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-siz     

西藏纳木错晚更新世以来湖面变化和湖相沉积中粘土矿物显示的环境信息

通过对西藏海拔最高、面积最大湖泊-纳木错周缘湖相沉积、湖岸堤的野外调查和湖岸阶地的水准测量,发现在纳木错沿岸拔湖48m以下,发育有6级湖岸阶地,拔湖48~139.2m发育有高位湖相沉积。湖相沉积物的同位素测年结果表明,纳木错湖泊发育与藏北高原东南部古大湖演化可划分为3个阶段:①116~37kaB.P.间的古大湖期;②37~30kaB.P.间的外流湖期;③30kaB.P.以来的纳木错期。根据纳木错晚更新世以来湖相沉积中粘土矿物的X光衍射分析结果,以及采用比值法、高岭石法和衍射峰法的研究,探讨了粘土矿物所显示的环境变化信息。粘土矿物成分变化表明,该区已具备了寒温带干旱、半干旱区的气候环境特征。为研究青藏高原的湖泊演化、气候变化、古地理变迁及其隆升过程等提供了新资料。      

纳木错湖相沉积与藏北高原古大湖

藏北高原古湖岸线分布广泛，湖相沉积与湖成地貌发育，目前，在纳木错沿岸可清晰地划分出4-6级湖岸阶地，最高湖相沉积高出现代湖面150m，沿岸堤可多达50条，雄曲-那曲谷地是连接纳木错盆地与其以西的仁错-久如错盆地的分水谷地，也是构成纳木错2湖岸阶地顶部的第四纪湖相沉积，构成宽谷的谷底，从最高湖岸线的分布与湖相沉积物、湖成地貌等标志综合判定，古大湖泊的面积要比现代湖泊面积大数十倍，末次古大湖的时代发生于末次冰期间冰段。     

西藏纳木错地区约120kaBP以来的古植被、古气候与湖面变化

西藏纳木错湖相沉积的U系和^11C测年结果表明，湖泊沿岸的6级湖岸阶地及拔湖约48～139．2m的高位湖相沉积形成于约120ka BP以来的晚第四纪。本文根据该套湖相层的发育和其中的孢粉组合特征对纳木错地区约120ka BP以来的湖面变化与古植被、古气候变迁进行了探讨。结果表明，纳木错地区晚更新世以来经历了频繁的湖面波动、气候的冷暖与干湿变化以及森林—草原与草原植被的交替演化。其总体特征是：约115．9ka BP时，纳木错湖面最高。在116～78ka BP期间，该区气候温和凉爽或温和偏湿，植被以疏林草原与森林草原或森林的交替出现为特征，湖面经历了较大幅度的波动，但基本保持在拔湖140～88m之间。在78～53ka BP期间，该区气候干冷，植被以疏林草原为主，湖面大幅度下降，并在拔湖约36～48m之间波动。约53～32ka BP期间，气候转为温暖偏湿或温暖湿润，湖面波动于拔湖约15～28m之间，波动较为频繁。与阶地的发育相对应，该时期内包含了3次明显的暖期和湖面波动过程，区域植被主要以松、蒿、桦为主，为含一定量的冷杉的森林。其中36ka BP左右气候最温暖湿润，区域内可能出现针叶林或针阔混交林。约32～12ka BP期间，该区气候最为干冷，古植被以草原和疏林草原为主，湖面再次发生较大幅度的下降，最低可至拔湖约8m处，但通常维持在拔湖约12～17m之间。约11．8～4．2ka BP期间，气候整体较为暖湿，其中在约8．4～4．2ka BP期间气候最温暖湿润，该区可能发育针叶林或针阔混交林，湖面波动于拔湖2～9m之间，整体波动幅度较小，但波动最为频繁。区域气候对比发现，纳木错地区的冷、暖气候变化过程与整个青藏高原乃至北半球的气候变化基本是一致的，特别是阶地下切所反映的湖面退缩过程与北大西洋的Henrich冷事件之间具有很好的对应关系。     

西藏纳木错盆地116ka以来沉积演化与青藏高原隆升

根据湖相或湖滨相沉积的铀系等时线年龄测定结果,116kaB.P.以来,在西藏纳木错沿岸,发育了拔湖48m以下的6级湖岸阶地和拔湖48m以上,最高至139.2m的高位湖相沉积.可划分出3个沉积相组合,其演化可划分为4个阶段:①116~72kaB.P.,为深湖环境,古湖面拔湖高于现今纳木错140~48m;②72~37kaB.P.,为半深湖环境,拔湖为48~26m;③37~30kaB.P.,为浅湖环境,拔湖26~19m;④30kaB.P.以来,湖水逐渐变浅,拔湖<19m.纳木错盆地沉积与青藏高原隆升响应关系,揭示出高原自116kaB.P.以来先后经历了稳定期、持续逐步较快隆升期(116~37kaB.P.)、急剧强烈阶段性隆升期(37~30kaB.P.)和较稳定期(30kaB.P.以来).青藏高原的隆升是一个多阶段、不等速和非均变的复杂过程.      

班戈错晚第四纪湖泊发育、湖面变化与藏北高原东南部末次大湖期湖泊演化

班戈错是因湖面阶段性下降而于晚更新世末期从母湖色林错东部分离出来的小离湖.2003年5-7月,我们对班戈湖沿岸进行了详细的地貌与第四纪地质调查,湖面高程及6条剖面湖岸阶地的水准测量,并采集了沿岸及邻区的湖相沉积物样品进行U系年龄测定.研究结果表明,班戈错湖岸阶地共6级,其中T1为与色林错分离后所形成,T2至T6的拔湖高...     

Major Ion Geochemistry of Nam Co Lake and its Sources, Tibetan Plateau

The major cations and anions from lake water samples and its sources, including glacier snow, precipitation, stream, and swamp water in the Nam Co basin, central Tibetan Plateau, were studied. The concentrations of the major ions varied significantly in the five environmental matrices. Generally, the mean concentrations of most ions are in the order of lake water > swamp water > stream water > precipitation > snow. Rock weathering is the dominant process controlling the chemical compositions of the stream and swamp waters, with carbonate weathering being the primary source of the dissolved ions. The Nam Co lake water is characterized by high Na⁺ concentration and extremely low Ca²⁺ concentration relative to other ions, resulting from evapoconcentration and chemical precipitation within the lake. Comparison with the water chemistry of other lakes over the Tibetan Plateau indicated that Nam Co is located in a transition area between non-saline lakes and highly saline lakes. The relatively low concentration of total dissolved solids is possibly due to the abundant inflow of glacial meltwater and relatively high annual precipitation.     

西藏纳木错地区116 ka以来的湖相沉积及其环境演化与气候变迁

水准测量表明,西藏纳木错沿岸发育了拔湖48m以下的6级湖岸阶地和拔湖48m以上、最高至139.2m的高位湖相沉积。根据实测剖面、地层序列和岩性特征,并结合同位素测年等资料,可将该套湖相沉积地层划分为1个群、2个组。通过易溶盐、pH值、地球化学、粘土矿物、介形类和孢粉分析等的研究发现,湖相沉积中记录了116 ka B.P.以来的环境演化与气候变迁的信息。自116 ka B.P.以来,以全新世气候最宜期时,最温暖湿润;在90.1 ka B.P.和86.5 ka B.P.的相对温暖期时,气温相当或略高于现今,属温和轻爽或偏干,湿度稍大;在36～35 ka B.P.时段,气温和湿度较现今略高或较高。这表明自晚更新世以来,该区环境在逐渐变暖的总趋势上,经历了多次明显的冷暖与干湿波动。     

西藏纳木错及邻区全新世气候与环境变化的地质记录

综合分析了全新世期间内的多种与气候和环境变化密切相关的地质记录,结果表明该区全新世期间的气候变化可划分为3个阶段:1)约11.8～8.4kaBP期间,处于微温期和升温期,气候相对温和稍湿.2)8.4～4.0kaBP期间,为全新世气候最适宜时期或大暖期.该期间的平均气温可能比现今高约5℃,降水量比今多100～200mm.3)4.0kaBP以来,气候整体较为干冷.纳木错湖面发生持续下降,其最大下降幅度可达11.4m.冰川进退和湖面波动表明,该期间内的气候波动过程分别与新冰期和小冰期相对应,其中又各包含了3次明显的冷期,其中新冰期期间的最低年平均气温可达-6℃左右.约1970年以来,区域气候向暖湿方向转化,造成念青唐古拉山西布冰川后退约120～200m,纳木错湖面上涨了约2m.     

西藏纳木错末次间冰期以来的气候变迁与湖面变化

在西藏纳木错沿岸,发育了6级湖岸阶地及拔湖48～139.2m的高位湖相沉积.根据湖相沉积的U系法测年和孢粉分析结果,本文探讨了纳木错及邻区末次间冰期(MIS5)以来的古植被、古气候与湖面变化.研究表明,纳木错与邻区的湖面变化可以划分为116～37kaB.P.间的古大湖--"羌塘东湖"期、37～30kaB.P.间的"古纳木错"外流湖-残余古大湖期和30kaB.P.以来的纳木错-藏北湖群期等3大阶段.在MIS5的古大湖阶段,包括纳木错、色林错等藏北高原东南部的众多大、中型湖泊,是互相连通的一个大湖,其范围可能超过了现代的藏北内、外流(怒江)水系的分水岭.在MIS5e末的最高湖面时期,湖面面积可达78800km²,它或许还与藏北高原西南部和中南部的其他古大湖相连,成为面积巨大的网格状深水大湖--"羌塘湖".通过纳木错湖面变化曲线与西昆仑古里雅、格陵兰、南极等冰芯和深海岩芯的氧同位素变化曲线的对比可以发现,全球MIS5的气温要高于末次冰期间冰阶(MIS3),此时藏北高原为气候温和轻爽与湖面最高的大湖期;在末次冰期的两个冰阶(MIS4和MIS2)中,湖面明显下降,邻近的念青唐古拉山发育了小型山谷冰川;而在间冰阶MIS3中,其气候波动的幅度,要比世界其他地区更加明显,湖面波动也较大,特别是36～35kaB.P.间,气温和湿度都较今略高或较高,但不及MIS1中的全新世气候最宜时期的暖湿程度.总之,MIS5和MIS3是亚洲夏季风强烈时期,但前者的强烈程度应大于后者.     

Geomorphic and chronometric evidence for high lake level history in Gahai Lake and Toson Lake of north‐eastern Qaidam Basin,north‐eastern Qinghai–Tibetan Plateau

Palaeoshorelines, highstand lacustrine sediments and lakeshore terraces are preserved around saline lakes in the arid Qaidam Basin. Previous research indicates that the chronology of a mega‐paleolake in the Qaidam Basin during the late Pleisotocene is controversial. Here we report quartz optically stimulated luminescence (OSL) age estimates of highstand lacustrine sediments, shoreline features and geomorphic exposures that contribute to a revision of the lake level history of Gahai and Toson lakes in the north‐eastern Qaidam Basin, on the northeastern Qinghai–Tibetan Plateau (QTP) margin. The results imply that: (i) high lake levels at Gahai and Toson lakes based on quartz OSL dating occurred at 85–72, 63–55, 31, 5.4 and 0.9–0.7 ka, probably corresponding to periods of warm and wet climate; (ii) periods of high lake levels are almost synchronous with other lakes on the QTP (e.g. Qinghai and Namco lakes), with the highest late Pleistocene levels occurring during Marine Oxygen Isotope Stage 5; and (iii) highstand phases on the QTP are out of phase with those of low‐latitude lakes in the southern hemisphere, possibly driven by solar insolation variability in the low‐latitude region. Copyright © 2012 John Wiley & Sons, Ltd.     

A REVIEW OF THE PALEO-HYDROLOGICAL AND GEOMORPHOLOGICAL CHARACTER OF LAKE NAM CO,SOUTH-CENTRAL TIBET

The endorheic Lake Nam Co,south Eastern Tibetan Plateau,was selected to investigate the interrelation between drainage basin processes,especially post-glacial glacier decay,and lake level fluctuations.Landforms of the drainage basin are highly influenced by tectonics,superimposed by fluvial and periglacial processes,and locally by glacial and eolian processes.Thus,geomorphological features and hydrological characteristics were compiled for the lake-basin to provide an overview of the landscape character.Data show that during the Last Glacial Maximum melt water from the mountains accumulated fluvial deposits in the foreland.Concurrently,an increase of the lake level occurred which is presently shown by a cliff line all around Nam Co with its base approximately 29m above the present lake level.The Holocene decrease of the lake level is traced by beach ridges.As Nam Co is an endorheic lake post-glacial water loss has to be primarily explained by evaporation and moisture conditions.However,more detailed conclusions on quantitative and chronological patterns of both factors,melt-water input and evaporation output,still remain to be drawn.     

青藏高原北麓河地区典型热融湖塘周边多年冻土特征研究

青藏高原多年冻土区广泛分布着热融湖塘, 热融湖塘的形成会对周边的多年冻土产生显著的影响. 选取北麓河地区一典型热融湖, 运用探地雷达技术对该湖塘周边的多年冻土进行了探测.结果表明: 湖岸坍塌剧烈区一侧的多年冻土上限深度大于湖岸轻微坍塌区和湖岸稳定区, 并且在湖水的热作用下, 湖岸多年冻土的上限深度随离湖岸距离的减小而增大; 湖岸坍塌剧烈区上限附近的地下冰含量也明显高于湖岸轻微坍塌区和湖岸稳定区. 同时, 通过对湖岸测温孔的地温观测数据的分析可以看出, 湖岸地温正在逐年升高且升高的速率快于天然状态, 湖岸地温随离湖岸距离的减小逐渐增大.     

2007-2011年西藏纳木错流域积雪时空变化及其影响因素分析

通过2007-2011年纳木错站人工积雪观测资料,对西藏纳木错流域MODIS两种积雪产品(MOD10A1和MOD10A2)进行了精度验证,分析了纳木错流域积雪累积和消融的空间差异,以及流域积雪覆盖率的时空变化;利用纳木错站人工积雪观测资料及自动气象站资料,分析了纳木错流域积雪要素(积雪深度、雪水当量、积雪密度)的时间变化及其与气候参数(气温、降水量、风速等)的关系.结果表明：纳木错流域MOD10A2数据的积雪识别精度(67.1%)高于MOD10A1(42.2%),总识别精度(73.0%)略低于MOD10A1数据(78.4%).纳木错流域积雪累积和消融存在空间差异,积雪在流域南部的念青唐古拉山脉最先累积,之后为流域东部,最后为流域西部;积雪消融的空间变化则相反.由此导致流域积雪日数南部最大、东部次之、西部及西北部最小.纳木错流域各积雪要素的年内变化存在双峰值特征,峰值分别出现在10-11月和1月,积雪在10-11月受降水和气温共同作用,12月至次年3月主要受气温影响.纳木错流域的平均积雪覆盖率为21.9%,受湖泊效应影响区域(主要为东部地区)达到50.6%,而其他区域仅为18.3%.同时,受湖泊效应影响,纳木错平均积雪深度、积雪水当量均显著大于周边地区.     

A REVIEW OF THE PALEO­HYDROLOGICAL AND GEOMORPHOLOGICAL CHARACTER OF LAKE NAM CO|SOUTH­CENTRAL TIBET

Department of Earth Sciences,Freie Universität Berlin,Malteserstraße 74－100,12249 Berlin,Germany)
The endorheic Lake Nam Co,south Eastern Tibetan Plateau,was selected to investigate the interrelation between drainage basin processes,especially post­glacial glacier decay,and lake level fluctuations. Landforms of the drainage basin are highly influenced by tectonics,superimposed by fluvial and periglacial processes,and locally by glacial and eolian processes. Thus,geomorphological features and hydrological characteristics were compiled for the lake­basin to provide an overview of the landscape character. Data show that during the Last Glacial Maximum melt water from the mountains accumulated fluvial deposits in the foreland. Concurrently,an increase of the lake level occurred which is presently shown by a cliff line all around Nam Co with its base approximately 29m above the present lake level. The Holocene decrease of the lake level is traced by beach ridges. As Nam Co is an endorheic lake post­glacial water loss has to be primarily explained by evaporation and moisture conditions. However,more detailed conclusions on quantitative and chronological patterns of both factors,melt­water input and evaporation output,still remain to be drawn.     

青藏高原古大湖与夷平面的关系及高原面形成演化过程

青藏高原经过古近纪挤压缩短和增厚地壳均衡隆升,晚新生代形成了以走滑和伸展为主的相对稳定构造环境。中新世早期与晚更新世分别发育巨型古大湖,上新世-早更新世发育很多规模较大的古湖泊,古大湖对夷平面形成演化具有重要的控制作用。中新世早期(（24.1±0.6） ~（14.5±0.5）Ma)以古大湖的湖面为侵蚀基准面,经过隆起区剥蚀夷平和长期湖相沉积,在高海拔环境下形成早期夷平面。中新世晚期-第四纪以湖面与五道梁群湖相沉积顶面为基准,在高海拔环境下继续发生剥蚀夷平和准平原化,逐步形成主夷平面或高原面。第四纪河流溯源侵蚀导致内外流水系分界线自东向西迁移,在青藏高原东部形成高山峡谷地貌。     

藏东南波堆藏布江谷地古冰碛堰塞湖初步研究

藏东南作为青藏高原内外动力作用最强烈的地区之一,是河流堰塞-溃决洪水链式灾害频发地区。研究该区域古堰塞湖的形成与演化,对认识、评估灾害风险具有重要意义。研究结果表明,波堆藏布江谷地保存有一套湖相沉积地层,通过地貌填图和光释光测年等手段,并结合前人研究成果,推测海因里希事件1（H1）以来波堆藏布江谷地可能发生了一期古堰塞湖事件。该古堰塞湖可能是由波堆藏布江侧蚀白玉沟沟口冰碛垄,致使冰碛物滑塌并阻江形成的,古湖的最大湖面面积约为18.8 km²,库容蓄水量约为0.13 km³。该古堰塞湖的形成时间可能介于H1~10 ka之间,其溃决时间可能在~6 ka之后,后期河流溯源侵蚀及下切作用形成了多级以湖相地层为基座的阶地。     

青藏高原典型冰川和湖泊变化遥感研究

青藏高原冰川和湖泊变化是气候变化敏感的指示器,利用地形图、航空照片、TM卫星遥感资料和其它相关研究文献资料,分析了青藏高原典型地区的冰川和湖泊变化情况.结果表明:1960-2000年期间,在气温上升、降水增加、最大可能蒸散降低的背景下,研究区内不同地区湖泊的面积变化存在比较大的空间差异.以冰川融水为主要补给的纳木错和色林错地区的主要湖泊以扩大为主,而以降水为主要补给的黄河源地区的主要湖泊则基本上全面萎缩.研究区的冰川在1960-2000年期间以退缩为主,但各地退缩的幅度有较大的差异.     

青藏高原近25年来主要湖泊变迁的特征

青藏高原分布有青海湖、纳木错、色林错3个特大型湖泊和扎日南木错、当惹雍错、阿牙克库木湖、班公错、哈拉湖、鄂陵湖、羊卓雍错、扎陵湖、赤布张错、乌兰乌拉湖、昂拉仁错11个大型湖泊。通过对20世纪70年代中期的MSS图像和90年代末期—21世纪初期的ETM 图像的解译,对近25年来青藏高原重点湖泊的变迁进行了分析。研究结果表明,哈拉湖、鄂陵湖面积相对稳定;青海湖、扎日南木错、当惹雍错、阿牙克库木湖、扎陵湖、乌兰乌拉湖等8个湖泊的面积都有不同程度的缩小,其中青海湖、乌兰乌拉湖面积减少最多,分别为60.60km2、59.80km2;纳木错、色林错、班公错3个湖泊的面积都有不同程度的增加,其中色林错面积增加最多,达140.52km2。重点湖泊的变迁分析为研究青藏高原的湖泊演化和气候、环境变迁提供了新资料。     

西藏纳木错晚更新世以来古降水量变化及其环境响应

通过对西藏面积最大(1940km2)和海拔最高(4718m)的大湖-纳木错的调查,发现纳木错周缘有大面积分布的湖相沉积。U系法和14C法测年结果表明,纳木错沿岸湖相沉积的时代为晚更新世和全新世。根据纳木错周缘不同时代湖相沉积物的范围分布的变化,探讨了湖泊演化,计算出纳木错流域古降水量。研究结果,本区自晚更新世以来气候环境由湿润转向干旱,自全新世以来降雨量呈下降趋势。