stable isotope and radiocarbon balances of two tibetan lakes sumxi co longmu co from 13 000 bp hydrologic and climatic changes in western tibet since 13 000 bp are inferred from mineralogical and isotopic analyses of lacustrine sediments from the sumxi longmu co basin the interpretation is based on isotope data from the modern system carbon isotope chemistry is complex because of the presence of old limestones on the watershed sediments contain detrital and authigenic calcites the proportions of which are quantitatively estimated by x ray diffractometry stable isotope contents of the authigenic calcite are reconstructed from mass balance equations the high 13c contents up to 6 are attributed to an enhancement of calcite precipitation from water surface during freezing periods the 18o content is related to residence time and evaporation the validity of 14c dates obtained from different types of material is discussed our record in good agreement with paleobiological data from the same material shows the sudden establishment of wet warm conditions at 10 000 bp which culminated at 7500 6000 bp after a brief reversal event at 7900 bp maximum aridity for the whole holocene is recorded at 4300 bp

the holocene indian monsoon variability over the southern tibetan plateau and its teleconnections abstract a high resolution stalagmite oxygen isotope record from tianmen cave located in the south central tibetan plateau characterizes detailed climatic variations between 8 7 and 4 3 ka bp on centennial and decadal time scales with a temporal resolution of 3 to 7 years the tianmen record is in good agreement with speleothem records from asian monsoon regions i e dongge cave dykoski et al 2005 wang et al 2005 qunf cave fleitmann et al 2003 upwelling records from the arabian sea gupta et al 2003 gupta et al 2005 and peat bog records from southeast tibetan plateau hong et al 2003 indicating that the indian summer monsoon ism gradually weakened as northern hemisphere summer insolation declined during the early mid holocene and that ism intensity rather than temperature dominates the precipitation 18o on centennial to decadal time scales in the southern tp on centennial to decadal time scales the detrended tianmen record correlates well with the greenland ice core record further confirming the mechanistic connection between the ism and high northern latitude temperature changes meanwhile the tianmen record bears significant solar activity cycles suggesting that the solar output changes may affect the variability of the ism and likely the position of the intertropical convergence zone itcz as well moreover due to joint effects of changes in monsoon precipitation moisture source and temperature the tianmen 18o record shows much larger amplitude changes than speleothem 18o records from low elevation asian monsoon regions which is similar to the previously reported marine isotope stage mis 5 record cai et al 2010 suggesting heightened sensitivity of precipitation isotope composition to climate changes over the high elevation regions and further demonstrating that the stable isotope lapse rate may change under different climatic conditions

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

carbonate isotopes from high altitude tso moriri lake nw himalayas provide clues to late glacial and holocene moisture source and atmospheric circulation changes abstract high resolution isotopic 18 o and 13 c investigations on endogenic carbonates calcite aragonite from tso moriri lake nw himalaya show dramatic fluctuations during the late glacial and the early holocene and a persistent enrichment trend during the late holocene changes in this lake are largely governed by the input meltwater monsoon precipitation evaporation i e ratio also reflected in changes in the carbonate mineralogy with aragonite being formed during periods of lowest i e using new isotopic data on endogenic carbonates in combination with the available data on geochemistry mineralogy and reconstructed mean annual precipitation we demonstrate that the late glacial and early holocene carbonate 18 o variability resulted from fluctuating indian summer monsoon ism precipitation in nw himalaya this region experienced increasing ism precipitation between ca 13 1 and 11 7 cal ka and highest ism precipitation during the early holocene 11 2 8 5 cal ka however during the late holocene evaporation was the dominant control on the carbonate 18 o regional comparison of reconstructed hydrological changes from tso moriri lake with other archives from the asian summer monsoon and westerlies domain shows that the intensified westerly influence that resulted in higher lake levels after 8 cal ka in central asia was not strongly felt in nw himalaya

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

early to mid holocene lake high stand sediments at lake donggi cona northeastern tibetan plateau china lake high stand sediments are found in three onshore terraces at lake donggi cona northeastern tibetan plateau and reveal characteristics of hydrological changes on lake shorelines triggered by climate change geomorphological processes and neo tectonic movements the terraces consist of fluvial alluvial to littoral lacustrine facies end member modeling of grain size distributions allowed quantification of sediment transport processes and relative lake levels during times of deposition radiocarbon dating revealed higher than modern lake levels during the early and mid holocene lake levels follow the trend of asian monsoon dynamics and are modified by local non climatic drivers site specific impacts explain fluctuations during the initial lake level rise 11 cal ka bp maximum lake extension reached 9 2 cal ka bp at 16 5 m above present lake level a p l l littoral and lacustrine sediment deposition paused during a phase of fluvial activity and post depositional cryoturbations at 8 5 cal ka bp when the lake level fell to 8 m a p l l after a second maximum at 7 5 cal ka bp lake level declined slightly at 6 8 cal ka bp probably due to a non climatic pulse that caused lake opening the level remained high until a transition towards drier conditions 4 7 cal ka bp though discontinuous high stand sediments provide a unique high resolution archive

variability of southwest indian summer monsoon precipitation during the bolling allerod we have generated a high resolution 20 yr 2 3 0 th dated stalagmite oxygen isotope record from timta cave in the western himalaya in india that documents southwest indian summer monsoon ism precipitation variations during the bolling allerod interstadial from 15 2 to 11 7 ka compared with the glacial and younger dryas ism precipitation was enhanced during the bolling allerod ism precipitation was apparently coupled to variations in the east asian monsoon and north atlantic climate on millennial and multicentennial time scales during the deglaciation analyses of a high growth rate interval 2 5 yr resolution encompassing the late bolling early alterod suggest that multidecadal monsoon variability was an important aspect of ism behavior at that time the frequency spectrum of ism precipitation during this time interval is similar to that of the 1 4 c record and other ism precipitation records during the latest holocene this raises the hypothesis that multidecadal climate dynamics during the late boiling early allerod may have been similar to those that operated during the last several millennia even though the boundary conditions of these two time intervals were very different

the retrospective prediction of el nino southern oscillation from 1881 to 2000 by a hybrid coupled model i sea surface temperature assimilation with ensemble kalman filter in this study we assimilated sea surface temperature sst data of the past 120 years into an oceanic general circulation model ogcm for el nino southern oscillation enso retrospective predictions using ensemble kalman filter enkf it was found that the ensemble covariance matrix in enkf can act as a time variant transfer operator to project the sst corrections onto the subsurface temperatures effectively when initial perturbations of ensemble were constructed using vertically coherent random fields as such the increments of subsurface temperatures can be obtained via the transfer operator during assimilation cycles the results show that the sst assimilation improves the model simulation skills significantly not only for the sst anomalies over the whole assimilated domain but also for the subsurface temperature anomalies of the upper 100 m over the tropical pacific off the equator along the equator the improvement of the assimilation is confined within the mixing layer because strong upwelling motions there prevent the downward transfer of sst information the retrospective prediction skills of enso over the past 120 years from 1881 to 2000 were significantly improved by the sst assimilation at all leads of 1 12 months especially for the 3 6 months leads compared with those initialized by the control run without assimilation the skilful predictions by the assimilation allow us to further study enso predictability using this coupled model

age constraints on the late quaternary evolution of qinghai lake tibetan plateau dating and geomorphology of shoreline features in the qinghai lake basin of northwestern china suggest that contrary to previous interpretations the lake likely did not reach levels 66 140 m above modern within the past 90 000 yr maximum highstands of 20 66 m above modern probably date to marine isotope stage mis 5 mis 3 highstands are undated and uncertain but may have been at or below post glacial highs the lake probably reached 3202 3206 m 8 12 m during the early holocene but stayed below 3202 m after 8 4 ka this shoreline history implies significantly different hydrologic balances in the qinghai lake basin before 90 ka and after 45 ka possibly the result of a more expansive asian monsoon in mis 5

lake level reconstruction for 12 8 2 3 ka of the ngangla ring tso closed basin lake system southwest tibetan plateau article i nfo we present a shoreline based millennial scale record of lake level changes spanning 12 8 2 3 ka for a large closed basin lake system on the southwestern tibetan plateau fifty three radiocarbon and eight u th series ages of tufa and beach cement provide age control on paleoshorelines ringing the basin supplemented by nineteen ages from shell and aquatic plant material from natural exposures generally recording lake regressions our results show that paleo ngangla ring tso exceeded modern lake level 4727 m asl continuously between 12 8 and 2 3 ka the lake was at its highstand 135 m 4862 m asl above the modern lake from 10 3 ka to 8 6 ka this is similar to other closed basin lakes in western tibet and coincides with peak northern hemisphere summer insolation and peak indian summer monsoon intensity the lake experienced a series of millennial scale oscillations centered on 11 5 10 8 8 3 5 9 and 3 6 ka consistent with weak monsoon events in proxy records of the indian summer mon soon it is unclear whether these events were forced by north atlantic or indian ocean conditions but based on the abrupt lake level regressions recorded for ngangla ring tso they resulted in significant periodic reductions in rainfall over the western tibetan plateau throughout the holocene

quartz cpo and kinematic analysis in deformed rocks devoid of visible stretching lineations an integrated ams and ebsd investigation abstract kinematic analysis of deformed rocks requires study of structures in a section parallel to the stretching lineation and perpendicular to the foliation i e xz section of the strain ellipsoid however presence of stretching lineation is more of an exception rather than a norm in naturally deformed rocks this raises challenges for kinematic studies in this study the authors advocate use of anisotropy of magnetic susceptibility ams to identify the three principal axes of ams ellipsoid k1 k2 k3 which are equated with principal axes of the strain ellipsoid x y z this helps identify x direction of strain ellipsoid in deformed rocks that lack visible stretching lineations it is proposed that a section prepared parallel to the k1k3 plane of a deformed rock can be treated as equivalent to xz section of strain ellipsoid thus making it possible to perform kinematic studies in a rock that did not have stretching lineation use of this method is demonstrated on massive metavolcanic rocks of hutti region dharwar craton south india which is replete with quartz veins that contain gold crystallographic preferred orientation cpo of quartz veins is measured using sem ebsd studies of thin sections prepared parallel to k1k3 plane of the host rock obtained data help recognize the presence of down dip sense of movement as well as strain partitioning within veins which are aspects that were not recognized in earlier studies it is concluded that integration of ams and sem ebsd studies will play an important role in kinematic studies in future

osl chronology and palaeoclimatic implications of aeolian sediments in the eastern qaidam basin of the northeastern qinghai tibetan plateau abstract aeolian sediments are widely distributed in the hyper arid qaidam basin and are good palaeoclimatic records due to limited age control aeolian processes and their relevance to palaeoclimatic change are poorly understood in this study we present 28 optically stimulated luminescence osl ages for both loess 14 samples and aeolian sand 14 samples from 8 profiles in eastern qaidam basin eqb in order to provide a detailed chronology for understanding the timing of aeolian processes and associated environmental conditions we reconstructed the history of aeolian activity in the eqb since deglaciation by combining osl chronologies lithologic stratigraphy and grain size analysis the results indicate that 1 aeolian sand underlying the loess accumulated at ca 12 4 11 5 ka and 10 8 ka but not during the last glacial maximum 2 loess accumulation started at 10 ka and lasted to 0 45 ka at least while most of the loess was deposited during 8 4 5 ka 3 palaeoclimates in the eqb are inferred to be arid during 12 4 11 5 ka relatively humid during 10 8 ka humid during 8 4 5 ka and relatively arid during 4 5 0 45 ka and 4 evolution of aeolian sediments were mainly controlled by effective moisture and also affected by local topography

last deglacial and holocene lake level variations of qinghai lake north eastern qinghai tibetan plateau qinghai lake is of significance for paleoclimate research because it lies in a pivotal region that is influenced by both the mid latitude westerlies and the low latitude asian summer monsoon asm most published lake level histories of qinghai lake are interpreted from drill core proxies here we combine geomorphic shoreline investigations with optically stimulated luminescence dating to constrain lake level variations since the last deglacial the results indicate that two periods of highstands occurred during the last deglacial approximate to 16 14 9 and approximate to 12 6 12 2 ka and that lake levels were 6 7 4m higher than at present lake levels dropped abruptly during the younger dryas and were generally low with frequent fluctuations during the early holocene qinghai lake reached its highest holocene level 9 1m higher than modern at approximate to 5 ka and has regressed during the past 2 ka we propose that high lake levels during the last deglacial were due mainly to melting glacial and permafrost waters supplemented by enhanced westerlies precipitation and decreased evaporation during heinrich event 1 approximate to 16 14 9 ka and increased asm rainfall during the bolling allerod warm period approximate to 14 12 ka lake level fluctuations during the holocene were generally in accordance with moisture variations in the marginal monsoon zones of inland china

assessing tectonic and climatic controls for late quaternary fluvial terraces in guide jianzha and xunhua basins along the yellow river on the northeastern tibetan plateau abstract this study focused on well preserved fluvial terrace sequences that span the past 100 ka in the guide jianzha and xunhua basins along the yellow river that drained the northeastern tibetan plateau new geomorphic stratigraphic sedimentologic and chronologic data from twelve depositional sequences within terraces yielded better constraints on rates of incision degradational and aggradational phases for the yellow river age control was established by sixteen osl ages on quartz grains from fluvial sediments three fluvial aggradational phases were identified between 100 and 80 ka 53 and 40 ka and 21 and 12 ka associated with terrace levels respectively at 120 to 95 61 to 45 and 25 to 15 m above river level these aggradational phases reflect multiple processes including enhanced fluvial discharge sediment availability with glaciation deglaciation and increased monsoonal precipitation the initiation of fluvial degradation was linked to mega floods released from landslide dammed lakes at ca 76 38 and 16 ka though these changes may also reflect variations in sediment load discharge relations with climate change the apparent net incision rate is 1 13 0 11 mm yr for the past 100 ka and is consistent with late cenozoic tectonic uplift rates 0 5 2 mm yr and recent gps based rates the fluvial dynamics of the upper reach of the yellow river was variably controlled by climate induced changes in discharge sediment load relations on stadial to interstadial timescales episodic mega floods from the breach of landslide dams and with net incision in the past 100 ka in response to tectonic uplift of the tibetan plateau

the influence of 14c reservoir age on interpretation of paleolimnological records from the tibetan plateau there is a great deal of controversy regarding the fate of glaciers and ice fields on the tibetan plateau in the face of continued anthropogenic global warming paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the tibetan plateau to changing conditions specifically the numerous lakes distributed across the tibetan plateau can provide high resolution spatial and temporal climate reconstructions to investigate past changes in the climate system in this paper we review the primary limitation to exploiting these valuable paleoclimate archives errors in radiocarbon based age models we review the techniques that have been used to estimate 14 c reservoir ages on the tibetan plateau and compile the published 14 c reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties using site specific evaluations of bangong co and lake qinghai we demonstrate that 14 c age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records we also examine 14 c induced uncertainties in the spatial climatic response on the tibetan plateau to 1 the termination of the last glacial maximum and 2 the holocene thermal maximum we conclude with recommendations for reducing uncertainties in future lake based paleoclimate studies on the tibetan plateau

cosmogenic 10be inferred lake level changes in sumxi co basin western tibet abstract most tibetan lakes are surrounded by conspicuous regressive shorelines attesting to high water levels in the past concentrations of the in situ produced cosmogenic radionuclide 10 be in bedrock from the three highest terraces surrounding sumxi co situated in western kunlun indicate that the highest lake level appeared before 10 000 11 500 yr and most likely between 11 000 and 12 800 yr younger ages for the two lower terraces imply regression of sumxi co during the early mid holocene the concurrency of the highest lake level with orbitally induced maximum northern hemisphere summer insolation suggests that the increase in water supply to sumxi co was most likely associated with increased recharge from melting glaciers we conclude that the enhanced indian monsoon during the early holocene did not penetrate the tibetan plateau and affect the northwestern part of tibet significantly

shrinking lakes in tibet linked to the weakening asian monsoon in the past 8 2 ka expansion or shrinkage of closed lakes is a natural response to fluctuations in precipitation and evaporation linked closely to changes in strength or position of atmospheric circulation in tibet there are many such lakes with paleo shorelines that can be used for reconstructions of climate history despite the fact that many paleo shorelines are well preserved in tibet dating them has been seriously hindered by various difficulties here we present the first optical dating chronology for a series of paleo shorelines in zhari namco the third largest inland lake in central tibet our results indicate that the lake level has dropped 128m over the past 8 2ka younger shorelines are found at lower altitudes indicating that the shorelines follow a geomorphic chronological order and a broadly continuous trend of stepwise shrinkage the surface area of zhari namco has shrunk in size from 4605km2 at 8 2ka ago to 996km2 at present 300km3 of water has been lost from this lake such a loss in water implies a significant reduction in precipitation over the past 8 2ka a likely result of a weakening asian monsoon following the decreasing precipitation since the early holocene this area has become increasingly arid

a tibetan lake sediment record of holocene indian summer monsoon variability article history sedimentological data and hydrogen isotopic measurements of leaf wax long chain n alkanes dwax from an alpine lake sediment archive on the southeastern tibetan plateau paru co provide a holocene perspective of indian summer monsoon ism activity the sedimentological data reflect variations in lake level and erosion related to local ism rainfall over the paru co catchment whereas dwax reflects integrated synoptic scale ism dynamics our results indicate that maximum ism rainfall occurred between 10 1 and 5 2 ka during which time there were five century scale high and low lake stands after 5 2 ka the ism trended toward drier conditions to the present with the exception of a pluvial event centered at 0 9 ka the paru co results share similarities with paleoclimate records from across the tibetan plateau suggesting millennial scale ism dynamics were expressed coherently these millennial variations largely track gradual decreases in orbital insolation the southward migration of the intertropical convergence zone itcz decreasing zonal pacific sea surface temperature sst gradients and cooling surface air temperatures on the tibetan plateau centennial ism and lake level variability at paru co closely track reconstructed surface air temperatures on the tibetan plateau but may also reflect indian ocean dipole events particularly during the early holocene when enso variability was attenuated variations in the latitude of the itcz during the early and late holocene also appear to have exerted an influence on centennial ism rainfall 2014 elsevier b v all rights reserved

holocene lake level variations on the qinghai tibetan plateau paleoshorelines indicative of multiple high lake stages can be found around many lakes on the qinghai tibetan plateau qtp conspicuous paleoshorelines associated with the most recent highstands can be readily observed on satellite images and during field investigations however earlier paleoshorelines have been identified at only a few sites around these lakes due to a lack of clear shoreline features and limited spatial extension of those that can be identified we investigated past lake highstands using published chronologies aster dem google earth and arcgis 9 2 software these data suggest that 1 paleoshorelines of the most recent lake highstand were formed during the holocene 2 during this highstand lake levels reached more than 90 60 90 and 30 60 m higher than present in the central gangdise and western qiangtang areas while in the eastern qiangtang holxil yushu and northeastern qtp areas highstands did not exceed 30 m above modern 3 during the early holocene some lakes on the southwestern qtp combined to form large lakes while lakes in the inland areas of the qtp were only a little larger during the holocene high lake level stages

late quaternary water depth changes in hala lake northeastern tibetan plateau derived from ostracod assemblages and sediment properties in multiple sediment records abstract late pleistocene and holocene climate dynamics along the marginal belt of the east asian summer monsoon in china and their responses to hydrological cycles in lake basins of the tibetan plateau are still a matter of scientific discussion hala lake a closed 65 m deep lake basin in the western qilian mountains qinghai province is considered a monitor of climate driven hydrological and environmental changes during the past 24 kyr bp the distribution patterns of ostracod assemblages stable isotopes sediment geochemical properties in four sediment records from different water depths and their combination with the unique limnological setting enabled us to reconstruct four major phases of centennial scale water depth fluctuations from the global last glacial maximum ca 24 kyr bp to the present our results show that hala lake experienced a very shallow and small water body during the lgm and lateglacial under cold and dry climate conditions rapid increase of water depth and contemporaneous lake expansion started at around 14 kyr bp phase i most likely as a result of glacier melt due to the onset of climate warming the lake reached 45 m water depth at around 13 5 kyr bp reduced water depth during the younger dryas spell ca 12 kyr bp may be attributed to a short term return to cooler and drier conditions during the early holocene phase ii water depth increased further toward lake highstands close to its present level with a highest lake level of up to 9 m above the present lakestand at 8 0 7 8 kyr bp besides continued glacier melt supply we assume that summer monsoon effective moisture contributed to the overall water budget but remained relatively unstable favoring water depth fluctuations a pronounced lower water depth falls into the period between 9 2 and 8 1 kyr bp perhaps the result of weak monsoon influence or its complete absence although the warming trend continued toward its optimum at ca 8 7 kyr bp a distinct mass flow most likely triggered by an earthquake occurred during a lake lowstand either at ca 7 0 kyr bp or at around 8 1 kyr bp the mid holocene phase iii was characterized by fluctuating water depths between 7 8 and 4 5 kyr bp conflicting trends of stable isotope data limit the validity of water depth estimations but may show higher lake levels between 5 5 and 4 5 kyr bp coincident with dated lake sediments in a cliff position at the northern lake shore this positive water balance can most likely be attributed to increased westerly derived moisture supply during autumn and late winter although summer monsoon influence could also be of significance coincident with the 4 2 ka event the lake experienced shallow water at around 4 1 kyr bp perhaps as a result of continued cooling and drier climate conditions supporting the arguments of a general cooling trend throughout the holocene the late holocene phase iv is characterized by extremely unstable hydrological conditions with rapid fluctuations in water depth more frequently controlled by westerly driven effective moisture supply since the lake lowstand at about 1 4 1 2 kyr bp the lake has developed toward its present level our research underlines the necessity for comparing multiple proxy records from different lake sites to better evaluate centennial scale climate driven variations throughout the late pleistocene and holocene periods all presented data suggest the variable influence of summer monsoon effective moisture on the hydrological budget of the lake water depth variations did not follow the long term pattern of the asian monsoon system due to a potential modulation by westerly derived moisture impact

luminescence dated aeolian deposits of late quaternary age in the southern tibetan plateau and their implications for landscape history abstract aeolian deposits are widely distributed in the interior of the tibetan plateau and their chronology is poorly known it is not yet clear whether they accumulated only after the last deglaciation or over a longer time we applied quartz osl dating to aeolian samples from the lhasa area with osl ages ranging from 2 9 0 2 to at least 118 11 ka the probability density frequency pdf distribution of 24 ages reveals age clusters at about 3 8 16 21 33 and 79 83 ka indicating enhanced sediment accumulation then the results show that aeolian deposition occurred throughout most of the last 100 ka this implies that 1 an ice sheet covering the whole tibetan plateau during the last glacial maximum lgm could not have existed and 2 erosion during the last deglaciation was not as strong as previously proposed such that not all pre holocene loess was removed the age distribution shown in the pdf indicates that aeolian accumulation is episodic sand formation events revealed by age clusters at 3 8 and 16 21 ka imply roughly synchronous environmental responses to corresponding global scale arid events

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

constraining holocene lake level highstands on the tibetan plateau by 10be exposure dating a case study at tangra yumco southern tibet abstract many lakes on the tibetan plateau are surrounded by palaeo shorelines that document former lake level highstands and hence past changes in climate establishing accurate chronologies for these shorelines is crucial to correlate lake level fluctuations with palaeo environmental histories that are commonly inferred from lake sedimentary records here we apply surface exposure dating to constrain the age of two lake level highstands at one of the largest tibetan lakes tangra yumco which has well developed palaeo shorelines located up to 185 m above the current lake for sampling we focussed on wave cut bedrock terraces that vary considerably in width because they were carved into rocks of different erodibility samples from the highest strath terrace 180 185 m above the lake at three different sites yield tightly clustered 10 be ages between 7 39 0 19 ka and 7 87 0 27 ka internal errors which constrain the end of an early holocene lake level highstand at 7 6 0 6 ka external error the consistency of the 10 be ages indicates that bedrock erosion by wave attack reduced the inherited 10 be component to negligible amounts because otherwise samples would show considerable age scatter two bedrock samples from a lower terrace 140 145 m above the lake and one amalgamated clast sample from a beach ridge on the same terrace yield 10 be ages between 4 04 0 14 ka and 4 50 0 15 ka these ages document that the lake level dropped by 40 m between 7 6 ka and 4 3 ka granite boulders from the two investigated terraces yield apparent 10 be ages that are 6 ka and 27 ka older than the ages of the respective terraces indicating that this sample type is not reliable in this setting overall our results demonstrate that exposure dating of bedrock terraces provides a valuable tool to reconstruct lake level histories on the tibetan plateau

holocene lake level changes of hurleg lake on northeastern qinghai tibetan plateau and possible forcing mechanism the palaeoshorelines of a lake are the direct geomorphic evidences to reflect past water levels and record information on palaeoclimatic changes previous research indicates that the timing and forcing mechanisms of climatic change on the northeastern qinghai tibetan plateau ne qtp are still controversial here we report quartz optically stimulated luminescence osl ages for beach deposits and accelerator mass spectrometry ams 14c age for plant remains shoreline features and geomorphic exposures that contribute to a reconstruction of the lake level history of hurleg lake on the ne qtp the results imply that 1 three high lake levels are dated to 6 8 6 4 5 0 4 7 and 2 2 1 4 kyr corresponding to relatively wet and stable climate from pollen records of sediment core in this lake during mid late holocene 2 the highest lake level period occurred at 5 0 4 7 kyr which is almost synchronous with the highest effective moisture phase from synthesized lake records influenced by the westerlies and 3

palaeoclimatic interpretation of a topographic profile across middle holocene regressive shorelines of longmu co western tibet most lakes and closed basins in tibet are surrounded by abandoned shorelines attesting for high water levels in the past two such lakes longmu co and sumxi co western tibet were the focus of detailed palaeoclimatic work during the 1989 sino french expedition based on the study of lake sediments and analysis of a piston core here it is shown that additional information may be deduced from the abandoned shorelines around longmu co a 1800 m long topographic profile was levelled from 75 m up to 230 m above the present lake elevation 5008 m on which the shorelines form a flight of horizontal terraces separated by more or less degraded scarps the elevations of the terraces were spaced regularly about 1 35 m except for 3 5 m high lacunae reccurring every 15 16 m the potential annual evapo transpiration was computed based on meteorological data collected at tien shui hai from 13 08 89 to 11 09 90 using a modified penman formula a value of 1 60 0 3 m yr was obtained under close system conditions no outlet and a synthetic curve of lake regression was derived which appears to be consistent with the measured shoreline heights it is concluded that the 1 35 m terraces represent annual regression of the lake level by contrast the 3 5 m high lacunae might reflect the periodic return about every 9 12 yr of particular climatic conditions responsible for a perturbation of the annual process of shoreline formation all the shorelines of this profile have formed probably within one century during a continuous and abrupt regression of the lake such evolution has also been identified in the sediments of a piston core collected at sumxi co and dated at about 6 5 5 kyr b p the lake level must have been at its highest stand shortly before that major regression the mechanism responsible for this middle holocene high stand and for the major sudden drop of the lake level remains uncertain

a holocene pollen record from the northwestern himalayan lake tso moriri implications for palaeoclimatic and archaeological research this paper presents a new fossil pollen record from tso moriri 32 54 n 78 19 e 4512 m a s l and seeks to reconstruct changes in mean annual precipitation map during the last 12 000 years this high alpine lake occupies an area of 140 km2 in a glacial tectonic valley in the northwestern himalaya the region has a cold climate with a map 300 mm and open vegetation the hydrology is controlled by the indian summer monsoon ism but winter westerly associated precipitation also affects the regional water balance results indicate that precipitation levels varied significantly during the holocene after a rapid increase in map a phase of maximum humidity was reached between ca 11 and 9 6 cal ka bp followed by a gradual decline in map this trend parallels the reduction in the northern hemisphere summer insolation comparison of different palaeoclimate proxy records reveal evidence for a stronger holocene decrease in precipitation in the northern versus the southern parts of the ism domain the long term trend of ism weakening is overlaid with several short periods of greater dryness which are broadly synchronous with the north atlantic cold spells suggesting reduced amounts of westerly associated winter precipitation compared to the mid and late holocene it appears that westerlies had a greater influence on the western parts of the ism domain during the early holocene during this period the westerly associated summer precipitation belt was positioned at mediterranean latitudes and amplified the ism derived precipitation the tso moriri pollen record and moisture reconstructions also suggest that changes in climatic conditions affected the ancient harappan civilisation which flourished in the greater indus valley from approximately 5 2 to 3 cal ka bp the prolonged holocene trend towards aridity punctuated by an interval of increased dryness between ca 4 5 and 4 3 cal ka bp may have pushed the mature harappan urban settlements between ca 4 5 and 3 9 cal ka bp to develop more efficient agricultural practices to deal with the increasingly acute water shortages the amplified aridity associated with north atlantic cooling between ca 4 and 3 6 and around 3 2 cal ka bp further hindered local agriculture possibly causing the deurbanisation that occurred from ca 3 9 cal ka bp and eventual collapse of the harappan civilisation between ca 3 5 and 3 cal ka bp

long term east west asymmetry in monsoon rainfall on the tibetan plateau variations in the strength and duration of the asian monsoon affect more than half the population of the planet and there is intense interest in where and how much rainfall amounts will change regionally in response to warmer climate conditions the modern monsoon region is divided into distinct subsystems so the response may be regionally heterogeneous northern hemisphere monsoon systems intensified during the early to mid holocene increasing summer rainfall and creating wetter conditions across much of eastern asia in this study we use the area encompassed by high shorelines of early holocene paleolakes in tibet to reconstruct paleorainfall and hence paleomonsoon patterns during this very wet period we found that the early holocene relative paleolake expansions of 130 closed basin lake systems in the central tibetan plateau display a strong east west gradient paleolake areas expanded by approximately fourfold in the western plateau compared to approximately twofold expansion in the eastern region this early holocene pattern mirrors the modern west east climate division on the plateau rainfall in the west is closely tied to the indian summer monsoon ism subsystem and in the east is closely tied to a probable mix of ism and east asian summer monsoon easm subsystems our results suggest that these modern climate divisions are an enduring feature of the plateau and that ism rainfall increased much more than easm rainfall in response to the same insolation forcing

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

lake level variations of qinghai lake in northeastern qinghai tibetan plateau since 3 7 ka based on osl dating abstract qinghai lake is the largest internally drained lake in china and its unique location makes it sensitive to climate changes late glacial climate changes associated with variation in qinghai lake levels have been intensively investigated for the past 40 years with particular attention paid to lake level fluctuation histories between the last interglacial and the holocene however the details of lake level fluctuations during the holocene are still unclear using both optically stimulated luminescence osl dating of quartz for 22 samples and infra red stimulated luminescence irsl of feldspars only for sample hyw1 whose irsl age is 37 15 years a total of 23 samples are dated from paleoshoreline deposits fluvial sediments and aeolian sands a total of 13 sections near the modern lake shore with ages from 37 15 to 3710 350 years these ages are used to reconstruct the lake level fluctuation history spanning the last 3700 years the results indicate that 1 the youngest irsl age of 37 15 years is in agreement with the independent age of 39 29 years suggesting that luminescence dating is able to date decadal samples for sediments from the study area 2 the lake experienced several oscillations imposed on an overall regressive trend during the past 3700 years 3 the dated paleoshoreline deposits are generally related to warm and wet periods suggesting that those shoreline deposits formed during cold and dry periods if any may have been modified by later transgressions 4 lake level fluctuations during the period of 3700 240 years ago are generally consistent with the climate conditions identified in other proxies with the highest lake level occurring about 1770 years ago and 5 after 240 years ago the lake level dropped more rapidly which is inconsistent with the proxy records showing a warmer and wetter phase

timing and spatial distribution of loess and loess like sediments in the mountain areas of the northeastern tibetan plateau abstract most studies on landscape evolution on the tibetan plateau during the late quaternary have mainly focused on using lacustrine records however mantles of sandy silt and paleosols also provide valuable archives for reconstructing holocene paleoenvironmental change yet little is known about the distribution and timing of these late quaternary aeolian sediments to enhance understanding and knowledge of aeolian sediments in tibet and to help reconstruct the nature of late glacial through mid holocene landscape development a loess paleosol sequence the suohuduo section located at the eastern margin of the tibetan plateau at about 4000 m above sea level is examined using sedimentological geochemical and geochronological methods a chronostratigraphy is established using nine optically stimulated luminescence and one radiocarbon ages sedimentation increased during the late glacial and the early holocene with an upwards fining of sediments in the lower part of the section two mid holocene paleosols that date to about 8 5 ka to 7 ka and 5 5 ka to 4 ka reflect more humid climate conditions during the mid holocene than earlier times the upper part of the section is mainly silt which reflects a more open landscape with higher aridity since 4 to 3 ka this time these data support evidence for similar climate paleoenvironmental change in adjacent regions on the tibetan plateau

rapid and punctuated late holocene recession of siling co central tibet this work was supported by a national science foundation grant from the tectonics program ear 0911587 to e k and k p f additional support to e w was provided by grants from the chinese academy of sciences xdb03010500 x s also thanks the support from the earth observatory of singapore nanyang technological university through its funding from the national research foundation singapore and the singapore ministry of education under the research centers of excellence initiative

climate change vegetation history and landscape responses on the tibetan plateau during the holocene a comprehensive review abstract numerous studies of changes in the climate vegetation and landscape responses of the tibetan plateau tp during the holocene have been published in recent decades however several conflicting interpretations are evident within these studies and a comprehensive review of the topic is needed to reconcile them and thus to provide an improved understanding of the history and forcing mechanisms of holocene environmental changes within the region here we review the evidence for changes in climate temperature precipitation moisture vegetation and landscape attributes glacier and eolian activity on the tp during the holocene our main conclusions are as follows 1 the patterns of holocene mean annual temperature change on the tp remain controversial however an early to middle holocene summer temperature maximum is evident which coincided with high summer insolation and a strengthening of the indian summer monsoon ism this suggests that the summer land sea thermal gradient impacted by the temperature of the tp may be an important factor driving orbital scale ism changes 2 lake level records indicate an optimum in moisture conditions on the southwestern sw tp in the early holocene while on the northeastern ne tp the optimum occurred in the middle to late holocene this out of phase or anti phased relationship may be linked to the role of the ism in dominating precipitation on the sw tp while the westerlies and east asian summer monsoon dominated the precipitation on the ne tp 3 most of the lake sediment based stable isotope records 18o and leaf wax d exhibit a pattern similar to that of stalagmite 18o records from monsoonal asia reflecting the dominance of large scale patterns of atmospheric circulation rather than localized moisture changes reflected by lake level records 4 a synthesis of pollen records reveals that the extent of forest was maximal in the mid holocene while from the early holocene onwards alpine steppe shrunk and alpine meadow and desert gradually expanded 5 evidence of glacier advance increased slightly during the early holocene decreased during the mid holocene and then increased substantially after 3 ka bp 6 the integrated ages of eolian sand and loess from the ne tp reveal that eolian activity intensified during the early and late holocene site inter comparisons reveal that regional climate change played a major role in modulating changes in vegetation and other landscape attributes overall producing holocene climate reconstructions for the entire tp remains a major challenge even though much progress has been made further improvements in terms of the spatial coverage of high resolution paleoclimatic records with robust chronological control and a deeper understanding of the specific climatic significance of several climatic proxies will facilitate an improved understanding of how the monsoon and the westerlies interacted and their impacts on vegetation and landscape changes on the tp

hydrological variations on the central tibetan plateau since the last glacial maximum and their teleconnection to inter regional and hemispheric climate variations decadal to sub decadal variability of inflow evaporation and biological productivity derived from lake nam co was used to reconstruct hydrological changes for the past ca 24 k cal a bp the timing of these variations corresponds to known climatic shifts on the northern hemisphere after a dry and cold last glacial maximum the lake level of nam co initially rose at ca 20 k cal a bp moist but further cold conditions between ca 16 2 and 14 k cal a bp correspond to heinrich event 1 a warm and moist phase between ca 14 and 13 k cal a bp is expressed as a massive enhancement in inflow and biological productivity and might be associated with a first intensification of the indian ocean summer monsoon coinciding with the bolling allerod complex a two step decrease in inflow and a contemporaneous decline in biological productivity until ca 11 8 k cal a bp points to cool and dry conditions during the younger dryas lake levels peak at ca 9 4 k cal a bp although hydrological conditions remain relatively stable during the holocene with only low amplitude variations observed

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

stratigraphy and palaeoenvironmental implications of pleistocene and holocene aeolian sediments in the lhasa area southern tibet china abstract along the middle and lower reaches of the kyichu river and its tributaries lhasa area southern tibet a multidisciplinary study was carried out in order to investigate the areal distribution sedimentological properties ages and palaeoenvironmental implications of aeolian deposits including intercalated palaeosols this research was initiated to investigate to what extent southern tibet is influenced by past human activity as even recent evaluations perceive the present treeless desertic environment as natural fifteen profiles were recorded at an altitude of 3540 4580 m a s l with subsequent sedimentological geochronological osl ams 14 c and palaeobotanical charcoal analyses sediment properties of both loesses and aeolian sands reveal an origin from aeolian sorting of nearby fluvial deposits the calculated ages are the oldest obtained thus far on aeolian sediments from southern and interior tibet revealing natural aeolian sedimentation before and around the last glacial maximum c 20 ka however a distinct portion of late holocene sandy aeolian sediments also occurs both the evidence for the aeolian dynamics widespread pleistocene loess and aeolian sand deposition local late holocene aeolian sand deposition modern reactivation of widespread pleistocene aeolian sands and the palaeobotanical findings late holocene vegetation change from a tree bearing to a widely treeless landscape provide evidence that the lhasa area was strongly influenced by human activity since at least the late neolithic c 4200 cal yrs bp thus the present day desertic environment might not primarily be a result of the semiarid climate or the high altitude conditions but rather of activities of the humans and their collateral effects however once established this semi natural ecosystem persisted controlled by strong grazing firewood extraction erosion and harsh edaphic conditions preventing the recovery of trees

drainage geomorphic evolution in response to paleoclimatic changes since 12 8 ka in the eastern kunlun mountains ne qinghai tibetan plateau abstract investigation of the geomorphologic evolution of drainage basins can provide insight into the response of mountain basin systems to paleoclimate fluctuations this study investigates the evolution of geomorphic units and their connectivity from upstream piedmont to downstream salt lake since the late quaternary in the golmud river catchment of the eastern kunlun mountains klm the study aims to elucidate the debate over linkages between 1 landform evolution and paleoclimatic change and 2 dynamic geomorphic processes and lake evolution in the lower basin based on geomorphic and sedimentological observations and an optically stimulated luminescence osl chronology we show three main phases of geomorphic processes 1 upstream piedmont alluvial fans and an alluvial delta fan at the salt lake margin have surface sediment osl ages of 12 8 11 4 ka suggesting a valley aggradation stage in which mass periglacial detritus were eroded and redeposited in the drainage basin 2 incision terraces in alluvial valley fills provide ages between 11 4 and 8 8 8 1 6 2 and 4 9 3 9 ka incision is ascribed to the reduction in supply of detritus owing to glacial recession and enhanced precipitation in the early to middle holocene and 3 widely distributed swamp sediments in the distal delta fan date to 3 2 1 8 ka suggesting a wetter stage within the late holocene climatic deterioration loess indicative of aridity was deposited intermittently during the middle to late holocene we reconstructed a wetness index based on wetness scores of drainage geomorphic units which is consistent with published moisture proxies this association implies that 1 landform processes in klm responded well to precipitation fluctuations in indian summer monsoon ism dominant regions indicating their climatic forcing and 2 precipitation variations in the eastern klm have been mainly controlled by ism intensity since 12 8 ka linking the geomorphologic evolution of mountain basin systems to downstream arid basin evolution shows that the periods of fluvial terrace incision early to middle holocene were probably important sources of lake salt mineral enrichment the landscape evolution patterns of mountain basin systems in the eastern klm offer a model for assessing the linkages between geomorphic processes paleoclimatic changes and lake evolution in other arid regions

morphodynamics and lake level variations at paiku co southern tibetan plateau china abstract proxy records from lakes on the tibetan plateau are commonly used to infer monsoon related climatic changes during the late quaternary specific influences of catchment processes and their interaction with the lake basin are seldom utilized based on morphological field investigations supported by remote sensing analyses in combination with radiocarbon dated sediment data from lacustrine sequences along paleoshorelines and terraces we can demonstrate that close relationships exist between glacier dynamics fluvial alluvial fan terrace formation and lake level and lake area changes of paiku co southern tibet our results show that the formation of large scale fluvial alluvial fans f1 predates the maximum advance of the xixiabangma glaciers the latter formed a distinct terminal moraine complex north of the present glaciers during the local lgm llgm at 42 21 cal ky bp a younger fan generation f2 developed from the llgm to the late holocene which was accompanied by lake level fluctuations with a generally decreasing trend the highest morphologically traceable lake level at 4665 m asl existed prior to 25 cal ky bp and induced a potential overflow to the neighboring langqiang co and pengqu river a high level also existed during the llgm followed by a minor decline until ca 15 cal ky bp owing to reduced meltwater discharge under cold and dry climatic conditions a return to the previous level during the late glacial early holocene period between 11 9 and 9 5 cal ky bp is likely caused by climate warming increased meltwater discharge and enhanced indian summer monsoon ism moisture supply afterwards paiku co shrank gradually toward its present level while the youngest fan f3 generation evolved as individual small sized bodies under ephemeral discharge conditions from the mid holocene to the present the formation of four terrace levels t4 1 is likely the result of sequential incision into the fan generations with a mean erosion rate of 50 cm ky caused by lake level lowering tectonic impact cannot be completely ruled out since 1976 the glaciers lost ca 15 in area accompanied by lake area loss of 3 7 between 1972 and june 2014 seasonal lake level variations of about 1 2 m in height occur in response to summer monsoon rainfall our data show a close interaction between glacial dynamics fluvial processes terrace formation and water budget changes throughout the last 25 cal ky bp in response to the well known insolation driven ism effective moisture supply during the late glacial and holocene period temperature driven meltwater dynamics were the controlling factors for variations in water balance of paiku co

spatial variability of 14c reservoir effects in tibetan plateau lakes abstract radiocarbon dating of lake sediments is often hampered by the presence of a lake reservoir effect lre also dead carbon or old carbon effect especially in dry and cold regions with a sparse plant cover in the catchment the tibetan plateau became a hotspot of the palaeoenvironmental and climate research community in recent years and the assessment of present day lres is a crucial prerequisite for the establishment of reliable radiocarbon age depth relationships for lake sediment cores this paper examines the spatial variability of lres within individual lakes through a discussion of new data for lake donggi cona and a compilation of previously published data for five additional lakes where lre data are available for different sites lake reservoir effects for lake donggi cona on the northeastern tibetan plateau were determined for shells of aquatic snails collected alive close to the lake s shore the largest determined lre of 20 000 14 c years is significantly larger than previously reported lres from the central part of the lake and larger than any previously published lre for the tibetan plateau relatively low lres in the central regions of lakes higher lres towards the margins and high lres in tributaries and spring waters are apparently a common pattern of tibetan plateau lakes the differences in lres within individual lakes or catchment areas are attributed to the more prolonged exchange of the lake water s dissolved inorganic carbon with the atmospheric co 2 in central lake regions on the one hand and the increasing influence of 14 c free or poor stream and groundwater due to the dissolution of carbonaceous basement rocks towards its margins generally higher lres were recorded in the three tectonically active lake regions of the six examined catchments and it is speculated that rising crustal co 2 further contributes to the lres in these catchments in addition to these observations and inferences elevated 14 c levels of the atmosphere as a result of nuclear bomb testing are often ignored if lres for modern materials are reported by convention relative to the atmospheric 14 c activity of the year 1950 lre data reported in this way represent unrealistic minimum estimates

constraints on paleoclimate from 11 5 to 5 0 ka from shoreline dating and hydrologic budget modeling of baqan tso southwestern tibetan plateau abstract 14c dating of shoreline deposits of closed basin lake baqan tso in the western tibetan plateau shows that lake level regressed from the undated highstand 46 m above modern 4 3 modern surface area of likely earliest holocene age by 11 5 ka and remained larger than modern until at least 5 0 ka the shoreline record broadly matches other regional climate records with lake level closely following northern hemisphere summer insolation overprinted by sub millennial lake level oscillations a model coupling modern land runoff and lake surface heat closely reproduces estimated modern precipitation of 240 mm yr we estimate that the baqan tso basin required 380 mm yr precipitation to sustain the maximum early holocene lake area a 55 increase over modern precipitation increases not glacial meltwater drove lake level changes as baqan tso basin was not glaciated during the holocene our estimate assumes early holocene insolation 1 3 overall increase and mean annual increases of 2 c in temperature and 37 in relative humidity we additionally developed a holocene precipitation history for baqan tso using dated paleolake areas using the modern and early holocene model results as end members we estimate precipitation in the western tibetan plateau which was 300 380 mm yr between 5 0 and 11 5 ka with error of 29 57 mm yr 12 15

holocene lake level variations of longmu co western qinghai tibetan plateau longmu co is surrounded by conspicuous regressive shorelines attesting to high water levels in the past in this study we dated paleoshoreline sediments around the lake using optically stimulated luminescence osl infrared stimulated luminescence irsl and radiocarbon dating then explored the forces that drove holocene lake level variations we found that 1 osl irsl ages are consistent with geomorphic sequences and some extant cosmogenic and u th shoreline ages however inorganic evaporite crust 14c ages are much older than corresponding osl irsl ages due to varying lake reservoir effects and should be used with caution 2 the highest lake levels of longmu co 160 145 m above present lasted from 12 8 to 11 3 ka two periods of abrupt lake level declines occurred at 11 3 and 7 4 ka lake level dropped 44 and 45 m respectively with a gradual regression of 18 m between these two intervals the lake expanded moderately from 7 to 5 5 ka then declined once more after 5 5 ka with this regression accelerating during the last 1 5 ka 3 the deglacial lake level transgression was likely due to glacier melt waters the indian summer monsoon reached the longmu co watershed and brought precipitation during the early holocene middle to late holocene lake regression was caused by the retreat of the monsoon and consequent environmental deterioration