spatial and temporal patterns of aeolian activities in the desert belt of northern china revealed by dune chronologies abstract as a part of the inqua project a global digital database and atlas of quaternary dune field and sand seas 337 age records from the desert dunes of china and 20 from mongolian dune fields have been compiled in the database this has opened the possibility of exploring and synthesizing the quaternary environmental changes in the asian mid latitudes dune fields directly from the on site aeolian sand archives this paper assessed the sand dune chronologies in terms of geographical distribution data quality and their implications for late quaternary palaeoenvironmental reconstructions the available ages are concentrated mainly in the last 20 ka and many are from the fields of stabilized dunes in the eastern portion of the desert belt in northern china the number of records and the ratio between the records of stable state and the total records could act as a proxy for the palaeoenvironmental interpretation the aeolian sand activities deciphered from the chronological data in the eastern portion of the desert belt in northern china show a reasonable correlation with the general global climatic curves at the glacial interglacial timescales the limited aeolian sand records from the glacial period however hamper the understanding of the detailed features e g forms and processes of the dune fields during glacial times in the last two millennia however there has not been any meaningful correlation between aeolian dune activity and climatic variation at the centennial time scales probably due to the complexity of the aeolian sand systems and human interventions extending the coverage of dune chronology both temporally and spatially is urgently needed for a full understanding of the environmental changes in the dune fields

holocene vegetation and climate of the alashan plateau nw china reconstructed from pollen data a set of 55 recent pollen spectra from the alashan plateau and the qilian mountains qilianshan northwestern china has been analyzed the established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by eastern juyan palaeolake 41 89 n 101 85 e 892 m a s l several qualitative approaches e g indicator plant species artemisia chenopodiaceae and ephedra fragilis type s l ephedra distachya type pollen ratios and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the eastern juyan pollen record fossil pollen data reveal pronounced environmental changes in the studied area of the alashan plateau between ca 10 700 and 1700 cal yr b p desert taxa as chenopodiaceae nitraria calligonum reaumuria were abundant in the vegetation cover around the study site through the whole record pollen spectra dated to ca 10 700 5400 cal yr b p are characterised by highest values of chenopodiaceae e fragilis type and other desert indicating taxa suggesting rather dry climate most favourable conditions are reconstructed between 5400 and 3900 cal year b p on the basis of relative increase in abundance of artemisia pollen a return to dry conditions occurred at about 3900 cal yr b p the lake finally desiccated after 1700 cal yr b p reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal yr b p correlate well with similar events found in the published records from northern and western china and central mongolia however eastern juyan record does not show the early holocene humidity maximum as suggested by the sedimentary data from monsoon influenced areas of china

holocene history of desertification along the woodland steppe border in northern china abstract the woodland steppe ecotone of the southeastern inner mongolian plateau in northern china is located at the northwestern limit of the pacific monsoon influence where the landscape may have been a sensitive recorder of past climatic changes physical chemical and biological analyses of ams 14 c dated sediment sequences from two lakes of this region were used to reconstruct the holocene vegetation and desertification history and distinguish four periods 1 a cold and humid period from 10000 to 8000 14 c yr b p 2 a warm and humid period from 8000 to 5900 14 c yr b p 3 a warm and dry period from 5900 to 2900 14 c yr b p and 4 a cool and dry period from 2900 14 c yr b p to the present the increased aridity during the middle holocene was likely caused by increased winter temperatures and enhanced winter evaporation the transition from a humid to an arid climate after 5900 14 c yr b p coincided with enhanced aeolian activity and deciduous woodlands were replaced by pine woodlands and then by steppes in response to the climatic deterioration these transitions led to the present desertification the records suggest that a simple association of thermal and moisture conditions such as warm wet or cold dry may be misleading

late quaternary aeolian activity in the mu us and otindag dune fields north china and lagged response to insolation forcing 1 dune fields in parts of northern china contain important stratigraphic records of late quaternary change in the east asian monsoon in this study 33 new optically stimulated luminescence osl ages and other measurements from aeolian sediment sections are used to reconstruct the timing of wet dry climate variation in the mu us and otindag dune fields of north china the results indicate dune activity and dry climate in the last few hundred years 14 ka to about 7 8 ka and 50 ka to 60 ka the dunes were mainly stable implying a wetter climate between about 7 8 ka and 2 4 ka these results imply a lag of several thousand years between peak summer insolation at 10 11 ka and high summer monsoon rainfall after 7 8 ka in the investigated regions the monsoon climate may not respond directly to orbital forcing over millennial time scales land surface feedbacks may account for lagged dune field response

evolution of megadunes and lakes in the badain jaran desert inner mongolia china during the last 31 000 years abstract the badain jaran desert located in western inner mongolia china is characterized by an arid climate and by occurrence of large dunes and permanent lakes within the dune field the main objective of this paper is to describe landscape evolution and climatic change in this desert since the late pleistocene special attention is given to the dune and lake deposits as well as to the water chemistry of the lakes on the megadunes of the desert several calcareous cementation layers and cemented plant roots were observed indicating a relatively moister climate during the last 31 000 years the present hypersaline lakes were filled with fresh or brackish water between 9 and 4 ka bp on the basis of dune morphology and stratigraphy and lacustrine deposits it is concluded that the enrichment of ions in the lakes and decline of their water surface result from aridification since the middle holocene the existence of more humid periods implies that the intensity of westerlies and asian monsoons has changed periodically in this desert since the late pleistocene

osl chronology and possible forcing mechanisms of dune evolution in the horqin dunefield in northern china since the last glacial maximum the evolution processes and forcing mechanisms of the horqin dunefield in northern china are poorly understood in this study systematic osl dating of multiple sites is used together with pollen analysis of a representative section in order to reconstruct the evolution of the dunefield since the last glacial maximum lgm our results show that there was extensive dune mobilization 25 10 ka transition to stabilization 10 8 ka considerable dune stabilization 8 3 ka and multiple episodes of stabilization and mobilization after 3 ka comparison of dune evolution of the dunefields in northern china during the holocene showed that asian monsoon and resultant effective moisture have played an important role in the evolution of dunefields at the millennial time scale further analysis indicated that the dune evolution in the horqin dunefield before 3 ka was synchronous with climatic changes however increasing human activity has impacted dune evolution during the last 3 ka c 2012 university of washington published by elsevier inc all rights reserved the evolution processes and forcing mechanisms of the horqin dunefield in northern china are poorly understood in this study systematic osl dating of multiple sites is used together with pollen analysis of a representative section in order to reconstruct the evolution of the dunefield since the last glacial maximum lgm our results show that there was extensive dune mobilization 25 10 ka transition to stabilization 10 8 ka considerable dune stabilization 8 3 ka and multiple episodes of stabilization and mobilization after 3 ka comparison of dune evolution of the dunefields in northern china during the holocene showed that asian monsoon and resultant effective moisture have played an important role in the evolution of dunefields at the millennial time scale further analysis indicated that the dune evolution in the horqin dunefield before 3 ka was synchronous with climatic changes however increasing human activity has impacted dune evolution during the last 3 ka c 2012 university of washington published by elsevier inc all rights reserved

cyclic rapid warming on centennial scale revealed by a 2650 year stalagmite record of warm season temperature 1 a 2650 year bc665 ad1985 warm season mjja may june july august temperature reconstruction is derived from a correlation between thickness variations in annual layers of a stalagmite from shihua cave beijing china and instrumental meteorological records observations of soil co2 and drip water suggest that the temperature signal is amplified by the soil organism co2 system and recorded by the annual layer series our reconstruction reveals that centennial scale rapid warming occurred repeatedly following multicentenial cooling trends during the last millennia these results correlate with different records from the northern hemisphere indicating that the periodic alternation between cool and warm periods on a sub millennial scale had a sub hemispherical influence

early middle holocene lake desert evolution in northern ulan buh desert china abstract located in southwestern inner mongolia in northern china the ulan buh desert ubd has evolved significantly during the holocene the northern desert is adjacent to hetao plain an important agriculture area since the han dynasty 200 b c a series of aeolian sand lacustrine sequences from the desert were measured and dated by using differential global positioning system dgps and optically stimulated luminescence osl technologies respectively these lacustrine remains with similar deposit sequences have almost identical elevations and depositional ages indicating that they belonged to a unified paleolake in addition the holocene paleolake desert evolution process in ubd is established aeolian activity prevailed before 8 3 ka and a unified ulan buh paleolake containing the modern jilantai salt lake covered the northern desert during 7 8 7 1 ka ago the paleolake shrank and broke apart after 6 5 ka ago thereafter the paleolake evolved into the modern ubd and jilantai salt lake the study of one sand lacustrine section at the southern edge of hetao plain shows that the tushenze paleolake had a similar evolution process to ulan buh paleolake though they may not be connected to each other as suggested by the elevation difference the ulan buh desert lake evolution was likely due to the climate changes in the monsoon influenced region during the early middle holocene

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

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

optical dating of dune sands in the northeastern deserts of china abstract optical dating has been used to obtain the ages of fossil stabilized sand dunes from four sections in the northeastern deserts of china our results indicate that the optically stimulated luminescence ages of the four sections correlate well even though the samples were collected from different deserts about 600 km apart our results also indicate that active dune formation in this region lasted from the last glacial maximum to about 10 ka and that the warm climate of the holocene was interrupted by a cold dry dune formation episode about 3 5 1 7 ka the holocene optimum in this region is between 10 and 3 6 ka and a later warm humid dune stabilization phase lasted from at least 1 6 to 1 0 ka the youngest age on the uppermost sand unit yielded an age of only 40 yr supporting the previous argument that the existence of modern active eolian sands in the regions with a mean annual precipitation of up to 450 mm is not mainly due to drought but to extensive land cultivation over historic time from the luminescence properties of the quartz grains it is hypothesized that the sands in most of the sections are probably derived from more than one source with a minor source of quartz having a different thermal history before deposition

dune mobility and aridity at the desert margin of northern china at a time of peak monsoon strength wind blown sands were mobile at many sites along the desert margin in northern china during the early holocene 11 5 8 ka ago based on extensive new numerical dating this mobility implies low effective moisture at the desert margin in contrast to growing evidence for greater than modern monsoon precipitation at the same time in central and southern china dry conditions in the early holocene at the desert margin can be explained through a dynamic link between enhanced diabatic heating in the core region of the strengthened monsoon and increased subsidence in drylands to the north combined with high evapotranspiration rates due to high summer temperatures after 8 ka ago as the monsoon weakened and lower temperatures reduced evapotranspiration eolian sands were stabilized by vegetation aridity and dune mobility at the desert margin and a strengthened monsoon can both be explained as responses to high summer insolation in the early holocene

the ion chemistry of lakes and late holocene desiccation in the badain jaran desert inner mongolia china abstract in the markedly arid badain jaran desert one of the least studied areas in the world over a hundred permanent lakes exist among the dunes the geochemistry of water samples from nine lakes and from the groundwater in the desert and on its periphery was investigated ion chemistry of the water from these desert lakes changes considerably on a regional scale we argue that there is a positive correlation between the ages of these lakes and their totally dissolved solids tds varying between 1 2 and 398 2 g l tritium analysis of groundwater in wells gives an age generally older than four decades and younger than 100 years the lacustrine deposits freshwater fauna and shorelines indicate the existence of large water bodies with low salinities in the inter dune hollows of this desert during the early and middle holocene the precipitation in this desert during the early and middle holocene was estimated to be ca 200 mm year on average at least twice as high as at present on the basis of paleoecology tl and radiocarbon ages it was concluded that the huge enrichment of ions in the lakes and decrease of water availability originated from climatic desiccation during the last 4000 years the paleoclimate of the badain jaran desert reported here was remarkably consistent with the late quaternary climatic histories of the regions to the immediate north west east and south of the study area

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

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

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

initiation and variation of the dune fields in semi arid china with a special reference to the hunshandake sandy land inner mongolia sedimentary sequences occurring in desert dunes reflect changes in desert systems and as such may contain signals useful for recognizing spatial and temporal changes of deserts and their response to regional or even global climate fluctuations geomorphological and palaeoenvironmental studies within the dune fields of the asian middle latitudes have provided some solid evidence for interpreting the history of these sand seas using the hunshandake otindag sandy land a sandy area covered primarily by stabilized dunes and located in the semi arid zone of eastern inner mongolia china fig 1 as an example we studied the initiation and variation in the dune landscape in the eastern portion of the desert belt in northern china on the basis of physical and biochemical indicators in the sediments and osl chronology we herein argue that this dune system in the middle latitudes of eastern asia is much younger than previously assumed and that it has responded sensitively to climate change during the late quaternary geological evidence from the sandy land suggests that most of the current dunes are of late pleistocene or even holocene age palaeosols intercalated in the aeolian sequences and their osl chronology show that the climate of the hunshandake was much wetter than today between 9 6 ka and 3 ka this resulted in stabilization of the dunes in the eastern and central portions of the sandy land epochs of reworking or stabilization of the dunes are broadly consistent with the fluctuations in northern hemisphere solar radiation although with an obvious time lag because the increase rate of annual precipitation was not sufficient to fully stabilize the dunes in more arid part of the region some active dunes persisted even during this long lasting wetter epoch we conclude that periods of holocene dune stabilization due to palaeosol formation varied along the climate gradients across the various sandy lands of northern china and in general it began earlier and lasted longer in the east than in the west the general nature of the sandy lands and their counterparts in the western portion of the desert belt during the lgm and mid holocene climate optimum is discussed in comparison with their current states

chemistry and late quaternary evolution of ground and surface waters in the area of yabulai mountains western inner mongolia china abstract in the extensive area of western inner mongolia china the water demand of local residents often depends mainly on shallow aquifers although scientific investigations of the quality and formation of the groundwater are still lacking in this study the chemistry and isotopic composition of groundwater and lake water samples collected at 22 sites in the area of yabulai mountains fig 1 in western inner mongolia were analysed chemical water analysis included the determination of na k ca2 mg2 li nh4 al3 co2 co32 hco3 cl so42 no3 f po43 hbo2 and sio2 and 18o and tritium isotopes solute concentrations in groundwater show significant differences within the study area while the water of the three lakes is dominated by sodium and chloride this study reveals the importance of spatial variation of groundwater chemistry in an arid environment that has a relatively homogeneous lithological basement the heterogeneity of groundwater chemistry suggests that the shallow groundwater in western inner mongolia is mainly recharged by infiltration of local rainfall the relatively high tritium content indicates that the water in the shallow aquifer of the study area is generally not older than 100 years former shorelines in the lake basin of shugui fig 1 suggest the presence of a much larger lake in the past under a wetter climate than present hyper arid conditions presumably because of increased east asian monsoon intensity during the middle holocene in the vicinity of commune administrations that have higher population density the tds of ground water is also higher probably owing to water pollution

holocene eolian activation as a proxy for broad scale landscape change on the gila river indian community arizona abstract eolian sediments are common within the middle gila river valley southern arizona and reflect variability in eolian and fluvial processes during the late holocene this study focuses on deciphering the stratigraphic record of eolian deposition and associated luminescence dating of quartz extracts by single aliquot regeneration sar protocols stratigraphic assessment coupled with luminescence ages indicates that there are four broad eolian depositional events at ca 3145 220 yr 1950 1360 yr 800 100 yr and 690 315 yr this nascent chronology correlated with regional archeological evidence and paleoclimate proxy datasets leads to two general conclusions 1 loess deposits transverse dune formation and sand sheet deposition in the late holocene are probably linked to flow variability of the gila river though the last two events are concordant with regional megadroughts and 2 the stability of eolian landforms since the 19th century reflects the lack of eolian sediment supply during a period of fluvial incision resulting in entisol formation on dunes the prime catalyst of eolian activity during the late holocene is inferred to be sediment supply driven by climate periodicity and variable flow within the gila river catchment

age and dynamics of linear dunes in the namib desert bristow c s duller g a t lancaster n 2007 age and dynamics of linear dunes in the namib desert geology 35 6 555 558 sponsorship american chemical society

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

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

hydrological and climatic changes in deserts of china since the late pleistocene article i nfo article history large areas in western china were wetlands or less arid between 40 and 30 ka corresponding to the greatest lake period on the adjacent tibetan plateau during the last glacial maximum some of these western chinese deserts again experienced wetter conditions however at the same time the sandy lands in the eastern chinese desert belt experienced an activation of aeolian dunes while interpretations of the mid holocene environment in the deserts of china are controversial it is quite likely that it was more humid not only in the eastern areas influenced by monsoon climate systems but also in the western deserts where moisture is currently associated with westerlies evaluation of lacustrine records in the lakes recharged by dryland rivers and the complex interactions of these systems as well as other paleoenvironmental proxies such as the artemisia chenopodiaceae ratio should be interpreted with greater caution facing the highlighted uncertainties in our understanding of climate changes in chinese deserts it is hoped that this special issue will improve our knowledge considerably

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

palaeoenvironmental reconstructions from linear dunefields recent progress current challenges and future directions abstract this paper reviews recent progress in the use of linear dunes as geoproxies of late quaternary environmental change summarises the challenges facing their use and explores some potential solutions to these challenges large areas of the swathes of linear dunes which occupy the continental interior of southern africa australia and parts of central asia and southern america currently have limited or negligible aeolian activity they have been recognised as offering potential information about past environments for more than a century but only with the widespread application of luminescence dating during the 1990s did they realistically start to offer the prospect of being an extensive dateable proxy of late quaternary palaeoenvironments and possibly palaeoclimates dating aeolian dune sands with luminescence methods is generally although not always relatively straightforward over the past twenty years a large number 1000 of luminescence ages have been added to the global dataset yet there has also been significant criticism of some of the rationale underpinning much of the interpretation of the records derived at the landscape scale developments of arguably equal importance have come from improved geomorphological understanding based on the wider availability of remotely sensed data and the paradigm of dunefield evolution as a self organising complex system current challenges are identified in three key regions incomplete understanding of how the process geomorphology of linear dunes affect the accumulation and preservation of sediment a lack of clarity regarding the temporal and spatial scale of the response in a dynamic environmental setting and uncertainty surrounding the drivers of changing rates of net accumulation solutions to these challenges lie within diverse research methodologies certainly further field study is required with improvement required in understanding system responses to changing environmental stimuli at scales from sedimentological to landscape in parallel the full implications of complex systems approaches to aeolian geomorphology for linear dunes lag behind the adoption of the concept to some other dune forms e g barchans the relationship between observed dune complexity and age from field data complicates previous suggestions that dune patterning may be purely a function of development time parallel to this lies the need to improve interpretation of the results of dune geochronological studies a suggestion is offered which aims to test the statistical significance of dune accumulation time series by comparison with a modelled system with unchanging external forcing despite the initial promise of linear dune records as a revolutionary source of palaeoenvironmental information in drylands the outcomes to date have been coarse although still valuable in resolution perhaps the most valuable realization has been that geomorphological understanding of these widespread landforms is incomplete

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

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

the evolution of mediterranean wetlands in the first millennium ad the case of les arenes floodplain tortosa ne spain abstract mediterranean wetlands are characterised by two factors 1 a remarkable seasonal fluctuation in the water table and 2 a long history of anthropisation being exceptional archives for palaeoenvironmental and archaeological research humid areas have been thoroughly studied to assess the interplay between people and the environment during the holocene we present here the study of a sedimentary sequence from a mediterranean wetland the les arenes floodplain tortosa ne spain fully dry to date les arenes is documented as a partially drained floodplain in the 12th century records with the aim of assessing the climatic and anthropic contribution to its desiccation we report here the results of bulk sediment analyses environmental magnetism soil micromorphology and ams dating of this sedimentary sequence plus a review of the available historical records the outcome is a clearer understanding of the evolution of this mediterranean floodplain during the 1st millennium ad which implications may be extrapolated to other floodplain wetlands in the iberian peninsula and the mediterranean wet conditions and a low to medium energy depositional environment are attested in les arenes between the 1st and 7th centuries coinciding with the iberian roman humid period irhp and the dark age humid period dahp drier conditions between the 7th and 10th centuries concur with enhanced fluvial dynamics the medieval climate anomaly mca and the first arrival of arabic berber populations in the iberian peninsula al andalus starting in ad 711 results suggest that although the shift from wet to dry conditions in les arenes complies with major climatic trends the construction of the first drainage canals by arab berber groups likely contributed to the enhancement of on going climate related environmental processes