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

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 initiation of sedimentary furrows by standing internal waves longitudinal helical vortices are generally considered to be the cause of longitudinal sedimentary bedforms in tidal oscillatory flows however it is not clear how a regular system of vortices will become fixed for long enough to establish the bedforms it is proposed that the presence of standing internal waves with axes parallel to the tidal current have provided the basic flow pattern on which longitudinal helical vortices develop in southampton water the observed furrows then developed in a pattern determined by the standing internal waves

mineral magnetism of lacustrine sediments and holocene palaeoenvironmental changes in dali nor area southeast inner mongolia plateau china mineral magnetic measurements and analysis of total organic carbon toc and carbon nitrogen c n were performed on two ams 14c dated lacustrine sequences recovered from xiaoniuchang and jiangjunpaozi 42 n 117 e the two sites lie in the dali nor area of southeast inner mongolia plateau where the semi humid climate transforms into a semi arid one sirm low frequency magnetic susceptibility lf irm20mt hirm and irm20mt sirm may largely reflect the erosion of catchment materials and dilution effect of organic matter on deposited magnetic minerals irm 100mt sirm and irm 300mt sirm likely indicate the aeolian activities sirm lf positively correlated to sand percentage of sediments is diagnostic of changes of lake levels or effective humidity complemented by the data of toc and c n and of previously accomplished analyses of grain size loss on ignition loi and pollen the variations in mineral magnetism reveal holocene palaeoenvironmental changes conditions were quite dry and cool before 9970 years bp and then humidified in jiangjunpaozi the effective humidity maximised prior to 8000 years bp and subsequently declined in the two sites the less wet but warmer conditions persisted in jiangjunpaozi until 6600 years bp and xiaoniuchang until 5600 years bp deterioration occurred since then and culminated during 4300 1300 years bp in jiangjunpaozi and 3000 730 years bp in xiaoniuchang which was followed by a moderate but probably very short amelioration in the two sites

eolian quartz flux to lake biwa central japan over the past 145 000 years abstract eolian quartz flux eqf g cm 2 103yr 1 to lake biwa central japan provides direct information on variations of the east asian winter monsoon lake biwa sediments spanning the past ca 145 000 yr are characterized by two main periods when eqf values were significantly greater than 5 50 g cm 2 103yr 1 and two main intervals during which eqf values were lower two periods with eqf values 5 50 g cm 2 103yr 1occurred from ca 145 000 to 125 000 and 73 000 to 13 000 yr b p while times of lower eqf values occurred from ca 125 000 to 73 000 yr b p and around ca 5500 yr b p between ca 125 000 and 73 000 yr b p three minimum eqf values and two intervening peaks of slightly higher eqf values are recorded eqf increased markedly from ca 73 000 to 13 000 yr b p whereas between ca 53 000 and 20 000 yr b p the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes the data imply that the east asian winter monsoon strengthened during the periods when eqf values were high and weakened during the intervals with low eqf values the eqf record of lake biwa can be correlated with the grain size record of the quartz fraction in chinese loess and with the specmap marine 18o record however the eqf record apparently lags ca 5000 yr behind the loess and 18o records during stage 6 5 and 2 1 transitions and ca 10 000 yr during stage 5 4 transition these apparent lags could be due to problems with the chronology alternatively they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions

trapped internal waves over undular topography we describe observations of slowly decelerating stratified flow over undular bottom topography in an estuary the flow which initially was supercritical with respect to the first internal wave mode approached a resonance after it had become subcritical a series of acoustic images showed large amplitude first mode trapped waves during this phase of the tide we derive a criterion for quasi steady response and present an extension of yih s class ii linear finite amplitude solutions that accounts for the waves observed

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

abrupt change of sediment records in the southern south china sea during the last glacial period and its environment significance abstract chemical compositions of sediments at core ns07 25 6 39 945 n 113 32 936 e water depth 2006 m are analyzed to discuss abrupt change of sediment records in the southern south china sea scs during the last glacial period and its environmental implications major and trace elements experienced three significant changes which occurred at 31 9 26 1 and 18 5 ka bp respectively at 31 9 ka bp when sea surface temperature remained relatively low terrigenous sediment flux increased but biogenic activities weakened greatly at 26 1 ka bp both terrigenous sediment flux and biogenic fractions number were steady however some elemental ratios changed noticeably at that time before 26 1 ka bp core sediments with low nb ta but high zr hf ratios were mainly derived from the paleo mekong and or molengraaff rivers exposed on the sunda shelf at that time after 26 1 ka bp sediments with high nb ta but low zr hf ratios probably relate to strengthened impact of deep water current since 18 5 ka bp sea level ascended rapidly from 110 m below the present terrigenous sediment flux decreased and biogenic activities strengthened continuously probably related with the east asian monsoon evolution

shear instability in a highly stratified estuary abstract shear instability is found to be the principal mechanism of vertical exchange within the pycnocline of a salt wedge estuary a field program involving high resolution velocity and density measurements as well as high frequency acoustic imagery allowed direct comparison of instantaneous richardson number distributions to the occurrence of shear instability the theoretical stability threshold of 0 25 is consistent with the measurements based on estimates of gradients that contain the mean as well as fluctuations due to internal waves an effective stability threshold based on mean gradients is found to be approximately one third reflecting a significant contribution of internal wave shear the integral effect of the mixing process is to homogenize the gradients of velocity and density producing linear profiles of these quantities across the pycnocline a turbulent prandtl number of unity is suggested by the vertical distributions of velocity and density during periods of active vertical mixin

advection of the salt wedge and evolution of the internal flow structure in the rotterdam waterway an analysis of field measurements recorded over a tidal cycle in the rotterdam waterway is presented these measurements are the first to elucidate the processes influencing the along channel current structure and the excursion of the salt wedge in this estuary the salt wedge structure remained stable throughout the measuring period the velocity measurements indicate decoupling effects between the layers and that bed generated turbulence is confined below the pycnocline the barotropic m4 overtide structure is imposed at the mouth of the estuary and the generation of m4 overtides within the estuary is found to be relatively small internal tidal asymmetry does not make a significant contribution to the m4 velocity frequency band instead the combination of barotropic and baroclinic forcing in conjunction with the suppression of turbulence at the interface provides the main explanation for the time dependence and mean structure of the flow in the rotterdam waterway this gives rise to the observed differences in the length of the flood and ebb in the magnitudes of the flood and ebb velocities in the length of the slack water periods and in the timing of the onset of slack water at the surface and near the bed it results in the formation of distinct exchange flow profiles at the head of the salt wedge around slack water and the creation of maximal velocities at the pycnocline during flood advection governs the displacement and structure of the salt wedge since turbulent mixing is suppressed the tidal displacement of the salt wedge controls the height of the pycnocline above the bed at a particular site hence it controls the height to which bed generated turbulence can protrude into the water column consequently the authors find asymmetries in the structure of the internal flow turbulent mixing and bed stresses that are not related to classical internal tidal asymmetry

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

gas aerosol ash interaction in volcanic plumes new insights from surface analyses of fine ash particles the reactions occurring between gases aerosols and silicate ash particles in volcanic eruption plumes remain poorly understood despite the fact that they are at the origin of a range of volcanic environmental atmospheric and health effects in this study we apply x ray photoelectron spectroscopy xps a surface sensitive technique to determine the chemical composition of the nearsurface region 2 10 nm of nine ash samples collected from eight volcanoes in addition atomic force microscopy afm is used to image the nanometer scale surface structure of individual ash particles isolated from three samples we demonstrate that rapid acid dissolution of ash occurs within eruption plumes this process is favoured by the presence of fluoride and is believed to supply the cations involved in the deposition of sulphate and halide salts onto ash afm imaging also has permitted the detection of extremely thin 10 nm coatings on the surface of ash this material is probably composed of soluble sulphate and halide salts mixed with sparingly soluble fluoride compounds the surface approach developed here offers promising aspects for better appraising the role of gas aerosol ash interaction in dictating the ability of ash to act as sinks for various volcanic and atmospheric chemical species as well as sources for others c 2007 elsevier b v all rights reserved

the immersion mode ice nucleation behavior of mineral dusts a comparison of different pure and surface modified dusts in this study we present results from immersion freezing experiments with size segregated mineral dust particles besides two already existing data sets for arizona test dust atd and fluka kaolinite we show two new data sets for illite nx which consists mainly of illite a clay mineral and feldspar a common crustal material the experiments were carried out with the leipzig aerosol cloud interaction simulator after comparing the different dust samples it became obvious that the freezing ability was positively correlated with the k feldspar content furthermore a comparison of the composition of the atd illite nx and feldspar samples suggests that within the k feldspars microcline is more ice nucleation active than orthoclase a coating with sulfuric acid leads to a decrease in the ice nucleation ability of all mineral dusts with the effect being more pronounced for the feldspar sample

revised tephra volumes for cascade range volcanoes abstract isopach maps from tephra eruptions from mount st helens were reported in carey et al 1995 and for tephra eruptions from glacier peak in gardner et al 1998 for exponential thinning the isopach data only define a single slope on a log thickness versus square root of area plot carey et al 1995 proposed a model that was used to estimate a second slope and volumes were presented in both studies using this model a study by sulpizio 2005 for estimating the second slope and square root of area where the lines intersect involves a systematic analysis of many eruptions to provide correlation equations the purpose of this paper is to recalculate the volumes of cascades eruptions and compare results from the two methods in order to gain some perspective on the methods for estimating the second slope we use data for thickness versus distance beyond the last isopach that are available for some of the larger eruptions in the cascades the thickness versus square root of area method is extended to thickness versus distance by developing an approximate relation between the two assuming elliptical isopachs with the source at one of the foci based on the comparisons made between the carey et al 1995 and sulpizio 2005 methods it is felt that the later method provides a better estimate of the second slope for mount st helens the estimates of total volume using the sulpizio 2005 method are generally smaller than those using the carey et al 1995 method for the volume estimates of carey et al 1995 the volume of the may 18 1980 eruption of mount st helens is smaller than six of the eight previous eruptions with the new volumes using the sulpizio 2005 method the 1980 eruption is smaller in volume than the upper end of the range for only three of the layers wn ye and yn and is the same size as layer we thus the 1980 eruption becomes representative of the mid range of volumes rather than being in the lower range

ice formation in ash influenced clouds after the eruption of the eyjafjallajokull volcano in april 2010 1 the influence of volcanic ash on heterogeneous ice nucleation in tropospheric clouds is investigated on the basis of 90 observed cloud cases the clouds were observed with polarization lidars at the two central european earlinet stations leipzig 51 3 n 12 4 e and maisach 48 2 n 11 3 e 25 km northwest of munich germany in volcanic aerosol layers which originated from the strong eruptions of the icelandic eyjafjallajokull volcano in april 2010 case studies of evolving boundary layer cumuli and long lasting free tropospheric cloud events with unusual behavior mixed phase cloud complex cirrus deck are discussed a clear impact of ash is observed the ice nuclei concentration derived from the lidar observations has been estimated to range from 2 20 per liter in the boundary layer and from 100 300 per liter at cirrus level the statistical analysis based on the 90 evaluated cloud cases revealed that all observed cloud layers with cloud top temperatures of below 15 c contained ice typically under non volcanic aerosol conditions such a high fraction of ice containing clouds is not reached before temperatures decrease below 25 c over central europe

resonant internal waves in fluid flow understanding the flow of a stratified fluid over an uneven bed is an important problem in hydrodynamics previous field experiments using acoustic imagery1 3 have enhanced our understanding of internal wave generation mechanisms these studies have generally concentrated on isolated topographic features that show large amplitude long internal waves and hydraulic jumps as the flow becomes critical defined in the hydraulic sense such that a long wave speed vanishes with respect to a fixed coordinate system we present field observations of stratified fluid flow over a nearly periodic topographic relief which show a unique series of resonant internal waves the observations carried out in the rotterdam waterway show the presence of internal waves with wavelengths commensurate with those of the topography of the waterway bed and amplitudes that are three to four times larger than the relief of the topography generating them resonant internal waves may be important in understanding the flow dynamics of stratified coastal environments and may have consequences for atmospheric flows over mountain ranges

a 13 000 year paleolimnological record from the uinta mountains utah inferred from diatoms and loss on ignition analysis paleolimnological research in mountainous regions of the western united states provide baseline understanding of how these lake systems will respond to ongoing climate change fossil diatom assemblage and loss on ignition data were investigated from a 13 000 year lake sediment core from the uinta mountains northeastern utah usa results indicate the presence of three major zones of environmental change 1 from 12 9 10 9 cal ka modern lake formation began temperatures were cool and water was turbid 2 from 10 9 3 5 cal ka conditions were warmer than present and the lake stratified during the summer and 3 beginning approximately 3 5 cal ka temperatures decreased relative to the previous zone and the lake appears to have become increasingly alkaline shifts in diatom taxa relative abundances within the middle zone ca 8 2 6 5 and 5 0 3 5 cal ka are probably caused by precipitation driven decreases in alkalinity and increases in lake depth this record reflects evolution of the lake system and suggests that currently rising temperatures will reduce ice cover and enhance lake stratification and internal nutrient cycling any future changes in precipitation patterns may also impact lake ecology through shifts in alkalinity and or depth

bimodal grain size distribution of chinese loess and its palaeoclimatic implications grain size analysis indicates that chinese loess generally shows a bimodal distribution with a coarse and a fine component the coarse component comprising the main part of the loess has pronounced kurtosis and is well sorted which is interpreted to be the product of dust storms generated by low altitude northwesterly winds its grain size reflects the strength of the low altitude circulation in the dust seasons of the year and its percentage provides an indicator of the source area aridity and the frequency of dust storms conversely the fine component has a wide grain size range and is poorly sorted sedimentary illustrations based on the grain size distribution characteristics of bulk samples and of detrital quartz suggest that the fine component probably represents the background dust load of the atmosphere and is mainly transported by high altitude westerly airstreams its grain size provides an estimate of the westerly air stream intensity the coarse and fine components of a loess sample can be mathematically separated by fitting a designated mathematical distribution function to the measured grain size data and this procedure constitutes an approach for reconstructing the palaeowind system of northern china c 2003 elsevier b v all rights reserved

age constraints on the late quaternary evolution of qinghai lake tibetan plateau dating and geomorphology of shoreline features in the qinghai lake basin of northwestern china suggest that contrary to previous interpretations the lake likely did not reach levels 66 140 m above modern within the past 90 000 yr maximum highstands of 20 66 m above modern probably date to marine isotope stage mis 5 mis 3 highstands are undated and uncertain but may have been at or below post glacial highs the lake probably reached 3202 3206 m 8 12 m during the early holocene but stayed below 3202 m after 8 4 ka this shoreline history implies significantly different hydrologic balances in the qinghai lake basin before 90 ka and after 45 ka possibly the result of a more expansive asian monsoon in mis 5

influence of atlantic meridional overturning circulation on the east asian winter monsoon east asian summer monsoon precipitation varied on millennial timescales during the last glacial period sediment records and climate modelling suggest that the winter monsoon was also affected by millenial scale variability and that the abrupt changes were driven by changes in the strength of the atlantic meridional overturning circulation

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

pedogenic response to millennial summer monsoon enhancements on the tibetan plateau abstract the asian summer monsoons experienced both rapid episodic enhancement and long term evolution with the uplift of tibet the response of pedogenesis to those events on the tibetan plateau at mean elevations of 4000 5000 m is of great interest and significance in deciphering the history of asian and tibetan summer monsoons and in understanding soil development deterioration and management the over 22 m loess paleosol sequence at hezuo on the eastern tibetan plateau extending back through the last interglaciation and the thickest late pleistocene sequence identified thus far on the plateau provides a unique opportunity to tackle the above topics detailed chronology and soil development determined by field pedofeatures and soil proxies have revealed a millennial fluctuation of the asian and tibetan summer monsoons resembling the late pleistocene north atlantic climatic record the end of each heinrich event is closely followed by formation of a stronger paleosol and then some much weaker thin soil horizons weathered loess or loess the episodes of stronger soil development or paleosol events correspond without exception to strongest summer monsoon enhancement at the beginning or in the early part of each bond cycle recorded in the north atlantic the strongest pedogenesis and summer monsoon enhancement is observed to occur during 43 36 ka bp which is not observed in climatic records outside tibet probably indicating a coherent enhancement of asian and tibetan summer monsoons in the last mega interstadial mis3 increase of organic matter excluding decomposition and change of soil types from last interglacial calcic cambisols to holocene chernozems suggests an increase of relative humidity implying partially an increase of elevation due to late pleistocene rapid uplift of the tibetan plateau

decoupled warming and monsoon precipitation in east asia over the last deglaciation our understanding of the continental climate development in east asia is mainly based on loess paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes delta o 18 of stalagmites from several chinese caves based on these records it is thought that east asian summer monsoon easm precipitation generally follows northern hemisphere nh summer insolation however not much is known about the magnitude and timing of deglacial warming on the east asian continent in this study we reconstruct continental air temperatures for central china covering the last 34 000 yr based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess paleosol sequence from the mangshan loess plateau the results indicate that air temperature varied in phase with nh summer insolation and that the onset of deglacial warming at similar to 19 kyr bp is parallel in timing with other continental records from e g antarctica southern africa and south america the air temperature increased from is c at the onset of the warming to a maximum of 27 degrees c in the early holocene similar to 12 kyr bp in agreement with the temperature increase inferred from e g pollen and phytolith data and permafrost limits in central china comparison of the tetraether membrane lipid derived temperature record with loess paleosol proxy records and stalagmite 5180 records shows that the strengthening of easm precipitation lagged that of deglacial warming by ca 3 kyr moreover intense soil formation in the loess deposits caused by substantial increases in summer monsoon precipitation only started around 12 kyr bp ca 7 kyr lag our results thus show that the intensification of easm precipitation unambiguously lagged deglacial warming and nh summer insolation and may contribute to a better understanding of the mechanisms controlling ice age terminations

temperature variability and vertical vegetation belt shifts during the last 50 000 yr in the qilian mountains ne margin of the tibetan plateau china abstract a 13 94 m long sediment core collected from a medium sized lake in the qilian mountains ne tibetan plateau china was analysed palynologically at 81 horizons the interpretation of indicator taxa yielded various vertical shifts of the vegetation belts these palaeovegetation results have been checked with lake surface pollen spectra from 8 lakes representing different altitudinal vegetation belts our main findings are the following a short period of the late marine isotope stage 3 around 46 000 yr ago was characterized by interglacial temperature conditions with a tree line above its present day altitude during the lgm the vicinity of the lake was not covered by ice but by sparse alpine vegetation and alpine deserts indicating that the climate was colder by 4 7 c than today markedly higher temperatures were inferred from higher arboreal pollen frequencies between 13 000 and 7 000 yr ago with a holocene temperature optimum and a maximal picea betula mixed forest expansion between 9 000 and 7000 yr ago when temperatures exceeded the present day conditions by at least 1 2 c alpine steppes and meadows and sub alpine shrub vegetation dominated around the lake since the middle holocene suggesting that vegetation and climate conditions were exceptionally stable in comparison to previous periods

holocene east asian monsoon variation inferred from species assemblage and shell chemistry of the ostracodes from hulun lake inner mongolia a sediment core from hulun lake inner mongolia was analyzed for species assemblages and shell chemistry of ostracodes to investigate changes in the hydrology and climate of the east asian summer monsoon margin during the holocene darwinula stevensoni was abundant ilyocypris spp scarce littoral ostracodes absent and mg ca sr ca and 18o were low 11 100 to 8300 yr ago indicating high lake levels and cool fresh waters darwinula stevensoni declined largely ilyocypris spp throve littoral ostracodes were rare and chemical indicators remained in low values 8300 to 6200 yr ago suggesting that the lake continued high stands but water became warm the lake then contracted and water became cool brackish 6200 to 4300 yr ago littoral ostracodes flourished 4300 to 3350 yr ago marking the lowest lake levels of the entire holocene the lake level recovered and water salinity decreased 3350 to 1900 yr ago from 1900 to 500 yr ago the lake maintained the preceding status albeit lowered stands and increased salinities 1100 to 800 yr ago during the recent 500 yr the lake expanded and water salinity decreased the data imply that the east asian summer monsoon did not intensify until 8300 yr ago and weakened dramatically 4300 to 3350 yr ago

a novel apparatus for the simulation of eruptive gas rock interactions the chemical interactions between hot volcanic gases and co erupted magmatic and lithic particles within eruption plumes and pyroclastic flows are increasingly investigated for their relevance to the impacts of ash emission on natural and human environments laboratory experiments are critical to our understanding of high temperature gas ash interactions but previous studies are yet to replicate the chemical composition of the high temperature volcanic gases involved here we present a unique apparatus the advanced gas ash reactor capable of generating an atmosphere of h2o co2 so2 and hcl at temperatures ranging from 200 to 900 c under variable heating and cooling rates experiments utilising the reactor can inform investigations of a range of topics from subsurface gas rock interaction and in plume gas adsorption processes to the effect of ash surface chemistry on marine nutrient loadings and atmospheric chemistry our results demonstrate the differences in high temperature gas uptake by volcanic glass powders under both hydrous and anhydrous atmospheres and accordingly demonstrate the utility of the new reactor

controls on the surface chemical reactivity of volcanic ash investigated with probe gases increasing recognition that volcanic ash emissions can have significant impacts on the natural and human environment calls for a better understanding of ash chemical reactivity as mediated by its surface characteristics however previous studies of ash surface properties have relied on techniques that lack the sensitivity required to adequately investigate them here we characterise at the molecular monolayer scale the surfaces of ash erupted from eyjafjallajokull tungurahua pinatubo and chaiten volcanoes interrogation of the ash with four probe gases trimethylamine tma n ch3 3 trifluoroacetic acid tfa cf3cooh hydroxylamine ha nh2oh and ozone o3 reveals the abundances of acid base and redox sites on ash surfaces measurements on aluminosilicate glass powders as compositional proxies for the primary constituent of volcanic ash are also conducted we attribute the greater proportion of acidic and oxidised sites on ash relative to glass surfaces evidenced by comparison of tma tfa and ha o3 uptake ratios in part to ash interaction with volcanic gases and condensates e g h2o so2 h2so4 hcl hf during the eruption the strong influence of ash surface processing in the eruption plume and or cloud is further supported by particular abundances of oxidised and reduced sites on the ash samples resulting from specific characteristics of their eruptions of origin intense interaction with water vapour may result in a higher fraction of oxidised sites on ash produced by phreatomagmatic than by magmatic activity this study constitutes the first quantification of ash chemical properties at the molecular monolayer scale and is an important step towards better understanding the factors that govern the role of ash as a chemical agent within atmospheric terrestrial aquatic or biotic systems

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

reconstruction of climate and vegetation changes of lake bayanchagan inner mongolia holocene variability of the east asian monsoon a high resolution pollen and pediastrum record spanning 12 500 yr is presented for lake bayanchagan 115 21 e 41 65 n and 1355 m a s l southern inner mongolia individual pollen taxa pt mat and the pft affinity scores pft mat were used for quantitative climatic reconstruction from pollen and algal data both techniques indicate that a cold and dry climate similar to that of today prevailed before 10 500 cal yr b p the wettest climate occurred between 10 500 and 6500 cal yr b p at which time annual precipitation was up to 30 60 higher than today the early holocene increases in temperature and precipitation occurred simultaneously but mid holocene cooling started at approximately 8000 cal yr b p 1500 yr earlier than the drying vegetation reconstruction was based on the objective assignment of pollen taxa to the plant functional type the results suggest that this region was dominated by steppe vegetation throughout the holocene except for the period 9200 to 6700 cal yr b p when forest patches were relatively common inner mongolia is situated at the limit of the present east asian monsoon and patterns of vegetation and climate changes in that region during the holocene probably reflect fluctuations in the monsoon s response to solar insolation variations the early to middle holocene monsoon undoubtedly extended to more northern latitudes than at present

holocene climate changes in the mid high latitude monsoon margin reflected by the pollen record from hulun lake northeastern inner mongolia pollen assemblage data from a sediment core from hulun lake in northeastern inner mongolia describe the changes in the vegetation and climate of the east asian monsoon margin during the holocene dry steppe dominated the lake basin from ca 11 000 to 8000 cal yr bp suggesting a warm and dry climate grasses and birch forests expanded 8000 to 6400 cal yr bp implying a remarkable increase in the monsoon precipitation from 6400 to 4400 cal yr bp the climate became cooler and drier chenopodiaceae dominated the interval from 4400 to 3350 cal yr bp marking extremely dry condition artemisia recovered 3350 2050 cal yr bp denoting an amelioration of climatic conditions both temperature and precipitation decreased 2050 to 1000 cal yr bp as indicated by decreased artemisia and the development of pine forests during the last 1000 yr human activities might have had a significant influence on the environment of the lake region we suggest that the east asian summer monsoon did not become intensified until 8000 cal yr bp due to the existence of remnant ice sheets in the northern hemisphere changes in the monsoon precipitation on millennial to centennial scales would be related to ocean atmosphere interactions in the tropical pacific

east asian monsoon variability since the mid holocene recorded in a high resolution absolute dated aragonite speleothem from eastern china abstract paleoclimatic conditions associated with the east asian monsoon are reconstructed for the mid to late holocene using 18o values 819 measurements from a precisely dated 10 230th dates aragonite stalagmite from lianhua cave hunan province china 18o values 1 6 to 7 0 are interpreted to reflect the precipitation amount effect related to the strength of summer monsoonal circulation throughout this period the intensity of east asian summer monsoonal circulation declined in response to changes in insolation and a southward shift in the intertropical convergence zone itcz punctuating this first order trend are abrupt millennial to decadal scale fluctuations the most prominent of which occurred around 3337 5 yr bp and records a dramatic weakening in summer monsoonal circulation that coincides with the beginning of neoglacial conditions comparisons between the 18o values of stalagmite a1 and previously published data from stalagmite hs 4 from heshang cave and stalagmites d4 and da from dongge cave china demonstrate a similar regional response to changes in east asian monsoonal circulation several spectral analysis techniques and wavelet analysis were applied to these stalagmite records to evaluate the nature and character of cyclicity in the east asian monsoon during the holocene multi taper method mtm lomb scargle and single spectrum analysis ssa results reveal common periodicities that are unlikely to be artifacts of any single technique the periodicities expressed in the stalagmite 18o records occur at both solar and non solar frequencies and support previous interpretations that variability in monsoonal circulation responds to both solar forcing and internal climatic mechanisms wavelet analysis demonstrates that some of these frequencies are intermittent and recur at semi regular intervals which may indicate long term cyclicity that is unconstrained by the chronology of the record

late marine isotope stage 3 palaeoclimate for east asia a data model comparison abstract climate prediction under impact of anthropological greenhouse gas emission is impossible to validate but it can be inferred from past climate and modeling in east asia a general warm wet period at late marine isotope stage 3 ca 30 40 ky bp has been identified based upon extensive geological records this provides an arid humid reference for possible future warming caused by human activities based upon syntheses of geological evidence and the agcm ssib modeling this paper presents climate simulations focused on 35 ky bp using forcing of insolation glaciation and land surface conditions for east asia results of the simulation can be compared with geological records and show that 1 the climate patterns of 35 ky bp were warm wet conditions in northern china but with warm dry conditions in southern china compared to today 2 mean annual temperatures were higher in most mid low latitude areas mainly contributed to by increased winter temperatures suggesting that insolation has generated significant climate effects through the coupling in atmospheric circulation with land surface patterns 3 quaternary ice sheets in the northern hemisphere played an important role in temperature decrease at the mid high latitudes and also enhanced the south north temperature gradients which in turn increased moisture transport from low to high latitudes and increased monsoonal precipitation over the tibetan plateau and 4 vegetation changes in east asia resulted from an increased temperature in the low latitudes extended rain belt northwards into china and an enlarged area of increased precipitation inland

a complete record of holocene glacier variability at austre okstindbreen northern norway an integrated approach arctic glaciers are currently undergoing major changes but accurate knowledge about how they varied during the entire holocene is still scarce here we present a new complete glacier record from austre okstindbreen in nordland northern norway this reconstruction is based on a number of short and long cores retrieved from several downstream basins which have been analyzed by a suite of methods including geochemical elements xrf rock magnetic properties dry bulk density dbd and loss on ignition loi lake sediment distribution was surveyed and mapped prior to coring by the use of ground penetrating radar gpr independently lichen dated marginal moraines and historical information about the glacier frontal positions from old photographs and maps have made it possible to link the moraine sequence to the 210pb dated lake sediment chronology this integrated approach reveals that austre okstindbreen is the first known glacier in scandinavia to possibly have survived the holocene thermal optimum it also brackets the four largest glacier advances to c 7400 7000 1400 1200 900 700 and 300 150 years before ad 2000 b2k in contrast to most reconstructed glaciers in scandinavia the largest glacier advance was not associated with the little ice age but rather to an earlier period centred at 1300 b2k both the moraine chronology and the lacustrine records document this neoglacial advance compared to other glacier reconstructions from the northern hemisphere we identify near synchronous glacier advances occurring roughly at 4000 b2k 2700 b2k 1300 b2k and during the little ice age these correlative advances across the northern hemisphere suggest that these observed centennial scale events are a shared feature regardless of the large geographical distances separating them some minor discrepancies between different geographical areas may be caused by lack of precise dating but local climatic conditions may play a role as well

paleoclimate of southwestern china for the past 50 000 yr inferred from lake sediment records abstract long sediment cores 12 5 and 13 5 m from two lakes in yunnan province were used to infer the paleoclimate of southwest china over the past 50 000 yr during the holocene and marine isotope stage mis 3 bio induced carbonate precipitation and organic matter om production was high suggesting warm temperatures and high primary productivity in contrast sediment inorganic carbon ic and organic carbon oc concentrations were low in last glacial deposits from 38 000 to 12 000 cal yr b p indicating cool temperatures and low productivity the 50 000 yr record has alternating peaks of carbonate and coarse grain 38 m quartz that reflect warm moist interglacial or interstadial conditions alternating with cold dry glacial or stadial conditions respectively spectral analysis of the carbonate and quartz signals reveals power concentrated at periods of 7200 and 8900 cal yr respectively that may reflect a nonlinear climate response to precessional forcing at a time of reduced eccentricity modulation mcintyre and molfino 1996 oxygen isotope values of calcite from yunnan lake cores indicate the summer monsoon was weak during the last glaciation from 50 000 to 12 000 cal yr b p the summer monsoon intensified between 12 000 and 8000 cal yr b p but weakened gradually in response to insolation forcing during the mid to late holocene our results support the overpeck et al 1996 model that posits a weak summer monsoon during the last glaciation that responded nonlinearly to insolation forcing when its intensity was affected by eurasian snow cover and ice sheet extent the summer monsoon intensified and responded linearly to seasonal insolation forcing in the holocene when ice volume diminished

holocene environmental changes in northern mongolia inferred from diatom and pollen records of peat sediment abstract the holocene paleoenvironment in nur sphagnum bog northern mongolia was reconstructed by diatom pollen analysis and measurement of chemical properties on a 3 7 m long peat boring sample development processes of peatland are well reflected in these multiproxy records showing that peat accumulation started as early as 9 ka cal bp and the present acidic peat bog was established no later than 6 ka cal bp synchronous trends in diatom and pollen assemblages revealed wetter climate in the early holocene and extensive drought in the mid late holocene centered at 5900 2800 cal bp as a result of temperature increase and low precipitation periods of shifts in proxy data were potentially correlated with other studies in not only mongolia and siberia but also the north atlantic ocean and the climatic periods at 8 4 and 2 8 ka cal bp were highly significant however responses to climate changes seem regionally varied in time and strength demonstrating that local differences in vegetation and orography greatly influence the balance of precipitation and evapotranspiration climate changes that coincided in time with the medieval climate anomaly and little ice age were observed as wetter 1200 980 cal bp and drier 370 240 cal bp conditions probably caused by meridional shifts of westerlies

a multiproxy lake record from inner mongolia displays a late holocene teleconnection between central asian and north atlantic climates in order to study how the holocene central asian climate is coupled to the global climate system a 4 24 m long lake core from western inner mongolia in china was studied using a multiproxy approach sedimentology and geochemical parameters such as gypsum and dolomite content presence of lakeshore sand changing to aeolian sand and changes in paleomagnetic properties bear witness to a trend toward a generally drier climate over the late holocene aridification is linked to the southward retreat of the northern boundary of the asian summer monsoon leaving central asia under the influence of the westerly belt the weakening of the asian summer monsoon in turn was caused by an orbitally driven decrease in summer insolation the weakening summer insolation also likely increased the intensity of the siberian high pressure system further promoting aridification of central asia on a shorter time scale the multiproxy record shows the climate to have been relatively dry during the medieval warm period ad 800 1100 with the ensuing humid environment at the end of this period gradually turning to become extremely dry ad 1100 1550 at the little ice age maximum switches in the north atlantic oscillation caused these changes through a teleconnection in the form of westerlies these westerlies provided most of central asia s moisture after the retreat of the asian summer monsoon the central asian climate therefore corresponds closely with late holocene european climate changes

holocene monsoon climate documented by oxygen and carbon isotopes from lake sediments and peat bogs in china a review and synthesis there has been much recent debate about holocene climate variation in the monsoon region of china especially the temporal pattern of variations in precipitation the time transgressive nature of the holocene precipitation maximum and the extent to which variations in regions influenced by the indian summer monsoon ism and the east asian summer monsoon easm have been synchronous we summarize and compare carbonate oxygen isotope records delta o 18 carb from ten lakes within the present day ism region we discuss their paleoclimate significance considering the present day moisture source isotopic composition of precipitation and the hydrological setting the delta o 18 carb records are controlled mainly by the isotopic composition of lake water which in turn is a function of regional precipitation evaporation p e balance and the proportion of precipitation that is monsoon derived we normalized the delta o 18 carb data and used these records to generate an integrated moisture index this index along with oxygen isotope records from speleothems and carbon isotope records delta c 13 org from peats within the monsoon region suggests that holocene climate was broadly synchronous across the monsoon region and within the limits of accuracy of the existing age models provides no strong evidence for previously proposed anti phasing of the ism and the easm stable isotope records from lake sediments and peat bogs have excellent potential for providing high quality paleoclimate data for monsoon asia and complement high resolution speleothem sequences which are only found in certain localities c 2011 elsevier ltd all rights reserved

last glacial climate instability documented by coarse grained sediments within the loess sequence at fanjiaping lanzhou china optically stimulated luminescence dating grain size analysis and magnetic susceptibility measurements were conducted on the fanjiaping loess section from the western chinese loess plateau the results confirm that last glacial high frequency climatic shifts were documented in mid latitude continental archives the grain size record indicated that coarse grained sediments with horizontal bedding and channel fill structures were only deposited in several short intervals equivalent to the beginning of marine oxygen isotope stage mis 4 and the early to middle mis 3 this probably implies brief rainfall intensification of the asian summer monsoon and its disappearance since the late mis 3 to mis 2 may have been a response to significant glacial cooling in the northern hemisphere previous investigations revealed high sea surface temperatures at high latitudes at the start of mis 4 and the early to middle mis 3 intensification of summer insolation in the northern hemisphere implying evident climate amelioration climate improvement favors boreal forest recovery enhancing both winter and summer air temperatures the resultant smaller equator polar temperature gradient probably helped the moisture laden summer monsoon to penetrate northward this study thus provides new significant information about the response of terrestrial loessic palaeoenvironments to millennial timescale climatic fluctuations during the last glacial period

evidence for a warm humid climate in arid northwestern china during 40 30 ka bp abstract former shorelines and sedimentary records from several lake basins in northwestern china xinjiang qinghai give evidence for warm and humid climatic conditions during 40 30 ka bp further indications of this favorable climate period are derived from palaeosols from the ili loess and from cemented calcareous layers on the terraces of the keriya river at the southern margin of the tarim basin and in the badain jaran desert in inner mongolia at that time annual mean temperature in the qaidam basin was 2 c higher and in the western part of inner mongolia even 2 3 c higher than today precipitation in most parts of northwestern china was between 60 300 mm greater than today these changes were probably a consequence of an increase in ocean surface temperature and evaporation resulting from a higher radiation input at middle and low latitudes caused by changes in the earth s precessional cycle as a result of these orbital changes it is suggested that the intensified westerly circulation was responsible for increased moisture over northwestern china

last glacial pollen record from lanzhou northwestern china and possible forcing mechanisms for the mis 3 climate change in middle to east asia abstract the vegetation on the northeastern margin of the tibetan plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive pollen samples from the fanjiaping loess section in lanzhou on the western chinese loess plateau clp were analyzed in conjunction with osl dating the results indicate that pollen zone b 60 6 46 0 ka correlative to the early mis 3 had the greatest abundances of cupressaceae tsuga gramineae and cyperaceae of the entire section suggesting a warm phase during the last glacial period these pollen taxa decreased significantly in abundance in the zones c 46 0 39 0 ka and d 39 0 27 0 ka reflecting a substantial climate cooling from the middle mis 3 to mis 2 these results correlate with climate records from the south china sea the clp baikal lake north america north atlantic ocean and other regions and probably correspond with the decline of northern high latitude insolation and the increase of global ice volume from 50 to 20 ka in particular arboreal pollen fern spore and algae abundances declined sharply since 40 ka while shrub and herb pollen reached the highest abundances conifer pollen picea and abies abundance also rose markedly and increased up the section this implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since 40 ka the decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a snow ice albedo feedback which would result in less climate sensitivity to radiative forcing meanwhile vegetation decline in the northern hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling enhancing the growth of polar ice sheets since 40 ka the development of polar ice sheets increased the polar to equator temperature and pressure gradients strengthening the westerlies and supplying plenty of moisture to northwest china during 40 30 ka lake sediments developed widely on the tibetan plateau during 40 30 ka probably related to an increase in the seasonality of middle to low latitude insolation which caused an enhancement of glacier melting on the plateau

reconstruction of the 30 40 ka bp enhanced indian monsoon climate based on geological records from the tibetan plateau abstract multi proxy records from ice caps lakes and pollen records from the tibetan plateau are used to reconstruct the palaeoclimate during the period 30 40 ka bp lake geomorphological and lacustrine sedimentological studies show that numerous high lake level stands and or freshwater lakes occurred in large areas of western china at this time including over the tibetan plateau where the area contains mostly shallow water and saline hypersaline water lakes under extremely dry conditions of today pollen based reconstruction of tibetan vegetation shows systematic differences from the present alpine steppe forests were shifted ca 400 km further north and the alpine conifer forest extended ca 400 800 km beyond their present western limits variations in 18 o curves from ice cores from the plateau suggest that the temperature was 2 4 c higher and precipitation was 40 to over 100 higher than today all of the evidence consistently suggests the existence of an exceedingly strong summer monsoon climate over the plateau the vigorous evaporation of the tropical ocean surface would also play an important role in promoting the penetration of moisture rich southwest monsoon over the tibetan plateau these climate patterns with strong summer monsoon circulation during the period 30 40 ka bp reflect the 20 ka earth orbital precessional cycle when the tibetan plateau region received greater solar radiation which thus enlarged the thermodynamical contrast between the plateau and the mid south portion of the indian ocean

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

volcanic ash leachates a review and recommendations for sampling methods tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur halogen and metal species these may then be leached e g by rainfall potentially releasing heavy loadings to soils and water bodies several eruptions have resulted in contamination of pasture sometimes with serious impacts on livestock water quality has also been an issue in some areas affected by tephra fall this work synthesises the literature on volcanic ash leachates and considers the controls on volatile adsorption general trends emerge for basaltic intermediate and silicic tephra as well as for variable particle size and transport distance the applications of ash leachate data to plume gas geochemistry calculation of volatile budgets and environmental impact assessment are evaluated comparisons for different eruptions are hampered by disparities in leachate analysis techniques a standardised methodology is therefore proposed to facilitate future health impact assessment and volcanological interpretation of results from different sites

a model for linking grain size component to lake level status of a modern clastic lake abstract grain size distributions of fluvial eolian and marine sediments were explicated decades ago for lake sediments however there is still great uncertainty in explaining the genesis of grain size components due to the inherent complexity of their polymodal distributions in this study the grain size components of the surface sediments of daihai lake inner mongolia were partitioned using a lognormal distribution function and the relationship between the identity of each component and the specific sedimentary environment was investigated the data indicate that the modern clastic sediments of daihai lake contain five distinct unimodal grain size distributions representing five grain size components each of the components retains its identity including modal size manner of transportation and environment of deposition although the relative percentage varies with the hydraulic condition throughout the lake these components are specified from fine to coarse modes as long term suspension clay offshore suspension fine silt and medium to coarse silt and nearshore suspension fine sand and saltation medium sand the percentage of the components interpreted as an indication of nearshore environments displays a negative correlation with water depth across the modern lakebed suggesting a model for linking the nearshore components in sediment cores to the lake level status in the geological past the model was applied to a sediment core from the lake where high percentages of the nearshore components in the core sediments were correlated with low regional precipitations reconstructed on the pollen profile of the same core the coincidences between two independent proxies do not only demonstrate the validity of lognormal distribution function in partitioning polymodal sediments but also reveals the potential of the grain size component lake level status model for lake s paleohydrological reconstruction

sensitivity of internal wave energy distribution over seabed corrugations to adjacent seabed features here we show that the distribution of energy of internal gravity waves over a patch of seabed corrugations strongly depends on the distance of the patch to adjacent seafloor features located downstream of the patch specifically we consider the steady state energy distribution due to an incident internal wave arriving at a patch of seabed ripples neighbouring i another patch of ripples i e a second patch and ii a vertical wall seabed undulations with dominant wavenumber twice as large as overpassing internal waves reflect back part of the energy of the incident internal waves bragg reflection and allow the rest of the energy to transmit downstream in the presence of a neighbouring topography on the downstream side the transmitted energy from the patch may reflect back partially if the downstream topography is another set of seabed ripples or fully if it is a vertical wall the reflected wave from the downstream topography is again reflected back by the patch of ripples through the same mechanism this consecutive reflection goes on indefinitely leading to a complex interaction pattern including constructive and destructive interference of multiply reflected waves as well as an interplay between higher mode internal waves resonated over the topography we show here that when steady state is reached both the qualitative and quantitative behaviour of the energy distribution over the patch is a strong function of the distance between the patch and the downstream topography it can increase or decrease exponentially fast along the patch or stay nearly unchanged as a result for instance the local energy density in the water column can become an order of magnitude larger in certain areas merely based on where the downstream topography is this may result in the formation of steep waves in specific areas of the ocean leading to breaking and enhanced mixing at a particular distance the wall or the second patch may also result in a complete disappearance of the trace of the seabed undulations on the upstream and the downstream wave field

non residual sr of the sediments in daihai lake as a good indicator of chemical weathering abstract the rb sr ratio of lake sediments has been demonstrated to be a potential indicator of chemical weathering by increasing work however rb and sr in lake sediments are derived from both chemical weathering and physical erosion rb and sr of different forms in lake sediments may record different environmental processes and information in this study the variation patterns of rb and sr of different forms in sediments of daihai lake were investigated the results show that rb and sr of different forms display noticeably different variation patterns due to their different sources and associated environmental processes using the rb sr ratios of bulk lake sediments to reflect chemical weathering is not accurate the non residual sr of the sediments without detrital carbonates representing the sr leached from the catchment can be used as an index of chemical weathering because the weathering of sr minerals is very sensitive to climate change and the non residual sr content of the sediment is determined more by sr2 influx than by the physicochemical conditions of lake water the correspondence between the non residual sr and tic toc in daihai lake also indicates that the non residual sr of the sediments is a good indicator of chemical weathering in the catchment

high resolution multi proxy climate records from chinese loess evidence for rapid climatic changes over the last 75 kyr the loess paleosol sequence in loess layer l1 malan loess is investigated in three regions of the western chinese loess plateau nine pedogenic layers are found in l1 and three proxy climate indices magnetic susceptibility ms grain size gs and caco3 content are measured at intervals of 0 2 kyr in order to recover records of monsoon climate variations time series of ms gs and caco3 content document the high resolution history of summer and winter monsoon climate variations over the last 75 kyr the records show a high degree of similarity to the warm interstadials recorded in ice cores from greenland and the antarctic and with heinrich events in the north atlantic during the last glacial cycle bond cycles are also recorded by the chinese loess records overall our results indicate that numerous rapid changes in climate occurred in china during the last glacial cycle but that the range of climate variations was smaller than recorded in greenland

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

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

volcanic ash ice nucleating activity can be enhanced or depressed by ash gas interaction in the eruption plume abstract volcanic ash can trigger ice nucleation when immersed in supercooled water this will impact several processes e g electrification aggregation precipitation in the eruption plume and cloud and in the wider atmosphere upon ash dispersal previous studies show that ash bulk properties reflecting the chemistry and phase state of the source magma likely contribute to the ice nucleating activity ina of ash however it remains unexplored how interaction with magmatic gases in the hot eruption plume which inevitably leads to altered ash surface properties affects the ash ina here we demonstrate that the ina of tephra is raised by exposure to h2o g mixed with so2 g at both 800 and 400 c but is substantially reduced by exposure to h2o g alone or mixed with hcl g at the same temperatures in contrast the ina of k feldspar and quartz is reduced by all three eruption plume processing treatments the decrease in ina of all silicates after heating with h2o g might relate to a loss of ice active sites by surface dehydroxylation and or oxidation in the presence of hcl g or so2 g respectively metal chloride or sulphate salts form on the tephra surfaces only while nacl and cacl2 seem to have no effect on the tephra ina caso4 is inferred to create ice active sites potentially through a particular combination of surface chemistry and topography overall our findings suggest a complex interplay of bulk mineralogy and surface alteration in influencing ice nucleation by volcanic ash and highlight the general sensitivity enhancement or depression of ash ina to interaction with magmatic gases in the eruption plume

measurements of internal gravity waves in a continuously stratified shear flow a theoretical wave action model based on the work of grimshaw 1974 is presented which describes broadbanded internal wave motions in a stratified shear flow with the viscous terms included the model shows that in the neighbourhood of the critical level viscosity can have important effects and can stabilize the flow with respect to convective overturning the predictions of the model are compared with the results of an experimental study where detailed measurements of the velocity and density fields are made within an internal wave packet propagating through a continuously stratified shear flow the results show that the model accurately predicts the occurrence or non occurrence of wave overturning due to interactions with the shear and provides an accurate description of the structure of the wave induced density and velocity fluctuations in those regions of the flow where the assumptions of the model are satisfied

how did the forest respond to holocene climate drying at the forest steppe ecotone in northern china abstract a sediment sequence from anguli nuur lake 41 18 24 n 114 20 27 e located at the forest steppe ecotone in the southern inner mongolia plateau of china was selected to reconstruct the holocene history of vegetation development and to determine the primary driver of forest dynamics the shifting of vegetation zones was reconstructed by pollen vegetation zone discriminant functions established by contemporary distribution of surface pollen in a transect along both precipitation and vegetation gradients in northern china pollen indicators for human disturbance were selected by comparison with a sediment sequence from west liao river basin which is also located in the forest steppe ecotone but is abundant in archeological sites changes of coarse sand percentage show great consistency with changes of regional humidity index suggesting a prominent role of climate in soil erosion the discriminant functions showed that long term replacement of the forest zone by steppe zone commenced at 2 1 ka bp pollen percentages also show that climate drying since 5 0 ka bp first led to replacement of broadleaf forest by pine forest due to soil coarsening further recession of pine forest from this region since 2 1 ka bp was primarily driven by climate deterioration because no pollen indicator of human disturbance was recognized the study also suggests an earlier arrival but later recession of pine forest in the study region implying pine pinus tabulaeformis migrated from the south and migration of pine forest in the current steppe region was driven by the pacific monsoon movement

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

holocene east asian monsoonal precipitation pattern revealed by grain size distribution of core sediments of daihai lake in inner mongolia of north central china abstract two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for grain size distribution grain size distributions of the lake sediments are inferred to be a proxy for past changes in east asian monsoon precipitation such that greater silt size percentage and higher median grain size reflect increased monsoonal precipitation rates the grain size record of daihai lake sediments spanning the last ca 10 000 yr indicates that the monsoonal precipitation in the lake region can be divided into three stages the early middle and late holocene during the early holocene before ca 7900 cal yr bp the median grain size md and the silt fraction content were relatively low and constant suggesting relatively low precipitation over the lake region the middle holocene between ca 7900 and 3100 cal yr bp was marked by intensified and highly variable monsoonal precipitation as indicated by high and variable md values and silt contents of the lake sediments during this period average precipitation rate gradually increased from ca 7900 to 6900 cal yr bp displayed intense oscillations between ca 6900 and 4400 cal yr bp and exhibited a decreasing trend while fluctuating from ca 4400 to 3100 cal yr bp although generally high during the middle holocene both the md and the silt content assumed distinctly low values at the short intervals of ca 6500 6400 6000 5900 5700 5600 4400 4200 cal yr bp implying that monsoonal precipitation might have been significantly reduced during these intervals during the late holocene since ca 3100 cal yr bp grain size values suggest that precipitation decreased however during the late holocene relatively higher md values and silt contents occurring between ca 1700 to 1000 cal yr bp may denote an intensification of hydrological cycles in the lake area changes in the east asian monsoonal precipitation were not only directly linked with the changing seasonality of solar insolation resulting from progressive changes in the earth s orbital parameters but also may have been closely related to variations in the temperature and size of the western pacific warm pool in the intensity of the el nino southern oscillation and in the path and strength of the north equatorial current in the western pacific

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

ice nucleus characteristics of mount st helens effluents aerosols were studied in situ and captured on membrane filters from an aircraft flown around mount st helens during its phreatic period in april 1980 bulk samples of volcanic ash were collected at ground level 120 km downwind on may 19 1980 and reaerosolized in a laboratory in ash cloud simulation studies the aerosol and or ash samples were tested for ice nucleus in activity using four different in measurement systems ncar acoustical counter bulk drop freezing ncar dynamic thermal diffusion chamber and filter drop freezing although threshold in activity was observed at 8 c in bulk ash in aerosols there were few in active at temperatures warmer than 12 c at 12 c in concentrations were less than 0 4 l 1 400 m 3 even when the aerosol concentrations were as high as 3000 g m 3 at aerosol concentrations of 500 g m 3 and less the in content of the ash was below background threshold temperatures of 18 c

delayed build up of arctic ice sheets during 400 000 year minima in insolation variability an east asian winter monsoon proxy record using grain size variations in chinese loess over the past 900 000 years shows that for up to 20 000 years after the interglacials at 400 000 year intervals the weak monsoon winds maintain a mild non glacial climate at high northern latitudes qingzhen hao and colleagues present a record of grain size variations in the chinese loess plateau a proxy of variations in the strength of the east asian winter monsoon and show that relatively high insolation at 400 000 year intervals held off the inception of the subsequent ice age for about 20 000 years relative to other glacial inceptions mechanistically the extension of warm conditions was probably linked to a weak siberian high pressure system associated with a delayed build up of northern ice and snow the authors speculate that these observations imply that arctic climate may remain in non glacial mode for more than 40 000 years even in the absence of anthropogenic greenhouse gases knowledge of the past variability of climate at high northern latitudes during astronomical analogues of the present interglacial1 may help to inform our understanding of future climate change unfortunately long term continuous records of ice sheet variability in the northern hemisphere only are scarce because records of benthic 18o content represent an integrated signal of changes in ice volume in both polar regions2 however variations in northern hemisphere ice sheets influence the siberian high3 an atmospheric pressure system so variations in the east asian winter monsoon eawm as recorded in the aeolian dust deposits on the chinese loess plateau can serve as a useful proxy of arctic climate variability before the ice core record begins here we present an eawm proxy record using grain size variations in two parallel loess sections representative of sequences across the whole of the chinese loess plateau over the past 900 000 years the results show that during periods of low eccentricity and precessional variability at approximately 400 000 year intervals the grain size inferred intensity of the eawm remains weak for up to 20 000 years after the end of the interglacial episode of high summer monsoon activity and strong pedogenesis in contrast there is a rapid increase in the eawm after the end of most other interglacials we conclude that for both the 400 000 year interglacials the weak eawm winds maintain a mild non glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records during these times the less severe summer insolation minima at 65 n ref 4 would have suppressed ice and snow accumulation leading to a weak siberian high and consequently weak eawm winds

late quaternary environments in the gobi desert of mongolia vegetation hydrological and palaeoclimate evolution abstract considerable efforts have been devoted to decipher the late quaternary moisture and thermal evolution of arid central asia however disparate interpretations still exist concerning different proxies the spatial and temporal heterogeneities have inhibited a holistic understanding of general patterns and underlying mechanisms to address these issues two parallel cores onw i 6 00 m onw ii 13 35 m were retrieved in the gobi desert of mongolia from lake orog nuur multidisciplinary investigations including geomorphological mapping radiocarbon dating sedimentological palynological and ostracod analyses enabled us to gain a comprehensive dataset for vegetation development and hydrological variability over the last 45 kyr higher lake levels during the marine isotope stage mis 3 and early mis 2 35 24 kyr were probably caused by increased precipitation the sharp transition of termination i 11 kyr is indicated by sedimentological palynological and ostracod data during the late pleistocene the lower area of the orog nuur catchment was dominated by artemisia steppe and gradually altered to chenopodiaceae desert steppe in the holocene the early holocene is also characterized by a relatively humid environment the humid pulses during the mis 3 and the early holocene were also recorded in other archives and are possibly the trait of a larger scale phenomenon in arid central asia four major harsh climatic periods were documented in the core at 43 kyr 36 kyr during the global last glacial maximum and the younger dryas as playa phases reduced westerlies moisture transport and a retreated east asian summer monsoon influence probably caused those dry phases in the gobi desert of mongolia

a 48 5 ka climate record from wulagai lake in inner mongolia northeast china abstract a 3 6 m long sediment core was collected from wulagai lake in the northern inner mongolia plateau northeast china data of grain size and loss on ignition at 550 c loi550 were used to reconstruct the climatic changes since the late marine isotope stage mis 3 the climate was generally warm and humid between 48 5 and 30 cal ka bp but was interrupted by a cold and dry period between 37 7 and 33 5 cal ka bp cold and dry climate occurred between 30 and 11 5 cal ka bp especially during the last glacial maximum lgm beginning at 11 5 cal ka bp until present day the climate was generally warm and humid our results are similar to the climate records from the chinese loess plateau since the late mis 3 which indicates that intensification and weakness of the asian summer monsoon responding to high and low june insolation are the main mechanism of climate evolution in wulagai lake area since the late mis 3 however loi550 content increased in wulagai lake since 2 5 cal ka bp which probably resulted from human activities

internal wave activity in rotterdam waterway a variety of internal wave mechanisms is observed in the partially mixed rotterdam waterway estuary due to the interaction between stratified tidal flow and topography the topographically generated waves include lee waves resonant trapped waves and critical layers freely propagating waves breaking internal hydraulic jumps at the banks and rotor formation acoustic images and profiles of density and velocity are presented the acoustic images are explained on the basis of basic internal wave theory mathematical models tend to ignore smallscale internal wave activity as a source of turbulent kinetic energy the paper investigates whether it is justified to do so on the scale of the topography on the basis of an estimate of the internal wave induced production of turbulent kinetic energy it is concluded that for the observed internal waves this source of energy may not always be neglected when compared with the production by the background flow in particular when first mode short internal waves are i

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds