青藏高原湖泊沉积记录与环境变化研究

 过去全球变化研究是人类认识气候与环境变化事实与规律,客观评价现代环境在气候与环境发展历史中位置的重要手段,能够为未来气候与环境变化的预测提供科学的检验工具。介绍了湖泊沉积物环境代用指标与气候要素关系定量化的研究,简要回顾利用湖泊沉积物重建高原最近2万年环境变化历史研究成果,阐述高原湖泊沉积对气候变化的敏感响应。     

Precise timing of lacustrine gypsum in Luobubo, Xinjiang using the thermal ionization mass spectrometry U-series method

Dating techniques including gypsum dissolution in water, iron hydroxide co-precipitation with uranium and thorium and mass spectrometric determination have been investigated in this note. The ages of the gypsum samples in a CK core from Luobubo lacustrine sediments are in the range of (12.85±0.21) kaBP (4 m distance from the top core) to (153.2±7.2) kaBP (49 m distance from the top core) with the relative errors of ±1.6%–±4.7%. It indicates that the sedimental environment of the CK core was situated in the middle-late Pleistocene and Holocene periods, corresponding to 1–6 stages of oxygen isotopes in the abyssal sediments and included much information from last interglacial to Holocene warm periods.     

青藏高原及周边地区云气候特征

利用25年(1983.7—2008.6)的ISCCP D2云气候资料,统计分析了青藏高原及其周边地区总云量时空分布特征,并根据高原地形特征、大气环流形势等作出了合理解释。     

青藏高原中西部湖泊生物标志物记录的过去两千年气候变化

以青藏高原中西部湖泊达则错和阿翁错为研究对象,通过分析湖泊沉积物岩芯中GDGTs、长链不饱和烯酮与叶蜡化合物单体氢同位素等生物分子标志物获得过去2000 a以来青藏高原中西部定量的温度与降水同位素记录,以期探讨晚全新世以来不同时段青藏高原气候变化区域特征,并揭示过去2000 a季风与西风对青藏高原影响范围的变化.结果表明:(1)青藏高原气候变化存在强烈的区域性特征,两个湖泊均存在中世纪暖期(MWP),但是暖期持续的时间有所不同,高原西部(阿翁错) MWP持续时间明显长于高原中部(达则错);达则错有明显的小冰期(LIA)降温,阿翁错没有发现明显的LIA,可能受样品分辨率低的影响;过去200 a达则错温度有缓慢降低趋势,可能是冰融水补给湖泊温度变化滞后于气候变化的表现.(2)过去2000 a印度夏季风在青藏高原的最北界线可能发生了北移,在距今1000～2000 a,夏季风边界线位于阿翁错以北、达则错以南;但在过去1000 a印度季风边界线移动到阿翁错和达则错以北.     

Climatic significance of n-alkanes and their compound-specific dD values from lake surface sediments on the Southwestern Tibetan Plateau

The content and hydrogen isotope ratios of n-alkanes extracted from recent lake surface sediments sampled from nine lakes in three different climate zones on the Southwestern Tibetan Plateau were analyzed.Values were compared with n-alkanes in plants from lake drainages,and dD values of meteoric water,lake water,and mean annual precipitation.The results showed that n-C23was predominantly derived from aquatic plants,and n-C27–n-C33from terrestrial higher plants.The average carbon chain length of n-C27–n-C33(ACL27–33)was positively correlated with the mean annual precipitation.dD values of the long-chain n-alkanes n-C29and n-C31of terrestrial origin(varying between-214%and-169%,and-226%and-185%,respectively)were inversely correlated with mean annual precipitation;but in accordance with the average annual variations in dD(OIPC),dD values of n-C31were strongly related to the dD values of growing season meteoric water(R2=0.74).The large difference between dD values of n-C23of aquatic origin and n-C31(an average of about 27%)demonstrates the enrichment of the lake water dD compared to precipitation,caused by strong evaporation in the semiarid–arid areas of the southwestern Tibetan Plateau.Average value of en C25 31=p(-95%)is evidently higher than the value observed in European wet regions(-128%);besides,en C31(about-116%)is constant along the study transect(SD=9),which indicates that n-C31is a useful proxy for the environment.     

Environmental changes reflected by n-alkanes of lake core in Nam Co on the Tibetan Plateau since 8.4 kaB.P.

The n-alkanes are extracted from NMLC-1 core that was drilled in the Nam Co, central Tibet. They are measured by using Gas Chromatography and Mass Spectrometry (GC/MS) for componential and quantitative analyses. According to the constructed depth-age model, the component and concentration of n-alkanes, together with total organic carbon (TOC), total nitrogen (TN) and carbonate are used to elu- cidate palaeoenvironmental changes of Nam Co during the past 8.4 ka. The results indicate that Holo- cene environment performs three stages in the lake area. In the stage of 8.4―6.7 kaB.P., it was warmer while precipitation slightly increased. This stage was ended by an obvious cold/dry event. During 6.7― 5.8 kaB.P., temperature increased rapidly and reached its maximum values at about 6.0 kaB.P. The environments were warm/wet optimum for the blooming of terrestrial plants and submerged aquatic plants. After that, temperature decreased continuously and showed the lowest values at about 3.0 kaB.P. From 2.9 kaB.P. to the present, temperature rose again but alternated with cold and warm. The lake area tended to be dry after 1.4 kaB.P. During 600―400 aB.P., the environmental feature was the reflection of "Little Ice Age".     

High－resolution precipitation variations in the Northeast Tibetan Plateau over the last 800 years documented by sediment cores of Qinghai Lake

Short cores of about 80-cm retrieved from three main basins of th e deepwater areas in Qinghai Lake,the largest inland enclosed lake in China, were studied. Sta-ble isotopes of authigenlc carbonates, grain-size, carbonate and organic matter content at 5-year resolution are used to reconstruct the climatic history over the last 800 years in the Northeastern Tibetan Plateau. Chronology was established according to 210^pb dating and 137^Cs methods and the core corrdation. It is found that cores from different deep basins of the lake can be well correlated. The sedimentary rate is highest in the western basin of the lake and lowest in the east.In the southern basin of the lake where the short core Qing-6is located, the recent average sedimentation rate is 0.1004cm/yr. Variations in effective precipitation recorded by the oxygen isotopes and grain size data durine the last 800 years are consistent with the glacial accumulation record form the Dunde and Guliya ice cores. A dry climate lasted for 300 years from 1200 AD to 1500 AD, followed by a wet period from 1500 to 1560 AD. The two dry periods, 1560 to 1650 AD and 1780 to 1850 AD, were the results of southwest monsoon weakening. The effective precipitation generally increased since 1650 AD due to the strengthening of the Asian South-west Monsoon, resulting in a wet period until the 1950s. Ex-cept the early stage, the Little Ice Age on the Plateau is characterized b y increased effective moisture. Organic mat-ter content, with nearly 200-year cycles, shows similar trend with the atmospheric delta earbon-14 before the 1850s, indi-eating that the bioproductivity responds to solar activity.     

不同分辨率下青藏高原对大西洋经向翻转流影响的耦合模式研究

利用耦合地球系统模式CESM1.0,探究不同分辨率下青藏高原对大西洋经向翻转流(AMOC)的影响.对比有青藏高原地形与无青藏高原地形的试验,发现移除青藏高原后AMOC的变化与模式分辨率有关,不同分辨率下AMOC的变化不一致,低分辨率试验中AMOC强度降低89％,高分辨率试验中仅降低13％.产生这种差异的原因是,不同分辨...     

Thermal difference between the Tibetan Plateau and the plain east of Plateau and its influence on rainfall over China in the summer

There exist thermal differences between the Tibetan Plateau (TP) and the plain east of the TP, and between land and sea in East Asia. The influence of the land-sea thermal contrast on the precipitation in East China has been widely investigated; however, a few studies have paid attention to the role of the TP-plain thermal difference. Thus, using the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and the observation data of China from 1951 t...     

A tropical paleosol at high elevation in the Yulong Mountains and its implication on the uplift of the Tibetan Plateau

A paleosol dated for about 500–700 kaBP and developed on a glacial deposit at ～3 000 m a.s.l. in the Yulong Mountains is studied using soil chemical, morphological and mineralogical methods. The analytical results indicate that this soil was formed under tropical and humid conditions and can be classified as red soil, which cannot be formed in the present alpine environment at the studied site. This implies that the southeast margin of the Tibetan Plateau has experienced intense uplift since the formation of the paleosol. According to the necessary conditions for the formation of the modern red soil in China, we estimate that the uplift height of the Plateau since 500–700 kaBP would have exceeded 800 m.     

Evolution of the East Asian monsoon and its response to uplift of the Tibetan Plateau since 1.8 Ma recorded by major elements in sediments of the South China Sea

Evolution of the East Asian monsoon and its response to uplift of the Tibetan Plateau has been investigated in the study of global change. Core sediment samples drilled in the South China Sea during ODP Leg184 are the best materials for studying long-term variability of the East Asian monsoon. R-mode factor analysis of major elements in the fine grain-sized carbonate-free sediments (<4 μm) of the upper 185 mcd splice of ODP Site 1146 drilled during Leg184 in the South China Sea shows that Ti, TFe2O3, MgO, K2O, P, CaO, and Al2O3 are representative of a terrestrial factor. The variation in the terrestrial factor score is subject to chemical erosion in the source region and thus indicates the evolution of the East Asian summer monsoon. The terrestrial factor score has three stepwise decreases at ~1.3 Ma, ~0.9 Ma, and ~0.6 Ma, indicating the phased weakening of the East Asian summer monsoon is related to wholly stepwise, quick uplifts of the Tibetan Plateau since 1.8 Ma. The periodic fluctuation of the terrestrial factor score since ~0.6 Ma indicates that the glacial-interglacial cycles have been the main force driving the evolution of the East Asian monsoon. As in the case of Chinese loess, the long-term evolution of the East Asian monsoon recorded in sediments of the South China Sea reflects a coupled effect of the glacial-interglacial cycle and uplift of the Tibetan Plateau.     

Environmental changes reflected by n-alkanes of lake core in Nam Co on the Tibetan Plateau since 8.4 kaB.P.

The n-alkanes are extracted from NMLC-1 core that was drilled in the Nam Co, central Tibet. They are measured by using Gas Chromatography and Mass Spectrometry （GC/MS） for componential and quantitative analyses. According to the constructed depth-age model, the component and concentration of n-alkanes, together with total organic carbon （TOC）, total nitrogen （TN） and carbonate are used to elucidate palaeoenvironmental changes of Nam Co during the past 8.4 ka. The results indicate that Holocene environment performs three stages in the lake area. In the stage of 8.4-6.7 kaB.P., it was warmer while precipitation slightly increased. This stage was ended by an obvious cold/dry event. During 6.7-5.8 kaB.P., temperature increased rapidly and reached its maximum values at about 6.0 kaB.P. The environments were warm/wet optimum for the blooming of terrestrial plants and submerged aquatic plants. After that, temperature decreased continuously and showed the lowest values at about 3.0 kaB.P. From 2.9 kaB.P, to the present, temperature rose again but alternated with cold and warm. The lake area tended to be dry after 1.4 kaB.P. During 600-400 aB.P., the environmental feature was the reflection of ＂Little Ice Age＂.     

Late Cenozoic high-resolution magnetostratigraphy in the Kunlun Pass Basin and its implications for the uplift of the northern Tibetan Plateau

The Kunlun Pass Basin, located in the middle of the eastern Kunlun Mountains, received relatively continuous late Cenozoic sediments from the surrounding mountains, archiving great information to understand the deformation and uplift histories of the northern Tibetan Plateau. The Kunlun-Yellow River Movement, identified from the tectonomorphologic and sedimentary evolution of the Kunlun Pass Basin by Cui Zhijiu et al. （1997, 1998）, is roughly coincident with many important global and Plateau climatic and environmental events, becoming a crucial time interval to understand tectonic-climatic interactions. However, the ages used to constrict the events remain great uncertainty. Here, we present the results of detailed magnetostratigraphy of the late Cenozoic sediments in the Kunlun Pass Basin, which show the basin sediments were formed between about 3.6 Ma and 0.5 Ma and the Kunlun-Yellow River Movement occurred at 1.2 to ～0.78 Ma. The lithology, sedimentary facies and lithofacies associations divide the basin into five stages of tectonosedimentary evolution, indicating the northern Tibetan Plateau having experienced five episodes of tectonic uplifts at ～3.6, 2.69-2.58, 1.77, 1.2, 0.87 and ～0.78 Ma since the Pliocene.     

Identification and significance of 3β-alkyl steranes in the Eogene lacustrine sediments and petroleum of China

The study on steranes with substitution at C-2, C-3 or C-4 positions in ring-A has become a hot field for their specific precursors in recent years[1-15]. Summons et al. firstly identified C28-C30 3β-methyl steranes in Michigan Basin and found that the p…     

Use of a multi-temporal grid method to analyze changes in glacier coverage in the Tibetan Plateau

This paper describes a multi-temporal grid method for quantifying changes in glacier coverage. A multi-temporal grid synthesizes spatial, attribute and process components of glacier information by sequentially combining spatial data from satellite images or maps. It enables us to identify glacier retreat and advance areas in individual grid cells for three or more periods of data sets. Discrepancies among the sequential data sets were detected graphically and numerically, including noise from geo-location error, misclassification, or different interpretation results in various pixel resolutions. Noise was detected and corrected to a large extent by visualization of the synthetic grid. The paper compares the results with that from a common method based on individual data sets, focusing on the Mt. Naimona'Nyi and Mt. Qomolangma regions at the northern slopes of the Himalayas. Results show that the identified noise (e.g. by 2.5 km2 in the Mt. Naimona'Nyi region) is much larger than measurement uncertainty calculated by sensor resolution and co-registration error (e.g. by 0.015 km2 in the Mt. Naimona'Nyi region). After noise removal, we notice that glacier recession clearly accelerates. The multi-temporal grid method results in a better quantification of glacier variation. It shows that glaciers in the Himalayas have both retreated and advanced during the last several decades, with retreat dominating and accelerating. Glaciers on the northern slope of Mt. Qomolangma in the middle Himalayas retreat more extensively and faster than those in the Mt. Naimona'Nyi region in the western Himalayas.     

Structural characteristics of middle and southern Xainza-Dinggye Normal Fault System and its relationship to Southern Tibetan Detachment System

The Xainza-Dinggye Normal Fault System (XDNFS) is a large-scale nearly-north-south trending extensional structure across central and southern Tibet. Its middle segment developed in Tethys Himalaya with features of earlier magmatic core complex and later normal faults dipping moderately to northwest-west. The magmatic core complex is made up by mylonitic leucogrante with a low-angle detachment fault on the top of it and overlain by lower-grade meta-sedimentary rocks. The structural pattern of the southern segment of XDNFS take the shape of a detachment fault dipping to southeast-east with the High-Himalayan rock series as the lower plate. The Southern Tibetan Detachment System (STDS) is expressed as a ductile shear zone composed of mylonitic leucogranite in the studied area of this note. STDS was cut by the later XDNFS, which presents that nearly-east-west striking STDS is not the controlling or adjusting structure of the nearly-north-south trending extensional structures. The origin of nearly-north-south trending extensional structures in Tibet may be the result of deform ational partition of north-south compression.     

Eclogites in the interior of the Tibetan Plateau and their geodynamic implications

Eclogites have been recently reported in the interior of the Tibetan Plateau, including in the central Qiangtang metamorphic belt, in the Basu metamorphic massif of the eastern Bangong-Nujiang suture zone, and at Songdo and Pengco in the eastern Lhasa terrane. Some typical ultrahigh-pressure （UHP） metamorphic phenomena, e.g., garnet exsolution from clinopyroxene, were documented in the Basu and Pengco eclogites. The UHP metamorphism in the interior of the Tibetan Plateau marked by these eclogites generally took place in the Early Mesozoic. Along with exhumation of these eclogites, （post-） collision-related magmatism extensively occurred around the central Qiangtang belt, the eastern Bangong-Nujiang suture zone, and the eastern Lhasa terrane. The occurrence of these Early Mesozoic eclogites manifests an out-of-sequence evolution of the Tethys, and they could be a product of diachronous collision between the eastern Qiangtang terrane and the irregular continental margin of the united western Qiangtang-Lhasa plate, along the linked eastern Bangong-Nujiang-central Qiangtang zone. The collision-related magmatic rocks could have been originated from lithospheric thickening, melting, or detachment due to the collision. The presence of UHP metamorphic rocks in central Qiangtang and Basu implies likely continental deep-subduction, and the denudation of these two metamorphic zones could have served as the source of the Triassic turbidites in the Songpan-Garze complex and the Jurassic turbidites in the western Bangong-Nujiang zone, respectively. However, studies of the eclogites in the interior of the Tibetan Plateau just began, and many principal aspects still remain to be explored, such as their distributions, typical lithologies and minerals, temperature-pressure conditions, timing of formation and exhumation, protoliths and tectonic setting, and relationship with the evolution of the Tethys and large-scale basins in Tibet.     

Magnetostratigraphy of Late Tertiary sediments from the Chinese Loess Plateau and its paleoclimatic significance

The Late Tertiary red clay/bed sediments underlying the Quaternary loess-paleosol in the Chinese Loess Plateau possesses high-resolution paleoclimatic changes related to the uplift of the Tibetan Plateau. Magnetostratigra-phy and susceptibility measurements are discussed in this paper. The paleomagnetic results show that the red clay/bed began to accumulate at about 8.1 Ma, which represents the oldest Late Tertiary deposit continuously in the central Loess Plateau. The magnetic susceptibility curves show stepwise increases since the initiation of red clay, superimposed on several peaks. Moreover, the magnetic susceptibility increased abruptly since 3.8 Ma, which probably indicates the inception of the modern East Asia monsoon system. Between 3.8 and 2.6 Ma, the stepwise increases of susceptibility may imply progressively intensified East Asia summer monsoon activity related with the stepwise uplift process of the Tibetan Plateau.     

近20a来青藏高原建设用地扩张过程及空间管制政策取向

青藏高原作为中国乃至亚洲重要的生态安全屏障区域,揭示其建设用地扩张新趋势是维护生态系统功能、规范青藏高原国土空间开发保护格局的重要前提,对实现建设用地高质量利用和生态环境高质量保护具有重要意义。本文基于2000、2010和2020年三期土地利用数据,采用建设用地扩张过程测度指标、洛伦兹曲线等,定量刻画了2000-2020年青藏高原建设用地的变化特征,结果表明：(1)青藏高原建设用地扩张显著,由2000年的233.28 km2^扩展至2020年的759.95 km2^{。青藏高原建设用地}规模集中化程度较高,2020年西宁、拉萨两地建设用地占比达到43.05%。空间上,建设用地呈“整体分散,局部组团”特征,青东河湟谷地、西藏“一江两河”中部流域、环青海湖盆地建设用地扩张较突出;(2)青藏高原建设用地在低山缓坡及较温暖湿润地带的分布指向特征明显,2000-2020年间呈现向高海拔、陡坡地以及较寒冷干旱地区扩张新趋势,自然环境限制作用有所减弱。(3)2000-2020年青藏高原建设用地来源以未利用地、耕地为主,未利用地为最大的建设用地转入源,转入占比达到62.63%。对此,未来青藏高原空间管制的政策取向包括：按“大集聚”与“大分散”并举方式优化青藏高原国土空间开发保护格局,以提升空间管制精度为抓手遏制建设用地快速扩张态势,按建设用地扩张新趋势构建“近零”扰动的人类生产生活活动监管体系、重塑高原基本公共服务均等化新模式。     

Dust storms and loess accumulation on the Tibetan Plateau：A case study of dust event on 4 March 2003 in Lhasa

Whether the Tibetan Plateau is a significant dust source area is of great importance, because this is related to the understanding of sources, accumulation and environmental effects of dusts on the Tibetan Plateau and inthe Far East-Pacific Ocean regions as well as to the evointion of coupling of the Tibetan Plateau and atmaspbere-oeean-continent exchange. Synoptic dynamics and remote sensing tracing of a dust storm on 3 to 5 March, 2003 in Lhasa onSouth Tibet demonstrate that the Tibetan Plateau possessesall factors and conditions of generating dust storms. Accompanied with this dust storm is a strong ascending stream onthe Plateau which has raised various sizes of durst particlesinto different levels. The lifted coarse particles were largelyfallen down and accumulated as loess on the eastern TibetanPlateau, and the fine particles were translated by the westerly jet and subsided in the northern Pacific Ocean. The spa-tial-temporal distribution of dust-storms between years 1961and 2000 ou the Plateau shows that duststorms mainly occurin winter and early spring with high frequency, and tile pathof dust storm moves gradually from south to north, which isclosely coupled with the northward moving of the westerlyjet from winter to spring over the Tibetan Plateau. Com-pared with other twelve dust source areas in China. the Ti-betan Plateau is one of the key dust souree areas for thelong-distance transport because its high occurring frequencyand elevation cause fine particles easily to be lifted into thezone of the westerly jet.