penetration of atlantic westerly winds into central and east asia abstract the geographical position of the convergence zone where the western atlantic climate system meets the asian winter monsoonal system depends on their relative strength these individual strengths are determined by the intensities of the air pressure gradients over the north atlantic and the siberian high pressure cell respectively since the factors that forced those gradients varied throughout glacial interglacial cycles the location of the convergence zone should have moved accordingly both the grain size characteristics of wind blown sediments and climate modelling prove that the atlantic influence extended remarkably far eastward at times the northeastern tibetan plateau was at the cross road of western and monsoonal influences during the last glacial this region was dominated by an atlantic signal with millennial scale climatic oscillations that are similar to the north atlantic marine and greenland ice core records in contrast that same region was only under monsoonal influence during the last interglacial it implies that the atlantic winds penetrated more vigorously eastward in full glacial conditions than in interglacial conditions

optically stimulated luminescence osl dating and palaeoenvironmental studies of pan playa sediment from witpan south africa abstract robust dateable sources of palaeoenvironmental proxy data are scarce in the southwestern kalahari desert and this study investigates the potential of pan playa floor sediments as an archive of late quaternary environmental change augering has revealed the presence of up to 3 m of clay and silt rich deposits in the base of witpan a small pan basin set amongst linear and lunette dunes the weakly stratified deposits include aeolian quartz sands and evaporites amongst a clay rich groundmass and are believed to have accumulated on a wetter than present pan surface the aeolian quartz fraction has been dated with optically stimulated luminescence osl and reveals accumulation of at least 50 cm of sediment at around 20 ka and previous accumulation at around 32 ka the northern and southern sections of the pan are shown to maintain some hydrological independence attributed to bedrock outcropping and also show distinct differences in their physical sedimentology biogenic proxies are poorly preserved with neither diatoms nor pollen found in adequate quantities although phytoliths found in both the pan floor sediments and the fringing lunette dune may offer a more resilient palaeoenvironmental indicator the possible value of pan floor sediments as dryland archives of physical and chemical and possibly selected biogenic palaeoenvironmental proxies combined with osl constrained chronologies should not be discounted

palaeo water depth estimation for a 600 year record from nam co tibet using an ostracod based transfer function a modern training set of ostracods from the large slightly saline lake nam co on the southeastern tibetan plateau is presented in total 44 samples covering the largest part of the lake and water depth from 2 to 93 m were taken there are eight ostracod species in surface sediments of nam co leucocytherella sinensis leucocythere dorsotuberosa fabaeformiscandona gyirongensis candona xizangensis candona candida ilyocypris cf mongolica eucypris gyirongensis and limnocythere inopinata in order of mean dominance a morphological variant of l dorsotuberosa the forma postilirata is an indicator form of deep water below the thermocline the 36 samples comprise a sufficient number of ostracods for analysis covering water depths between 3 7 and 89 3 m two transfer function models based on weighted average binomial regression wa br and weighted average partial least square regression wa pls using the programs excel and c2 were established to estimate past water depths of nam co transfer functions were applied to ostracod data from two short cores from nam co covering approximately the past 600 years model results show a lake level minimum occurring during the little ice age lia between about 1490 and 1760 ad this minimum corresponds to results from previous stable isotope analysis and indicates a lake level which was about 5 m below the present day level the more exact transfer function model wa pls was set up using c2 and revealed a higher correlation index r o f 0 91 and a lower standard error of 6 7 m however the more selective because of using indicator taxa only wa br model using excel r 0 88 standard error 10 6 m seems to represent palaeo water depths better at least for the studied short cores

holocene climatic changes revealed by aeolian deposits from the qinghai lake area northeastern qinghai tibetan plateau and possible forcing mechanisms previous palaeoclimatic studies in the northeastern qinghai tibetan plateau netp during the holocene mainly using lake sediments have deepened our understanding of the climatic system in this remote region the timing and forcing mechanisms of climatic change in this region are still controversial however aeolian sand and silt deposits which are widely distributed in the netp can be readily dated by optically stimulated luminescence osl techniques and reveal the sensitive response of the landscape to climatic change in this study aeolian sand and loess at six sites around qinghai lake were studied to reconstruct millennial scale climatic changes during the holocene multiproxy data along with 24 osl age determinations show that low effective moisture and aeolian activity occurred at c 13 ka 10 9 1 ka and 8 9 7 8 ka periods of greater effective moisture may have occurred at 11 ka and 9 ka and there is evidence for a previously undocumented wet climate at 4 3 ka these results show that mi

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

synchronism of holocene east asian monsoon variations and north atlantic drift ice tracers eighteen radiocarbon dated eolian and paleosol profiles within a 1500 km long belt along the arid to semi arid transition zone of north central china record variations in the extent and strength of the east asian summer monsoon during the holocene dated paleosols and peat layers represent intervals when the zone was dominated by a mild moist summer monsoon climate that favored pedogenesis and peat accumulation brief intervals of enhanced eolian activity that resulted in the deposition of loess and eolian sand were times when strengthened winter monsoon conditions produced a colder drier climate the monsoon variations correlate closely with variations in north atlantic drift ice tracers that represent episodic advection of drift ice and cold polar surface water southward and eastward into warmer subpolar water the correspondence of these records over the full span of holocene time implies a close relationship between north atlantic climate and the monsoon climate of central china

early to mid holocene lake high stand sediments at lake donggi cona northeastern tibetan plateau china lake high stand sediments are found in three onshore terraces at lake donggi cona northeastern tibetan plateau and reveal characteristics of hydrological changes on lake shorelines triggered by climate change geomorphological processes and neo tectonic movements the terraces consist of fluvial alluvial to littoral lacustrine facies end member modeling of grain size distributions allowed quantification of sediment transport processes and relative lake levels during times of deposition radiocarbon dating revealed higher than modern lake levels during the early and mid holocene lake levels follow the trend of asian monsoon dynamics and are modified by local non climatic drivers site specific impacts explain fluctuations during the initial lake level rise 11 cal ka bp maximum lake extension reached 9 2 cal ka bp at 16 5 m above present lake level a p l l littoral and lacustrine sediment deposition paused during a phase of fluvial activity and post depositional cryoturbations at 8 5 cal ka bp when the lake level fell to 8 m a p l l after a second maximum at 7 5 cal ka bp lake level declined slightly at 6 8 cal ka bp probably due to a non climatic pulse that caused lake opening the level remained high until a transition towards drier conditions 4 7 cal ka bp though discontinuous high stand sediments provide a unique high resolution archive

playa lake basins on the southern high plains of texas and new mexico part i hydrologic geomorphic and geologic evidence for their development playa lake basins of the southern high plains texas and new mexico may originate wherever water periodically can collect in a surficial depression they expand however by hydrologic and geomorphic processes including 1 dissolution of lithologic carbonates by infiltrating water 2 transport downward of fine grained clastic and organic material by the infiltrating ground water leading to continuing processes of oxidation and carbonate dissolution in the subsurface and 3 eolian removal of clastic material from the floor of playa lakes which at some sites appears to have deepened playa depressions evidence for largely hydrologic processes of playa basin development on the southern high plains includes 1 a geographic occurrence restricted to relatively flat areas of the high plains surface that have poorly developed fluvial drainage and which are underlain by generally unsaturated clastic and calcrete beds 2 a tendency to occur where water collects and infiltrates as along ephemeral streams and lineations suggestive of fracture systems and 3 hydrologic geochemical petrographic and bore hole data which suggest that recharge to the high plains aquifer is principally from playa lakes that various geochemical changes including carbonate dissolution and enhancement of secondary porosity occur as water moves downward through the unsaturated zone beneath playa lakes and that calcrete beds often are missing or significantly dissolved beneath playa floors

ostracod distribution and habitat relationships in the kunlun mountains northern tibetan plateau abstract surface sediment samples were collected from the lakes heihai kusai haiding nuur and yan hu and from streams and ponds in the kunlun mountains at the northern margin of the tibetan plateau to investigate the sub fossil ostracod micro crustacean fauna of the region among 65 collected samples 46 ostracod shell rich samples were used to study the relationship between the ostracod distribution and specific conductivity sc of the water which ranged from 0 6 to 53 0 ms cm 1 a total of eleven ostracod species was identified from this region with about half of the species restricted to the tibetan plateau and its adjacent mountain areas and the other half representing holarctic taxa tonnacypris cf estonica and tonnacypris tonnensis are reported from the tibetan plateau for the first time leucocythere sp is the dominant species and ilyocypris cf bradyi is also relatively abundant the other seven species were recorded with limited abundances apparently due to lower sc tolerances leucocythere sp was recorded over the full sc range from 0 6 to 53 ms cm 1 eucypris mareotica is a typical brackish and saline water species which was found at sample sites with high sc 2 8 53 0 ms cm 1 in contrast leucocythere dorsotuberosa candona candida and eucypris afghanistanensis prefer freshwater to slightly oligohaline waters with sc 1 the sc optimum and tolerance range for each species were determined and compared to earlier reported data from other regions of central asia the results indicate that species assemblage data from fossil ostracod shells have a large potential to provide information on past sc levels and more general climate determined moisture conditions

late holocene forcing of the asian winter and summer monsoon as evidenced by proxy records from the northern qinghai tibetan plateau abstract little is known about decadal to centennial scale climate variability and its associated forcing mechanisms on the qinghai tibetan plateau a decadal resolution record of total organic carbon toc and grainsize retrieved from a composite piston core from kusai lake nw china provides solid evidence for decadal to centennial scale asian monsoon variability for the northern qinghai tibetan plateau during the last 3770 yr intensified winter and summer monsoons are well correlated with respective reductions and increases in solar irradiance a number of intensified asian winter monsoon phases are potentially correlated with north atlantic climatic variations including bond events 0 to 2 and more recent subtle climate changes from the medieval warm period to the little ice age our findings indicate that asian monsoon changes during the late holocene are forced by changes in both solar output and oceanic atmospheric circulation patterns our results demonstrate that these forcing mechanisms operate not only in low latitudes but also in mid latitude regions the northern qinghai tibetan plateau

water salinity and productivity recorded by ostracod assemblages and their carbon isotopes since the early holocene at lake qinghai on the northeastern qinghai tibet plateau china abstract lake qinghai the largest saline lake in china is a closed basin lake with a salinity of 16 g l and is situated in the sensitive semi arid zone between the asian monsoon controlled area and the westerly jet stream influenced area with the support of the international continental drilling program icdp lake qinghai was drilled in 2005 using the icdp glad800 drilling system two ostracod species i e limnocythere inopinata and eucypris mareotica were found only in the upper 5 15 m of the drilled core 1f covering 12 ka where the depths of 5 15 to 3 15 m 12 0 7 4 ka are dominated by e mareotica and the depths of 3 15 to 0 m 7 4 ka present are dominated by l inopinata the presence of the ostracod eucypris mareotica was related to the high salinity of the water exceeding 30 g l and the dominant species of ostracod limnocythere inopinata was related to the brackish water 3 16 g l in the lake qinghai area li et al 2010 the changes in the carbon isotope in the modern ostracod shells were related to the water salinity and productivity on the lake bottom in lake qinghai li et al 2012 on this basis this study evaluated the changes in lake salinity and productivity and their relation to climatic change using changes in the relative abundances of ostracod fossil species assemblages and the stable carbon isotope in ostracod shells from core 1f and other published data e g total organic carbon content 13 c toc and ice core 18 o the single occurrence of ostracod eucypris mareotica and the highest average 13 c values 0 2 in their shells indicated that the lake salinity and productivity were very high a phenomenon that was related to the high temperature and low lake level caused by intense evaporation even though the precipitation increased sharply in the early holocene the deceased abundance of ostracod e mareotica and the lowest average 13 c values 2 0 in ostracod shells showed that the lake salinity and productivity decreased because of the increased lake level and decreased temperatures in the middle holocene finally the lake level decreased but the water salinity and the lake productivity gradually increased because of the high e i ratio related to the increased temperature in the late holocene

holocene environmental variations recorded by organic related and carbonate related proxies of the lacustrine sediments from bosten lake northwestern china we reconstructed a multiproxy record of the holocene climate changes from a 9 53 m core from bosten lake in the southern xinjiang of northwestern china based on a chronology supported by nine ams 1

a 14 ka high resolution δ18o lake record reveals a paradigm shift for the process based reconstruction of hydroclimate on the northern tibetan plateau abstract the influence of the mid latitude westerlies mlw competing with the asian summer monsoons asm over the tibetan plateau tp remains a matter of discussion on how and to which extent both atmospheric systems have been controlling hydro climate during the holocene depleted oxygen isotopes in lake deposits were commonly interpreted in terms of enhanced summer monsoon moisture supply implying a migration of the asm deep into the interior of the plateau during holocene periods in order to test this relationship we used a high resolution oxygen isotope record mean 20 yr resolution in combination with carbonates and mineral phases titanium flux grain size and ostracod abundances derived from a 6 84 m long sediment core in the endorheic kuhai lake basin north eastern tp the results confirm 1 continuous positive co variance between enriched 18ocarb and total carbonates during the last 14 ka indicative of dominant seasonal influence on multi decadal to centennial scale isotopic signatures in lake water and respective carbonate precipitation 2 negative co variance between allochthonous sediment flux and 18ocarb and carbonates attributed to relative increase of flux rates during non summer seasons 3 correspondence of lake level variations with carbonate mineral phases and the occurrence disappearance of ostracod assemblages and 4 inverse relationships between isotopic signatures in asm dominated and mlw controlled lake records across the tp enriched 18ocarb in kuhai lake sediments was primarily a result of high evaporation during the summer seasons while asm related rainfall amount did not play an important role likely counterbalanced by isotopic signatures from different water sources conversely depleted 18ocarb was mainly attributed to water supply during non summer seasons of colder temperatures and generally light isotopic signatures from mlw derived sources this finding may lead to a paradigm shift in such way that depleted 18o in carbonates is primarily not the result from asm related rainfall as previously assumed the reconstructed hydro climatic history of kuhai lake indicates the dominance of westerly derived climate during the younger dryas interval 12 8 11 5 ka under very shallow pond like conditions despite climate amelioration during the early holocene 11 5 7 5 ka hydrological conditions remained unstable with frequent alternations between dominance of summer and winter seasons during the middle holocene 7 5 5 5 ka the lake experienced highest lake levels dominated by summer monsoon related water supply assigned to the holocene hydro climatic optimum frequent high amplitude fluctuations afterwards 5 1 2 9 ka refer to cooling drying events under enhanced mlw influence accompanied by a strong lake level decline the late holocene 2 9 ka present period experienced moderate isotopic variations and fluctuating lake levels in response to variable influence of summer or winter related hydro climatic conditions this seesaw like pattern with amplitudes of 10 in 18ocarb resembles fluctuations in cave records and variations between air and seawater dole effect high correspondence with cooling events derived from north atlantic drift ice and meltwater discharge indicate close ties to northern hemispheric climate transmitted by the mlw across the tp

complex holocene lunette dune development south africa implications for paleoclimate and models of pan development in arid regions closed depressions pan or playa basins are very common landscape features in arid or formerly arid regions many have associated downwind dune assemblages lunettes that have been explained in terms of deflation of sediments from the basin these widespread features have also been used as proxies of late quaternary rainfall and atmospheric circulation change we use a detailed program of optically stimulated luminescence dating at witpan south africa to show that lunette construction may be rapid and spatially complex this study presents 33 ages from 9 sample sites on the dune that show how accumulation of the present dune largely occurred over the past 2 k y but with marked sectoral variability in accumulation rates and timing variability is attributed largely to local sediment supply factors geochemical analysis shows that primary deflation from the pan has not contributed significantly to the construction of much of the current lunette most sand is derived from recycling of older lunette sediments preserved today at only a few locations and from neighboring linear dunes these findings if representative of lunettes in other localities have marked implications for the types of paleoclimatic information that these features may yield

comparison of particle size characteristics of the tertiary red clay and pleistocene loess in the chinese loess plateau implications for origin and sources of the red clay the origin of the tertiary red clay underlying the pleistocene loess in the chinese loess plateau remains controversial although several lines of evidence have suggested a wind blown origin this study examines the particle size parameters of the late miocene and pliocene red clay by comparing it with those of the late pleistocene loess the particle size distribution of a total of 15 339 loess and 6394 red clay samples taken from 12 loess sections along a north south transect and two red clay sequences at lingtai and jingchuan was systematically analysed the median grain size skewness and kurtosis of the late pleistocene loess all show a systematic southward change and are principally influenced by distance from source region the spatial and temporal differentiation of dust deposits is expressed in a skewness kurtosis median grain size ternary diagram from which the distance to the source region can be inferred the particle size characteristics of the tertiary red clay sediments are very similar to those of the palaeosols within the late pleistocene loess deposits suggesting an aeolian origin for the red clay based on the comparison of red clay and loess in the ternary diagrams it is inferred that the source sink distance was greater in the neogene than in the last and penultimate interglacials and that the dust source region in north western china underwent a progressive expansion during the period from at least 7ae0 ma to the present

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

hydroclimatic changes in china and surroundings during the medieval climate anomaly and little ice age spatial patterns and possible mechanisms abstract investigating hydroclimatic changes during key periods such as the medieval climate anomaly mca 1000 1300 ad and the little ice age lia 1400 1900 ad is of fundamental importance for quantifying the responses of precipitation to greenhouse gas induced warming on regional and global scales this study synthesizes the most up to date and comprehensive proxy moisture precipitation records during the past 1000 years in china and surroundings the proxy data collected include 34 records from arid central asia aca and 37 records from monsoonal asia our results demonstrate a pattern of generally coherent regional moisture variations during the mca and lia in mid latitude asia north of 30 n monsoonal northern china north china and northeast china was generally wetter while aca northwest china and central asia was generally drier during the mca than in the lia a west east mode the boundary between wetter northern china and drier aca was roughly consistent with the modern summer monsoon boundary in monsoonal china to the east of 105 e the northern part was generally wetter while the southern part was generally drier during the mca than in the lia a north south mode with a boundary roughly along the huai river at about 34 n these spatial patterns of moisture precipitation variations are also identified by instrumental data during the past 50 years in order to understand the possible mechanisms related to the moisture variations during the mca and lia we investigate the major sst and atmospheric modes e g the el nino southern oscillation enso the atlantic multidecadal oscillation amo and the north atlantic oscillation nao which affect the moisture precipitation variations in the study region using both the instrumental data and the reconstructed time series it is found that the enso may play an important role in determining hydroclimatic variability over china and surroundings on a multi centennial time scale and that the foregoing spatial patterns could be attributed to the la nina like el nino like condition during the mca lia in addition amo and nao may also have their own contributions

late holocene isotope hydrology of lake qinghai ne tibetan plateau effective moisture variability and atmospheric circulation changes a sub centennial resolution record of lacustrine carbonate oxygen isotopes 18oc from the closed basin lake qinghai on the ne tibetan plateau shows pronounced variability over the past 1500 years changes in 18oc in hydrologically closed lakes are often interpreted in terms of changing effective moisture under this interpretation our record would imply increasing effective moisture during the little ice age lia compared to the medieval warm period mwp however independent evidence from other archives strongly suggests the asian summer monsoon was stronger during the mwp and weakened during the lia controls other than effective moisture the balance of water inputs over evaporative loss must therefore have contributed to the 18oc values we propose the lia signal in lake qinghai resulted from a reduction in evaporation caused by colder air temperatures coupled with a decrease in oxygen isotope composition of input waters as a result of an increase in the relative importance of westerly derived precipitation our results caution against simplistic interpretations of carbonate oxygen isotope records from hydrologically closed lakes and suggest all possible controlling factors must be taken into account in order to avoid misleading palaeoclimatic reconstructions

last deglacial and holocene lake level variations of qinghai lake north eastern qinghai tibetan plateau qinghai lake is of significance for paleoclimate research because it lies in a pivotal region that is influenced by both the mid latitude westerlies and the low latitude asian summer monsoon asm most published lake level histories of qinghai lake are interpreted from drill core proxies here we combine geomorphic shoreline investigations with optically stimulated luminescence dating to constrain lake level variations since the last deglacial the results indicate that two periods of highstands occurred during the last deglacial approximate to 16 14 9 and approximate to 12 6 12 2 ka and that lake levels were 6 7 4m higher than at present lake levels dropped abruptly during the younger dryas and were generally low with frequent fluctuations during the early holocene qinghai lake reached its highest holocene level 9 1m higher than modern at approximate to 5 ka and has regressed during the past 2 ka we propose that high lake levels during the last deglacial were due mainly to melting glacial and permafrost waters supplemented by enhanced westerlies precipitation and decreased evaporation during heinrich event 1 approximate to 16 14 9 ka and increased asm rainfall during the bolling allerod warm period approximate to 14 12 ka lake level fluctuations during the holocene were generally in accordance with moisture variations in the marginal monsoon zones of inland china

reduced early holocene moisture availability in the bayan har mountains northeastern tibetan plateau inferred from a multi proxy lake record abstract a late glacial and holocene lake sediment record from the northeastern tibetan plateau was investigated using ostracod and geochemical analysis after lake koucha was established about 16 cal ka bp oligohaline conditions gradually converted to mesohaline conditions about 10 cal ka bp clearly suggesting that the water body was a closed basin lake from about 10 cal ka bp the salinity of the lake rose continuously until hyperhaline levels were reached about 7 5 cal ka bp this increase in salinity was accompanied by a falling lake level extreme rainfall and flooding events in a generally dry climate hit the shallow saline lake around 8 5 cal ka bp causing a unique thin gravel containing layer within the continuous fine grained lake sediments the age control of our record does not allow us to correlate this event exactly to the widely recorded 8 2 cal ka bp event however the recovered sediments from lake koucha provide strong evidence that climate changes around 8 5 cal ka bp had significant environmental implications in northeastern tibet after about 7 3 cal ka bp the available moisture significantly increased causing a continuous salinity decline until the present day freshwater conditions of a through flow lake were established about 6 5 cal ka bp in lake koucha this major shift from a shallow saline to a deeper freshwater lake was probably accompanied by a fundamental change from a macrophyte dominated to a phytoplankton dominated lake a slight reduction in available moisture in comparison to the periods before and afterward was recorded between 4 3 and 2 0 cal ka bp in phase with numerous records from monsoonal asia the reconstructed overall change in moisture availability from dry conditions before about 7 3 cal ka bp to wetter conditions afterwards contradicts most palaeoclimate records from the tibetan plateau and its surroundings which show that wetter conditions in the early holocene were replaced by drier and probably cooler conditions in the mid and late holocene however in the semi arid region of lake koucha with a mean annual precipitation of about 500 mm the insolation driven strengthened monsoon in the early holocene may have resulted in a temperature rise and higher evaporation rates which outweighed the increase in precipitation and therefore led to significantly lower moisture availability our record provides further evidence for a regionally non uniform response of the available moisture evolution to the overall monsoonal signal in the holocene climate history of central asia

chronologies for late quaternary barchan dune reactivation in the southeastern arabian peninsula abstract the liwa region of the united arab emirates contains some of the largest and most areally extensive megabarchanoid sand dunes on a global scale here we present optical dating results on samples of aeolian sediment from deep drill cores extracted from the largest dune field of the liwa area optical dating of these core sediments using the single aliquot regeneration protocol indicates mid late holocene phases of rapid dune deposition the most recent period of reactivation began at ca 2 8 ka this event was preceded by a period of deposition at ca 5 ka these results suggest that the dune systems of the southeastern arabian peninsula are closely linked to changes in late quaternary global climate particularly linked to the intensity and spatial extent of palaeomonsoon rainfall since the last precessional maxima at ca 9 ka at which time a peak in monsoonal rainfall has been recognised a significant environmental transition to widespread desert conditions occurred in an apparently abrupt fashion during the initial period of aridification large quantities of sand were transported and deposited in the form of large and very large up to 160 m high scale aeolian bedforms following the initial phase of aeolian accumulation the system appears to have remained in stasis

late quaternary lacustrine ostracoda and their implications for hydro climatic variation in northeastern tibetan plateau abstract ostracoda from non marine waters have a significant potential role in monitoring ecological conditions and reconstructing paleoenvironments during the last decades the increase in research on ostracods on the tibetan plateau tp has been achieved although there are still taxonomical and ecological problems in their application in quaternary studies the aim of this review is to summarize the occurrences of ostracods in surface samples from four selected lakes qinghai lake lake donggi cona lake kuhai and hala lake along the modern monsoon marginal zone on the northeast tibetan plateau and to compare the ostracod associations in sediment cores from different sites with available proxy data after re evaluation of chronologies in order to reconstruct hydroclimatic conditions and monsoon influence during the late quaternary comprehensive reanalysis of ostracod data from selected lakes including 3 closed and 1 open lake basins on the northeastern tp shows that their occurrence and disappearance responded sensitively to salinity and related water depth changes during the late quaternary this could lead to a re interpretation of other proxy data related to hydro climatic interpretation ostracod based reconstructions of lake level changes along the modern summer monsoon marginal zone of the northeastern tp during the late quaternary indicate an overestimation of the contribution from monsoonal rainfall to strong lake level changes while the glacier snow meltwater supply was underestimated in previous studies this inference sheds more light on moisture source and the interplay between westerlies and asian summer monsoon on the northern tp

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

methanogenic pathways 13c isotope fractionation and archaeal community composition in lake sediments and wetland soils on the tibetan plateau 1 lakes are a significant source of atmospheric ch4 and play an important role in the global carbon cycle little information on methane production in high altitude lakes is available we determined the methanogenic archaeal community composition the methanogenic pathways and carbon isotope fractionation in lake sediments and wetland soils on the tibetan plateau at about 4000 m above sea level asl we measured ch4 production rates and the 13c of co2 ch4 and acetate in the presence and absence of methyl fluoride an inhibitor of acetotrophic methanogenesis in sediments of five lakes awong co bangong co gongzhu co daze co and ranwu and wetland soils adjacent to bangong co and ranwu methane in bangong co sediment and in the wetland soil near ranwu was mainly produced by acetotrophic methanogenesis whereas methane in the sediments of the two saline lakes awong co and gongzhu co was mainly generated by hydrogenotrophic methanogensis chemolithotrophic acetogenesis and methanol dependent methanogenesis may also have played a role the stable carbon isotope fractionation during ch4 production from co2 was relatively large average e 78 the methanogenic communities were similar to those found in lowland lake sediments but those of saline and nonsaline tibetan lakes differed hydrogenotrophic methanogens were dominant in lake sediments while acetotrophic methanogens were dominant in wetland soils our results revealed diversity in the methanogenic communities and their methanogenic pathways and indicated that they are affected by sediment characteristics such as salinity however the ch4 production rates ranging from 6 to 122 nmol day 1 g dry weight 1 showed no relationship to environmental characteristics and were not limited by microbial abundance

late quaternary lake level fluctuations in the mababe depression middle kalahari palaeolakes and the role of zambezi inflows abstract a systematic drilling and optical dating programme on middle kalahari beach ridge relict shoreline sediments has enabled the identification of multiple episodes of lake high stands of an extensive palaeolake system at the terminus of the okavango delta northern botswana this paper presents 23 ages from the mababe depression and establishes four shoreline construction phases in the late quaternary coeval with other sub basin lake high stands lake ngami these synchronous lake phases result from a coalescence of the sub basins into a unified palaeolake lake thamalakane covering an area of 32 000 km2 six additional ages are also presented from the chobe enclave to the north of the basin where shoreline ridges were emplaced at the same time as lake thamalakane phases this suggests that increased flow in the chobe and zambezi system significantly contributed to the middle kalahari lake phases in both the post glacial and holocene periods the integration of these new data and their compatibility with other regional and tropical palaeo archives is discussed in the light of understanding quaternary climate drivers within the kalahari

late cenozoic climate changes in china s western interior a review of research on lake qinghai and comparison with other records abstract we review late cenozoic climate and environment changes in the western interior of china with an emphasis on lacustrine records from lake qinghai widespread deposition of red clay in the marginal basins of the tibetan plateau indicates that the asian monsoon system was initially established by 8 ma when the plateau reached a threshold altitude subsequent strengthening of the winter monsoon along with the establishment of the northern hemisphere ice sheets reflects a long term trend of global cooling the few cores from the tibetan plateau that reach back a million years suggest that they record the mid pleistocene transition from glacial cycles dominated by 41 ka cycles to those dominated by 100 ka cycles during terminations i and ii strengthening of the summer monsoon in china s interior was delayed compared with sea level and insolation records and it did not reach the western tibetan plateau and the tarim basin lacustrine carbonate 18 o records reveal no climatic anomaly during mis3 so that high terraces interpreted as evidence for extremely high lake levels during mis3 remain an enigma following the last glacial maximum lsm several lines of evidence from lake qinghai and elsewhere point to an initial warming of regional climate about 14 500 cal yr bp which was followed by a brief cold reversal possibly corresponding to the younger dryas event in the north atlantic region maximum warming occurred about 10 000 cal yr bp accompanied by increased monsoon precipitation in the eastern tibetan plateau superimposed on this general pattern are small amplitude centennial scale oscillations during the holocene warmer than present climate conditions terminated about 4000 cal yr bp progressive lowering of the water level in lake qinghai during the last half century is mainly a result of negative precipitation evaporation balance within the context of global warming

hydro climatic and lake change patterns in arctic permafrost and non permafrost areas this paper investigates patterns of lake area and hydro climatic change in arctic river basins and possible influence of permafrost change reflected in such patterns a salient change pattern eme

wetland evolution in the qinghai lake area china in response to hydrodynamic and eolian processes during the past 1100 years abstract the daotanghe riverine wetland in close proximity to the qinghai lake was investigated to demonstrate the interrelationships between qinghai lake hydrodynamic processes eolian mobility and ecological conditions during the past 1100 years in response to climate change we used ostracod assemblages from various sites east of qinghai lake and from the sediment core qw15 of daotanghe pond and combined them with grain size and geochemical data from the same core the statistical extraction of grain size endmembers em revealed three different transportation processes responsible for pond related fluvio lacustrine pure fluvial and eolian deposits identified seasonal effects eolian mobility phase and timing of ice cover are possible tracers for the competing influence between the asian summer monsoon and the westerlies in the daotanghe wetland and surrounding area our results show that ostracod associations and sediment properties are evidence of a fluvio lacustrine fresh water environment without ingression of qinghai lake into the wetland hydrodynamic variations coupled with phases of eolian input indicate highly variable water budgets in response to climate induced effective moisture supply the medieval warm period mwp until about 1270 ce displays generally moist and warm climate conditions with minor fluctuations likely in response to variations in summer monsoon intensity the three partite period of the little ice age lia shows hydrologically unstable conditions between 1350 and 1530 ce with remarkably colder periods assigned to a prolonged seasonal ice cover pond desiccation and replacement by fluvial deposits occurred between 1530 and 1750 ce superimposed by eolian deposits the phase 1730 1900 ce is recorded by the re occurrence of a pond environment with reduced eolian input principal component analysis pca on ostracod abundances shows similar trends all three phases of the lia developed during a weak summer monsoon influence favoring westerly derived climate conditions until ca 1850 ce in accordance with records from the adjacent regions seasonal freezing periods in excess of the average time of frozen water bodies also occurred in periods of the well known grand solar minima and indicate stronger seasonality possibly independent from variations in summer monsoon strength but with links to global northern hemispheric climate

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

the onset of dune formation in the strzelecki desert south australia abstract this study is concerned with the late quaternary climatic chronology of the strzelecki desert dunefields in central australia the sand ridges comprise layers of quartz sand some of which include palaeosol horizons with carbonated rootlets providing excellent opportunity for dating of alternations of dune building and stability by using optically stimulated luminescence osl deduced from the osl age of the oldest aeolian layer dated we conclude that the onset of aridity dates back to at least 65 ka older phases of aeolian activity though following a fluvial depositional phase 160 ka ago cannot be excluded although no aeolian layers giving evidence for this have been found in the two dunes dated here unconsolidated dune sands in the upper part of one section with late holocene 4 ka to modern depositional ages indicate a reactivation of the dunefield in recent times from the crosscheck of 14 c ages of the carbonated rootlets with osl results it is concluded that under the given environmental conditions radiocarbon dating of the calcareous rootlets is not able to provide reliable ages for the phase of soil development

late holocene geochemical history inferred from sambhar and didwana playa sediments thar desert india comparison and synthesis abstract the sambhar and didwana playas from the eastern margin of the thar desert annual precipitation of 300 450 mm have been investigated for mineralogy major and trace element geochemistry of near surface sediments geochemical data and evaporite mineralogy of sediments from the playa surface and shallow depths provide insight to the present day geochemical processes and the different vertical phases of pore water activity detrital minerals from both the playas reflect igneous and metamorphic source rocks in their catchments the zeolite type mineral analcime naalsi 2 o 6 h 2 o is assumed to be authigenic in origin a product of chemical reaction between the hypersaline brine and detrital feldspars the evaporite mineralogy is dominated by halite calcite and dolomite major differences between the evaporite mineralogy of the surface sediments of two playas are the occurrence of trace amounts of the h 2 o bearing carbonate trona na 3 h co 3 2 2h 2 o in the didwana and k and mg bearing sulphate and chloride minerals e g polyhalite k 2 mgca 2 so 4 4 2h 2 o carnallite kmgcl 3 6h 2 o and sylvite kcl in the sambhar based on the distribution of major and trace elements the surface sediments from both playas are divided into three geochemical zones fed by river and rainwaters the playa surfaces show enrichment of insoluble cations and hydrolysates in the outermost zone and soluble oxides and cations in the innermost zone further the shallow depth profiles are also divided into distinct geochemical zones based on the elemental ratios the sub recent zone i reflects low chemical weathering and higher aeolian input the middle zone ii indicates relatively higher weathering index and zone iii enriched in evaporites also shows low chemical weathering despite the fact that the sambhar and didwana are separated only by 50 km they show significant differences in terms of evaporite mineralogy and inorganic composition of surface sediments we interpret this to be a manifestation of local variations in precipitation inflow and aeolian influx

late quaternary water depth changes in hala lake northeastern tibetan plateau derived from ostracod assemblages and sediment properties in multiple sediment records abstract late pleistocene and holocene climate dynamics along the marginal belt of the east asian summer monsoon in china and their responses to hydrological cycles in lake basins of the tibetan plateau are still a matter of scientific discussion hala lake a closed 65 m deep lake basin in the western qilian mountains qinghai province is considered a monitor of climate driven hydrological and environmental changes during the past 24 kyr bp the distribution patterns of ostracod assemblages stable isotopes sediment geochemical properties in four sediment records from different water depths and their combination with the unique limnological setting enabled us to reconstruct four major phases of centennial scale water depth fluctuations from the global last glacial maximum ca 24 kyr bp to the present our results show that hala lake experienced a very shallow and small water body during the lgm and lateglacial under cold and dry climate conditions rapid increase of water depth and contemporaneous lake expansion started at around 14 kyr bp phase i most likely as a result of glacier melt due to the onset of climate warming the lake reached 45 m water depth at around 13 5 kyr bp reduced water depth during the younger dryas spell ca 12 kyr bp may be attributed to a short term return to cooler and drier conditions during the early holocene phase ii water depth increased further toward lake highstands close to its present level with a highest lake level of up to 9 m above the present lakestand at 8 0 7 8 kyr bp besides continued glacier melt supply we assume that summer monsoon effective moisture contributed to the overall water budget but remained relatively unstable favoring water depth fluctuations a pronounced lower water depth falls into the period between 9 2 and 8 1 kyr bp perhaps the result of weak monsoon influence or its complete absence although the warming trend continued toward its optimum at ca 8 7 kyr bp a distinct mass flow most likely triggered by an earthquake occurred during a lake lowstand either at ca 7 0 kyr bp or at around 8 1 kyr bp the mid holocene phase iii was characterized by fluctuating water depths between 7 8 and 4 5 kyr bp conflicting trends of stable isotope data limit the validity of water depth estimations but may show higher lake levels between 5 5 and 4 5 kyr bp coincident with dated lake sediments in a cliff position at the northern lake shore this positive water balance can most likely be attributed to increased westerly derived moisture supply during autumn and late winter although summer monsoon influence could also be of significance coincident with the 4 2 ka event the lake experienced shallow water at around 4 1 kyr bp perhaps as a result of continued cooling and drier climate conditions supporting the arguments of a general cooling trend throughout the holocene the late holocene phase iv is characterized by extremely unstable hydrological conditions with rapid fluctuations in water depth more frequently controlled by westerly driven effective moisture supply since the lake lowstand at about 1 4 1 2 kyr bp the lake has developed toward its present level our research underlines the necessity for comparing multiple proxy records from different lake sites to better evaluate centennial scale climate driven variations throughout the late pleistocene and holocene periods all presented data suggest the variable influence of summer monsoon effective moisture on the hydrological budget of the lake water depth variations did not follow the long term pattern of the asian monsoon system due to a potential modulation by westerly derived moisture impact

stable isotopic variations in west china a consideration of moisture sources 1 in this study individual precipitation samples collected over 2 years at stations in different climatic regions of west china tibetan plateau region tianshan region and altay were analyzed for the stable isotopes of precipitation to improve our understanding of how vapor transport impacts the modern stable isotopic distribution our results identify regional patterns in both 18o and deuterium excess d excess defined as d 8 18o and in particular we have identified the northward maximum extent of the southwest monsoon over the tibetan plateau this demarcation is also the boundary for the fractionation effect of temperature on stable isotopes in precipitation the patterns we have identified are as follows 1 in the southern tibetan plateau along the southern slope of the himalayas our results show a distinct seasonality for both 18o and d excess as a result of the shift of summer monsoon moisture and winter westerly moisture transport the signals of 18o in the western tibetan plateau reveal that the region receives southwest monsoonal moisture in the east of the plateau stable isotopic variation shows alternation between monsoon intrusion and recycling of northern moisture 2 in contrast in tianshan there is an apparent temperature effect in 18o with enriched values occurring in summer and depleted values occurring in winter seasonal d excess values opposite to those observed in the southern tibetan plateau are controlled by differing seasonal evaporation conditions 3 in altay the most northern mountain region the seasonal 18o shows the same variation with that in tianshan region however d excess shows no apparent seasonal variation

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the tibetan plateau abstract aeolian sediments are an important archive for palaeoclimate reconstructions on the tibetan plateau the accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases respectively during the last decade the number of osl optically stimulated luminescence ages of aeolian sediments has been rapidly increasing this study summarises the results from more than 300 individual osl ages despite the widespread occurrence of aeolian sediments on the tibetan plateau nearly all osl samples are located on the northeastern and the southern part in most regions the strongest accumulation occurred during the late glacial and in the early holocene this coincides with the strengthening of the asian summer monsoon on the tibetan plateau and wetter climate conditions after the relatively dry glacial times the development of a sufficient vegetation cover acting as a sediment trap seems to be an important requirement for the preservation of aeolian archives short dry periods like the younger dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions the formation of palaeosols occurred mainly during the wet early and mid holocene but the number of ages is relatively small in contrast a second phase of aeolian accumulation during the late holocene was related to the weakening of the asian summer monsoon and drier climate conditions this indicates that the reaction of aeolian accumulation on the tibetan plateau depends on the previous climate state a comparison between the osl ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types while the sand deposits in different basins resemble wet and dry phases loess deposits show no common signal between the analysed areas this indicates an influence of local factors such as varying source areas and erosive processes on the slopes in general the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence

early to mid holocene lake high stand sediments at lake donggi cona northeastern tibetan plateau china comment to the paper published by dietze et al quaternary research 79 2013 325 336

a 100 ka record of water tables and paleoclimates from salt cores death valley california abstract sedimentary and petrographic features of evaporites and associated sediments from a 185 m deep core taken in death valley ca together with uranium series dating have been used to reconstruct the history of water table fluctuations and climate changes in death valley for the past 100 ka death valley has been arid during the holocene 0 10 ka with predominantly mudflat and saline pan subenvironments a perennial lake up to 90 m deep existed in death valley from 10 to 35 ka saline pan and mudflat subenvironments dominated death valley from 35 to 100 ka the chronology of changing subenvironments and water table fluctuations in death valley generally correlates with other climate records in the western us owens lake and searles lake ca browns room cave calcite nv the marine oxygen isotope record and the vostok ice core record core intervals through saline pan sediments are composed of interbedded halite chaotic muddy halite and mud the halite contains abundant vertical dissolution pipes cemented with clear halite these sediments record repeated flooding by dilute waters dissolution of subaerially exposed surface salt crusts deposition of mud from suspension precipitation of halite during the saline lake phase and cementation by diagenetic halite mudflat sediments consist of clayey silt with sand patches and mud cracks which document long periods of desiccation and the formation of efflorescent salt crusts from the evaporation of groundwater brines saline pan and mudflat deposits formed during periods when death valley was relatively arid similar to the modern climate lacustrine deposits consist of mudhalite cycles accumulated during the early lake stage bedded thenardite na 2 so 4 and mud above and a cap of massive halite formed during the latest lake stage all of which record fluctuating salinities and lake levels in a perennial system such deposits document a relatively wet climate with a high ratio of water inflow to evaporation ostracodes in mud layers represent the least saline deepest lake phases halite layers are made of fine grained cumulates and clear vertically oriented crystals precipitated during shallower perennial lake stages of significance is the nearly complete absence of syndepositional dissolution of saline minerals in the lacustrine interval indicating that accumulated salts were permanently protected from dissolution by saline lake waters such evidence strongly suggests that lakes existed continually without desiccating for 25 ka between 10 and 35 ka b p

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

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

late pleistocene wetting and drying in the nw kalahari an integrated study from the tsodilo hills botswana abstract the sediments and landforms at the tsodilo hills in the northwestern kalahari desert provide an opportunity to directly investigate the late quaternary wetting and drying of the region from evidence at a single site lacustrine carbonates including incorporated molluscs and diatoms a lake shoreline feature and stabalised linear dunes were investigated for their constituent palaeoenvironmental signals chronometric control is provided by calibrated 14 c ams and osl dating the evidence suggests that linear dune construction has not occurred since the last glacial maximum with particular development from 36 to 28 ka lake stands indicating wetter regional conditions than present occurred at 40 32 ka with more seasonal conditions from 36 ka and at 27 12 ka with a possible drying out at 22 19 ka data are consistent with other independent studies from the region and with recent evidence obtained from atlantic cores off the coast of namibia it is concluded that careful consideration of multi proxy data from a single location can assist in resolving discrepancies that arise from independent studies of lake cave and dune records in the kalahari

u series chronology of lacustrine deposits in death valley california uranium series dating on a 186 m core dv93 1 drilled from badwater basin in death valley california and on calcareous tufas from nearby strandlines shows that lake manly the lake that periodically flooded death valley during the late pleistocene experienced large fluctuations in depth and chemistry over the last 200 000 yr death valley has been occupied by a long standing deep lake perennial shallow saline lakes and a desiccated salt pan similar to the modern valley floor the average sedimentation rate of about 1 mm yr for core dv93 1 was punctuated by episodes of more rapid accumulation of halite arid conditions similar to the modern conditions prevailed during the entire holocene and between 120 000 and 60 000 yr b p from 35 000 yr b p to the beginning of the holocene a perennial saline lake existed over 70 m at its deepest a much deeper and longer lasting perennial lake manly existed from about 185 000 to 128 000 yr b p with water depths reaching about 175 m if not 330 m this lake had two significant dry excursions of 102 103yr duration about 166 000 and 146 000 yr b p and it began to shrink to the point of halite precipitation between 128 000 and 120 000 yr b p the two perennial lake periods correspond to marine oxygen isotopic stages ois 2 and 6 based on the shoreline tufa ages we do not rule out the possible existence 200 000 yr ago of yet a third perennial lake comparable in size to the ois 6 lake the234u 238u data suggest that u in tufa owes its origin mainly to ca rich springs fed by groundwater that emanated along lake shorelines in southern death valley and that an increase of this spring water input relative to the river water input apparently occurred during ois 6

distribution patterns of gypsum and kalistrontite in a dry lake basin of the southwestern kalahari omongwa pan namibia the deposits of the omongwa pan southwestern kalahari namibia are partly gypsiferous and locally contain small amounts of kalistrontite the distribution patterns of gypsum caso4 2h2o and kalistrontite k2sr so4 2 are mainly determined by groundwater depth and by the lithological composition of the deposits the latter determines the hydraulic conductivity for saturated and unsaturated flow and therefore controls the depth of the interval within the deposits where evaporation and mineral precipitation can take place other factors that affect the distribution of the evaporite minerals are the patterns of groundwater flow within the basin and the occurrence of a redistribution of salts during short flooding stages gypsum occurs as crystals of four distinct morphological types which each developed in different conditions prismatic crystals formed both as subaqueous precipitates and as crystals that developed within the sediment matrix of a brine saturated surface layer sub euhedral tabular crystals formed within brine filled macropores hemi bipyramidal crystals formed in a nearly permanently brine saturated part of a subsurface horizon phreatic zone as the product of recrystallization of an older gypsum occurrence and lenticular crystals formed by intrasediment growth in the vadose zone the development of these morphological types of gypsum crystals is marked by differences in the differential inhibition of growth of the various crystal forms the further growth of lenticular crystals which are most strongly affected by differential growth inhibition is still characterized by a difference in degree of inhibition between the 111 and 103 forms expressed as a change in orientation of the plane of flattening copyright 1999 john wiley sons ltd

lake level variations of qinghai lake in northeastern qinghai tibetan plateau since 3 7 ka based on osl dating abstract qinghai lake is the largest internally drained lake in china and its unique location makes it sensitive to climate changes late glacial climate changes associated with variation in qinghai lake levels have been intensively investigated for the past 40 years with particular attention paid to lake level fluctuation histories between the last interglacial and the holocene however the details of lake level fluctuations during the holocene are still unclear using both optically stimulated luminescence osl dating of quartz for 22 samples and infra red stimulated luminescence irsl of feldspars only for sample hyw1 whose irsl age is 37 15 years a total of 23 samples are dated from paleoshoreline deposits fluvial sediments and aeolian sands a total of 13 sections near the modern lake shore with ages from 37 15 to 3710 350 years these ages are used to reconstruct the lake level fluctuation history spanning the last 3700 years the results indicate that 1 the youngest irsl age of 37 15 years is in agreement with the independent age of 39 29 years suggesting that luminescence dating is able to date decadal samples for sediments from the study area 2 the lake experienced several oscillations imposed on an overall regressive trend during the past 3700 years 3 the dated paleoshoreline deposits are generally related to warm and wet periods suggesting that those shoreline deposits formed during cold and dry periods if any may have been modified by later transgressions 4 lake level fluctuations during the period of 3700 240 years ago are generally consistent with the climate conditions identified in other proxies with the highest lake level occurring about 1770 years ago and 5 after 240 years ago the lake level dropped more rapidly which is inconsistent with the proxy records showing a warmer and wetter phase

evaluation of oxygen isotopes in carbonate as an indicator of lake evolution in arid areas the modern qinghai lake qinghai tibet plateau abstract the oxygen isotopic composition of carbonate in lakes has been used as a useful indicator in palaeolimnological research and has made some important contributions to our understanding of lacustrine systems for modern lakes in arid or cold areas however there are few data available to test the effect of lake salinity and temperature on the oxygen isotopic composition of various carbonate sources such as ostracod bulk carbonate and fine grained carbonate for arid high altitude lake qinghai our results suggest that variations in the 18o values of carbonate in lake qinghai are mainly controlled by the oxygen isotope ratio of the lake water changing with water salinity as a secondary effect increasing water depth leads to cooler bottom and surface water which may result in more positive 18o values of ostracod and bulk carbonate

late quaternary paleoenvironments in the southwestern kalahari abstract landforms of the southwestern kalahari in southern africa include linear dune systems pans and associated lunette dunes and the valleys of ephemeral rivers present day climates in the region are transitional from arid to semi arid making the area sensitive to climatic change the linear dunes are part of an extensive system of fixed dunes developed in the surface kalahari sands the dunes were in existence prior to 32 000 yr b p but have been reactivated on a number of occasions since then in conditions of increased wind velocities more nw winds and reduced rainfall especially in northern and eastern parts of the region periods of dune activity probably occurred at 19 000 17 000 10 000 6000 and 4000 3000 yr b p the development of pans in the region has been strongly influenced by changes in groundwater conditions deflation from pans and formation of lunettes occurred in periods when groundwater levels were higher and fluctuated seasonally more than they do today such periods probably occurred 25 000 20 000 yr b p around 10 000 yr b p and just prior to 1000 yr b p still higher groundwater discharges promoted by increased regional rainfall resulted in the formation of spring tufas and seasonal or permanent lakes in the pans which were also fed by surface runoff during the intervals between 33 000 28 000 23 000 21 000 17 000 15 000 and 12 000 11 000 yr b p the headwaters of the major ephemeral streams lie outside the region but within the same climatic zone increased flow in the molopo river occurred prior to 19 000 and between 15 000 and 13 000 yr b p

an environmental tolerance index for ostracodes as indicators of physical and chemical factors in aquatic habitats abstract continental ostracode occurrences reflect salinity solute composition temperature flow conditions and other environmental properties of the water they inhabit their occurrences also reflect the variability of many of these environmental parameters environmental tolerance indices etis offer a new way to express the nature of an ostracode s environment as defined herein etis range in value from zero to one and may be calculated for continuous and binary variables for continuous variables such as salinity the eti is the ratio of the range of values of salinity tolerated by an ostracode to the total range of salinity values from a representative database in this investigation the database of continuous variables consists of information from 341 sites located throughout the united states binary etis indicate whether an environmental variable such as flowing water affects ostracode presence or absence the binary database consists of information from 784 sites primarily from illinois usa etis were developed in this investigation to interpret paleohydrological changes implied by fossil ostracode successions eti profiles may be cast in terms of a weighted average or on presence absence the profiles express ostracode tolerance of environmental parameters such as salinity or currents tolerance of a wide range of values is taken to indicate shallow water because shallow environments are conducive to thermal variability short term water residence and the development of currents from wind driven waves

a 106ka paleoclimate record from drill core of the salar de atacama northern chile abstract a 100 m long salt core sqm 2005 from the salar de atacama northern chile 23 s 68 w a dry lake bed contains a 106 kyr paleoclimate record of hydrologic balances on the western slopes of the central andes of south america six u series disequilibrium dates range sequentially from 106 1 6 4 to 5 4 2 7 ka based on sedimentary structures and petrographic textures of salts and associated siliciclastic sediments interpretations of paleoenvironments and net hydrologic balance suggest that relatively wet periods saline lakes and expanded mudflats existed in the salar de atacama from 75 7 to 60 7 ka and from 53 4 to 15 3 ka with the wettest perennial lake interval from 26 7 to 16 5 ka short relatively wet periods also occurred in the holocene from 11 4 to 10 2 ka and from 6 2 to 3 5 ka these wet periods at salar de atacama correspond well with other late pleistocene climate records from the central andes that are a function of the net hydrologic budget the minchin tauca lake sequence from salar de uyuni bolivia is synchronous with the 53 4 15 3 ka saline lake wet period at salar de atacama the tauca phase coincided with the wettest perennial lake interval at salar de atacama from 26 7 to 16 5 ka the coipasa lake phase from uyuni was probably contemporaneous with the early holocene wet period at salar de atacama from 11 4 to 10 2 ka the early holocene wet interval at salar de atacama was also synchronous with the maximum holocene lake levels of the chilean altiplano lakes to the east and with grass rich rodent middens between 11 8 and 10 5 ka in age from the atacama basin the lake period at salar de atacama between 26 7 and 15 3 ka compares closely with low 18o values low anion concentrations and high accumulation rates from the sajama glacial ice core southwestern bolivia between 25 and 15 5 ka it is concluded that wet and dry phases were synchronous in the central andean plateau of southwestern bolivia and along the western flank of the andes of northern chile over the past 50 kyr this region which today receives its moisture from the amazon basin to the east probably also did so in the past the wet periods at salar de atacama are in phase with january insolation maxima at 15 s at 70 45 and 20 ka which suggests that past changes in summer insolation influenced precipitation patterns in the central andes however there are no major wet periods linked to the january insolation maximum at 93 ka and the present day extremely dry climate in the atacama desert is associated with a peak in summer insolation therefore there must be other important influences over precipitation in the central andes which modify the first order insolation controls

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

dry periods on the ne tibetan plateau during the late quaternary abstract environmental conditions on the tibetan plateau are changing rapidly this study reconstructs late quaternary environmental changes on the northeastern tibetan plateau based on sand deposits the study area is located close to the present maximum extent of the east asian summer monsoon and is likely to register shifts in monsoon extent furthermore different sediment deposits are available that allow reconstruction of sediment pathways between the different archives sediment deposition in the catchment is dominated by deposition of sand sandy deposits in the form of dune fields and sand sheets are widespread on the northeastern tibetan plateau and are an important archive for paleoclimatic reconstruction this study shows that sand deposits on the northeastern tibetan plateau are local phenomena that still bear the sedimentological and geochemical fingerprint of their source materials reconstruction of transport processes in the local sediment cascade shows that local sand deposits are the main source of tibetan mountain loess six long sections were sampled and analysed for their geochemical and sedimentological characteristics showing that both sand and loess deposits have a local source a special focus was placed on the manganese concentration and the related environmental implications in several sections an increase in mn concentration from 318 44 to 878 294 ppm was found independent of concentrations in fe and organic compounds since the increase in mn is caused by solid mn3 and mn4 alone it is interpreted as increased dust input the synchronicity with climatic variations on the northeastern tibetan plateau confirms the climatic interpretation of the variations in mn sand and dust transport both took place around 11 ka followed by a period of fixation or even erosion of sediments although increased sand transport in the catchment already started around 3 ka the increased dust input did not take place before 0 7 ka therefore the mn concentrations are interpreted as an indication of increased dust transport during the very late holocene related to colder and drier circumstances during that time the use of manganese as a proxy for dust is a valuable addition to the toolbox of paleoclimate reconstruction since it is a direct proxy of dust in deposits however further validation and testing should be performed before general acceptation of mn as a paleoclimate proxy in terrestrial sediments

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

holocene fluctuations of lake ngami middle kalahari chronology and responses to climatic change abstract lake ngami a 3000 km 2 basin at the distal end of the okavango delta botswana has a complex suite of shorelines ranging from the lake sump at 919 m asl up to 945 m asl linked to topographic thresholds and inflows current and fossil in the okavango system the lake has been ephemeral throughout the 20th century and completely dry since 1982 yet held a substantial body of water up to a level of 930 m asl when visited by european travellers in the mid nineteenth century the historical decline in the lake has been well documented and used as evidence for regional desiccation but the holocene record based on archaeological studies and radiocarbon dating of inorganic carbonates is more speculative a study of a 30 km 2 diatomite at the eastern end of the basin indicates that a substantial freshwater lake at a level of at least 932 m asl was present throughout the holocene linked to a now abandoned inflow of the kunyere river a programme of 18 luminescence age determinations of the peripheral dautsa and magotlwanen shoreline sequences suggests that they are old features that have been constructed on a lacustrine substrate dating back to 90 100 ka or earlier and have been modified by holocene fluctuations in lake level and subsequent aeolian reworking the water level peaked at 936 m asl between 4 and 3 ka returned to 934 m at 2 8 2 ka ponding water into the phatane gap and fell rapidly thereafter to 932 m and thence to historical levels the 936 m level can be correlated with increased throughflow in the okavango delta hence increased rainfall in the catchment the subsequent decline can be attributed to episodic closure and rerouting of okavango distributaries in particular the thaoghe perhaps aided by anthropogenic activities as such the desiccation of the lake is not indicative of regional climatic change

paleosalinity from trace metals in fossil ostracodes compared with observational records at devils lake north dakota usa abstract the chemistry of closed basin lakes responds directly to the hydrologic budget through evaporative concentration of dissolved salts and the sediments of these basins contain several excellent fossil and geochemical proxies for past changes in water chemistry and salinity the trace metal content of ostracode shells among the most promising of these paleosalinity methods is further explored in this study of mg and sr partitioning in candona rawsoni a widespread ostracode of the north american great plains the molar distribution coefficients kd mg and kd sr for this species k d mg ca caco 3 0 004 mg 2 ca 2 h 2 o 9 68 10 5 t c k d sr sr ca caco 3 sr 2 ca 2 h 2 oz 0 406 are determined from laboratory experiments in which c rawsoni are cultured under controlled temperatures and salinities our formulation of kd mg contains a correction term for excess mg that is incorporated into the shell during early calcification the accuracy of the distribution coefficients is tested against field collections of live ostracodes from a suite of 12 dakota lakes the kd inferred values for mg2 ca2 h2o and sr2 ca2 h2o are in close accord with the same ratios measured in the lakes a comparison of ostracode reconstructed and historically measured salinities for devils lake north dakota shows good agreement within the salinity range preferred by c rawsoni 1 10 0 although salinity excursions beyond this optimum are poorly represented in the sedimentary record in most lakes salinity is more readily inferred from mg ca h2o than sr ca h2o because sr solubility is a complex function of several carbonate phases as shown for devils lake sr ca h2o may not vary systematically with the salinity of some brines

total organic carbon isotopes a novel proxy of lake level from lake qinghai in the qinghai tibet plateau china abstract the isotopic compositions of total organic carbon toc in lakes have been widely used to interpret paleoclimatic changes and the depositional environments of lake sediments however the main factors that affect the carbon isotopes of toc source of organic material water condition and others may vary in different lake sediment records which have limited the applicability of organic carbon isotopes in explaining biogeochemical and environmental changes in lakes in this study the organic carbon isotopic compositions of aquatic plants and surface sediments from lake qinghai and the living terrestrial plants and surface soils around the lake were systematically investigated to identify the sources of toc in the sediments and the significance of the organic carbon isotopes of sedimentary toc we found that the aquatic plants in the deep water areas 10 m were primarily dominated by cladophora but submerged plants potamogeton and ruppia l are the dominant species in shallow water 13 c org values 33 6 to 28 6 that are caused by c 3 like photosynthesis but the submerged plants have enriched 13 c org values 17 8 to 15 4 that are caused by c 4 like photosynthesis in addition the 13 c org values of cladophora become more negative with increasing water depth because of the slow photosynthetic rate caused by the weak light intensity at depth the isotopic data indicate that the carbon isotopes of organic material in the surface sediments are primarily controlled by the types of aquatic plant and that the 13 c org values of toc can be used to indicate the variation of the water depth lake level the organic carbon isotopic data from the 1f core showed that the water was shallow

time marker of 137cs fallout maximum in lake sediments of northwest china abstract caesium 137 137cs has no natural source and is commonly employed in establishing the chronology of recent lake sediments in the anthropocene epoch because of their location in the northern mid latitude westerlies circulation region downwind of the chernobyl accident and their proximity to the lop nur chinese nuclear testing cnt site lake sediments in nw china record a137cs fallout maximum of global atmospheric thermonuclear weapon tests gtwt in 1963 1964 common era ce with probably local fallout subpeaks due to the chernobyl accident in 1986 ce and cnt in 1976 ce this complexity means that the use of 137cs fallout maximum in lake sediments as a time marker in nw china is thus far not well constrained impeding assessment of recent and future changes in paleoclimate and human activities to identify the 137cs time marker and provide a reliable chronology of surface lake sediments for investigating paleoclimatic changes and for defining the anthropocene epoch in nw china during the last 50 100 years here we describe chronologies of 6 near surface sediment cores from nw china based on 137cs and 210pb activities and review the chronology of 23 lake sediments and 10 ice cores from nw china and central asia based on 137cs 210pb 239 240pu 3h 241am and beta activity dating methods and annual layer counting as well as 240pu 239pu isotopic ratios based on the potential influence of radioactivity transport from the chernobyl accident and cnt and the comparison with deposition records of 26 european lake sediments and 5 alpine ice cores we propose that the 137cs fallout maximum of lake sediments in nw china and central asia is primarily attributable to gtwt and that there is no unambiguous evidence to confirm the chernobyl and cnt derived 137cs local fallout subpeaks taking into account the approximately one year delay between injection of 137cs into the atmosphere and its incorporation in lake sediment records we conclude that the 137cs fallout maximum in lake sediments of nw china provides a reliable gtwt time marker for 1964 ce

environmental dose rates and radioactive disequilibrium from some australian luminescence dating sites abstract determination of geological archaeological ages by luminescence dating requires the measurement of the rate of delivery of radiation dose from the sample and its environment for all age determinations it is necessary to assess whether the dose rate has been constant during the time that the dose has been accumulating and to make allowance for it if it was not we report here results from a number of australian sites to illustrate the information that can be found about element concentrations about their distribution and about dose rates tests for radioactive disequilibrium form part of these measurements such tests take the form of comparison of independent measurements of dose rates and or individual elements in general there is little or no evidence for disequilibrium in aeolian dune systems even when the age of the system exceeds 500 ka however disequilibrium has been found in several sites subject to wet conditions

late glacial and holocene development of lake donggi cona north eastern tibetan plateau inferred from sedimentological analysis abstract sediments of lake donggi cona on the northeastern tibetan plateau were studied to infer changes in the lacustrine depositional environment related to climatic and non climatic changes during the last 19 kyr the lake today fills a 30 8 km big and 95 m deep tectonic basin associated with the kunlun fault the study was conducted on a sediment core transect through the lake basin in order to gain a complete picture of spatio temporal environmental change the recovered sediments are partly finely laminated and are composed of calcareous muds with variable amounts of carbonate micrite organic matter detrital silt and clay on the basis of sedimentological geochemical and mineralogical data up to five lithological units lu can be distinguished that document distinct stages in the development of the lake system the onset of the lowermost lu with lacustrine muds above basal sands indicates that lake level was at least 39 m below the present level and started to rise after 19 ka possibly in response to regional deglaciation at this time the lacustrine environment was characterized by detrital sediment influx and the deposition of siliciclastic sediment in two sediment cores upward grain size coarsening documents a lake level fall after 13 cal ka bp possibly associated with the late glacial younger dryas stadial from 11 5 to 4 3 cal ka bp grain size fining in sediment cores from the profundal coring sites and the onset of lacustrine deposition at a litoral core site 2 m water depth in a recent marginal bay of donggi cona document lake level rise during the early to mid holocene to at least modern level in addition high biological productivity and pronounced precipitation of carbonate micrites are consistent with warm and moist climate conditions related to an enhanced influence of summer monsoon at 4 3 cal ka bp the lake system shifted from an aragonite to a calcite dominated system indicating a change towards a fully open hydrological lake system the younger clay rich sediments are moreover non laminated and lack any diagenetic sulphides pointing to fully ventilated conditions and the prevailing absence of lake stratification this turning point in lake history could imply either a threshold response to insolation forced climate cooling or a response to a non climatic trigger such as an erosional event or a tectonic pulse that induced a strong earthquake which is difficult to decide from our data base

present day lunette sediment cycling at witpan in the arid southwestern kalahari desert abstract witpan is a pan depression in the southwestern kalahari desert the pan fringing lunette dune has a number of notable characteristics a highly active crest the lower lunette pediment is cemented and the lower lunette supports a highly developed and active gully system geomorphological and sedimentological considerations are used to evaluate the interaction of wind and water in shaping contemporary lunette processes it is considered that like other pans in the area groundwater activity influences pan floor sediment availability and transport that the present highly sea sonal climatic regime permits the interaction of aeolian transport of sediment to the dune and its return to the pan floor by water during storm events creating a cycling process favoured by sedimentary properties that promote surface runoff

200 k y paleoclimate record from death valley salt core a 186 m long core dv93 1 from death valley california composed of interbedded salts and muds contains a 200 k y record of closed basin environments and paleoclimates interpreted on the basis of sedimentology ostracodes homogenization temperatures of fluid inclusions in halite and correlation with shoreline tufa the 200 k y paleoclimate record is dominated by two dry and or warm and wet and cold cycles that occurred on a 100 k y time scale these cycles begin with mud flat deposits 192 ka to bottom of core and 60 ka to 120 ka wetter and or colder conditions produced greater effective moisture saline pan and shallow saline lake evaporites overlie mud flat sediments 186 ka to 192 ka and 35 ka to 60 ka eventually enough water entered death valley to sustain perennial lakes that had fluctuating water levels and salinities 120 ka to 186 ka and 10 ka to 35 ka when more arid conditions returned mud flat deposits accumulated on top of the perennial lake sediments completing the cycle 120 ka and 10 ka of particular significance are the major lacustrine phases 10 ka to 35 ka and 120 ka to 186 ka oxygen isotope stages 2 and 5e 6 which represent markedly colder and wetter conditions than those of modern death valley of the two major lake periods the penultimate glacial lakes were deeper and far longer lasting than those of the last glacial

an absolute chronology for the raised beach and associated deposits at sewerby east yorkshire england the raised beach sediments revealed in the cliffs at sewerby east yorkshire are widely regarded as ipswichian in age previously reported evidence for this dating is reviewed and new results from a range of luminescence dating techniques applied to the blown sand deposit overlying the raised beach are reported these provide the first absolute date for the sewerby site of 120 84 11 82 ka which places the blown sand at the boundary between oxygen isotope stages ois 5e and 5d as the underlying raised beach is little older than the blown sand it probably formed during ois stage 5e as suggested by the faunal evidence

abrupt changes in indian summer monsoon strength during the last 900 years and their linkages to socio economic conditions in the indian subcontinent abstract abrupt shifts in indian summer monsoon ism precipitation largely affected regional hydrometeorology accelerating socio economic and cultural adaptations of agrarian economies in south asia in the last millennium linking ism variability to human history in the indian subcontinent is still limited by the scarcity of high resolution paleoclimatic data for the period encompassing the last 1000 years or earlier we present a new high resolution oxygen isotope proxy record from the wah shikar cave northeastern india and identified abrupt shifts in the ism that had profound impact on human societies during the last 900 yrs the ism was strong during the medieval climate anomaly mca and the current warm period cwp and show multiple shifts during the little ice age lia the abrupt shifts in the ism were more frequent during warm intervals showing a secular trend with few exceptions during the cold periods intervals of prolonged summer monsoon weakening are correlated to the decline of major dynasties in india possibly due to decrease in agriculture productivity declining economy and societal crisis changes in atmospheric temperature due to volcanic eruptions and sun spot activity have played major role in the onset of the lia and other prolonged weak intervals of the ism during the last 900 yrs

morphodynamics and lake level variations at paiku co southern tibetan plateau china abstract proxy records from lakes on the tibetan plateau are commonly used to infer monsoon related climatic changes during the late quaternary specific influences of catchment processes and their interaction with the lake basin are seldom utilized based on morphological field investigations supported by remote sensing analyses in combination with radiocarbon dated sediment data from lacustrine sequences along paleoshorelines and terraces we can demonstrate that close relationships exist between glacier dynamics fluvial alluvial fan terrace formation and lake level and lake area changes of paiku co southern tibet our results show that the formation of large scale fluvial alluvial fans f1 predates the maximum advance of the xixiabangma glaciers the latter formed a distinct terminal moraine complex north of the present glaciers during the local lgm llgm at 42 21 cal ky bp a younger fan generation f2 developed from the llgm to the late holocene which was accompanied by lake level fluctuations with a generally decreasing trend the highest morphologically traceable lake level at 4665 m asl existed prior to 25 cal ky bp and induced a potential overflow to the neighboring langqiang co and pengqu river a high level also existed during the llgm followed by a minor decline until ca 15 cal ky bp owing to reduced meltwater discharge under cold and dry climatic conditions a return to the previous level during the late glacial early holocene period between 11 9 and 9 5 cal ky bp is likely caused by climate warming increased meltwater discharge and enhanced indian summer monsoon ism moisture supply afterwards paiku co shrank gradually toward its present level while the youngest fan f3 generation evolved as individual small sized bodies under ephemeral discharge conditions from the mid holocene to the present the formation of four terrace levels t4 1 is likely the result of sequential incision into the fan generations with a mean erosion rate of 50 cm ky caused by lake level lowering tectonic impact cannot be completely ruled out since 1976 the glaciers lost ca 15 in area accompanied by lake area loss of 3 7 between 1972 and june 2014 seasonal lake level variations of about 1 2 m in height occur in response to summer monsoon rainfall our data show a close interaction between glacial dynamics fluvial processes terrace formation and water budget changes throughout the last 25 cal ky bp in response to the well known insolation driven ism effective moisture supply during the late glacial and holocene period temperature driven meltwater dynamics were the controlling factors for variations in water balance of paiku co

an end member algorithm for deciphering modern detrital processes from lake sediments of lake donggi cona ne tibetan plateau china abstract deciphering significant sedimentological processes from a set of sediment samples is an important step in reconstructing environmental changes one approach going beyond classical methods is the unmixing of grain size distributions this paper presents a flexible end member modelling algorithm that is based on eigenspace analysis and considers inherent uncertainties it has been applied to the detrital grain size components of lacustrine surface sediment samples of lake donggi cona qinghai province china it allows up to five grain size end members to be characterised and quantified in an optimal model an end member with a major mode in the clay domain accounts for 34 of variance within the grain size data set it may represent sedimentation of suspension load from linear and laminar runoff during heavy precipitation events in summer three end members in the fine sand to medium silt domains make up 60 of lacustrine sedimentation they may represent local to remote aeolian processes that peak in wintertime a multimodal end member explaining the remaining 6 of variance may represent further fluvial and littoral dynamics or random fluctuations and measurement errors several model runs of different scaling and numbers of end members provided a suitable way to determine uncertainties inherent to the model a comparison of 12 different model runs and their respective uncertainties yielded a distinct model of robust end members the clay and medium silt end members are robust features of detrital sedimentation within lake donggi cona they alone explain 54 4 of total variance in the data however no spatial pattern or relation to water depth is found for any of the grain size end members thus when past detrital sedimentation at lake donggi cona is reconstructed a special focus should be on the robust features attributed to aeolian and suspension related sedimentation processes as well as on effective sediment mixing processes impeding a distinct correlation between grain size and spatial attributes further applications of the end member modelling algorithm to other depositional environments are encouraged to demonstrate its universal applicability

desert paleoenvironmental data from cave speleothems with examples from the chihuahuan somali chalbi and kalahari deserts abstract pollen bearing lake bog and spring sediments are relatively scarce in many arid and semiarid regions of the world and few are dateable beyond the 14c range we have obtained pollen spectra from speleothems collected from caves in the somali chalbi and kalahari deserts suggesting that these deposits may be an important future source of desert paleovegetation data as cave speleothems can be dated by the 230th 234u method to c 350 000 yr b p and by the tl and esr methods potentially to 1 m y b p and can sometimes give paleotemperature and paleohydrologic data they could provide a first glimpse of desert paleoenvironments during isotope stages 4 9 ages of speleothems from the chihuahuan kalahari and somali chalbi deserts suggest that there was more available moisture in the southwestern u s a and in northwestern bostwana during glacials and interstadials of the last c 300 000 years but that wetter conditions in the horn of africa corresponded with interglacials and perhaps to a lesser extent with interstadials pollen from three northern somalia speleothems indicate more mesic conditions in the horn of africa at 10 000 11 800 and 176 500 yr b p while speleothem pollen spectra from matupi cave in northeastern zaire presently surrounded by tropical rainforest suggest a savanna grassland at this cave c 14 000 yr b p

linkages between quaternary climate change and sedimentary processes in hala lake northern tibetan plateau china profundal lake sediment cores are often interpreted in line with diverse and detailed sedimentological processes to infer paleoenvironmental conditions the effects of frozen lake surfaces on terrigenous sediment deposition and how climate changes on the tibetan plateau are reflected in these lakes however is seldom discussed a lake sediment core from hala lake 590 km 2 northeastern tibetan plateau spanning the time interval from the last glacial maximum to the present was investigated using high resolution grain size composition of lacustrine deposits seismic analysis along a north south profile across the lake was used to infer the sedimentary setting within the lake basin periods of freezing and melting processes on the lake surface were identified by modis mod10a1 satellite data end member modeling of the grain size distribution allowed the discrimination between lacustrine eolian and fluvial sediments the dominant clay sedimentation slack water type during the global last glacial maximum lgm reflects ice interceptions in long cold periods in contrast to abundant eolian input during abrupt cold events therefore fluvial and slack water sedimentation processes can indicate changes in the local paleoclimate during periods of the lake being frozen when eolian input was minor inferred warm i e similar to 22 7 and 19 5 cal ka bp and cold i e similar to 11 9 and 3 1 5 cal ka bp spells have significant environmental impacts not only in the regional realm but they are also coherent with global scale climate events the eolian input generally follows the trend of the mid latitude westerly wind dynamics in winter contributing medium sized sand to the lake center deposited within the ice cover during icing and melting phases enhanced input was dominant during the younger dryas heinrich event 1 and at around 8 2 ka equivalent to the well known events of the north atlantic realm c 2015 elsevier ltd all rights reserved

playa lake basins on the southern high plains of texas and new mexico part ii a hydrologic model and mass balance arguments for their development hydrologic geologic geomorphic and mass balance data suggest that most of the 30 000 playa lake basins on the southern high plains have developed by a combination of dissolution of caliche and piping of surface material into the unsaturated zone rather than by eolian processes as has generally been stated a conceptual model suggests that particulate organic material much of which is sorbed on smectite clays is carried downward from the surface into the unsaturated zone by recharging water the organic material is oxidized to co 2 which dissolves in the water forms carbonic acid and dissolves lithologic carbonates because organic material is transported and oxidized deep in the unsaturated zone co 2 concentrations are much higher at depth than in the soil zone and recharging water remains thermodynamically subsaturated with respect to carbonates and thus able to dissolve them throughout the unsaturated zone dissolution promotes lithologic instability leading to piping and eluviation of material within the unsaturated zone playa basins expand laterally as recharge is concentrated at the edge of the playa floor because of lowered permeability in the center that results from accumulation of clays and other fine sediment mass balance calculations of gas liquid and solid fluxes beneath a playa basin suggest that sufficient mass is transported to account for the volume of the depression particulate flux is estimated by relating it to the co 2 flux out of the unsaturated zone solute flux is estimated from the difference between input values from the playa lake water and that observed in ground water gas flux is measured directly from gas samples at specific depths below the surface

lake eyre palaeohydrology from 60 ka to the present beach ridges and glacial maximum aridity lake eyre is presently an ephemeral playa lake in an extremely large 1 3 million km2 internal drainage basin with most of its inflow derived from monsoon watered northern australia the hydrologic state of the lake has varied in the past in response to climate change from a perennial lake up to 25 metres deep to a groundwater controlled playa marked by substantial sediment deflation this paper is concerned with the stratigraphic record of the last 60 ka of that hydrologic history particularly the character and age of a playa marginal unit formed by deflation from the playa and of stranded high beach ridges a major deflation episode between 60 and 50 ka excavated the present lake eyre basin and deposited a gypsum and clay rich aeolian phase the williams point aeolian unit at a number of sites around the lake after deflation ceased a thick secondary gypsum profile developed on the dune early in oxygen isotope stage 3 evidence for the state of lake eyre at this time is equivocal preliminary results from a substantial suite of amino acid racemization aar analyses of mollusc shell and bird eggshell samples from beach ridges at 5 and 10 m australian height datum ahd suggest that they are oxygen isotope stage 5 in age sedimentologic evidence suggests that it is unlikely that the shells are reworked from older deposits these aar results apparently conflict with early oxygen isotope stage 3 thermoluminescence tl dates from the 5 m ahd beach ridge nanson et al this volume however the age difference is not substantial the calibration of the aar is still at a preliminary stage and only one site was sampled for both techniques further stratigraphic and chronologic work is required to fully assess the apparent discrepancy between about 30 000 and 12 000 yr b p lake eyre was at least as dry as it is today at many sites around madigan gulf a lunette like playa marginal aeolian unit the shelly island unit was deposited during this period formed by material deflated from the playa floor forty ams radiocarbon dates span the period 35 000 to 10 000 yr b p from the shelly island unit 11 and from aeolian sediment close to playa level 29 indicating that the lake was dry during this period this evidence conflicts strongly with 2 tl dates from latest oxygen isotope stage 3 and oxygen isotope stage 2 from the 5 and 10 m ahd beach ridges nanson et al this volume additionally the aar results from the high beach ridges cannot be reconciled with these tl dates after 10 000 yr b p a minor lacustral phase occurred until the modern ephemeral playa regime became established at 3000 4000 yr b p

response of lake catchment processes to holocene climate variability evidences from the ne tibetan plateau abstract investigating the so called third pole environment tpe became a major concern during the last decades since it was recognized that the high altitude region of the tibetan plateau tp is a key area for the understanding of cause effect mechanisms driven by climate change and geodynamic processes studies on the hydro climatic evolution during the late quaternary were mainly carried out by single lake records or alternatively by individual terrestrial sites integrated source to sink studies considering lake catchment interactions were extremely seldom utilized we investigated such relationships in the kuhai basin on the north eastern tibetan plateau and analysed sedimentary processes based on 30 onshore sections and three sediment cores from different locations and water depth in the lake basin grain size variations ostracod assemblages geochemical proxies and absolute dating luminescence radiocarbon 210pb 137cs were applied as key indicators that reveal interacting sediment fluxes under different hydro climatic settings during the younger dryas interval and the holocene our results indicate that wind induced transportation processes and allocation of respective aeolian sands in the catchment are attributed to distinct phases of reduced effective moisture availability during summer time those phases corresponded to weak summer monsoon influence during the younger dryas interval the early holocene 11 6 7 5 ka dry cold interlude dci ca 4 5 3 0 ka dark ages cold period dacp ca 1 8 1 1 ka and the little ice age lia ca 0 6 0 1 ka contemporaneous low lake levels during these periods corresponded with respective aeolian sand flux and variable composition of mixed sediments fluvial and aeolian in lake deposits different flux rates at the core sites could be assigned to local conditions in respect to inflow behaviour of individual drainage systems and nearshore morphology aeolian deposits in the catchment were not always preserved and underwent re mobilisation during succeeding episodes and or erosion during phases of high water availability wetter climatic conditions during the mid holocene ca 7 5 5 1 ka roman warm period rwp ca 2 8 1 5 ka and medieval climate anomaly mca ca 0 9 0 6 ka revealed significant lake level rise due to enhanced river discharge well documented by highest suspended flux rates disappearance of ostracod communities at core sites and very low sand input climate shifts during the holocene were linked to variations in effective moisture supply under the influence of the asian summer monsoon asm and the interplay with the mid latitude westerlies mlw cold dry phases were likely a response to north atlantic climatic anomalies transmitted by the mlw across the tp

luminescence dating of holocene playa sediments of the egyptian plateau western desert egypt abstract this study is part of a multidisciplinary project dealing with the investigation of geoarchaeological sites on the egyptian plateau with the aim of reconstructing the palaeoecological background providing age assessment which put the various results in an age frame that is of special interest here results of one particular section have been selected because of a discrepancy in age determination based on different approaches radiocarbon ages were inconsistent with the age range provided by the archaeological context in this area the underestimation observed is inferred to be caused by poor 14 c sample quality an attempt to overcome this problem was the determination of the depositional ages of the non organic sediments by using optically stimulated luminescence osl equivalent doses of four sediment samples were estimated from osl measurements carried out on sand sized quartz grains using the single aliquot regenerative dose sar protocol dose rates were calculated from neutron activation analysis results from the osl ages obtained we conclude that the sediment sequence exposing an alternation of lacustrine and eolian layers was deposited in a short period of time during the mid holocene mean of osl ages 7 8 ka compared to the 14 c ages the luminescence ages fit better into the archaeological context confirmed by surface dating