25 May 1997, Volume 19 Issue 2

    

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  Glaciers and Environments during the Last Glacial Maximum (LGM) on the Tibetan Plateau

  Shi Yafeng, Zheng Benxing, Yao Tandong

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 97-113. https://doi.org/10.7522/j.issn.1000-0240.1997.0017

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  It was 7℃ colder than present on the Tibetan Plateau during the Last Glacial Maximum (LGM) about 16～32 ka BP. Precipitation was 30%～70% of present in that time. Polar type glaciers developed extensively. The equilibrium line in the LGM was 500～300 m lower than present in the major interior part of the plateau, while a small number of temperate glaciers, subpolar type glaciers mjght exist in the eastern, southern and western edges of the plateau, with an ELA decrease of 800 m, even up to 1 000～1 200 m. According to preliminary statistics, the glaciated area on the plateau (including the surrounding high mountains) in LGM is about 350 000 km²,7.5 times larger than at present, and the ice volume on the plateau at that time was estimated to be about 87500 km³ and equivalent to a decrease of 24.2 cm of the global sea level. Permafrost developed extensively to its maximum, about 2200000 km². Lakes in the eastern part of the plateau, which remarkably depended on the monsoon precipitation, shrank or even disappeared during the LGM, while those located in the northwestern part of the plateau got their level lower than that in former interglacial stadial and higher than that during the post glacial period due to the effect of the westlies. Almost all lakes on the plateau became more salted, and several salt lakes formed in the Qaidam Basin and in the plateau proper. The conifers and broad leaved forests withdrew to the southeast margin of the plateau, while the desert and steppe covered the most part of the plateau.
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  Holocence Megathermal Environment in the Tibetan Plateau

  Liu Guangxiu, Shi Yafeng, Shen Yongping, Hong Ming

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 114-123. https://doi.org/10.7522/j.issn.1000-0240.1997.0018

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  Basic features of Holocence Megathermal environment in the Tibetan Plateau are discussed by using pollen-spore, paleobiological, paleosole, lake fluctuation, peat deposit, ice core, periglacial landforms and loess recordes from the plateau. Holocence Megathermal event took place about 9.0～3.5 ka BP. in the plateau, earier than other places of China. Starting and ending times of the Megathermal had a regional difference in inland of the plateau, in general, early in the northeastern, western and southern parts and late in the other parts. During the Megathermal, vegetation on the plateau was very different to present time, and altitude zonation of vegetation moved upforeward and forest extended. In the maximum megathermal stage, mean annual air temperature was 3～5℃ higher than that of the present, annual precipitation increased by 100～400 mm with strengthened summer monsoon, lakes extended and their levels rose with freshened water in them. In addition, highland peat formed, glaciers retreated and permafrost degraded during the Holocene Megathermal in the plateau.
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  Permafrost Evolution in the Northeastern Qinghai-Tibetan Plateau during the Last 150 000 Years

  Pan Baotian, Chen Fahu

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 124-132. https://doi.org/10.7522/j.issn.1000-0240.1997.0019

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  In the northeastern Qinghai-Tibetan Plateau, There were at least four periods in which permafrost intensive expanded during the last 150 ka BP. The first one, in which ice wedges extensively developed,was the penultimate glaciation 140 ka BP. The second was early Last Glacial(80～53 ka BP),when involution appeared in Zoige Basin. Ice wedges developed in Gonghe Basin and Qinghai Lake region in the third Period(27～23 ka BP). In the fourth period from 20 to 10 ka BP, regional difference of natural environment became very clear. Ice wedges developed in Zoige Basin and Bayanhar Mountain because of humid and cold climate. However, sand wedges appeared in the source of the Yellow River, Gonghe Basin and Qinghai Lake region due to the dry and cold climate. The altitudes of lower limits of permafrost zone in the cold periods were 1 700～1 800 m lower than the present, leaving out the tectonic uplift.
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  The Change of Thaw Bulb under Asphalt Pavement in the Region of Permafrost on the Tibetan Plateau

  Li Shuxun, Wu Ziwang

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 133-140. https://doi.org/10.7522/j.issn.1000-0240.1997.0020

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  After a highway is built with dark asphalt pavement in the region of permafrost on the Tibetan Plateau, the relationship of heat exchange between atmospher and highway surface is changed. Especially, water evaporation from highway surface greatly decreases, thus the temperature of highway surface suddenly icreseases. Then the permafrost temperature increases and the permafrost table under roadbed drops year by year. As a result, veritically unlinked condition of permafrost appears and a residual thawed layer occurs between the bottom of seasonal freezing layer and the top of permafrost (named thawing bulb). The residual thawed layer is gradually developing year by year, ground ice in permafrost layer is thawing, a settlement of roadbed appears, and the communication and transportation will suffer from the thaw bulb.
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  Dynamic Strength Characteristics and Failure Criterion of Frozen Silt

  Shen Zhongyan, Zhang Jiayi

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 141-148. https://doi.org/10.7522/j.issn.1000-0240.1997.0021

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  Under a cyclic loading with constant amplitude strain controlled by constant strain rate, dynamic strength of frozen silt increases at first with increase of static effective normal stress, reaches the peak strength at the static effective normal stress of 7～8 MPa and then decreases with further increase of static effective normal stress. The failure envelopes of dynamic strength of frozen silt under different strain rates resemble each other in shape, namely, obey the parabola failure criterion. Equivalent angle φ_e and coefficient tgφ_e of dynamic internal friction are derived in this paper, so the parabola failure criterion equation formally coincides with the linear one. φ_e is a dynamic variable one depending on temperature, strain rate, frequency and soil behaviour beside static effective normal stress. It is less than initial angle of dynamic internal friction when there is no static effective normal stress and decreases with increasing static effective normal stress. The nomogram of φ_e is also provided in this paper.
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  A Experimental Study on the Acoustic Wave Parameters of Artifical Frozen Soil

  Yang Ping, Li Qiang, Yu Chuhou

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 149-153. https://doi.org/10.7522/j.issn.1000-0240.1997.0022

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  In this article, the relation among longitudinal wave velocity, transversal one,cofficient of amplitude decay, the dynamic elestic modulus and temperature, the water content, the unit weight of frozen sand and clay are presented, according to a determination using SYC-2 rock acoustic detection device. The relations can be well described as exponent sign formulas, among them, the effects of unit weight on velocity, amplitude decay and dynamic elestic modulus are greatest. Then, it is temperature and water content by turns. The attenuation coeffisent of amplitude is more sensitive than longitudinal wave velocity to variation of physical properties of frozen soil. The difference between forzen sand and caly, and the acoustic wave properties of frozen soil varying with load and loading duration is studied, too.
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  Grey Prediction Method on Snowmelt Runoff in the Hexi Area

  Lan Yongchao, Zeng Qunzhu

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 154-160. https://doi.org/10.7522/j.issn.1000-0240.1997.0023

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  The Hexi area is an important place of grain production The peroid from March to June when snowmelt runoff occupys a great proportion in stream flow is a high time of irrigation in this area In this paper, two forecast models on the base of GM (0, N) and GM (1, 1) are presented and they are used for the mid and long-range forecast on snowmelt runoff, which may provide an scientific basis for making rational use of water resources The two forecast models are very accurate in the practical application.
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  Estimation of Lake Evaporation by Stable Isotopic Ratio

  Zhang Xinping, Yao Tandong

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 161-166. https://doi.org/10.7522/j.issn.1000-0240.1997.0024

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  According to the measured stable isotopic ratio data and relevant hydrometeorological data, the mean annual evaporation, 877 mm, in the Qinghai Lake was calculated by a stable isotopic model The calculated value is basically equivalent to 904 6 mm, measured evaporation during the same period The simulations show that stable isotopic ratios in different natural waters have different impact on lake evaporation, i e, the stable isotopic ratio in precipitaiton and inflows is in proportion to evaporation, and that in lake water or evaporated water is in inverse proportion to evaporation In addition, evaporation increases with temperature over the lake; the increasing range of evaporation is in proportion to that of precipitation.
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  Study on AAR of Valley Glaciers in the Steady State

  Wang Ninglian, Pu Jianchen, Liu Shiyin, Huang Maohuan

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 167-172. https://doi.org/10.7522/j.issn.1000-0240.1997.0025

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  In this paper, the possible values of AAR of valley glaciers with various shapes in the steady state are estimated They are mainly governed by the altitudinal distribution of mass balance, shape factor and variation of surface slope of a glacier The relation between the altitudinal distribution of mass balance, shape factor of a glacial plan view and AAR of a valley glacier in the steady state is acquired The method of AAR for determining an ancient equilibrium line altitude is appropriate for a valley glacier.
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  A Geochemical Study on an 8 m Depth Ice Core of Guliya Ice Cap

  Li Yuefang, Yao Tandong, Sheng Wenkun, Huang Cuilan, Xie Chao

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 173-179. https://doi.org/10.7522/j.issn.1000-0240.1997.0026

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  The major cations (Ca²⁺, Na⁺, Mg²⁺, K⁺) and anions (Cl^-, SO₄^2-,NO₃^-) of an 8 m depth ice core were analysed The results indicate that the concentration of Ca²⁺ is the highest in cations, the pH value is in the range of 6.62～9.36, and that of 85% samples are more than 7, indicating that the snow/ice water of Guliya Ice Cap is weak alkaline Statistical treatment of the data reveals that obvious positive correlations exist between Cl^- and Na⁺, implying that they mainly originate from the matter including NaCl salt Both the value of pH and conductivity have obvious positive correlations with Ca²⁺, suggesting that they attribute to alkaline matter including Ca²⁺ rather than acid matter Assuming that the total Na⁺ comes from sea salt, the excess Ca²⁺ (non-sea salt) is calculated at least to be 96.6%～99.75% in total Ca²⁺, suggesting that Ca²⁺ mainly comes from terrestrial matter The chemical elements of the Guliya Ice Cap mainly come from the arid areas in the northern part of the Tibetan Plateau, revealed by the concentations, the value of pH, conductivity as well as by comparison with the southern part of the plateau and the polar glaciers.
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  Principal Component Analysis of the Snow Disaster Factors in the Pastoral Nagqu Prefecture, Tibet Region

  Lu Anxin, Feng Xuezhi, Zeng Qunzhu, Wang Lihong

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 180-185. https://doi.org/10.7522/j.issn.1000-0240.1997.0027

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  Snow is an active natural fact or with various attributes.Appropriate amount of snow can bring benefits to farming, animal husbandry and people slife.Overabundance of snow in an extensive area can cause disasters, such as disaster to cattle.Whether a snow fall can lead to a disaster depends on many factors, but the effect of each fact or is different.In this paper.Snow disaster factors in a pastoral area is analyzed in case study in Nagqu, Tibet, and the method of principal component analysis is used.The results show that the maximum depth of snow, the duration of snow cover, the amount of precipitation and the wind speed are the principal factors.This result is important to modeling of distinguishment and forecast of snow disaster.
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  Progresses in the Researches of Environmental and Climatic Records from Trace Organic Compounds in Snow and Ice

  Long Jiangping, Qin Dahe

  JOURNAL OF GLACIOLOGY AND GEOCRYOLOGY. 1997, 19(2): 186-192. https://doi.org/10.7522/j.issn.1000-0240.1997.0028

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  Trace organic compounds in snow and ice, mainly including methane concentrations of gas inclusions, soluble organic acids, trace anthropogenic pollutants etc Have been studied recently Trace organic compounds deposited in snow and ice mainly have their natural origins and are extremely sensitive to environmental and climatic changes With fast advance of pre-handling and analytic techniques understanding of environmental and climatic recrds from trace organic compounds in snow and ice will be greatly enhanced.