style and timing of glaciation in the lahul himalaya northern india a framework for reconstructing late quaternary palaeoclimatic change in the western himalayas

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

deep mantle forces and the uplift of the colorado plateau 1 we introduce a quantitative model of global mantle convection that reconstructs the detailed motion of a warm mantle upwelling over the last 30 ma towards the interior of the southwestern usa from observed present day mantle heterogeneity the onset and evolution of uplift in the central basin and range province and colorado plateau during this time is determined by tracking the topographic swell due to this mantle upwelling we show that 1 the extension and basaltic volcanism post 25 ma in the central basin and range coincides with the arrival and eastward progression of this upwelling and 2 dynamic uplift of the southern colorado plateau totaling about 1 km transpired in the last 20 ma since 10 ma the center of uplift continued northeastward from the southwestern rim of the plateau consistent with a young grand canyon model and eastward sweep of magmatism in the western colorado plateau

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

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

palaeoclimatological and chronological implications of the vostok core dust record the2 083 m vostok ice core recovered by the soviet antarctic expeditions has provided much information of climatic and environmental interest for a period covering a full glacial inter glacial cycle1 6 here we present and discuss the dust record obtained down to 2 202 m the final depth to which this core was extended in 1986 first we document the fact that major changes in aeolian deposits as recorded in the vostok core appear to be of global significance and confirm the existence of a link between high latitude aeolian deposits and the earth s orbital parameters7 8 second we propose atmospheric dust as a strati graphic marker to compare timing with other records of palaeocli mate and use the magnetic susceptibility profile measured along the rc11 120 indian ocean core9 for this purpose assuming that major dust events correspond to common aeolian inputs this approach indicates that the vostok and marine records were roughly in phase at the previous glacial interglacial transition

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

paleoenvironmental and archaeological investigations at qinghai lake western china geomorphic and chronometric evidence of lake level history abstract qinghai lake located on the northeastern qinghai tibet plateau qing zang gaoyuan is china s largest extant closed basin lake its position relative to major asian climate systems makes it sensitive to global climate change the lake has been the subject of numerous paleoenvironmental investigations including dating of shoreline features around the lake basin here we report new age estimates of shoreline features geomorphic exposures and archaeological sites that contribute to the development of a lake level history for qinghai lake and a landscape model of the qinghai lake basin lake highstands above 3230 m 36 m above the modern lake level appear to date to late mis 5 70 110 ka the lake has had much more modest highstands since then no evidence of mis 3 lake stands higher than modern were found and early holocene highstands are no more than 12 m above modern if the age of highstands greater than 3230 m is confirmed through future work then the qinghai lake basin hydrologic balance prior to 70 ka was dramatically different than after that time including during the holocene a simple hydrologic balance model provides insights into the combination of precipitation evaporation and runoff generation needed to sustain the lake at 3260 m the highest shoreline observed a range of factors may explain the difference primarily the relative strength of the east asian monsoon the basin was apparently subject to extensive alluviation during mis 3 interrupted by widespread erosion and development of cryogenic features before and during the last glacial maximum lgm loess that presently drapes much of the lower basin landscape began to be deposited after the lgm 16 18 ka the landscape model outlined here has implications for archaeological visibility of early human occupation of the qinghai tibet plateau

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

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

reconstruction of the 2 4 million km2 late pleistocene ice sheet on the tibetan plateau and its impact on the global climate during 20 expeditions new data were obtained on the maximum extent of glaciation in tibet and the surrounding mountains evidence was found of moraines at altitudes as low as 460 m on the southern flank of the himalayas and 2300 m on the northern slope of the tibetan plateau in the qilian shan on the northern slopes of the karakorum aghil and kuen lun moraines occurred as far down as 1900 m in southern tibet radiographic analyses of erratics document former ice thicknesses of at least 1200 m glacial polishing and knobs in the himalayas and karakorum are proof of glaciers as thick as 1200 2000 m on the basis of this evidence a 1100 1600 m lower equilibrium ela line was reconstructed for the ice age which would mean 2 2 4 million km2 of ice covering almost all of tibet since the equilibrium ela line was far below the average altitude of tibet on mount everest and k2 radiation was measured up to 6650 m yielding values of 1200 1300 w m2 because of the subtropical latitude and the high altitude solar radiation in tibet is 3 4 times greater than the energy intercepted between 60 and 70 n or s with an area of 2 2 4 million km2 and an albedo of 90 the tibetan ice sheet caused the same heat loss on the earth as a 6 9 6 million km2 sized ice sheet at 60 70 n because of its proximity to the present day equilibrium ela line tibet must have undergone large scale glaciation earlier than other areas being subject to intensive radiation the tibetan ice must have performed an amplifying function during the onset of the ice age

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

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

teleconnections between the subtropical monsoons and high latitude climates during the last deglaciation the major deglacial intensification of the southwest monsoon occurred at 11 450 150 calendar years before present synchronous with a major climate transition as recorded in greenland ice an earlier event of monsoon intensification at 16 000 150 calendar years before present occurred at the end of heinrich layer 1 in the atlantic and parallels the initial rise in global atmospheric methane concentrations and the first abrupt climate changes in the antarctic thus the evolution of the monsoonal and high latitude climates show teleconnections but hemispheric asymmetries superimposed on abrupt events the monsoonal climate shows high frequency variability of 1785 1450 and 1150 year oscillations and abrupt climate change seems to occur when at least two of these oscillations are in phase

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

the environmental effects of the uplift of the qinghai xizang plateau the intense upheaval of the qinghai xizang plateau took place 2 ma bp the terraces of the yellow river in the lanzhou region and its upper sections provide a record of the uplift of the plateau the interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the plateau three tectonic climatic events which are termed respectively the qinghai xizang movement the huanghe yellow river movement and the gonghe movement occurred 2 1 5 1 0 and 0 15 ma bp the upheaval of the qinghai xizang plateau was the trigger mechanism of the asian monsoon the loess plateau was formed in the monsoon triangle of east asia human origins and human evolution may have been stimulated by the uplift of the qinghai xizang plateau

mineral magnetic study of lacustrine sediments from lake pumoyum co southern tibet over the last 19 ka and paleoenvironmental significance abstract high resolution proxy records from tibetan plateau are essential to understand the past climatic and environmental changes in this work we conducted systematic environmental magnetic studies on lacustrine sediments from lake pumoyum co southern tibet spanning from the last deglaciation 19 ka to present we correlated the magnetic proxies in the lake core with environmental changes the magnetic proxies from the 3 units were studied both unit 3 19 13 2 ka and unit 2 13 2 8 4 ka contain evidences for an anoxic or sub anoxic environment fine grained greigite dominates the bulk magnetic properties of unit 3 while both magnetite and greigite coexist in unit 2 overall this reveals a transition from an anoxic environment to an oxic environment in contrast unit 1 8 4 ka present spans the holocene when the lake environment was oxic there is an increasing trend in the concentration of magnetic minerals which reflects an increasing transport of magnetic minerals from the catchment into the lake due to the increased post glacial melt water flow although different mechanisms affect the magnetic assemblage and associated magnetic properties in the different units our results suggest that the magnetic proxies of the local lake environment on southern tibet are sensitive to environmental changes

glacial advances constrained by 10be exposure dating of bedrock landslides kyrgyz tien shan abstract numerous large landslide deposits occur in the tien shan a tectonically active intraplate orogen in central asia yet their significance in quaternary landscape evolution and natural hazard assessment remains unresolved due to the lack of absolute age constraints here we present the first 10be exposure ages for three prominent 107 m3 bedrock landslides that blocked major rivers and formed lakes two of which subsequently breached in the northern kyrgyz tien shan three 10be ages reveal that one landslide in the alamyedin river occurred at 11 15 ka which is consistent with two 14c ages of gastropod shells from reworked loess capping the landslide one large landslide in aksu river is among the oldest documented in semi arid continental interiors with a 10be age of 63 67 ka the ukok river landslide deposit s yielded variable 10be ages which may result from multiple landslides and inheritance of 10be two 10be ages of 8 2 and 5 9 ka suggest that one major landslide occurred in the early to mid holocene followed by at least one other event between 1 5 and 0 4 ka judging from the regional glacial chronology all three landslides have occurred between major regional glacial advances whereas alamyedin and ukok can be considered as postglacial in this context aksu is of interglacial age none of the landslide deposits show traces of glacial erosion hence their locations and 10be ages mark maximum extents and minimum ages of glacial advances respectively using toe to headwall altitude ratios of 0 4 0 5 we reconstruct minimum equilibrium line altitudes that exceed previous estimates by as much as 400 m along the moister northern fringe of the tien shan our data show that deposits from large landslides can provide valuable spatio temporal constraints for glacial advances in landscapes where moraines and glacial deposits have low preservation potential

east asian monsoon climates and gobi dynamics in marine isotope stages 4 and 3 abstract several thick last glacial loess sequences in the western part of the chinese loess plateau and an eolian colluvial sequence in the central mongolian plateau are used to understand how the summer and winter monsoons responded to global forcing factors during marine isotope stages mis 4 and 3 the magnetic susceptibility data are compared with other climatic proxy data to improve the well publicized reconstruction of the past monsoons this study suggests that different sensitivities between the summer and winter monsoons in responding to the northern insolation resulted in transitional climates between marine isotope stages which were characterised by cold and wet climates in the western part of chinese loess plateau after forest steppe in mis 5 coniferous forest emerged at the mis 5 mis 4 transition in cold and moist conditions these imply that the lower latitude oceans were still capable of supplying water vapour to the continental interior and that the mongolian high became dominant when the northern insolation entered a stadial state mis 4 coniferous forest dominated mis 4 but thereafter deteriorated to a steppe towards the end of the mis 4 probably because the lower latitude oceans failed to supply water vapour to the interiors a coniferous forest emerged again at the mis 3 mis 2 transition after forest steppe in mis 3 consequently the southern boundary of the gobi desert retreated northwards during the coniferous tree dominated periods between 73 and 60 ka and between 27 and 19 ka and expanded to maxima between 60 and 50 ka and between 19 and 10 ka the extent of the gobi desert was considerably smaller for several times around 47 ka and 41 ka and 27 ka during mis 3 than during the holocene and the northern boundary retreated 5 times around 20 ka 24 ka 29 ka 31 ka and 34 ka in just the later part of mis 3

a late pleistocene holocene lacustrine record from lake manas zunggar northern xinjiang western china information on the late quaternary palaeoclimate in the zunggar desert northern xinjiang is deduced from the study of three 5 m long cores taken from lake manas analyses including the mineralogical composition of bulk sediments stable isotope contents of carbonates organic matter pollen and diatoms were performed to help reconstruct the environmental evolution of the area the chronology is provided by 9 ams 14c dates done on carbonates or organic matter the record suggests a late pleistocene humid episode radiocarbon dated at 37 000 32 000 yr b p this episode is followed by a period of extreme aridity attributed to the last glacial maximum the early mid holocene record indicates conditions generally wetter than today as previously established for western china however our results show that the holocene period is rather complex after a minor wet warm pulse estimated to be around 12 000 yr b p the most important environmental change is recorded at 10 000 yr b p it led to the establishment of a steppic vegetation cover in the catchment and of a permanent lake which lasted 4000 years fluvial sedimentation took place between about 6000 and 4500 yr b p and it coincided with a decrease in moisture availability for vegetation growth a second lacustrine episode is recorded from about 4500 to 2500 yr b p although the pollen record and a sudden influx in detrital organic matter suggest a short term dry event around 3800 3500 yr b p the last 2500 years show climate unstability and the step wise establishment of hypersaline conditions in lake manas the major post glacial environmental changes appear to be roughly in phase with those observed in tibet

on the problem of quaternary glaciations and the extent and patterns of pleistocene ice cover in the qinghai xizang tibet plateau abstract data accumulated during investigations since the 1960s indicate that up to four pleistocene glaciations can be recognized in the qinghai xizang tibet plateau and the adjacent himalaya mountains in order of decreasing age these are the xixabangma nyanyaxungla guxiang and baiyu glacial episodes the history of pleistocene glacial evolution in various areas throughout the plateau differs and the pattern is very complex throughout the early pleistocene the elevation of the qinghai xizang plateau was approximately 2000 m above sea level during the xixabangma glacial episode recorded at higher elevations the climate and topographical conditions on the plateau were largely unfavourable for the development of glaciers present investigations have revealed that the oldest till is only found at isolated localities on the plateau glaciofluvial or alluvial deposits such as the gongba conglomerate dating from 2 4 to 0 73 ma bp and the fluvial lacustrine deposits of the qiantang group dating from 2 4 to 1 7 ma bp are present rather than glacial till therefore the postulate of a large early pleistocene ice sheet proposed previously has been disproves during the most recent glaciation uplift of the plateau and the himalayas continued the majority of the qinghai xizang plateau reached 4000 m a s l and the great himalaya were approximately 6000 m a s l the mountains formed a barrier against the incursion of the indian monsoon so that precipitation decreased sharply on the northern flank of the himalayas and the climate to the north became cold and dry all of the glaciers on the qinghai xizang plateau underwent extensive retreat thus during the pleistocene no unified glacial cover existed over the qinghai xizang plateau similarly the source area of the hwang he yellow river did not support a local ice sheet

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

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

ice volume forcing of east asian winter monsoon variations in the past 800 000 years particle size measurements of some typical loess soil samples taken in different localities of the chinese loess plateau demonstrate that the grain size ratio of 10 m can be used as an indicator of variations in intensity of the east asian winter monsoon winds grain size curves of the baoji and weinan sections show that this proxy indicator is very sensitive to loess soil alterations analytical results also suggest that during soil forming periods eolian dust accumulation was still substantial and hence loess deposition can be regarded as a nearly continuous process during the quaternary period in this study we compared the baoji grain size time series with the specmap marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation both records show good agreement at both time and frequency domains in particular the winter monsoon variations are also dominated by a 100 000 yr period over the past 800 000 yr it is thus inferred that direct local insolation forcing could be less important in driving the east asian winter monsoon variability and alternatively variations in glacial age boundary conditions may have played a key role in modulating and pacing its strength and timing

controversy regarding the existence of a large ice sheet on the qinghai xizang tibetan plateau during the quaternary period

cosmogenic 10be and 26al dating of paleolake shorelines in tibet abstract we have used in situ produced cosmogenic nuclides 10be and 26al to date lacustrine shorelines around eight lakes in tibet two lakes located south of the yarlung tsangpo river discharged at high lake levels one of them drolung co co is a local term meaning lake became closed its water level fell below its outlet channel at 3 8 ka and lowered over 120 m vertically since then this implies a significant change in intensity of precipitation driven by the indian monsoon over southern tibet in the middle late holocene nam co and dajia co located to the north of the yarlung tsangpo river also drained at high lake levels and became closed 53 36 ka and 48 ka respectively of four other lakes developed closely in the qiangtang basin north of the yarlung tsangpo river tangra yum co and siling co located at 31 32 n show exposure ages for high lake shorelines of over 220 ka the oldest lake shorelines reported for tibet while towards the north and west the high lake of zhari nam co appeared after the last glacial maximum lgm the different pattern of lake development to the north of yarlung tsangpo river may reflect regional climate effects

the impact of latitude and altitude on the extent of permafrost during the last permafrost maximum lpm in north china abstract this paper examines the relationship between the extent of permafrost during the last permafrost maximum lpm largely between 22 and 17 ka bp and the altitudinal and latitudinal temperature gradients that controlled its extent the region chosen namely the qinghai tibet plateau and the transition to the northern adjacent plains in the north china plain is of relatively limited extent in order to avoid regional effects this area extends over 15 degrees of latitude while altitudes vary from 1000 to 1500 m above sealevel asl in the northern plains to more than 4000 m asl in the central to south part of the qinghai tibet plateau the respective lowest southernmost permafrost occurrences at a northern and a southern position are used for reconstruction of the latitudinal and altitudinal gradients as a first approximation we conclude that the elevation compensation during the lpm for a 1 latitude change was between 309 m and 385 m this is considerably higher than the value calculated for existing permafrost in the region that uses thermal data at a depth of zero amplitude change 139 198 m altitudinal compensation for 1 latitude

paleoshoreline geomorphology of boon tsagaan nuur tsagaan nuur and orog nuur the valley of lakes mongolia abstract we conducted a preliminary study of paleoshoreline features associated with boon tsagaan nuur tsagaan nuur and orog nuur lakes located in the gobi altai transition zone of the valley of lakes dolina ozor which stretches from central to western mongolia the paleoshoreline features were first identified on radarsat satellite sar imagery we investigated the features during the 1998 field season of the joint mongolian russian american archaeological expedition to the gobi altai region we identified paleoshorelines of multiple elevations in the field which are considered to be relict beach ridges and wave cut terraces other paleolake landforms include spits and gilbert type deltas these landforms are complex large and well established implying that the paleolakes were stable for extended periods the reconstructed paleolakes cover extensive areas of the valley floor implying that hydrological and climatic conditions were very different in the past paleolake expansions may have occurred under a variety of circumstances one hypothesis is that the high lake stands occurred during the wetter period corresponding to the oxygen isotope stage 3 prior to the last glacial maximum lgm during the warmest early holocene and the late holocene or during all these periods if low evaporation rates due to lower temperatures glacier meltwater and possibly increased precipitation are important factors then the expansions may have occurred during the terminal late glacial period after the last glacial maximum the greatly expanded lakes in the gobi altai could have significantly affected the quaternary human demography and migration in the region

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

cyclic quaternary alluviation and terracing in a nonglaciated drainage basin on the north flank of the qinling shan central china abstract pleistocene alluvial terraces of the nonglaciated ba river drainage basin on the north flank of the qinling shan are capped by a succession of loess units and paleosols that correlate with the standard marine isotope chronology and are used to date the subjacent alluvial gravels alluvial fills were deposited during isotope stages 2 6 8 12 and 16 whereas terracing occurred during interglacial stages 1 5 7 11 and 15 the apparent absence of terraces dating to stage 14 and stage 4 may be due to the lesser intensity of these glaciations compared to that of stage 2 although disruption of the alluvial regime by local tectonism is a likely alternative for the lack of a stage 4 terrace a stage 10 terrace was not positively identified from available exposures its possible absence could be related to post stage 12 uplift aggradational episodes correlate with glaciations and loess deposition whereas degradational episodes correlate with interglaciations or interstades and soil formation implying that climate is the primary control on quaternary paleohydrology this in turn points to variations in the earth s orbital geometry as the major factor that modulates both climate and ultimately the fluvial system in the qinling shan in this region glaciations were dominated by a cold dry winter monsoon climate whereas during interstades and interglaciations a warmer and wetter climate prevailed implying strengthening of the summer monsoon both the loess paleosol and the alluvial records are consistent with climate model simulations spanning the last 18 000 yr that show a change from cold dry conditions during the last glacial maximum to a climate warmer and wetter than present during the first half of the holocene

snowline elevation and eolian dust flux in the japanese islands during isotope stages 2 and 4 abstract changes in snowline elevation and dust flux clearly contrast the paleoenvironments of the japanese islands during isotope stages 2 and 4 a lower snowline elevation and a smaller dust flux during isotope stage 4 suggests a climate with a cold and dry summer dominated by winter monsoonal precipitation between 70 and 55 ka a higher snowline elevation and a larger dust flux during isotope stage 2 indicates a climate with a cold and very dry summer with a minimized winter monsoon precipitation especially around 18 ka a drier climate during stage 2 can be explained by 1 a lowering of sea surface temperature in the japan sea by blocking the warm tsushima current during a sea level lowering 2 the extension of sea ice over the northern part of the japan sea and the sea of okhotsk and 3 weakening of the summer monsoon and the southern migration of the polar front the increase in dust flux in both stages 2 and 4 suggests an intensification of westerlies and winter monsoon during these stages a bigger dust flux in stage 2 than stage 4 reflects 1 stronger westerlies and winter monsoon and 2 the emergence of continental shelf which became an important dust source

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

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

global change over the last climatic cycle from the vostok ice core record antarctica abstract the study of ice cores provides the opportunity of access to numerous parameters which are related to climate or environmental changes many of these variables are of regional or even global geographical significance there are now several ice cores which penetrate into ice which has formed at the surface of polar ice sheets during the last ice age and the recently obtained vostok antarctica record provides detailed information over the last climatic cycle 160 ka in comparison with current holocene conditions the last glacial maximum 20 ka bp is characterized by much colder conditions up to 10 c and reduced precipitation 1 2 a large increase of continental and marine aerosols is explained by a more vigorous large scale atmospheric circulation associated with changing continental deserts and shelves as well as changes in sea ice extent the drastic climatic change occurring at the last glacial termination is correlated with a large increase of atmospheric co 2 from about 200 to 270 ppmv the isotopic temperature record from the vostok ice core depicts two drastic glacial interglacial terminations around 15 and 140 ka bp and a long glacial period 110 15 ka bp which includes two interstadials full glacial stages are characterized by larger aerosol loadings the co 2 record of global significance is well correlated with the isotope temperature profile with high 270 ppmv during interglacials and low 200 ppmv during full glacial conditions spectral analysis of the yostok temperature record supports the existence of a relationship between the pleistocene climate and orbital forcing on the other hand the existence of a co 2 climate correlation suggests that co 2 changes have had an important climatic role in amplifying the relatively weak orbital forcing

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

holocene dust deposition in the ili basin and its implications for climate variations in westerlies dominated central asia abstract understanding holocene paleoclimate in arid central asia aca is helpful for predicting future climate however holocene climate patterns and their forcing mechanisms across aca are vigorously debated in the context of global climate change here we present a holocene loess profile sgx from the ili basin in the westerlies dominated central asia based on high resolution medium grained 38 63 m quartz optically stimulated luminescence osl dating and grain size and color measurements we reconstruct the holocene paleoclimate osl geochronology indicate that this sgx loess profile covers the last 11 5 ka and grain size analyses reveal that the sediments are sandy loess and the environmentally sensitive fractions are

relic permafrost structures in the gobi of mongolia age and significance relict permafrost structures ice wedge casts and cryoturbation structures are present in the gobi of southern mongolia luminescence dates of sediments are presented to constrain the age of formation of permafrost structures these data show that there was a phase of permafrost development during the latter part of the last glacial after about 22 to 15 ka that resulted in cryoturbated sediments and ice wedge casts furthermore permafrost degradation occurred during late pleistocene times 13 10 ka and was absent during the early holocene these permafrost structures mark the southernmost evidence of permafrost in northern asia during late quaternary times and indicate that the mean annual air temperature was below approximately 6 c during their formation 1998 john wiley sons ltd

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

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

response of surface processes to climatic change in the dunefields and loess plateau of north china during the late quaternary this paper draws on recent optically stimulated luminescence osl dating to evaluate the long held assumption that dust accumulation rates in the loess plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time because both are controlled by the strength of the asian monsoons and also possibly because the dunefields are proximal loess sources the results show there is little evidence that high rates of loess accumulation coincided with well dated episodes of extensive dune activity in the mu us otindag and horqin dunefields at 11 8 ka and 1 0 ka explanations for the apparent lack of coupling include local variation in the trapping of dust and post depositional preservation of the loess and dune sediments in response to varying local environmental conditions in addition a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields the results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale the dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale but the timing of late quaternary dune activity along with a variety of other evidence indicates that moisture changes in many of the drylands of northern china may not be in phase with precipitation in core regions of the asian monsoons copyright 2011 john wiley sons ltd

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

holocene environmental changes in lake bangong basin western tibet part 1 chronology and stable isotopes of carbonates of a holocene lacustrine core abstract a 12 4 m core collected from the eastern part of lake bangong is analyzed for mineralogy radiometric chronology and stable isotope contents of authigenic inorganic carbonate isotopic compositions of the modern lake waters and of its major tributaries are first presented radiocarbon activity of these waters show that equilibrium with the atmospheric co2 is not reached because of admixture of dead carbon in solution in the system a model is thus developed to correct the radiocarbon ages of fossil material of aquatic origin for this ageing the core provides a continuous holocene record changes in mineralogy of bulk sediments and in 13c and 18o contents of authigenic carbonates reveal extremely large changes in environmental conditions induced by climate changes and or local hydrological factors e g closure opening of the lake system controlled by the altitude of the outflow sill the eastern basin of lake bangong was closed before 9 6 and after 1 2 ka b p in response to aridity on the catchment wet warm conditions attributed to the monsoon influence were established suddenly at 9 6 ka b p and maintained until 6 2 ka b p although minor reversal events occurred between 8 6 and 7 7 ka b p the return towards aridity is non linear dry spells at 6 2 3 9 3 2 and 1 3 ka b p are alternated with short term periods with positive precipitation evaporation balance

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

variability of monsoon climate in east asia at the end of the last glaciation abstract high resolution paleomonsoon proxy records from peat and eolian sand paleosol sequences at the desert loess transition zone in china denote a rapid oscillation from cold dry conditions 11 200 10 60014c yr b p to cool humid conditions 10 600 10 20014c yr b p followed by a return to cold dry climate 10 200 10 00014c yr b p variations in precipitation proxies suggest that significant climatic variability occurred in monsoonal eastern asia during the younger dryas interval late glacial climate in the chinese desert loess belt that lies downwind from europe was strongly influenced by cold air from high latitudes and from the north atlantic via the westerlies the inferred precipitation variations were likely caused by variations in the strength of the siberian high which influenced the pressure gradient between land and ocean and therefore influenced the position of the east asian monsoon front

episode of strengthened summer monsoon climate of younger dryas age on the loess plateau of central china abstract the baxie loess section just east of the tibetan plateau contains evidence showing that the asian monsoon climate experienced an abrupt reversal near the end of the last glacial age rapid deposition of dust under cool dry full glacial conditions gave way to an interval of soil development and reduced dust influx attributed to a strengthening of the warm moist summer monsoon a subsequent abrupt increase in dust deposition a response to a weakening of the summer monsoon was later followed by renewed soil formation as summer monsoon circulation again intensified during the early holocene by one interpretation the thin upper loess is a manifestation of the european younger dryas oscillation however in this case the available 14c ages require either that 1 onset of loess deposition lagged the beginning of the younger dryas event in europe by as much as 2000 calibrated 14c years or 2 all the 14c ages are too young possibly due to contamination alternatively the late glacial paleosol the top of which is synchronous with the abrupt end of the late glacial 18o anomaly in the dye 3 greenland ice core records the younger dryas event such an interpretation is consistent with general circulation model simulations of younger dryas climate that show strong seasonality and a strengthened summer monsoon and with marine cores from the western pacific ocean that contain evidence of pronounced cooling of surface waters during younger dryas time

climate change loess and palaeosols proxy measures and resolution in north china the loess plateau of north china is a key region for the study of records of quaternary climatic change various techniques to abstract climatically sensitive data were first applied to the classic loess palaeosol site at luochuan and current views on climatic change in asia have been strongly moulded by results from this central part of the loess plateau data including the magnetic susceptibility granulometry mineralogy geochemistry micromorphology fossil content and inorganic and organic carbon content of asian loess palaeosol series have been used singly and in combination as surrogate measures of palaeoclimates to infer climatic changes with particular reference to changes in the asian monsoon some of this work is reviewed and the status of a number of parameters as climatic proxies is discussed some lithostratigraphic sequences from which proxy measures of climate have been derived are incomplete as shown by erosion surfaces water laminated zones and truncated palaeosol profiles while others provide records of relatively low resolution most descriptions of quaternary climatic changes based on studies of the loess emphasize alternations in the relative dominance of warm and moist v cool dry and dust laden monsoons some recent studies of the much higher resolution loess palaeosol successions on the western margins of the loess plateau have suggested that such changes may sometimes be out of phase with the inference that the current climate model is too simple means of testing this hypothesis are proposed

continuous dust concentration profile of pre holocene ice from the greenland ice sheet project 2 ice core dust stadials interstadials and the eemian in this paper we present and discuss the pre holocene dust profile of the greenland ice sheet project 2 gisp2 ice core retrieved from central greenland measured using laser light scattering lls from ice and compare it with the electrical conductivity method and oxygen isotope profiles we describe how we dated the pre holocene ice using the annual dust peaks observed with lls starting from the accepted chronology to 2250 m and obtained a chronology in substantial accord with the gas age dating of the ice we also show that the gisp2 ice core penetrated the eemian and that a record of a 10 2 kyr penultimate glaciation is present in the gisp2 core

evidence for a warm humid climate in arid northwestern china during 40 30 ka bp abstract former shorelines and sedimentary records from several lake basins in northwestern china xinjiang qinghai give evidence for warm and humid climatic conditions during 40 30 ka bp further indications of this favorable climate period are derived from palaeosols from the ili loess and from cemented calcareous layers on the terraces of the keriya river at the southern margin of the tarim basin and in the badain jaran desert in inner mongolia at that time annual mean temperature in the qaidam basin was 2 c higher and in the western part of inner mongolia even 2 3 c higher than today precipitation in most parts of northwestern china was between 60 300 mm greater than today these changes were probably a consequence of an increase in ocean surface temperature and evaporation resulting from a higher radiation input at middle and low latitudes caused by changes in the earth s precessional cycle as a result of these orbital changes it is suggested that the intensified westerly circulation was responsible for increased moisture over northwestern china

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

the sequence of quaternary glaciation in the bayan har mountains four periods of quaternary glaciation in the pleistocene have been found in the area of the bayan har mountains they represent respectively the two stages of the last glacial age the penultimate ice age and an earlier ice age during the late stage of the last glacial age glaciers developed only near the mountain ridges of the bayan har in the earlier stage glaciers expanded down to the piedmont of the bayan har mountains and were as much as 40 km long in the penultimate ice age an extensive ice cover developed depositing an areally widespread till sheet erratics were transported 60 km from bayan har peak to qingshuihe town to the south and to yematan land to the north granitic erratics are also distributed over elevated geomorphological positions such as chalaping ridge the area of ice cover encompassed up to 50 000 km2 furthermore evidence including glacial landforms and sediments shows that a larger glaciation existed in this area in an earlier time possibly during the third most recent ante penultimate glaciation the scale of this glaciated area is greater than those of the more recent events in the qinghai xizang plateau extending over 80 000 km2 this glaciation covered the source area of the yellow river from xingsuhai in the west to duogerangtan in the east including the areas of gyaring and ngoring lakes based on the extent and locations of the glaciations the bayan har stage and galalahai stage of the last glacial age the yematan ice age and the huanghe glacial age can be recognized

a 40 000 year record of aridity and dust activity at lop nur tarim basin northwestern china abstract the taklamakan desert is a major dust source area for northwestern china the history of aridification and sandstorm activity of the desert is recorded in the lacustrine sediments of the lop nur paleolake on the eastern margin of the desert in this study we used accelerator mass spectrometry 14c dating the ln al ca ratio and the grain size of the non biogenic fraction of sediment core ky01 taken from the center of lop nur to produce a 40 kyr record of local climate change during mid late marine isotope stage mis 3 increases in the ln al ca ratio alluvial mud content and atmospheric dust content and a decrease in the dust storm content indicate an overall wet climate during mis 2 marked decreases in the ln al ca ratio and alluvial mud content especially during the last glacial maximum and heinrich event 1 cold interval indicate lowered atmospheric temperatures as also recorded in greenland ice cores during mis 2 fluvial input to the site was reduced and almost ceased suggesting extreme aridity at lop nur very strong low altitude winds and frequent dust storms during early mis 1 the contribution of dust storms to the lake sediments fell gradually and was then relatively constant even during the younger dryas cold interval this result might be ascribed to the increased supply of meltwater from snow and ice to lop nur representing a response to the rise in atmospheric temperatures during the deglacial accompanied by strong high level winds during 9 7 kyr bp there was an increase in the input of sediment from sandstorms and hence an increase in low level wind strength possibly relating to the 8 2 kyr bp cold event from 7 0 to 1 5 kyr bp there was a decrease in sandstorm input and thus a gradual weakening of the strength of low level winds however after 1 5 kyr bp the sandstorm input increased overall we conclude that dust storm activity in the region of lop nur since 40 kyr bp has been controlled mainly by northern hemisphere cold events with atmospheric dust providing a background sedimentary component that was dominant during warm intervals our findings contribute to an improved understanding of the dynamics of dust transport and to the history of dust activity and the lacustrine sedimentary record in northwestern china

thermoluminescence chronology of sand profiles in the mu us desert china abstract thermoluminescence tl is used to calculate the ages of two sand loess profiles in the marginal zone of the mu us desert china alternating units of dune sand and loess with palaeosols in the two profiles imply episodes of dune formation separated by periods of loess accumulation and pedogenesis our results indicate that there are three layers of dune sand intercalated in sediments of the last full glacial cycle suggesting the occurrence of three arid episodes during this time the first arid episode within this period occurred between

radiocarbon dating of playa lake hydrologic changes examples from northwestern china and central australia accurate radiocarbon dating of arid zone playas is restricted by shortage of suitable organic matter analyses from two large systems in australia lake frome and china qarhan playa in the qaidam basin demonstrate the problems associated with the use of carbonates for dating organic carbon although requiring treatment of large samples 1 2 kg provides the most accurate basis for establishing chronologic control in qarhan a deposit of halite averaging about 30 m thick extends over an area of 5800 km2 carbonate in the system is dominantly derived as clastics from loess transported by northwesterly winds the large component of dead carbon thus involved explains anomalous patterns of dates derived from these materials such results are consistently much older than those based on organic carbon in lake frome subject to a more maritime climate in central australia the carbonate component is dominantly authigenic lacustrine in origin contaminated by a small detrital component it provides ages about one half life older than those from organic carbon the sequence from qarhan supplemented by evidence of lacustral pluvial episodes in two other sub basins in qaidam kunteyi and xiao qaidam illustrates the presence there of expanded waterbodies persisting from at least 40 000 to about 15 000 yr b p in areas where little surface water persists today the large evaporite deposits formed between about 25 000 to sometime after 15 000 yr b p holocene climate appears to have remained hyperarid like that of today at lake frome an early lacustral phase gave way before 18 000 yr b p to drying and aeolian activity water had returned to the system by 16 000 yr b p signalling a decline if not the end of aridity lacustrine conditions persisted through early holocene with drying and development of playa facies about 7000 yr b p after a brief return to lacustrine conditions between about 6000 4000 yr b p a dry playa environment has continued to the present day the frome and qarhan playas although in comparable latitudes lie in very different climatic and tectonic settings their palaeohydrologic records are neither in phase nor in distinct anti phase emphasizing the complexity of comparing palaeoclimatic records from different circulation systems

lake evolution during the past 30 000 years in china and its implications for environmental change abstract taking china as a whole lake expansion occurred 500 b c 0 a d 650 950 a d and 1250 1650 a d over the past 3000 yr the expansions were mainly due to climatic fluctuations and correspond to frequent flood reports three regional characteristics of lake development have been recognized 1 fluctuations of near coastal lakes and those in other regions as well were out of phase during 500 b c 500 a d which possibly resulted from out of phase fluctuations of climate and sea level on 10 to 100 yr time scale 2 as the lower yellow river channel migrated southward the lakes in the south of the north china plain formed and reached their largest sizes much later than those in the north 3 for the lakes in the middle and lower yangtze river valley the higher a lake basin lies above a neighboring river and the further the lake is from the river s mouth in general the younger the lake is through land reclamation the ancient chinese have changed most of the lakes greatly however human activities were also constrained in certain ways by the natural changes of the lakes reclamation usually was banned and farmland was abandoned to repair reservoirs while lakes were expanding

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

geomorphological investigations and luminescence dating in the southern part of the khangay and the valley of the gobi lakes central mongolia geomorphological investigations in the catchment area of the baydragiyn river along the southern slope of the khangay and in the valley of the gobi lakes in western mongolia provide evidence for late quaternary glaciations and lake level changes thermoluminescence tl and infrared optically stimulated luminescence irsl dating of aeolian and colluvial sediments from the central khangay place the sediments that overlie fluvial and glaciofluvial terraces in the holocene an age of 21 ka is determined for a sand deposit overlying the terrace that is related to the last glacial ice margin lacustrine sediments from higher beach lines in the valley of the gobi lakes provide evidence for a slightly more humid period around 1 5 ka and a larger extent of the lakes in the early holocene at about 8 5 ka as also reported from other parts of central asia remnants of lacustrine sediments buried by alluvial gravel and indicating a huge palaeolake in the basin of the orog nuur however date to the early stage of the last glaciation around 70 ka copyright 2001 john wiley sons ltd

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

late pleistocene late glacial and holocene glacier advances on the tibetan plateau abstract many end moraine sequences in various mountain areas of the tibetan plateau have already been investigated in detail but a homogeneous chronostratigraphy is still lacking the ice marginal limits are commonly given local names and often the classification does not seem to be secure this is one reason for controversial discussions on the ice extent at the lgm because most organic material in tibet developed at the beginning of the holocene only a few older radiocarbon dates are available up to now late glacial terminal moraines have been found in the western kunlun shan and in the tian shan their radiocarbon ages ca 15 ka bp correspond to a glacier advance south of the qaidam basin which can be correlated with late glacial lacustrine sediments in eastern tibet different ages of peat development in different tongue like basins have been obtained even the bases of peat bogs in basins at nianbaoyeze mountains enclosed by apparent lgm end moraines gave holocene ages three main holocene intervals have been radiocarbon dated from palaeosols and basal peat layers in the area except for a younger glacier re advance at about 3000 bp and those of the little ice age the age of many last glaciation glacier advances on the tibetan plateau are constrained only on the basis of organic matter lying on top of the moraines and therefore might be of late glacial or pleistocene age

230th 234u and 36cl dating of evaporite deposits from the western qaidam basin china implications for glacial period dust export from central asia the western qaidam basin contains numerous hydrologically closed lakes and playas we have measured uranium thorium and chlorine radioisotopes in sediments from drill cores at two of these gasikule lake and dalangtan dry playa in order to date cycles of high and low lake level the sediment chronologies from the two sub basins are generally concordant and the u th ages indicate transitions from high to low lake levels at 302 56 ka at 138 6 ka and at 16 3 2 2 ka these ages indicate that high lake stands in the qaidam basin were terminated at the end of continental glacial maxima this result is unexpected because previously the large eolian dust fluxes out of central asia during glacial maxima have been considered to be associated with increased aridity in the region not increased humidity the lacustrine evidence combined with previous data from ice cores suggests instead that the persistence of strong winds may have played a more important role in enhanced dust fluxes than did variations in dust availability due to changes in aridity

lake evolution in the tengger desert northwestern china during the last 40 000 years climatic changes inferred from lacustrine deposits and lake level fluctuations in northwestern and central china are mainly based on paleoclimatic records from the tibetan plateau while there is still a lack of data relating to the semiarid arid desert regions of inner mongolia in the tengger desert different paleolake levels at baijian hu are documented by six paleoshorelines and stratified lake carbonates the highest lake level occurred ca 39 000 14c yr b p and prevailed over about 16 000 km2 from sediment structure geochemical composition and ostracods we infer humid cool conditions until 23 000 14c yr b p in the northern badanjilin desert at gaxan nur sogu nur high lake levels can be deduced from mollusc bearing paleobeaches and lake carbonates which have been dated to 34 000 14c yr b p and indicate a lake that covered some 32 000 km2 after ca 20 000 yr b p the climate became dry with increased eolian activity and decreasing lake levels reestablishment of wet conditions occurred ca 13 000 yr b p the holocene is represented by stratified lake deposits that alternate with fluvial and eolian deposits indicating a longterm oscillating trend toward arid conditions the existence of widespread freshwater lakes during the late pleistocene indicates a semihumid climate without an accompanying fall in temperature to arctic conditions

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

quaternary glaciation of tibet the geological evidence the question of the number and extent of pleistocene glaciations on the qinghai xizang tibet plateau remains contentious there has been considerable research activity in tibet by chinese scientists since the late 1950s and their principal findings including data on glacial and periglacial geomorphology sedimentology tectonics stratigraphy and lake history have been used to reconstruct ice margins and palaeosnowlines three and in places four distinct glaciations have been recognised the most extensive occurring in the later middle pleistocene valley and piedmont glacial systems with some mountain ice caps and a small ice sheet on the upper reaches of the huang he have been recognised but there is no evidence of a single tibetan ice sheet as the plateau and the himalaya karakoram underwent accelerating uplift through the quaternary there occurred progressive desiccation in the interior as the influx of indian ocean moisture was constrained equilibrium line elevations in the last glacial maximum were 4000 m in the south east and northeast plateau margins rising to 5500 m in the northwest interior the heat island provided by the plateau the progressive reduction in precipitation most marked during the glacials and the strong southeast to northwest precipitation gradients produced a glacier distribution pattern dominated by the trans tibetan mountain ranges tectonics and periglacial including aeolian processes have played an equal role with glaciation in generating the plateau s quaternary sedimentary succession

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

the last 140 ka in the afro asian arid semi arid transitional zone abstract during the last ten years a great number of geological or other proxy records provided radiocarbon u th or tl dated information on the past climatic oscillations in the arid semi arid zones extending between the atlantic and the pacific comparisons and a synthetic view of these results can now be attempted for the last 140 ka and compared with global changes as registered in oceanic or ice cores and with palaeomonsson models for this purpose wide spatial and time scales have to be used on the whole arid humid alternations roughly fit global changes cold phases corresponding to an extension of the arid areas to the south warm phases corresponding to the shrinking of the same to the north the last interglacial is associated with an increase of precipitation throughout the area considered isotopic stage 4 brings no evidence whatsoever of humid conditions two wetter episodes are registrated during stage 3 a major rainfall decrease is everywhere associated with the last glacial maximum 21 15 ka in most regions the arid or semi arid zones extending several hundred kilometers southwards relative to the present day pattern the two abrupt deglaciation steps and the younger dryas are recorded in all of the most sensitive regions at the margins of the present day monsoonal range during the holocene the precipitation increases everywhere by 100 400 mn relative to the present day values the optimum being at 8 5 6 5 ka a climatic deterioration follows with an irregular pattern of dry wet episodes according to the different geographic conditions the humid phase terminates at 3 5 3 ka in the whole transitional zone the major southward shift of the monsoonal precipitation range since its optimum some 8000 years ago fits the astronomical neoglacial trend and may possibly be correlated with past stage 5d although its rapidity and spatial importance may just reflect one of the sharp successive cold warm variations registered by grip during the whole stage 5

asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean rea d k and leinen m 1988 asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean palaeogeogr palaeoclimatol palaeoecol 66 1 8 a 30 000 year record of eolian deposition in the northwestern pacific ocean provides a history of the aridity of the asian source region and information on the changing latitude and intensity of the zonal westerlies the position of the maximum in eolian flux to the deep sea remained unchanged at 38 to 40 n during this entire time period but the dust flux record of aridity is greatest 6000 years ago at the holocene climatic optimum eolian grainsize data indicate that the northern margin of the westerly jet stream retreated northward during the holocene to a poleward extreme at about 6000 years ago and then moved back toward the equator the change in wind intensity across this margin was continually reduced throughout the holocene these sorts of data enhance our understanding of the behavior of the atmosphere during times of climate change and can be used to test computer generated models of past climatic conditions

late quaternary transition from lacustrine to a fluvio lacustrine environment in the north western nam co tibetan plateau china abstract holocene sediments from a 9 m high outcrop at the gangyasang qu s entry into lake nam co on the south eastern tibetan plateau were studied in a multiproxy approach the lowermost part of the section is of early holocene age and consists of varved sediments deposited in a proglacial lake geomorphological investigations of fossil beach ridges and fossil cliff lines in the littoral zone of nam co indicate a late pleistocene lake level high of 29 m above the present level a warming is visible in ostracode rich silts deposited after 9 6 ka bp an ostracode based transfer function estimates a lake level 28 m higher than today from this time until about 5 2 ka bp a late pleistocene lake level high was accompanied by an increase in lake size causing nam co to overflow into the lower course of gangyasang qu where a bay with slack water conditions formed between 4 2 and 1 3 ka bp the lake level was approximately 10 m higher than today the progradation of the gangyasang qu delta into nam co and the decreasing lake level shifted the study site into a fluvio lacustrine environment the sandy character and relatively low numbers of ostracode valves in the topmost sediments indicate increased fluvial activity possibly due to a temporary increase in flood frequency this facies lasted at least until 1 3 ka bp when the lake level of nam co dropped again and the river incised more than 10 m into the underlying fluvio lacustrine and lacustrine sediments

on the ages of humid holocene and late pleistocene phases in north africa remarks on late quaternary climatic reconstruction for the maghreb north africa by p rognon discussion sur l article de rognon p paru en 1987 dans palaeogeogr palaeoclimatol palaeoecol vol 58 p 11 34

quaternary paleoenvironmental change on the tibetan plateau and adjacent areas western china and western mongolia abstract this paper summarises the nature of climatic change during the last glacial interglacial cycle on the tibetan plateau and adjacent areas the results are derived from inland glacier fluctuations lake level changes and dust loess records of central asia including tibet these are based on our field investigations from 1988 to 1998 and literature surveys the changing extents of different climatic controlled geomorphic landscapes and vegetation zones help to provide estimates of the magnitude of climatic change features such as ice wedge casts loess and palaeosols ela reconstruction s and palaeobotanical data are used to help reconstruct palaeoprecipitation and palaeotemperatures weathering characteristics the overlying strata and some luminescence dates indicate that there are two main glacial ice advances during the last glacial cycle these correspond to marine oxygen isotope stages ois 2 and 4 in some areas as the eastern or northern margin of the tibetan plateau remnants of older glaciations are preserved higher lake levels in the deserts of central asia and on the tibetan plateau are dated to 40 to 25 ka ois 3 and to late glacial early to mid holocene periods our work supports the view that in many areas of central asia cold phases during the last glacial correspond with the maximum extent of glaciers and the periglacial activity the last glaciation produced large alluvial fans alternating with periods of high lake stands on the tibetan plateau however at the northern margin of the plateau in the qaidam basin and in some particular desert areas in western china high lake levels occurred also during the pleistocene and are related with alluvial fans

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

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

the evolution of dry lands in northern china and in the republic of mongolia since the last glacial maximum abstract the dry lands in china and mongolia include sand seas gravel deserts stable sand dunes desert steppe steppe and scrub woodlands environments distributed in a wide range of geomorphological and tectonic settings from 155 m below sea level to more than 5000 m asl in china the sandy deserts and gravel deserts are located in the arid regions mainly west of the helan mountains 106 e whereas the stable dune regions are distributed in the semi arid areas east of the helan mountains in mongolia deserts cover more than 40 of the country they are mainly distributed in the southern and southwestern part of the country in inter mountain valleys and basins of the altai mountains and in the uvs nuur basin in northwestern mongolia the desert regions enclose mainly gravel desert gobi and comprise some areas with sand fields and dune fields especially in western mongolia relict frost wedges and moraines in the chaidamu and tarim basins of china indicate that the coldest time of the last glaciation occurred at 30 25 ka in these two areas the stratigraphy of the dunes in the badain jaran desert high lake levels in the areas near and within the large deserts in china and in mongolia suggest a much more humid climate in western china and in mongolia during marine isotope stage three however the period after 24 ka to the end of the pleistocene was mostly characterised by increased temperature and reduced precipitation in the chaidamu and tarim basins paleoenvironmental conditions in the eastern part of the chinese desert belt were marked by an extensive widening of dune formation at 21 13 ka reflecting a weaker intensity of east asian summer monsoon during the holocene higher lake levels stratigraphy of dunes and results of palynological isotopical and sedimentological analyses of lacustrine sediments in the western china and mongolia suggest a few wetter periods especially in the earlier part of the holocene the holocene climatic conditions in the eastern part of the chinese deserts have enabled stabilisation of dunes and formation of soils the presently active dunes in this region are a result of desertification due to human influences recent investigations in the dry lands of china and mongolia demonstrate broad regional differences that must be given attention for the understanding of palaeoclimates

late pleistocene evolution of salt lakes in the qaidam basin qinghai province china abstract the qaidam basin is a tectonically controlled depression at 2700 m altitude on the northern margin of the qinghai xizang tibet plateau rimmed by the high aljun qilian ranges to the north and kunlun peaks to the south rising above 5000 m the basin floor experiences hyper arid conditions with evaporation precipitation ratios exceeding 100 1 periglacial and glacial conditions prevail on montane peaks with permafrost above 3800 m on the basin floor small waterbodies lie on extensive halite salt flats on the largest the qarhan salt flat 5800 km2 in extent the small lakes dabuxun and taijinier represent contracted remnants of a once expansive water body throughout neogene time a succession of clastic sediments indicates lake depo centre migration from nw to se towards late pliocene evaporitic conditions developed with formation of gypsum halite celestite mirabilite and bloedite continued deformation through pleistocene time has developed a series of nw se trending domes and troughs this setting has continued to exert a controlling influence on basin and brine evolution with progressive development through sulfate to chloride brines as dry conditions intensified in late pleistocene expanded lake conditions qarhan mega lake corresponding to near the 2800 m contour indicate the existence of past climates much more humid than those of today a drilling program has defined the lateral and vertical extent of evaporitic halite deposits freshwater clastics and shell deposits which predate the halite phase indicate humid lacustral conditions until after 40 000 30 000 yr b p desiccation from about 25 000 yr until about 9000 yr b p resulted in deposition of halite to 60 m thick with thin parting muds representing brief returns to more humid environments high lake shorelines with aragonitic ooids surrounding the dry playa kunteyi and high level ostracod rich beach and near shore deposits on xiao qaidam attest to the presence of expanded late pleistocene lacustral conditions on lakes other than qarhan preceding the final evaporite stage clastic sediments associated with the halite are dominated by loessial silts equivalent to the late pleistocene malan deposits of central china simultaneous halite and loess deposition reflect the dry conditions that developed in the qaidam basin during the latter part of the last glaciation and which have persisted ever since the final evolution of brines has resulted in development of extensive potassium rich brines and salts with the mineral carnallite providing the basis for a large potash extraction industry near golmud the hydrologic history documented by the analyses of lake sediments reflects the interaction of tectonic deformation and climatic change in the development of brines to the potash stage