800 kaBP至6．98 kaBP之间经历了以松为主的针叶林、山地针阔叶混交林、寒温性针叶林的多次相互演替;从6．98 kaBP开始,植被发生了转折性变化,森林植被迅速退化,以草本为主,此时开始受到人类活动的影响,人类活动表现在砍伐森林和种植农作物等方面.与植被演替相应的古气候可划分为五个大的阶段,包含多次冷暖、干湿旋回． 相似文献
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太湖沉积物-水界面生源要素迁移机制及定量化—2.磷释放的热力学机制及源-汇转换 总被引：12，自引：0，他引：12
通过对云贵高原西北部鹤庆钻孔古湖相沉积岩芯的粒度、碳酸盐含量和烧失量等指标的综合分析、研究,重建了鹤庆盆地2．78 Ma以来的古环境演化过程．岩芯磁性地层表明,鹤庆湖盆形成于约2．78 Ma．环境代用指标的综合分析显示:鹤庆盆地2．78 Ma以来有过三次大的环境转变,即2．65 Ma鹤庆湖盆积水成湖,1．55 Ma、0．99 Ma左右山盆高差两次加大,这分别与青藏运动B幕、C幕和昆黄运动耦合． 相似文献
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云南鹤庆盆地HQ钻孔剖面分析出介形类13属．32种．根据介形类丰度、分异度及百分含量的变化情况，结合孢粉、总有机碳含量(TOC)、碳氮比(C／N)、碳酸盐含量等的分布，将鹤庆盆地近15万年以来的古气候、古环境变化初步划分为5个阶段，同时又划分出若干亚阶段．总的气候特征为冷期偏湿、暖期偏干，在冷湿和暖干的宏观波动背景上存在次级波动，反映出其气候变化的区域特性．同时．各气候阶段基本可与深海氧同位素V28-38钻孔、黄土／古土壤序列邙山剖面反映的气候阶段相对比，又显示出其气候变化的协同性．在构造与气候的双重作用下．在11790aBP左右湖盆被彻底切开． 相似文献
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南疆博斯腾湖湖相沉积物碳酸盐稳定同位素,孢粉及地化元素含量的波动揭示了于１１．０￣１０．０ｋａＢＰ期间的相对冷湿的环境特征,这次变冷事件在年代上可与末次冰消期的新仙女木气候突然变冷事件相对应,虽然目前还无法圆满解释此事件的成因机制,但此事件在极端干昌的南疆博斯腾湖湖相沉积中的发现,无疑对深入认识此事件发生的全球性以及探讨其成因机制具有重要意义。 相似文献
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Preliminary analysis on the relationships between Tibetan Plateau NDVI change and its surface heat source and precipitation of China 总被引：2，自引：0，他引：2
Wei Hua GuangZhou Fan DingWen Zhou ChangJian Ni XueMin Li YongLi Wang YaQin Liu XianLun Huang 《中国科学D辑(英文版)》2008,51(5):677-685
The tectonic-sedimentary cycles and environmental evolution in Southwest Monsoon area since 2.78 Ma were reconstructed, based
on the analyses of lithology, grain size, carbonate content, loss-on-ignition (LOI) and pollen in a 737.72 m sediment core
from the Heqing Basin, China. The results indicated that the lake basin was formed in about 2.78 Ma. Continuous lacustrine
sediment was preserved since 2.65 Ma. Three stages of tectonic-sedimentary cycle were revealed, which were 2.78–1.55, 1.55–0.99
and 0.99–0 Ma. The environmental evolution in Heqing area was influenced by uplift of the Qinghai-Tibetan Plateau, the resulting
variation of Southwest Monsoon and the earth orbital-scale periodicity.
Supported by the Key Projects of the National Natural Science Foundation of China (Grant Nos. 40331003 and 40625007) 相似文献
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Palynological evidence for vegetational and climatic changes from the HQ deep drilling core in Yunnan Province, China 总被引：6，自引：0，他引：6
The high-resolution pollen study of a 737.72-m-long lake sediment core in the Heqing Basin of Yunnan Province shows that the vegetation and climate of mountains around the Heqing Basin went through six obvious changes since 2.780 Ma B.P. Namely, Pinus forest occupied most mountains around the studied area and the structure of vertical vegetational belt was simple between 2.780 and 2.729 Ma B.P., reflecting a relatively warm and dry climate. During 2.729―2.608 Ma B.P., the areas of cold-temperate conifer forest (CTCF) and Tsuga forest increased and the structure of vertical vegetational belt became clear. According to percentages of tropical and subtropical elements growing in low-altitude regions rifely increased, we speculate that the increase of CTCF and Tsuga forest areas mainly resulted from strong uplift of mountains which provided upward expanding space and growing condition for these plants. Thus, the climate of the low-altitude regions around the basin was relatively warm and humid. Between 2.608 and 1.553 Ma B.P., Pinus forest occupied most mountains around the studied area and forest line of CTCF rose, which reflects a moderately warm-dry climate on the whole. During 1.553―0.876 Ma B.P., the structure of vertical vegetational belt in mountains around the studied area became complicated and the amplitude of vegetational belts shifting up and down enlarged, which implies that the amplitude of climatic change increased, the climatic associational feature was more complex and the climate was moderately cold at a majority of the stage. During 0.876―0.252 Ma B.P., there were all vertical vegetational belts existing at present in mountains around the studied area. The elements of each belt were more abundant and complex than earlier. At different periods in the stage vertical vegetational belts occurred as expanding or shrinking, and alternated each other. The amplitude of vegetational belts shifting up and down was the maximum in the whole section. This change suggests that the amplitude of climatic change was evidently larger than earlier, but the frequency reduced and the climatic associational feature was more complex. From 0.252 Ma B.P. to the present, the most time was characteristic of the expanding of Pinus forest and semi-humid evergreen broad-leaved forest (SEBF) in mountains around the studied area, while expanding time of other vegetational belts was very short, which reflects a smaller amplitude of cold and warm fluctuation. On the basis of the six obvious cycles of vegetational and climatic changes, there were still many times of secondary vegetational successions and climatic oscillations. Based on the above analysis, the forcing mechanism of vegeta-tional succession and climatic change in the Heqing Basin is further discussed. It is primarily consid-ered that main influential factors were exterior factors such as orbital parameters, etc., but the uplift of the Qinghai-Tibet Plateau played a very important function for environmental changes in the Heqing Basin at two times obvious increase of vertical vegetational belts and three climatic transitions. 相似文献
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《中国科学:地球科学(英文版)》2021,(8)
Obtaining a continuous sedimentary record of Cenozoic East Asian paleoclimate change is key to understand the origin, evolution and driving mechanism of the East Asian monsoon and climate change. Based on the continuous Cenozoic fluvial and lacustrine sedimentary sequence in the Weihe Basin, central China, we carried out research on the content and crystal parameters of clay minerals. The paleoclimate change since the middle Eocene was reconstructed accordingly. The results show that smectite and illite are the dominant clay minerals in fluvial-lacustrine sediments of Weihe Basin. The crystallinity of illite,the chemical index of illite, the ratio of smectite to illite and chlorite decrease gradually, which indicates that chemical weathering in the Weihe River watershed stepwise weakened since the middle Eocene, under the background of a semi-arid and semi-humid climate. The formation of palygorskite may be affected by a weak diagenesis. In this case, the content of smectite and the illite crystallinity caused by the weathering in the corresponding period may be actually higher than that of the current,which indicates that the climate in the Weihe Basin region was relatively warm and humid from the middle Eocene to Pliocene.With the decrease of Cenozoic global temperature and the continuous accumulation of sediments, the intensity of chemical weathering in the Weihe Basin gradually weakened, and the East Asian monsoon climate gradually evolved until becoming dry in the Quaternary. Evidence from clay minerals also indicates that the aridification in the Weihe Basin from the late Eocene to the Oligocene may be a response to the global cooling event at the Eocene-Oligocene transition. 相似文献
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A comparative study of the atmospheric circulations associated with rainy-season floods between the Yangtze and Huaihe River Basins 总被引：1，自引：0，他引：1
Here we present the results from the composite analyses of the atmospheric circulations and physical quantity fields associated with rainy-season for the selected floods cases over the Yangtze and Huaihe River basins for the 21 years(1990–2010),using the daily rain gauge measurements taken in the 756 stations throughout China and the NCEP/reanalysis data for the rainyseasons(June–July)from 1990 to 2010.The major differences in the atmospheric circulations and physical quantity fields between the Yangtze and Huaihe River basins are as follows:for flooding years of the Yangtze River Basin,the South Asia high center is located further east than normal,the blocking high over the Urals and the Sea of Okhotsk maintains,and the Meiyu front is situated near 30°N whereas for flooding years of the Huaihe River Basin,the South Asia high center is further west than normal,the atmospheric circulations over the mid and high latitudes in the Northern Hemisphere are of meridional distribution,and the Meiyu front is situated near 33°N.In addition,there are distinct differences in water vapor sources and associated transports between the Yangtze and Huaihe River basins.The water vapor is transported by southwesterly flows from the Bay of Bengal and monsoon flows over the South China Sea for flooding years of the Yangtze River Basin whereas by southeast monsoons from the eastern and southern seas off China and monsoon flows over the South China Sea for flooding years of the Huaihe River Basin. 相似文献
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Subbarao Pichuka 《水文科学杂志》2017,62(3):467-482
An attempt is made to assess the future trend of spatio-temporal variation of precipitation over a medium-sized river basin. The Statistical Downscaling Model (SDSM, version 4.2) is used to downscale the outputs from two general circulation models (GCMs) for three future epochs: epoch-1 (2011–2040), epoch-2 (2041–2070) and epoch-3 (2071–2100). Considering the Upper Mahanadi Basin as a test bed, the study results indicate a “wetter” monsoon (June–September) and the annual increase in precipitation is 12% during epoch-3, which is consistent for both GCMs. Monthly analyses indicate that the precipitation totals are likely to increase and the magnitude of increase is greater during monsoon months than non-monsoon months. The number of month-wise daily extremes increases in most months in the year. However, the maximum percentage increase (with respect to baseline period, 1971–2000) in the number of extreme events is found in the non-monsoon months (specifically before and after the monsoon). 相似文献
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Appukuttanpillai Krishnakumar Sanal Kumar Aditya Krishnan Anoop Krishnan Nandakumar Vivekanandan Seenipandi Kaliraj Jeenu Jose 《洁净——土壤、空气、水》2023,51(2):2200382
Based on the detailed geochemical studies of 184 soil samples from Periyar River Basin (PRB), a tropical monsoon dominated river basin (5398 km2) in the southern western Ghats (WGs) of India, a baseline reference data is established. The soils are mildly acidic with sandy loam and silt loam facies in non-monsoon to sandy loam and sandy clay loam in monsoon. The mean metal concentrations follow the upper continental crust and world shale values. The Geoaccumulation index (Igeo) shows unpolluted to moderately polluted category, except for Cu, Zn, and Ba, while Enrichment Factor (EF) indicates no to minor enrichment for all elements. Contamination factor (Cf) indicates low to considerable contamination for V, Rb, Sr, Ni, and low to very high contamination for Cu, Zn, and Ba. Three significant components are extracted by Principal Component Analysis (PCA), explaining 78.09% and 74.10% of the total variance for monsoon and non-monsoon seasons. Ti, Al, Fe, Ca, Na, K, V, Cr, Ni, Sr, and Ba exhibited common source of origin while anthropogenic origin is identified for Zn and Cu. The study will provide valuable information into the pedological characteristics of WGs river basins. 相似文献