palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

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

a general cooling trend on the central tibetan plateau throughout the holocene recorded by the lake zigetang pollen spectra abstract a 741 cm long laminated sediment core covering the last 10 800 years was collected from lake zigetang central tibetan plateau 90 9 e 32 0 n 4560 m a s l and analysed palynologically at 69 horizons biome reconstruction suggests a dominance of temperate steppe vegetation mainly artemisia and poaceae on the central tibetan plateau during the first half of the holocene 10 8 4 4 cal ka bp while alpine steppes with desert elements mainly cyperaceae poaceae chenopodiaceae and characteristic high alpine herb families tend to dominate the second half 4 4 0 cal ka bp the artemisia cyperaceae ratio a semi quantitative measure for summer temperature indicates a general cooling trend throughout the holocene dense temperate steppe vegetation and maximum desert plant withdrawal however indicate that a suitable balance of wet and warm conditions for optimum vegetation growth likely occurred during the middle holocene 7 3 4 4 cal ka bp severe early holocene cold events have been reconstructed for 8 7 8 3 and 7 4 cal ka bp

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

environmental conditions in the donggi cona lake catchment ne tibetan plateau based on factor analysis of geochemical data abstract we present a methodological approach for the characterization of spatial variations of environmental and transport conditions based on geochemical data we analyzed the geochemical characteristics of terrestrial sediments on an alluvial fan and adjacent areas in the eastern part of the donggi cona catchment the geochemical characteristics of the sediment samples were measured using x ray fluorescence spectroscopy a factor model based on nine elements sr rb zn fe mn v ti ca and k gave the best results using factor analysis our results show that factor analysis of geochemical data can explain spatial variations in the catchment even within a relatively small area with more or less constant climatological conditions the four most important factors of our model explain 68 4 of the total variance within the dataset the four factors represent a carbonate weathering and two redox condition signals respectively the spatial distribution of factor loadings points to regions with specific environmental conditions these regions show a certain carbonate input or production factor 1 specific weathering rates factor 2 or specific redox conditions factors 3 and 4 the factor loadings of the first and second factor are used to reclassify the data into four groups being dune loess lake and fluvial gravel sediments this reclassification confirms or improves the prior field classification in 70 of all cases for 23 of the samples the model gave a different interpretation the factor loadings in these cases represent the origin of the material rather than its present sediment type thereby giving valuable information about sediment provenance since the third and fourth factor seem more dependent on location they do not differentiate between different sediment types multivariate statistics of the geochemistry of terrestrial sediments i allows the subdivision of samples into different sediment types ii indicates dominant regions for weathering carbonate production and manganese washout and iii gives suggestions about the provenance of the sediments this is the first detailed study of geochemical parameters on the tibetan plateau not focusing on lake cores resulting in a spatial characterization of the local geochemistry this gives insight in the sediment transport connections between the catchment and the lake illustrating the value of terrestrial sediments as additional indicator of environmental variations

a pollen record of holocene climatic changes from the dunde ice cap qinghai tibetan plateau pollen preserved in ice cores from the dunde ice cap provides a sensitive record of holocene climatic changes and vegetational response in the northern qinghai tibetan plateau at time scales ranging from millennia to centuries and decades pollen analysis of the annually resolvable ice layers for a 30 yr period 1957 1986 suggests that total pollen concentration is correlated positively with summer precipitation and negatively with summer temperature thus it is a sensitive indicator of moisture availability and vegetation density in the steppe and desert regions around dunde high pollen concentrations between 10 000 and 4800 yr b p suggest that the summer monsoon probably extended beyond its present limit to reach dunde and westernmost tibet in response to orbital forcing the summer monsoon retreated time transgressively across the qinghai tibetan plateau during the middle holocene relatively humid periods occurred at 2700 2200 1500 800 and 600 80 yr b p probably as a result of neoglacial cooling prominent pollen changes during the medieval warm period 790 620 yr b p and the little ice age 330 80 yr b p suggest that the vegetation in the qinghai tibetan plateau region is sensitive to abrupt century scale climatic changes such as those anticipated in scenarios of greenhouse warming

late quaternary aeolian sedimentation in central and south eastern tibet abstract the geomorphology and the cover sediments in the central and south eastern part of the tibetan plateau provide information about climatic change luminescence dating of aeolian and colluvial silts on top of different moraine sequences provides the first indications for the timing of these sediments during the late quaternary and holocene although there is a widespread cover of aeolian mantles in tibet only a few papers have focussed on them up to now samples from silt layers on top of pleistocene moraines or solifluction debris from central and southern tibet at elevations above 4000 m asl provide early holocene ages in most sections the aeolian silt on top of the bomi moraine in southeastern tibet situated at an elevation of about 3000 m asl provides an age of 25 ka according to geomorphological investigations the bomi moraine dates from the last ice age which can be confirmed by the luminescence data moreover one sample from a silt layer in between gravel layers xainxa is also pleistocene in age according to its sedimentary and geomorphological situation in the tibetan plateau pleistocene loess mainly occurs below 4000 m asl the holocene material a more sandy silt lying above 4000 m asl however aeolian material capping the moraines provides only minimum ages for the terminal moraines the time interval between glacier retreat and the accumulation of aeolian sediments may be several thousand years the most important fact is the trapping of dust in general lakes and a denser vegetation cover are or were the main traps for the typical loess found in the mountain areas of the tibetan plateau

extent and spatial distribution of pleistocene glaciations in eastern tibet as a contribution to the controversial discussion regarding the nature and extent of the pleistocene glaciation on the tibetan plateau additional observations and results were obtained during several chinese german joint expeditions in the investigation area of the eastern and central tibetan plateau it will be shown that the maximum extent of the last glaciation was limited to the glaciation of isolated mountain groups or smaller plateau glaciations these glaciations are characterized by glacial erosional features such as u shaped valleys in the inner mountain massifs and cirques in the higher summit areas accumulation forms such as terminal and lateral moraines less common than basal moraines are marked by granitic and basaltic erratics using two examples from the eastern margin of the tibetan plateau nianbaoyeze shan and northern chola shan the extent of pleistocene glaciations can be mapped by the distribution of terminal and lateral moraines and erratic granite boulders on the slopes of the surrounding schists two to three main pleistocene glaciations can be separated using weathering criteria paleosols and the overlying stratum on the moraines and associated terrace sequences overlying stratum consist of aeolian sandy silt or solifluction debris the younger moraines are found to be characterized by large erratics were therefore named big boulder moraine and can be found over the investigated area the ice free areas are characterized by pleistocene terraces along the main rivers loess deposits with sand and ice wedges at higher elevations e g the basin of zoige and paleosols in the basins below 3500 m a s l e g aba basin or garze basin the hypothesis of an extensive plateau glaciation could not be verified for this region a rising snowline equilibrium line altitudes elas is revealed in two cross sections during the last glacial maximum lgm at the eastern and northern margin of the tibetan plateau snowlines migrated from about 4000 m in the east minshan to 4300 m in the nianbaoyeze and to about 4700 m in the west bayan har shan a rise was also recorded from about 3800 m in the north central qilian shan up to a range of 4300 4950 m different exposures in the kunlun shan to approximately 5200 m in the tanggula shan in the center of the tibetan plateau the general increase of modern and lgm snowlines or elas towards the plateau corresponds with a decrease of precipitation from east to west and from north to south respectively precipitation was more pronounced at the eastern margin during glacial times than compared to present

holocene land cover changes on the tibetan plateau information on changes in land surface features on the tibetan plateau tp during the holocene may help our understanding of the forcing of monsoonal circulation we analyse vegetation changes during the last 9000 years from pollen records of four lakes hurleg lake in the qaidam basin qinghai lake on the northeastern tp zigetang lake on the central tp and koucha lake on the eastern tp which represent different regions and vegetation types on the plateau today a set of modern pollen assemblages from 111 lake sediment samples originating from different vegetation types is used for the interpretation of the holocene pollen records four types of numerical analyses are used to infer different aspects of pollen stratigraphical and inferred vegetation changes biome reconstruction ordination to infer palynological compositional turnover rate of assemblage change analysis and a pollen lai leaf area index transfer function our results show strong regional differences in inferred vegetation change in

holocene aeolian activity in the zoige basin northeastern tibetan plateau china abstract the zoige basin is located in the northeastern tibetan plateau at an altitude of around 3500 m to fully understand and assess the current status and future trend of aeolian activity in the zoige basin it is necessary to reveal the history of aeolian activity of this region in this study 11 optically stimulated luminescence osl ages from three typical sections were used to reconstruct the history of aeolian activities in the region during the holocene the results of the chronologies show that the oldest osl age 10 27 0 81 ka occurred in the early holocene but aeolian sediment deposition primarily occurred in the late holocene after around 3 20 0 33 ka in the whole holocene the aeolian activities of the zoige basin occurred contemporaneously with nearby sites in the northeastern tibetan plateau episodic weak aeolian activities were recorded in nearby sites in the northeastern tibetan plateau however we postulate here that the combination of a flat low lying landscape along with higher precipitation during the mid holocene resulted in this area being relatively insensitive to short term arid climatic changes and aeolian activity

correlation between indian ocean summer monsoon and north atlantic climate during the holocene there has been a number of investigations for the correlation between the asia monsoon and the north atlantic climate for the last glacial however little research has been done for the present interglacial the holocene here we present for the first time a high resolution composite proxy record for the indian ocean summer monsoon spanning around 12 000 years based on the 13c time series of both a single plant species carex mulieensis remains cellulose and the total plant assemblage cellulose in the hongyuan peat bog from the tibet plateau the records show that the strength of the indian ocean summer monsoon had abrupt variations during the last 12 000 years the weakest monsoon occurred in the younger dryas period following rapid strengthening from around 11 200 to 10 800 a bp the monsoon kept a generally strong level for around 5300 years from around 5500 a bp onwards the monsoon strength tended to gradual decrease in addition there are a series of abrupt variation events of the monsoon strength on centennial to millennial time scales which superimpose the general tendency of the monsoon variation in every case when the ice rafted debris events in the north atlantic occurred the summer monsoon strength decreased correspondingly these evidences show that teleconnection between the indian ocean summer monsoon and the north atlantic climate is present not only in the last glacial but also in the holocene which may be linked to abrupt reorganizations of the ocean thermohaline circulation leading to redistribution of energy changing temperature and moisture gradient over the southern subtropical indian ocean and eventually controlling the variability of the indian ocean summer monsoon

timing and style of late quaternary glaciation in northeastern tibet glacial successions in the anyemaqen and nianbaoyeze mountains of northeastern tibet are reassessed and new glacial chronologies are presented for these regions cosmogenic radionuclide and optically stimulated luminescence dating indicates that two glacial advances occurred in marine isotope stage mis 3 and mis 2 in the anyemaqen mountains a third advance occurred in the early holocene we suggest that glaciation was synchronous in the anyemaqen and nianbaoyeze mountains as well as in other glaciated areas of tibet and the himalaya that are influenced by the asian monsoon the maximum extent of glaciation occurred early in the last glacial cycle mis 3 during a time of increased insolation when the monsoon intensified and supplied abundant precipitation as snow at high altitude to feed high altitude glaciers this suggests that precipitation as snow is fundamental in controlling glaciation in these regions however the occurrence of glacial advances during the insolation minimum of mis 2 suggests that despite reduced precipitation at this time the annual temperatures were cold enough to maintain positive glacier mass balances the numerically defined chronologies for the anyemaqen and nianbaoyeze mountains presented here provide a framework for comparing glacial advances in other parts of high asia

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

later pleistocene holocene climate conditions of qinghai xizhang plateau tibet based on carbon and oxygen stable isotopes of zabuye lake sediments abstract we present a time series of carbon and oxygen stable isotope records of the last 30 000 14c years throughout the last glacial postglacial cycle from western qinghai xizhang tibet plateau a 20 m core drilled in the south basin of zabuye salt lake was analyzed for inorganic and organic carbon and total sulfur contents 13c and 18o values of carbonates our results indicate that climatic changes have led to a drastic negative shift of stable isotope ratios at the transition between the last full glacial and the postglacial phase during later pleistocene times 16 2 kyr bp and a rapid positive shift at the transition from pleistocene to holocene 10 6 kyr bp the first shift is marked by the drop of 18ocarb values of about 10 from 2 to 8 and 13ccarb values of about 3 from 5 to 2 the second shift which occurred at the transition from pleistocene to holocene was of similar magnitude but in the opposite direction isotope data combined with total organic and inorganic carbon contents and the lithological composition of the core suggest this lake was an alluvial pre lake environment prior to ca 28 14c kyr bp during ca 28 16 2 14c kyr bp zabuye lake was likely a moderately deep lake with limited outflow the cool and arid glacial climate led the lake level to drop drastically extended residence time overwhelmed the lower temperature and caused a steady increase of 13ccarb and 18ocarb values and total inorganic carbon content in the sediments during ca 16 2 10 6 14c kyr bp this lake probably overflowed and received abundant recharge from melting glaciers when the deglaciation was in its full speed a spike of markedly enhanced 13ccarb and 18ocarb is seen at 11 5 kyr bp probably due to the isotopic effects left behind by the short but severe younger dryas yd event after ca 10 6 14c kyr bp zabuye lake probably closed its surface outflow due to strong desiccation and drastic climate warming the early and middle holocene were characterized by unstable climatic conditions with alternating warmer cooler episodes as indicated by the severe fluctuations of total organic carbon 13c and 18o values a hypersaline salt lake environment was finally formed at zabuye after 5 14c kyr bp when the mirabilite and halite concentrations steadily increased and became the dominant minerals in the sediments severe imbalance of inflow outflow resulted in the drastic increase of total sulfur 13ccarb and 18ocarb values and dominance of halite in the lake since ca 3 8 kyr bp to present

aeolian sediments on the north eastern tibetan plateau abstract aeolian sediments on the tibetan plateau are an important archive of palaeoclimatic information this study presents a detailed analysis of sediments from the donggi cona catchment on the north eastern part of the tibetan plateau long and short distance sediment transport leads to a complex pattern of aeolian sediment deposition that depends on climatic changes as well as on the availability of sediments based on the largest dataset of osl datings 51 from a single catchment on the tibetan plateau so far different periods of increased sediment transport have been reconstructed increased aeolian deposition in this high elevation environment started in the early holocene with the accumulation of sands from around 10 5 to 7 ka loess sediments have been preserved from a period from 10 5 to 7 5 ka both archives are related to the strengthening of the asian summer monsoons characterized by wetter and warmer climate this change in climate supported the trapping of aeolian sediments under full monsoon conditions from around 9 ka onwards fluvial processes resulted in erosion of the aeolian archives and the formation of colluvial sediments until 6 ka a dry and cooler climate resulted in the reactivation of dune sands from 3 ka to present possibly in combination with stronger human influence aeolian sediments on the tibetan plateau therefore indicate two different climatic modes during the early holocene wetter conditions were favourable to retain aeolian sediments the reactivation of sediment in the late holocene due to small scale disturbances in the vegetation cover points to a cooler and drier climate

environmental change during the holocene in western china on a millennial timescale recent data on the evolution of the inland lakes loess palaeosol sequences and glacier variations in western china are briefly reviewed the lake history shows three distinct stages in the holocene i e low water levels before 7500 bp a stage of expansion during the climatic optimum between 7500 and 3500 bp and contraction after 3500 bp three stages wooded grassland mixed woodland wooded grassland becoming steppe also appear indicated by the holocene loess palaeosol sequence in the lanzhou region the optimal period for soil development being between 7500 and 3500 bp there were seven periods of glacier advance the continental glaciers advanced at about 8300 5700 4000 and 400 bp in northwestern china and the maritime glaciers advanced at about 3000 2000 1000 and 200 bp it is suggested that the climatic changes show two periodicities during the holocene namely at intervals of about 2500 and 1000 years

temperature variability and vertical vegetation belt shifts during the last 50 000 yr in the qilian mountains ne margin of the tibetan plateau china abstract a 13 94 m long sediment core collected from a medium sized lake in the qilian mountains ne tibetan plateau china was analysed palynologically at 81 horizons the interpretation of indicator taxa yielded various vertical shifts of the vegetation belts these palaeovegetation results have been checked with lake surface pollen spectra from 8 lakes representing different altitudinal vegetation belts our main findings are the following a short period of the late marine isotope stage 3 around 46 000 yr ago was characterized by interglacial temperature conditions with a tree line above its present day altitude during the lgm the vicinity of the lake was not covered by ice but by sparse alpine vegetation and alpine deserts indicating that the climate was colder by 4 7 c than today markedly higher temperatures were inferred from higher arboreal pollen frequencies between 13 000 and 7 000 yr ago with a holocene temperature optimum and a maximal picea betula mixed forest expansion between 9 000 and 7000 yr ago when temperatures exceeded the present day conditions by at least 1 2 c alpine steppes and meadows and sub alpine shrub vegetation dominated around the lake since the middle holocene suggesting that vegetation and climate conditions were exceptionally stable in comparison to previous periods

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

pedogenesis permafrost substrate and topography plot and landscape scale interrelations of weathering processes on the central eastern tibetan plateau article i nfo weathering indices wi and pedogenic oxidesratios por were used to describe patterns of weathering inten sities and pedogenesis along climatic gradients mainly affected by varying influences of the asian and indian monsoon these climate settings induce particular soil moisture sm conditions in turn closely related to per mafrost state substrate and topography nine sites including a total of 30 soil profiles were examined along an eastern and a western transect across the central eastern qinghai tibet plateau additionally differences between four soil groups were analysed according to our knowledge the presented study is the first attempt of a comprehensive application of different wi and por to substrates of currently permafrost affected soils it providesanevaluation ofvarious tools intermsof chemicallydescribinganddifferentiating the relatedprocesses todistinctenvironmentalsettingsinlow weatheringregions wefoundthatweatheringtrendsalongtheclimat ic gradients could be clearly outlined by wi whereas por rather account for small scale variations describing significant differences of pedogenesis between continuous and discontinuous permafrost conditions pyrophos phate soluble iron fep proved to be useful for differentiating permafrost and ground water influenced soils showing a strong correlation to total organic carbon r 0 89 the chemical index of alteration cia is the

holocene environmental changes in bangong co basin western tibet part 3 biogenic remains abstract a 12 4 m core collected from the eastern part of lake bangong provided a continuous holocene record this core was analyzed for diatoms ostracods charophytes content in total organic carbon and identification of organic particles contained in the sediments the record is remarkable for the abundance and diversity of its microorganisms an oligo to mesosaline marsh occupied the core site before 9 5 ka b p bangong was most likely closed a sudden filling of the lake basin by dilute nutrient poor water occurs around 9 4 ka b p maximum lake extent seems to have occurred around 9 4 8 7 ka b p generally freshwater relatively deep conditions were maintained up to 6 3 ka b p although interrupted by short term regressive events between 8 6 and 7 5 ka b p a trend towards palustral conditions begins after 6 3 ka b p and the interval 3 9 3 2 ka b p rich in detrital organic material coincides with an extremely low lake level a last lacustrine episode of minor amplitude is recorded from about 3 to 2 ka b p before the closure of the system leading again to slightly saline conditions the resemblances and synchronism between environmental changes recorded at bangong and in lake sumxi situated 200 km northwards and 800 m higher in elevation indicate that regional climatic changes have been the major driving factor on ecological and hydrobiological changes in lakes of western tibet

fluvial suspended sediment yields over hours to millennia in the high arctic at proglacial lake linnevatnet svalbard sediment yield can be a sensitive indicator of catchment dynamics and environmental change for a glacierized catchment in the high arctic we compiled and analyzed diverse sediment transfer data spanning a wide range of temporal scales to quantify catchment yields and explore landscape response to past and ongoing hydroclimatic variability the dataset integrates rates of lake sedimentation from correlated varve records and repeated annual and seasonal sediment traps augmented by multi year lake and fluvial monitoring consistent spatial patterns of deposition enabled reconstruction of catchment yields from varve and trap based fluxes we used hydroclimatic data and multivariate modeling to examine annual controls of sediment delivery over almost a century and to examine shorter term controls of sediment transfer during peak glacier melt particle size analyses especially for annual sediment traps were used to further infer sediment transfer mechanisms and timing through the medieval warm period and little ice age there were no apparent multi century trends in lake sedimentation rates which were over three times greater than those during the mid holocene when glaciers were diminished twentieth century sedimentation rates were greater than those of previous millennia with a mid century step increase in mean yield from 240 to 425 mg km 2 yr 1 annual yields through the twentieth century showed significant positive relations with spring summer temperature rainfall and peak discharge conditions this finding is significant for the future of sediment transfer at linnevatnet and perhaps more broadly in the arctic where continued increases in temperature and rainfall are projected for 2004 2010 annual yields ranged from 294 to 1330 mg km 2 yr 1 sediment trap volumes and particle size variations indicate that recent annual yields were largely dominated by spring to early summer transfer of relatively coarse grained sediment fluvial monitoring showed daily to hourly sediment transfer to be related to current and prior discharge diurnal hysteresis air temperature and precipitation

paleoclimatic evolution of the uvs nuur basin and adjacent areas western mongolia abstract the investigations presented in this paper focus on the shifts in pleistocene glaciations and the geomorphic changes in landforms as well as lake level changes and aeolian deposits of the last glacial interglacial cycle including the holocene geomorphic evidence and high lake levels show that the climate was more humid before the last glacial maximum lgm however at least one arid phase also occurred during the second half of the lgm the climate was dry and cold turning to wet and cold during the late glacial of the last ice age fluctuations in humidity and temperature occurred during the holocene since about 2000 yr bp the impact of human activity has increased

sedimentary response of lake el tobar spain to climate lake level changes after the maunder minimum lake level reconstructions from a littoral core in lake el tobar spain are presented for the last 350 years these are based on plant macrofossils and stable isotopes from lacustrine carbonates our data suggest five episodes of advance and regression of the shoreline coupled with changes in water retention in the lake a low lake level and high water renewal episode at ca ad 1650 1715 is indicated by oxidized facies with abundant remains from terrestrial marsh plant macrofossils and low d18o and d13c values a fluctuating lake level episode at ca ad 1715 1772 during changing climatic conditions in the little ice age lia caused periods of erosion and sediment deposition that intermittently blocked the lake outlet resulting in more positive d18o and d13c values the lake became progressively more closed with increased level in the wet years at the end of the lia ca ad 1772 1850 during the dalton minimum d13c values reached a minimum indicating low productivity but increased after this with development of submerged chara from ca ad 1850 to 1960 lake levels were high but are marked by changes in marsh communities mainly the shift from juncus to typha ca ad 1850 1960 predominance which indicates low and high levels respectively

role of the tibetan plateau thermal forcing in the summer climate patterns over subtropical asia the mechanism of the tibetan plateau tp thermal forcing in influencing the summer climate patterns over subtropical asia is investigated by means of ncep ncar reanalysis diagnosis results show that since the tp is a huge elevated heating source with the strongest heating in the surface layers in summer the thermal adaptation results in a shallow cyclonic circulation near the surface and a deep anticyclonic circulation above it according to the steady barotropic vorticity equation for large scales airflow must converge in the lower layers and diverge in the higher layers over the eastern side of the tp however the western side of the tp is characterized by a reversed structure i e divergence in lower layers but convergence in higher layers hence pumping and sucking processes bring in upward and downward movement over the east and west sides of the tp respectively such a circulation is embedded in the large scale circulation that is forced by the eurasian continental heating because the tp together with iran plateau are located at the central and eastern parts of the continent and because the orography induced circulation is in phase with the continental scale circulation the role of the tp thermal forcing is to intensify the east asian monsoon to its east and the dry and hot desert climate in mid asia to its west the summertime thermal forcing of the rockies and andes can generate similar circulations along the two subtopics as the tp does since they are located near the western coasts but the lower troposphere poleward flow that is induced by orographic thermal forcing does not coincide with the poleward flows over the eastern coastal region that is induced by continental heating and the monsoon rainfall in north and south america is not as strong as in east asia however the equatorward flow and the associated subsidence induced by the two mountain ranges along the western coasts of both north and south america are in phase with those induced by continental heating these contribute to the formation of the stable low stratus clouds and strong long wave radiative cooling over the eastern subtropical pacific regions just off the western coast of the continent

holocene aeolian activity and climatic change in qinghai lake basin northeastern qinghai tibetan plateau abstract aeolian deposits in the qinghai lake basin on the northeastern qinghai tibetan plateau netp were studied in order to reconstruct changes in aeolian activity related to climatic changes over the last 12 5 ka we used 20 optically stimulated luminescence and conventional radiocarbon dates to construct chronological frameworks for four aeolian sections the results indicate that aeolian activity occurred episodically at 12 5 ka 11 2 ka 9 0 ka 8 5 ka 5 5 ka 2 6 2 4 ka and 1 0 9 ka paleosols developed mainly during 9 5 4 ka the field stratigraphy of the sections together with measurements of grain size magnetic susceptibility ms and total organic carbon toc indicate that aeolian activity was strong during the last glacial period following the younger dryas yd holocene interglacial conditions began to develop in the qinghai lake basin at 12 ka with the strengthened asian summer monsoon asm and the decrease in insolation the climate became warm and humid according to the record of aeolian activity the early holocene can be divided into two intervals before and after 9 5 ka aeolian activity remained strong from 12 ka 9 5 ka although the climate was more humid than that of the last glacial period between 9 5 ka and 8 5 ka the aeolian activity weakened and the climate became warm and wet but variable following the mid holocene climatic optimum the climate became significantly drier at 4 ka and aeolian activity strengthened again overall the asm dominated aeolian activity in the qinghai lake basin during the holocene with enhanced aeolian activity corresponding to a weakened asm paleosol development exhibited a lagged response to the strengthened asm and therefore aeolian sand layers in the section do not always indicate a cold and dry climate

how old is pastoralism in tibet an ecological approach to the making of a tibetan landscape abstract the tibetan highlands host one of the world s largest pastoral ecosystems but the evolutionary impact of the tibetan nomadic livestock economy on the environment has not yet been investigated despite this grazing impact the vegetation of the tibetan highlands is widely believed to be natural our ecological approach to reconstructing the making of a pastoral environment uses the present composition of the plant cover as a baseline today s prevailing plant functional types are grazing weeds highly adapted to grazing the first pollen record of grazing weeds can thus be assumed to mark the onset of pastoralism supposedly with goats and sheep introduced from the middle east and the endemic large bovid of the yak domesticated in the tibetan highlands this study represents the first attempt to determine the age of pastoralism with the help of palynomorphs using the indicator species approach this is independently corroborated 1 by the synchronous occurrence of pollen clumps indicating disturbance effects from trampling and 2 the precipitous decline of forest pollen on the eastern declivity of the highland during the mid holocene climatic optimum as all pollen core sites currently have a climatic potential of forest as demonstrated by fruiting and progenitive forest relicts it is suggested that early livestock holders continued to burn these forests to obtain pastures the charcoal record supports this conclusion it is hypothesized that the making of a pastoral environment in the tibetan highlands started around 8 8 ka cal bp during the mid holocene climatic optimum as the pattern of arboreal pollen decline at these sites contrasts with 13c 18o toc content c n ratio and ostracod assemblages that are independent of rangeland management decisions of early pastoralists we may conclude that pastoralists took advantage of the mid holocene climatic optimum to convert forests into high yield pastures using pollen clumps as a proxy for herbivore load suggests a tenfold higher amount of livestock than of wildlife before the introduction of pastoralism in contrast to pastoralism in arid environments of the old world s desert belt pastoralists in the eastern tibetan highlands created their own environment transforming forests and tall grassland into the present golf course like pastures

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

vegetation evolution and human expansion on the qinghai tibet plateau since the last deglaciation abstract the spatial patterns and changes of vegetation on the qinghai tibet plateau qtp since the last deglaciation 16 5 cal ka bp are reconstructed by fossil pollen records from 36 sampling sites the modern analogues technique and isochrones of 15 of arboreal pollen are used the results show that the plateau vegetation pattern has been meadow steppe since 14 cal ka bp which replaced desert dominated pattern during the last glacial maximum lgm vegetation zones of qtp have moved and expanded from the southeast to the northwest the edge to the hinterland and low altitude to high altitude the most significant expansion occurred during 14 11 cal ka bp and 8 6 cal ka bp reached the westernmost extent at 6 cal ka bp and then began to retreat to the east in the meantime human activities began to flourish in the northeastern margin of the plateau at 14 cal ka bp the age of the earliest human remains of the plateau the vegetation expansion during 8 6 cal ka bp drove humans further to the hinterland and the western regions such as kekexili and the qiangtang plateau moreover the archaeological chronology of human remains in the eastern region is earlier than those from the hinterland these all indicate that human activities have been greatly affected by changes and expansion of vegetation on the qtp

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

quaternary environmental changes in the drylands of china a critical review abstract this paper reviews our current understanding of quaternary climate and landscape changes in the desert areas of northern china a key portion of the middle latitude drylands on earth combining earlier studies with our recent research and experience we offer a comprehensive picture of the state of chinese deserts during the quaternary and in the interest of enhancing future research identify knowledge gaps and areas of uncertainty lacustrine deposits found over an area ranging from china s western taklamakan desert to the eastern hunshandake sandy lands suggest that extensive lakes occurred in china s deserts during the pleistocene analysis of digital elevation models from srtm shuttle radar topography mission data supports this interpretation and shows the significant extent of these former lakes new estimates of mean annual evaporation of ca 1000 mm from lake surfaces and ca 100 mm from land surfaces confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone especially during intervals when the mean annual rainfall is more than 100 mm rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of china are very sensitive ephemeral systems and not long lasting as previously thought available chronologies suggest that there were large lakes in the western taklamakan desert and the chadamu basin during mis marine isotope stage 3 at 30 ka probably related to a period of strong influence of northern hemispheric westerly winds channels and elevation models revealed by srtm data and remains of lacustrine sediments also indicate that there was a large lake in the hunshandake sandy lands in the eastern portion of the desert belt during the quaternary there is significant evidence that during the middle holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern china lacustrine records from the badain jaran desert in western inner mongolia suggest that it was generally dry before 10 cal ka becoming wetter from 10 to 4 cal ka and dry again afterwards study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt suggests that there was a period of wet and warm climate in this region during the mid holocene optimum at a minimum between 6 ka and 4 ka but possibly lasting longer recent observations dealing with the generation and transport of dust from central asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed these results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in chinese deserts are somehow similar to that having occurred in the sahara desert of north africa deserts in northern china were also important focal regions for neolithic cultures during intervals when environmental conditions supported a denser vegetative cover there is evidence that some areas of woody vegetation to the west of badain jaran desert were deforested by humans by ca 4000 yr b p although it is still debatable whether humans have had a significant impact in other areas at that time opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long term field based investigations

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

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

lake qinghai china closed basin like levels and the oxygen isotope record for ostracoda since the latest pleistocene abstract in 1985 a sino swiss limnogeological expedition to china s largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern tibet qinghai plateau since the last glacial maximum lake qinghai a perennial lake with an area of 4278 km2 1985 at 3194 m above sea level receives drainage from 30 000 km2 of catchment near the northwest corner of the plateau the 26 5 m deep terminal lake 1985 with brackish alkaline magnesium sulphate rich waters 14 g 1 1 tds has not overflowed since the last glacial but its levels have responded to climatic and hydrologic changes seismic reflection profiles for the sub bottom sediment structures revealed a complex topography with channels relict terraces tectonic tilting and deformation in deposits buried under a 4 6 m packet of mainly flat bedded sediments from which core samples were recovered the lowermost cored material 14 500 yr b p comprises mainly water lain loess deposited in a smaller flood plain lake of up a few metres depth under cold arid climatic conditions ams radiocarbon dating indicates average sedimentation rates for latest pleistocene and holocene deposits in central basin regions of 0 3 0 5 mm yr 1 the 18o values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation evaporation budgets which have controlled the palaeo levels for lake qinghai the precipitation evaporation budget for the lake qinghai region is largely determined by the asian monsoon system the lake qinghai sediment record shows that there was no large influx of glacoer melt waters into the lake basin during the post glacial the regional climate remained arid until at least 12 500 yr b p when an incipient monsoon was possibly initiated river transported silts first reached the basin centre at 11 800 yr b p when the lake depth may have increased to 5 m possibly a monsoonal weakening for several centuries after 10 800 yr b p europe younger dryas caused a further period of aridity at 10 200 yr b p the basin began filling towards modern lake dimensions in response to a permanent strengthening of the asian monsoon substantial lake level rises probably characterised the periods 10 200 9800 9500 8500 8300 7200 yr b p and through perhaps a century at about 6800 yr b p decreasing levels probably characterised the intervening intervals short term lake level fluctuations through the mid holocene climatic optimum were minimal indicating a very stable climatic hydrologic regime an isotopic steady state for the lake waters since 3000 500 yr b p obscures the climatic hydrologic regime dependent 18o gradient but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time three negative 18o excursions for the lake waters may correspond to known glacier advances on the plateau at 3000 2000 and 1500 yr b p during china s neoglacial

holocene climatic and environmental changes in the arid and semi arid areas of china a review this paper reviews recently published literature most of which was published in chinese and searches for regional patterns of holocene changes useful in depicting global patterns the holocene in the xinjiang region can be divided into three stages a warming and dry early stage from 11 similar to 10 to 8 similar to 7 ka bp a warm and wet middle stage from 8 similar to 7 to 4 5 similar to 3 ka bp and a fluctuating cool and dry late stage since 4 5 similar to 3 ka bp the holocene in the northern tibetan plateau can also be divided into three stages a warming and wet stage from 10 5 similar to 10 to 5 similar to 4 ka bp followed by a variable drying and probably warm stage 5 similar to 4 to 3 ka bp and ending with a cool and dry stage since 3 ka bp in the inner mongolian plateau the early holocene from 10 5 similar to 9 5 to 8 similar to 7 5 ka bp was warming and dry and a warm and wet climate occurred from 7 5 to 3 5 during which the best time was 6 3 3 8 ka bp the climate has been variably drying and probably cooling since 3 5 ka bp in the northwestern part of the loess plateau several holocene palaeosols have been identified 10 9 7 5 5 4 3 and 2 7 2 ka bp with the 7 5 5 ka bp palaeosol being most strongly expressed the best developed palaeosol equivalent in major valleys is a swamp wetland facies deposited between 8885 and 3805 c 14 yr bp under an extremely wet regime the climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp wetland facies depositional period our summary shows that the holocene climatic optimum occurred nearly contemporaneously 8 5 ka bp at all sites in the xinjiang region in the inner mongolian plateau and in the northwestern part of the loess plateau a warming and wet early holocene 10 8 ka bp in the northern tibetan plateau is most likely related to high effective soil moisture resulting from snow and ice melting we propose here that the middle holocene climatic optimum 8 5 ka bp in arid to semi arid china was primarily a delayed response of the low latitude oceans to high latitude peak insolation 9 8 ka bp

climatic changes in the qinghai xizang tibetan region of china during the holocene climatic changes in the qinghai xizang plateau of china were studied by analyzing the composition of peat and layers of sand and gravel distributed along the southern slopes of nianqing tanggula and gangdise mountains cross sections of deposits near a number of interior lakes in xizang past glacial variations on the southern slope of nianqing tanggula mountain and landform changes south of the yaluzangbu river such geologic evidence suggests a division of five climatic periods since the beginning of the holocene 1 the wumadung interval 10 000 7500 yr b p slightly cold and dry 2 qilongduo interval 7500 3000 yr b p warm and moist 3 the mid neoglacial period 3000 1500 yr b p cold except between 2500 and 200 yr b p when it was warmer 4 the dawelong interval 1500 300 yr b p mild and 5 the little ice age 300 0 yr b p cold these changes progressed in a similar but not identical pattern as those in the northeastern part of china and in the northern region of europe

palaeoecological and experimental evidence of former forests and woodlands in the treeless desert pastures of southern tibet lhasa a r xizang china abstract palaeoecological and palaeopedological investigations around lhasa 3650 m 29 40 n 91 04 e a r xizang china provide evidence of human induced environmental changes which have occurred over the past 4600 years the present desert pastures of southern tibet most probably replaced forests of juniperus convallium j tibetica and cupressus gigantea along with prunus mira and buddleja crispa in the understorey paleosol investigations and determined charcoal indicate a likeliness of forest destruction followed by increased erosion and sedimentation of colluvial soils for the first time cereal pollen types could be clearly distinguished in southern tibet juniperus pollen has been proved to have only a short dispersal range the presence of cereal pollen and other human indicator pollen proves that it is more likely that human activity rather than climatic changes caused the forest decline during the younger holocene successful non irrigated reforestation trial experiments since 1997 on southern slopes around lhasa with indigenous cupressaceae have demonstrated that desertification of southern tibet is a reversible process as lhasa receives 443 mm annual precipitation and has summer temperatures of above 10 c it follows that the natural vegetation should be a forest as opposed to the desert status quo that presides at present

late quaternary aeolian activity in gonghe basin northeastern qinghai tibetan plateau china abstract aeolian deposits at four sites in the gonghe basin were used to reconstruct the history of aeolian activity over the late quaternary these deposits include well sorted aeolian sand paleosols and or loess aeolian sand represents dune field expansion and or dune buildup whereas paleosols indicate stabilization of dunes accompanying ameliorated vegetation cover on the basis of 25 dates by optically stimulated luminescence osl it appears that aeolian activities occurred episodically at 33 5 20 3 13 9 11 8 11 0 9 4 7 8 and 5 7 5 5 ka which is largely consistent with the recent findings from the adjacent semi arid areas aeolian sand mobility occurring during the early to mid holocene conflicts with a climatic optimum inferred from lacustrine records in the northeastern qinghai tibetan plateau this inconsistency may be resolved by interpreting aeolian activity as a response to decreased effective moisture due to enhanced evaporation induced by higher summer insolation at that time together with local terrain and its effects on moisture our results suggest that aeolian sand and paleosol cannot be simply ascribed to regional dry and wet climates respectively and they most likely reflect changes in effective moisture

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

holocene vegetation and climate histories in the eastern tibetan plateau controls by insolation driven temperature or monsoon derived precipitation changes abstract the climates on the eastern tibetan plateau are strongly influenced by direct insolation heating as well as monsoon derived precipitation change however the moisture and temperature influences on regional vegetation and climate have not been well documented in paleoclimate studies here we present a well dated and high resolution loss on ignition peat property and fossil pollen record over the last 10 000 years from a sedge dominated fen peatland in the central zoige basin on the eastern tibetan plateau and discuss its ecological and climatic interpretations lithology results indicate that organic matter content is high at 60 80 between 10 and 3 ka 1 ka 1000 cal yr bp and shows large magnitude fluctuations in the last 3000 years ash free bulk density as a proxy of peat decomposition and peatland surface moisture conditions oscillates around a mean value of 0 1 g cm 3 with low values at 6 5 4 7 ka reflecting a wet interval and an increasing trend from 4 7 to 2 ka suggesting a drying trend the time averaged mean carbon accumulation rates are 30 6 gc m 2 yr for the last 10 000 years higher than that from many northern peatlands tree pollen mainly from picea mostly reflecting temperature change in this alpine meadow forest ecotonal region has variable values from 3 to 34 during the early holocene reaches the peak value during the mid holocene at 6 5 ka and then decreases until 2 ka the combined peat property and pollen data indicate that a warm and wet climate prevailed in the mid holocene 6 5 4 7 ka representing a monsoon maximum or optimum climate for the region the timing is consistent with recent paleo monsoon records from southern china and with the idea that the interplays of summer insolation and other extratropical large scale boundary conditions including sea surface temperature and sea level change control regional climate the cooling and drying trend since the mid holocene likely reflects the decrease in insolation heating and weakening of summer monsoons regional synthesis of five pollen records along a south north transect indicates that this climate pattern can be recognized all across the eastern tibetan plateau the peatland and vegetation changes in the late holocene suggest complex and dramatic responses of these lowland and upland ecosystems to changes in temperature and moisture conditions and human activities

holocene environmental changes in bangong co basin western tibet part 2 the pollen record abstract a better knowledge of environmental variations in key regions such as the tibetan plateau which plays a fundamental role in the indian monsoon dynamics and thus on the whole northern hemisphere atmospheric circulation is of great importance we present here a detailed paleoenvironmental study based on pollen analyses of a sediment core from lake bangong results on the modern pollen rain are also discussed as they give valuable information for the interpretation of the fossil pollen data the pollen results of the bangong sequence and their paleoclimatic interpretation are integrated into a chronological framework on the basis of palynostratigraphical methods because of dead carbon in the lake system it has been difficult to establish a reliable chronology of the bangong sequence using a geochemical model for correcting measured 14c ages the pollen record from lake bangong compares well with the record from lake sumxi in western tibet lake bangong core provides a continuous holocene pollen record before 9600 yr b p the dominance of desertic elements in the pollen record reflects an arid environment at about 9600 yr b p an abrupt shift to steppe vegetation suggests the onset of moister conditions and from 9500 to 6200 yr b p proxy data indicate conditions warmer and wetter than today proxy data also indicate short term changes during this interval climate instability is suggested by the development of a local palustral flora which peaks at 7700 yr b p and is interpreted as a lake regression in phase with increase in the percentage of littoral and saline water diatom species between 8600 and 7700 yr b p the first humid pulse culminating at 9000 8500 yr b p is thus followed by drier conditions around 8000 7700 yr b p the interval between 7200 and 6500 yr b p regarded as optimal for vegetation growth from the pollen record corresponds to a second humid pulse a trend towards aridity is observed during the following period with dry events centered around 5500 3900 3200 and 700 yr b p

glacial advances in tibet during the younger dryas evidence from cosmogenic 10be 26al and 21ne was the abrupt climate cold reversal called the younger dryas yd a global climate excursion this study presents the first evidence for yd glacial advances on the tibetan plateau derived from 10be 26al and 21ne exposure ages of two erratics with a weighted mean age of about 11 600 years bp from a moraine at the eastern margin of the tibetan plateau this implies that the yd climate signal commonly thought to be initiated by decreased north atlantic deep water formation and transferred by ocean circulation was even recorded at the inner continental high altitude site of tibet implying atmospheric transport and thus a global character for this abrupt climatic change

holocene climatic change and the nomadic anthropocene in eastern tibet palynological and geomorphological results from the nianbaoyeze mountains abstract our study provides detailed information on the lateglacial landscape and vegetation development of tibet based on a suite of geomorphological and palynological proxy data from the nianbaoyeze shan on the eastern margin of the tibetan plateau 33 n 101 e 3300 4500 m asl we reconstruct the current state as a function of climate history and the longevity of human influence study results constrain several major phases of aeolian sedimentation between 50 15 ka and various glacier advances during the late pleistocene the holocene and the little ice age increased aeolian deposition was primarily associated with periods of more extensive glacial ice extent fluvial and alluvial sediment pulses document an increase of erosion starting at 3926 79 cal yr b p coinciding with cooling neoglacial and a growing anthropo zoogenic influence evidence for periglacial mass movements indicate that the late holocene cooling started at around 2000 cal yr b p demonstrating increased surface activity under the combined effects of human influence and climate deterioration the onset of peat growth generally depended on local conditions that include relief meso climate and in more recent times also on soil compaction due to animal trampling we distinguish three initiation periods of peat growth 12 700 10 400 cal yr b p for flat basins inside last glacial terminal moraines 7000 5000 cal yr b p for the main valley floors and 3000 1000 cal yr b p for the higher terrace surfaces the holocene vegetation history started with an open landscape dominated by pioneer shrubs along braided rivers picea juniperus abies and betula trees accompanied by a successive closing of the vegetation cover by poaceae cyperaceae and herbs 9800 8300 cal yr b p first signs of nomadic presence appear as early as 7200 cal yr b p when temperatures were up to 2 c warmer than today forest remained very patchy with strong local contrasts during the following cooling phase 5900 2750 cal yr b p the natural vegetation was transformed by nomadic grazing to bistorta rich kobresia pygmaea pastures modern nomadic migration routes were established at least 2200 years ago overgrazing and trampling led to the shrinking of bistorta and the spreading of annual weeds short lived cold events 8000 6200 3500 cal yr b p impacted on the vegetation only temporarily as the transformation of the natural poaceae rich vegetation into kobresia pastures modified the influence of the tibetan plateau hot plate on the monsoon system our data even point to an early start of a nomadic anthropocene nearly 6000 years ago against the background of a very long grazing history modern tibet must be seen as a cultural landscape