12 kaBP lake environment on the Tibetan Plateau

The systemic analyses have been carried out in this paper to the paleolake shorelines, paleolake sediments and paleoclimatic proxies of 20 lakes, in which there were 12 kaBP dating data on the Tibetan Plateau. The results showed that the paleolake level had apparently risen during 14-11 kaBP, the glaciers melting period, in the Tibetan area and Northwest China. Especially, much more increasing amplitude supplied by thawy glaciers water occurred than in the best period of Holocene. The temperate-humid climate around 12 kaBP appeared in the Tibetan area and even in the whole China. This event may be compared with the Bolling/Allerod warm period which was reflected by Europe and Greenland ice core records. It showed that the B/A event was not a regional one in the North Atlantic area.

     

21kaBP青藏高原有远高于现代降水量的可能性吗?

古气候模拟特别对有关青藏高原的古气候模拟是比较复杂和困难的工作.可喜的是近年国内已有几位同志(陈隆勋等[1],刘晓东等[2,3])开展这项研究,取得了相当进展.本刊本期陈星、于革、刘健3同志《中国21kaBP气候模拟的初步试验》(以下称《陈文》)[4]也是这方面的有益尝试,他们采用改进的9层15波谱的AGCM大气环流模式和简化的陆地植被模型SSiB耦合,进行研究,得出结果,如认为东亚夏季风明显减弱、冬季风增强无疑是合适的,但关于青藏高原的模拟结果,笔者认为和地质记录矛盾较大,前人研究较普遍的认为末次冰盛期时,青藏高原夏季风衰弱,降水少于…     

40-30kaBP青藏高原及邻区高温大降水事件的特征、影响及原因探讨

40－30kaBP相当于末次冰期大间冰阶或海洋氧同位素MIS3晚期。青藏高原在岁差周期夏季高太阳辐射作用下,据古里雅冰芯与若干孢粉记录指示温度比现在高2－4℃,高原及邻区众多大湖的高湖面记录指示大范围降水丰沛。应用Kutzbach水能平衡方程推算了封闭湖泊流域（青海湖、扎布耶／拉果错、阿克塞钦／甜水海）年平均降水可达640mm,560mm,260mm,分别是现代降水的1．7倍,3倍,5倍。高原及邻区包括祁连山以北和云南部分区域在内的大降水对水系河流产生了重大影响。高原内部河湖串联,水系合并;如色林错、班戈错、纳木错串联为高原上最大的内陆水系;若尔盖古湖外流并入黄河水系;长江上游大水在三峡束狭形成强烈旋涡掏蚀成低于海平面的深槽,形成了深槽中、底部的砂砾沉积。这次高温大降水事件是由高太阳辐射导致的由青藏高原高温热低压加强、热带洋面增暖蒸发强烈、南半球越赤道气流增强共同作用而形成的高原特强夏季风,同时极地冰盖迫使西风带南移也可能加强了对高原尤其是西部的降水．H3事件（27kaBP)促进了高温大降水事件的结束,H4事件（35.5kaBP)则可能短期萎缩了夏季风,使高温大降水事件呈现不稳定性特点。     

Pollen-inferred vegetation and environmental changes in the central Tibetan Plateau since 8200 yr BP

The ecotone between alpine steppe and meadow in the central Tibetan Plateau is sensitive to climate changes. Here we used the pollen records from three lakes in this region to reconstruct the evolution of local vegetation and climate since 8200 cal. yr BP. The history of temperature and precipitation was reconstructed quantitatively with multi-bioclimatic indexes and a transfer function from pollen records. Results show that the steppe/meadow dominated during the period of 8200–6500 cal. yr BP, especially 8200–7200 cal. yr BP, indicating the central Tibetan Plateau was controlled by strong monsoon. The steppe dominated during the periods of 6000–4900, 4400–3900, and 2800–2400 cal. yr BP. The steppe decreased gradually and the meadow expanded during the period of 4900–4400 cal. yr BP. Three century-scale drought events occurred during 5800–4900, 4400–3900 and 2800 cal. yr BP, respectively. The first time when the regional climate shifted to the present level was at 6500 cal. yr BP in the central Plateau. Since 3000 cal. yr BP, the temperature and precipitation have decreased gradually to the present level. However, the cold climate between 700–300 cal. yr BP likely corresponds to the Little Ice Age. Supported by Chinese Academy of Sciences 100 Talents Project (Grant No. 29082762), National Natural Science Foundation of China (Grant Nos. 40671196, 40372085, 49371068, 49871078), and U.S. National Science Foundation (Grant Nos. ATM-9410491, ATM-008194)     

13kaBP以来滇池地区古环境演化

根据DC93一1孔孢粉组合、总有机碳（TOC）、总氮（TN）、碳氮比（C／N）、有机碳同位素δ13Corg、磁化率（χ）、频率磁化率（χfd）等资料,结合14C、210Pb和137Cs测年,滇池地区13ka以来的古环境演化历史经历了以下几个阶段：13—10．2kaBP．气候偏凉湿,湖水深度不大;10．2－7．5kaBP,气候向暖湿过渡．湖水渐深;7．5－4．0kaBP,气候暖湿,出热条件达到最佳配制,湖水也最深．6．5kaBP前后,气温最高,这一时段古气候状况存在次级波动;4．0－2．7kaBP,气候突转干旱．湖水最浅;2．7－1．7kaBP,气候温湿,湖面扩大,湖水变深;1．7kaBP,人类活动影响的加剧,使湖泊环境的变化更为复杂．     

四万年以来青海湖的三期高湖面及其降水量研究

孢粉学、地貌学与沉积学的证据揭示了青海湖自４０ｋａＢＰ以来经历了至少三期高湖面,即３０－４０ｋａＢＰ,１１－１３ｋａＢＰ,７．５－５ｋａＢＰ。其中第一期与第三期的高湖面是全球性暖温气候的产物,第二期的高湖面同暖温气修及高山区冰川消融均有关系。根据Ｍ．Ｎ．Ｂｙｄｕｋｋｏ（Ｍ．И．Ｂｙлｂｉｋｏ）公式和Ｊ．Ｅ．Ｋｕｔｚｂａｃｈ公式计算年蒸发量,依据封闭流域全流域水面平衡模式,模拟了青海湖在第一期与第三     

西藏中部申扎—定结地堑系北段中新世以来构造地貌学研究

利用ETM遥感影像与30 m分辨率的ASTER DEM数据, 构建申扎—定结地堑系北段遥感影像三维数字高程模型, 结合野外地质地貌调查结果, 对地堑系地貌特征进行总体分析。并根据对主要断裂的产状和活动性野外调查与活动断裂展布的遥感解译结果, 认为地堑系由一条东倾的铲式主要断裂和一系列同倾向和反倾向的次级断裂组成的半地堑构造。基于半地堑系模式, 将地堑系简化成书斜式模型, 根据地堑的沉降量和地堑宽度值, 计算地堑系的滑脱面深度在3.6～9.7 km之间, 因此地堑中地震震源深度也多集中于滑脱面附近。最后探讨地堑的形成机制, 表明在印度板块的挤压作用下, 高原上地壳与下地壳发生应力解耦, 上地壳在重力作用下, 向南向东发生滑脱, 形成东倾的半地堑构造。     

The uplifting processes of the Tibetan Plateau since 0.5 Ma B.P.

There is no final conclusion yet on the uplifting mechanism and epoch of the Tibetan Plateau, which is a hot point of the geological research. This paper discusses the epoch and scales of the hydrothermal activities based on the ESR ages of hot-spring sediments. The ESR ages show that hydrothermal activities mainly happened in four periods: 50×10⁴a, 50×10⁴–47×10⁴, 40×10⁴–35×10⁴, 27×10⁴–20×10⁴ and 10×10⁴—0 aB.P. This conclusion is supported by the geophysical data and the inner plateau and surrounding sediments. Through analyzing the constraints of the deep restraint mechanism and uplift tensile function of the plateau, the uplifting processes of the Tibetan Plateau since 50×10⁴a B.P. is elucidated.     

2000年以来青藏高原湖泊面积变化与气候要素的响应关系

青藏高原星罗密布的湖泊对气候变化十分敏感,在自然界水循环和水平衡中发挥着重要作用.以MODIS MOD09A1和SRTM DEM为数据源,提取了2000-2016年青藏高原丰水期面积大于50 km²的湖泊边界,从内外流分区、湖泊主要补给来源和湖水矿化度三个方面对2000年以来湖泊面积变化进行分析,并结合青藏高原近36年气象数据,根据气象要素变化趋势分区,初步探讨青藏高原湖泊面积变化与气候要素的关系.结果表明：青藏高原面积大于50 km²的138个湖泊整体扩张趋势显著,总面积增加2340.67 km²,增长率为235.52 km²/a.其中,扩张型湖泊占67.39%,萎缩型湖泊占12.32%,稳定型湖泊占20.29%.内流湖扩张趋势显著,外流湖扩张趋势较明显;以冰雪融水为主要补给来源的湖泊整体扩张趋势明显,以地表径流和河流补给为主要补给源的湖泊也呈扩张趋势;盐湖和咸水湖以扩张为主,淡水湖的扩张、萎缩和稳定三种类型较均衡.在青藏高原气候暖湿化方向发展背景下,湖泊面积变化与气候要素具有显著的区域相关性.气温和降水变化趋势分区结果表明,气温增加、降水增加强趋势的高原Ⅰ区湖泊扩张程度（78.18%）依次大于气温降低、降水量呈增加趋势的Ⅴ区（66.67%）,气温、降水量呈增加趋势的Ⅱ区（60.78%）,气温呈降低、降水量呈增加强趋势的Ⅳ区（58.83%）和气温呈增加、降水量呈减少趋势的Ⅲ区（50.00%）.湖泊面积变化对气候变化响应研究表明,升温引起的冰雪融水补给对Ⅰ区、Ⅱ区和Ⅲ区湖泊面积扩张的影响显著,加之降水量的增加,湖泊扩张速率明显;Ⅳ区和Ⅴ区湖泊面积扩张主要受降水量增加影响显著.整体而言,气温主要影响以冰雪融水为主要补给来源的湖泊,降水量主要影响以降水和地表径流为主要补给来源的湖泊.     

Biome reconstruction on the Tibetan Plateau since the Last Glacial Maximum using a machine learning method

Historical biome changes on the Tibetan Plateau provide important information that improves our understanding of the alpine vegetation responses to climate changes.However,a comprehensively quantitative reconstruction of the historical Tibetan Plateau biomes is not possible due to the lack of quantitative methods that enable appropriate classification of alpine biomes based on proxy data such as fossil pollen records.In this study,a pollen-based biome classification model was developed by applying a random forest algorithm(a supervised machine learning method)based on modern pollen assemblages on and around the Tibetan Plateau,and its robustness was assessed by comparing its results with the predictions of the biomisation method.The results indicated that modern biome distributions reconstructed using the random forest model based on modern pollen data generally concurred with the observed zonal vegetation.The random forest model had a significantly higher accuracy than the biomisation method,indicating the former is a more suitable tool for reconstructing alpine biome changes on the Tibetan Plateau.The random forest model was then applied to reconstruct the Tibetan Plateau biome changes from 22 ka BP to the present based on 51 fossil pollen records.The reconstructed biome distribution changes on the Tibetan Plateau generally corresponded to global climate changes and Asian monsoon variations.In the Last Glacial Maximum,the Tibetan Plateau was mainly desert with subtropical forests distributed in the southeast.During the last deglaciation,the alpine steppe began expanding and gradually became zonal vegetation in the central and eastern regions.Alpine meadow occupied the eastern and southeastern areas of the Tibetan Plateau since the early Holocene,and the forest-meadow-steppe-desert pattern running southeast to northwest on the Tibetan Plateau was established afterwards.In the mid-Holocene,subtropical forests extended north,which reflected the“optimum”condition.During the late Holocene,alpine meadows and alpine steppes expanded south.     

Erosion history of the Tibetan Plateau since the last interglacial: constraints from the first studies of cosmogenic 10Be from Tibetan bedrock

The cosmogenic ¹⁰Be exposure histories of in situ bedrock surfaces from the Tibetan Plateau indicate low erosion rates of <30 mm/ka in southern and central Tibet during the last interglacial–glacial cycle that contrast strongly with unusually rapid erosion rates (60–2000 mm/ka) for Kunlun in northern Tibet during the Holocene, comparable with published values from the Himalaya. By comparing apatite fission-track ages with cosmogenic data, erosion rates in southern Tibet appear to be decelerating since the Miocene, whereas in the Kunlun, erosion rates have accelerated over the same timescale. Such secular changes suggest that the southern and central regions of the plateau had formed their present flat relief by the Pleistocene. Unusually high erosion rates along the northern margin of the plateau may reflect intense tectonic activity during the Holocene. These findings indicate that over much of the high plateau erosion rates are exceptionally low, and therefore the sources of detritus carried by the great Asian rivers that rise in Tibet lie overwhelmingly in bedrocks at lower altitudes. This study illustrates the potential of cosmogenic studies for unraveling the most recent phase of the erosion/exhumation history of orogenic belts that cannot be resolved by either Ar-isotope or fission-track thermochronometers.     

近40 a西藏那曲当惹雍错湖泊面积变化遥感分析

西藏著名圣湖之一的当惹雍错,是藏北高原腹地内陆封闭大湖,对湖泊面积变化的长时间序列研究较少,本文通过高分辨率陆地资源卫星Landsat TM/ETM+数据源,利用遥感和地理信息系统软件,通过人工目视解译方法对1977-2014年当惹雍错湖泊面积变化进行系统分析,并结合流域临近气象站资料,流域冰川等辅助数据对其湖泊面积变化原因进行综合分析.结果表明,1977-2014年当惹雍错湖泊平均面积为835.75 km~2,1977-2014年湖泊面积总体呈上升趋势,1970s湖泊平均面积为829.15 km~2,1980s和1990s湖泊平均面积分别为827.50和826.42 km~2,2000年之后湖泊面积明显增加,2000s湖泊平均面积与1970s相比,增幅为8.04 km~2.当惹雍错湖泊空间变化特点是,位于最大河流入口处达尔果藏布的湖泊东南部扩大明显,湖泊西南部小湖1于2014年9月开始明显扩大并与当惹雍错有相连趋势;流域冰川融水是当惹雍错主要补给源,近40 a当惹雍错湖泊面积变化是在气温升高的背景下,冰川、降水量和蒸发量三者共同变化作用的结果.     

Tectonic uplift and sedimentary evolution of the Jiuxi Basin in the northern margin of the Tibetan Plateau since 13 Ma BP

Sediments shed from the northern margin of the Tibetan Plateau, the Qilian Mountains, are widely deposited in the foreland basin, the Jiuxi Basin, archiving plenty of information about the mountain surface uplift and erosion history. The Laojunmiao section, 1960 m thick, representing the upper sequence of the Cenozoic basin sediments, is paleomagnetically dated to about 13-0 Ma BP. Detailed sedimentary study of this sequence has revealed five sedimentary facies associations which determine four stages of sedimentary environment evolution. They are: (I) the half-deep lake system before 12.18 Ma BP, (II) the shallow lake system between 12.18 and 8.26 Ma BP, (III) the fan delta dominated sedimentary system in dry climate between 8.26 and 6.57 Ma BP, and (IV) alluvial fan system since 6.57 Ma BP. The associated mountain erosion and uplift are suggested to have experienced three phases, that is, tectonic stable (13-8.26 Ma BP), gradual uplift (8.26-<4.96 Ma BP), and rapid intermittent uplift (>3.66-0 Ma BP). The uplift at ∼3.66 Ma BP is of great importance in tectonics and geomorphology. Since then, tectonic uplift and mountain building have been accelerated and become strong intermittent. At least three significant tectonic events took place with ages at <1.80-1.23, 0.93-0.84 and 0.14 Ma BP, respectively. Thus, the uplift of the northern Tibetan Plateau is a complex process of multiple phases, unequal speed and irregular movements.

     

雅鲁藏布大峡谷格嘎古堰塞湖沉积岩石磁学性质指示的溃决事件

末次冰期时,在雅鲁藏布大峡谷入口处发育了一个古冰川堰塞湖,称为格嘎古堰塞湖.该堰塞湖是认识冰川阻江地貌效应的重要地质证据.古冰川堰塞湖可能会发生多次溃决洪水,通过堰塞湖沉积的分析可以获取堰塞期间的水文事件的信息.本文通过对古堰塞湖沉积39个样品多种磁学参数的详细分析发现,湖相沉积中的砂层低频磁化率（Xlf）为291×10-8m3/kg,泥质沉积的Xlf仅为42×10-8m3/kg;而非磁滞剩磁磁化率（XARM）和饱和等温剩磁（SIRM）的差别则较小.进一步的X-T、Loop和IRM研究以及XARM/Xlf表明,砂层中包含较多的粗颗粒磁铁矿是Xlf较高的主要原因,说明砂层中的磁性矿物没有经过风化破坏,应为近源沉积,并且快速埋藏,指示了溃决事件.本文的结果表明,利用岩石磁学性质以检测古堰塞湖溃决事件是一种可行的新方法.     

近40a西藏羊卓雍错湖泊面积变化遥感分析

羊卓雍错(以下简称羊湖)作为西藏高原三大圣湖之一和藏南重要的高原特色风景旅游景区,其具体面积众说纷纭.本文利用遥感和地理信息空间分析方法对1972-2010年羊湖面积变化进行了系统研究,并结合流域气象站资料对其原因进行初步分析.结果表明,1972-2010年湖泊平均面积为643.98 km2.1972-2010年羊湖面积呈波动式减少趋势,其中,1970s平均面积为658.78 km2,之后至1999年面积显著减少;1980s面积为636.55 km2;1990s为635.06 km2;1999-2004年面积有所增加;2004-2010年持续缩小,减幅为8.59 km2/a.湖泊空间变化特点是除了空母错和珍错两个小湖面积变化较小之外,羊湖整体面积呈现萎缩态势,其中东部嘎马林曲入口附近退缩程度最大,达1.62 km.流域气象站资料分析表明,湖泊面积和降水的变化波动存在显著耦合关系,降水变化是羊湖面积变化的主要原因;其次,流域蒸发量的明显增加,特别是2004年来连续较高的蒸发量是导致近期面积显著减少的重要原因,气温的升高进一步加剧了这一过程.羊湖的面积变化基本反映了西藏高原南部半干早季风气候区以降水补给为主的高原内陆湖泊对气候变化的响应.     

青藏高原湖泊古今变化的遥感分析—以达则错为例

青藏高原湖泊受人类活动干扰较少,主要受气候变化导致的冰川融化和蒸发的影响,是气候变化直观敏感的反映区。因此,研究青藏高原湖泊变化对区域以至全球气候、环境变化的研究具有深远意义。本文在遥感影像的基础上发展了综合指数计算与空间分异的现存湖迭代提取方法,对影像数据上的湖泊进行动态监测;并结合DEM数据发展了半自动化的古岸线提取方法,进而分析古湖泊的变化,二者相结合直观全面地反映出了青藏高原湖泊的古今变化情况。并以达则错湖为例进行提取,分析了其近25年以来以及大湖期以来的缩减情况     

Origin of the Red Earth sequence on the northeastern Tibetan Plateau and its implications for regional aridity since the middle Miocene

Desiccation in the interior of Asia is an important aspect of paleoclimate change during the Cenozoic era[1,2]. Research[3,4] shows that the widely distributed loess deposits in China were mainly transported by northwesterly and northerly winds from deserts and the Gobi region; in addition, an indispensable re- quirement for the generation of aeolian sediment is the presence of dry lands in central Asia[5,6]. The aeolian deposits in China provide an especially useful record of desiccation pr…     

Precipitation variation in the northeastern Tibetan Plateau recorded by the tree rings since 850 AD and its relevance to the Northern Hemisphere temperature

With their high resolution and reliability, tree rings play a very important role in global climate change study. The long tree-ring chronology is considered as one of the most important information sources to study the climatic change in the past several thousands years. In recent years, the tree-ring researches in China have made great progress, and the temperature and precipita- tion in some areas were reconstructed[1-20] which on- tributed to the global change studies in China. Due to the…     

A 2.8 Ma record of environmental evolution and tectonic events inferred from the Cuoe core in the middle of Tibetan Plateau

Based on a multi-proxy investigation into the deep core of the Cuoe Lake in the middle of Tibetan Plateau, a 2.8 Ma paleoclimatic and paleoenvironmental evolution is reconstructed. The result of magnetic stratum indicates that the lake basin was formed at about 2.8 MaBP, while the multi-proxy analyses of lithology, grain size, magnetic susceptibility and geochemical elements reveal that there have been three major environmental evolution stages and at least two intensive uplifts of the Tibetan Plateau in the lake basin area, i.e. during 2.8-2.5 MaBP, the lake basin came into being as a result of the disaggregation of the planation surface and rapid rising of the Tibetan Plateau. During 2.5-0.8 MaBP, with gradual uplift of the Tibetan Plateau, the environment of this area was more effectively controlled by the climatic cycle of the alternative glacial-interglacial stages. After 0.8 MaBP, the middle part of the Plateau accelerated its uplift and entered cryoshere.     

Magnetotelluric sounding results in eastern Tibetan Plateau

The results of Zayü-Qingshuihe MT sounding profile carried out in eastern Tibetan Plateau are presented in this paper. Using 2-D RRI method, the resistivity distribution with depth is obtained along the profile. It is featured by the resistivity zones in the horizontal direction and layers in the vertical direction. The Bangong-Nujiang suture zone and Jinshajiang suture zone are both important electrical conductivity-separating zones in the plateau, and the former is a zone with relatively low resistivity while the latter is an electrical conductivity gradient zone. The highly electrical conductive bodies in the mid and lower crust of northern Qiangtang and Bayan Har Terrain might be caused by regional melting due to shear heating during the process of subduction in tectonic evolution.