The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigr...The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore-shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo-Eurasian plate collision and that the direction of stress in the study area was NE-SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin （around 53.8 Ma） was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo-Eurasian collision.展开更多
The Qaidam Basin, located in the northern margin of the Qinghai-Tibet Plateau, is a large Mesozoic-Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian- Eurasian plate-plate collisio...The Qaidam Basin, located in the northern margin of the Qinghai-Tibet Plateau, is a large Mesozoic-Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian- Eurasian plate-plate collision since -55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast- southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin.展开更多
The Qiangtang basin is located in the central Tibetan Plateau. This basin has an important structural position, and further study of its tectonic and thermal histories has great significance for understanding the evol...The Qiangtang basin is located in the central Tibetan Plateau. This basin has an important structural position, and further study of its tectonic and thermal histories has great significance for understanding the evolution of the Tibetan Plateau and the hydrocarbon potential of marine carbonates in the basin. This study focuses on low temperature thermochronology and in particular conducted apatite fission track analysis. Under constraints provided by the geological background, the thermal history in different tectonic units is characterized by the degree of annealing of samples, and the timing of major （uplift-erosion related） cooling episodes is inferred. The cooling history in the Qiangtang basin can be divided into two distinct episodes. The first stage is mainly from the late Early Cretaceous to the Late Cretaceous （69.8 Ma to 108.7 Ma）, while the second is mainly from the Middle- Late Eocene to the late Miocene （10.3 Ma to 44.4 Ma）. The first cooling episode records the uplift of strata in the central Qiangtang basin caused by continued convergent extrusion after the Bangong- Nujiang ocean closed. The second episode can be further divided into three periods, which are respectively 10.3 Ma, 22.6-26.1 Ma and 30.8-44.4 Ma. The late Oligocene-early Miocene （22.6-26.1 Ma） is the main cooling period. The distribution and times of the earlier uplift-related cooling show that the effect of extrusion after the collision between Eurasian plate and India plate obviously influenced the Qiangtang basin at 44.4 Ma. The Qiangtang basin underwent compression and started to be uplifted from the middle-late Eocene to the early Oligocene （45.0-30.8 Ma）. Subsequently, a large-scale and intensive uplift process occurred during the late Oligocene to early Miocene （26.1-22.6 Ma） and the basin continued to undergo compression and uplift up to the late Miocene （10.3 Ma）. Thus, uplift-erosion in the Qiangtang basin was intensive from 44.5 Ma to about 10 Ma. The timing of cooling in the second episode shows that the uplift of the Qiangtang basin was caused by the strong compression after the collision of the Indian plate and Eurasian plate. On the whole, the new apatite fission-track data from the Qiangtang basin show that the Tibetan Plateau started to extrude and uplift during 45-30.8 Ma. The main period of uplift and formation of the Tibetan Plateau took place about 22.6-26.1 Ma, and uplift and extrusion continued until the late Miocene （10.3 Ma）.展开更多
This paper introduces relative and absolute gravity change observations in the eastern portion of the Tibetan Plateau. We analyze and discuss a change that occurred in 2010 in the gravity along the eastern margin of t...This paper introduces relative and absolute gravity change observations in the eastern portion of the Tibetan Plateau. We analyze and discuss a change that occurred in 2010 in the gravity along the eastern margin of the plateau and the relationship between this change and the 2013 Lushan Ms7.0 earthquake. Our results show that： （1） before the Lushan MsT.0 earthquake, gravity anomalies along the eastern margin of the Tibetan Plateau changed drastically. The Lushan earthquake occurred at the bend of the high gradient zone of gravity var- iation along the southern edge of the Longmenshan fault zone. （2） The 2013 Lushan earthquake occurred less than 100 km away from the epicenter of the 2008 Wenchuan earthquake. Lushan and Wenchuan are located at the center of a four- quadrant section with different gravity anomalies, which may suggest that restoration after the Wenchuan earthquake may have played a role in causing the Lushan earthquake. （3） A medium-term prediction based on changes in gravity anoma- lies was made before the Lushan Ms7.0 earthquake, in par- ticular, a prediction of epicenter location.展开更多
Changes in the lake areas of Xainza basin in the past 33 years （1976 to 2008） were studied using Landsat data from Multispectral Scanners （1973- 1977）, Thematic Mapper （1989-1992, 2007-2009）, and Enhanced Themat...Changes in the lake areas of Xainza basin in the past 33 years （1976 to 2008） were studied using Landsat data from Multispectral Scanners （1973- 1977）, Thematic Mapper （1989-1992, 2007-2009）, and Enhanced Thematic Mapper Plus （1999-2002）. The results indicated that lakes in the study area evidently expanded from 1976 to 2008, with total expansion of 1512.64km2. The mean annual air temperature presented an upward trend with certain fluctuations from 1966 to 2008. The air temperature rise rates in the cold season （o.31~C/loa） were higher than those in the hot season （0.24℃/1oa）, in the Xainza station example. Precipitation exhibited evident seasonal differences. Mean annual precipitation in hot season is 281.48 mm and cold season is 32.66 mm from 1966 to 2008 in study area. Precipitation in the hot season was the major contributor to the increase in annual precipitation. Grey relational analysis （GRA） was used to study the response of lake areas to climatic factors. The mean air temperature and precipitation were selected as comoared series, and the lake areas were regarded as the reference series. The grey relational grade （GRG） between compared series and reference series were calculated through GRA. The results indicated that changes in lake areas were mainly affected by climatic factors in the hot season. Lakes in this region were classified into three grades, namely, Grades I, II, and III according to the recharge source and elevation. The GRGs of each series varied for different grade lakes： the area of Grade III lakes were the most relevant to the hot season factors, the GRGs of precipitation and air temperature were 0.7570 and 0.6606; followed by the Grade II lakes; Grade I lakes were more sensitive to the air temperature.展开更多
The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode globa...The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode global position system （GPS） stations throughout the northwest of Longmenshan fault. A new GPS field over 1999-2011 is derived from measurements of the newly built and pre-existing stations in this region. Sequentially, two strain rate fields, one preceding and the other following the 2008 MwT.9 Wenchuan earthquake, are obtained using the Gausian weighting approach. Strain field over 1999-2007 shows distinct strain partitioning prior to the 2008 MwT.9 Wenchuan earthquake, with compression spreading over around Longmenshan area. Strain fieldderived from the two measurements in 2009 and 2011 shows that the area around Longmenshan continues to be under striking compression, as the pattern preceding the Wenchuan earthquake, implying a causative factor of the sequent of 2013 Mw6.7 Lushan earthquake. Our GPSderived dilatation shows that both the Wenchuan and Lushan earthquakes occurred within the domain of pro- nounced contraction. The GPS velocities demonstrate that the Longriba fault underwent slight motion with the faultnormal and -parallel rates at 1.0 -4- 2.5 mm and 0.3 4-2.2 mm/a; the Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 4- 1.7 mm/a. Longriba fault is on a par with Longmenshan fault in strain partitioning to accommodate the southeastward motion of eastern margin of the Tibetan Plateau. Integrated analysis of principal strain tensors, mean principal stress, and fast directions of mantle anisotropy shows that west of Sichuan is characterized as mechanically strong crust-mantle coupling.展开更多
Significant CO2 fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO2 fluxes and est...Significant CO2 fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO2 fluxes and estimated annual soil respiration in two contrasting coniferous forest ecosystems （a Picea asperata plantation and a natural forest）. Mean winter soil CO2 effluxes were 1.08 μmol m-2 s-1 in the plantation and 1.16 μmol m-2 s-1 in the natural forest. These values are higher than most reported winter soil CO2 efflux values for temperate or boreal forest ecosystems. Winter soil respiration rates were similar for our two forest ecosystems but mean soil CO2 efflux over the growing sea- son was higher in the natural forest than in the plantation. The estimated winter and annual soil effluxes for the natural forest were 176.3 and 1070.3 g m-2, respectively, based on the relationship between soil respiration and soil temperature, which were 17.2 and 9.7 % greater than their counterparts in the plantation. The contributions of winter soil respiration toannual soil efflux were 15.4 % tor the plantation and 16.5R for the natural forest and were statistically similar. Our results indicate that winter soil CO2 efflux from frozen soils in the alpine coniferous forest ecosystems of the eastern Tibetan Plateau was considerable and was an important component of annual soil respiration. Moreover, reforesta- tion （natural coniferous forests were deforested and refor- ested with P. asperata plantation） may reduce soil respiration by reducing soil carbon substrate availability and input.展开更多
The distribution characteristics of cloud-top and tropopause height in the tropics and subtropics in boreal summer are analyzed based on CALIPSO data for the period 2008-2012.The maximum values of cloud-top vertical c...The distribution characteristics of cloud-top and tropopause height in the tropics and subtropics in boreal summer are analyzed based on CALIPSO data for the period 2008-2012.The maximum values of cloud-top vertical cumulative frequency above the tropopause （CTAT） are concentrated in three tropical regions：the Asian summer monsoon region,Central America,and western Africa.The contributions to the area-weighted CTAT frequency in the three regions from the Northern Hemisphere are 49.0%,13.5%,and 12.4%,respectively.Moreover,the contribution of troposphere-to-stratosphere transport （TST） in the Asian monsoon region to global TST can be far greater than 50%,according to analysis of the continuous equation,velocity potential,and divergent wind from ERA-Interim data.Furthermore,the Asian summer monsoon circulation system controls the distribution of the cloud top.On the south side of the Tibetan Plateau,the maximum frequency of the cloud top,more than 10% per 500 m vertically,is most likely to appear in the core of the high-level easterlyjet near the tropopause height （16.5 km）.Over the Tibetan Plateau,the maximum frequency of the cloud top,greater than 3% per 500 m vertically,is suppressed below 11 km,far away from the thermodynamic tropopause height but close to the dynamic tropopause height of 2 PVU （potential vorticity units）.展开更多
The study presented herein investigated the main characteristics of carbon monoxideintraseasonal variability and evaluated its possible impact factors using the upper troposphere and lowerstratosphere (UT/LS) Aura Mic...The study presented herein investigated the main characteristics of carbon monoxideintraseasonal variability and evaluated its possible impact factors using the upper troposphere and lowerstratosphere (UT/LS) Aura Microwave Limb Sounder (MLS) observations over Tibetan Plateau and itsadjacent areas in summer (June to August) of 2005 and 2006. Observations show a persistent constituentextreme extending up into the UT/LS throughout summer, as well as a temporally reversed phase variationbetween the carbon monoxide and ozone in UT/LS. The intraseasonal oscillations (ISOs) of carbonmonoxide during summer are investigated by using methods of wavelet and band pass filter analysis. It isfound that ISOs over the Tibetan Plateau have periods of 10 to 20 days and 30 to 60 days. The formermainly appeared in upper troposphere while the latter in lower stratosphere. Further analysis shows thatthese two periods of ISOs in UT/LS are mainly in phase to the activities of convection over the south of theplateau and the variation of South Asia High, respectively. The above two factors and their dynamicalcoupling may be responsible for the tracer ISOs at different levels.展开更多
The southeastern Tibetan Plateau,which profoundly affects East Asia by helping to maintain the stability of climate systems,biological diversity and clean water,is one of the regions most vulnerable to water erosion,w...The southeastern Tibetan Plateau,which profoundly affects East Asia by helping to maintain the stability of climate systems,biological diversity and clean water,is one of the regions most vulnerable to water erosion,wind erosion,tillage erosion,freeze-thaw erosion and overgrazing under global climate changes and intensive human activities.Spatial variations in soil erosion in terraced farmland(TL),sloping farmland(SL)and grassland(GL)were determined by the^(137)Cs tracing method and compared with spatial variations in soil organic carbon(SOC)and total nitrogen(total N).The^(137)Cs concentration in the GL was higher in the 0-0.03 m soil layer than in the other soil layers due to weak migration and diffusion under low precipitation and temperature conditions,while the^(137)Cs concentration in the soil layer of the SL was generally uniform in the 0-0.18 m soil layer due to tillage-induced mixing.Low^(137)Cs inventories appeared at the summit and toe slope positions in the SL due to soil loss by tillage erosion and water erosion,respectively,while the highest^(137)Cs inventories appeared at the middle slope posi-tions due to soil accumulation under relatively flat landform conditions.In the GL,the^(137)Cs data showed that higher soil erosion rates appeared at the summit due to freeze-thaw erosion and steep slope gradients and at the toe slope position due to wind erosion,gully erosion,freeze-thaw erosion and overgrazing.The^(137)Cs inventory generally increased from upper to lower slope positions within each terrace(except the lowest terrace).The^(137)Cs data along the terrace toposequence showed abrupt changes in soil erosion rates between the lower part of the upper terrace and the upper part of the immediate terrace over a short distance and net deposition on the lower and toe terraces.Hence,tillage erosion played an important role in the soil loss at the summit slope positions of each terrace,while water erosion dominantly transported soil from the upper terrace to the lower terrace and resulted in net soil deposition on the flat lower terrace.The SOC inventories showed similar spatial patterns to the^(137)Cs inventories in the SL,TL and GL,and significant correlations were found between the SOC and^(137)Cs inventories in these slope landscapes.The total N inventories showed similar spatial patterns to the inventories of,37Cs and SOC,and significant correlations were also found between the total N and^(137)Cs inventories in the SL,TL and GL Therefore,^(137)Cs can successfully be used for tracing soil,SOC and total N dynamics within slope landscapes in the southeastern Tibetan Plateau.展开更多
基金supported by Foundation of Geological Survey of China(no.1212011121261)the National Natural Science Foundation of China (no.40902049)+1 种基金the Special Fund for Basic Scienctific Research of Central Colleges, China University of Geoscience (Wuhan) (no.CUGL09206)the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences(no.GBL11207)
文摘The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore-shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo-Eurasian plate collision and that the direction of stress in the study area was NE-SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin （around 53.8 Ma） was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo-Eurasian collision.
基金co-supported by the President Fund and Innovation Program of Chinese Academy of Sciences(no.:kzcx2-yw-104)the Chinese National Science Foundation grants(no.:40334038)the Science and Technology Key Project of Ministry of Education of China(no.:306016).
文摘The Qaidam Basin, located in the northern margin of the Qinghai-Tibet Plateau, is a large Mesozoic-Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian- Eurasian plate-plate collision since -55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast- southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin.
基金the National Natural Science Foundation of China (No.41372128)the State Key Laboratory of Continental Dynamics project in Northwest University (No.BJ08133-1)
文摘The Qiangtang basin is located in the central Tibetan Plateau. This basin has an important structural position, and further study of its tectonic and thermal histories has great significance for understanding the evolution of the Tibetan Plateau and the hydrocarbon potential of marine carbonates in the basin. This study focuses on low temperature thermochronology and in particular conducted apatite fission track analysis. Under constraints provided by the geological background, the thermal history in different tectonic units is characterized by the degree of annealing of samples, and the timing of major （uplift-erosion related） cooling episodes is inferred. The cooling history in the Qiangtang basin can be divided into two distinct episodes. The first stage is mainly from the late Early Cretaceous to the Late Cretaceous （69.8 Ma to 108.7 Ma）, while the second is mainly from the Middle- Late Eocene to the late Miocene （10.3 Ma to 44.4 Ma）. The first cooling episode records the uplift of strata in the central Qiangtang basin caused by continued convergent extrusion after the Bangong- Nujiang ocean closed. The second episode can be further divided into three periods, which are respectively 10.3 Ma, 22.6-26.1 Ma and 30.8-44.4 Ma. The late Oligocene-early Miocene （22.6-26.1 Ma） is the main cooling period. The distribution and times of the earlier uplift-related cooling show that the effect of extrusion after the collision between Eurasian plate and India plate obviously influenced the Qiangtang basin at 44.4 Ma. The Qiangtang basin underwent compression and started to be uplifted from the middle-late Eocene to the early Oligocene （45.0-30.8 Ma）. Subsequently, a large-scale and intensive uplift process occurred during the late Oligocene to early Miocene （26.1-22.6 Ma） and the basin continued to undergo compression and uplift up to the late Miocene （10.3 Ma）. Thus, uplift-erosion in the Qiangtang basin was intensive from 44.5 Ma to about 10 Ma. The timing of cooling in the second episode shows that the uplift of the Qiangtang basin was caused by the strong compression after the collision of the Indian plate and Eurasian plate. On the whole, the new apatite fission-track data from the Qiangtang basin show that the Tibetan Plateau started to extrude and uplift during 45-30.8 Ma. The main period of uplift and formation of the Tibetan Plateau took place about 22.6-26.1 Ma, and uplift and extrusion continued until the late Miocene （10.3 Ma）.
基金supported by the National Natural Science Foundation of China(41274083)Special Earthquake Research Project Grant by China Earthquake Administration(201208009)
文摘This paper introduces relative and absolute gravity change observations in the eastern portion of the Tibetan Plateau. We analyze and discuss a change that occurred in 2010 in the gravity along the eastern margin of the plateau and the relationship between this change and the 2013 Lushan Ms7.0 earthquake. Our results show that： （1） before the Lushan MsT.0 earthquake, gravity anomalies along the eastern margin of the Tibetan Plateau changed drastically. The Lushan earthquake occurred at the bend of the high gradient zone of gravity var- iation along the southern edge of the Longmenshan fault zone. （2） The 2013 Lushan earthquake occurred less than 100 km away from the epicenter of the 2008 Wenchuan earthquake. Lushan and Wenchuan are located at the center of a four- quadrant section with different gravity anomalies, which may suggest that restoration after the Wenchuan earthquake may have played a role in causing the Lushan earthquake. （3） A medium-term prediction based on changes in gravity anoma- lies was made before the Lushan Ms7.0 earthquake, in par- ticular, a prediction of epicenter location.
基金financially supported by National Science and Technology Support Project (Grant No. 2012BAC19B05)
文摘Changes in the lake areas of Xainza basin in the past 33 years （1976 to 2008） were studied using Landsat data from Multispectral Scanners （1973- 1977）, Thematic Mapper （1989-1992, 2007-2009）, and Enhanced Thematic Mapper Plus （1999-2002）. The results indicated that lakes in the study area evidently expanded from 1976 to 2008, with total expansion of 1512.64km2. The mean annual air temperature presented an upward trend with certain fluctuations from 1966 to 2008. The air temperature rise rates in the cold season （o.31~C/loa） were higher than those in the hot season （0.24℃/1oa）, in the Xainza station example. Precipitation exhibited evident seasonal differences. Mean annual precipitation in hot season is 281.48 mm and cold season is 32.66 mm from 1966 to 2008 in study area. Precipitation in the hot season was the major contributor to the increase in annual precipitation. Grey relational analysis （GRA） was used to study the response of lake areas to climatic factors. The mean air temperature and precipitation were selected as comoared series, and the lake areas were regarded as the reference series. The grey relational grade （GRG） between compared series and reference series were calculated through GRA. The results indicated that changes in lake areas were mainly affected by climatic factors in the hot season. Lakes in this region were classified into three grades, namely, Grades I, II, and III according to the recharge source and elevation. The GRGs of each series varied for different grade lakes： the area of Grade III lakes were the most relevant to the hot season factors, the GRGs of precipitation and air temperature were 0.7570 and 0.6606; followed by the Grade II lakes; Grade I lakes were more sensitive to the air temperature.
基金supported by the National Natural Science Foundation of China (Nos. 41174004, 41461164004, 41491240265)International Science & Technology Collaborative Program of China (No. 2010DFB20190)+2 种基金the project of Far Eastern Federal University, Russia (14-08-01-05_m)State Key Basic Research Development and Programming Project of China (No. 2008CB425704)Basic Research Program of the Institute of Earthquake Science, CEA (No. 2014IES010102)
文摘The eastern margin of Tibetan Plateau is one of the most active zones of tectonic deformation and seismicity in China. To monitor strain buildup and benefit seismic risk assessment, we constructed 14 survey-mode global position system （GPS） stations throughout the northwest of Longmenshan fault. A new GPS field over 1999-2011 is derived from measurements of the newly built and pre-existing stations in this region. Sequentially, two strain rate fields, one preceding and the other following the 2008 MwT.9 Wenchuan earthquake, are obtained using the Gausian weighting approach. Strain field over 1999-2007 shows distinct strain partitioning prior to the 2008 MwT.9 Wenchuan earthquake, with compression spreading over around Longmenshan area. Strain fieldderived from the two measurements in 2009 and 2011 shows that the area around Longmenshan continues to be under striking compression, as the pattern preceding the Wenchuan earthquake, implying a causative factor of the sequent of 2013 Mw6.7 Lushan earthquake. Our GPSderived dilatation shows that both the Wenchuan and Lushan earthquakes occurred within the domain of pro- nounced contraction. The GPS velocities demonstrate that the Longriba fault underwent slight motion with the faultnormal and -parallel rates at 1.0 -4- 2.5 mm and 0.3 4-2.2 mm/a; the Longmenshan fault displayed slow activity, with a fault-normal rate at 0.8 ± 2.5 mm/a, and a fault-parallel rate at 1.8 4- 1.7 mm/a. Longriba fault is on a par with Longmenshan fault in strain partitioning to accommodate the southeastward motion of eastern margin of the Tibetan Plateau. Integrated analysis of principal strain tensors, mean principal stress, and fast directions of mantle anisotropy shows that west of Sichuan is characterized as mechanically strong crust-mantle coupling.
基金supported by the National Natural Science Foundation of China(31200474,31270552)the National Key Technologies R&D in China(2011BAC09B05)Postdoctoral Science Foundation of China(2013M540714 and 2014T70880)
文摘Significant CO2 fluxes from snow-covered soils occur in cold biomes. However, little is known about winter soil respiration on the eastern Tibetan Plateau of China. We therefore measured winter soil CO2 fluxes and estimated annual soil respiration in two contrasting coniferous forest ecosystems （a Picea asperata plantation and a natural forest）. Mean winter soil CO2 effluxes were 1.08 μmol m-2 s-1 in the plantation and 1.16 μmol m-2 s-1 in the natural forest. These values are higher than most reported winter soil CO2 efflux values for temperate or boreal forest ecosystems. Winter soil respiration rates were similar for our two forest ecosystems but mean soil CO2 efflux over the growing sea- son was higher in the natural forest than in the plantation. The estimated winter and annual soil effluxes for the natural forest were 176.3 and 1070.3 g m-2, respectively, based on the relationship between soil respiration and soil temperature, which were 17.2 and 9.7 % greater than their counterparts in the plantation. The contributions of winter soil respiration toannual soil efflux were 15.4 % tor the plantation and 16.5R for the natural forest and were statistically similar. Our results indicate that winter soil CO2 efflux from frozen soils in the alpine coniferous forest ecosystems of the eastern Tibetan Plateau was considerable and was an important component of annual soil respiration. Moreover, reforesta- tion （natural coniferous forests were deforested and refor- ested with P. asperata plantation） may reduce soil respiration by reducing soil carbon substrate availability and input.
基金supported by National Key Research and Development Program of China[grant number 2017YFC1501802]the National Natural Science Foundation of China[grant number 41375047],[grant number 91537213],and[grant number 41675039]
文摘The distribution characteristics of cloud-top and tropopause height in the tropics and subtropics in boreal summer are analyzed based on CALIPSO data for the period 2008-2012.The maximum values of cloud-top vertical cumulative frequency above the tropopause （CTAT） are concentrated in three tropical regions：the Asian summer monsoon region,Central America,and western Africa.The contributions to the area-weighted CTAT frequency in the three regions from the Northern Hemisphere are 49.0%,13.5%,and 12.4%,respectively.Moreover,the contribution of troposphere-to-stratosphere transport （TST） in the Asian monsoon region to global TST can be far greater than 50%,according to analysis of the continuous equation,velocity potential,and divergent wind from ERA-Interim data.Furthermore,the Asian summer monsoon circulation system controls the distribution of the cloud top.On the south side of the Tibetan Plateau,the maximum frequency of the cloud top,more than 10% per 500 m vertically,is most likely to appear in the core of the high-level easterlyjet near the tropopause height （16.5 km）.Over the Tibetan Plateau,the maximum frequency of the cloud top,greater than 3% per 500 m vertically,is suppressed below 11 km,far away from the thermodynamic tropopause height but close to the dynamic tropopause height of 2 PVU （potential vorticity units）.
基金Natural Science Foundation of China(41105027,41130960)
文摘The study presented herein investigated the main characteristics of carbon monoxideintraseasonal variability and evaluated its possible impact factors using the upper troposphere and lowerstratosphere (UT/LS) Aura Microwave Limb Sounder (MLS) observations over Tibetan Plateau and itsadjacent areas in summer (June to August) of 2005 and 2006. Observations show a persistent constituentextreme extending up into the UT/LS throughout summer, as well as a temporally reversed phase variationbetween the carbon monoxide and ozone in UT/LS. The intraseasonal oscillations (ISOs) of carbonmonoxide during summer are investigated by using methods of wavelet and band pass filter analysis. It isfound that ISOs over the Tibetan Plateau have periods of 10 to 20 days and 30 to 60 days. The formermainly appeared in upper troposphere while the latter in lower stratosphere. Further analysis shows thatthese two periods of ISOs in UT/LS are mainly in phase to the activities of convection over the south of theplateau and the variation of South Asia High, respectively. The above two factors and their dynamicalcoupling may be responsible for the tracer ISOs at different levels.
基金supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP2019QZKK0307)+1 种基金the Sichuan Science and Technology Program(2022YFS0500)the National Natural Science Foundation of China(No.41401313).
文摘The southeastern Tibetan Plateau,which profoundly affects East Asia by helping to maintain the stability of climate systems,biological diversity and clean water,is one of the regions most vulnerable to water erosion,wind erosion,tillage erosion,freeze-thaw erosion and overgrazing under global climate changes and intensive human activities.Spatial variations in soil erosion in terraced farmland(TL),sloping farmland(SL)and grassland(GL)were determined by the^(137)Cs tracing method and compared with spatial variations in soil organic carbon(SOC)and total nitrogen(total N).The^(137)Cs concentration in the GL was higher in the 0-0.03 m soil layer than in the other soil layers due to weak migration and diffusion under low precipitation and temperature conditions,while the^(137)Cs concentration in the soil layer of the SL was generally uniform in the 0-0.18 m soil layer due to tillage-induced mixing.Low^(137)Cs inventories appeared at the summit and toe slope positions in the SL due to soil loss by tillage erosion and water erosion,respectively,while the highest^(137)Cs inventories appeared at the middle slope posi-tions due to soil accumulation under relatively flat landform conditions.In the GL,the^(137)Cs data showed that higher soil erosion rates appeared at the summit due to freeze-thaw erosion and steep slope gradients and at the toe slope position due to wind erosion,gully erosion,freeze-thaw erosion and overgrazing.The^(137)Cs inventory generally increased from upper to lower slope positions within each terrace(except the lowest terrace).The^(137)Cs data along the terrace toposequence showed abrupt changes in soil erosion rates between the lower part of the upper terrace and the upper part of the immediate terrace over a short distance and net deposition on the lower and toe terraces.Hence,tillage erosion played an important role in the soil loss at the summit slope positions of each terrace,while water erosion dominantly transported soil from the upper terrace to the lower terrace and resulted in net soil deposition on the flat lower terrace.The SOC inventories showed similar spatial patterns to the^(137)Cs inventories in the SL,TL and GL,and significant correlations were found between the SOC and^(137)Cs inventories in these slope landscapes.The total N inventories showed similar spatial patterns to the inventories of,37Cs and SOC,and significant correlations were also found between the total N and^(137)Cs inventories in the SL,TL and GL Therefore,^(137)Cs can successfully be used for tracing soil,SOC and total N dynamics within slope landscapes in the southeastern Tibetan Plateau.
