Aeolian-fluvial sediments as palaeoenvironmental records in the eastern Qaidam Basin, NE Tibetan Plateau, since MIS6

2020 ◽  
Author(s):  
Lupeng Yu ◽  
Noam Greenbaum ◽  
Joel Roskin
Keyword(s):  
Tibetan Plateau ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
Qaidam Basin ◽  
Sedimentary Facies ◽  
Fluvial Sediments ◽  
Last Deglaciation ◽  
Aeolian Sand ◽  
The Holocene ◽  
New Interpretation

<p>Aeolian sediments sensitively respond to climatic changes. Continuous Quaternary loess deposits plays important roles in palaeoclimatic reconstructions. However, application of aeolian sand for such reconstructions is limited by its discontinuous depositional nature. Aeolian-fluvial sediments are widely distributed in arid and semi-arid regions where dunefields interact with watercourses. These palaeoenvironmental archives have been sparsely studied mainly due to their mixed character that requires new interpretation approaches.</p><p>We have found that climate fluctuations lead good preservation of aeolian sand deposits that underlay fluvial sediments, making the sedimentary records more continuous. In this study, aeolian and fluvial sediments (elevation of 3400-3500 m a.s.l.) were studied in the eastern margin of Qaidam Basin (QB), northeastern Tibetan Plateau to reconstruct palaeoenvironmental and palaeoclimatic changes since the MIS6, based on sedimentary facies, 120 OSL ages (with age range of 143-1 ka), grain size distribution, MS, TOC, and carbonates.</p><p>Within a deeply (10-65 m) incised 1.5-km-long valley, aeolian-fluvial cycles displayed frequent dune-damming of a stream since MIS6. Dune sands were dated to MIS's 6, 5d, 4, 3c, 3a, and the last deglaciation, while fluvial and dune-dammed lake sediments were dated to MIS's 5c, 3c, 3a, and deglaciation.</p><p>Large-scale A-F interactions mainly occurred during MIS3 and deglaciation, when the QB dunefields were still mobile after LGM and MIS4 and precipitation started to increase. No ages fall within LGM, suggesting an extremely arid and windy environment in which the dune sand kept reworking and cannot record OSL ages. This further confirms that only with the covering of fluvial sediments, aeolian sand can be well preserved. On the other hand, OSL ages of aeolian sand might only present periods when aeolian activities were not too strong.</p><p>During the Holocene, loess-paleosol accumulated in the QB margins, with loess accumulation since 10 ka and development of paleosols during ca. 8.5-3 ka, the Holocene optimum. These results demonstrate that aeolian-fluvial sediments are important palaeoenvironmental records in arid region and indicate that the climate of the eastern QB was mainly controlled by the temperature (solar insolation) and precipitation (Asian Summer Monsoon) changes since MIS6. <strong> </strong></p>

scholarly journals Large-scale atmospheric circulation control on stable water isotopes in precipitation over the northwestern and southeastern Tibetan Plateau

2016 ◽  
Author(s):  
Xiaoxin Yang ◽  
Sunil Acharya ◽  
Tandong Yao
Keyword(s):  
Tibetan Plateau ◽  
Atmospheric Circulation ◽  
Large Scale ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
The Tibetan Plateau ◽  
Stable Water Isotopes ◽  
South Asian Summer Monsoon ◽  
Westerly Jet ◽  
Large Scale Atmospheric Circulation

Abstract. The mid-latitude westerlies and South Asian Summer Monsoon (SASM) are two major atmospheric circulation systems influencing the Tibetan Plateau (TP). We report a seven-year (2007/2008–2013/2014) dataset of δ18O in precipitation (δ18Op) collected at three stations. Taxkorgan (TX) and Bulunkou (BLK) are located on the northwestern TP where westerly winds dominate while Lulang (LL) is situated on the southeastern TP where the SASM dominates. δ18O in precipitation (δ18Op) in northwestern TP varies with surface temperature (T) throughout the study period, and is depleted in 18O in precipitation during June to September when the monsoonal circulation enters the TP. Integration with model outputs suggests that large-scale atmospheric circulation plays a major role in isotopic seasonality in both regions. A teleconnection between precipitation on the northwestern TP and the El Niño-Southern Oscillation (ENSO) warm phase is suggested by changes in the relationship between δ18O and δD (e.g., reduced slope and weighted d-excess) in precipitation samples. These observations are indicative of a weakening of the mid-latitude westerly jet allowing local processes in the continental interior to become more dominant, thereby increasing the contribution of secondary evaporation from falling raindrops and kinetic fractionation. Under the conditions of a high Northern Annular Mode (NAM) the westerly jet is intensified over the southeastern TP which enhances local evaporation and continental recycling as revealed by a lower δD-δ18O slope and intercept, but higher d-excess average in contemporaneously collected precipitation samples. The significant correlation between T and δ18Op in the northwestern TP during various composite periods highlights a variation from 0.39 ‰ / ℃ (ENSO warm) to 0.77 ‰ / ℃ (high NAM), attributable to decreased (increased) water vapor availability over the northwestern TP during the ENSO warm (strong positive NAM) phase. ENSO cold and strong negative NAM phases show analogous effects on atmospheric circulation over both regions.

Late Mesozoic−Cenozoic cooling history of the northeastern Tibetan Plateau and its foreland derived from low-temperature thermochronology

2021 ◽  
Author(s):  
Chen Wu ◽  
Andrew V. Zuza ◽  
Jie Li ◽  
Peter J. Haproff ◽  
An Yin ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Low Temperature ◽  
Large Scale ◽  
Qaidam Basin ◽  
Tectonic Deformation ◽  
Formation Mechanisms ◽  
The Tibetan Plateau ◽  
Thrust Belt ◽  
The South ◽  
Late Mesozoic

The growth history and formation mechanisms of the Cenozoic Tibetan Plateau are the subject of an intense debate with important implications for understanding the kinematics and dynamics of large-scale intracontinental deformation. Better constraints on the uplift and deformation history across the northern plateau are necessary to address how the Tibetan Plateau was constructed. To this end, we present updated field observations coupled with low-temperature thermochronology from the Qaidam basin in the south to the Qilian Shan foreland in the north. Our results show that the region experienced a late Mesozoic cooling event that is interpreted as a result of tectonic deformation prior to the India-Asia collision. Our results also reveal the onset of renewed cooling in the Eocene in the Qilian Shan region along the northern margin of the Tibetan Plateau, which we interpret to indicate the timing of initial thrusting and plateau formation along the plateau margin. The interpreted Eocene thrusting in the Qilian Shan predates Cenozoic thrust belts to the south (e.g., the Eastern Kunlun Range), which supports out-of-sequence rather than northward-migrating thrust belt development. The early Cenozoic deformation exploited the south-dipping early Paleozoic Qilian suture zone as indicated by our field mapping and the existing geophysical data. In the Miocene, strike-slip faulting was initiated along segments of the older Paleozoic suture zones in northern Tibet, which led to the development of the Kunlun and Haiyuan left-slip transpressional systems. Late Miocene deformation and uplift of the Hexi corridor and Longshou Shan directly north of the Qilian Shan thrust belt represent the most recent phase of outward plateau growth.

scholarly journals The East Asian Summer Monsoon at mid-Holocene: results from PMIP3 simulations

2013 ◽  
Vol 9 (1) ◽  
pp. 453-466 ◽  
Author(s):  
W. Zheng ◽  
B. Wu ◽  
J. He ◽  
Y. Yu
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
East Asian Summer Monsoon ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
Eastern China ◽  
Large Scale Circulation ◽  
Asian Summer ◽  
Yangzi River

Abstract. Ten Coupled General Circulation Models (CGCMs) participated in the third phase of Paleoclimate Modelling Intercomparison Project (PMIP3) are assessed for the East Asian Summer Monsoon (EASM) in both the pre-Industrial (PI, 0 ka) and mid-Holocene (MH, 6 ka) simulations. Results show that the PMIP3 model median captures well the large-scale characteristics of the EASM, including the two distinct features of the Meiyu rainbelt and the stepwise meridional displacement of the monsoonal rainbelt. At mid-Holocene, the PMIP3 model median shows significant warming (cooling) during boreal summer (winter) over Eurasia continent that are dominated by the changes of insolation. However, the PMIP3 models fail to simulate a warmer annual mean and winter surface air temperature (TAS) over eastern China as derived from proxy records. The EASM at MH are featured by the changes of large-scale circulation over Eastern China while the changes of precipitation are not significant over its sub-domains of the Southern China and the lower reaches of Yangzi River. The inter-model differences for the monsoon precipitation can be associated with different configurations of the changes in large-scale circulation and the water vapour content, of which the former determines the sign of precipitation changes. The large model spread for the TAS over Tibetan Plateau has a positive relationship with the precipitation in the lower reaches of Yangzi River, yet this relationship does not apply to those PMIP3 models in which the monsoonal precipitation is more sensitive to the changes of large-scale circulation. Except that the PMIP3 model median captured the warming of annual mean TAS over Tibetan Plateau, no significant improvements can be concluded when compared with the PMIP2 models results.

Simulation of the Last 21 000 Years Using Accelerated Transient Boundary Conditions*

2007 ◽  
Vol 20 (17) ◽  
pp. 4377-4401 ◽  
Author(s):  
Oliver Timm ◽  
Axel Timmermann
Keyword(s):  
Boundary Conditions ◽  
Large Scale ◽  
Model Simulation ◽  
Valuable Insight ◽  
Last Deglaciation ◽  
Initial State ◽  
Climate History ◽  
Local Climate ◽  
The Holocene ◽  
Transient Simulations

Abstract The earth system model of intermediate complexity ECBilt-CLIO has been used for transient simulations of the last deglaciation and the Holocene. The forcing effects of the ice sheets, greenhouse gas concentrations, and orbital configurations are prescribed as time-varying boundary conditions. In this study two key aspects of the transient simulations are investigated, which are of broader relevance for long-term transient paleoclimate modeling: the effect of using accelerated boundary conditions and of uncertainties in the initial state. Simulations with nonaccelerated boundary conditions and an acceleration factor 10 were integrated. These simulations show that the acceleration can have a significant impact on the local climate history. In the outcropping regions of the high southern latitudes and the convective regions in the North Atlantic, the acceleration leads to damped and delayed temperature response to the boundary conditions. Furthermore, uncertainties in the initial state can strongly bias the climate trajectories in these areas over 500–700 model years. The affected oceanic regions are connected to the large heat capacities of the interior ocean, which cause a strong delay in the response to the forcing. Despite the shown difficulties with the acceleration technique, the accelerated simulations still reproduce the large-scale trend pattern of air temperatures during the Holocene from previous simulations with different models. The accelerated transient model simulation is compared with existing proxy time series at specific sites. The simulation results are in good agreement with those paleoproxies. It is shown that the transient simulations provide valuable insight into whether seasonal or annual signals are recorded in paleoproxies.

scholarly journals Climatology and physical mechanisms of the tropospheric warm cores over the Tibetan Plateau and its vicinity

2021 ◽  
Author(s):  
Ke Shang ◽  
Xiaodong Liu ◽  
Buwen Dong
Keyword(s):  
Tibetan Plateau ◽  
Active Region ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
Warm Pool ◽  
Formation Mechanisms ◽  
The Tibetan Plateau ◽  
Temperature Deviation ◽  
Physical Mechanisms ◽  
Pacific Warm Pool

AbstractThe frequently observed tropospheric warm cores over the Tibetan Plateau (TP) are unique climate phenomena and are crucial to the Asian summer monsoon development. However, their climatological structure and formation mechanisms remain elusive and inconsistent among previous studies. In this work, two vertically separated warm cores, the upper-level warm cores (ULWCs) and lower-level warm cores (LLWCs), are identified based on the zonal temperature deviation. The LLWCs are basically confined below 450 hPa, and the ULWCs are mostly observed at 200–400 hPa. The active region of the LLWCs is generally within the TP domain and characterized by regional patches with high frequency occurrences. In contrast, the active region of the ULWCs is featured by a zonally elongated band along the southern TP. The physical mechanisms for the formations of these two distinct types of warm cores are revealed: the LLWCs are mainly generated and maintained by the surface diabatic heating, while the ULWCs are dominated by the large-scale circulation associated with the convection over the Indo-Pacific warm pool. During March–June, the ULWCs within the TP domain occur most frequently and the intensities attain their maxima. In March–April, the ULWCs are mainly determined by the TP adiabatic subsidence induced by the convection over the Indo-Pacific warm pool. In May–June, the warm advection induced by westerlies generates the downstream ULWCs and enhances the ULWCs formed in previous months. Hence it might be inappropriate in traditional view to attribute the tropospheric warm cores around the TP solely to the direct thermal effect of the elevated topography.

Persistent Weakening Trend in the Spring Sensible Heat Source over the Tibetan Plateau and Its Impact on the Asian Summer Monsoon

2011 ◽  
Vol 24 (21) ◽  
pp. 5671-5682 ◽  
Author(s):  
Anmin Duan ◽  
Fei Li ◽  
Meirong Wang ◽  
Guoxiong Wu
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
East Asian ◽  
The Tibetan Plateau ◽  
South Asian Summer Monsoon ◽  
Spatial Nonuniformity ◽  
Asian Summer ◽  
The Tropics

Abstract Using a dataset extended by the addition of data for 2004–08, this study reexamined the trend in the sensible heating (SH) flux at 73 meteorological stations over the Tibetan Plateau (TP) during 1980–2008 and investigated its impact on monsoon precipitation in the surrounding region. In contrast to ongoing climate warming, a weakening trend in SH is persistent over most of the plateau, despite a sharp increase in the ground–air temperature difference in 2004–08. The weakening trend in SH over the TP is primarily a response to the spatial nonuniformity of large-scale warming over the East Asian continent, which is characterized by much greater warming amplitude at mid- and high latitudes than over the tropics and subtropics. Furthermore, the suppressed air pump effect, which is driven by SH over the TP and acts as a strong forcing source, gives rise to reduced precipitation along the southern and eastern slopes of the plateau, and increased rainfall over northeastern India and the Bay of Bengal. No significantly stable correlation exists between the SH source over the TP and the overall trend or interdecadal variability in the East Asian or South Asian summer monsoon.

scholarly journals A 7000-year record of coastal evolution, Vejers, SW Jutland, Denmark

2006 ◽  
Vol 53 ◽  
pp. 1-22 ◽  
Author(s):  
Lars B. Clemmensen ◽  
Karsten Pedersen ◽  
Andrew Murray ◽  
Jan Heinemeier
Keyword(s):  
Large Scale ◽  
Coastal Dunes ◽  
Aeolian Sand ◽  
Coastal System ◽  
Dune Field ◽  
The Holocene ◽  
The North ◽  
Sedimentary Evolution ◽  
Sand Drift ◽  
Aeolian Activity

The Holocene coastal lowland at Vejers in western Jutland has formed during the last 7000 years. The lowland is composed of a large, NNE-SSW trending spit system associated with minor and only locally developed strandplain or beach ridge systems. The main spit and back-barrier system is bounded to the north and east (inland) by old moraine landscapes (Varde Bakkeø). Most of the coastal system and also large parts of the adjacent moraine landscape is covered by aeolian sand. In this study one of the minor strandplain systems is investigated. This system is developed at the south-western margin of the old moraine landscape at Grovsø, a lake near Vejers. The Holocene sedimentary evolution of this latter system is evaluated on the basis of data from two closely situated cores and Ground-Penetrating Radar (GPR) mapping. Both cores consist of a lowermost unit with marine sediment, a middle unit with lake-aeolian sand and an uppermost unit with aeolian sandplain deposits. Peat layers and peat-rich paleosols are common. These peat-rich horizons are dated by the Accelerator Mass Spectrometry (AMS) radiocarbon technique, while the intervening sand layers are dated by Optically Stimulated Luminescence (OSL). Combined evidence from the sedimentological and chronological studies of the cores and the GPR survey, indicate that the area was first transgressed at about 5100 BC. During the subsequent period (5100–2700 BC) relative sea level rose about 5 meters, the strandplain prograded, and small coastal dunes formed. During this progradational event a large strandplain lake formed behind the frontal dune ridge and this lake was filled primarily by aeolian sand. Aeolian sand drift may have been most intense around 3000 BC. This first period of large-scale aeolian activity ended some time before 2300 BC with formation of a peat-rich paleosol. Aeolian activity, however, was soon re-established and resulted in the formation of a large sandplain with small dunes. Aeolian sand movement and accumulation, however, was punctuated by periods of landscape stabilisation and peat-rich paleosol formation. Changes from landscape stabilisation to dune field activity took place at about 2300 BC, 1450 BC, 800 BC, and 650 BC. Aeolian accumulation at the study site terminated at about AD 0, but other evidence indicates renewed aeolian activity in the dune field after AD 300 and between AD 1100 and 1900. The chronology of some of these aeolian activity phases are synchronous with cooling events in the North Atlantic region suggesting that climatic change strongly influenced dune field dynamics.

scholarly journals Upstream Subtropical Signals Preceding the Asian Summer Monsoon Circulation

2004 ◽  
Vol 17 (21) ◽  
pp. 4213-4229 ◽  
Author(s):  
Song Yang ◽  
K-M. Lau ◽  
S-H. Yoo ◽  
J. L. Kinter ◽  
K. Miyakoda ◽  
...  
Keyword(s):  
Middle East ◽  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Large Scale ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Jet Stream ◽  
The Tibetan Plateau ◽  
Physical Processes ◽  
Asian Summer

Abstract In this study, the authors address several issues with respect to the antecedent signals of the large-scale Asian summer monsoon that were earlier identified by Webster and Yang. In particular, they revisit the changes in the subtropical upper-tropospheric westerlies preceding the monsoon, depict the detailed structure of the monsoon's antecedent signals, and investigate the physical processes from the signals to the monsoon. They also explore the teleconnection of these signals to various large-scale climate phenomena and emphasize the importance of the upstream location of the signals relative to the Tibetan Plateau and the monsoon. Before a strong (weak) Asian summer monsoon, the 200-mb westerlies over subtropical Asia are weak (strong) during the previous winter and spring. A significant feature of these signals is represented by the variability of the Middle East jet stream whose changes are linked to the Arctic Oscillation, North Atlantic Oscillation, El Niño–Southern Oscillation, and other climate phenomena. When this jet stream intensifies and shifts southeastward, cold air intrudes frequently from eastern Europe into the Middle East and southwestern Asia. As a result, in subtropical Asia, snow and precipitation increase, the ground wetness increases, and surface temperature decreases. A strengthening Middle East jet stream is also accompanied by increases in both stationary wave activity flux and higher-frequency eddy activities. The Tibetan Plateau acts to block these westerly activities propagating eastward and increase the persistence of the low-temperature anomalies, which in turn prolongs the atmospheric signals from winter to spring. A strong link is found between the persistent low-temperature anomalies and the decrease in geopotential height over southern Asia, including the Tibetan Plateau, in spring. The latter indicates a late establishment of the South Asian high, and implies a delay in the atmospheric transition from winter to summer conditions and in the development of the summer monsoon. The preceding scenario for a strong Middle East jet stream and a weaker Asian monsoon can be applied accordingly for the discussion of the physical processes from a weak jet stream to a strong monsoon. The current results of the relationship between the extratropical process and Asian monsoon resemble several features of the tropical–extratropical interaction mechanism for the tropospheric biennial oscillation (TBO). While the role of tropical heating is emphasized in the TBO mechanism, compared to the variability of the sea surface temperature related to El Niño–Southern Oscillation, the extratropical process examined in this study is more strongly linked to the Asian summer monsoon.

scholarly journals Response of Regional Asian Summer Monsoons to the Effect of Reduced Surface Albedo in Different Tibetan Plateau Domains in Idealized Model Experiments

2021 ◽  
pp. 1-49
Author(s):  
MENGMENG LU ◽  
SONG YANG ◽  
JUNBIN WANG ◽  
YUTING WU ◽  
XIAOLONG JIA
Keyword(s):  
Tibetan Plateau ◽  
Thermal Effect ◽  
Summer Monsoon ◽  
Thermal Condition ◽  
Large Scale ◽  
Surface Albedo ◽  
Asian Summer Monsoon ◽  
Spatial Scales ◽  
South Asian Summer Monsoon ◽  
Asian Summer

AbstractThe thermal effect of entire Tibetan Plateau (TP) tends to strengthen the South Asian summer monsoon (SASM); however, how does this monsoon component respond to the thermal conditions of different TP domains? How do the thermal condition of entire TP influences other monsoons including the East Asian summer monsoon (EASM) and the Southeast Asian summer monsoon (SEASM)? These questions are addressed by conducting an experiment with the CESM, which is forced by reducing the surface albedo over the plateau by half, from a TP-averaged 0.20 to 0.10, from May to September, and similar experiments for different TP domains. Both observation and model results show that the entire-TP heating intensifies the large-scale Asian monsoon, the SASM, and the EASM, but surprisingly weakens the SEASM. It is also surprising that the TP heating exerts a stronger effect on the EASM than on the SASM. The southern TP (south of 35°N) does not show the strongest impact on the SASM compared to other TP domains and it exerts a weakest impact on the EASM, which is most strongly influenced by the thermal effect of eastern (east of 90°E) and northern TP. The western TP weakens the SEASM as the other domains, while it strengthens other monsoon components. The thermal condition of southern and eastern TP are accompanied by signals of tropical atmospheric response at relatively broader spatial scales, while that of northern TP more apparently leads to a significant wave train extending eastward from the TP to western Eurasia over the higher latitudes.

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