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

pollen and lignin records of late quaternary vegetation lake washington analyses of lignin oxidation products and pollen for an 11 meter core from lake washington provide independent but similar reconstructions of the late quaternary vegetation in the puget lowland an exception is in sediments of the late pleistocene where pollen percentages and influx values suggest conifer forest whereas lignin compositions suggest a treeless source region this dissimilarity appears to result from different major provenances eolian transport of pollen to the lake from adjacent or downstream drainage basins as opposed to fluvial transport of lignified plant debris only from the lake washington drainage basin

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

late quaternary palaeoenvironment change and landscape evolution along the keriya river xinjiang china the relationship between high mountain glaciation and landscape evolution in foreland desert regions abstract the sedimentology and geomorphology of landforms along keriya river that traverse the kunlun mountains and taklamakan desert were studied to examine the relationship between environmental change and landscape evolution in mountains and desert margins of the taklamakan desert the region is divided into four geomorphic provinces desert with active dunes and sand seas desert pediment with fans and foothills with deep gorges and glaciated mountains a succession of three fans with dunes is differentiated on the basis of morphostratigraphy and relative weathering the oldest fan and dunes are radiocarbon dated to 29 ka this fan probably formed as a response to increased meltwater and sediment loads as glaciers retreated at the end of the local last glacial maximum in the kunlun mountains periglacial and glacial features throughout the region show that during the last glacial the snowline was lowered to 4000 m a s l permafrost existed down to an altitude of 1800 m a s l and that the likely temperature depression was 10 c radiocarbon dates on sand dunes and tamarisk hills help define the age of the lower two terraces to 1 5 ka and a few hundred years bp this suggests that these terraces may have formed in response to increased precipitation during more humid times at 2 ka and during the little ice age respectively the landforms and sediments in this region are polygenetic in origin being transported eroded and deposited by glacial fluvial aeolian and lacustrine processes particle size characteristics show that the fluvial sediments were substantially modified down basin in contrast the aeolian sediments were modified as they were transported toward the mountains from the desert by the dominant northerly winds this complex interaction between environmental change and earth surface processes provides an important framework for examining the environmental consequences of the recently growing population and intensified agricultural activities along the mountain and desert margins of the taklamakan desert

peat brgdgts based holocene temperature history of the altai mountains in arid central asia abstract due to their effects on snow ice melting in mountains and evaporation in basins temperature variations are an important influence on the hydrological cycle and water resources in arid central asia aca we present independently dated peat brgdgts based mbt mbt 5me records from an alpine sahara sand peatland ssp in the southern altai mountains in aca during the past 11 kyr the ssp mbt and mbt 5me profiles exhibit consistently increasing trends and they are significantly positively correlated using a global peat specific mbt 5me tempeature calibration the long term holocene warming trend indicated by the quantitative ssp mean annual temperature matpeat reconstruction is supported by the peat cellulose 13c summer temperature record from the ssp and by an independent peat cellulose 18o winter temperature record from a nearby site i e temporal validation the increasing trends are also evident in holocene peat mbt records from the hongyuan hy peatland in the ne tibetan plateau and in the shuizhuyang szy peatland in se china notably both the mbt data of the surface samples and the averaged mbt data of the holocene peat cores are consistent with the modern spatial temperature gradient at the ssp hy and szy i e spatial validation this evidence demonstrates the temperature significance of peat mbt mbt 5me records the long term holocene warming trend indicated by the ssp mbt mbt 5me records is supported by recently acquired holocene temperature records from the eurasian continent this trend is the opposite to the traditional viewpoint of a long term holocene cooling trend and it indicates that more effort is needed to obtain a reliable holocene temperature history

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

comparison of the paleoclimatic significance of higher land plant biomarker concentrations and pollen data a case study of lake sediments from the holsteinian interglacial abstract a sediment core from the dethlingen paleolake holsteinian interglacial northern germany was subjected to integrated organic geochemical and palynological paleobotanical analyses in order to reconstruct past environmental conditions the fractionated lipid extracts were investigated using gas chromatography mass spectrometry gc ms and gc combustion isotopic ratio ms ring a aromatized pentacyclic triterpenoids most likely glutinane derivatives were the only higher plant derived pentacyclic triterpenoids found the saturated ring a degraded triterpenoid des a lupane was the most abundant aliphatic hydrocarbon throughout the core based on published pollen data which imply the strong presence of betula and alnus around the paleolake the des a lupane would be expected to originate mainly from lupane type precursors synthesized by betulaceae the carbon isotopic composition of des a lupane varied from 28 2 to 30 6 and no significant trend or isotopic shift was observed however the discrepancy between the variation in pollen data and biomarker concentration i e quasi absence of diterpenoids in the core argues for a scenario in which the two proxies represent different components of the vegetation in the catchment area of the paleolake

the role of pingos in the development of the dzhangyskol lake pingo complex central altai mountains southern siberia abstract dzhangyskol is a small lake of glacial origin in the central part of the altai mountains in southern siberia pollen stratigraphies and chronologies of two cores record the vegetational development of the area from the late glacial treeless landscape to the forest and steppe of today the modern lake is a remnant of a much larger ice dammed lake which was reduced in size and then temporarily drained after diversion of the inflowing mountain meltwater stream which had low 18o values the dry lake floor allowed development of permafrost and small pingos frozen mounds of lake sediments with the onset of greater climatic humidity in the mid holocene the input of local water with higher 18o caused a rise in lake level drowning the earlier pingos growth of a broad fen on the margin of the lake led to formation of a modern pingo complex

late quaternary temperature record from buried soils of the north american great plains we present the first comprehensive late quaternary record of north american great plains temperature by assessing the behavior of the stable isotopic composition 13 c of buried soils after examining the relationship between the 13 c of topsoil organic matter and july temperature from 61 native prairies within a latitudinal range of 46 38 n we applied the resulting regression equation to 64 published 13 c values from buried soils of the same region to construct a temperature curve for the past 12 k y estimated temperatures from 12 to 10 ka 1 k y 1000 14 c yr b p fluctuated with a periodicity of 1 k y with two cool excursions between 4 5 and 3 5 c and two warmer excursions between 1 and 0 c relative to modern early holocene temperatures from ca 10 7 5 ka were 1 0 to 2 0 c before rising to 1 0 c in the middle holocene between 6 0 and 4 5 ka after a cool interlude from 4 2 to 2 6 ka when temperatures dropped to slightly below modern another warm interval ensued from 2 6 to 1 ka as temperatures increased to 0 5 c a final decline in temperature to below modern occurred beginning ca 0 5 ka cooler than present temperatures in the great plains indicate telecommunications with cool water episodes in the gulf of mexico and north atlantic potentially governed by a combination of glacial meltwater pulses and low solar irradiance

the palaeolimnology of the aral sea a review abstract formerly the fourth largest inland water body in the world the volume and area of the aral sea have decreased dramatically over the past 30 yr largely as a result of human actions throughout its approximately 2 million year history the fate of this water body has been intimately linked with that of its two main in flowing rivers the amu darya and the syr darya we present a review of the hydrological palaeontological and sedimentological evidence for the evolution of the aral sea based largely on russian literature although the structure of the aral basin can be traced back to the late neogene the sea has only existed in its present form for the past 8 10 ka and the holocene history has been shaped by regional climatic variations the development of the associated drainage system and anthropogenic forces past hydrological changes in the aral basin have led to systematic shifts in the level of the aral sea which are reflected sedimentologically through the deposition of transgressive and regressive sedimentary units and geomorphologically through the development of terraces all the above data are integrated to produced a late quaternary history of this important water body

mid to late holocene climate change in north central mongolia as recorded in the sediments of lake telmen abstract a record of climatic change has been reconstructed for the past 7110 calibrated calendar cal years for lake telmen mongolia based upon sedimentologic and geomorphic evidence from the lake watershed system lake telmen is a saline presently 4 g l 1 closed basin lake and is therefore sensitive to changes in effective moisture balance between 7110 and 6260 cal yr ago conditions in the lake telmen region were hyperarid and a small saline approximately 20 g l 1 lake was present increased effective moisture balance but still arid conditions prevailed between 6260 and 4390 cal yr ago since 4390 cal yr ago generally more humid conditions prevailed in the lake telmen region as the lake deepened a hypoxic hypolimnion became established below a well developed summer thermocline resulting in varved sediment accumulation since 4390 cal yr ago between about 2710 and 1260 cal yr ago a greater than present day effective moisture balance is recorded by a series of four lake highstand terraces sedimentologic profiles from lacustrine cores suggest an increase in effective moisture during the past approximately 680 cal yr

late glacial and holocene vegetational changes on the ulagan high mountain plateau altai mountains southern siberia three well dated pollen diagrams from 1985 m 2050 m and at the tree line at 2150 m asl show the vegetational succession in the central altai mountains since 16 cal ka bp pioneer vegetation after deglaciation was recorded first at the lowest site subsequently dense dry steppe vegetation developed coincident with the change from silt to organic sediments at the two lower sites but silt lasted longer at the highest site indicating the persistence of bare ground there forests of pinus sibirica pinus sylvestris picea obovata larix sibirica abies sibirica and betula pendula started to develop about 12 cal ka bp with the change to a warmer and wetter climate at the beginning of the holocene results indicate that the timberline did not rise above the highest site mesophilous dark coniferous forests were fully developed by 9 5 cal ka bp the role of abies and picea decreased by about 7 5 cal ka bp suggesting cooler climate after which the forests changed little until today the vegetational development in this portion of the central altai mountains is compatible with that described in neighbouring areas of the altai southern siberia mongolia and kazakhstan

parallel climate and vegetation responses to the early holocene collapse of the laurentide ice sheet parallel changes in lake level and pollen data show that the rapid decline of the laurentide ice sheet lis between 10 000 and 8000 cal yr bp triggered a step like change in north american climates from an ice sheet and insolation dominated climate to a climate primarily controlled by insolation maps of the lake level data from across eastern north america show a reorganization of climate patterns that the pollen data independently match raised lake levels and expanded populations of moist tolerant southern pines pinus document that summer monsoons intensified in the southeastern united states between 9000 and 8000 cal yr bp simultaneously low lake levels and an eastward expansion of the prairie illustrate an increase in mid continental aridity after the hudson bay ice dome collapsed around 8200 cal yr bp lake levels rose in new england as populations of mesic plant taxa such as beech fagus and hemlock tsuga replaced those of dry tolerant northern pines pinus available moisture increased there after a related century scale period of colder than previous conditions around 8200 cal yr bp which is also recorded in the pollen data the comparison between pollen and lake level data confirms that vegetations dynamics reflect climatic patterns on the millennial scale

response of vegetation to holocene evolution of westerlies in the asian central arid zone abstract based on 50 pollen sequences inferred from the westerlies influenced asian central arid zone we reconstructed the holocene vegetation dynamics of four forest types indicated by picea betula pinus sibirica and pinus sylvestris as well as steppe type by artemisia and desert type by chenopodiaceae the sensitivities of these vegetation types to holocene temperature and precipitation changes were analyzed according to four grouping temperature precipitation latitude and elevation of sites the results revealed that there was a clear delay of forest expansions in the early holocene along the s n gradient most likely influenced by the existed permafrost extent in the northern hemisphere the increasing precipitation driven by the westerlies in the early holocene would have first reached the threshold for forest expansion in high elevation sub region but was significantly delay for low elevation sub region steppe expanded in low elevation and highland sub regions in the cooling and wetting late holocene holocene vegetation dynamics differed across vegetation types with pinus sibirica and pinus sylvestris that were very sensitive to westerlies associated precipitation changes while picea and artemisia were more sensitive to temperature changes a decreasing sensitivity of forests was found with different types following an evident increase in precipitation and an increasing sensitivity for steppe was observed following a gradual reduction of temperature in the late holocene our research offers new insights into the mechanisms of individualistic responses of plant types and the different responses of vegetation to the holocene westerlies evolution in the asian central arid zone and improves our ability to predict the vegetation dynamics particularly forest in the asian central arid zone under global warming conditions

oxygen isotopes in lacustrine carbonates of west china revisited implications for post glacial changes in summer monsoon circulation five lakes in the qinghai tibet plateau and north xinjiang have provided oxygen isotope records covering the past 17 11 cal kyr bp the modern lakes are first presented within the major atmospheric circulation and climate patterns of china with the climate related isotope composition of input water equations used to extract hydrological and climatic information from 18o in carbonates are then given after a discussion on potential causes for 18o changes each of the five isotope profiles is interpreted in the light of its specific environmental data the most significant event observed in all records occurred at 12 11 cal kyr bp an abrupt intensification of summer rainfall associated with an extremely rapid 1000 1500 km westward migration of the monsoon fronts the monsoon regime weakened in stages after 8 7 cal kyr bp holocene maximal aridity is recorded at all sites between about 4 5 and 3 5 cal kyr bp long term changes in monsoon strength as inferred from our isotopic interpretation are in good agreement with climate model reconstructions in the tibet qinghai plateau while observed hydrological changes in north xinjiang are not simulated by the models also the non linearity of the holocene monsoon variations cannot be accounted for by orbital forcing

dry late glacial and early holocene climate in arid central asia indicated by lithological and palynological evidence from bosten lake china abstract stratigraphical and chronological investigations of four sediment cores from bosten lake the largest inland freshwater lake in china provide a reliable regional environmental evolution record since the late glacial the stratigraphy of the four cores has been well correlated according to their lithology and chronology osl and 14c dates pollen and grain size data from bosten lake show evidence for a dry regional climate during late glacial and early holocene 16 8 cal ka bp indicated by a thick layer of aeolian sand deposit 100 cm although the climate became humid after 8 cal ka bp analysis of pollen assemblages pollen a c ratio and ephedra percentage also indicates that the climate was relatively dry in the bosten lake area between 8 and 6 cal ka bp while afterwards more humid conditions ca 6 1 5 cal ka bp are assumed comparison with other lake records from arid central asia influenced by the westerly winds generally supports the assumption of late glacial to early holocene dry climates in westerly dominated regions hence they contrast the holocene climate development in monsoon asia relatively wet conditions during the late holocene 6 1 5 cal ka bp might be induced by stronger westerly circulation

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

moisture dynamics in central asia for the last 15 kyr new evidence from yili valley xinjiang nw china based on high resolution palynological investigations and ams 14 c dating the continuous lacustrine sediments contained in yili valley xinjiang provide an opportunity to reconstruct the effective moisture changes for the last 15 kyr in central asia the relatively warm and humid climate of the bolling allerod 15 12 9 cal kyr bp is a generalization but it seems to show some fluctuations the time of the younger dryas yd interrupted the increasing trend of effective moisture in the study region the climate was cold and relatively dry in the early yd period 12 9 12 0 cal kyr bp whereas the desert vegetation community appeared around 11 8 cal kyr bp almost the driest time since the 15 cal kyr br a sharp increase in effective moisture marked the beginning of the holocene in the yili valley the early holocene 10 6 7 6 cal kyr bp was the wettest time with a developed temperate steppe a dry climate with desert vegetation arose in the early mid holocene 7 6 6 5 cal kyr bp spanning 1100 years a second humid phase emerged between 6 5 and 5 2 cal kyr bp whose vegetation community was represented by temperate steppe moisture was reduced again and the climate became drier between 5 2 and 3 3 cal kyr bp when vegetation was dominated by desert steppe in the yili valley regional comparisons indicate that the moisture changes in yili valley were mainly influenced by the north atlantic ocean ssts through the westerlies the mean position of the siberian high pressure cell probably made a great contribution to the drought between 7 6 and 6 5 cal kyr bp the climate changes were generally consistent between the westerly dominant central asia and asian monsoon regions since the last deglaciation possibly forced by summer insolation conditions in the northern hemisphere c 2011 elsevier ltd all rights reserved

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

a 10 000 year record of dune activity dust storms and severe drought in the central great plains dune fi elds and loess deposits of the great plains of north america contain stratigraphic records of eolian activity that can be used to extend the short observational record of drought we present a 10 000 yr reconstruction of dune activity and dust production in the central great plains region based on 95 optically stimulated luminescence ages the integration of data from both eolian sand and loess is an important new aspect of this record clusters of ages defi ne episodes of extensive eolian activity which we interpret as a response to frequent severe drought at 1 0 0 7 ka and 2 3 4 5 ka with peaks centered on 2 5 and 3 8 ka sustained eolian activity occurred from 9 6 to 6 5 ka parts of this record may be consistent with hypotheses linking holocene drought to sea surface temperature anomalies in the pacifi c or atlantic oceans or to the el nino southern oscillation phenomenon but the record as a whole is diffi cult to reconcile with any of these hypotheses

a 5500 year proxy climate and vegetation record from blanket mire at talla moss borders scotland a monolith of peat taken from an upland blanket mire at talla moss southern scotland was sub jected to peat humification and pollen analyses to produce both a proxy climate record and a vegetational history covering the last 5500 years while the peat showed little visible stratigraphy with no intimation of major peat humification changes colorimetric data indicate a markedly oscillatory climate record which is apparently largely independent of or out of phase with major vegetational changes the raw data imply particular wet shifts in climate at c 3455 bp c 2600 bp c 1930 bp c 1095 bp with a markedly wet or cool and wet episode commencing at c 540 bp these are central age estimates and should not be regarded as precise dates for the inferred climate shifts other wet shifts apparently date from c 3070 bp c 2265 bp and c 1700 bp although the first of these corresponds with pollen evidence for significant prehistoric human activity in the locality spectral analysis of the peat h

holocene climatic change in the northern midwest pollen derived estimates mapping of holocene pollen data in the midwestern united states has revealed several broadscale vegetational changes that can be interpreted in climatic terms these changes include 1 the early holocene northward movement of the spruce dominated forest and its later southward movement after 3000 yr b p and 2 the eastward movement of the prairie forest border into southwestern wisconsin by 8000 yr b p and its subsequent westward retreat after 6000 yr b p when certain basic assumptions are met multiple regression models can be derived from modern pollen and climate data and used to transform the pollen record of these vegetational changes into quantitative estimates of temperature or precipitation to maximize the reliability of the regression equations we followed a sequence of procedures that minimize violations of the assumptions that underlie regression analysis reconstructions of precipitation during the holocene indicated that from 9000 to 6000 yr b p precipitation decreased by 10 to 25 over much of the midwest while mean july temperature increased by 0 5 to 2 0 c at 6000 yr b p precipitation was less than 80 of its modern values over parts of wisconsin and minnesota after 6000 yr b p precipitation generally increased while mean july temperature decreased in the north and increased in the south the time of the maximum temperature varies within the midwest and is earlier in the north and later in the south

isotopic and rock magnetic expression of environmental change at the pleistocene holocene transition in the central great plains abstract in a region too dry for the effective use of the traditional palynological approach loess deposits of the central great plains offer a source of proxy information for the reconstruction of past climates the brady soil a ubiquitous feature developed within the uppermost late pleistocene peoria loess recorded the character of vegetation change associated with climate shifts during the pleistocene holocene transition stable carbon isotope ratio analysis and two room temperature magnetic parameters were used to examine the nature of the change during this period 13 c values derived from soil organic matter indicate that in the late pleistocene minor populations of drought tolerant c4 plants were interspersed among the dominant cool season grasses c3 in the west while c3 grasses were accompanied by trees in the east by the early holocene c4 grasses were the dominant vegetation in the west and contributed substantially to the 13 c signal in the east magnitude of the 13 c shift suggests an increase in july mean daily temperature of 8 10 c according to existing models magnetic susceptibility and frequency dependence signal the cessation of loess deposition and development of the brady soil and indicate a spatial pattern in the intensity of weathering across the region

high resolution evidence from southern china of an early holocene optimum and a mid holocene dry event during the past 18 000 years abstract computer models suggest that the holocene optimum for east asian summer monsoon precipitation occurred at different times in different regions of china previous studies indicate that this time transgressive holocene optimum should have been experienced about 3000 yr ago in southern china in this study we describe a section which allows us to test this timing directly we have closely examined high resolution eutrophic peat mud sequences covering the past 18 000 cal yr at dahu jiangxi on the southern boundary of the mid subtropical zone in china late pleistocene successions in the dahu record indicate cooler and much wetter conditions relative to synchronous events in north central china our results indicate that the holocene optimum occurred between ca 10 000 and 6000 cal yr ago in southern china consistent with the global pattern conditions were relatively dry and cold from 6000 to 4000 cal yr ago our data also support the conclusion that the last deglaciation to early holocene in the south was much wetter resulting in the formation of dense broad leaved forests which could have acted to moderate land temperature 10 000 to 6000 cal yr ago yielding a stable early holocene climate after 6000 cal yr forest reduction led to unstable land temperatures and possibly to a northerly shift of the subtropical high pressure system whatever the mechanism these changes resulted in decreased precipitation between 6000 and 4000 cal yr b p in southern china

holocene moisture variations across china and driving mechanisms a synthesis of climatic records based on the review of 33 holocene moisture reconstructions that passed quality scrutiny temporal and spatial patterns of regional moisture variations are delineated the regionally averaged moisture index from xinjiang demonstrates that the moisture index has been persistently climbing since 10 ka cal bp and that the period between 4 and 0 ka cal bp is the holocene moisture optimum comparison of the moisture index of xinjiang region with the winter climate of northern europe leads us to propose that the holocene moisture variations in xinjiang region have been controlled by the winter temperature variations in the north atlantic region the regionally averaged moisture index from the tibetan plateau shows that the moisture has been persistently declining since 11 ka cal bp and that the period between 11 5 and 7 5 ka cal bp was the holocene moisture optimum the parallel trends between the moisture level in the tibetan plateau and the indian summer monsoon strength retrieved from the arabian sea suggest that the tibetan plateau has been under influence of the indian summer monsoon throughout the holocene the regionally averaged moisture index curves from northern china and southern china are the delayed reflections of the east asian summer monsoon strength to the solar radiation that is the peak insolation was responded by the holocene oceanic thermal optimum with significant time lags and the oceanic thermal optimum was then responded by the holocene moisture optimum in southern china and northern china also with some time lags the differences in the moisture index curve shapes and in the durations of the holocene moisture optimum between northern china and southern china suggest that the strength of the east asian summer monsoon had gradually transgressed northward in the early holocene and gradually regressed southward in the late holocene

rapid time transgressive and variable responses to early holocene midcontinental drying in north america the end pleistocene to early holocene drying of the north american midcontinent is an important case study for understanding regional drought its drivers and its impacts this paper synthesizes pollen 13c eolian and paleohydrological proxies to document the spatial and temporal patterns in the onset and rate of drying the timing of onset ranged from 14 to 6 ka with most sites drying between 10 and 8 ka calendar years ago the dominant spatial pattern is time transgressive with interior great plains sites beginning to dry before peripheral sites this time transgressive trend can be explained as a region wide drying that caused ecotones to shift eastward or could indicate a progressive shift in atmospheric drying from west to east one third of sites responded rapidly to drying a cluster of rapid responses occurred ca 8 ka the combination of onsets between 14 and 6 ka and rapid responses at 8 ka strongly suggests that 1 the combination of high summer insolation laurentide ice sheet retreat and lake agassiz drainage drove midcontinental drying and 2 drying accelerated with laurentide ice sheet collapse at 8 4 ka local factors strongly mediate the timing and rate of site responses to regional drying local responses to future drying in the great plains also should be highly variable which challenges impact assessments of future climate changes

paleoenvironmental and paleoclimatic variations around lake van eastern turkey recorded by sedimentary source specific biomarkers 250 130 ka mis7 and mis6 abstract paleoclimatic changes during mis7 and mis6 remain poorly described in the near east we quantified source specific biomarkers in lake van sediments during the interglacial glacial cycle mis7 mis6 long chain n alkanes produced by land derived vegetation as well as long chain alkenones and sterols namely brassicasterol and dinosterol produced by aquatic algae were investigated stable hydrogen isotopic measurements 2h on n c29 alkanes were used as a proxy for aridity and revealed three wetter periods interrupted by two drier intervals during mis7 in contrast during the mis6 glaciation a generally drier climate was predominant during the warmer and wetter periods of mis7 a higher input of aquatic organic matter to lake van sediments was recorded by higher concentrations of long chain alkenones dinosterol and brassicasterol long chain alkane abundances do not show a pattern related to aridity and were observed in higher concentrations in wetter as well as drier periods generally in the eastern mediterranean a wetter interglacial interrupted by drier episodes followed by a dry glacial period was the common feature observed during the mis7 mis6 interglacial glacial cycle however in comparison to the last interglacial glacial cycle the extreme dry glacial period registered around lake van from mis5d to mis2 was apparently unique and not equaled by a similar event within the last 250 ka

palynological record of holocene vegetation and climate changes in a high resolution peat profile from the xinjiang altai mountains northwestern china abstract a high resolution pollen record in a peat sequence from the altai mountains of xinjiang china allows reconstruction of the regional vegetation and climate changes that occurred during the holocene pollen distributions from the sequence indicate that the vegetation community in the altai mountains region transitioned through five general phases forest and desert steppe wet steppe desert steppe steppe and finally forest and desert steppe these vegetative phases imply that the regional climate changed from a cold and dry early holocene to a warmer and wetter early mid holocene and then to a cold and rather dry mid holocene that was followed by a cool and wet late holocene and finally by warm and dry conditions for the last millennium these regional changes in climate are roughly consistent with local changes previously reconstructed from organic geochemical paleoclimate proxies in the same peat sequence by zhang et al 2016 but with some minor but important differences that reflect local factors regional comparisons reveal that the holocene climate changes in the altai mountains are generally consistent with those of most arid central asian regions that are influenced mainly by westerlies however they are out of phase with the climate histories of regions controlled by the asian monsoons indicating that the asian monsoons did not extend to the high altitude mountain regions of arid central asia during the holocene we postulate that the regional holocene moisture variations have been mainly modulated by nao variations that affected transport of water vapor from the north atlantic ocean by the westerlies moreover local factors that include topography of the mountains and glacial meltwater events in the high altitude regions also contributed to the climate changes in the altai mountains in addition air temperatures related to summer insolation of the northern hemisphere might have played an important role in modulating moisture in the region but only after the local montane ice sheets had disappeared by the mid holocene

a persistent holocene wetting trend in arid central asia with wettest conditions in the late holocene revealed by multi proxy analyses of loess paleosol sequences in xinjiang china abstract there are significant differences in the interpretation of the moisture precipitation history of arid central asia aca during the holocene as inferred on one hand from speleothem oxygen isotope records and on the other from lake sediments here we present the results of measurements of climatically sensitive magnetic properties and soil color from four well dated loess paleosol sequences from the northern slopes of the tienshan mountains and the yili river valley xinjiang china in the core area of aca our results demonstrate that the characteristic holocene paleosol indicating relatively moist conditions generally formed after 6 ka 1 ka 1000 cal yr bp in the study region and that the accumulation of unweathered loess prevailed during the early holocene indicating a dry climate at that time the magnetic proxies further reveal a trend of generally increasing moisture since the last glacial maximum with the wettest climate occurring during the late holocene this trend of increasing moisture during the holocene is representative of the xinjiang region and possibly of the whole of the core area of aca and is in marked contrast both to the mid holocene moisture maximum observed in the east asian summer monsoon region and to the general decrease in the strength of the indian summer monsoon since the early holocene our findings are supported by the results of a climate simulation which indicate a trend of increasing summer and winter precipitation during the holocene in the core area of aca caused mainly by an increase in the strength of the westerlies effected by an increasing latitudinal insolation gradient and by a negative trend of the arctic oscillation ao or north atlantic oscillation nao

basin wide sedimentation changes and deglacial lake level rise in the hovsgol basin nw mongolia abstract a study of 15 gravity cores reveals consistent patterns of lithologic change throughout the lake hovsgol basin sediments of the last glacial are composed of calcareous clayey silt with an admixture of coarse material from sand to gravel during the last deglaciation a basin wide deposition of finely laminated carbonate mud took place and was ultimately succeeded by the deposition of diatomaceous clayey ooze during the entire holocene interval diatom productivity in lake hovsgol during the early holocene was higher than today but declined by ca 6 6 cal ka bp sedimentation rate estimates for post glacial section range from 1 5 to over 6 7 cm ka for different parts of lake hovsgol rates appear to have decreased in the late holocene the last glacial maximum lgm corresponded to a dramatic low stand of lake hovsgol on the order of 100 m below today s level as reflected by littoral facies retrieved in cores from intermediate depths age dating of plant fragments in these sediments suggests that lake level started rising no later than 15 4 cal ka bp by the beginning of the holocene lake hovsgol evolved from a low level closed basin lake to an overflowing freshwater lake the observed dramatic lithologic change and evidence for lake level change suggest that lake hovsgol may in fact serve as a sensitive water gauge in continental interior asia and that the hovsgol sedimentary record preserves reliable proxies for past changes in effective moisture balance in the lake baikal catchment area

reply to the comments on reconciling the westerlies and monsoon models a new hypothesis for the holocene moisture evolution of the xinjiang region nw china by dongliang zhang and yunpeng yang

chironomid record of late quaternary climatic and environmental changes from two sites in central asia tuva republic russia local regional or global causes abstract sediment cores from two mountain lakes lake grusha at 2413 m a s l and ak khol at 2204 m a s l situated in the tuva republic southern siberia russia just north of mongolia were studied for chironomid fossils in order to infer post glacial climatic changes and to investigate responses of the lake ecosystems to these changes the results show that chironomids are responding both to temperature and to changing lake depth which is regarded as a sensitive proxy of regional effective moisture the post glacial history of this mountain region in central asia can be divided into seven successive climatic phases the progressive warming during the last glacial interglacial transition ca 15 8 14 6 cal kyr bp the warm and moist bolling allerod like interval ca 14 6 13 1 cal kyr bp the cool and dry younger dryas like event ca 13 1 12 1 cal kyr bp warmer and wetter conditions during ca 12 1 8 5 cal kyr bp a warm and dry phase ca 8 5 5 9 cal kyr bp cold and wet conditions during ca 5 9 1 8 cal kyr bp as well as cold and dry climate within the last 1800 years the chironomid records reveal patterns of climatic variability during the late glacial and holocene which can be correlated with abrupt climatic events in the north atlantic and the asian monsoon dominated regimes apparently the water balance of the studied lakes is controlled by the interrelation between the dominant westerly system and the changing influence of the summer monsoon as well as the influence of alpine glacier meltwater supply it is possible that monsoon tracks could have reached the southwest tuva resulting in an increase in precipitation at ca 14 6 13 1 and ca 12 1 8 5 cal kyr bp whereas cyclonic westerlies from the north atlantic were likely responsible for considerable moisture transport accompanying the global neoglacial cooling at ca 5 9 1 8 cal kyr bp these events suggest the changes of the regional pattern of atmospheric circulation which could be in turn induced by the global climatic shifts some discrepancies compared with other reconstructions from central asia may be associated with regional spatial differences between the changing predominant circulation mechanisms and with local differences in uplift and descent of air masses within the complicated mountain landscape in this paper we also discuss the possibilities and perspectives for using chironomids in reconstructions of past temperatures and climate induced changes in water depth of lakes in central asia

postglacial floral and climate changes in southeastern china recorded by distributions of n alkan 2 ones in the dahu sediment peat sequence abstract long chain n alkane 2 ones occur widely in lacustrine and peat depositional settings however their paleobotanical and paleoclimate implications are less understood compared with their n alkyl counterparts n alkanes n fatty acids in this study we have performed a molecular stratigraphic investigation of changes in the plant contributions and depositional conditions using n alkan 2 ones in the dahu lacustrine peat sequence spanning the last 17 kyr a series of n alkan 2 ones ranging from c23 to c33 with a maximum at c29 appears to be contributed by microbial oxidation of both n alkanes and n alkanoic acids the values of the average chain length acl and the ratios of mid to long chained n alkan 2 ones display a trend comparable with the abundance of trees relative to herbs and ferns in addition the carbon predominance index cpi of n alkan 2 ones varied in pace with lithology paleoenvironment with higher values seen in peat deposits the alternating layers represent a succession of shallow lakes and peatlands that filled the depositional basin in response to paleoclimate changes between wetter and less wet conditions the succession of paleohydrologic conditions is responsible for the variation of ketone cpi values in this peat sediment sequence

a continuous late glacial and holocene record of vegetation changes in kazakhstan the late glacial and holocene vegetation history of northern kazakhstan is reconstructed using a well dated continuous pollen record from ozerki swamp 50 degrees 24 n 80 degrees 28 e altitude 210 m near semipalatinsk a montane steppe taiga community chenopodiaceae artemisia picea larix and betula dominated in this area between 13 000 and 10 100 yr b p at the beginning of the holocene poaceae and artemisia dominated the steppe and picea and larix disappeared from 7800 to 7250 yr b p a sharp increase in betula pollen percentages suggests afforestation after 5800 yr b p pinus sylvestris spread through the steppe zone of kazakhstan these changes in vegetation distribution are interpreted in terms of changing absolute winter temperatures due to orbitally induced insolation changes the absence of boreal conifers during the early holocene can be explained by absolute minimum temperatures below 60 degrees c or 8 degrees c colder than today c 1997 elsevier science b v

early holocene change in atmospheric circulation in the northern great plains an upstream view of the 8 2 ka cold event elk lake in northwestern minnesota contains numerous proxy records of climatic and environmental change contained in varved sediments with annual resolution for the last 10 000 years these proxies show that about 8200 calendar years ago 8 2 cal ka 7300 radiocarbon years elk lake went froma well stratified lake that was wind protected in a boreal forest to a wellmixed lake in open prairie savanna receiving northwesterly wind blown dust probably from the dry floor of lake agassiz this change in climate marks the initiation of the widely recognized mid holocene altithermal in central north america the coincidence of this change with the so called 8 2 cal ka cold event recognized in ice core and other records fromthe circum north atlantic and thought by some to be caused by catastrophic discharge of freshwater from proglacial lakes agassiz and ojibway suggests that the two events might be related our interpretation of the elk lake proxy records and of other records from less accurately dated sites suggests that change in climate over north america was the result of a fundamental change in atmospheric circulation in response to marked changes in the relative proportions of land water and especially glacial ice in north america during the early holocene this change in circulation probably post dates the final drainage of proglacial lakes along the southern margin of the laurentide ice sheet and may have produced a minor perturbation in climate over greenland that resulted in a brief cold pulse detected in ice cores r 2002 elsevier science ltd all rights reserved

palaeoclimatic changes in the qinghai lake area during the last 18 000 years abstract multi proxy analysis of a sediment core from qinghai lake including pollen carbonate toc tn and 13 c of organic matter was used to document regional climatic changes during the last 18 000 years climate was very cold and dry before 16 9 cal kyr bp the warm and wet period which began at about 14 1 cal kyr bp culminated at 6 5 cal kyr bp and came to its end at about 4 5 cal kyr bp after that the climate gradually became colder and drier during the transitional period from the late glacial to the holocene the climate fluctuated frequently the short term climatic oscillations including the bolling allerod younger dryas and the cooling event at ca 8 2 cal kyr bp appear to be recorded in the qinghai lake sedimentary record the climatic evolution in the qinghai lake area during the past 18 000 years indicates that solar insolation changes on the ten thousand year scale are the likely driving force of the east asia monsoon

a high resolution record of holocene environmental and climatic changes from lake balikun xinjiang china implications for central asia a high resolution record of holocene environmental and climatic change in the balikun area was reconstructed from a sediment core from the lake balikun multiproxy data show that the climate was extremely arid during the early holocene before 8 6 cal ka bp moisture began to increase after 8 6 cal ka bp and the climate was humid between 7 9 and 4 3 cal ka bp a significant dry event occurred around 4 3 3 8 cal ka bp the climate became generally wet during the late holocene after 3 8 cal ka bp the holocene pollen and geophysical records do not indicate a wet early holocene making it evident that there was no early holocene humid period associated with peak asian monsoon strength regional comparisons indicate that this region has a different pattern of holocene environmental and climatic change from the asian monsoonal area and south siberia

quantitative climate and vegetation trends since the late glacial on the northeastern tibetan plateau deduced from koucha lake pollen spectra quantitative information on vegetation and climate history from the late glacial holocene on the tibetan plateau is extremely rare here we present palynological results of a 4 30 m long sediment record collected from koucha lake in the bayan har mountains northeastern tibetan plateau vegetation change has been traced by biomisation ordination of pollen data and calculation of pollen ratios the application of a pollen climate calibration set from the eastern tibetan plateau to koucha lake pollen spectra yielded quantitative climate information the area was covered by alpine desert steppe characteristic of a cold and dry climate with 50 less precipitation than today between 16 700 and 14 600 cal yr bp steppe vegetation warm 1 c higher than today and wet conditions prevailed between 14 600 and 6600 cal yr bp these findings contradict evidence from other monsoon influenced areas of asia where the early holocene is thought to have been moist low effective moisture on the northeastern tibetan plateau was likely due to high temperature and evaporation even though precipitation levels may have been similar to present day values the vegetation changed to tundra around 6600 cal yr bp indicating that wet and cool climate conditions occurred on the northeastern tibetan plateau during the second half of the holocene

holocene vegetation dynamics and associated climate changes in the altai mountains of the arid central asia abstract this study reconstructed the vegetation dynamics and associated climate change of the past 4100 years based on the pollen data from a short peat core i e klsz 2 in kelashazi peat 48 12 n 88 37 e 2422 m a s l in the altai mountains the reconstructed vegetation and climate were then stacked with those from a longer peat core i e klsz 1 to evaluate the vegetation dynamics and associated climate change of the entire holocene and to examine the 13ccellulose and 18ocellulose based temperature reconstructions in the same peat this study shows that vegetation in kelashazi valley was dominated by alpine meadows before 8200 cal yr bp by taiga forests at 8200 5600 cal yr bp and by an expansion of alpine meadows since 5600 cal yr bp this study also examined the vegetation dynamics and associated climate in the context of the entire altai mountains and the surrounding areas our examination suggests that the forest expansion in high elevations was initiated when the temperature reached a threshold level during the early holocene and the forest expansion in low elevations i e below the down treeline was initiated when the moisture reached a threshold level during the middle holocene or even late holocene it is also notable that the forest expansion at low elevations appears to have been longitude dependent i e time transgressive eastward a possible mechanism to explain the longitude dependency is that a gradual shrinking trend of the siberian high linked to the holocene increase in winter insolation allowed the domination of the water vapor enriched westerlies to gradually encroach eastward

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

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

holocene environmental and climatic changes inferred from wulungu lake in northern xinjiang china abstract sedimentological geochemical and palynological data from wulungu lake in northern xinjiang china are used to reconstruct environmental and climate changes since 9550 cal yr bp high abundance of sparganium and poaceae low md median diameter and 13 c organic values indicate aridity between 9550 and 6730 cal yr bp high md and 13 c organic values and the prevalence of desert steppe and steppe vegetation between 4200 and 560 cal yr bp indicate that effective moisture increased after 6730 cal yr bp peaking at 4200 and 560 cal yr bp low md values a negative excursion of 13 c org and the transition from steppe to desert vegetation since 560 cal yr bp reflect a decrease in effective moisture during the latest holocene late holocene human activities were indicated by sharp increase in the abundance of pediastrum then variations in carbonate contents indicate that temperature was generally high between 9550 and 7740 cal yr bp low between 7740 and 6730 cal yr bp intermediate between 6730 and 560 cal yr bp and low during the last 560 yr regional comparison indicates that the asian monsoon did not extend to wulungu lake and westerlies were the main factor in determining the moisture availability during the holocene

spatial and temporal variability of holocene temperature in the north atlantic region the early holocene climate of the north atlantic region was influenced by two boundary conditions that were fundamentally different from the present the presence of the decaying laurentide ice sheet lis and higher than present summer solar insolation in order to assess spatial and temporal patterns of holocene climate evolution across this region we collated quantitative paleotemperature records at sub millennial resolution and synthesized their temporal variability using principal components analysis pca the analysis reveals considerable spatial variability most notably in the time transgressive expression of the holocene thermal maximum htm most of the region but especially areas peripheral to the labrador sea and hence closest to the locus of lis disintegration experienced maximum holocene temperatures that lagged peak summer insolation by 1000 3000 years many sites from the northeastern north atlantic sector including the nordic seas and scandinavia either warmed in phase with maximum summer insolation 11 000 9000 years ago or were less strongly lagged than the baffin bay labrador sea region these spatially complex patterns of holocene climate development which are defined by the pca resulted from the interplay between final decay of the lis and solar insolation forcing

holocene vegetation and climate dynamics of ne china based on the pollen record from sihailongwan maar lake abstract high resolution palynological analysis on annually laminated sediments of sihailongwan maar lake shl provides new insights into the holocene vegetation and climate dynamics of ne china the robust chronology of the presented record is based on varve counting and ams radiocarbon dates from terrestrial plant macro remains in addition to the qualitative interpretation of the pollen data we provide quantitative reconstructions of vegetation and climate based on the method of biomization and weighted averaging partial least squares regression wa pls technique respectively power spectra were computed to investigate the frequency domain distribution of proxy signals and potential natural periodicities pollen assemblages pollen derived biome scores and climate variables as well as the cyclicity pattern indicate that ne china experienced significant changes in temperature and moisture conditions during the holocene within the earliest phase of the holocene a large scale reorganization of vegetation occurred reflecting the reconstructed shift towards higher temperatures and precipitation values and the initial holocene strengthening and northward expansion of the east asian summer monsoon easm afterwards summer temperatures remain at a high level whereas the reconstructed precipitation shows an increasing trend until approximately 4000 cal yr bp since 3500 cal yr bp temperature and precipitation values decline indicating moderate cooling and weakening of the easm a distinct periodicity of 550 600 years and evidence of a mid holocene transition from a temperature triggered to a predominantly moisture triggered climate regime are derived from the power spectra analysis the results obtained from shl are largely consistent with other palaeoenvironmental records from ne china substantiating the regional nature of the reconstructed vegetation and climate patterns however the reconstructed climate changes contrast with the moisture evolution recorded in s china and the mid latitude semi arid regions of n china whereas a clear insolation related trend of monsoon intensity over the holocene is lacking from the shl record variations in the coupled atmosphere pacific ocean system can largely explain the reconstructed changes in ne china

glacial lake agassiz a 5000 yr history of change and its relationship to the δ18o record of greenland lake agassiz was the largest lake in north america during the last period of deglaciation the lake extended over a total of 1 5 10 6 km 2 before it drained at ca 7 7 14 c ka 8 4 cal calendar ka new computer reconstructions controlled by beaches isostatic rebound data the margin of the laurentide ice sheet outlet elevations and a digital elevation model dem of modern topographic data show how variable the size and depth of this lake were during its 4000 14 c yr 5000 cal yr history abrupt reductions in lake level ranging from 8 to 110 m occurred on at least 18 occasions when new outlets were opened reducing the extent of the lake and sending large outbursts of water to the oceans three of the largest outbursts correlate closely in time with the start of large 18 o excursions in the isotopic records of the greenland ice cap suggesting that those freshwaters may have had an impact on thermohaline circulation and in turn on climate

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

modelling of melt segregation processes by high temperature centrifuging of partially molten granites ii rayleigh taylor instability and sedimentation summary the present experimental study deals with the laboratory modelling of two different mechanisms of gravitational percolation in partially melted rocks 1 diapiric percolation of heavy material and 2 the sedimentation of heavy particles these two mechanisms of mass transport in partially melted rocks result in different scales of the segregation process in the melt crystal matrix a centrifuge furnace was used to simulate the percolation of the heavy particle layer through the partially molten granite at temperatures of up to 1000 c samples of beauvoir granite massif central france grain size 0 16 0 5 mm with an initial degree of partial melting 45 per cent were used as a matrix a layer of pt powder suspended in a melt of the same composition as the partially melted matrix was placed on the top of the granite sample after centrifuging for various times up to 2 x lo4 s x ray images of samples were obtained and the evolution of the percolation process of heavy suspension in the partially molten granite was monitored from the pt particle distribution the diapiric or finger regime of percolation starts when the growth rate of a raleigh taylor instability of the heavy layer is faster than the stokes sedimentation velocity of individual particles in the upper layer this relationship is a complex function of the size and initial concentration of heavy particles as well as the ratio of particle to crystal size the permeability of the matrix and the heterogeneity scale in the partially melted matrix at small concentrations several per cent and at large concentrations where close packing of heavy particles results in an anomalous viscosity increase in the upper heavy layer stokes sedimentation is dominant in the vertical percolation of the heavy material the sinking velocity of the diapir decreases when the size of heavy particles in it becomes comparable with the size of crystals in the partially melted granite in this situation the vertical sinking of the diapir is not stable and the horizontal instability of the vertical mass transport starts to become important mass transport via diapiric percolation results in more efficient crystal melt segregation of partially melted rocks the percolation of individual particles provides only local melt crystal flow on a scale comparable with the heavy particle size the diapiric percolation provides a much larger scale of partial melt segregation with a length scale comparable with the diapir size

holocene climate changes in the central asia mountain region inferred from a peat sequence from the altai mountains xinjiang northwestern china abstract a continuous peat sequence collected in the altai mountains xinjiang province northwestern china provides a new opportunity to reconstruct the holocene climate history in the arid central mountain region of asia based on ams 14 c dating high resolution records of the humification degree and n alkane distributions reveal that the region experienced a relatively warm and dry early holocene 10 0 8 0 ka and a cold and wet early mid holocene 8 0 6 3 ka followed by a warm and dry mid holocene 6 3 5 5 ka a shift to cold and wet conditions occurred between 5 5 and 4 0 ka and then the climate entered into a warmer period from 4 0 to 2 5 ka in the late holocene 2 5 1 0 ka the region experienced a colder and wetter climate a gradual shift to warm and dry conditions occurred during the last 1 0 ky in this region the regional climate patterns have been generally dominated by alternations of warm dry and cold wet episodes during the holocene that were quite different from the warm wet and cool dry episodes in the asian summer monsoon region regional comparisons indicate that the climate changes in arid central asia have been mainly influenced by the north atlantic ocean sea surface temperatures ssts via the westerlies however owing to the mountainous character of the study areas glacial meltwater and other local factors the climate changes in the altai mountains region have not always been concordant with variations of north atlantic ocean ssts we postulate that the history of moisture balance between regional precipitation glacier and snow meltwater and evaporation has been modulated by air temperatures that were mainly influenced by changes in the summer insolation of the northern hemisphere

simulated influences of lake agassiz on the climate of central north america 11 000 years ago eleven thousand years ago large lakes existed in central and eastern north america along the margin of the laurentide ice sheet the large scale north american climate at this time has been simulated with atmospheric general circulation models1 2 but these relatively coarse global models do not resolve potentially important features of the mesoscale circulation that arise from interactions among the atmosphere ice sheet and proglacial lakes here we present simulations of the climate of central and eastern north america 11 000 years ago with a high resolution regional climate model nested within a general circulation model the simulated climate is in general agreement with that inferred from palaeoecological evidence our experiments indicate that through mesoscale atmospheric feedbacks the annual delivery of moisture to the laurentide ice sheet was diminished at times of a large cold lake agassiz relative to periods of lower lake stands the resulting changes in the mass balance of the ice sheet may have contributed to fluctuations of the ice margin thus affecting the routing of fresh water to the north atlantic ocean a retreating ice margin during periods of high lake level may have opened an outlet for discharge of lake agassiz into the north atlantic a subsequent advance of the ice margin due to greater moisture delivery associated with a low lake level could have dammed the outlet thereby reducing discharge to the north atlantic these variations may have been decisive in causing the younger dryas cold event3 4

holocene moisture evolution across the mongolian plateau and its surrounding areas a synthesis of climatic records abstract based on the review of 26 high standard holocene climatic reconstructions mainly pollen based from the mongolian plateau and its surrounding areas temporal and spatial patterns of the holocene moisture evolution are synthesized the regionally averaged moisture history from the summer monsoon influenced semiarid belt in china i e region a demonstrates that the moisture index curve is broadly in agreement with the synthesized east asian monsoon strength curve both following the general trend of the west tropical pacific sst that is in turn the delayed response to the northern hemispheric summer solar insolation the regionally averaged moisture indices from the winter monsoon dominated southern siberia including lake baikal area and the altai mountains i e region b exhibit a general declining trends since 10 6 9 6 cal kyr bp being largely consistent with the trends of the annual precipitation and the warm season temperature in the russian plain the consistency might be attributable to the holocene declining trend of the warm season temperature in north atlantic region the predominant feature of the regionally averaged moisture index from the westerlies affected northern xinjiang i e region c is a persistent increasing trend since 8 cal kyr bp the wetting trend of northern xinjiang during the past 8000 years might be attributable to the increasing trend of winter insolation and to the associated increasing trend of cold season temperature in northwestern europe the chronological correspondences between dry phases and warm intervals in the arid areas of the mongolian plateau i e northern mongolian plateau within mongolia and southern mongolian plateau within china region d lend a support to the proposal that the mid holocene dry phase was most likely the result of mid holocene high warm season temperature

reconstruction of postglacial to early holocene vegetation history in terrestrial central europe via cuticular lipid biomarkers and pollen records from lake sediments high resolution environmental reconstruction for central european terrestrial settings is commonly based on sediment records that provide the pollen spectra used for reconstruction of vegetation development alternatively complementary algal insect or zooplankton assemblages and or carbonate 18 o isotope profiles are investigated in this study vegetation development and inferred climate evolution were documented on a decadal to centennial scale by analysis of land plant cuticular lipids accumulated in lake sediments wax lipids derived from land plant leaves and blades are source diagnostic and highly resistant to degradation their aerodynamic properties favor short distance eolian transport but they are less affected by possible long distance transportation that complicates pollen analysis the late glacial to holocene sedimentary record of lake steisslingen southwestern germany was investigated by palynological and geochemical means tundra type pioneer vegetation consisting predominantly of grasses and herbs is dominated by nc31 alkanes whereas pioneer birch forest yields preferentially nc27 alkanes establishment of a pine assemblage is recognizable by elevated nc29 and nc31 leaf wax alkanes and the diversification of deciduous forests in the holocene is marked by nc29 dominance lipid geochemistry and palynology resolve decadal excursions such as the mid younger dryas event centennial climate trends with pronounced and rapid changes at the oldest dryas bolling allerod younger dryas and younger dryas preboreal transitions are consistently reflected by molecular and palynological proxy data the demonstrated suitability of an independent molecular proxy in paleoenvironmental studies provides new perspectives in high resolution climate reconstruction

late quaternary environmental changes in the taklamakan desert western china inferred from osl dated lacustrine and aeolian deposits sediment records from the tarim basin of western china are of great importance for understanding late quaternary climatic variability in central asia a chronology of aeolian and lacustrine deposits from the centre and southern margin of the taklamakan desert central tarim basin has been established using optical dating methods distinct variations in humidity during the last 40 000 a in this extremely arid inland basin have been identified lacustrine sediments were deposited in the centre of the taklamakan during two periods of wetter than present day conditions at around 2000 and 30 000 a ago another humid period is recorded between 40 000 and 30 000 a ago aeolian processes the development of large migrating dune fields dominated during periods of more arid conditions sand wedges at the southern margin of the taklamakan are dated at ca 40 000 a and ca 18 000 a and imply a significant temperature decrease in that area sedimentological evidence for a late holocene humid period are consistent with records in ancient chinese literature wetter environmental conditions in the past within the taklamakan as indicated by the presence of lacustrine deposits are also supported by data from adjacent regions it is assumed that changes of global westerlies and of the mobile polar high triggered the fluctuations of precipitation in the study area however variations in temperature in the taklamakan desert are presumed to be mainly controlled by the intensity of the winter monsoon

holocene flood frequency across the central alps solar forcing and evidence for variations in north atlantic atmospheric circulation the frequency of large scale heavy precipitation events in the european alps is expected to undergo substantial changes with current climate change hence knowledge about the past natural variability of floods caused by heavy precipitation constitutes important input for climate projections we present a comprehensive holocene 10 000 years reconstruction of the flood frequency in the central european alps combining 15 lacustrine sediment records these records provide an extensive catalog of flood deposits which were generated by flood induced underflows delivering terrestrial material to the lake floors the multi archive approach allows suppressing local weather patterns such as thunderstorms from the obtained climate signal we reconstructed mainly late spring to fall events since ice cover and precipitation in form of snow in winter at high altitude study sites do inhibit the generation of flood layers we found that flood frequency was higher during cool periods coinciding with lows in solar activity in addition flood occurrence shows periodicities that are also observed in reconstructions of solar activity from 14 c and 10 be records 2500 3000 900 1200 as well as of about 710 500 350 208 suess cycle 150 104 and 87 gleissberg cycle years as atmospheric mechanism we propose an expansion shrinking of the hadley cell with increasing decreasing air temperature causing dry wet conditions in central europe during phases of high low solar activity furthermore differences between the flood patterns from the northern alps and the southern alps indicate changes in north atlantic circulation enhanced flood occurrence in the south compared to the north suggests a pronounced southward position of the westerlies and or blocking over the northern north atlantic hence resembling a negative nao state most distinct from 4 2 to 2 4 kyr bp and during the little ice age south alpine flood activity therefore provides a qualitative record of variations in a paleo nao pattern during the holocene additionally increased south alpine flood activity contrasts to low precipitation in tropical central america cariaco basin on the holocene and centennial time scale this observation is consistent with a holocene southward migration of the atlantic circulation system and hence of the itcz driven by decreasing summer insolation in the northern hemisphere as well as with shorter term fluctuations probably driven by solar activity

a chronological framework for the holocene vegetational history of central minnesota the steel lake pollen record abstract paleorecords from minnesota and adjacent areas have often been used to evaluate large scale climatic processes in the mid continent of north america however most of these records are compromised by chronological flaws making problematic any comparisons with climatic interpretations based on other records e g gisp2 in greenland we report here a high resolution pollen record with a secure chronology constrained by 26 14 c dates on terrestrial macrofossils from steel lake central minnesota about 11 2 ka cal bp 11 000 calibrated yr before present the late glacial picea forest near steel lake was succeeded abruptly by pinus banksiana and or resinosa the pinus forest began to open 9 4 ka cal bp with the expansion of prairie taxa and a pine parkland or savanna prevailed until about 8 ka cal bp when quercus replaced pinus to become the dominant tree in the prairie areas for 4500 yr the close chronological control permits the correlation of key vegetational changes with those at other reliably dated sites in the eastern dakotas and in minnesota suggesting that the abrupt decline of the spruce forest was time transgressive from southwest to northeast during 2000 yr and that the development of prairie was time transgressive in the same direction over 2600 yr correlation of key pollen horizons at steel lake with those in the high resolution pollen profiles of elk lake ca 50 km northwest of steel lake suggests that the well known elk lake varve chronology for the early holocene is about 1000 yr too young

pleistocene hydrology of north america the role of ice sheets in reorganizing groundwater flow systems 1 while the geomorphic consequences of pleistocene megafloods have been known for some time it has been only in the past 2 decades that hydrogeologists and glaciologists alike have begun to appreciate the important impact that ice sheet aquifer interactions have had in controlling subsurface flow patterns recharge rates and the distribution of fresh water in confined aquifer systems across north america in this paper we document the numerous lines of geochemical isotopic and geomechanical evidence of ice sheet hydrogeology across north america we also review the mechanical thermal and hydrologic processes that control subsurface fluid migration beneath ice sheets finite element models of subsurface fluid flow permafrost formation and ice sheet loading are presented to investigate the coupled nature of transport processes during glaciation deglaciation these indicate that recharge rates as high as 10 times modern values occurred as the laurentide ice sheet overran the margins of sedimentary basins the effects of ice sheet loading and permafrost formation result in complex transient flow patterns within aquifers and confining units alike using geochemical and environmental isotopic data we estimate that the volume of glacial meltwater emplaced at the margins of sedimentary basins overrun by the laurentide ice sheet totals about 3 7 104 km3 which is about 0 2 of the volume of the laurentide ice sheet subglacial infiltration estimates based on continental scale hydrologic models are even higher 5 10 of meltwater generated these studies in sum call into question the widely held notion that groundwater flow patterns within confined aquifer systems are controlled primarily by the water table configuration during the pleistocene rather groundwater flow patterns were likely much more complex and transient in nature than has previously been thought because pleistocene recharge rates are believed to be highly variable these studies have profound implications for water resource managers charged with determining sustainable pumping rates from confined aquifers that host ice sheet meltwater

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 glacial and holocene vegetational history of the altai mountains southwestern tuva republic siberia two lakes of glacial origin grusha at 2413 m and akkol at 2204 m are located on a broad high mountain plateau on the dry eastern end of the russian altai mountains in the republic of tuva just north of mongolia the present vegetation of the area is an open high mountain tundra steppe mosaic with patches of larix and pinus sibirica forests on north facing slopes 30 km northwest of the lakes alpine meadows occur near streams and snow patches pollen diagrams and radiocarbon dates 16 for grusha and 12 for akkol were used to reconstruct the vegetational history since the last glaciation the core from grusha contains about 50 cm of late glacial sediment of relatively low organic content mostly correlated with the younger dryas episode because of the high percentages of artemisia gramineae and chenopodiaceae along with a diversity of non arboreal pollen types indicating tundra steppe and meadow steppe in the earliest holocene starting with increased organic matter at about 195 cm 12 000 cal yr bp the artemisia gramineae chenopodiaceae pollen assemblage continued along with an increase in shrub betula but without the diversity of minor non arboreal types the interpretation of dry and warm climate at this time is supported by the unconformity at akkol implying a dried lake then after about 1000 years the increase of pinus sibirica p sylvestris picea obovata and abies sibirica suggests that forests developed in response to increased humidity first at the higher elevation grusha and then at akkol after about 6000 cal yr bp the role of forests decreased sharply in the area the picea and abies components almost disappeared as they did also in more westerly areas of the altai mountains steppe elements increased along with alpine herbs especially after 2000 cal yr bp as a result of cooling or increased aridity as well as probable human activity correlation of the vegetation sequence for the tuva sites with those to the west in the central altai mountains indicates that the late glacial open landscapes persisted in the earliest holocene but then were invaded by coniferous forests as a result of increased moisture and temperature associated with atlantic storm systems as well as with insolation enhanced asian monsoon cooling and drying after about 6000 cal yr bp brought the decline of abies and picea and the expansion of tundra steppe

vegetation changes and associated climatic changes in the southern altai mountains within china during the holocene the location of the altai mountains at the limits of both the pacific and atlantic influences implies that this mountain range is an important climatic boundary based on pollen data of 188 samples