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…     

Ice cap erosion patterns from bedrock 10Be and 26Al,southeastern Tibetan Plateau

Quantifying glacial erosion contributes to our understanding of landscape evolution and topographic relief production in high altitude and high latitude areas. Combining in situ ¹⁰Be and ²⁶Al analysis of bedrock, boulder, and river sand samples, geomorphological mapping, and field investigations, we examine glacial erosion patterns of former ice caps in the Shaluli Shan of the southeastern Tibetan Plateau. The general landform pattern shows a zonal pattern of landscape modification produced by ice caps of up to 4000 km² during pre-LGM (Last Glacial Maximum) glaciations, while the dating results and landforms on the plateau surface imply that the LGM ice cap further modified the scoured terrain into different zones. Modeled glacial erosion depth of 0–0.38 m per 100 ka bedrock sample located close to the western margin of the LGM ice cap, indicates limited erosion prior to LGM and Late Glacial moraine deposition. A strong erosion zone exists proximal to the LGM ice cap marginal zone, indicated by modeled glacial erosion depth >2.23 m per 100 ka from bedrock samples. Modeled glacial erosion depths of 0–1.77 m per 100 ka from samples collected along the edge of a central upland, confirm the presence of a zone of intermediate erosion in-between the central upland and the strong erosion zone. Significant nuclide inheritance in river sand samples from basins on the scoured plateau surface also indicate restricted glacial erosion during the last glaciation. Our study, for the first time, shows clear evidence for preservation of glacial landforms formed during previous glaciations under non-erosive ice on the Tibetan Plateau. As patterns of glacial erosion intensity are largely driven by the basal thermal regime, our results confirm earlier inferences from geomorphology for a concentric basal thermal pattern for the Haizishan ice cap during the LGM. © 2018 John Wiley & Sons, Ltd.     

青藏高原及其周缘地区各向异性研究进展

首先简要介绍了青藏高原目前主流的4种动力学模型, 即俯冲模型、 碰撞模型、 挤出模型和拆沉-板片断离模型. 然后概述了青藏高原及其周地区各向异性的研究进展, 展望各向异性研究的方向, 并着重探讨了各向异性研究中需要重视的几个问题： ① 各向异性的多种来源; ② 各向异性与深部结构的关系; ③ 面波等新方法的应用. 为了更好地定量解释各向异性, 需要了解深部结构与各向异性之间的关系, 发展更加精细的研究手段. 就目前来看, 面波与体波的联合反演可以更好地约束各向异性的分辨率, 而将地球动力学模拟等正演手段与地震波各向异性等反演手段相结合也可能是未来的趋势之一.     

A review on the lithospheric structures in the Tibetan Plateau and constraints for dynamics

In the last decade, several international joint projects were conducted in the Tibetan Plateau by Chinese, American and French geophysicists and geologists. In the present review, the results from vertical reflections, wide-angle reflections and broadband digital seismic recordings are reviewed and compared. Constraints for the dynamics of continent-continent collision from the lithospheric structures, seismicity, focal mechanism and anisotropy are discussed.The velocities ofPn,Sn, , were accurately determined by using their travel times from local events. They evidenced that the uppermost mantle underneath the Tibetan Plateau was similar to that of the ordinary continental mantle.The reflection profile from INDEPTH-I furnishes convincing evidence that the Indian crust penetrates into the Tibetan lower crust. The results from teleseismic waveform inversion reveal that the Moho discontinuity dips northwards, and an offset of Moho occurs near Bangong suture.The fact that materials within the Tibetan Plateau escape laterally has been proposed by several authors. Recent data and studies provide further convincing evidence that eastward mass transfer does occur, and their paths and natures are investigated.Some authors suggested that the large strike slip faults (Kun Lun, Xianshuihe) in the eastern plateau may be related to the lateral extrusion. However, most of the strike slips are left-lateral, and extrusion could not occur without right-lateral strike slips. Recent observations of the focal mechanisms and geological structure indicate that the earthquakes in the Yanshiping-Changdu belt are left-lateral strike slip. It is the southeast zone of the left-lateral slip faults in the eastern Tibetan plateau. Geological and seismological evidence show that the Bencuo-Jiali belt is the only large right-lateral fault in the eastern plateau. It was proposed that the present eastward extrusion occurs between the Yangshiping-Changdu left-lateral strike slip and the Bencuo-Jiali right-lateral strike slip. The other left-lateral strike slips north of the Yangshiping-Changdu belt are considered to be the fossils of the ancient flow paths.     

青藏高原地震的震源深度及其构造意义

在本研究的前一项工作中，根据ＷＷＳＳＮ的长周期无震体波记录，采用广义反演技术，确定了１９６６年至１９８０年期间发生在西藏高原及其周围地区的１１个主要地壳地震和地震矩张量，同时得到了震源时间函数和震源深度。所分析的地震具有较浅的震源深度，且均分布于上部地壳范围内，本文根据上述结果，结合其它逐个测定的１９６４年至１９８６年发生在青藏高原的７８个中强地震的震源深度的结果，讨论了青藏高原地震的震源深度分布     

The Pn wave velocities and the relief of Moho in the Tibetan Plateau

Eleven PASSCAL broadband digital seismic stations were employed in the Tibetan Plateau by the Sino-US team from September, 1991 to June, 1992. Seven of them were distributed along the Qinghai-Tibet highway, others in Maqin and Yushu of Qinghai Province, Linzhi and Xigatze of Tibet. The data included 31 local earthquakes recorded by these stations from July, 1991 to January, 1992. Considering the characters of digital data, we identified the seismic phases carefully in several methods using SAC softwares (Seismic Analysis Code) in SUN workstation. We compared the seismic phases after converting the seismograms of the single stations to the seismic profiles; analyzed the first arrivals of P waves in the incident planes by rotating 3 component seismic records; identified the seismic phases from the particle motion pictures. The Pn apparent velocities were calculated in the distance range of 230–1200 km from Linzhi earthquakes, western Changtang earthquakes, Xitieshan and Gonghe earthquakes and the earthquakes in India. The results show that the Pn velocities change slightly in the Tibetan Plateau (8.0–8.1 km/s). These values near the velocities at the uppermost mantle of the normal continents. The Moho undulation in the Tibetan Plateau was also studied by using Pn data by the time-term method. The primary results indicate that the Moho beneath the Tibetan Plateau is flat, and its depths are 67–70 km. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, Supp., 593–600, 1992.     

青藏高原下地壳流动方式的数值模拟研究

青藏高原存在柔性下地壳流动被越来越多的学者接受, 但是关于下地壳流动方式及速度存在争议。 地表运动有GPS等直接测量, 上地幔运动有S波分裂间接反映, 下地壳运动目前没有直接观测手段, 使得开展数值分析非常重要。 本文利用三维球壳黏弹性有限元模型研究了青藏高原下地壳柔性流动方式和流动速度。 本文通过对地表GPS观测资料的拟合与不同数值模型的对比分析, 认为青藏高原柔性下地壳东向流动遇到四川盆地的抵阻, 下地壳物质可能仅在高原东南方向存在物质外溢通道, 而在高原东北方向不存在类似的物质通道; 下地壳的流动速度比地表运动速率每年快几毫米至十几毫米, 对应的黏滞系数为10¹⁸~10¹⁹ Pa·s。     

Tidal effects on intra-continental earthquake initiation in the Tibetan Plateau and its adjacent areas*

To investigate the tidal effects on intra-continental earthquake initiation in the Tibetan Plateau and its surrounding areas, we selected over 1,500 focal mechanism solutions of inland earthquakes (epicenter locates at least 100 km to the coastlines) from Global Centroid Moment Tensor (GCMT) project and analyzed the p-values of tidal normal and shear stress as well as tidal Coulomb failure stress. For Coulomb failure stress calculation, we used Coulomb 3.40 software. We find that: (1) p-values of tidal stress change suggests a high tidal correlation of earthquake imitations with tidal normal stress change; (2) when tidal normal stress reached the local maximum values of compression and when tidal shear stress were closed to the positive peaks, earthquakes generated more frequently; (3) particular seismogenic environments such as strong continental plate interactions and the existence of fluids or rheologic substance possibly raise the tidal correlations and (4) higher sensitivity of earthquake initiation to earth tide presents along with higher seismicity, suggesting the rate of rain energy accumulation somehow has a dominating effect on the tidal correlation of earthquake initiation.     

青藏高原达则错近1000年来生态系统变化及可能机制

在全球变化的背景下,厘清湖泊生态系统对气候环境以及人类活动的响应机制对制定社会的适应政策非常重要.目前的研究手段如现场观测和围隔实验等可以很好地揭示湖泊生态系统在有观测记录以来的演替和变化过程,但是不能提供历史时期湖泊生态系统的变化及其对气候环境变化和人类活动的响应.古湖沼学可以为探讨湖泊生态系统的长期变化及其对气候环...     

利用InSAR技术研究青藏高原冻土形变特征

由于自然环境的限制,青藏高原的大地测量网络十分稀疏,不能满足区域地壳运动监测的需求。干涉合成孔径雷达(InSAR)是非接触监测地壳运动的一种重要方式,但在高原上受到冻土的影响。本文基于2014～2018年的Sentinel-1卫星C波段雷达数据,采用InSAR时序技术分析了冻土形变的时空特征。针对InSAR位移时间序列,采用空间滤波去除了大气延迟、地形效应等局部公共误差,提高了时间序列的信噪比。结果显示,青藏高原的冻土运动可分为差异较大的两类:在大部分冻土区域,与周边高山(基岩)区域相比,冻土地区显示类似的季节波动或一定的长期沉降;在部分冻土地区存在异常快速下沉区域,例如在西藏中部布若错湖西南侧的沉积盆地内,存在一个直径约2 km的漏斗型沉降区, LOS向沉降速率可达约10±2.1 mm/a。构造运动造就了高原上大量沿断裂线分布的河流、湖泊,河床和沉积盆地等广泛分布着冻土,给准确分析构造形变带来很大挑战,本文所得的结果可作为区分冻土运动与构造变形的一种有效判据,也有益于研究高原冻土的物理特性及变形机理。     

青藏高原北部活动层土壤热力特性的研究

利用2003年10月～2004年9月期间高原北部可可西里(QT01)、北麓河(QT02)、开心岭(QT05)、通天河(QT06)等地活动层土壤温度梯度、土壤热通量及土壤水分的观测资料,计算了高原北部活动层土壤的导热率、土壤容积热容量、导温率等土壤热力参数.结果显示,QT02、QT05、QT06三站导热率、导温率夏秋季节较大而冬季较小,容积热容量则相反,表现为秋冬季节大而夏季较小;QT01站导热率表现为春季大,夏季较小;表层土壤粒度较小及较低的土壤湿度是冬季导热率较小的可能原因;冻土的热力特征参量可描述为相应深度的温度、体积含冰量及土壤盐度的函数,土壤含水量是融土热特征参数的主要影响因子;土壤水分含量小于某一临界值时,导温率随土壤水分含量的增大而增大,反之则减小.     

青藏高原东南缘构造旋转的古地磁学证据

本文在总结青藏高原东南缘近年来地质研究进展的基础上,从古地磁学的角度讨论其新生代以来的构造运动特征.结果表明:相对稳定的欧亚大陆,新生代以来山泰地块发生了约20°～80°顺时针旋转,局部地区旋转量甚至高达135°,且中部地区的旋转量明显高于南北地区;印支地块经历了～30°的顺时针旋转;川滇地块的顺时针旋转量沿102°E经度线由南向北由30°逐渐减小;另一方面,古地磁数据还揭示出山泰地块新生代以来发生了～8°的南向滑移运动.旋转量随时间的变化表明主要构造旋转发生在始新世与中中新世之间,与哀牢山—红河断裂的左行走滑时间相一致.这表明青藏高原东南缘的新生代构造运动具有差异性和复杂性,现今国际流行的挤出逃逸、地壳缩短增厚及下地壳流模式均有其局限性.值得注意的是,青藏高原东南缘可靠的新生代古地磁数据在时空分布上的严重不足,制约了我们对印度与欧亚大陆碰撞在青藏高原东南缘的运动学响应过程的深入探讨和正确理解.因此,进一步对该地区新生代地层开展深入细致的古地磁学等综合研究,无疑具有重要的科学意义.     

δ18O record and temperature change over the past 100 years in ice cores on the Tibetan Plateau

The 213 m ice core from the Puruogangri Ice Field on the Tibetan Plateau facilitates the study of the regional temperature changes with its δ18O record of the past 100 years. Here we combine information from this core with that from the Dasuopu ice core (from the southern Tibetan Plateau), the Guliya ice core (from the northwestern Plateau) and the Dunde ice core (from the northeastern Plateau) to learn about the regional differences in temperature change across the Tibetan Plateau. The δ18O changes vary with region on the Plateau, the variations being especially large between South and North and between East and West. Moreover, these four ice cores present increasing δ18O trends, indicating warming on the Tibetan Plateau over the past 100 years. A comparative study of Northern Hemisphere (NH) temperature changes, the δ18O-reflected temperature changes on the Plateau, and available meteorological records show consistent trends in overall warming during the past 100 years.     

青藏高原GRACE卫星重力长期变化

本文采用最新的GRACE(Gravity Recovery and Climate Experiment)(RL05)数据,通过水文模型(Global Land Data Assimilation System, GLDAS与Climate Prediction Center, CPC)扣除土壤水及雪水的影响,利用Paulson提供的冰川模型结果扣除GIA(Glacial Isostatic Adjustment)的影响,采用尺度因子的方法减少数据处理过程中误差的影响,最终基于最小二乘计算方法得到2003—2013中国及周边地区长期性重力异常变化情况.结果发现青藏高原有较为明显的重力上升信号,我们认为该信号可能由印度板块俯冲欧亚板块导致青藏高原地壳增厚所引起.接着依据GPS观测结果和艾黎均衡假说构建了地壳形变模型并通过直立长方体模型予以正演模拟分析.以班公湖—怒江断裂带为界将青藏高原划分为南北两大区块,结果显示青藏高原重力异常大致以0.2 μGal·a-1的速率在递增,小于GRACE得到的0.3±0.08 μGal·a-1的增长速率(对应于地壳增厚速率约3 mm·a-1),剩余未解释部分可能与湖水、冰川因素、冻土因素等有关.该结果对于认识青藏高原隆升动力学有一定参考意义.     

基于横波分裂的青藏高原多圈层各向异性研究进展

有关青藏高原横波分裂的各向异性研究已经开展了近30年,在理论方法和实际应用方面取得了重要进展,并获取了大量的横波分裂测量结果,为认识青藏高原壳幔各向异性变形特征和动力学机制提供了重要的依据.本文首先介绍了地震各向异性的来源与应用,随后回顾了横波分裂分析方法的发展,简述了各种横波分裂方法的原理,最后通过总结近30年来青藏高原上地壳、整个地壳和上地幔横波分裂各向异性研究成果,系统分析了青藏高原壳幔各向异性变形特征.基于各横波分裂结果的对比分析来看,XKS波分裂测量结果最为稳定,近震直达S波分裂测量结果次之,而Pms波分裂测量结果相对离散,往往相同区域内不同的研究结果差异较大,主要原因可能是相比XKS波和近震直达S波,Pms波的信噪比较低,次要原因可能是各研究在方法和处理分析等方面的差异.     

Evaluation of snow products over the Tibetan Plateau

Four satellite‐based snow products are evaluated over the Tibetan Plateau for the 2007–2010 snow seasons. The Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua snow cover daily L3 Global 500‐m grid products (MOD10A1 and MYD10A1), the National Oceanic and Atmospheric Administration Interactive Multisensor Snow and Ice Mapping System (IMS) daily Northern Hemisphere snow cover product and the Advanced Microwave Scanning Radiometer – Earth Observing System Daily Snow Water Equivalent were validated against Thematic Mapper (TM) snow cover maps of Landsat‐5 and meteorological station snow depth observations. The overall accuracy of MOD10A1, MYD10A1 and IMS is higher than 91% against stations observations and than 79% against Landsat TM images. In general, the daily MODIS snow cover products show better performance than the multisensor IMS product. However, the IMS snow cover product is suitable for larger scale (~4km) analysis and applications, with the advantage over MODIS to allow for mitigation for cloud cover. The accuracy of the three products decreases with decreasing snow depth. Overestimation errors are most common over forested regions; the IMS and Advanced Microwave Scanning Radiometer – Earth Observing System Snow Water Equivalent products also show poorer performance that the MODIS products over grassland. By identifying weaknesses in the satellite products, this study provides a focus for the improvement of snow products over the Tibetan plateau. The quantitative evaluation of the products proposed here can also be used to assess their relative weight in data assimilation, against other data sources, such as modelling and in situ measurement networks. Copyright © 2015 John Wiley & Sons, Ltd.     

Variations of stable isotopic compositions in precipitation on the Tibetan Plateau and its adjacent regions

There is no temperature effect in the southern Tibetan Plateau and South Asia to the south of the Tanggula Mountains. Amount effect has been observed at a few sampling stations accounting for about a half of the statistical stations. There is notable temperature effect in the middle and northern Tibetan Plateau and its adjacent Central Asia to the north of the Tanggula Mountains. Because vapor directly originates from low-latitude oceans, the relative heavy δ¹⁸O with small variation characterizes the rainfall in South Asia. A sharp depletion of the stable isotopic compositions in precipitation takes place from Kyangjin on the southern slope of the Himalayas to the Tanggula Mountains in the middle plateau. From the Tanggula Mountains to the northern Tibetan Plateau, the δ¹⁸O in precipitation increases with increasing latitude.     

青藏高原现代地壳运动与活动断裂带关系的模拟实验

本文以GPS观测、大地热流测量、较高精度地形数据、全球板块相对运动的REVEL模型为基础,建立了以青藏高原现代构造活动为主要研究对象的东亚地区构造形变场有限元模型.数值模拟结果显示,青藏高原内部和周边地区走滑断裂带的活动对东亚地区地壳运动速率和方向有较大的影响,特别是对青藏高原物质向东南方向运动有显著影响;不同构造块体岩石圈强度的差异直接影响了川滇菱形地块边界断层错动性质.在考虑青藏高原地形附加重力作用和周边板块汇聚作用对现今大型断裂带运动特征控制作用的同时,岩石圈之下的橄榄岩软流圈至转换带物质对流对岩石圈的拖曳力也是必须考虑的底部边界条件.     

Experimental study on soil CO2 emission in the alpine grassland ecosystem on Tibetan Plateau

The Tibetan Plateau, the Roof of the World, is the highest plateau with a mean elevation of 4000 m. It is characterized by high levels of solar radiation, low air temperature and low air pressure compared to other regions around the world. The alpine grassland, a typical ecosystem in the Tibetan Plateau, is distributed across regions over the elevation of 4500 m. Few studies for carbon flux in alpine grassland on the Tibetan Plateau were conducted due to rigorous natural conditions. A study of soil respiration under alpine grassland ecosystem on the Tibetan Plateau from October 1999 to October 2001 was conducted at Pangkog County, Tibetan Plateau (31.23°N, 90.01°E, elevation 4800 m). The measurements were taken using a static closed chamber technique, usually every two weeks during the summer and at other times at monthly intervals. The obvious diurnal variation of CO2 emissions from soil with higher emission during daytime and lower emission during nighttime was discovered. Diurnal CO2 flux fluctuated from minimum at 05:00 to maximum at 14:00 in local time. Seasonal CO2 fluxes increased in summer and decreased in winter, representing a great variation of seasonal soil respiration. The mean soil CO2 fluxes in the alpine grassland ecosystem were 21.39 mgCO2 · m-2 · h-1, with an average annual amount of soil respiration of 187.46 gCO2 · m-2 · a-1. Net ecosystem productivity is also estimated, which indicated that the alpine grassland ecosystem is a carbon sink.     

青藏高原对流层臭氧含量变化的太阳周期活动信号分析

利用1979~1992年卫星TOR对流层臭氧数据库资料,以及同期太阳辐照度数据序列,考察青藏高原对流层臭氧含量变化与太阳辐射周期变化之间的关系.分析表明,青藏高原对流层臭氧分布表现出与太阳辐照度相同的变化趋势,存在着明显的太阳周期变化特征.逐月线性回归分析表明,太阳辐照度增加导致青藏高原对流层臭氧增加的正效应.在太阳周期内,太阳辐射增加可使青藏高原对流层臭氧、平流层臭氧和臭氧总量分别增加1.31、4.97、6.628DU,或4.07%、2.04%、2.28%.该特征与赤道太平洋地区完全相反,分析产生差异的原因,至少应包括两方面因素：一是背景大气NOX和水汽含量的差异;二是青藏高原频繁发生的平流层-对流层大气物质交换和输送.