carbonate crusts of paleolake zhuyeze tengeri desert china formation mechanism and paleoenvironmental implications abstract carbonate crusts with unusual morphologies are scattered on the holocene sand surface i e dunes which cover the paleolake zhuyeze bed in the tengeri desert china two types of the crusts were identified the first type contained fossilized wrinkles of plant root cortex while the second type consisted of hollow chambers without the wrinkle features optical microscopy scanning electron microscopy and cathodoluminescence analyses were performed to investigate the mineralogy and geochemistry of the crusts fossilized cortex texture imprints on the first type of crusts suggested that the crusts formed around the deceased rhizomes of reeds phragmites communis as the nuclei of encrustation weakly oxidizing soil sediment with rhizome was a prerequisite which was favorable for rhizome decomposition to produce sufficient co2 and hco3 and generate carbonate minerals of encrustation on rhizome surfaces with lake water as the main ca2 supply a conceptual formation mechanism of the encrustation was conjectured similar to the formation mechanism of the first type another type of crusts with chambers and without fossilized imprints of the cortex textures formed around the spherical rhizomes of scirpus maritimus the crust characteristics and other evidence suggested that the lake water was fresh water plants such as p communis and s maritimus and snails previously inhabited the water and encrustation reflected a stable slow oxidizing soil sediment environment these desert crusts provided insights to study paleoecology paleohydrology and water soil sediment interface environment in the paleolake

site effects investigation in the city of chlef formerly el asnam algeria using earthquake and ambient vibration data weak motion recordings of local earthquakes and ambient vibration data in the 0 2 15 hz frequency range were used to quantify site effects in downtown chlef city algeria nine short period stations were installed in the city a total of 15 local events with 3 1 m l 4 9 were selected three experimental techniques were applied standard spectral ratios receiver functions and horizontal to vertical spectral ratios using ambient vibrations hvsrn theoretical hvsrn curves were also calculated from suggested soil models for each site fundamental frequencies obtained from all techniques showed good agreement two groups of fundamental frequencies were distinguished in the city in the northern part of the study area the frequency peaks varied from 0 3 to 0 4 hz in the southern part they varied from 0 6 to 1 6 hz the amplification factors of these frequency peaks were 4 8 earthquake and ambient vibration data were able to identify fundamental frequency peaks successfully however the amplitudes of the peaks were slightly lower for ambient vibrations moreover the fundamental frequency peak progressively increased from northwest to southeast which is consistent with the direction of decreasing thickness of a miocene layer overlying the basement we infer as expected that the large impedance contrast between miocene deposits and mesozoic basement which can be interpreted as seismic bedrock is the cause of the fundamental frequency furthermore earthquake data were more appropriate for identifying peaks at frequencies higher than the fundamental one indeed a clear peak was observed at all northwestern sites in the 3 4 hz range with an amplification factor of 3 5 at the other sites particularly in the center of the city the peak was less evident

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 site response of two rock and soil station pairs to strong and weak ground motion abstract the site response to strong and weak ground motion depends largely on the subsurface conditions at the soil site for the two rock soil station pairs studied the first station pair consists of a soft soil site treasure island and a sandstone and shale site yerba buena island these stations recorded strong ground shaking from the loma prieta mainshock and weak ground motion from four aftershocks the range of peak ground acceleration is from approximately 0 00006 to 0 07 g at the rock site compared to the rock site the strong ground motion at the soft soil site is amplified by a factor of about 3 over a frequency range from 0 5 to 2 0 hz the amplification is much higher for weak motion and suggests a dependence on signal amplitude for example near 1 hz the site response shows an increasing amplification as magnitude and the peak velocity at the rock site decreases for events of local magnitude 7 0 4 3 4 1 3 5 and 3 3 the maximum soil site amplifications are 4 12 17 19 and 25 respectively a second station pair consisting of a stiff soil site gilroy 2 and a sandstone site gilroy 1 was also studied with contrasting results these two stations recorded strong ground shaking from the 1979 coyote lake 1984 morgan hill and 1989 loma prieta mainshocks weak ground motion was recorded at these stations after the loma prieta mainshock the range of peak ground acceleration is from 0 006 to 0 43 g at the rock site unlike the results for the soft soil study above the estimated stiff soil site responses are not significantly different for strong and weak motion from 0 5 to 2 0 hz near 0 7 hz the stiff soil site responses range from 2 5 to 4 5 for strong ground shaking from three mainshocks and from 1 5 to 4 0 for weak ground shaking from thirteen aftershocks

east asian monsoon variations during oxygen isotope stage 5 evidence from the northwestern margin of the chinese loess plateau abstract we present the results of high resolution multi proxy climate studies of the s1 palaeosol corresponding to oxygen isotope stage ois 5 from the northwestern margin of the chinese loess plateau area here s1 is much thicker ca 6 8 m than in the central loess plateau areas ca 2 m where most previous studies have been conducted hence much higher resolution stratigraphic studies are possible yielding more insight into the temporal variations of the east asian monsoon during mis 5 the frequency dependent magnetic susceptibility as well as the concentration of secondary carbonate is used as an indicator of the summer monsoon intensity and the median particle size as an indicator of the winter monsoon intensity the results suggest that the northwestern margin of the chinese loess plateau experienced the strongest summer monsoon intensity in sub stage oiss 5e and the weakest in oiss 5a among the three warmer periods during stage 5 the summer monsoon was weaker in oiss 5b than in oiss 5d a dusty interval interrupted the second warmer period 5c and a soil forming event interrupted the first colder period 5d the results also suggest that the directions of changes in the intensities of summer and winter monsoons may not always have been proportionately opposite for example the weakest summer monsoon occurred in oiss 5a during which the winter monsoon was not the strongest we further conclude that the winter monsoon during the last interglacial was probably driven by global ice volume fluctuations while the summer monsoon was primarily controlled by the northern hemisphere solar insolation and was probably modified by a feedback mechanism that is the climatic buffering effect of low latitudinal oceans may have distorted the response of the summer monsoon to insolation variations finally our results do not show the degree of climatic instability comparable to that recorded in the grip ice core for the last interglacial oiss 5e even though the study area is situated in a region which has been sensitive to climatic changes

holocene evolution of huangqihai lake in semi arid northern china based on sedimentology and luminescence dating the pattern of holocene palaeoclimatic change in arid semiarid northern china is debated the terminal huangqihai lake is located at the northern margin of the modern east asian summer monsoon and

milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr bp an atmospheric general circulation model has been used to simulate the climates of january and july at 3 000 yr intervals from 15 kyr bp onwards the model simulates a strengthened monsoon circulation and increased precipitation in the northern hemisphere tropics culminating at 9 6 kyr bp the computed hydrological budgets were used to estimate the area of closed lakes between 8 9 and 26 6 n giving with minor exceptions results in good agreement with geological evidence

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

huygens principle the capture of seismic energy by a soft soil layer 1 possible nonlinear coupling in surface waves is described at the texcoco array txc in mexico city shear coupled surface waves may be caused by interaction between rayleigh modes in the basement and resonant shear modes in the uppermost mud layer large amplitude monochromatic wave trains of long duration appear to be modulated by the fundamental mode of the mud layer particle motion features frequent reversals from prograde to retrograde ground motion earthquake damage in mexico city might be related to unrecognized effects related to nonlinear coupling in soft soil conditions

formation and paleoenvironment of rhizoliths of shiyang river basin tengeri desert nw china abstract rhizoliths found in bed of the late quaternary paleolake zhuyezhe minqin basin central tengeri desert nw china were studied vegetation coverage is present at some locations in the paleolake area although much of the bed area is covered with moving dunes rhizoliths are occasionally eroded out and exposed to the air the morphology of the rhizoliths resembles singular or branching carbonated tubules which are hollow in their central part the rhizoliths are black to grey and are broken and scattered randomly on the sand surface of the lake bed the lacustrine deposits are black greenish silt or silty clay with a large quantity of white petite lake snail shells the possible plant types sources and formation conditions of carbon dioxide and calcium the sedimentary and diagenetic environments and the process of rhizolith formation were discussed via examining rhizoliths macromorphology studying the micromorphology and mineralogy by microscopy cathodoluminescence and scanning electron microscope and studying the chemical compositions of cementing minerals and fragments by energy dispersive x ray spectra the original roots of the rhizoliths belong to hydrophytes such as typha latifolia scirpus maritimus and carex stenophylla lake snails and previous pollen data indicate that the rhizoliths formed in a sedimentary environment of shallow fresh water lake like marginal or palustrine areas during the holocene shallow lake water disturbance by desert wind above the loose sandy sediment or soil was favoring the rhizoliths formation a continuous supply of oxygen through water disturbance led to complete oxidation of roots and producing carbon dioxide dissolution of co2 in water and so carbonic acid production resulted in minerals weathering such as feldspar and primary carbonate particles and the release of k and ca2 ions at presence of co2 and ca2 saturated in the pore water around the roots of hydrophytes within the sediments or soil carbonate precipitation occurred around the root channel and led to rhizoliths formation as tubules the petrifaction process therefore has happened in margin of the paleolake with shallow water and weak redox condition which implies the suitability of rhizolith for reconstructing paleoenvironment

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

nonlinear ground motion amplification by sediments during the 1994 northridge earthquake it has been known since at least 1898 ref 1 that sediments can amplify earthquake ground motion relative to bedrock for the weak ground motion accompanying small earthquakes the amplification due to sediments is well understood in terms of linear elasticity hooke s law 2 but there has been a long standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes the view of geotechnical engineers based largely on laboratory studies is that hooke s law breaks down at larger strains causing a reduced nonlinear amplification seismologists on the other hand have tended to remain sceptical of this nonlinear effect mainly because the relatively few strong motion observations seemed to be consistent with linear elasticity although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3 4 the significance of nonlinearity for the type of stiff soil sites found in the greater los angeles region remains unresolved5 here we report that ground motion amplification due to sediments for the main shock of the 1994 northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks these observations imply significant nonlinearity in such amplification and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

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

dilatancy induced p waves as evidence for nonlinear soil behavior a much discussed topic in seismology deals with how and under which loading conditions soil shows nonlinear behavior and how this can be verified from seismograms seismologists have been seriously searching for signatures of nonlinear soil response to earthquakes for about two decades a mechanism explaining the dispersion in the p wave spectra due to the interaction between compressional p and shear s waves is presented shear waves in granular materials induce longitudinal dilatancy waves so called waves with approximately double frequency this can be explained with dilatancy and contractancy which is characteristic of granulates under shear deformations the predicted dispersion is observed in laboratory experiments and verified by comparing accelerograms from hard rock and soil stations from the vrancea region romania the arrival time difference between waves and s waves may theoretically be indicative of the thickness of nonsaturated granular layers these results modeled with nonlinear constitutive relations of the rate type show a specific type of nonlinearity in granular sediments also for earthquakes of moderate magnitudes

limits to recharge of groundwater from tibetan plateau to the gobi desert implications for water management in the mountain front multiple isotopic and hydrogeochemical tracers were utilized to understand the limits to recharge from tibetan plateau to gobi desert the average direct recharge rate according to chloride mass balance is between 0 9 2 5 mm yr 1 based on an annual rainfall of 120 mm yr 1 indicating that this has negligible impact on groundwater the groundwater shows markedly depleted stable isotopic composition compared to modern rainfall the signature of groundwaters around 10 4 parts per thousand to 9 6 parts per thousand delta 18 o in several wells from dajing and south lake playa differ clearly from that of the alluvial fan and modern rainfall and has lower or undetected tritium activity implying that the aquifer in the desert is maintained by palaeowater this groundwater has an estimated 14 c age of similar to 4 kyr with a recharge temperature of 7 3 degrees c at current hydraulic head gradients transit time from the recharge zone wuwei gulang alluvial fan to south lake is approximately 2200 3500 yrs indicating that groundwater flow is relatively slow and that the water resources are non renewable the geochemical information is comparable to the isotopic results of limit recharge sources of groundwater from tibetan plateau to the gobi desert the buildup of dissolved solids through evaporation is a major control on groundwater composition and the dominant anion species change systematically from hco 3 so 4 2 to cl but the dissolved ions from albite calcite dolomite and gypsum also have a significant contribution it is advised to re consider seriously the immigration policy of south lake to meet the groundwater management in the mountain front to gobi desert c 2008 elsevier b v all rights reserved

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

basin wide holocene environmental changes in the marginal area of the asian monsoon northwest china in arid regions because of spatial variability using single climate records is difficult to reconstruct the past climate change for the drainage basins holocene environmental records were collected from the upper middle and lower regions of the shiyang river drainage basin in the marginal area of the asian monsoon northwest china the main objective of this paper was to compare the records from the terminal lake and the middle and upper reaches of the basin to study the basin wide environmental changes during the early holocene the vegetation was sparse and the effective moisture was relatively low in the basin the holocene climatic optimum started between 7 0 and 8 0 cal ka bp during which the lake level reached the highest level in the terminal lake the vegetation density and the effective moisture reached the highest level during the holocene in the drainage basin from 4 7 cal ka bp the terminal lake began to shrink while the vegetation density decreased dramatically in the middle and upper regions of the drainage the effective moisture began to decrease since 3 5 cal ka bp and the arid tendency was earlier in the terminal lake than it was in the middle and upper regions of the drainage basin during the early holocene the relatively arid environment was affected by the gradually intensifying east asian monsoon and the dry westerly winds the mid holocene optimum benefited from the intensive east asian monsoon and the humid westerly winds then the east asian monsoon retreated since the late holocene in the basin the arid tendency may be related to the retracting of the east asian monsoon however the intensifying acidification after 1 5 cal ka bp may be correlated to the increasing dryness of the westerly winds

a late pleistocene holocene lacustrine record from lake manas zunggar northern xinjiang western china information on the late quaternary palaeoclimate in the zunggar desert northern xinjiang is deduced from the study of three 5 m long cores taken from lake manas analyses including the mineralogical composition of bulk sediments stable isotope contents of carbonates organic matter pollen and diatoms were performed to help reconstruct the environmental evolution of the area the chronology is provided by 9 ams 14c dates done on carbonates or organic matter the record suggests a late pleistocene humid episode radiocarbon dated at 37 000 32 000 yr b p this episode is followed by a period of extreme aridity attributed to the last glacial maximum the early mid holocene record indicates conditions generally wetter than today as previously established for western china however our results show that the holocene period is rather complex after a minor wet warm pulse estimated to be around 12 000 yr b p the most important environmental change is recorded at 10 000 yr b p it led to the establishment of a steppic vegetation cover in the catchment and of a permanent lake which lasted 4000 years fluvial sedimentation took place between about 6000 and 4500 yr b p and it coincided with a decrease in moisture availability for vegetation growth a second lacustrine episode is recorded from about 4500 to 2500 yr b p although the pollen record and a sudden influx in detrital organic matter suggest a short term dry event around 3800 3500 yr b p the last 2500 years show climate unstability and the step wise establishment of hypersaline conditions in lake manas the major post glacial environmental changes appear to be roughly in phase with those observed in tibet

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

east asian summer monsoon precipitation variations in china over the last 9500 years a comparison of pollen based reconstructions and model simulations to better understand the long term changes of the east asian summer monsoon precipitation p jja quantitative reconstructions and model simulations are needed here we develop continental scale pollen based transfer functions for p jja with weighted averaging partial least squares wa pls regression and a bayesian multinomial regression method we apply these transfer functions to a set of fossil pollen data from monsoonal china for quantitatively reconstructing the p jja changes over the last 9500 years we compare the reconstructions with p jja simulations from a coupled atmosphere ocean sea ice general circulation model the kiel climate model kcm the results of cross validation tests for the transfer functions show that both the wapls model r2 0 83 root mean square error of prediction rmsep 112 11 mm and the bayesian model r2 0 86 rmsep 107 67 mm exhibit good predictive performance we stack all p jja reconstructions from northern china to a summary curve the stacked record reveals that p jja increased since 9500 cal yr bp attained its highest level during the holocene summer monsoon maximum hsmm at similar to 7000 4000 cal yr bp and declined to present the kcm output and the reconstructions differ in the early holocene similar to 9500 7000 cal yr bp where the model suggests higher p jja than the reconstructions moreover during the hsmm the amplitude of the p jja changes similar to 20 60 mm above present in simulations is lower than the reconstructed changes similar to 70 110 mm above present the rising declining p jja patterns in reconstructions before after the hsmm are more pronounced and fluctuating than in simulations other palaeohydrological data such as lake level reconstructions indicate substantial monsoon precipitation changes throughout the holocene our results therefore show that the kcm underestimates the overall amplitude of the holocene monsoon precipitation changes

problems of nonlinear seismology abstract experimental seismic activations in situ undertaken during recent years reveal the character of three different types of nonlinear effect these are wave velocity temporal changes due to temporal changes of the stress field seismic wave interactions during comparatively small deformations 1 2 10 12 strong influence of the slow changes of the stress field and seismic vibrations on the seismic activity of the real geological media i e parameters of the seismic emission process new opportunities for detailed investigation of nonlinear effects are provided by the use of seismic vibrators that generate sinusoidal signals as well as by highly sensitive narrow frequency band recording channels these two tools open up broad new possibilities for investigation of nonlinear effects in a large variety of geological conditions and wave propagation situations these results change our opinion that nonlinear effects play a remarkable role only for strong wave propagation even very weak but detectable nonlinear effects can be used for purposes of investigating media structure and geodynamical processes for seismic prospecting and for the monitoring of oil and gas exploration

a comparison of observations of ground response to weak and strong ground motion at coalinga california abstract measurements of the response to earthquake motion of an unsaturated soil in coalinga california indicate that this response is linear within the limits of random errors for frequencies below 10 hz and for accelerations up to 0 7 g the response of the soil site relative to a bedrock site was determined by dividing the amplitude spectrum of the soil site ground motion for a given event by the amplitude spectrum of the bedrock site ground motion for the same event the relative response of this pair of sites to 23 regional and small local earthquakes is the same in the 1 to 10 hz band as the response to seven strong motion events within a random error of a factor of 1 3 at 10 to 11 hz the relative response to strong motion is significantly reduced by as much as a factor of 2 from the relative response to the 23 regional and small local earthquakes at the 95 per cent confidence level suggesting the possibility of nonlinear response the response of the soil site is a factor of 2 to 3 times larger than that of the bedrock site the variation in the spectral ratios for strong motion events and for regional and small local events about their respective averages has a standard deviation of about a factor of 2

equatorial electrojet responses to intense solar flares under geomagnetic disturbance time electric fields large enhancement in the equatorial electrojet eej current can occur due to sudden increase in the e layer density arising from solar flare associated ionizing radiations as also from background electric fields modified by magnetospheric disturbances when present before or during a solar flare we investigate the eej responses at widely separated longitudes during two x class flares that occurred at different activity phases surrounding the magnetic super storm sequences of 28 29 october 2003 during the 28 october flare we observed intense reverse electrojet under strong westward electric field in the sunrise sector over jicamarca sources of westward disturbance electric fields driving large eej current are identified for the first time model calculations on the e layer density with and without flare and comparison of the results between jicamarca and sao luis suggested enhanced westward electric field due to the flare occurring close to sunrise over jicamarca during the flare on 29 october which occurred during a rapid ae recovery a strong overshielding electric field of westward polarity over jicamarca delayed an expected eej eastward growth due to flare induced ionization enhancement in the afternoon this eej response yielded a measure of the overshielding decay time determined by the storm time region 2 field aligned current this paper will present a detailed analysis of the eej responses during the two flares including a quantitative evaluation of the flare induced electron density enhancements and identification of electric field sources that played dominant roles in the large westward eej at the sunrise sector over jicamarca

local site effects on weak and strong ground motion abstract this is a review of the current state of the art in characterizing effects of local geology on ground motion a new horizon is clear in this aspect of strong motion studies non linear amplification at sediment sites appears to be more pervasive than seismologists used to think several recent observations about the weak motion and the strong motion suggest that the non linear amplification at sediment sites may be very common first on average the amplification is always greater at the younger sediment sites for all frequencies up to 12 hz in the case of weak motion while the relation is reversed for frequencies higher than 5 hz in the case of strong motion secondly the application of the amplification factor determined from weak motion overestimates significantly the strong motion at sediment sites observed during the loma prieta earthquake within the epicentral distance of about 50 km thirdly the variance of peak ground acceleration around the mean curve decreases with the increasing earthquake magnitude finally the above non linear effects are expected from geotechnical studies both in the magnitude of departure from the linear prediction and in the threshold acceleration level beyond which the non linearity begins

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

holocene wetland environmental change based on major element concentrations and organic contents from the cheollipo coast korea abstract organic and inorganic geochemical and mineralogical analyses from core cl4 drilled in the cheollipo wetland were carried out to investigate the holocene climatic optimum the formation of pyrite and the humidity of the korean western coast during the holocene time lithostratigraphy mineralogy major element concentrations and organic contents of the sediments of the cl4 borehole core indicate that the holocene climatic optimum occurred from about 7400 to 4500 bp and that pyrite formed in brackish water tidal flat or salt marsh at least during 7400 6400 bp in addition sediments coarser in mean grain size and larger in standard deviation corresponded with periods of 8500 5400 5000 and 1700 bp during the periods the coarse sediments seem to have been delivered by high energy storm events the periods partially overlap with those of high ratios of si al na al and na ti these phenomena indicate that the weakly weathered terrigenous sediments were delivered to the cheollipo borehole core site by storm events

simultaneous study of the source path and site effects on strong ground motion during the 1989 loma prieta earthquake a preliminary result on pervasive nonlinear site effects we considered the effects of source propagation path and local site conditions on strong ground motion from the loma prieta earthquake in the following steps first the local site effect was removed from the strong motion records applying the weak motion amplification factors estimated from nearby stations of usgs regional network using the coda method then we confirmed the approximate validity of the 1 r law of geometrical spreading factor for the crustal model applicable to the region and we determined the attenuation parameter q f and source spectrum s f empirically from the site effect corrected spectral amplitude both q f and s f are consistent with the results obtained earlier for major california earthquakes we then synthesized the time history of ground acceleration by applying the stochastic simulation technique the agreement between the observed and predicted records was good for duration and spectral content we found however a strong systematic discrepancy with regard to peak acceleration namely for distances less than 50 km the predicted peak acceleration consistently overestimated the observed for sediment sites and underestimated it for the franciscan formation sites since the above systematic discrepancy applies to all the available stations within about 50 km from the hypocenter it is unlikely that the effect is due to the radiation pattern near source structure or topography it appears that the strong difference in the amplification factor between the franciscan and the sediment sites observed for weak motion disappears at acceleration levels higher than about 0 1 to 0 3 g if this is due to the nonlinear response of the sediment sites it is in the range expected from geotechnical engineering studies

inducing in situ nonlinear soil response applying an active source 1 it is well known that soil sites have a profound effect on ground motion during large earthquakes the complex structure of soil deposits and the highly nonlinear constitutive behavior of soils largely control nonlinear site response at soil sites measurements of nonlinear soil response under natural conditions are critical to advancing our understanding of soil behavior during earthquakes many factors limit the use of earthquake observations to estimate nonlinear site response such that quantitative characterization of nonlinear behavior relies almost exclusively on laboratory experiments and modeling of wave propagation here we introduce a new method for in situ characterization of the nonlinear behavior of a natural soil formation using measurements obtained immediately adjacent to a large vibrator source to our knowledge we are the first group to propose and test such an approach employing a large surface vibrator as a source we measure the nonlinear behavior of the soil by incrementally increasing the source amplitude over a range of frequencies and monitoring changes in the output spectra we apply a homodyne algorithm for measuring spectral amplitudes which provides robust signal to noise ratios at the frequencies of interest spectral ratios are computed between the receivers and the source as well as receiver pairs located in an array adjacent to the source providing the means to separate source and near source nonlinearity from pervasive nonlinearity in the soil column we find clear evidence of nonlinearity in significant decreases in the frequency of peak spectral ratios corresponding to material softening with amplitude observed across the array as the source amplitude is increased the observed peak shifts are consistent with laboratory measurements of soil nonlinearity our results provide constraints for future numerical modeling studies of strong ground motion during earthquakes

lake evolution of the terminal area of shiyang river drainage in arid china since the last glaciation investigations of geomorphology and sedimentology and analyses of radiocarbon dates grain size and carbonate of the sediment at the present dry closed basin in the terminal area of shiyang river in and china were conducted to recover the history of palaeolake change since the last glacial the terminal area was covered by eolian sand before 13 000 c 14 bp lacustrine deposits covered the eolian sand after 13 000 c 14 bp but were succeeded rapidly by eolian or fluvial deposits ca 11 200 10 000 bp this fact plus the grain size distribution and caco3 content showed that climate was extremely dry during the last glacial but wet dry oscillations characterized the late glacial a single coalescent lake over 45 m deep and 2130 km 2 formed between 10 000 6400 c 14 bp in the basin the lake disintegrated into several shallow carbonate lakes or swamps gradually after 6400 c 14 bp eolian sand reached into the most part of the basin during the period the lake evolution in the area generally reflects the east asian summer monsoon history forced by northern hemisphere insolation short time scale lake fluctuations also existed in the area since the last glacial c 2002 elsevier science ltd and inqua all rights reserved

hard rock spectral models for intermediate depth vrancea romania earthquakes the frequency dependent amplification for rock sites as well as apparent source spectra were studied using an earthquake ground motion database collected in romania almost all events occurred in the vrancea focal zone southeast carpathians which is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume the seismic activity ranges within an almost vertical stripe in depths between 60 and 170 km the database used includes several hundred records from more than 100 small magnitude m w 3 5 5 3 earthquakes that occurred in 1996 2004 and six acceleration records obtained during four large m w 7 2 6 9 6 3 and 6 0 earthquakes the characteristics of amplification were evaluated using the well known technique of horizontal to vertical h v fourier spectral ratio of the s wave phase lermo and chavez garcia 1993 the apparent source spectra were obtained from horizontal components using site h v propagation path geometric spreading and anelastic attenuation and near surface attenuation kappa factor corrections seismic radiation within the frequency range from 0 2 0 3 to 15 20 hz during the earthquakes of various magnitudes in the vrancea zone may be described by an omega square single corner frequency spectral model 2 brune spectrum the stress parameter which controls high frequency spectral amplitudes increases with magnitude from 20 30 bars for m w 3 5 up to 200 250 bars for m w 4 8 5 3 and up to 1000 bars for the case of large m w 6 0 6 5 events empirical amplification h v for rock sites showing stability for particular locations reveal high variability from station to station which together with variations of values of kappa reflects influence of local geologic and geomorphologic factors

abrupt early to mid holocene climatic transition registered at the equator and the poles paleoclimatic records from equatorial east africa antarctica and greenland reveal that atmospheric circulation changed abruptly at the early to mid holocene transition to full postglacial conditions a climatic reorganization occurred at all three sites between 8200 and 7800 years ago that lasted 200 years or less and appears to have been related to abrupt transitions in both marine and terrestrial records around the world

seismic response of liquefaction sites the authors of this technical paper focus on the seismic response of liquefaction sites by evaluating the transient shear strains and strong motion characteristics at treasure island during the 1989 loma prieta earthquake the strain levels are used to model soil and buried pipeline deformations observed in the marina district of san francisco during the same earthquake the authors found that transient strains play a critical role in lifeline performance based on the favorable comparisons of predicted and observed pipeline damage a simple model for liquefaction sites reveals that shear modulus reduction caused by increased pore pressure can amplify either acceleration or transient displacement depending on soil properties and deposit thickness liquefaction of thick loose sand deposits can attenuate accelerations while amplifying long period displacements the model offers a quantitative means of characterizing the phenomenon of ground oscillation that has been noted at liquefaction sites

lateglacial and holocene variation in aeolian sediment flux over the northeastern tibetan plateau recorded by laminated sediments of a saline meromictic lake predominantly laminated lake sediments from a saline closed basin lake on the northeastern tibetan plateau were investigated using a multi proxy approach 14c accelerator mass spectrometry dating smear slide analysis loss on ignition grain size x ray diffraction elemental concentration ostracod assemblages stable isotopes of ostracod shells to trace the regional environmental and climatic history in the lateglacial and holocene before about 15 cal ka bp small saline water bodies probably filled the basin under unstable cold and harsh environmental conditions soon after about 14 9 cal ka bp a relatively deep saline lake was established probably as a result of runoff from melting snow ice and frozen ground in the lake s catchment large changes in flux of aeolian material to the lake were recorded during this initial period of formation of lake kuhai highest lake levels a low sediment accumulation rate and less saline conditions were maintained between about 12 8 and 7 1 cal ka bp when the aeolian influx diminished significantly after about 7 1 cal ka bp the aeolian influx remained at a moderate level apart from a strongly increased dust delivery to the lake between about 6 1 and 5 4 cal ka bp and a minor short lived period of slightly enhanced aeolian influx at about 2 7 cal ka bp the strongly enhanced dust input to the lake between 6 1 and 5 4 cal ka bp represented the largest influx of aeolian material to lake kuhai during the entire holocene however evidence for climatic deterioration during this period is not seen at most other palaeoclimate sites on the tibetan plateau but instead a significant increase in aridity has been recorded at numerous sites in the northern foreland of the tibetan plateau and on the chinese loess plateau the large dust input to lake kuhai between 6 1 and 5 4 cal ka bp probably did not result from a severe climate deterioration on the tibetan plateau itself but from the pronounced aridity in its northern and eastern foreland in contrast the increase in dust influx about 2 7 cal ka bp seems to correspond to a brief warming spell recorded at other sites on the tibetan plateau too a slight increase in lake level and decrease in salinity after about 0 6 cal ka bp suggests a slightly higher effective moisture during the final lake stage accompanied by a somewhat larger dust influx this apparent contradiction possibly results from enhanced human activities on the northeastern tibetan plateau during the last 600 years copyright 2009 john wiley sons ltd

nonlinear soil amplification its corroboration in taiwan nonlinear ground response at two strong motion arrays in taiwan is studied using the spectral ratio technique at the smart1 array we calculate the frequency dependent soil amplification functions as a ratio of the spectra at alluvium to rock sites and study their dependence on the excitation level hor izontal components of shear waves are considered we compare 1 the average spectral ratios on weak and strong motions 2 the ratios for the mainshocks and aftershocks and 3 the ratios for the strong shear waves and their coda at the smart1 array weak motions have a peak horizontal acceleration pha less than 30 gal strong motions are in the range of 100 to 267 gal comparison of the average weak and strong motion spectral ratios shows a significant deamplification of strong motion between 2 and 9 hz exceeding the error margin estimated by the standard deviations the maximum deamplifi cation occurs at approximately 6 5 hz where the average weak motion ampli fication is 2 9 versus 0 40 in the strong motion a similar pattern is exhibited by the ratios calculated for the mainshocks and the aftershocks as well as for the shear waves and their coda the spectral ratio calculated from a single re alization of coda is identical to the average ratio obtained from many small earthquakes at the smart2 we analyze spectral ratios between the stations on pleistocene terrace deposits and recent alluvium which characterize the rel ative response at these two types of sediments weak motion is pha less than 13 gal while strong motion extends from 100 to 295 gal strong motion spec tral ratios between terrace and alluvial sites are consistently reduced in the fre quency range from 1 to 10 hz compared with the weak motion this effect is insensitive to the variation in distance between stations from 7 9 to 11 4 km as well as the azimuthal change of up to 80 in the station pair strike we attribute the observed discrepancies between weak and strong motion ampli fications to the differential nonlinear response occurring at terrace and alluvial sites our results document a significant nonlinear ground response at both ar rays

experimental investigations of nonlinear seismic effects abstract special experimental investigation using seismic vibrators allowed the propagation of periodic seismic signals accompanied by strong nonlinear effects to be demonstrated these effects are caused by the physical nonlinearity of a real geological medium the effects of higher harmonic generation and self demodulation of signals are studied over a large range of distances from a source a conclusion is that nonlinear properties of the medium should be taken into account in corresponding physical models used in seismology and seismic prospecting

sedimentary evidence and luminescence and esr dating of early pleistocene high lake levels of megalake tengger northwestern china the timing of high lake level stands during the late pleistocene in western china remains controversial here we report new results from megalake tengger based on a study of palaeo shorelines and a drill core from baijian lake in the northwestern tengger desert multiple dating methods based on luminescence signals quartz optically stimulated luminescence k feldspar post infrared infrared stimulated luminescence and electron spin resonance signals of quartz were used to date beach sands from palaeo shoreline profiles at altitudes of similar to 1310 m 20 m above lake level similar to 1320 m 30 m and similar to 1350 m 60 m and from the top 20 m of sandy sediments from the drill core obtained from the modern beach of baijian lake the dating results show that high lake level stands associated with the previously reported megalake tengger similar to 1310 1320 m occurred during the late early to middle pleistocene which is much earlier than previously reported in addition no geomorphological evidence of shorelines and sedimentary evidence from the drill core profile were found to support the previously reported late pleistocene lake levels our results indicate that the exact age of the previously reported high lake level event in a large part of northwestern china during the late pleistocene needs to be re evaluated copyright c 2020 john wiley sons ltd

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

nonlinear site effects on strong ground motion at a reclaimed island recently there has been an increased interest in the study of the nonlinearity in soil response for large strains through in situ earthquake observations in this paper the downhole array acceleration data recorded at a reclaimed island kobe during the 1995 kobe earthquake are used to study nonlinear site effects particular attention is given to the liquefaction induced nonlinear effects on the recorded ground motions by using the spectral ratio and the spectral smoothing technique the characteristics of the ground motions are analyzed it is shown that the peak frequencies in spectral ratios were shifted to lower frequencies when the strongest motions occurred the increase in the predominant period was caused primarily by a strong attenuation of low period waves rather than by amplification of long period motions based on the spectral analyses the nonlinearity occurring in the shallow liquefied layer during the shaking event is identified manifested by a significant reduction of the shear modu

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

response of the african monsoon to orbital forcing and ocean feedbacks in the middle holocene simulations with a climate model that asynchronously couples the atmosphere and the ocean showed that the increased amplitude of the seasonal cycle of insolation in the northern hemisphere 6000 years ago could have increased tropical atlantic sea surface temperatures in late summer the simulated increase in sea surface temperature and associated changes in atmospheric circulation enhanced the summer monsoon precipitation of northern africa by more than 25 percent compared with the middle holocene simulation with prescribed modern sea surface temperatures and provided better agreement with paleorecords of enhanced monsoons

wood types and human impact between 4300 and 2400 yr bp in the hexi corridor nw china inferred from charcoal records based on identification of fossil charcoals from 11 sites in the hexi corridor we reconstruct the local vegetation community and human impact on it in the period from 4300 to 2400 cal yr bp more

magnitude of nonlinear sediment response in los angeles basin during the 1994 northridge california earthquake the study of nonlinear site response has practical difficulties due to large ambiguities in isolating local response from other competing effects we chose a sedimentary site lf6 in los angeles basin that 1 has the closest reference rock sites available compared to other stations allowing an accurate estimation of local amplification and 2 illustrates clear resonance in the near surface in our opinion this case represents the least ambiguity in the identification of possible nonlinearity the site responses during the northridge the 1987 whittier narrows events and the northridge aftershocks are compared the station shows a fundamental resonance frequency change between the higher and lower amplitude motions in the entire ensemble of 17 events used the net shear modulus reduction during the northridge event is a factor of 1 3 to 1 4 compared to the whittier narrows event and is a factor of 1 7 compared to the aftershocks this result provides guidance of what to expect at other sites in the basin where the nonlinear response is less easy to characterize

nonlinear soil response a reality geotechnical models consistently indicate that the stress strain relationship of soils is nonlinear and hysteretic especially at shear strains larger than 10 5 to 10 4 nonlinear effects such as an increase in damping and reduction in shear wave velocity as excitation strength increases are commonly recognized in the dynamic loading of soils on the other hand these effects are usually ignored in seismological models of ground motion prediction because of the lack of compelling corroborative evidence from strong motion observations the situation is being changed by recently obtained data explicit evidence of strong motion deamplification accompanied by changes in resonant frequencies are found in the data from the 1985 michoacan mexico and the 1989 loma prieta california earthquakes the events recorded by the vertical and surface accelerograph arrays in taiwan as well as a number of other events throughout the world evidence of nonlinear behavior becomes apparent beyond a threshold acceleration of 100 to 200 gal nonlinearity is considerable in cohesionless soil but may be negligible in stiff soils the findings of recent years indicate that nonlinear site effects are more common than previously recognized in strong motion seismology

geochemical evidence of the sources of aeolian sands and their transport pathways in the minqin oasis northwestern china identification of aeolian sand sources occurring in oases of desert environments is of great importance for understanding desertification processes and for developing strategies for sustainable development in arid regions combined with wind data and hierarchical cluster analysis we analyzed the spatial characteristics of major and trace elements of sands sampled at the margins of the minqin oasis northwestern china and its adjacent deserts the badain jaran desert and the tengger desert with the purpose to identify the aeolian sand sources and their transport pathways in the region the spatial distribution revealed by bivariate plots of cr ni cr v y ni al v zr hf zr hf and ternary plots of major and trace elements showed that sands between the west b badain jaran desert bm the dune belt between badain jaran and the minqin oasis and tne dune field located in the northeast margin of the minqin oasis and southeast tsw dune field located in the southeast margin of the minqin oasis sides of the oasis have different provenances while the composition of sands in the minqin oasis m and in the dune field located in the south margin tm is associated with both the variations in abundance of k rb ba and sr were used as indicators of aeolian transport processes our results show that while aeolian sands from the badain jaran desert can be transported over mountains and over long distances by northwest winds to the west sides of the minqin oasis they cannot directly reach neither bypass the oasis to the east side our interpretation is that the oasis can act as an effective barrier to stop the migration of dune fields both in the badain jaran desert and the tengger desert however the extensive occurrence of aeolian sands in the minqin oasis indicates that its role in preventing desert encroachment should not be overestimated c 2014 elsevier ltd and inqua all rights reserved

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

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

holocene climatic and environmental changes in the arid and semi arid areas of china a review this paper reviews recently published literature most of which was published in chinese and searches for regional patterns of holocene changes useful in depicting global patterns the holocene in the xinjiang region can be divided into three stages a warming and dry early stage from 11 similar to 10 to 8 similar to 7 ka bp a warm and wet middle stage from 8 similar to 7 to 4 5 similar to 3 ka bp and a fluctuating cool and dry late stage since 4 5 similar to 3 ka bp the holocene in the northern tibetan plateau can also be divided into three stages a warming and wet stage from 10 5 similar to 10 to 5 similar to 4 ka bp followed by a variable drying and probably warm stage 5 similar to 4 to 3 ka bp and ending with a cool and dry stage since 3 ka bp in the inner mongolian plateau the early holocene from 10 5 similar to 9 5 to 8 similar to 7 5 ka bp was warming and dry and a warm and wet climate occurred from 7 5 to 3 5 during which the best time was 6 3 3 8 ka bp the climate has been variably drying and probably cooling since 3 5 ka bp in the northwestern part of the loess plateau several holocene palaeosols have been identified 10 9 7 5 5 4 3 and 2 7 2 ka bp with the 7 5 5 ka bp palaeosol being most strongly expressed the best developed palaeosol equivalent in major valleys is a swamp wetland facies deposited between 8885 and 3805 c 14 yr bp under an extremely wet regime the climate has fluctuated significantly at least three times around a dry and probably cool regime after the swamp wetland facies depositional period our summary shows that the holocene climatic optimum occurred nearly contemporaneously 8 5 ka bp at all sites in the xinjiang region in the inner mongolian plateau and in the northwestern part of the loess plateau a warming and wet early holocene 10 8 ka bp in the northern tibetan plateau is most likely related to high effective soil moisture resulting from snow and ice melting we propose here that the middle holocene climatic optimum 8 5 ka bp in arid to semi arid china was primarily a delayed response of the low latitude oceans to high latitude peak insolation 9 8 ka bp

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

climatic changes in the qinghai xizang tibetan region of china during the holocene climatic changes in the qinghai xizang plateau of china were studied by analyzing the composition of peat and layers of sand and gravel distributed along the southern slopes of nianqing tanggula and gangdise mountains cross sections of deposits near a number of interior lakes in xizang past glacial variations on the southern slope of nianqing tanggula mountain and landform changes south of the yaluzangbu river such geologic evidence suggests a division of five climatic periods since the beginning of the holocene 1 the wumadung interval 10 000 7500 yr b p slightly cold and dry 2 qilongduo interval 7500 3000 yr b p warm and moist 3 the mid neoglacial period 3000 1500 yr b p cold except between 2500 and 200 yr b p when it was warmer 4 the dawelong interval 1500 300 yr b p mild and 5 the little ice age 300 0 yr b p cold these changes progressed in a similar but not identical pattern as those in the northeastern part of china and in the northern region of europe

timing and spatial distribution of mid holocene drying over northern china response to a southeastward retreat of the east asian monsoon 1 to determine the timing and spatial distribution of mid holocene drying over northern china the mineralogical and oxygen isotopic composition of authigenic carbonate from a closed lake at bayanchagan southern inner mongolia were measured further analysis and synthesis of the spatial geological data were performed results from lake bayanchagan show a significant drying at 6000 calendar years cal years b p indicated by dolomite precipitation and a striking rise in 18o values the synthesis of spatial data reveals a zonal distribution for timing of drying over northern china in the mid holocene which began at 9000 7000 cal years b p in deserts of north central china at 7000 5500 cal years b p drying extended into the desert steppe transitional zone and at 4500 cal years b p into northeastern and south central china this pattern indicates that the east asian summer monsoon has significantly retreated southeastward since the mid holocene which may be related to orbitally induced northern hemisphere insolation changes a retreat of 400 550 km is inferred for the front of the summer monsoon from 6500 to 4500 cal years b p

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

wildfire history and climatic change in the semi arid loess tableland in the middle reaches of the yellow river of china during the holocene evidence from charcoal records high resolution macroscopic charcoal and sediment analysis was used to reconstruct fire history and environmental changes from three loess paleosol profiles on the semi arid loess tableland landsca

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

a holocene dust record in arid central asia inferred from lake barkol northwest china grain size distributions and detrital minerals were investigated for modern dust and for lacustrine sediment in lake barkol region northwest china characteristics of the modern dust and lacustrine sediments principle component analysis and changes of quartz contents all suggest grain size 45 138 m in the core sediment is the dust sensitive component it indicates that high dust flux climate occurred at mid holocene 5 5 4 5 cal ka bp corresponding to the high dust flux record in northwest pacific and the drought interval of deserts in northwest china during the mid holocene the strong dust activity is in contradiction with the climatic optimum recorded by the lacustrine evidence in xinjiang different responses of the dust source region and watershed to the regional climate may have led to the inconsistency between dust and climate records during the mid holocene in arid central asia

late quaternary river terrace sequences in the eastern kunlun range northern tibet a combined record of climatic change and surface uplift the kunlun range a reactivated orogenic belt constitutes the northern margin of the tibetan plateau the extreme relief and major landforms of the kunlun range are a product of late cenozoic tectonics and erosion however well developed late quaternary terraces that occur along the northern slope of the kunlun range probably resulted from climatic change rather than surface uplift the terrace sequences formed in thick quaternary valley fills and have total incision depths of 50 60 m optically stimulated luminescence dating was employed to place time controls on the valley fills and associated terraces dating results suggest that periods of significant aggradation were synchronous between different rivers and correspond to the last glacial stage the abrupt change from aggradation to incision occurred between 21 9 2 7 and 16 2 2 ka coincident with the last glacial interglacial transition additional terraces developed during the late glacial period and early to middle holocene based on a broader set of chronological data in northern tibet at least four regional incision periods can be recognized chronological data terrace elevation profiles and climate proxy records suggest that these terracing periods were triggered by cool and or wet climatic conditions a geometric survey of the riverbed longitudinal profile suggests that surface uplift serves as a potential dynamic forcing for long term incision a model is proposed for terrace formation as a response to climatic perturbation in an uplifted mountain range

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