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

holocene environmental changes in bangong co basin western tibet part 4 discussion and conclusions abstract a 12 4 m core taken in lake bangong provides a continuous holocene climatic record we summarize information on changes in stable isotope and radiocarbon balances in the lake hydrobiology and vegetal cover in the catchment deduced from detailed analytical results given in the three preceding papers the bangong record is then compared with the environmental history of the neighbouring lake sumxi also constructed from multidisciplinary analyses the two records show a major environmental change at 10 9 5 ka b p attributed to a rapid strengthening of the summer monsoonal circulation which led to wet warm conditions this event was followed by a long term trend toward aridity which culminated around 4 3 ka b p in western tibet maximum monsoon rainfall seems to have occurred from 9 5 to 8 7 ka b p and from 7 2 to 6 3 ka b p as two wet pulses separated by a reversal event centered on 8 0 7 7 ka b p our results broadly agree with the records from lake seling in central tibet and lake qinghai at the plateau s northeastern margin and with palaeoclimatic studies in western china which document conditions wetter and warmer than those of today during the early middle holocene the environmental fluctuations recorded in western tibet appear in phase with climatic changes recognized in tropical north africa suggesting that the 8 0 7 7 ka b p and the 4 0 3 0 ka b p dry events were caused by abrupt disequilibrium in the climatic system

response of δd values of sedimentary n alkanes to variations in source water isotope signals and climate proxies at lake nam co tibetan plateau abstract compound specific d values of sedimentary n alkanes from nam co were compared with oxygen isotope values from three different ice cores of the tibetan plateau and other climate proxies including temperature and solar radiation this enabled estimation of the importance of source water and of environmental factors at the ecosystem scale on variations of the isotopic composition of sedimentary n alkanes the ice core records from dasuopu puruogangri and rongbuk glacier of the past 1000 years recording the source water isotopes show a continuous deuterium enrichment indicating a warming trend or decreased precipitation sedimentary n alkane d values also represent the same general tendency to enrichment in heavier isotopes however the correlation to the 18o values derived from the ice record is very weak the d values of n alkanes agree with known climatic events such as the little ice age and medieval warm period showing depleted and enriched d values respectively the d values of the n alkanes were best related to environmental drivers including temperature and solar radiation the results suggest that d values of sedimentary n alkanes mainly record evapotranspiration and relative humidity that strongly influence d values at the plant level while variability of the source signal is less important

asynchronous holocene climatic change across china a review of holocene climatic variations in different parts of china shows that they were asynchronous proxy data from ice cores pollen loess lacustrine sediments and changes of sea and lake levels demonstrate that many warm and cold oscillations have occurred in china during the holocene including a most important climatic event known as the holocene optimum a milder and wetter period and that the duration and amplitude of the optimum period as well as its start and end times differed in different parts of china uplift of the tibetan plateau over the past millions of years led to the development of the monsoon climate and to complex atmospheric circulation over continental china during the holocene as a result the holocene optimum began and terminated earlier in high altitude regions of western china than at lower elevations in eastern china and the amplitude of the variations was lower in the east this suggests that the western higher altitude areas were more sensitive to climatic change than were the eastern lower altitude areas holocene climatic records in the dunde and guliya ice cores do not correspond inverse 18o variations between the two cores indicate that the effects of climate and atmospheric processes on the stable isotopes at the two sites differed the correlation between the isotopic composition of carbonates in lake deposits in western china and climatic variations is similar to that in the ice cores the climatic resolution in ice cores and lake sediments is higher than that in other media the lack of precise correspondence of climatic records constructed on the basis of proxy data from different parts of china is a result of the different locations and elevations of the sampling sites the different resolutions of the source material and the varied climatic conditions within china further work is needed to confirm both the conclusions and the inferences presented here

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

precise 40ar 39ar age for the initiation of palaeogene volcanism in the inner hebrides and its regional significance sanidine crystals from two tuff layers at the base of the palaeocene eigg lava formation on the isle of muck inner hebrides yield step wise ar release plateau ages of 62 8 0 6 2 and 62 4 0 6 ma using the laser 40 ar 39 ar dating technique these determinations which are in accord with but significantly more precise than earlier results provide a definitive age for the inception of igneous activity in the small isles from stratigraphical inferences the muck ages provide precise maximum constraints on the possible age of skye magmatism and possibly most of the british tertiary volcanic province the new ages significantly predate the oldest ages determined so far for tertiary magmatism in ne greenland but are similar to ages obtained from w greenland and offshore se greenland and support the concept that the initiation of regional volcanism was primarily controlled by lithospheric thin spots the muck sanidine age appears to precisely date the first manifestation of the impingement of the iceland mantle plume on the lithosphere beneath nw scotland

an interpretive analysis of magnetotelluric data a simple analysis to determine the dimensionality of magnetotelluric resistivity variations to separate the near surface resistivity variation from the variations at depth and to find the relative resistivity variations with depth is described parameters derived from the magnetotelluric impedance tensor are mapped in pseudosection and planar view for two dimensional 2 d model data and for survey data from montana these data illustrate procedures that can qualitatively map complex resistivity structures in the lateral distance frequency domain or equivalently the lateral distance scaled vertical distance domain phase dependent parameters have better vertical resolution than parameters related to scalar apparent resistivity but the latter allow estimates of the resistivities encountered phase parameters for the montana data provide a semiquantitatively accurate cross section of a geologically known anticlinal structure this suggests a means of subsurface structural mapping with magnetotelluric data the use of these parameters with sufficiently dense and accurate data provides a first order indication of structure for subsequent quantitative modeling

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

westerly jet stream controlled climate change mode since the last glacial maximum in the northern qinghai tibet plateau abstract climate change from the northern qinghai tibet plateau qtp is affected by the combined effects of the asian summer monsoon and the westerlies however changes in monsoon vapor transport and the westerly jet stream as well as their effect to climate change mode there are not clear at different time scales here we present composite research using paleoclimate reconstructions and ensemble simulations since the last glacial maximum lgm on the basis of an eolian sedimentary sequence in the northern qtp results from 317 surface sediment samples show that pedogenic carbonate 18 o is affected both by precipitation and temperature and organic carbon isotope 13 corg reflects the vegetation growth status in areas where precipitation is greater than 290 mm proxies from the sedimentary sequence and the paleoclimate modeling intercomparison project 3 pmip3 simulations show a close relationship between climate change mode in the northern qtp and the westerly jet stream whose movement is triggered by warm or cold conditions in the high latitude regions that is when the climate is in cold glacial period the westerly jet stream strengthens and moves southward and the mountains become wetter this climate change mode can be validated by records from mountains of north america and africa according to the cmip5 simulations the westerly jet stream will strengthen in the future and climate in the northern qtp and the high altitude region of the mid latitudes will become wetter with global warming

multi decadal periods of enhanced aeolian activity on the north eastern tibet plateau during the last 2ka abstract the north eastern tibetan plateau is regarded as key area for the understanding of the holocene paleoclimate in central asia during the last decade a special emphasis has been placed on multi decadal to millennial scale climate fluctuations especially in the context of the recent climate change however most reconstructions are based on lake sediments tree rings and speleothems whereas only little information from terrestrial archives is included this study presents multi decadal scale climate fluctuations based on optical stimulated luminescence osl ages from aeolian sediments from three catchment areas six phases of enhanced aeolian accumulation during the last 2000 years each lasting around 80 200 years were identified the first three phases 1630 1725 ce 1450 1530 ce and 1250 1350 ce occurred during the little ice age the other three 750 950 ce 390 540 ce 50 225 ce during the so called dark ages cooling aeolian processes were strongly reduced during the medieval climate anomaly a comparison with other proxy records indicates that the formation of aeolian archives on the north eastern tibetan plateau during the late holocene is facilitated by cool and dry climate conditions during times of weaker asian summer monsoon and probably enhanced westerlies the results show that short term climate fluctuations can be reconstructed from non continuous and heterogeneous terrestrial archives in a semi arid environment provided a sufficient number of osl ages from aeolian sediments is available

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

understanding the offshore flood basalt sequence using onshore volcanic facies analogues an example from the faroe shetland basin flood basalts in associated volcanic rifted margins such as the north atlantic igneous province have a significant component of lavas which are preserved in the present day in an offshore setting a close inspection of the internal facies architecture of flood basalts onshore provides a framework to interpret the offshore sequences imaged by remote techniques such as reflection seismology a geological interpretation of the offshore lava sequences in the faroe shetland basin using constraints from onshore analogues such as the faroe islands allows for the identification of a series of lava sequences which have characteristic properties so that they can be grouped these are tabular simple flows compound braided flows and sub aqueously deposited hyaloclastite facies the succession of volcanic rocks calculated in this study has a maximum thickness in excess of 6800 m down to the top of the sub volcanic sediments the offshore volcanic succession has a thickness of about 2700 m where it can be clearly identified across much of the area with a further 2700 m or more of volcanic rock estimated from the combined gravity and seismic modelling to the north and west of the region a large palaeo waterbody is identified on the basis of a hyaloclastite front apron consisting of a series of clinoforms prograding towards the eastern part of the basin this body was 500 m deep must have been present at the onset of volcanism into this region and parts of the water body would have been present during the continued stages of volcanism as indicated by the distribution of the hyaloclastite apron

holocene treeline shifts and monsoon variability in the hengduan mountains southeastern tibetan plateau implications from palynological investigations abstract the upper 8 45 m of a sediment core from lake naleng were analysed for its pollen and charcoal content to detect vegetation climate and human activity changes on the southeastern tibetan plateau tp since the pleistocene holocene transition 11 7 cal kyr bp the application of pollen indicator taxa pollen sums biomisation and multivariate analysis helped to reconstruct environmental conditions during the holocene furthermore 64 surface samples from the southeastern tp and its foreland were analysed to investigate the relationship between modern pollen assemblages and vegetation the modern vegetation was recorded in the surface pollen assemblages by pollen indicator types although sediments also contain pollen spectra extra regional pollen transported from lower vegetation belts which is seen as a consequence of steep elevation gradients at the southeastern margin of the tp the relation between different vegetation belts and temperature from the modern sample sites was used to infer quantitative temperature trends for the holocene record spreading of forests at the beginning of the holocene marks the transition to warmer conditions from 10 7 to 4 4 cal kyr bp open abies betula forests were found at lake naleng probably reflecting a stronger than present summer monsoon temperature range reconstructions suggest a temperature that was about 2 3 c warmer and a treeline position that was 400 600 m higher than today a severe climate deterioration with temperatures about 1 2 c colder than before is documented by a retreating forest between 8 1 and 7 2 cal kyr bp forests retreated while subalpine rhododendron shrubs spread around lake naleng indicating colder conditions with temperatures 1 2 c below early and mid holocene level after 4 4 cal kyr bp the forest decline at 4 4 cal kyr bp is considered to reflect climatic conditions as low concentrations of charcoal particles found in this period exclude human induced fires as reason for the forest retreat however grazing indicators imply human influence on the environment since 3 4 cal kyr bp around lake naleng we therefore consider the rapid treeline shift seen at 3 4 cal kyr bp as partly generated by human activity and partly by climatic conditions

holocene vegetation and climate histories in the eastern tibetan plateau controls by insolation driven temperature or monsoon derived precipitation changes abstract the climates on the eastern tibetan plateau are strongly influenced by direct insolation heating as well as monsoon derived precipitation change however the moisture and temperature influences on regional vegetation and climate have not been well documented in paleoclimate studies here we present a well dated and high resolution loss on ignition peat property and fossil pollen record over the last 10 000 years from a sedge dominated fen peatland in the central zoige basin on the eastern tibetan plateau and discuss its ecological and climatic interpretations lithology results indicate that organic matter content is high at 60 80 between 10 and 3 ka 1 ka 1000 cal yr bp and shows large magnitude fluctuations in the last 3000 years ash free bulk density as a proxy of peat decomposition and peatland surface moisture conditions oscillates around a mean value of 0 1 g cm 3 with low values at 6 5 4 7 ka reflecting a wet interval and an increasing trend from 4 7 to 2 ka suggesting a drying trend the time averaged mean carbon accumulation rates are 30 6 gc m 2 yr for the last 10 000 years higher than that from many northern peatlands tree pollen mainly from picea mostly reflecting temperature change in this alpine meadow forest ecotonal region has variable values from 3 to 34 during the early holocene reaches the peak value during the mid holocene at 6 5 ka and then decreases until 2 ka the combined peat property and pollen data indicate that a warm and wet climate prevailed in the mid holocene 6 5 4 7 ka representing a monsoon maximum or optimum climate for the region the timing is consistent with recent paleo monsoon records from southern china and with the idea that the interplays of summer insolation and other extratropical large scale boundary conditions including sea surface temperature and sea level change control regional climate the cooling and drying trend since the mid holocene likely reflects the decrease in insolation heating and weakening of summer monsoons regional synthesis of five pollen records along a south north transect indicates that this climate pattern can be recognized all across the eastern tibetan plateau the peatland and vegetation changes in the late holocene suggest complex and dramatic responses of these lowland and upland ecosystems to changes in temperature and moisture conditions and human activities

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

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

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

the holocene indian monsoon variability over the southern tibetan plateau and its teleconnections abstract a high resolution stalagmite oxygen isotope record from tianmen cave located in the south central tibetan plateau characterizes detailed climatic variations between 8 7 and 4 3 ka bp on centennial and decadal time scales with a temporal resolution of 3 to 7 years the tianmen record is in good agreement with speleothem records from asian monsoon regions i e dongge cave dykoski et al 2005 wang et al 2005 qunf cave fleitmann et al 2003 upwelling records from the arabian sea gupta et al 2003 gupta et al 2005 and peat bog records from southeast tibetan plateau hong et al 2003 indicating that the indian summer monsoon ism gradually weakened as northern hemisphere summer insolation declined during the early mid holocene and that ism intensity rather than temperature dominates the precipitation 18o on centennial to decadal time scales in the southern tp on centennial to decadal time scales the detrended tianmen record correlates well with the greenland ice core record further confirming the mechanistic connection between the ism and high northern latitude temperature changes meanwhile the tianmen record bears significant solar activity cycles suggesting that the solar output changes may affect the variability of the ism and likely the position of the intertropical convergence zone itcz as well moreover due to joint effects of changes in monsoon precipitation moisture source and temperature the tianmen 18o record shows much larger amplitude changes than speleothem 18o records from low elevation asian monsoon regions which is similar to the previously reported marine isotope stage mis 5 record cai et al 2010 suggesting heightened sensitivity of precipitation isotope composition to climate changes over the high elevation regions and further demonstrating that the stable isotope lapse rate may change under different climatic conditions

the upper crustal 3 d resistivity structure of the kristineberg area skellefte district northern sweden revealed by magnetotelluric data a 3 d model of the crustal electrical resistivity was constructed from the inversion of magnetotelluric data in the kristineberg area skellefte district the location of one of sweden s most succe

chemistry microstructure petrology and diagenetic model of jurassic dinosaur bones dinosaur national monument utah abstract the fossil bone mineral in dinosaurs from the morrison formation is well crystallized stoichiometric francolite the closely packed subparallel francolite crystals have equidimensional cross sections mostly 10 40 nm wide in contrast crystallites in unaltered mammal bone tissue are poorly crystallized nonstoichiometric carbonate hydroxyapatite a few nanometers thick and plate rod or needle shaped the diagenetic francolite crystals are elongated in the c axis direction as are bone tissue crystallites along permeable cracks francolite crystals grew to 250 nm wide compared to unaltered crystallites in mammal bones the francolite has higher concentrations of ba ce cr f la mn ni pb rb sr th u v and y and perhaps zr na and mg are lower in concentration diagene ic francolite grew from groundwater enriched in ions from silicic ashes in the brushy basin member and from dissolution of bone tissue crystallites after burial francolite grew on crystallite seeds filling the space formerly occupied by collagen perhaps half the tissue volume and dissolved crystallites the micron scale structures such as haversian canals and laminae are preserved because the diagenetic francolite retains the orientations of the seeds the laminae 1 10 m thick commonly preserve an orthogonal plywood structure the diagenetic growth of francolite during this type of bone fossilization implies that oxygen isotopic ratios measured in dinosaur bones even those that appear fresh and unaltered may dominantly reflect groundwater temperature rather than dinosaur body temperature trace element concentrations in the francolite may reflect groundwater composition rather than dinosaur diet pore filling cements precipitated in the sands and bones at shallow burial depths as evidenced by the 35 52 minus cement porosities of the sandstones and numerous uncompacted oversize pores filled by cements gypsum and calcite were precipitated from shallow alkaline groundwater as the groundwater became increasingly dominated by ions from silicic ash argentite chalcopyrite native gold native silver tiemannite and uraninite replaced areas of bone a few microns to tens of microns in size along cracks a thin chlorite crust commonly mantled francolite crystals along bone cracks and lined openings in bones and sandstones pervasive precipitation of a chalcedony crust followed with pseudomorphs of chalcedony after gypsum in larger cancellous openings the remaining space was fi led by the various forms of silica the bones are brown due to goethite filled cracks that cut pore filling minerals

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

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

mapping the geometry of volcanic systems with magnetotelluric soundings results from a land and marine magnetotelluric survey performed during the 2018 2019 mayotte seismovolcanic crisis abstract a major seismovolcanic crisis has afflicted the islands of mayotte comoros archipelago since may 2018 although the origin is debated magnetotellurics mt which is sensitive to hydrothermal and or magmatic fluids and can map the subsurface electrical resistivity structure can provide insight by revealing the internal structure of the volcanic system in this paper we report the results of a preliminary land and shallow marine mt survey performed on and offshore the island nearest the crisis the 3d inversion derived electrical resistivity model suggests that the island is underlain by a shallow 500 m thick conductive layer atop a deeper more resistive layer possibly associated with a high temperature geothermal system at depths of 15 km the resistivity drops by almost two orders of magnitude possibly due to partial melting further petrophysical and geophysical studies are underway for confirmation and to map the geometry and evolution of the volcanic system

the 3d facies architecture of flood basalt provinces and their internal heterogeneity examples from the palaeogene skye lava field quantifying the facies architecture of flood basalt provinces is important as it can be used to understand the physical volcanology and rock property variations throughout the lava sequence the 3d facies architecture and internal heterogeneity of the skye lava field for example provides important insights into the evolution of the british tertiary igneous province and valuable information to aid in the exploration of potential offshore reservoirs underlying significant flood lavas along the north atlantic margin the volcanic stratigraphy of the talisker bay area of skye comprises 1 lower compound braided lavas flow lobes 3 the transitional sequence 7 4 km 3 and the upper sequence 17 0 km 3 the lower sequence lavas formed on the flanks of a shield volcano and were sourced from the ne volcanological features such as lava feeder tubes pahoehoe textures and lobes indicate a scale of volcanism similar to that of present day hawaii the within flow heterogeneity of the basalts is characterized using an intrafacies scheme allowing comparison of variations in lithofacies with characteristic geophysical rock properties of compressional wave velocity and density

a lateglacial and holocene lake record from the nianbaoyeze mountains and inferences of lake glacier and climate evolution on the eastern tibetan plateau abstract our 12 81 m long record from lake ximencuo provides insight into the lateglacial and holocene evolution of the lake and the nianbaoyeze glacier in its catchment and the regional climate history since 19 kyr lake ximencuo was a permanent deep lake throughout its history in contrast to numerous lakes on the tibetan plateau which experienced shallow lake levels or even desiccation during the lateglacial lake ximencuo was fed by large quantities of meltwater in the lateglacial the existence of glaciated upper catchment areas is apparently a prerequisite for lakes on the tibetan plateau which maintained relatively high water levels during the generally cold and dry periods following the global lgm 21 kyr a minor re advance of the nianbaoyeze glacier was recorded coeval with the greenland stadial 2a 16 4 and 14 5 kyr followed by rapid warming apparently synchronous with the greenland interstadial 1 warmest conditions were recorded at lake ximencuo during the early holocene which was punctured by a remarkable pulse of climate deterioration around 8 3 kyr this spell represents probably the 8 2 kyr event of the north atlantic region suggesting that it had a significant impact on the tibetan plateau colder conditions of longer duration occurred from 4 7 to 3 7 kyr apparently in phase with numerous records signalling colder and drier conditions on the tibetan plateau two minor spells of colder conditions and probably catchment erosion were recorded in the late holocene between 2 0 and 1 4 kyr and between 0 5 and 0 1 kyr with the latter representing the little ice age it is unclear whether human activities may have accelerated or even solely triggered the late holocene erosion events

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

influences of subtropical jet and tibetan plateau on precipitation pattern in asia insights from regional climate modeling abstract large topographic features like the tibetan plateau tp and the rocky mountains have significant impacts on earth s climate numerical experiments were carried out using a regional climate model in order to study the sensitivity of rainfall distribution to the tp s thermal dynamic effects and meridional position of the subtropical westerly jet the sensitivity experiments under the present winter conditions characterized by weaker solar radiation and westerly jet located to the south of the tp reveal that broad arid climate characterizes northeast asia covering north china and mongolia the results are consistent with previous studies indicating that tp dynamic forcing is dominant in winter in sensitivity experiments under present summer conditions characterized by stronger solar radiation and the westerly jet located to the north of tp a prominent subsidence occurred over north china where the taklimakan and gobi deserts are located in summer dynamic forcing of tp is very weak whereas the thermal forcing of tp mainly induces subsidence relatively smaller mountain ranges such as the tianshan mountains also modify the atmospheric circulation even during the summer season the active convection zone along the baiu front which produces an elongate rain belt that extends from east china to korea and japan is near the boundary of two moisture sources transported by the westerly wind over the eurasian continent and by the asian summer monsoon flow the millennial scale variation in the location of the boundary reflects corresponding changes in east asian climate including monsoon intensity storm activity and the subtropical jet

the coast effect in terms of deviated electric currents a numerical study abstract a numerical thin sheet model is used to study the coast effect and to determine the magnitude of the near surface part of the anomalous field theoretical induction arrows are computed for australia california japan and the british isles and compared with the observed arrows this comparison shows that the main part of the coast effect and in some cases the whole coast effect is due to the deviation of currents flowing in the ocean by the upper part of the resistive continents it is suggested that the term coast effect should refer to the anomalous field whose source is near surface the coast effect so defined behaves like a regional anomaly superimposed on other anomalous features of the transient geomagnetic field a numerical determination of the geometrical features of the coast effect allows consideration of its elimination this elimination is performed for california and japan a correlation between the resulting residual and heat flow data is apparent in both cases

ecological development of lake donggi cona north eastern tibetan plateau since the late glacial on basis of organic geochemical proxies and non pollen palynomorphs organic geochemical proxy data from surface sediment samples and a sediment core from lake donggi cona were used to infer environmental changes on the northeastern tibetan plateau spanning the last 18 4 kyr long chain n alkanes dominate the aliphatic hydrocarbon fraction of the sediment extract from most surface sediment samples and the sediment core unsaturated mid chain n alkanes nc23 1 and nc25 1 have high abundances in some samples especially in core samples from the late glacial and early holocene toc contents organic biomarker and non pollen palynomorph concentrations and results from organic petrologic analysis on selected samples suggest three major episodes in the history of lake donggi cona before ca 12 6 cal ka bp samples contain low amounts of organic matter due to cold and arid conditions during the late glacial after 12 6 cal ka bp relatively high contents of toc and concentrations of botryococcus fossils as well as enhanced concentrations of mid chain n alkanes and n alkenes suggest a higher primary and macrophyte productivity than at present this is supported by high contents of palynomorphs derived from higher plants and algae and was possibly triggered by a decrease of salinity and amelioration of climate during the early holocene since 6 8 cal ka bp lake donggi cona has been an oligotrophic freshwater lake proxy data suggest that variations in insolation drive ecological changes in the lake with increased aquatic productivity during the early holocene summer insolation maximum short term drops of toc contents or biomarker concentrations at 9 9 cal ka bp after 8 0 and between 3 5 and 1 7 cal ka bp can possibly be related to relatively cool and dry episodes reported from other sites on the north eastern tibetan plateau which are hypothesized to occur in phase with northern hemisphere cooling events

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

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

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

seismic structure of basalt flows from surface seismic data borehole measurements and synthetic seismogram modeling we use the wide angle wavefield to constrain estimates of the seismic velocity and thickness of basalt flows overlying sediments wide angle means the seismic wavefield recorded at offsets beyond the emergence of the direct wave this wide angle wavefield contains arrivals that are returned from within and below the basalt flows including the diving wave through the basalts as the first arrival and p wave reflections from the base of the basalts and from subbasalt structures the velocity structure of basalt flows can be determined to first order from traveltime information by ray tracing the basalt turning rays and the wide angle base basalt reflection this can be refined by using the amplitude variation with offset avo of the basalt diving wave synthetic seismogram models with varying flow thicknesses and velocity gradients demonstrate the sensitivity to the velocity structure of the basalt diving wave and of reflections from the base of the basalt layer and below the diving wave amplitudes of the

holocene variations in the asian monsoon inferred from the geochemistry of lake sediments in central tibet we present a record of monsoon variations for the early and middle holocene that is inferred from the geochemistry of sediment cores from ahung co a lake in central tibet the resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal which eliminates errors associated with the lake hard water effect we made down core geochemical measurements of carbonate organic carbon c n and 13c of bulk organic matter 13c and 18o of carbonate and dolomite proxy calibration and modern water balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation we find that lake level and monsoon precipitation have been decreasing at ahung co since the early holocene 7500 cal yr b p superimposed on this trend are rapid declines in monsoon rainfall at 7000 7500 and 4700 cal yr b p and seven century scale wet dry oscillations the cores do not contain sediment from the last 4000 yr surface sediments from the lake accumulated during the 20th century however from this we argue that lake levels have risen again recently following a late holocene dry period

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

ice core evidence for asynchronous glaciation on the tibetan plateau over the last two decades ice core records have been systematically recovered from low latitude high elevation ice fields from across the tibetan plateau tp and each core has provided new information about regional climate and environmental change when viewed collectively these ice core histories provide compelling evidence that the growth glaciation and decay deglaciation of large ice fields in the lower latitudes are often asynchronous with high latitude glaciation and deglaciation that occur on milankovitch time scales here we examine the evidence for asynchronous glaciation on the tp as recorded in ice cores from the guliya ice cap on the northwestern margin and the puruogangri ice cap and dasuopu glacier in central tibet and along the southern margin of the tp respectively we contend that although stable isotopic records from antarctica greenland tanzania peru and bolivia suggest global scale cooling during the last glacial stage over much of the tp precipitation is a stronger driver of glaciation here we present evidence suggesting that glacier expansion on the southern and central tp is driven mainly by variations in monsoonal precipitation that is modulated by precession driven insolation changes the basal oldest ice in the puruograngri and dasuopu ice fields was deposited in the early to mid holocene while ice near the base of guliya is more than 500 000 yr old

geological inheritance and crystal dynamics of the northwest scottish continental shelf abstract deep seismic reflection profiles have been combined with conventional seismic surveys across the northwest scottish continental shelf to interpret basin development in the region post caledonian basins are built upon partially reactivated older structures which have strongly influenced their internal structure and stratigraphy we show that the minch basin along with several others developed in the hangingwall of the partially reactivated outer isles fault a planar fault dipping at about 30 ese that reaches nearly to the moho the internal structure of these hangingwall basins is compared with appropriate scaled analogue models to show that they have developed by passive hangingwall collapse above a footwall block that moved towards the wnw this geometry is incorporated into a lithospheric dynamic model with northwest extension towards the rockall trough from a fixed lithosphere beneath the scottish highlands this model requires non linear lithosphere extension which is accommodated by movements on faults and block rotation in the upper crust extension and thinning of the lower crust along a network of anastomosing ductile shears extensional movement of the flannan fault in the upper mantle and horizontal displacement along the moho beneath the outer hebrides this dynamic model has wider application for other extensional regions

hydroclimate in the pamirs was driven by changes in precipitation evaporation seasonality since the last glacial period the central asian pamir mountains pamirs are a high altitude region sensitive to climatic change with only few paleoclimatic records available to examine the glacial interglacial hydrological changes in the region we analyzed the geochemical parameters of a 31 kyr record from lake karakul and performed a set of experiments with climate models to interpret the results d values of terrestrial biomarkers showed insolation driven trends reflecting major shifts of water vapor sources for aquatic biomarkers positive d shifts driven by changes in precipitation seasonality were observed at ca 31 30 28 26 and 17 14 kyr bp multiproxy paleoecological data and modelling results suggest that increased water availability induced by decreased summer evaporation triggered higher lake levels during those episodes possibly synchronous to northern hemispheric rapid climate events we conclude that seasonal changes in precipitation evaporation balance significantly influenced the hydrological state of a large waterbody such as lake karakul while annual precipitation amount and inflows remained fairly constant

mid to late holocene climate change an overview the last 6000 years are of particular interest to the understanding of the earth system because the boundary conditions of the climate system did not change dramatically in comparison to larger glacial interglacial changes and because abundant detailed regional palaeoclimatic proxy records cover this period we use selected proxy based reconstructions of different climate variables together with state of the art time series of natural forcings orbital variations solar activity variations large tropical volcanic eruptions land cover and greenhouse gases underpinned by results from general circulation models gcms and earth system models of intermediate complexity emics to establish a comprehensive explanatory framework for climate changes from the mid holocene mh to pre industrial time the redistribution of solar energy due to orbital forcing on a millennial timescale was the cause of a progressive southward shift of the northern hemisphere nh summer position of the intertropical convergence zone itcz this was accompanied by a pronounced weakening of the monsoon systems in africa and asia and increasing dryness and desertification on both continents the associated summertime cooling of the nh combined with changing temperature gradients in the world oceans likely led to an increasing amplitude of the el nin o southern oscillation enso and possibly increasingly negative north atlantic oscillation nao indices up to the beginning of the last millennium on decadal to multi century timescales a worldwide coincidence between solar irradiance minima tropical volcanic eruptions and decadal to multi century scale cooling events was not found however reconstructions show that widespread decadal to multi century scale cooling events accompanied by advances of mountain glaciers occurred in the nh e g in scandinavia and the european alps this occurred namely during the little ice age lia between ad w1350 and 1850 when the lower summer insolation in the nh due to orbital forcing coincided with solar activity minima and several strong tropical volcanic eruptions the role of orbital forcing in the nh cooling the southward itcz shift and the desertifi cation of the sahara are supported by numerous model simulations other simulations have suggested that the fingerprint of solar activity variations should be strongest in the tropics but there is also evidence that changes in the ocean heat transport took place during the lia at high northern latitudes with possible additional implications for climates of the southern hemisphere sh

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

causes of early holocene desertification in arid central asia paleoclimate records of effective moisture precipitation minus evaporation or p e show a dry low effective moisture period in mid latitude arid semi arid central asia during the early holocene 11 000 8 000 years ago relative to the middle and late holocene in contrast to evidence for greater than present precipitation at the same time in the south and east asian monsoonal areas to investigate the spatial differences in climate response over mid latitude central asia and monsoonal asia we conducted a series of simulations with the community climate system model version 3 coupled climate model for the early middle and late holocene the simulations test the climatic impact of all important forcings for the early holocene including changes in orbital parameters the presence of the remnant laurentide ice sheet and deglacial freshening of the north atlantic model results clearly show the early holocene patterns indicated by proxy records including both the decreased effective moisture in arid central asia which occurs in the model primarily during the winter months and the increase in summer monsoon precipitation in south and east asia the model results suggest that dry conditions in the early holocene in central asia are closely related to decreased water vapor advection due to reduced westerly wind speed and less evaporation upstream from the mediterranean black and caspian seas in boreal winter as an extra forcing to the early holocene climate system the laurentide ice sheet and meltwater fluxes have a substantial cooling effect over high latitudes especially just over and downstream of the ice sheets but contribute only to a small degree to the early holocene aridity in central asia instead most of the effective moisture signal can be explained by orbital forcing decreasing the early holocene latitudinal temperature gradient and wintertime surface temperature we find little evidence for regional subsidence related to a stronger summer asian monsoon in forcing early holocene aridity in central asia as has been previously hypothesized

dynamic processes controlling evolution of rifted basins abstract the extension of the lithosphere controlling the development of rifted basins is driven by a combination of plate boundary forces frictional forces exerted on the base of the lithosphere by the convecting asthenosphere and deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system although mantle plumes are not a primary driving force of rifting they play an important secondary role by weakening the lithosphere and by controlling the level of rift related volcanic activity a distinction between active and passive rifting is only conditionally justified the extension of the lithosphere depending on its rate and magnitude and the potential temperature of the asthenosphere can cause by adiabatic decompression partial melting of the lower lithosphere and upper asthenosphere in rift systems the level and timing of volcanic activity is highly variable the lack of volcanic activity implies passive rifting an initial passive rifting stage can be followed by a more active one during which magmatism plays an increasingly important role magmatic destabilization of the moho may account for the frequently observed discrepancy between upper and lower crustal extension factors combined with evidence for thermal thinning of the mantle lithosphere this suggest that the volume of the lithosphere is not necessarily preserved during rifting as advocated by conventional stretching models the structural style of rifts is controlled by the rheological structure of the lithosphere the availability of crustal discontinuities that can be tensionally reactivated the mode orthogonal or oblique and amount of extension and the lithological composition of pre and syn rift sediments simple shear extension prevails in rifts that subparallel the structural grain of the basement pure shear extension is typical for rifts cross cutting the basement grain pre existing crustal and mantle lithospheric discontinuities contribute to the localization of rift systems the duration of the rifting stage of extensional basins is highly variable stress field changes can cause abrupt termination of rifting in major rift systems progressive strain concentration on the zone of future crustal separation entails abandonment of lateral rifts depending on constraints on lateral block movements crustal separation can be achieved after as little as 9 my and as much as 280 my of rifting activity syn rift basin subsidence is controlled by isostatic adjustment of the crust to mechanical stretching of the lithosphere its magmatic inflation and thermal attenuation of the mantle lithosphere post rift basin subsidence is governed by thermal reequilibration of the lithosphere asthenosphere system deep seated thermal anomalies related to syn rift pull up of the asthenosphere lithosphere boundary have decayed after 60 my by about 65 and after 180 my by about 95 the magnitude of post rift subsidence is a function of the rift induced thermal anomaly and crustal density changes the potential temperature of the asthenosphere and initial water depths intraplate stresses can have an overprinting effect on post rift subsidence stretching factors derived from post rift subsidence analyses must be corrected for such effects

exploring quaternary paleolake evolution and climate change in the western qaidam basin based on the bulk carbonate geochemistry of lake sediments abstract this study focuses on the concentration of major and trace elements in the diluted acetic acid soluble fraction of sg 1 core lacustrine sediments from the western qaidam basin tibetan plateau in order to explore the potential of applying bulk carbonate analysis to tracing paleolake evolution and climate change the sg 1 core sediments are considered highly suited to the exploration of the paleoenvironmental significance of bulk carbonate geochemistry because most carbonates in the core are authigenic in origin based on a principal component analysis of the elemental composition of diluted acetic acid leachate four major components with distinct characteristics have been extracted accounting for 80 of the total variance the first and most important component is associated with a high positive loading of mn p y sc and rare earth elements ree the second component is characterized by a high positive loading of ca sr and u the third component displays a high negative loading of mg li and b and the fourth component is associated with a relatively high positive loading of fe v and cr after considering the geochemical behavior of these element assemblies during acid leaching we have concluded that these four components contain information indicative of watershed climate conditions carbonate precipitation lake water salinity and iron oxide content respectively reconstructions of watershed climate change and paleolake evolution using the component scores are comparable to those reconstructed from other independent proxy records indicating a long term trend of lake shrinkage and climatic drying since 2 7 ma with abrupt drying events at 2 5 ma 1 8 ma 1 2 ma and 0 6 ma our results suggest that lake carbonates bear more information about watershed climate and lake evolution than expected and that occurrences of some elements in particular trace elements in the diluted acetic acid leachate are not solely and necessarily linked to carbonate minerals

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

dry or humid mid holocene humidity changes in arid and semi arid china abstract spatial changes of effective moisture during the mid holocene have been reconstructed based on the compilation of recently published paleoclimate records including ice core lake level pollen assemblage and loess paleosol records both geological data and the spatial pattern indicate that it was dry in deserts during the mid holocene but the timing of the beginning and end of dry intervals differs from place to place deserts having higher aridity index values remain dry longer dry intervals during the mid holocene are more possibly asynchronous than synchronous in arid and semi arid china in the xinjiang region except in sites located in deserts the climate is generally wet during 7000 5000 a bp in the northern qinghai tibetan plateau effective moisture in most sites began to decrease after 5000 a bp the climate became dry after 4000 a bp except in the deserts in the loess plateau and the inner mongolia plateau

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

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

the holocene salinity history of bosten lake xinjiang china inferred from ostracod species assemblages and shell chemistry possible palaeoclimatic implications abstract a sediment core from bosten lake the largest freshwater lake in the tianshan mountains and in the northwesternmost province of china provided a high resolution record of environmental change covering the last 8500 cal a bp higher salinity levels of bosten lake were reconstructed from assemblages the stable isotope composition and sr ca and mg ca ratios of ostracod shells between 7800 and 5600 cal a bp a period of low and moderate salinities between 5600 and 4900 cal a bp was followed by the re establishment of higher salinities between 4900 and 4300 cal a bp since then bosten lake has recorded fluctuating conditions with a number of multi centennial phases of low and moderate salinities although the salinity lake level relationship of bosten lake is not fully understood a higher salinity at the core site seems to correspond to periods of higher lake levels this contradictory interpretation is explained tentatively by the changing distance of the core site to the freshwater providing river mouth with changing lake levels and potentially resulting lateral shifts of the salinity distribution pattern within the lake assuming this explanation is correct the record from bosten lake reflects higher moisture availability and a strong climatic influence of the indian monsoon in the early mid holocene until about 4000 cal a bp and more unstable drier conditions susceptible to minor changes in the regional circulation patterns and temperature variations afterwards

stable isotope and ostracode species assemblage evidence for lake level changes of nam co southern tibet during the past 600 years abstract ostracode species assemblages and stable oxygen and carbon isotopes of shells from two 210 pb dated short cores of 78 cm and 47 cm length taken from lake nam co southern tibet provide information about lake level history of the past approximately 600 years at decadal resolution a transfer function is applied to reconstruct paleo water depths from modern ostracodes ostracode assemblages and isotope data from five species allow a subdivision into phases of lake level evolution before 1600 ad relatively low oxygen isotope values and high abundances of deep water 30 m ostracodes i e leucocythere dorsotuberosa leucocythere dorsotuberosa f postilirata suggest a lake level 10 m higher than today between 1600 ad and 1800 ad more positive oxygen isotope values and higher abundances of shallow water ostracodes i e ilyocypris cf mongolica candona xizangensis suggest a lake level approximately 40 m below modern level between 1800 ad and 1920 ad oxygen isotopes are characterized by a trend to more negative values followed by a trend to more positive ones these trends are interrupted by several short term fluctuations but overall oxygen isotope values suggest a drop in lake level a clearer lake level picture is provided by species assemblages that suggest a continuously increasing lake level since 1900 ad precipitation data from meteorological stations nearby show an increase in precipitation in the last 30 years the low lake level between 1600 ad and 1800 ad is contemporary to the little ice age during that cold period meltwater input into the lake decreased this underlines the sensitivity of the level of lake nam co to temperature changes on the tibetan plateau

how old is the asian monsoon system palaeobotanical records from china the recent discovery of monsoon records in early miocene raised a question of the time when the east asian monsoon system initiated a distinguishing feature of the modern monsoon system is its geographic distribution which disturbs the zonal pattern indigenous to the planetary climate system and the appearance of the monsoonal climate pattern in the geological records should signify the onset of the monsoon system here we present the results of a compilation of palaeobotanical and lithological data from 125 sites over china that has revealed two completely different patterns of climate zones the palaeogene pattern with a broad belt of aridity stretched across china from west to east and the neogene pattern with the arid zone restricted to northwest of china which has persisted until today the reorganization of the climate system around the oligocene miocene boundary provides evidence for the establishment of the modern east asian monsoon since then the neogene has witnessed significant variations of the monsoon system including enhancement of aridity and monsoon intensity at about 15 13 my around 8 my and 3 my the new data do not support the onset of the asian monsoon system around 8 my rather the new data led to a hypothesis that the transition to the monsoon climate system in east asia occurred in the latest oligocene

a lake level chronology based on feldspar luminescence dating of beach ridges at tangra yum co southern tibet many lakes on the tibetan plateau exhibit strandplains with a series of beach ridges extending high above the current lake levels these beach ridges mark former lake highstands and therefore dating their formation allows the reconstruction of lake level histories and environmental changes in this study we establish a lake level chronology of tangra yum co fifth largest lake on the tibetan plateau based on luminescence dating of feldspar from 17 beach ridge samples the samples were collected from two strandplains southeast and north of the lake and range in elevation from the current shore to 140 m above the present lake using a modified post infrared irsl protocol at 170 c we successfully minimised the anomalous fading in the feldspar irsl signal and obtained reliable dating results the luminescence ages indicate three different stages of lake level decline during the holocene 1 a phase of rapid decline 50 m from 6 4 to 4 5 ka 2 a period of slow decline between 4 5 and 2 0 ka 20 m and 3 a fast decline by 70 m between 2 ka and today our findings suggest a link between a decrease in monsoonal activity and lake level decline since the early holocene

the influence of 14c reservoir age on interpretation of paleolimnological records from the tibetan plateau there is a great deal of controversy regarding the fate of glaciers and ice fields on the tibetan plateau in the face of continued anthropogenic global warming paleoclimate reconstructions and spatial analyses aimed at mapping past climate changes are the key to understanding the climatic response of the tibetan plateau to changing conditions specifically the numerous lakes distributed across the tibetan plateau can provide high resolution spatial and temporal climate reconstructions to investigate past changes in the climate system in this paper we review the primary limitation to exploiting these valuable paleoclimate archives errors in radiocarbon based age models we review the techniques that have been used to estimate 14 c reservoir ages on the tibetan plateau and compile the published 14 c reservoir ages to examine their spatial and temporal patterns and to assess the imposed chronological uncertainties using site specific evaluations of bangong co and lake qinghai we demonstrate that 14 c age model uncertainties permit equally probable and contrasting interpretations of existing paleoclimate records we also examine 14 c induced uncertainties in the spatial climatic response on the tibetan plateau to 1 the termination of the last glacial maximum and 2 the holocene thermal maximum we conclude with recommendations for reducing uncertainties in future lake based paleoclimate studies on the tibetan plateau

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

sub surface geology and velocity structure of the krafla high temperature geothermal field iceland integrated ditch cuttings wireline and zero offset vertical seismic profile analysis abstract the krafla geothermal area in northern iceland comprises one of the best studied examples of a high temperature geothermal field associated with an active volcanic rift zone of key importance to improved resource exploration and development in volcanic areas such as krafla is the interpretation and understanding of the subsurface geology within this study we present results from an integrated analysis of the downhole volcanic stratigraphy from the k 18 borehole within the krafla caldera based on combined wireline ditch cuttings and zero offset vsp vertical seismic profile analyses this study presents the first published sonic log velocity data from a high temperature geothermal borehole in iceland and clearly demonstrates the importance of borehole velocity data for improving volcanic facies interpretations the shallow subsurface geology of the k 18 site from c 0 380 m comprises an inter layered sequence of sub aerial basaltic lavas hyaloclastites and tuffaceous lithologies of both felsic and basic composition which are progressively replaced by basaltic sheet intrusions with increasing depth an interval of variably basic to more evolved mixed tuffaceous facies is identified based on cuttings analysis gamma and sonic velocities between c 790 1120 m depth discrete high sonic vp units cut the lower c 100 m of this interval and are interpreted as either sheet intrusions or lava interiors at c 1800 m a sharp increase in p wave velocity from c 4 5 to c 5 5 km s represents the transition from a mixed lava and sheet intrusion dominated sequence into a dense basic intrusion forming the local basement that persists to the bottom of the borehole at c 2215 m reduced travel time analysis of processed zero offset vsp results reveal good correspondence with the major stratigraphic boundaries in the borehole supporting the potential for vsp studies to robustly characterize complex volcanic stratigraphy in high temperature geothermal fields finally the application of percentage based ditch cuttings analyses methods for volcanic facies analysis in geothermal boreholes is tested and assessed to have future potential

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

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

extraordinary floods of 4100 4000 a bp recorded at the late neolithic ruins in the jinghe river gorges middle reach of the yellow river china abstract holocene palaeohydrological investigations were carried out in the middle reach of the jinghe river that drains the central part of the loess plateau a set of palaeoflood slackwater deposits was found interbedded in the holocene loess soil sequence within the cliff riverbanks both the sedimentary criteria and the analytical results show that this sediment was sourced from a suspended sediment load of floodwater the major cultural layer of a late neolithic settlement 4300 4000 a bp occurring at the same site is blanketed by this flood deposit directly slopewash with pottery shards charcoal and burnt earth occurs in between the palaeoflood slackwater deposit beds it indicates that each of the slackwater deposit beds has recorded one individual flood event and that these extraordinary floods occurred when the late neolithic people occupied the riverbank terrace land this pre historical settlement was abandoned after the floods eventually due presumably to repeated inundation by overbank floodwater the flood events were osl dated to between 4100 and 4000 a bp and checked by archaeological dating of the anthropogenic remains retrieved from the sequences peak discharges of the floods were estimated to between 19 500 and 22 000 m3 s 1 which is several times gauged maximum floods during the 4200 4000 a bp climatic event severe droughts were documented in china s monsoonal regions and great floods were known from an ancient legend this study provides a well dated sediment record of pre historical floods which occurred at the transition from the neolithic to the bronze age in the yellow river basin it shows that extraordinary floods were part of the abrupt climatic variability during the 4200 4000 a bp climatic event the highly variable unstable and catastrophic climate typified by both droughts and floods resulted in settlement abandonment and possibly the decline of the highly developed late neolithic civilizations in china s monsoonal regions

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

holocene climate development on the central tibetan plateau a sedimentary record from cuoe lake abstract we present a climate record for central tibet spanning the time between 10500 and 1600 cal years bp from a 5 3 m long sediment core from cuoe lake the analyses show that high sr concentration high toc content high c n ratio and enriched 13c of lake sediments corresponded to stronger chemical weathering high productivity high lake level and warmer wetter climate and vice versa as revealed by the variations of these proxies the climatic evolution during this period can be divided into five stages and several substages these are a cold dry stage before 10140 cal years bp a transition stage from 10140 to 8560 cal years bp an optimum stage warm wet from 8560 to 5750 cal years bp a cool dry stage from 5750 to 4000 cal years bp a transition stage from 4000 to 3000 cal years bp and a drying up stage after 3000 cal years bp these changes are presumably reflections of variations in indian monsoon intensity which according to that interpretation should have been enhanced from 8560 cal years bp slightly weakened after 5750 cal years bp and gradually diminished since 3000 cal years bp in this region

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

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

focusing iterative migration of gravity gradiometry data acquired in the nordkapp basin barents sea abstract geological interpretation based on gravity gradiometry data constitutes a very challenging problem rigorous 3d inversion is the main technique used in quantitative interpretation of the gravity gradiometry data an alternative approach to the quantitative analysis of the gravity gradiometry data is based on 3d smooth potential field migration this rapid imaging approach however has the shortcomings of providing smooth images since it is based on direct integral transformation of the observed gravity tensor data another limitation of migration transformation is related to the fact that in a general case the gravity data generated by the migration image do not fit the observed data well in this paper we describe a new approach to rapid imaging that allows us to produce the density distribution which adequately describes the observed data and at the same time images the structures with anomalous densities having sharp boundaries this approach is based on the basic theory of potential field migration with a focusing stabilizer in the framework of regularized scheme which iteratively transfers the observed gravity tensor field into an image of the density distribution in the subsurface formations the results of gravity migration can also be considered as an a priori model for conventional inversion subsequently we demonstrate the practical application of migration imaging using both synthetic and real gravity gradiometry data sets acquired for the nordkapp basin in the barents sea

holocene lake level variations of longmu co western qinghai tibetan plateau longmu co is surrounded by conspicuous regressive shorelines attesting to high water levels in the past in this study we dated paleoshoreline sediments around the lake using optically stimulated luminescence osl infrared stimulated luminescence irsl and radiocarbon dating then explored the forces that drove holocene lake level variations we found that 1 osl irsl ages are consistent with geomorphic sequences and some extant cosmogenic and u th shoreline ages however inorganic evaporite crust 14c ages are much older than corresponding osl irsl ages due to varying lake reservoir effects and should be used with caution 2 the highest lake levels of longmu co 160 145 m above present lasted from 12 8 to 11 3 ka two periods of abrupt lake level declines occurred at 11 3 and 7 4 ka lake level dropped 44 and 45 m respectively with a gradual regression of 18 m between these two intervals the lake expanded moderately from 7 to 5 5 ka then declined once more after 5 5 ka with this regression accelerating during the last 1 5 ka 3 the deglacial lake level transgression was likely due to glacier melt waters the indian summer monsoon reached the longmu co watershed and brought precipitation during the early holocene middle to late holocene lake regression was caused by the retreat of the monsoon and consequent environmental deterioration

electrical resistivity cross section across northern part of saurashtra region an insight to crystallized magma and fluids abstract saurashtra region forms the western part of the deccan volcanic province dvp in india and is bounded by the cambay rift basin crb in the east narmada rift basin nrb in the south and kachchh rift basin krb in the north this region is uplifted due to different stages of inter continental breakup madagascar india seychelles india different stages of rifting reactivation of fault zones and deccan volcanism the major portion of saurashtra region is covered by deccan basalts underlain by mesozoic sediments detailed magnetotelluric mt and long period magnetotelluric lmt soundings have been carried out in the northern part of saurashtra with an aim to bring out the geoelectrical configuration of different basins jamnagar jasdan and cambay along the profile 2d inversion carried out for different modes transverse electric te transverse magnetic mode tm and te tm independently the inversion of different modes shows distinct electrical signatures due to the 3d nature of the data we have considered the tm mode of interpretation because it is less prone to 3d distortions the final model represents large scale heterogeneities in the crust due to the presence of different resistive and conductive blocks high conductive lithosphere denotes the thermal influx of the mantle material to the base of the crust exchange of heat with the lower crust during basaltic magmatic underplating released carbonate fluids and or dehydration of minerals resulting in high conductivity anomalies a prominent conductive feature on the east side of the profile at upper crustal depths may be due to partial melts associated with mafic ultra mafic intrusions related to the reunion plume activity different resistive blocks in conjunction with seismic tomography studies represent recrystallized older precambrian crust that forms the uplifted blocks of jamnagar jasdan and western part of cambay basins

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

pollen and diatom inferred climatic and hydrological changes in sumxi co basin western tibet since 13 000 yr b p although the tibetan plateau greatly influences the atmospheric circulation of the nortbern hemisphere few continuous paleoclimatic records are available from the plateau a 13 000 yr pollen and diatom record from the sumxi longmu co basin in western tibet gives information on major changes both in regional vegetation and in local hydrology after the basin first filled ca 13 000 yr b p a dry spell occurred about 10 500 yr b p within the interval spanned by the european younger dryas chronozone a major environmental change occurred suddenly at 10 000 yr b p with the establishment of wet conditions and was followed by a long term trend toward maximum aridity which lasted approximately 6000 yr short term oscillations are superimposed on this general climatic change with a major reversal event about 8000 yr b p and a second wet pulse leading to a maximum lake volume ca 7500 6000 yr b p maximum aridity occurred 4300 yr b p the major environmental fluctuations recorded at sumxi longmu co appear in phase with climatic changes recognized in north tropical africa suggesting that the 8000 to 7000 yr b p event was caused by an abrupt disequilibrium in the climatic system as was the younger dryas and possibly the 4300 yr b p event

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

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

late 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

holocene climatic and environmental change on the western tibetan plateau revealed by glycerol dialkyl glycerol tetraethers and leaf wax deuterium to hydrogen ratios at aweng co mean annual air temperature maat and precipitation isotope records for the holocene were obtained from the analysis of the relative distribution of branched glycerol dialkyl glycerol tetraethers and compound specific hydrogen isotope ratios of leaf waxes from a sediment core from aweng co on the western tibetan plateau wtp our results indicate that the indian monsoon mainly influenced aweng co during the holocene during the early holocene when summer insolation was at a maximum the monsoonal influence was strong and the climate was warm and wet both the summer and winter insolation were relatively weak and aweng co was cool and dry during the middle holocene 6 3 ka indicating a weakening of the indian monsoon the southward displacement of the intertropical convergence zone and relatively low atmospheric methane content may have contributed to the middle holocene cooling on the wtp during the late holocene with a further increase in winter insolation and decrease in summer insolation the summer monsoon weakened and the maat on the wtp gradually increased depleted leaf wax hydrogen isotope ratios during the late holocene can be attributed to accelerated glacier melting because of the elevated maat

evolution of chaka salt lake in nw china in response to climatic change during the latest pleistocene holocene abstract the late pleistocene and holocene hydrologic balance of chaka salt lake in the eastern qaidam basin of nw china was studied based on the analysis of lithostratigraphy mineralogy total organic carbon and total nitrogen from a 9 0 m long sediment core an age depth model for the lake sediments is based on eight accelerator mass spectrometry ams 14 c measurements of organic matter and a 1700 year radiocarbon reservoir correction the pitzer model was used to calculate the sequence of minerals precipitated as a function of salinity assuming that the initial lake water was recharged from adjacent rivers and springs lake salinity values were derived from a good match between the calculated and observed mineral sequences our multi proxy based hydrologic reconstruction of chaka lake indicates that it was a clastic dominated freshwater lake between 17 2 and 11 4 cal ka bp which may have resulted from the input of glacial water into the lake at that time during the lateglacial and holocene a warm climatic regime predominated between 13 9 and 12 7 cal ka bp and then a cold climatic regime prevailed between 12 7 and 11 4 cal ka bp these warm and cold periods correlate with the bolling allerod and younger dryas events in the region beginning at 11 4 cal ka bp a saline or hypersaline lake developed which may have resulted from increased summer insolation and temperatures these conditions persisted throughout the holocene modeling indicates that lake salinity fluctuated between 66 and 223 ppt from 11 4 to 7 2 cal ka bp and then increased to 223 322 ppt between 7 2 and 6 0 cal ka bp when most regions of china recorded high moisture availability i e the so called mid holocene climatic optimum lake salinity decreased to 66 223 ppt during a short time period between 6 0 and 5 3 cal ka bp possibly caused by reduced evaporation subsequently salinity values rapidly increased to 223 322 ppt between 5 3 and 5 2 cal ka bp and a hypersaline lake with a salinity higher than 324 ppt similar to modern chaka salt lake became established around 5 2 cal ka bp this establishment may have been related to the weakening of asian monsoon regional comparisons of paleoclimatic records indicate that large temporal and spatial variations exist in the occurrence and intensity of drought over western china since the lateglacial

3 d magnetotelluric inversion and model validation with gravity data for the investigation of flood basalts and associated volcanic rifted margins summary 20 magnetotelluric mt soundings were collected on the isle of skye scotland to provide a high resolution three dimensional 3 d electrical resistivity model of a volcanic province within the framework of a project jointly interpreting gravity seismic geological and mt data the full 3 d inversion of the mt data jointly interpreted with gravity data reveals upper crustal structure the main features of the model are interpreted in conjunction with previous geological mapping and borehole data our model extends to 13 km depth several kilometres below the top of the lewisian basement the top of the lewisian basement is at approximately 7 8 km depth and the topography of its surface was controlled by precambrian rifting during which a 4 5 km thick sequence of torridonian sediments was deposited the mesozoic sediments above which can reach up to 2 2 km thick have small scale depocentres and are covered by up to 600 m of tertiary lava flows the interpretation of the resistivity model shows that 3 d mt inversion is an appropriate tool to image sedimentary structures beneath extrusive basalt units where conventional seismic reflection methods may fail

ostracods and stable isotopes of a late glacial and holocene lake record from the ne tibetan plateau abstract ostracod assemblage changes and stable isotopes of ostracod shells were used to reconstruct the salinity history of lake donggi cona on the northeastern tibetan plateau in response to the late glacial and holocene climate history brackish and relatively unstable conditions were inferred for the earlier part of the late glacial between 18 9 and 13 4 cal ka bp and for the early to mid holocene 11 9 6 8 cal ka bp a saline lake existed in the intervening period probably representing colder and drier conditions during the greenland stadial 1 younger dryas in north atlantic region freshwater conditions similar to the present stage of lake donggi cona were established for the first time at 6 8 cal ka bp this inference and the implied increase in moisture availability in the latter half of the holocene is in contrast to most climate records from the tibetan plateau which suggest drier and colder conditions however three lake records from the eastern tibetan plateau including our new record show that the holocene insolation driven monsoonal weakening and temperature decrease caused a catchment specific opposite response of the moisture availability in comparison to those at the majority of sites catchments with relatively low precipitation at present experienced apparently a moisture availability increase during the colder second half of the holocene in contrast to the inferred drier conditions at predominantly generally wetter sites the increase in moisture availability at relatively dry sites mainly results from the lowered temperature and evaporation but is probably further controlled by a complex of factors including the amount and timing of precipitation the altitudes of the lake basins and upper reaches and the existence or development of glaciers snow fields and frozen ground in a given catchment our record from lake donggi cona suggests that the recently observed reduction in yellow river discharge in response to present global warming will likely continue or even increase under warmer climatic conditions in the future

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

basin morphology and seismic stratigraphy of lake donggi cona north eastern tibetan plateau china basin morphology and depositional stratigraphy of lake donggi cona on the north eastern tibetan plateau has been studied with echo depth sounding and shallow seismic sub bottom profiling the basin is a pull apart structure situated at the highly active kunlun fault it is characterised by a 92 m deep graben structure in the western part of the lake basin and a shallow eastern lake part the latter filled up with fluvial sediments from a large alluvial plain three prominent morphological levels were identified at 24 m 39 m and 57 m below present lake level they were partly created by basin subsidence while the deposition of prograding delta sediments primarily formed the morphological steps the inherited tectonic structures control on going neotectonic activity which seems to have only minor influence on present basin morphology the basin is filled by sediments of at least 30 m thickness in the depocentre three major depositional units can be distinguished in comparison with lithological changes in a sediment core they give evidence of pronounced lake level fluctuations and dramatic changes in lake volume a numerical age datum of w19 cal ka bp at the base of the sediment core allows a tentative reconstruction of late glacial to holocene lake development a very low base level preceded a time of delta formation during higher lake level i e w26 m lower than present during last glacial maximum creating a lake of only 18 of its present size at the transition to holocene the lake level rose very quickly changing to a deep lake environment thus transgression may have promoted maximum lake stands

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

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

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