Effects of permafrost degradation on thermokarst lake hydrochemistry in the Qinghai-Tibet Plateau,China

Thermokarst lakes play a key role in the hydrological and biogeochemical cycles of permafrost regions. Current knowledge regarding the changes caused by permafrost degradation to the hydrochemistry of lakes in the Qinghai-Tibet Plateau (QTP) is limited. To address this gap, a systematic investigation of thermokarst lake water, suprapermafrost water, ground ice, and precipitation was conducted in the hinterland of the QTP. The thermokarst lake water in the QTP was identified to be of the Na-HCO₃-Cl type. The mean concentrations of HCO₃⁻ and Na⁺ were 281.8 mg L⁻¹ (146.0–546.2 mg L⁻¹) and 73.3 mg L⁻¹ (9.2–345.8 mg L⁻¹), respectively. The concentrations of Li⁺, NH₄⁺, K⁺, F⁻, NO₂⁻, and NO₃⁻ were relatively low. Freeze-out fractionation concentrated the dissolved solids within the lake water during winter, which was deeply deepened on lake depth and lake ice thickness. Owing to solute enrichment, the ground ice was characterized by high salinity. Conversely, repeated replenishment via precipitation led to lower solute concentrations in the ground ice near the permafrost table compared to that within the permafrost. Although lower solute concentration existed in precipitation, the soil leaching and saline ground ice melting processes enhanced the solute load in suprapermafrost water, which is considered an important water and solute resource in thermokarst lakes. The influencing mechanism of permafrost degradation on thermokarst lake hydrochemistry is presumably linked to: (1) the liberation of soluble materials sequestered in ground ice; (2) the increase of solutes in suprapermafrost water and soil pore water; and (3) the changes in lake morphometry. These results have major implications on the understanding of the effects of ground ice melting on ecosystem functions, biogeochemical processes, and energy balance in a rapidly changing climate.     

青藏高原冻土带天然气水合物的形成条件与分布预测

冻土带是天然气水合物发育的两个重要地质环境之一.青藏高原平均海拔在4000m以上,多年冻土面积约1.4×106km2.本文根据青藏高原冻土层厚度和地温梯度特征,运用天然气水合物的热力学稳定域预测方法,确定中低纬度高海拔区冻土带天然气水合物的产出特征.青藏高原多年冻土带热成因天然气水合物形成的热力学相平衡反映,水合物顶界埋深约27~560m,底界埋深约77~2070m.初步计算表明,青藏高原冻土带水合物天然气资源约1.2×1011~2.4×1014m3.在冻土层越厚、冻土层及冻土层之下沉积层的地温梯度越小的地区,最有利于天然气水合物的发育.气温的季节性变化对天然气水合物影响不大.在全球气温快速上升的背景下,青藏高原天然气水合物将处于失稳状态,天然气水合物顶界下降、底界上升,与冻土带的退化相似,分布区逐渐缩小,最终将完全消失.     

Thermal regimes and degradation modes of permafrost along the Qinghai-Tibet Highway

Permafrost on the Qinghai-Tibet Plateau (QTP) is widespread, thin, and thermally unstable. Under a warming climate during the past few decades, it has been degrading extensively with generally rising ground temperatures, the deepening of the maximum summer thaw, and with lessening of the winter frost penetration. The permafrost has degraded downward, upward and laterally. Permafrost has thinned or, in some areas, has totally disappeared. The modes of permafrost degradation have great significance in geocryology, in cold regions engineering and in cold regions environmental management. Permafrost in the interior of the QTP is well represented along the Qing-hai-Tibet Highway (QTH), which crosses the Plateau through north to south and traverses 560 km of permafrost-impacted ground. Horizontally, the degradation of permafrost occurs more visibly in the sporadic permafrost zone in the vicinity of the lower limit of permafrost (LLP), along the margins of taliks, and around permafrost islands. Downward degradation develops when the maximum depth of seasonal thaw exceeds the maximum depth of seasonal frost, and it generally results in the formation of a layered talik disconnecting the permafrost from the seasonal frost layer. The downward degrada- tion is divided into four stages: 1) initial degradation, 2) accelerated degradation, 3) layered talik and 4) finally the conversion of permafrost to seasonally frozen ground (SFG). The upward degradation occurs when the geothermal gradient in permafrost drops to less than the geothermal gradients in the underlying thawed soil layers. Three types of permafrost temperature curves (stable, degrading, and phase-changing transitory permafrost) illustrate these modes. Although strong differentiations in local conditions and permafrost types exist, the various combinations of the three degradation modes will ultimately transform permafrost into SFG. Along the QTH, the downward degradation has been proceeding at annual rates of 6 to 25 cm, upward degradation at 12 to 30 cm, and lateral degradation in the sporadic permafrost zone at 62 to 94 cm during the last quarter century. These rates exceed the 4 cm per year for the past 20 years reported for the discontinuous permafrost zone in subarctic Alaska, the 3 to 7 cm per year reported in Mongolia, and that of the thaw-stable permafrost in subarctic Yakutia and Arctic Alaska.     

Impacts of permafrost changes on alpine ecosystem in Qinghai-Tibet Plateau

Alpine cold ecosystem with permafrost environment is quite sensitive to climatic changes and the changes in permafrost can significantly affect the alpine ecosystem. The vegetation coverage, grassland biomass and soil nutrient and texture are selected to indicate the regime of alpine cold ecosystems in the Qinghai-Tibet Plateau. The interactions between alpine ecosystem and permafrost were investigated with the depth of active layer, permafrost thickness and mean annual ground temperature (MAGTs). Based on the statistics model of GPTR for MAGTs and annual air temperatures, an analysis method was developed to analyze the impacts of permafrost changes on the alpine ecosystems. Under the climate change and human engineering activities, the permafrost change and its impacts on alpine ecosystems in the permafrost region between the Kunlun Mountains and the Tanggula Range of Qinghai-Tibet Plateau are studied in this paper. The results showed that the per- mafrost changes have a different influence on different alpine ecosystems. With the increase in the thickness of active layer, the vegetation cover and biomass of the alpine cold meadow exhibit a significant conic reduction, the soil organic matter content of the alpine cold meadow ecosystem shows an exponential decrease, and the surface soil materials become coarse and gravelly. The alpine cold steppe ecosystem, however, seems to have a relatively weak relation to the permafrost environment. Those relationships resulted in the fact that the distribution area of alpine cold meadow decreased by 7.98% and alpine cold swamp decreased by 28.11% under the permafrost environment degradation during recent 15 years. In the future 50 years the alpine cold meadow ecosystems in different geomorphologic units may have different responses to the changes of the permafrost under different climate warming conditions, among them the alpine cold meadow and swamp ecosystem located in the low mountain and plateau area will have a relatively serious degradation. Furthermore, from the angles of grassland coverage and biological production the variation characteristics of high-cold eco- systems in different representative regions and different geomorphologic units under different climatic conditions were quantitatively assessed. In the future, adopting effective measures to protect permafrost is of vital importance to maintaining the stability of permafrost engineering and alpine cold eco- systems in the plateau.     

Prediction of permafrost distribution on the Qinghai-Tibet Plateau in the next 50 and 100 years

The Qinghai-Tibet Plateau(QTP)has the highestand largest permafrost coverage in the low-middlelatitudes all over the world.With the progress ofChina’s Western Development,human activities areincreasing significantly on the QTP.For instance,theQinghai-Tibet Railway project started in June2001iscurrently under construction,but permafrost problemwill be one of the critical factors for the engineeringconstruction.Frost heave and permafrost settlementmay destroy engineering construction[1,2]…     

Impact of permafrost change on the Qinghai-Tibet Railroad engineering

Permafrost along the Qinghai-Tibet Railroad produces the great change under the influence of climate change, such as the decreasing of permafrost table, the rising of permafrost temperatures, etc. Climate effect on permafrost is the long-term process. Engineering action makes rapidly permafrost the large extent change. On the basis of analyzing the permafrost change under the climate change and engineering action, the thermal regime and spatial distribution of permafrost are predicted for air temperature rising 1℃ and 2℃ after 50 years in this paper. The results show that climate change results in the larger change for the thermal regime and spatial distribution of permafrost. Permafrost change will produce the great effect on the Qinghai-Tibet Railroad engineering, not only resulting in the decreasing of permafrost table beneath the roadbed, but also resulting in thawing settlement due to the thawing of ground ice near permafrost table. The idea of cooling roadbed and active protecting permafrost for the Qinghai-Tibet Railroad engineering could adjust and control the permafrost thermal state, some better methods are provided to ensure the engineering stability in the areas of warm permafrost and high ice content.     

SBAS-InSAR技术监测青藏高原季节性冻土形变

冻土的冻结和融化的反复交替会造成地质环境与结构的破坏,从而导致房屋和道路等地面工程建筑物的地基破裂或者塌陷,还会引起山体滑坡、洪水暴发以及冰川移动等.因此,监测冻土形变对确保冻土区工程建筑的稳定性和安全性,同时保证冻土区社会经济可持续发展具有重要的意义.目前,在冻土监测方面并没有能大面积监测冻土形变时间演化情况的有效方法,本文提出将InSAR技术中的小基线集方法(SBAS-InSAR)应用于监测冻土来获取其形变时间序列中.考虑到冻土形变呈现明显的季节性特征,本文提出利用周期形变模型来代替传统SBAS方法中的线性形变模型,从而更好地分离出高程残差和大气误差.利用ENVISAT卫星获取的21景ASAR影像图作为实验数据,采用改进的SBAS技术成功获取了青藏高原从羊八井站至当雄站铁路段冻土区的地表形变时间序列图,揭示了该冻土区从2007年到2010年的季节性形变演化情况.通过与研究地区温度变化的联合分析,发现所得到的地表形变结果与冻土的物理变化规律非常吻合,证明了SBAS-InSAR技术在冻土形变监测中具有良好的发展应用前景.     

Effect of a thermokarst lake on soil physical properties and infiltration processes in the permafrost region of the Qinghai-Tibet Plateau,China

Changes in the hydrological processes in alpine soil constitute one of the several key problems encountered with studying watershed hydrology and ecosystem stability against the background of global warming. A typically developing thermokarst lake was chosen as a subject for a study using model simulation based on observations of soil physical properties, infiltration processes, and soil moisture. The results showed that the selected thermokarst lake imposed certain changes on the soil infiltration processes and, with the degree of impact intensifying, the initial infiltration rate decreased. The greatest reduction was achieved in the area of moderate impact. However, the stable infiltration rate and cumulative infiltration gradually increased in the surface layer at a depth of 10 and 20 cm, both decreasing initially and then increasing, which is correlated significantly with soil textures. Moreover, the cumulative infiltration changed in line with steady infiltration rate. Based on a comparative analysis, the Horton model helps better understand the effect on the soil infiltration processes of the cold alpine meadow close to the chosen thermokarst lake. In conclusion, the formation of the thermokarst lake reduced the water holding capacity of the alpine meadow soil and caused the hydraulic conductivity to increase, resulting in the reduction of runoff capacity in the area of the thermokarst lake.     

Long-distance atmospheric moisture dominates water budget in permafrost regions of the Central Qinghai-Tibet plateau

Precipitation plays an important role in permafrost hydrology; it can alter the hydrothermal condition of the active layer and even influence the permafrost aggradation or degradation. Moisture recycling from evaporation and transpiration can greatly contribute to local precipitation in some regions. This study selected four monitoring sites and used an isotope mixing model to investigate local moisture recycling in permafrost regions of the central Qinghai-Tibet Plateau (QTP). The results showed that the local water vapour flux in the summer and autumn were dominantly influenced by westerlies and the Indian monsoon. Moistures for precipitation in Wudaoliang (WDL) and Fenghuoshan (FHS) mainly came from the western QTP, eastern Tianshan Mountains, western Qilian Mountains, and the surrounding regions. In comparsion, more than half of precipitation at Tanggula (TGL) was mostly sourced from the Indian monsoon. Local moisture recycling ratios at the four sites ranged from 14% ± 3.8% to 31.6% ± 4.8%, and depended on the soil moisture and relative humidity. In particular, the higher soil moisture and relative humidity promoted local moisture recycling, but frozen ground might be a potential influencing factor as well. The moisture recycling ratios of the study area were consistent with the results from both the Qinghai Lake Basin and the Nam Co Basin, but differed from those of the northwestern QTP. This difference may indirectly confirm the great spatial variability in precipitation on the QTP. Moreover, the rising air temperature and ground temperature, increasing precipitation, higher soil moisture, higher vegetation cover, and expanding lakes in the study area may be conductive to enhancing future local moisture recycling by altering ground surface conditions and facilitating the land surface evaporation and plant transpiration.     

应力释放模型在青藏高原地区的应用

介绍了应力释放模型、耦合应力释放模型及其在时、空两个方面经过改进的模型。利用改进后的模型研究了青藏高原地区的地震活动,结果显示,在青藏高原地区改进后的应力释放模型仍然适用,并且改进后的耦合应力释放模型要优于简单的应力释放模型,其预测地震的效能和精度都要优于泊松模型。     

青藏高原地表温度的比较分析

利用青藏高原改则、甘孜、拉萨和那曲气象站的地面水银温度计观测的地面0 cm温度和地面向上、大气向下长波辐射观测资料,计算和比较分析了地面水银表温度与地表辐射温度的差异.分析表明,由于地面水银温度计接触式测温方法的局限性,使得气象台站观测场地的地面水银表温度存在较大的误差：在裸露地表,夏季白天的正偏差可达4℃以上,夜间的负偏差在-2℃左右;在稠密植被地表,白天正偏差最高可达16℃以上,夜间的负偏差可达-3℃.由于偏差的不均衡性和离散性,即使对地面水银表温度作简单平均或积分平均处理,其代表性仍然很差.在对地表温度准确性要求较高的定量化研究与应用中,应避免直接采用地面水银表温度资料,即使由于资料缺乏而以其代之,也应对其采取适当的订正补偿等处理措施.随着科学研究对地表温度准确性的更高要求,推广使用地表辐射测温的观测方法是必要的.     

Cenozoic sedimentary records and geochronological constraints of differential uplift of the Qinghai-Tibet Plateau

Geological mapping data (1:250000) in the Qinghai-Tibet Plateau and its adjacent regions reveal the sediment sequences, distribution and tectonic evolution of the 92 Tertiary remnant basins. Southern Tibet and the Yecheng area in Xinjiang, located at southern and northwestern margins of the Qinghai-Tibet Plateau, respectively, were parts of the Neo-Tethys remnant sea in the Paleogene. In southern Tibet, both the subabyssal and abyssal sequences occur at the Gyangze, Saga, Guoyala, and Sangmai areas. The deep-water facies successions outcrop in the west, whereas the shallow-water facies sequences in the east, indicating the east to the west retreat of the Neo-Tethys Ocean. The retreat of the Neo-Tethys Ocean in the east was contributed to the earlier tectonic uplift of the eastern Qinghai-Tibet Plateau. The uplift process of the Plateau from the Late Cretaceous to Pliocene is described as follows: During the Late Cretaceous, tectonic uplift of the Qinghai-Tibet Plateau occurred in the northeastern part and the configuration of the Qinghai-Tibet Plateau was characterized by rise in the northeast and depression in the west. In the Paleocene-Eocene interval, the Tengchong-Baingoin and Kuyake-Golmud areas experienced local tectonic uplifting, the West Kunlun uplift zone broadened easterly, the Qilian uplift zone broadened southerly, and the Songpan-Garzê uplift zone shrank easterly. The Oligocene configuration of the Qinghai-Tibet Plateau was characterized by mountain chains rising along its margins and sedimentary basins in the central part because of tectonic uplifts of the Gangdisê and the Himalaya blocks. Meanwhile, the Kunlun-Altyn-Qilian uplift zones have also broadened southerly and northerly. In contrast, the great uplift zones of the Gangdisê, the Himalaya, the Karakorum, and the Kunlun blocks characterize the paleogeographic contours of the Qinghai-Tibet Plateau during the Miocene-Pliocene. Additionally, the thermochronological data on tectonic uplift events in southern Tibet, West Kunlun Mountains, Altyn Tagh, eastern Tibet, and western Sichuan all suggest that the most intense deformation occurred at 13-8 Ma and since 5 Ma, respectively, corresponding to two great uplift periods in Neogene. As a result, turnover of paleogeographic configuration of the Qinghai-Tibet Plateau occurred during the Neogene, experiencing a change from high contours in the east in the pre-Oligocene to high contours in the west at the end-Pliocene. The uplift of the Qinghai-Tibet Plateau during the Cenozoic was episodic, and the uplifts of various blocks within the Plateau were spatially and chronologically different.     

青藏高原北部地区中强震前地磁低点位移特征研究

分析了1994年以来青藏高原北部地区中强震前地磁低点位移的分布特征后,发现在该区中强震前均出现地磁低点位移异常。表明根据地磁低点位移异常对地震三要素（时间、地点和震级）的短临预报有一定的指导作用。     

块、带、源观点与青藏高原北块边界大震

介绍了块、带、源观点的产生和不断完善的过程,以及最新的相关研究成果。根据块、带、源观点,将青藏高原巨块划分为南块和北块,并讨论了北块边界上大震的活动性。     

Isotopic characteristics of shoshonitic rocks in eastern Qinghai-Tibet Plateau: Petrogenesis and its tectonic implication Isotopic characteristics of shoshonitic rocks in eastern Qinghai-Tibet Plateau: Petrogenesis and its tectonic implication

The Cenozoic magmatic rocks of shoshonitic series in the easternQinghai-Tibet Plateau include potassic alkaline plutonic rocks, volcanic rocks, lamprophyres and acidic porphyries. Analytical results show that these different lithological rocks are extremely similar in Sr, Nd and Pb isotopic compositions with the range of 0.705 187-0.707 254 for 87Sr/86Sr, 0.512 305-0.512 630 for 143Nd/144Nd, 18.53-18.97 for 206Pb/204Pb, 15.51-15.72 for 207Pb/204Pb and 38.38-39.24 for 208Pb/204Pb. They are isotopically similar to the EMII end-member. This indicates that mantle metasomatism must have taken place in their source region. The formation of these particular rocks is related to crustal thinning and mantle upwelling in a large-scale strike-slip and pull-apart fault zone at about 40 Ma in northern and eastern Qinghai-Tibet Plateau.     

基于星载被动微波遥感的青藏高原湖冰物候监测方法

湖冰物候影响着区域及全球气候,是全球变化的敏感因子,青藏高原湖泊众多,冻融现场监测数据缺乏,而微波具有对冰水相变敏感、时间分辨率高、历史存档数据长等特点,这对于长时间序列湖冰物候研究具有重要意义.然而,被动微波遥感空间分辨率低、湖泊亮温的精准定位难.论文通过获取AMSR-E/Aqua和AMSR-2/Gcom-W1的亮温数据,构建了基于轨道亮温数据的阈值判别法,通过对青藏高原不同区域和不同大小的青海湖、色林错、哈拉湖以及阿其克库勒湖进行测试研究:与青海湖现场观测对比,湖泊完全冻结日期与开始融化日期最大误差小于3天;与无云光学遥感判别结果相比,4个湖泊的冻融参数误差为2~4天.结果表明,被动微波轨道亮温数据可实现青藏高原地区亚像元级中大型湖泊冻融信息的获取,历史卫星资料可为湖冰物候的监测提供重要的支撑.     

青藏高原南缘中强地震震源机制的研究

利用全球数字化地震台网（ＧＳＮ）长周期数字地震波形资料,对发生在喜马拉雅碰撞带的３ 次中强地震事件, 根据广义射线理论, 就其震源物理过程进行了反演。结果表明, 印度洋板块向欧亚板块内部的俯冲作用过程仍在继续进行。     

九寨沟地震发震断层属性及青藏高原东南缘现今应变状态讨论

九寨沟地震（M_S7.0或M_W6.5）震中位于青藏高原巴颜喀拉块体东缘东昆仑断裂带东端塔藏断裂、岷江断裂和虎牙断裂交汇部位,中国地震局相关科研机构的研究人员曾将该震中区判定为玛沁-玛曲高震级地震危险区.地震应急科学考察期间没有发现地震地表破裂带,但地震烈度等震线长轴方位、极震区基岩崩塌和滑坡集中带、重新定位余震空间展布和震源机制解等显示出发震断层为NNW向虎牙断裂北段,左旋走滑性质,属东昆仑断裂带东端分支断层之一.此外,汶川地震后,在青藏高原东缘和东南缘次级活动断层上发生了包括2017年九寨沟地震（M_W6.5）、2014年鲁甸（M_W6.2）、景谷（M_W6.2）、康定（M_W6.0）等多次中强地震,显示出青藏高原东缘至东南缘各块体主干边界活动断层现今处于中等偏高的应变积累状态,即在巴颜喀拉、川滇等块体主干边界活动断层上具备了发生高震级（M_W ≥ 7.0）地震的构造应力-应变条件,未来发生高震级地震的危险性不容忽视.

     

青藏高原区M_S-L回归关系式的不确定性分析

本文收集了青藏高原区7级以上以走滑为主的30个地震的地表破裂参数资料,拟合出了青藏高原区新的震级与破裂带长度统计关系式,并结合前人的统计关系式,分别通过破裂带长度估算震级,求出了估算震级与仪器震级的差值。同时将差值为正值(即估算震级偏大)的归为一类,差值为负值(估算震级偏小)的归为另一类,做了分析和对比。研究发现,差值为正值的地震所处的走滑断裂带一般位于一级块体或次级块体的边界断裂带上;差值为负值的地震所处的走滑断裂带大多位于一级块体或次级块体内部断裂带或断裂带的交汇处。基于上述分类的差异,作者对不同回归关系计算的差值数据进行了统计分析,分别给出了修正计算结果不确定性的参考值,为降低估算震级的不确定性提供了理论依据。