Quaternary Lake Deposits of Nam Co, Tibet, with a Discussion of the Connection of Nam Co with Ring Co-Jiuru Co

Shorelines are widespread and lake deposits and lake geomorphology are welldeveloped on the northern Tibetan Plateau. Through field observations of lacustrine deposits of NamCo-the highest and largest Quaternary lake in Tibet, the authors found four-step shore terracescomposed of sands and clays with well-developed horizontal bedding and 3-12 m, 15-22 m, 25-30 m and35-45 m higher than the lake surface respectively, lacustrine deposits resting on the bedrocks and60-150 m higher than the lake surface, and up to approx 50 levees composed of oblate lakeshoregravels. Moreover they found lacustrine and lakeshore deposits making up the terraces and levees onthe bottoms of wide dividing valleys connecting Nam Co with the Rencoyuema, Rencogongma and Jiuru Conorthwest of Nam Co (the valley bottoms are 20 m, 90 m and 60 m higher than the above-mentionedthree lakes) and on slopes north of it, i.e. terraces II and III of Nam Co. Thus they confirm thatNam Co and Ring Co-Jiuru Co had connected with each other several times, i.e. formed a unified largelake several times, rather than had been different lakes connected only by river channels. Fromindications such as the distribution of the highest shoreline and lake deposits and geomorphology,the authors conclude that the total area of the old large lakes on the northern Tibetan Plateau is afew times larger than that of the modern lakes and that the last-stage old large lakes formed inthe interglacial interval of the last glaciation.

Evidence of the Pan-Lake Stage in the Period of 40-28 ka B.P. on the Qinghai-Tibet Plateau

The Qinghai-Tibet plateau is one of major saline lake regions in China, where saline lakes are widespread and constitute an important object of researches on the palaeoclimatic change in the region. On the basis of comprehensive investigations of the evolution of the lake's surface and sediments on the plateau, the authors have further demonstrated the existence of a pan-lake stage (river and lake flooding stage) on the Qinghai-Tibet plateau during the period of about 40+-28 ka B.P. and analyzed the palaeoclimatic characteristics of the pan-lake period and relationships between the ancient monsoons and the uplift of the plateau since the beginning of the Quaternary.

Glacier extent changes and possible causes in the Hala Lake Basin of Qinghai-Tibet Plateau

Glacier is a common sensitivity indicator of environmental and global climate change.Examining the relationship between glacier area and climate change will help reveal glacier change mechanisms and future trends.Glacier changes are also of great significance to the regulation of regional water resources.This study selected the Hala Lake Basin in the northeastern Qinhai-Tibet Plateau as a study area,and examined the relationships between the temporal and spatial change of glaciers in the northeastern Qinghai-Tibet Plateau and climate change based on remote sensing imagery,climatological data,and topographic data during the past 30 years.Results showed that glacier area in the Hala Lake basin fluctuated and decreased from106.24 km2 in 1986 to 78.84 km2 in 2015,with a decreasing rate of 0.94 km2·yr-1.The number of glacier patches,mean patch area,and largest patch index all decreased from 1986 to 2015,while the splitting index increased from 1986 to 2015,indicating that the landscape fragmentation of glacier in the Hala Lake Basin was increasing significantly during the study period.Glacier area change was mainly concentrated in the slopes>25°with an altitude of 4500-5000 m,and the retreating rate of glacier of sunny slope was obviously higher than that of shady slope.Geometric center of glacier in the basin moved from southwest to northeast towards high altitude.Results of the response of glacier extent to climate change showed that temperature was the dominant factor affecting glacier area dynamic change in the Hala Lake Basin.It is predicted that in future several years,the glacier area will decrease and fragment continually as a result of global warming on the Tibetan Plateau.

The Quaternary Pan-lake (Overflow) Period and Paleoclimate on the Qinghai-Tibet Plateau

Lake geomorphology and high-level lacustrine deposits since the mid-late Pleistocene are well preserved in lakes of the Qinghai-Tibet Plateau. According to geological surveys of 17 lake districts in different locations of the plateau, combined with interpretations of satellite images and topographic maps, the authors studied the timing of formation and scopes of the pan-lake areas of the plateau and their paleoclimate. The latest two high lake levels （overflow surfaces） on the Qinghai-Tibet Plateau in the Quaternary occurred at N40 to 30/35 ka and N65 to 53 ka respectively. In these time intervals, the plateau was covered by huge interconnected pan-lake systems with a total area of -36 km^2 and a total volume of lake water of 〉530 million km^2, which are about 38 times and 659 times larger than those of the modern lakes respectively. Before this pan-lake period in the late Pleistocene, there had been three high lake levels that occurred at N 132-112 ka, 110-95 ka and 91-72/-83-75 ka respectively, suggesting that the late Quaternary climate on the plateau was unstable and changed rapidly. The -40-30 ka high lake level also appeared in the Tengger desert north of the plateau, suggesting that there existed very strong summer monsoons from South Asia then; the variation in solar radiation with a 20,000 precessional period has special importance for the high-altitude Qinghai-Tibet Plateau in the low-latitude zone of the Earth. Around 30 ka, the pan-lakes at the peripheries of the Qinghai-Tibet Plateau drained out suddenly with rapid uplift of the plateau and cooling. In a short time the huge amount of cold lake water emptied into the Indian Ocean and Western Pacific. The draining event of the pan-lakes brought about the environmental changes of rivers and lakes at peripheries of the plateau.

Climatic changes have led to significant expansion of endorheic lakes in Xizang (Tibet) since 1995

Robust climate warming has led to significant expansion of lakes in the central Tibetan Plateau. Using remote sensing data, our quantitative analysis indicates that Siling Co, a saline lake in a characteristic endorheic basin in the central region of the Plateau, has expanded more than 600 km2 in area since 1976. Particularly since 1995, the lake has signif- icantly expanded in response to increasing precipitation, decreasing water surface evaporation caused by weaker winds and less solar radiation, and increased glacier meltwater draining to the lake. Glacie^lake interactions are important in governing lake expansion and are also part of a feedback loop that influences the local climate. Worsening climatic conditions （decreased precipitation and increased temperatures） that could have caused the lake to shrink during 1976-1994 were offset by increasing glacier meltwater feeding the lake, which made the lake nearly stable. We demonstrate that this pattern changed during 1995-2009, when glacier meltwater actually decreased but participation runoff increased and evaporation decreased, leading to expansion of the lake. If climatic conditions became suitable for further lake development, which would be indicated by expansion in lake area, glacier meltwater could be saved in a stable reservoir.

Hydrochemical Dynamic Characteristics and Evolution of Underground Brine in the Mahai Salt Lake of the Qaidam Basin Qinghai-Tibet Plateau

The mineral rock salts present in the Mahai Salt Lake of the Qaidam basin exhibit high solubilities in water. In addition, the multicomponent underground brine exhibits a high salinity and is easily precipitated. In the natural state, brine transport in the brine layer is extremely slow, and the brine is in a relatively stable chemical equilibrium state with the rock salt media. However, during mining, both the seepage and the chemical fields fluctuate significantly, thereby disrupting the equilibrium and leading to variations in the chemical composition and dynamic characteristics of the brine. Therefore, we selected underground brine from the Mahai Salt Lake, collecting a total of 183 brine samples over three stages of mining（i.e., the early stage of underground brine extraction, the initial stage of mining, and the later stage of mining）. Using a range of analytical techniques, the chemical dynamics of the underground brine water and its evolution were systematically studied. We found that evaporation and enrichment were the main mechanisms of underground brine evolution in the Mahai Salt Lake, with cation exchange and mineral dissolution/precipitation being key factors in determining the dynamic characteristics and evolution of the brine.

Climatic Signals in the Last 200 Years from Stable Isotope Record in the Shells of Freshwater Snails in Lake Xingcuo, Eastern Tibet Plateau, China

Lake Xingcuo is a small closed, hard\|water lake, situated on eastern Tibet Plateau. Stable isotope data (\{δ\{\}\+\{18\}O\} and \{δ\{\}\+\{13\}C\}) from the freshwater snail Gyraulus sibirica (Dunker) in a 34 cm long, radioactive isotope\|dated sediment core represent the last 200 years of Lake Xingcuo environmental history. Carbon and oxygen isotope ratios in the shells of the freshwater snail bear information on the isotopic composition of the water in which the shells were formed, which in turn characterizes the climatic conditions prevailing during the snail’s life span. Whole\|shell and incremental growth data were collected from modern and fossil shells from Lake Xingcuo. The \{δ\{\}\+\{18\}O\} values of modern shells from Lake Xingcuo are in equilibrium with those of modern waters, while \{δ\{\}\+\{13\}C\} values are indicative of snail dietary carbon and a lake with high \{δ\{\}\+\{13\}C\}\-\{TDIC\}. By calibrating \{δ\{\}\+\{18\}O\} and \{δ\{\}\+\{13\}C\} in the shell Gyraulus sibirica (Dunker) with instrument\|measured data for the period 1954-1992, we found that the \{δ\{\}\+\{18\}O\} of the snail shells is an efficient indicator to reveal air temperature in the warmer half year instead of that around the whole year, and that there is a certain positive correlation between index\{δ\{\}\+\{18\}O\} and the running average temperature in the warmer half\|year period. Climatic variability on eastern Tibet Plateau, for the last two centuries, has been successfully inferred from the\{δ\{\}\+\{18\}O\} record in freshwater snails in the sediments of Lake Xingcuo. As such, the last 200 years of palaeoclimatic record for this region can be separated into three periods representing oscillations between warming and cooling, which are confirmed by the Guliya ice record on the Tibet Plateau.

Prevention and management of wind-blown sand damage along Qinghai-Tibet Railway in Cuonahu Lake area

This paper analyzes the characteristics of climate, geology and geomorphology, vegetation, and sand dune distribution in the Cuonahu Lake area beside the Qinghai-Tibet Railway. The types and causes of railway blown-sand hazards are discussed, and the effectiveness of various sand-controlling measures is assessed. From the perspective of integrated management, a sand-controlling system that combines several engineering measures, including nylon net sand barriers, concrete sand barriers, movable-board sand barriers, sand interception ditches, gravel/rock cover, film sandbags, and permanent vegetation is most beneficial.

Diversity of the T4-like Myoviruses Community in Response to Salinity in Saline Lakes of the Qinghai-Tibetan Plateau

1 Introduction Viruses are the most abundant biological entities on Earth.They can influence the succession of individual microbial populations,biogeochemical cycles of C/N and,ultimately,microbial community structure through killing

Applying multivariate statistics for identification of groundwater chemistry and qualities in the Sugan Lake Basin, Northern Qinghai-Tibet Plateau, China

The Sugan Lake Basin is located in the inland arid region of northwestern China,in which groundwater is of great significance to human and ecology.Therefore,it is necessary to understand the chemical characteristics and quality of groundwater in the basin.Based on samples collected from 35 groundwater wells in Sugan Lake Basin,the spatial distribution characteristics of groundwater chemistry,main hydrogeochemical processes and groundwater quality have been discussed in this paper by using the multivariate statistics and hydrochemistry analysis methods.The results showed that the groundwater is weakly alkaline,and its total dissolved solid(TDS)and total hardness(TH) are high,with the average values of 1244.03 mg/L and 492.10 mg/L,respectively.The types of groundwater are mainly HCO_3^--SO_4^(2-)-Ca^(2+)type in the runoff area and Cl^--SO_4^(2-)-Na^+type in the catchment area.Rock weathering and ion exchange are the main controlling factors of regional groundwater chemistry,followed by evaporative crystallization,and human activities have less impact on groundwater.The spatial difference of groundwater quality is obvious,the water quality of the catchment area is not suitable for drinking,and the suitability for plant growth is also poor.The groundwater in the runoff area can be used for drinking,but the hardness is slightly higher,which is more suitable for ecological purpose.

The Two Main Mechanisms of Glacier Lake Outburst Flood in Tibet,China

With the global warming,the disasters of Glacier Lake Outburst Flood(GLOF) have taken place frequently in Tibet in recent years and attracted more and more attention.A systematic survey was conducted on the 19 GLOFs in Tibet to study their two main mechanisms.Investigations indicated that all the events occurred in end-moraine lakes,and the outburst occurred partially and instantly.And the breach had the shape of an arc or a trapezoid in overflow outburst and its top width was 3-5 times more than the height.The two main mechanisms of GLOFs in Tibetan end-moraine Lake were overflow and piping,and the overflow mechanism caused by iceberg collapse was dominated in most cases.A formula was proposed to calculate the critical thickness of iceberg tongue that determines the collapse.Granular analysis of the moraine materials revealed that seepage deformation is crucial in the outburst process.Finally,we conducted a case study of the Guangxiecuo Lake to show its possible process of outburst and estimated the peak discharge of the resulted flood.

Dating of two thermokarst lakes in Beiluhe Basin, Qinghai-Tibetan Plateau

Most of the thermokarst lakes are spread appreciably in Beiluhe Basin,Qinghai-Tibet Plateau,China,where ice-rich permafrost exists.Two typical thermokarst lakes with differing area and depth were examined to ascertain their age.We obtained lake-bottom samples of 50 cm length from lake BLH-A and 25 cm length from lake BLH-B.Environmental 137 Cs and 210 Pb and radiocarbon age dating techniques were applied to the 50 cm and 25 cm samples,respectively.The results indicate that the initiation of BLH-A is about 800-900 a B.P.,and approximately 1,450±30 a B.P.to 2,230±30 a B.P.for BLH-B.These results will provide scientific bases for sedimentological study and thermokarst activity in Beiluhe Basin.

Dynamic Changes of Lakes in Tibet Plateau and the Climate Interaction in the Past Forty Years

Lake change,as a mirror of climate change,has obvious indication and warning effect on climate.By extracting information of all lakes in Tibet Plateau from Landsat of the 1970’s,the 1990’s,around 2000 and 2010 based on RS and GIS,and,in combination with on-the-spot investigations to a few representative lakes,the authors

Compare on characteristic of different chemical type salt lake brines from Tibet during evaporating

1 Introduction China is a country which has many salt lakes.Tibet is the area where have numerous salt lake,because the sources of water have multiple chemical type,resulting in Tibet salt

Origin of boron in the Damxung Co Salt Lake(central Tibet):Evidence from boron geochemistry and isotopes

The origin of boron in boron-rich salt lakes in the Tibetan Plateau has long been the subject of debate.The Damzung Co Salt Lake in central Tibet has high boron concentrations(B=276–313 mg/L)and is an ideal site for

Evolution of an Ancient Large Lake in the Southeast of the Northern Tibetan Plateau

Nam Co is the largest (1920 km2 in area) and highest (4718 m above sea level) lake in Tibet. According to the discovery of lake terraces and highstand lacustrine deposits at several places in Nam Co and its adjacent areas, the authors confirm the existence of an ancient large lake in the southeastern part of the northern Tibetan Plateau. On the basis of the U-series, 14C and ESR dating, coupled with the levelling survey of lake deposits and geomorphology, the evolutionary process of the ancient large lake in the southeastern part of the northern Tibetan Plateau may fall into three stages: (1) the ancient large lake stage at 115-40 ka BP, when the ancient lake level was 140-26 m above the level of present Nam Co; (2) the outflow lake stage at 40-30 ka BP, when the ancient level was 26-19 m above the present lake level; and (3) the Nam Co stage since 30 ka BP, when the ancient lake level was < 19 m above the present lake level. During the ancient large lake stage, a large number of modern large, medium-sized and small lakes, including Nam Co, Siling Co and Zhari Namco, in the southeastern part of the northern Tibetan Plateau, were connected into a single large ancient lake, rather than several separate lakes connected by river channels. Its areal extent may have gone beyond the watersheds of the modern endorheic and exorheic drainage systems; so it may be called the 'ancient east lake', 'ancient south lake' and 'ancient west lake'. It might also be connected with other ancient lakes in the southern and western parts of the northern Tibetan Plateau to form a unified 'ancient large lake' on the northern Tibetan Plateau.

Tectonic Landform of Quaternary Lakes and Its Implications for Deformation in the Northern Qinghai-Tibet Plateau

The Hohxil region in the northern Qinghai-Tibet Plateau is occupied by numerous plateau lakes, which have long been inferred as being tectonic products. However, so far little evidence has been found to support this tentative inference. Field survey and morphotectonic analysis of TM satellite images in the eastern segment of the Hohxil region revealed that Kusai Lake and Yelusu Lake are S- shaped pull-apart basins, which were dominated by left strike-slip master faults trending WNW-ESE. The pull-apart distances of the two lakes are analyzed to be 〈15-20 km and 15 km respectively. Based on studies of the faulting rate, the initiation ages of the pull-apart basins are suggested to be approximately in the Early Pleistocene. The pull-apart basin tectonics is further regarded as a common mechanism for the widely distributed large lake basins in the northern Qinghai-Tibet Plateau. Regional distribution of these pull-apart basins and their substantial intra-block slip suggest that a sinistral shear stress, which is independent of the distinguished strike-slip faults, has been imposed on across the northern Qinghai-Tibet Plateau. Thus, the intra-block slip may be an important expression of the eastward extrusion of the Plateau crustal material in accommodating the ongoing continent-continent convergence between India and Eurasia. The revelation of pull-apart tectonics within the Plateau hinterland provides field evidence and a possible style of deformation for the newly proposed continuous deformation by the global positioning system （GPS） measurement across the northern Qinghai-Tibet Plateau. A model, with respect to systematic tectonic landform development, for pull- apart basins is finally proposed.

Salt Lakes In Tibet

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青藏高原盐湖硼、锂同位素变化规律及其对当雄错盐湖资源评价应用

近年,硼、锂同位素地球化学理论和分馏机理的深入,为盐湖体系硼、锂同位素示踪奠定了基础。基于现有大量研究数据,文章系统归纳盐湖体系硼、锂同位素分馏变化特征,总结盐湖演化过程硼、锂同位素组成的变化规律,建立它们的示踪方法。并以此为基础,对西藏典型富硼、锂盐湖−当雄错开展了硼同位素示踪,解决了当雄错与其物源硼同位素特征不符的难题,提出当雄错湖底蕴含大型硼、锂矿床的新认识,并预测了湖底的硼、锂资源量。根据盐湖体系硼、锂同位素地球化学特征,揭示了溶蚀湖的盐湖资源评价意义,为盐湖体系硼、锂同位素示踪和盐湖资源评价奠定理论基础。此外,借助硼同位素地球化学手段建立的当雄错“围岩−地热水−盐湖”的物源补给模式在西藏和全球具有普遍性。

1985—2021年青藏高原典型湖泊水文特征及关键影响因素

[目的]青藏高原的湖泊是气候变化的重要指示器,其扩张或缩减亦对青藏高原自然环境产生重要影响。[方法]选取位于青藏高原不同气候子区的3个典型湖泊(青海湖、羊卓雍错、乌兰乌拉湖),采用遥感监测手段,研究3个典型湖泊1985—2021年水文特征的时空变化规律,揭示关键气候因子的作用,并进一步探讨冰川和冻土对典型湖泊的影响。[结果]研究期间,青海湖的面积和水位呈显著上升趋势,面积增长238.68 km^(2),水位增长1.32 m,空间上则向东西方向扩张;羊卓雍错湖泊面积呈先波动上升后减少趋势,面积和水位分别减少16.31 km^(2)和3.25 m,在空间上整体由四周向中心的萎缩态势;乌兰乌拉湖面积和水位呈显著上升趋势,分别增长125.57 km^(2)和8.12 m,扩张区域主要集中在南部。[结论]在暖湿化环境下,降水增多和冰川冻土加速融化导致的湖泊扩张是青藏高原最为突出的环境变化特征,其中,降水量变化是影响青海湖和羊湖面积变化的关键因素,且面积变化和降水量具有滞后性;而乌兰乌拉湖水位上升的主要原因是气温升高引起冻土的季节融化。探索青藏高原湖泊面积的变化,对深入研究全球气候变化及地表水资源评估具有重要指导意义。