lake level and climate changes between 42 000 and 18 000 c 14 yr bp in the tengger desert northwestern china multiple lines of stratigraphic geochemical and fossil data suggest that fresh mesohaline paleolakes were widespread in the tengger desert of northwestern china and underwent major fluctuations during the late pleistocene the paleolakes started to develop at ca 42 000 c 14 yr b p the lake levels were the highest between 35 000 and 22 000 c 14 yr b p during which megalake tengger dominated the landscape the climatic conditions at this time were unique for this area and have no modem analogue after an episode of decline between 22 000 and 20 000 c 14 yr b p and an episode of rebound between 20 000 and 18 600 c 14 yr b p the paleolakes started to desiccate and completely disappeared around 18 000 c 14 yr b p the environmental proxy data indicate that the megalake tengger formed under warm humid climates the reconstructed climatic variations appear to be correlative with the abrupt climatic events reconstructed for the north atlantic c 2002 university of washington

unsaturated zone hydrostratigraphies a novel archive of past climates in dryland continental regions natural chemical tracers contained in moisture within unsaturated zone usz sediments have very significant potential as a novel archive of past climate and palaeoenvironmental conditions in dryland environments however this potential has yet to be fully realised the tracer signature is established in the near surface zone with evapotranspiration processes enriching the concentration inherited from input from atmospheric deposition predominantly rainfall this pore moisture tracer signature then moves vertically through the usz sediments toward the water table producing a hydrostratigraphy that with increasing depth records changes to the moisture balance at the surface through time the small fluxes of water through the usz in dryland climates means that this hydrostratigraphy approach is particularly valuable in these environments for providing climate records longer than the instrumental data period this paper sets out the current state of the art in the use of the usz as an archive we explain the nature of the usz the basis of the tracer technique and also the field and sampling methodologies employed examples of application worldwide by broad geographic region are also evaluated this shows that the usz hydrostratigraphy approach can be used across three key timescales i decadal to multi decadal resolution records covering hundreds of years that provide information about recent climate fluctuations and patterns of land use change ii multi decadal through to millennial scale length records which may record wetter and drier events down to decadal scale resolution and iii last interglacial through to the holocene records of lower resolution that indicate broad shifts over multi millennial timescales we also explore the questions and challenges surrounding the depositional flux of tracer inputs and the extent to which infiltration is non uniform before setting the agenda for their future potential use alongside related proxies for palaeohydrology

investigation of the sand sea with the tallest dunes on earth china s badain jaran sand sea abstract china s badain jaran sand sea features the tallest dunes on earth and a unique mega dune lake landscape it had been explored little until the 1990s though early scientific explorations surrounding the sand sea had begun by the early 20th century heated debates now focus on the desert environment and particularly how the mega dunes and desert lakes develop and evolve this paper reviews the status of these debates and summarizes the supporting evidences the environmental research mainly concerns formation and evolution of the sand sea and its relationship with climate change the proposed formation time ranges from the early pleistocene to the holocene opinions vary about climate change on different time scales the reconstructed climate change history is shorter than the sand sea s history with the longest record extending to the late pleistocene the mega dune research focuses on sediments dune morphology and formation processes it remains unclear whether the mega dunes result primarily from wind action control by the underlying topography or groundwater maintenance the sources of lake water are also debated but there are four main hypotheses atmospheric precipitation groundwater from nearby areas precipitation and snowmelt in remote areas such as the qilian mountains and the qinghai tibetan plateau or paleowater that formed during past periods of wet climate we believe that the sand sea deserves further study in terms of its dune geomorphology evolution and hydrology and their responses to climate change meteorological and hydrological observations and monitoring in the sand sea are particularly necessary

soil water flux in the southern great basin united states temporal and spatial variations over the last 120 000 years the disposal of hazardous and radioactive waste in arid regions requires a thorough understanding of the occurrence of soil water flux and recharge soil water chemistry and isotopic data are presented from three deep vadose zone boreholes 230 m at the nevada test site located in the great basin geographic province of the southwestern united states to quantify soil water flux and its relation to climate the low water contents found in the soils significantly reduce the mixing of tracers in the subsurface and provide a unique opportunity to examine the role of climate variation on recharge in arid climates tracing techniques and core data are examined in this work to reconstruct the paleohydrologic conditions existing in the vadose zone well beyond the timescales typically investigated stable chloride and chlorine 36 profiles indicate that the soil waters deep in the vadose zone range in age from approximately 20 000 to 120 000 years secondary chloride bulges that are present in two of the three profiles support the concept of recharge occurring at or near the last two glacial maxima when the climate of the area was considerably wetter and cooler the stable isotopic composition of the soil water in the profiles is significantly more depleted in heavy isotopes than is modern precipitation suggesting that recharge under the current climate is not occurring at this arid site past and present recharge appears to have been strongly controlled by surface topography with increased incidence of recharge where runoff from the surrounding mountains may have been concentrated the data obtained from this detailed drilling and sampling program shed new light on the behavior of water in thick vadose zones and in particular show the sensitivity of arid regions to the extreme variations in climate experienced by the region over the last two glacial maxima

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

geomorphology of the megadunes in the badain jaran desert the badain jaran desert features the highest megadunes on earth and a unique megadune lake alternation landscape based on field survey and interpretation of aerial photographs this paper examines the general characteristics of the badain jaran megadunes their morphometry and formation as well as the formation of megadune lake alternation landscape it is suggested that the megadunes in the badain jaran desert were developed in a low wind energy environment the compound transverse megadunes the dominant megadune type have a similar wind regime to barchanoid dunes and the compound star megadunes which occur near the mountains have a similar wind regime to star dunes similar to the barchanoid dunes the height base area and spacing of the compound transverse megadunes show reasonably good inter correlation the base area of the megadunes and the area of the leeward interdune lake basins are also inter correlated the alignment and spacing of the badain jaran megadunes implies that wind is the most important factor in their development the morphology underneath the megadunes does not determine the general pattern of the megadunes as previously suggested repetitions of dune fixation and reactivation in the development process played an important role in increasing the megadunes height hence their size the interdune lakes in the megadune area were mainly formed by talus springs and are only partly fed by atmospheric precipitation

a 700 year history of groundwater recharge in the drylands of nw china a 700 year semi quantitative history of diffuse groundwater recharge in the badain jaran desert inner mongolia is proposed on the basis of solute data from multiple unsaturated zone groundwater profiles using mass balance of chloride to establish recharge rates and profile chronologies four relatively humid 1330 1430 1500 1620 1700 1780 and 1950 1990 and three relatively arid phases 1430 1500 1620 1700 and 1900 1950 are discernable across the profiles the recharge history broadly reflects multidecadal to centurial timescale precipitation changes in the northern tibetan plateau and suggests that variations in east asian summer monsoon intensity affect desert recharge rates uncertainties in the records owing to assumptions about the cl inputs are examined by comparing deterministic and stochastic cl input scenarios such records are valuable for assessing spatial aspects of climate changes in the region as well as for informing sustainable water resource management strategies for northwestern china s drylands

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

rate and historical change of direct recharge from precipitation constrained by unsaturated zone profiles of chloride and oxygen 18 in dry river bed of north china plain quantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well irrigated agriculture in the north china plain the land use is dominated by groundwater irrigated farmland where the direct recharge derived from precipitation and irrigation to characterize the mean rate and historical variance of direct recharge derived from precipitation unsaturated zone profiles of chloride and d18o in the dry river bed of the beiyishui river were employed the results show that archival time scale of the profile covers the duration from 1980 to 2002 corresponding to depths from 5 to 2 m which is indicated by matching the d18o peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation using the chloride mass balance method the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3 8 0 8 mm year 1 which accounts for about 0 7 of the long term average annual precipitation further the direct recharge rates vary from 2 1 to 6 8 mm year 1 since 1980 despite the subhumid climate the estimate of recharge rates is in line with other findings in semiarid regions the low rate of direct recharge is considered as a result of the relative dry climate in recent decades in dry river bed unsaturated zone profiles of chloride and d18o combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts copyright c 2011 john wiley sons ltd

a 2 326 year tree ring record of climate variability on the northeastern qinghai tibetan plateau 1 high resolution climate proxy records covering the last two millennia on the qinghai tibetan plateau are scarce yet essential to evaluation of the patterns synchroneity and spatial extent of past climatic changes including those in the medieval warm period mwp and the little ice age lia here we present a 2326 year tree ring chronology of sabina przewalskii kom for dulan area of northeastern qinghai tibetan plateau we find that the annual growth rings mainly reflect variations in regional spring precipitation the greatest change in spring precipitation during the last two millennia seems to occur in the second half of the 4th century the north atlantic mwp was accompanied by notable wet springs in the study region during a d 929 1031 with the peak occurring around a d 974 three intervals of dry springs occurred in the period of lia our tree ring data will facilitate intercontinental comparisons of large scale synoptic climate variability for the last two millennia

recharge in karst and dune elements of a semi arid landscape as indicated by natural isotopes and chloride abstract the rates and mechanisms of local recharge in a semi arid environment have been investigated beneath two major landscape settings in the murray basin in south australia these were calcrete flats with sinkholes and sand dunes in adjacent landscape settings five minor settings were investigated and identified as undisturbed calcrete primary older sinkholes secondary younger sinkholes sand dunes with native vegetation and sand dunes with introduced pasture data from a limited series of boreholes were interpreted to suggest that recharge varied from in excess of 100 mm yr 1 for secondary sinkholes to less than 0 1 mm yr 1 beneath sand dunes with native vegetation the data suggest that recharge under sand dunes has increased by more than two orders of magnitude following clearing of the native vegetation 50 yr ago as 90 of an area of 10 000 km2 has been cleared this clearing has ensured that inflow of saline groundwater to the adjacent river murray will increase and in view of the amount of salt stored in both the unsaturated and saturated zones will continue for a very long time at sites where the inferred recharge is lowest profiles of the chloride concentration of soil water are consistent with the hypothesis that there is in excess of 50 000 yr recharge stored in the thick unsaturated zone some evidence for changes in recharge rate over this time scale is seen

millennial scale holocene climate variability in the nw china drylands and links to the tropical pacific and the north atlantic abstract a loess paleosol sequence and a lake sediment record from the central hexi corridor in the drylands of nw china show patterns of persistent millennial to centennial scale climate variability during the holocene epoch which can be well correlated with abrupt climatic events reported from the north atlantic and the asian monsoon dominated regimes our results show that the drylands in nw china might have been regulated both by the westerlies and by the east asian summer monsoon easm in a roughly synchronous manner it seems that cold dry intervals in the central hexi corridor may generally correspond to cooling phases in high latitudes of the northern hemisphere and that cold warm wet intervals largely correlate with relatively warm phases in northern high latitudes a candidate mechanism involving nao ao and enso dynamics is tentatively proposed to account for this synchroneity climatic patterns may be spatially different in the nw china drylands in response to the changing predominant control of either the westerlies or the easm depending on the contrast of their relative strengths glacier meltwater discharges associated with alpine warming may be partly responsible at least for the two records discussed in this paper for such spatial heterogeneity of climatic changes during the holocene more work is needed to evaluate the individual roles and combined impacts of the easm the westerlies and alpine glacier meltwater regulation on the nw china dryland dynamics

groundwater discharge to a gobi desert lake during mid and late holocene dry periods abstract high levels of lake eastern juyanze and a wetter climate in the gobi desert nw china were recorded between 5100 and 4100 cal year bp from ostracod distribution shell geochemistry sedimentology and palynological data after about 4100 cal year bp lake levels decreased and groundwater discharge became dominant source of water during short term regressive events at about 4000 3800 and 3500 cal year bp as suggested by a significant difference in modern river water and groundwater chemistry and the geochemical signal of fossil ostracod shells the overall trend towards lower lake levels culminated in repeated episodes of desiccation of lake eastern juyanze between 3200 and 2900 cal year bp individual regressive events as well as the rapid environmental fluctuations of lake eastern juyanze at about 3000 cal year bp were likely caused by mid to late holocene temperature fluctuations recorded by the dunde ice core yao t thompson l g 1992 trends and features of climatic changes in the past 5000 years recorded by the dunde ice core annals of glaciology 16 21 24 and shifts of the southeastern asian monsoon

climate variability in the past 19 000 yr in ne tibetan plateau inferred from biomarker and stable isotope records of lake donggi cona abstract we investigated 4 84 m long sediment record spanning over the late glacial and holocene from lake donggi cona to be able to reconstruct circulation pattern on the tibetan plateau tp presently lake donggi cona is located at the boundaries of westerlies and asian monsoon circulations in the northeastern tp however the exact timing and stimulating mechanisms for climatic changes and monsoon shifts in this region are still debated we used a 19 ka long stable isotope record of sedimentary n alkanes to address this discrepancy by providing insights into paleohydrological conditions the d of n c 23 is influenced by lake water evaporation the d values of sedimentary n c 29 are mainly controlled by moisture source and temperature changes long chain n alkanes dominate over the core whereas three mean clusters i e microbial aquatic and terrestrial can be inferred multi proxies suggest five major episodes in the history of lake donggi cona the lake donggi cona record indicates that the late glacial 18 4 14 8 cal ka bp was dominated by low productivity of mainly microbial and aquatic organisms relatively low d values suggest low temperatures and moist conditions eventually caused by stronger westerlies winter monsoon and melt water influence likely the shift 17 9 cal ka bp from microbial to enhanced aquatic input suggests either a change from deep to shallow water lake or a break in local stratification between 14 8 and 13 0 cal ka bp variable climatic conditions prevailed although the westerlies weekend the increase in temperature enhanced the permafrost and snow melting displayed by a high sedimentary accumulation rate higher d values indicate increasingly arid conditions with higher temperatures which eventually lead to high evaporative conditions and lowest lake levels low vegetation cover and high erosion rates led to high sediment accumulation resulting in stratification followed by anoxia in the terminal lake from 13 0 to 9 2 cal ka bp lowered values of d along with high contents of terrestrial organic matter marked the early holocene warming indicating a further strengthening of summer precipitation and higher lake levels a cooling trend was observed in the mid holocene between 9 2 and 3 0 cal ka bp accompanied by higher moisture availability displayed by lowered d values caused by reduced evaporative conditions due to a drop in temperature and recovering westerlies after 3 0 cal ka bp a decrease in lake productivity and cold and semi arid conditions prevailed suggesting lower lake levels and reduced moisture from recycled air masses and westerlies we propose that the summer monsoon was the predominant moisture source during the bolling allerod warm complex and early holocene followed by westerlies in mid to late holocene period stable carbon isotope values 32 indicate the absence of c 4 type vegetation in the region contradicting with their presence in the lake qinghai record the d record from lake donggi cona highlights the importance of the interplay between westerlies and summer monsoon circulation at this location which is highly dynamic in northeastern plateau compared to the north atlantic circulation and insolation changes consequently lake donggi cona might be an important anchor point for environmental reconstructions on the tibetan plateau

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

variations in flow and transport in thick desert vadose zones in response to paleoclimatic forcing 0 90 kyr field measurements modeling and uncertainties 1 an understanding of unsaturated flow and potential recharge in interdrainage semiarid and arid regions is critical for quantification of water resources and contaminant transport we evaluated system response to paleoclimatic forcing using water potential and cl profiles and modeling of nonisothermal liquid and vapor flow and cl transport at semiarid high plains texas and arid chihuahuan desert texas amargosa desert nevada sites infiltration in response to current climatic forcing is restricted to the shallow 0 3 3 m subsurface subsurface cl accumulations correspond to time periods of 9 90 kyr bulge shaped cl profiles generally represent accumulation during the holocene 9 16 kyr lower cl concentrations at depth reflect higher water fluxes 0 04 8 4 mm yr during the pleistocene and earlier times low water potentials and upward gradients indicate current drying conditions nonisothermal liquid and vapor flow simulations indicate that upward flow for at least 1 2 kyr in the high plains and for 12 16 kyr at the chihuahuan and amargosa desert sites is required to reproduce measured upward water potential gradients and that recharge is negligible 0 1 mm yr in these interdrainage areas index terms 1809 hydrology desertification 1815 hydrology erosion and sedimentation 1833 hydrology hydroclimatology keywords paleoclimate chloride mass balance unsaturated zone unsaturated flow modeling

field study of spatial variability in unsaturated flow beneath and adjacent to playas we quantified unsaturated flow beneath playa and adjacent interplaya settings at a site in the southern high plains united states to resolve issues related to where and how water moves through the unsaturated zone this is the first study in which the data density 39 boreholes and the variety of techniques used physical chemical and isotopic were sufficient to quantify spatial variability in unsaturated flow water contents water potentials and tritium eoneentrations were much higher and chloride eoneentrations were much lower beneath playas than in interplaya settings which indicated that playas focus recharge these results refute previous hypotheses that playas act as evaporation pans or that recharge is restricted to the annular region around playas water fluxes estimated from environmental tracers ranged from 60 to 120 mm yr 1 beneath playas and were 0 1 mm yr 1 during the past 2000 5000 years beneath natural interplaya areas not subjected to ponding to evaluate the apparent inconsistency between high recharge rates and thick clay layers beneath playas we applied bromide and fd c blue dye to evaluate flow processes these applied tracer experiments showed preferential flow along roots and desiccation cracks through structured clays in the shallow subsurface in playas

geochemical estimates of paleorecharge in the pasco basin evaluation of the chloride mass balance technique the pasco basin in southeastern washington state provides a unique hydrogeologic setting for evaluating the chloride mass balance technique for estimating recharge this basin was affected by late pleistocene catastrophic floods when glacial dams in western montana and northern idaho were breached it is estimated that multiple missoula floods occurred between 13 000 and 15 000 years b p and reached a high water elevation of 350 m these floods removed accumulated chloride from the sediment profile effectively resetting the chloride mass balance clock at the beginning of the holocene the rate of chloride accumulation qcl in the sediments was determined by two methods and compared the first method measured qcl by dividing the calculated natural fallout of 36cl by a measured ratio of 36cl cl in the pore water while the second method used the total mass of chloride in the profile divided by the length of time that atmospheric chloride had accumulated since the last flood although the two methods are based on different approaches they showed close agreement in laboratory studies the sediment to water ratio for chloride extraction was sensitive to the grain size of the sediments low extraction ratios in silt loam sediments led to significant underestimation of pore water chloride concentration br cl ratios were useful for distinguishing nonatmospheric e g rock sources of chloride field studies showed little spatial variability in estimated recharge at a given site within the basin but showed significant topographic control on recharge rates in this semiarid environment an extension of the conventional chloride mass balance model was used to evaluate chloride profiles under transient time varying annual precipitation conditions this model was inverted to determine the paleorecharge history for a given soil chloride profile and the parameters of the root extraction model required to estimate paleoprecipitation

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

hydrological changes and holocene climate variations in nw china inferred from lake sediments of juyanze palaeolake by factor analyses abstract the eastern juyanze palaeolake in hyperarid north western china 41 75 42 n 101 5 102 e provides evidence of a complex hydrological pattern during the holocene multivariate statistics based on lithological geochemical and mineral data from the reference site g36 in the centre of the lake were performed to reconstruct the interrelation between lake hydrology and climate variability of the last 11 000 yr principal component analyses pca analyses enabled us to extract the three system variables runoff lake level water budget and salinity as the major factors which have influenced the lake history during a highly variable holocene climate we can also demonstrate that the independent variable total organic carbon toc is not only a function of bio productivity in lakes under warm wet climate conditions but more frequently related to surface runoff processes which can result in over estimation of pollen types used for climate reconstructions a combined consideration of all system variables with lithological parameters catchment characteristics and the local groundwater situation show that lake formation and its persistence strongly depended on local rainfall runoff and the status of the underlying aquifer our results indicate remarkable differences between the early holocene and mid to late holocene lake formation owing to changes in the aquifer system beneath the lake at about 10 700 cal bp freshwater lake formation starts with extreme runoff events under a wet climate repeated dry climate spells of reduced runoff the overall climate during the early holocene points to wet conditions with frequent phases of very high runoff and highest lake levels until about 8900 cal bp extremely low runoff occurred between 8900 and 8100 cal bp indicating already dry climate conditions some hundred years prior to the worldwide recorded responses of the 8 2 ka cold dry event a second period of major dry climate conditions with generally low but fluctuating runoff unstable water budget and deposition of aeolian sand lasted for about 2100 yr between 7500 and 5400 cal bp these climate conditions corroborate previous assumptions of a mid holocene dry period in arid north western china increased runoff after 5400 cal bp under wet climate conditions led to a complete refill of the aquifer at about 5000 cal bp and favoured the development of a saline lake for about 3500 yr in terms of hydrology the time between 5400 and 4000 cal bp appears to be the climate optimum compared with the early holocene wet climate the mid to late holocene local rainfall was less pronounced and displays a general decreasing trend towards complete desiccation of the lake our results indicate an extremely variable moisture availability in arid regions of north western china during the entire holocene owing to the interplay of the east asian summer monsoon with the westerly waves at the boundary of the summer monsoon limit variations from dry to wet climate conditions seem to have been more pronounced than in other monsoon regions of china

estimating paleorecharge and paleoclimate from unsaturated zone profiles unsaturated zone solute and isotope profiles may be interpreted in terms of past changes in recharge rate in cases where water movement can be approximated by piston flow a model is presented which describes water movement in terms of piston flow below a surface mixing layer below the mixing layer diffusion and dispersion occur in the liquid phase in the case of solutes and in both the liquid and gas phases in the case of isotopically labeled water climatic events of 4 5 years duration may be preserved in the unsaturated zone for more than 50 years if the recharge rate is greater than approximately 20 mm yr 1 longer term fluctuations in climatic conditions century scale might be preserved for over 1000 years provided the recharge rate is greater than approximately 2 mm yr 1 and the unsaturated zone is sufficiently deep profiles from cyprus and northern senegal appear to record changes in recharge rate over periods up to 400 years the profiles are well correlated with known variations in rainfall and fluctuations in lake levels the model provides limiting conditions to be applied to the interpretation of profiles

a holocene sedimentary record from bosten lake china abstract a 9 24 m long sediment record from the kaidu river delta margin of bosten lake northwestern china provides evidence for changes in water balance of the lake during the past 8600 calendar years quantitative and qualitative analyses of detrital components authigenic calcite toc and sr ca molar ratios as well as comparisons with selected ostracod assemblages show that lake level fluctuations at minimum 5 6 m display changes in effective moisture supply mainly driven by the west wind system distinct periods of negative water balances and thus dry conditions are dated to 8 5 8 1 7 3 7 1 around 6 0 at 5 4 5 0 4 6 4 3 3 9 3 6 3 4 3 2 2 6 2 5 1 9 1 1 0 5 0 3 and 0 18 0 05 cal ky bp and match the regional and global pattern of climate shifts during the holocene temporal shifts of moisture availability during mid holocene time were recognised as well and may be attributed to regionally different airflow conditions the last 150 years of rising lake levels are accompanied by strong eutrophication as a result of increased human impact

alkenone based reconstruction of late holocene surface temperature and salinity changes in lake qinghai china china the alkenone temperature proxy u k 0 37 indicates up to a 1 c change in mean annual air temperature or a 2 c change in summer lake water temperature during the late holocene oscillating warm and cold periods could be related to the 20th century warm period the little ice age the medieval warm period the dark ages cold period and the roman warm period the relative importance of c37 4 alkenone to total c37 alkenone production c37 4 fluctuated between 15 45 with higher values during warm periods suggesting that lake water was also fresher during these periods the coupled late holocene surface temperature and salinity changes suggest that asian monsoons strongly influenced the climate of the lake qinghai region citation liu z a c g henderson and y huang 2006 alkenone based reconstruction of lateholocene surface temperature and salinity changes in lake qinghai china geophys res lett 33 l09707 doi 10 1029 2006gl026151

oligocene miocene magnetostratigraphy and magnetic anisotropy of the baxbulak section from the pamir tian shan convergence zone as the northernmost part of the indo eurasian collision belt the pamir tian shan convergence zone ptcz is a strategic location for understanding intracontinental deformation here we present a magnetostratigraphic investigation of a continuous section from the baxbulak region to better constrain regional tectonic history rock magnetic analyses indicate that hematite and magnetite are the main carriers of characteristic remanent magnetization the resulting polarity sequence allows a distinct correlation to the geomagnetic polarity time scale showing that the section spans the interval of 29 1 20 7 ma rock magnetic results further suggest that paramagnetic and antiferromagnetic minerals dominantly contribute to anisotropy of magnetic susceptibility ams of the sequence thus the ams would indicate the preferred orientations of the mineral grains that are sensitive to tectonic strain at around 26 ma the grouped principal minimum perpendicular to the bedding diverts to a girdle distribution in a n s direction demonstrating the overprint of tectonic fabric to previous weakly deformed sedimentary fabric this would be interpreted as a marked increase in tectonic strain consistent with various evidence from the pamir and the neighboring basin that show the pamir began to migrate northward moreover the coincident changes in distribution of ams principal axes in both direction and magnitude are comparable to the regional counterclockwise rotations observed from paleomagnetic data likely related to orogenesis

deep arid system hydrodynamics 2 application to paleohydrologic reconstruction using vadose zone profiles from the northern mojave desert 1 site specific numerical modeling of four sites in two arid alluvial basins within the nevada test site employs a conceptual model of deep arid system hydrodynamics that includes vapor transport the role of xeric vegetation and long term surface boundary transients surface boundary sequences spanning 110 kyr that best reproduce measured chloride concentration and matric potential profiles from four deep 230 460 m boreholes concur with independent paleohydrologic and paleoecological records from the region simulations constrain a pluvial period associated with infiltration of 2 5 mm yr 1 at 14 13 ka and denote a shift linked to the establishment of desert vegetation at 13 9 5 ka retrodicted moisture flux histories inferred from modeling results differ significantly from those determined using the conventional chloride mass balance approach that assumes only downward advection the modeling approach developed here represents a significant advance in the use of deep vadose zone profile data from arid regions to recover detailed paleohydrologic and current hydrologic information

geochemistry of sediment moisture in the badain jaran desert implications of recent environmental changes and water rock interaction abstract unsaturated zone pore water has the potential to record history of recharge palaeoenvironment pollution movement and water rock interaction as it percolates through and moves towards the water table in this study two 6 m cores from the badain jaran desert nw china were collected to explore this potential using directly extracted moisture pore waters in these unsaturated zone sediments 1 5 moisture by wet weight were directly extracted using immiscible liquid displacement and then analysed for major anions cations and trace elements results show enrichment in pore water chemistry in the top 1 2 m where strong temperature and moisture fluxes occur the enrichment in cations relative to chloride is primarily due to silicate mineral dissolution during infiltration high nitrate and low iron concentrations indicate the overall oxidizing environment which allows the mobility of oxyanions such as uranium arsenic and chromium the trace elements show enrichment in the upper zone of fluctuation where chemical gradients are strong but with lesser reaction lower in the profile the calculated groundwater recharge rates using the chloride mass balance are negligible in this arid region between 1 5 and 3 0 mm year the modern rainfall infiltration signature contrasts with that of the underlying groundwater body which has a distant regional recharge signature this reconnaissance study demonstrates the potential for a new geochemical approach to studying geochemical processes in the unsaturated sediments in semi arid environments due to both natural and human influences the use of directly extracted water rather than extraction by dilution elutriation facilitates an improved understanding of hydrological and geochemical processes in the unsaturated zone and into the capillary fringe at the water table because it avoids potential chemical changes induced during elutriation

mid to late holocene climate evolution of the lake telmen basin north central mongolia based on palynological data abstract palynological and sedimentological data from lake telmen in north central mongolia permit qualitative reconstruction of relative changes in moisture balance throughout the mid to late holocene the climate of the atlantic period 7500 4500 yr ago was relatively arid indicating that lake telmen lay beyond the region of enhanced precipitation delivered by the expanded asian monsoon maximum humidity is recorded between 4500 and 1600 cal yr b p during the subboreal 4500 2500 yr ago and early subatlantic 2500 yr present periods additional humid intervals during the medieval warm epoch 1000 1300 a d or 950 650 ago and the little ice age 1500 1900 a d or 450 50 yr b p demonstrate the lack of long term correlation between temperature and moisture availability in this region a brief aridification centered around 1410 cal yr b p encompasses a decade of cold temperatures and summer frost between a d 536 and 545 1414 1405 yr b p inferred from records of mongolian tree ring widths these data suggest that steppe vegetation of the lake telmen region is sensitive to centennial and decadal scale climatic perturbations

unsaturated zone tritium and chlorine 36 profiles from southern australia their use as tracers of soil water movement in this paper we present seven unsaturated zone profiles of 36cl and three 3h profiles from southern australia all profiles show single peaks corresponding to high radionuclide fallout from nuclear testing in the 1950s and 1960s the profiles are used to estimate rates of water movement leading to recharge of the groundwater among these profiles is the first profile on which high concentrations of 36cl have been found below a 2 m depth in this profile 3h and 36cl peaks coincide in six of the seven profiles total 36cl fallout was found to be between 1 2 and 2 4 1012 atoms m 2 and is of similar magnitude to that found at similar latitudes in the northern hemisphere comparisons of soil water fluxes estimated with 3h 36cl and chloride are briefly discussed

no 3 sources and circulation in the shallow vadose zone in the edge of dunhuang mingsha sand dunes in an extremely arid area of northwestern china abstract the unsaturated zone is a significant feature of the nitrogen cycle in arid areas connecting atmospheric precipitation and surface water to groundwater to measure no3 cl and nh4 concentrations precipitation samples 39 9592 n 94 3302 e were collected at the western edge of the mingsha sand dunes soil profiles were taken along the northern edge of the dunes to determine no3 and cl concentrations and 18o no3 and 15n no3 levels in soil water the mno3 cl mnh4 cl and nh4 n no3 n values in precipitation showed seasonal variations reflecting the influence of distinct anthropogenic sources the 15n no3 and 18o no3 of the lt profile ranged from 2 38 to 7 84 and 14 72 to 57 5 respectively and that of gc profile ranged from 1 36 to 2 35 and 5 07 to 21 3 respectively these results suggest that the main sources of vadose zone nitrogen in the profiles are no3 fertilizer and nh4 in fertilizer and precipitation all of which are influenced by agricultural sources obvious nitrification and the mixing of different sources were noted but the profiles showed no evidence of denitrification the findings of this study show that migration of no3 and cl in the desert vadose zone is influenced by heavy rainfall events vegetation and evaporation heavy rainfall events promote leaching of no3 and cl into the deep vadose zone while evaporation at the surface prevents leaching and vegetation hinders the downward migration of no3 and cl migration of no3 n and cl in sand dunes is affected by the solute gradient concentration difference of the soil water moving from areas of higher concentrations to lower concentration the no3 n and cl accumulations were 1 02 kg n ha 1 and 3 45 kg ha 1 respectively throughout autumn these were larger than could be attributed to the input flux of atmospheric precipitation especially in the near surface soil layer likely illustrating the influence of atmospheric dry deposition

a 2000 year geochemical record of palaeoclimate and hydrology derived from dune sand moisture abstract chloride concentrations in the interstitial water of the unsaturated zone in dune sands of the badain jaran desert northwestern china have been used to examine the recharge history over the last 2000 years using a chloride mass balance approach the estimated 0 9 mm yr 1 recharge represents approximately 1 of annual precipitation in the western part of the desert and this low but finite infiltration allows preservation of this record the 30 m deep profile yields a total archive equivalent to 2050 years with well preserved climatic events of 30 50 years duration periods of relatively dry years occurred during ad 100 250 350 600 870 1220 1330 1450 1570 1720 1780s and 1900 1970 the unsaturated zone profile provides a robust climate record with a resolution of 20 yr comparable favourably to tree ring and ice core records in this region

climatic or tectonic control on organic matter deposition in the south china sea a lesson learned from a comprehensive neogene palynological study of iodp site u1433 abstract palynomorphs and other organic particles are basic key components of palynofacies yet quantitative analyses of all types are rarely used together to investigate organic matter assemblage changes and evaluate the driving forces behind the observed changes in this paper eight organic walled microfossil and particle morphologies sporopollen pediastrum concentricystes fungi dinoflagellate cysts structured amorphous organic matters stomatal apparatus and scolecodonts are tabulated and their concentrations and fluxes are evaluated over the past 17 million years ma in sediments recovered from the south china sea at international ocean discovery program iodp site u1433 overall these morphologies show roughly similar increasing trends but with different levels of fluctuations the uniform increase in all morphologies at 8 ma named the 8 ma event is the most notable feature of the past 17 ma to explain the trend and because these various organic matters reflect various environmental conditions we argue that the uniformity of the signal implies that tectonically driven basin and drainage evolution played the key role rather than paleoclimate asian summer monsoon the 8 ma event was likely triggered by the onset of the mekong river in its present location although the role of monsoon evolution cannot be excluded completely

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

late holocene temperature fluctuations on the tibetan plateau abstract proxy data of palaeoclimate like ice cores tree rings and lake sediments document aspects of climate changes on the tibetan plateau during the last 2000 years the results show that the tibetan plateau experienced climatic episodes such as the warm intervals during ad 800 1100 and 1150 1400 the little ice age between ad 1400 and 1900 and an earlier cold period between the 4th and 6th centuries in addition temperatures varied from region to region across the plateau a warm period from ad 800 to 1100 in the northeastern tibetan plateau was contemporaneous with cooling in the southern tibetan plateau which experienced warming between ad 1150 and 1400 large scale trends in the temperature history from the northeastern tibetan plateau resemble those in eastern china more than the trends from the southern plateau the most notable similarities between the temperature variations of the tibetan plateau and eastern china are cold phases during ad 1100 1150 1500 1550 1650 1700 and 1800 1850

spatial distribution of chloride and nitrate within an unsaturated dune sand of a cold arid desert implications for paleoenvironmental records abstract based on chloride mass balance approach we used two tracers cl and no 3 to study the interstitial water in four profiles of an unsaturated dune sand the aim was to reconstruct the recharge history and use this to infer the long term related climate changes and vegetation transitions in a cold arid desert region of northwestern china the estimated recharge rate of 0 21 to 0 59 mm year 1 represented approximately 0 2 to 0 7 of the annual precipitation in the western badain jaran desert the orientation of a megadune s slopes appeared to greatly affect recharge variability below the near surface peaks the total cumulative no 3 n inventories ranged from 61 to 121 kg ha 1 the near surface peaks in no 3 n with larger no 3 n cl molar ratios reflected active modern n fixation by cyanobacteria and the nitrate enrichment deeper in the unsaturated moisture zone indicated drier periods with less vegetation limited nitrate fixation or a combination of the two

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

geostatistical characterization of soil moisture and chloride distribution in deep vadose profiles of the badain jaran desert northwestern china geostatistical analysis of soil moisture and ion accumulation can provide a deep understanding of aspects of a region s hydrology such as recharge rates and flow paths by combining this approach with detrended canonical correspondence analysis the present study investigated the vertical and spatial variation of soil moisture and chloride cl in vadose profiles of megadunes near lakes in the southeastern badain jaran desert northwestern china soil moisture varied vertically within the dune profiles following exponential logarithmic or log normal distributions at different sites as a result of regulation by different local controls the main local controls for cl concentration were slope and orientation of the dune cl was not affected by local controls at depths 5 m sills of spatial variation in soil moisture and cl in the variogram analysis were highly sensitive to local controls in the top 4 m of the profiles and the values were three times those at depths 4 m the lag for soil moisture was insensitive to local controls and was 50 60 m in the top 4 m of the profiles and 20 m in deeper layers whereas the lag for cl was about 20 m at all depths the results demonstrate that understanding recharge rates using factors such as cl accumulation requires a careful survey to ensure that the local controls that regulate these factors are adequately accounted for

sustainability of groundwater usage in northern china dependence on palaeowaters and effects on water quality quantity and ecosystem health a synthesis of groundwater ages recharge rates and information on processes affecting groundwater quality in northern china highlights the major challenges faced for sustainable management of the region s groundwater direct recharge rates range from hundreds of millimetres per year in the north china plain to tens of millimetres per year in the loess plateau to less than 4 mm year in the arid northwest recharge rates and mechanisms to deep semiconfined and confined aquifers are poorly constrained however on the basis of available data these are likely to be mostly negligible severe groundwater level declines 0 53 m year have occurred throughout northern china in the last three to four decades particularly in deep aquifers radiocarbon dating stable isotope and noble gas data show that the most intensively extracted deep groundwater is palaeowater recharged under different climate and land cover conditions to the present reservoir construction has reduced surface runoff in mountain front areas that would naturally recharge regional quaternary aquifers in many basins in combination with intensive irrigation practices this has resulted in the main recharge source shifting from surface runoff and mountain front recharge to irrigation returns this has reduced infiltration of fresh recharge at basin margins and rapidly increased nitrate concentrations and overall mineralisation in phreatic groundwater over wide areas in some cases to 400 mg l and 10 g l respectively in some basins there is evidence that poor quality shallow water has leaked into deep layers 200 m via preferential flow mixing with palaeowaters stored in semiconfined aquifers high concentrations of naturally occurring fluoride and arsenic locally 8 5 and 4 mg l respectively have recently lead to the abandonment of numerous supply wells in northern china creating further pressure on stressed water resources increasing water demand from direct and indirect consumption poses major challenges for water management in northern china which must consider the full water cycle copyright c 2012 john wiley sons ltd

holocene environmental change inferred from a high resolution pollen record lake zhuyeze arid china a high resolution pollen record c 50 yr sample from terminal lake sediments in the shiyang river drainage basin on the present margin of the summer monsoon was used to reconstruct vegetation and climate history during the holocene forest trees from mountainous areas of the drainage including sabina picea and pinus dominated pollen assemblages in the early holocene 11 6 7 1 cal ka in the mid holocene 7 1 3 8 cal ka desert and steppe shrubs and herbs around the lake including nitraria poaceae compositae and artemisia were dominant the late holocene 3 8 0 cal ka was again dominated by alternation of pinus sabina tree pollen and desert steppe pollen the early holocene forest expansion in the mountains and subsequent increase in the river transport of tree pollen corresponds with maximum precipitation during the east asian summer monsoon maximum the timing of these changes in our record from arid china is different from that of east china where the holocene monsoon maximum appeared in

chloride and the environmental isotopes as the indicators of the groundwater recharge in the gobi desert northwest china the long term recharge in gobi desert from hexi corridor to inner mongolia plateau was estimated to be 1 mm year 1 by using the chloride mass balance method from one unsaturated zone profile which shows that no effective modern recharge is taking place a good rainfall database from zhangye provides definition of the stable isotopic composition of modern rainfall the signature of groundwater from the late pleistocene differs markedly from that of the holocene shown clearly by the compositions of 10 5 18o as compared with values of 7 at the present day it is apparent that the groundwaters in the minqin basin ejina basin and feeding the lake system of the badain jaran are part of a regional flow network related to a wetter past climate as source of recharge the recharge source in the past and to a limited extent in the more arid conditions of the present day included the foothills of the mountains of the tibetan plateau the tritium age determinations accurate to the year are impossible and of no meaning to groundwater studies a tritium value in the groundwater means multiple recharge ages in this region

paleohydrologic implications of some deep soilwater chloride profiles murray basin south australia abstract a chloride mass balance approach to estimating soilwater ages and paleorecharge rates was tested in an area where considerable paleoclimatic data were available for comparison application of the method to data from four cores of the unsaturated zone taken in the western murray basin showed that the soil water at the base of the chloride build up or bulge associated with the root zone of the native mallee vegetation was emplaced during the last glacial interval at least 20 000 years bp furthermore recharge rates at this time were very low these observations agree with independent paleoclimate evidence that suggest that this time was colder windier and drier results are consistent with the notion that the root zone chloride bulge so typical of the murray mallee region developed in response to aridity that peaked during the last full glacial interval in australia the chloride method is a useful tool in paleohydrology especially when used in concert with other evidence

late holocene coupled moisture and temperature changes on the northern tibetan plateau the northern tibetan plateau involves complex interactions between the mid latitude westerly circulation and the subtropical asia monsoon circulation acting as a bridge communicating high and low latitude climatic processes previous studies from the region suggest relatively wet conditions in cold periods during the late holocene for instance the little ice age lia however the inference of such temperature moisture association is subject to the large uncertainty in lacustrine 14c chronology due to the particularly large lake reservoir effect in the region here we take a different approach by reconstructing paired temperature and moisture records from the same sediment cores to assess the temperature moisture association independent of chronology uncertainty we use alkenone indices uk 37 and c37 4 to reconstruct high resolution temperature and moisture changes simultaneously from two lakes in the qaidam basin northern tibetan plateau over the last 2500 years characterized by marked climatic variability our paired records confirm the warm dry and cold wet association in arid northwestern china during the late holocene opposite to the warm wet and cold dry association in subtropical asian monsoonal regions our moisture records further suggest substantially drier conditions during the medieval warm period mwp than the current warm period lastly the temperature and moisture changes inferred from our records can be well correlated with solar irradiance changes suggesting a possible link between solar forcing and natural climate variability during the late holocene on the northern tibetan plateau