the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

pedogenic carbonates forms and formation processes abstract soils comprise the largest terrestrial carbon c pool containing both organic and inorganic c soil inorganic carbon sic was frequently disregarded because 1 it is partly heritage from soil parent material 2 it undergoes slow formation processes and 3 has very slow exchange with atmospheric co2 the global importance of sic however is reflected by the fact that sic links the long term geological c cycle with the fast biotic c cycle and this linkage is ongoing in soils furthermore the importance of sic is at least as high as that of soil organic carbon soc especially in semiarid and arid climates where sic comprises the largest c pool considering the origin formation processes and morphology carbonates in soils are categorized into three groups geogenic carbonates gc biogenic carbonates bc and pedogenic carbonates pc in this review we summarize the available data and theories on forms and formation processes of pc and relate them to environmental factors after describing the general formation principles of pc we present the specific forms and formation processes for pc features and the possibilities to use them to reconstruct soil forming factors and processes the following pc are described in detail earthworm biospheroliths rhizoliths and calcified roots hypocoatings nodules clast coatings calcretes and laminar caps the second part of the review focuses on the isotopic composition of pc 13c 14c and 18o as well as clumped 13c and 18o isotopes known as 47 the isotopic signature of pc enables reconstructing the formation environment the dominating vegetation 13c temperature 18o and 47 and the age of pc formation 14c the uncertainties in reconstructional and dating studies due to pc recrystallization after formation are discussed and simple approaches to consider recrystallization are summarized finally we suggest the most important future research directions on pc including the anthropogenic effects of fertilization and soil management in conclusion pc are an important part of sic that reflect the time periods and formation processes in soils a mechanistic understanding of pc formation is a prerequisite to predict terrestrial c stocks and changes in the global c cycle and to link the long term geological with short term biological c cycles

holocene vegetation and climate of the alashan plateau nw china reconstructed from pollen data a set of 55 recent pollen spectra from the alashan plateau and the qilian mountains qilianshan northwestern china has been analyzed the established relationships between the pollen spectra and modern vegetation and precipitation patterns of the studied area have been applied to 65 fossil pollen spectra from a 825 cm long sediment record collected in the topographic depression formerly occupied by eastern juyan palaeolake 41 89 n 101 85 e 892 m a s l several qualitative approaches e g indicator plant species artemisia chenopodiaceae and ephedra fragilis type s l ephedra distachya type pollen ratios and quantitative methods of vegetation and climate reconstruction have been tested with the surface pollen and then applied to the eastern juyan pollen record fossil pollen data reveal pronounced environmental changes in the studied area of the alashan plateau between ca 10 700 and 1700 cal yr b p desert taxa as chenopodiaceae nitraria calligonum reaumuria were abundant in the vegetation cover around the study site through the whole record pollen spectra dated to ca 10 700 5400 cal yr b p are characterised by highest values of chenopodiaceae e fragilis type and other desert indicating taxa suggesting rather dry climate most favourable conditions are reconstructed between 5400 and 3900 cal year b p on the basis of relative increase in abundance of artemisia pollen a return to dry conditions occurred at about 3900 cal yr b p the lake finally desiccated after 1700 cal yr b p reconstructed dry climate oscillations between 5900 and 5400 and 3100 cal yr b p correlate well with similar events found in the published records from northern and western china and central mongolia however eastern juyan record does not show the early holocene humidity maximum as suggested by the sedimentary data from monsoon influenced areas of china

holocene climate variations from zhuyeze terminal lake records in east asian monsoon margin in arid northern china zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved zhuyeze palaeolake is a terminal lake situated in the arid northern china in the east asian monsoon margin in order to examine the holocene palaeoclimatic change in the east asian monsoon margin qingtu lake section qtl from zhuyeze palaeolake is sampled in high resolution palaeoclimatic proxies such as grain size carbonate toc c n and delta 13 c of organic matter were analyzed eleven 14 c samples and six optically stimulated luminescence osl samples were dated to provide chronological control we also investigated the geomorphic features of lake shorelines in this area the results show that the climate was warm and dry in early holocene 9 5 7 0 cal ka bp cool and humid in mid holocene 7 0 4 8 cal ka bp and increasingly drier in late holocene since 4 8 cal ka bp comparisons of our records with other records in adjacent areas as well as with the records in the asian monsoon areas suggested that changes in effective moisture was synchronous in east asian monsoon marginal zone i e the pattern of dry early holocene humid mid holocene and aridity increasing late holocene and that the moisture optimum during the holocene was out of phase between asian monsoon margin and asian monsoonal dominated region possibly due to the high temperature at that time c 2010 university of washington published by elsevier inc all rights reserved

amount effect recorded in oxygen isotopes of late glacial horse equus and bison bison teeth from the sonoran and chihuahuan deserts southwestern united states stable oxygen isotopes from fossils both vertebrate and invertebrate or inorganic sedimentary minerals frequently have been used to make interpretations about ancient global climates oxygen isotope values measured from terrestrial vertebrates or sedimentary carbonates provide information about paleotemperature and amounts of precipitation at a particular site in general these inferences are made on the centennial to millennial scale serial i e ontogenetic sampling of equus and bison tooth enamel provides climatic data on the scale of months to a few years we present models showing how annual environmental patterns of d 18 o would be replicated in the tooth enamel of equus and bison changes in d 18 o due to shifts in temperature in terrestrial environments d 18 o increases with increased temperature and amount and timing of precipitation increased precipitation may result in a decrease in d 18 o a phenomenon called the amount effect are archived in both equus and bison teeth the input signal is better resolved in bison due to its more rapid enamel growth modeled patterns are compared with actual data from modern sites in the sonoran and chihuahuan deserts of the southwestern united states the isotopic patterns from modern teeth agree with that predicted from known variations in meteoric water known floral and faunal assemblages as well as computer models suggest summer rain for the chihuahuan desert of late glacial time 15 000 10 000 years ago but little summer rain for the sonoran desert at that same time serial data from fossil teeth show a clear pattern interpreted to represent the amount effect that includes increased summer rains in the chihuahuan desert and only minor summer rains in the sonoran desert d 2004 elsevier b v all rights reserved

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

morphological characters and multi element isotopic signatures of carbonates from chinese loess paleosol sequences abstract morphological characters and multi element isotopic compositions of carbonates from the loess paleosol sequences in northwestern china are examined to explore the origin of the minerals samples are collected from various sections ranging from holocene to 0 9 ma within the sequences and fractions with grain sizes 45 and 45 m exhibit an almost perfect spherical shape while those 13 c and 18 o values between minerals and biologically originated samples indicates that the 206 pb 204 pb 207 pb 204 pb 208 pb 204 pb and 87 sr 86 sr these results suggest the utility of fine carbonate particles in the soil profile in reconstructing a potentially higher resolution 13 c and 18 o time series to elucidate the paleoclimatic fluctuation in the chinese loess plateau during pleistocene the discovery of the nano rod calcite in chinese loess together with previous findings of the similar mineral form in asian dust strongly suggests the possibility that these highly reactive caco 3 form may alter the aerosol properties during transport

mesozoic evolution of the tisza mega unit the south eastern part of the basement of the pannonian basin is made up of variscan crystalline complexes and early mesozoic formations showing striking affinity with the corresponding formations in the southern margin of the european plate this large composite structural unit which is actually an exotic terrane of european plate origin has been named the tisza mega unit based upon relevant data of the pre tertiary basement of southern hungary the reconstruction of the position of the tisza terrane in the early alpine evolutionary stages the process of its separation and break off from the european plate and results of its eo alpine deformations are summarised in the present paper in the variscan and early alpine evolutionary stages the area of the later tisza mega unit was located at the margin of the european plate during variscan orogeny terrane accretion led to intensive deformation and metamorphism in this belt this was followed by transpressional tectonics and the development of molasse basins in the late and post variscan stages and passive margin evolution after the neotethys opening in the middle triassic the separation of the tisza mega unit began with incipient continental rifting along the axis of the later ligurian penninic vahic oceanic branch in the late triassic the end of terrigenous material deposition in the most external zones and a coeval change in fossil assemblage point to the separation of the tisza block from the european plate in the early bathonian significant rotation of the tisza mega unit and coeval paroxysm of alkaline rift type basalt volcanism took place in the early cretaceous in the mid cretaceous due to the northward motion of the adria block and the related closure of the westernmost neotethys basin the extensional regime changed to a compressional one leading to onset of the nappe stacking and low grade regional metamorphism within the tisza microplate in the foreland of the nappe systems flexural basins came into existence that are characterised by flysch type sedimentation in the early tertiary the north eastward motion of the alcapa and tisza dacia blocks led to the formation of the present day heterogeneous basement of the pannonian basin

younger dryas event recorded by the mirabilite deposition in huahai lake hexi corridor nw china abstract deposits from the huahai ancient lake in the hexi corridor were dated using conventional and ams 14c a 2500a carbon storage effect was defined at 9 25 m depth according to the 14c age difference between a plant macrofragment and detrital organic matter from the same layer the chronology of this strata indicated that the mirabilite layer at the depth of 8 05 m 9 15 m had formed during the younger dryas yd event the formation of the mirabilite layer indicated that the mean annual temperature in the hexi corridor dropped by 11 c during the yd event compared with today the lowest cold event occurred early in the yd which is consistent with what has been revealed by other high resolution records such as those of arctic ice cores and stalagmites in mid latitude regions

mean and turbulent flow structure during the amalgamation process in fluvial bed forms 1 fluvial channels present bed forms such as dunes and ripples that alter instantaneous hydrodynamics parameters such as flow velocities water surface profiles bed shear stresses and reynolds stresses and create turbulent coherent structures that are significantly different from those presented in flat bed conditions it is known that les based models are more suitable than rans models to reproduce the complex hydrodynamics around bed forms herein a les model is applied to describe the mean and turbulent flow structure under superimposed bed forms three cases were simulated run i train of ripples run ii superimposed bed forms and run iii amalgamated bed forms the les modeling was performed using a free surface condition to allow the model to develop undulations and boils on the water surface caused by effect of the bed forms some important conclusions from this study are the division of high and low shear stresses on the stoss side of the dune the progression of the flow field topology from run i and run iii and the type of turbulent coherent structures found in each stage the region of high shear stresses was related to turbulence production in which the streamwise velocity fluctuations where strips structures are related to streaks were associated to the modification of the bed morphology the turbulence horseshoes vortices thv were more frequent in run i than in the other two cases where streamwise rolls were more frequent finally the frequency of the bursting events increased from run i to run ii and decreased from run ii to run iii implications of detailed hydrodynamics into bed forms processes are also presented and discussed

multiple expansions of c4 plant biomass in east asia since 7 ma coupled with strengthened monsoon circulation the expansion of plants using the c4 photosynthetic pathway is one of the most prominent changes in the global ecosystem during the cenozoic era a significant late miocene expansion is well documented however the existence and cause of subsequent expansions are still not clear owing in part to the lack of long continuous climate vegetation records here we present two high resolution carbon isotope time series covering the past 7 m y derived from eolian deposits on the chinese loess plateau the data indicate three intervals of significant c4 plant expansions within the semiarid monsoonal region of east asia ca 2 9 2 7 ma 1 3 0 9 ma and 0 6 ma present these expansions covary with strengthened east asian summer monsoon circulation we conclude that in east asia large scale late miocene c4 c3 vegetation changes in semiarid areas have been primarily driven by warm seasonal precipitation and temperature variations associated with changes in monsoon circulation

reconstructing palaeoenvironments on desert margins new perspectives from eurasian loess and australian dry lake shorelines abstract desert margins preserve evidence of more extensive arid conditions in the past and represent global hot spots with respect to climate change the balance of scientific evidence now suggests that dryland landscape reactivation did not correspond simply to ice age aridity peaks as previously assumed this paper provides a new perspective on and more nuanced understanding of desert marginal landscapes as palaeoenvironmental archives the two case studies represent ends of a sediment availability spectrum both environments experience substantial spatial and temporal variability in deposition with implications for reconstructing past environments at individual sites recently generated chronostratigraphic data from the dry subhumid dobrogea loess romania are synthesised to provide quantitative insights into the spatial and temporal organisation of loess plateaux loess accumulation peaks during the lgm and mis4 but not at all sites accumulation rates vary substantially between sites comparison of geographical context yields no clear driving mechanism for this variability secondly two transverse lunette dunes in semi arid willandra lakes australia yield comparable chronostratigraphies and distribution of stratigraphic units a first attempt is made to identify changes in wind regime through time on the australian desert margins and suggests that high latitude climate forcing may have acted upon semi arid australia over millennial scales the novel perspectives generated from the new datasets provide unprecedented insights into past climate circulation and land surface processes along desert margins these new perspectives coupled with the new geochronological and quantitative palaeoclimate proxy tools now available represent the next frontier for palaeoenvironmental research on desert margins

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

do stable isotope data from calcrete record late pleistocene monsoonal climate variation in the thar desert of india late pleistocene terrestrial climate records in india may be preserved in oxygen and carbon stable isotopes in pedogenic calcrete petrography shows that calcrete nodules in quaternary sediments of the thar desert in rajasthan are pedogenic with little evidence for postpedogenic alteration the calcrete occurs in four laterally persistent and one nonpersistent eolian units separated by colluvial gravel thermoluminescence and infrared and green light stimulated luminescence of host quartz and feldspar grains gave age brackets for persistent eolian units i iv of ca 70 000 60 000 ca 60 000 55 000 ca 55 000 43 000 and ca 43 000 25 000 yr respectively the youngest eolian unit v is 10 000 yr old and contains no calcrete stable oxygen isotope compositions of calcretes in most of eolian unit i in the upper part of eolian unit iv and in the nonpersistent eolian unit range between 4 6 and 2 1 pdb these values up to 4 4 greater than values from eolian units ii and iii are interpreted as representing nonmonsoonal18o enriched normal continental waters during climatic phases when the monsoon weakened or failed conversely 25 000 60 000 yr old calcretes eolian units ii and iii probably formed under monsoonal conditions the two periods of weakened monsoon are consistent with other paleoclimatic data from india and may represent widespread aridity on the indian subcontinent during isotope stages 2 and 4 the total variation in 13c is 1 7 0 0 1 7 and 13c covaries positively and linearly with 18o 13c values are highest when 18o values indicate the most arid climatic conditions this is best explained by expansion of c4grasses at the expense of c3plants at low latitudes during glacial periods when atmosphericpco2was lowered c4dominance was overridingly influenced by global change in atmosphericpco2despite the lowered summer rainfall

megarhizoliths in pleistocene aeolian deposits from gran canaria spain ichnological and palaeoenvironmental significance the pleistocene dune field of tufia located on the east of gran canaria spain contains different stratigraphic levels of indurated pillar like structures that are interpreted as megarhizoliths the megarhizoliths occur at the top of different aeolian sets and reach 31 5 cm in diameter and over 1 m in height these scattered free standing vertical cylindrical to slightly conical columns usually appear as hollow cylinders displaying elliptical cross sections aligned with the prevailing wind on the leeward side of some specimens the external wall shows a tail of rock matrix resembling a sort of wind shadow these tails and other remains of the associated rock matrix show a texture composed of long horizontal parallel cylinders orientated with the wind internally the most complete structures show five concentrically arranged zones zone a is a central pore corresponding to the cavity originally occupied by the root zones b and c which include alveolar and laminated carbonate textures indicating that carbonate precipitation was mostly induced by the roots and their associated microorganisms and zones d and e consisting mostly of aeolian sands in d the sand grains show thin micritic coatings whereas in e vadose aragonite cements can be seen on the grain surface suggesting a less biogenic influence in their formation the degree of cementation and the time of the precipitation of carbonate around the roots controlled the preservation of these zones thus in some cases zones b c and or d are not preserved cylinders are up to 30 the diameter of the root that nucleated them the presence of the megarhizoliths at the top of the aeolianite beds indicates that aeolian sedimentation halted several times allowing soil formation and plant colonisation during slightly more humid periods the occurrence of megarhizoliths is further proof of the alternation of arid and slightly more humid climates in the north atlantic during the last glacial period it is also noted that they may be misinterpreted as animal trace fossils or tree trunk casts resulting in incorrect ichnological or palaeoenvironmental interpretations

ice volume forcing of east asian winter monsoon variations in the past 800 000 years particle size measurements of some typical loess soil samples taken in different localities of the chinese loess plateau demonstrate that the grain size ratio of 10 m can be used as an indicator of variations in intensity of the east asian winter monsoon winds grain size curves of the baoji and weinan sections show that this proxy indicator is very sensitive to loess soil alterations analytical results also suggest that during soil forming periods eolian dust accumulation was still substantial and hence loess deposition can be regarded as a nearly continuous process during the quaternary period in this study we compared the baoji grain size time series with the specmap marine isotope record with the objective of elucidating the dynamic linkage between changes in global ice volume and the winter monsoon circulation both records show good agreement at both time and frequency domains in particular the winter monsoon variations are also dominated by a 100 000 yr period over the past 800 000 yr it is thus inferred that direct local insolation forcing could be less important in driving the east asian winter monsoon variability and alternatively variations in glacial age boundary conditions may have played a key role in modulating and pacing its strength and timing

radiocarbon dating of aquatic gastropod shells and its significance in reconstructing quaternary environmental changes in the alashan plateau of northwestern china abstract using landform evolution and lake sediment records to reconstruct quaternary environmental changes requires reliable chronology however there is an ongoing debate regarding the fossil shells of aquatic gastropods in carbonate rock area to be used for radiocarbon dating the focus of this debate is whether living gastropods incorporate the dead carbon which would affect the accuracy of the dating results living aquatic gastropods were selected from habitats on carbonate terrain in arid region in this study 64 shell samples from living gastropods including cipangopaludina chinensis gyraulus convexiusculus and radix auricularia collected from the alashan plateau of northwestern china were dated by accelerator mass spectrometry ams 14c dating the results revealed that only five samples 8 from the same site contained no dead carbon the other 59 samples 92 contained dead carbon in various amounts 59 samples contained 0 10 dead carbon and 33 samples contained more than 10 dead carbon of the samples 56 were radix auricularia and their 14c ages varied from present to 3253 cal yr bp two of the samples were gyraulus convexiusculus samples dated at 379 and 290 cal yr bp which are highly consistent with 14c ages of radix auricularia samples from the same site the other six cipangopaludina chinensis samples were dated at 407 863 cal yr bp thus most of living aquatic gastropods from habitats on carbonate terrain contained dead carbon the amount of dead carbon in the gastropod shells was nonselective among the three species radiocarbon dating of aquatic gastropod shells may not be useful for studying processes that occurred over multi millennial timescales at different localities in areas of carbonate rock it is difficult to establish high resolution chronologies using 14c ages of gastropod shells in arid regions with carbonate rocks unless the limestone effect has been corrected

holocene development of the yellow river s subaqueous delta north yellow sea high resolution seismic profiles from the north yellow sea reveal a 20 40 m thick subaqueous clinoform delta that wraps around the eastern end of the shandong peninsula extending into the south yellow sea this complex sigmoidal oblique clinoform containing an estimated 400 km 3 of sediment overlies prominent relict transgressive surfaces the nearshore topset of the clinoform 50 m contain less than 1 m of holocene sediment with low sedimentation rates 1 mm year in contrast to other clinoforms the shandong clinoform appears to be a compound subaqueous deltaic system with what we interpret to be proximal and distal phases of clinoform development the underlying proximal sequence formed proximally between f11 and 9 2 ka in response to a temporary pause in the rapid postglacial sea level rise after the meltwater pulse 1b mwp 1b and increased discharge from the yellow river to the north yellow sea due to intensification of the summer monsoon a flooding surface appears to separate the proximal and distal phases corresponding to the next rapid sea level rise 9 5 9 2 ka bp mwp 1c since 9 2 ka bp an overlying distal sedimentary sequence has accumulated reflecting the backstepping and shifting river mouth westward to the gulf of bohai some inputs from coastal erosion and nearby small streams may be locally important along shore transport cross shelf advection and upwelling in the north yellow sea have reworked post lgm sediment and have helped maintain the morphology of the clinoform in the shandong mud wedge d 2004 elsevier b v all rights reserved

a physiological mechanism for the formation of root casts abstract root casts are calcified structures in the shape of roots often found exposed on aeolian sand dunes a central channel of the cast may be void or filled with soft carbonate transpiration drives water flux towards the roots resulting in mass flow of dissolved nutrients towards the root it was hypothesised that root casts form in cation rich substrates as a consequence of transpiration driven mass flow of cations to roots in excess of that required by the plant with subsequent cementation of sediments around the root mould through formation of carbonates the elemental compositions of both ancient root casts 6870 60 bp of an unknown plant from still bay western cape south africa and concreted sediments associated with cluster roots of a presently occurring dune plant morella cordifolia l killick myricaceae were found to have similar elemental compositions and were positively correlated both root casts and cluster root sediments had higher ca and other cations and also higher inorganic c than that of dune sand from isotope analysis the most likely sources of c for formation of carbonates in the cluster root sediment 13c 0 8 0 29 and in the root casts 13c 5 3 0 6 to 7 6 0 3 was a varying combination of the bulk atmosphere predicted 13c of concretion 1 3 and plant respiration derived co2 predicted 13c of concretion 11 5 despite extremely low p 0 05 mol g 1 sand in dune sand the leaves of m cordifolia accumulated amounts of p comparable to other cluster rooted plants in the adjacent somewhat nutrient richer fynbos it was concluded that in the generally nutrient poor but cation rich sand transpiration driven water flux would deliver scarce nutrients to the cluster root rhizosphere of m cordifolia in the process of this mass flow ca is delivered in excess of plant demand and accumulates in both the root tissue and the rhizosphere this ca is chemically converted to caco3 over time resulting in the formation of persistent root casts

mio pliocene monsoonal record from himalayan foreland basin indian siwalik and its relation to vegetational change carbon and oxygen isotope ratios of soil carbonate nodules and carbon isotope ratio of associated organic matter were measured from three indian siwalik stratigraphic successions in order to reconstruct vegetational history and change in contemporaneous precipitation 13c values of soil carbonates show that from 10 5 to 6 ma the vegetation was c3 type and around 6 ma c4 grasses appeared the 18o variations of soil carbonates suggest that the monsoon system intensified with one probable peak at around 10 5 ma and a clear onset at 6 ma with peak at 5 5 ma after 5 5 ma monsoon strength decreased and attained the modern day condition with minor fluctuations which is supported by marine proxy of upwelling in the arabian sea and sedimentary morphology in siwalik the covariation between 18o and 13c data suggests that a change in precipitation pattern was partly responsible for expansion of c4 grasses in a mixed c3 c4 environment estimation of abundance of c3 and c4 plants using soil carbonate in one case and residual soil organic matter in another may differ this can be explained by assuming that the plant respired co2 is the main contributor of carbon in soil carbonate and may have different isotopic composition from that of the residual organic matter in the soil in addition the abundance estimate of c3 c4 plants also shows variation with time probably caused by change in growing season conditions through time

gravel deposits on the margins of the qinghai xizang plateau and their environmental significance abstract the thick deposits of quaternary gravels found along the margins of the qinghai xizang tibet plateau have been studied for decades here we concentrate on two sediment series widely developed along the kunlun tian shan and qilian mountains the xiyu formation a molassic series of lower pleistocene age and the middle and upper pleistocene gobi gravels these two series with their contained fossil assemblages throw light on the question of the mean altitudes and uplift rates of the tibetan plateau during the quaternary and on the related problem of the vigour and penetration of advected summer monsoonal moisture into central asia the sedimentary series on the northern piedmonts of the tibetan plateau considered here challege the view that plateau uplift accelerated in the upper pleistocene they indicate that the plateau had reached mean altitudes in the range 4000 5000 m perhaps by the end of the lower pleistocene and certainly by the middle pleistocene this diminished the incursion of southerly monsoonal moisture and so imposed arid and semi arid conditions across much of a vast region north of the plateau which among other effects precluded widespread mountain glaciation in the lower pleistocene and general ice sheet glaciation of the tibetan plateau as a whole

stable isotope compositions sources and paleoenvironmental significance of holocene calcareous root tubes in the tengger desert northwest china abstract valuable archives of paleoenvironmental changes are scarce in the hinterlands of deserts calcareous root tubes crts a form of pedogenic carbonate are widely distributed in the hinterland of the tengger desert northwest china the investigations of 13c and 18o values within crts from the tengger desert have a great potential to provide new significant archives for paleoenvironmental reconstructions in this area in this study 30 crt samples from the tengger desert were collected all the samples were described using cathodoluminescence cl and their 13c and 18o values were measured the results revealed that limited marine carbonate was incorporated in the crts in the tengger desert and 13c and 18o values of the inner belt of the crts were not affected by recrystallization therefore 13c and 18o values of the crts could accurately record environmental conditions in the tengger desert the carbon source of the crts was a mixture of soil co2 derived from root respiration and atmospheric co2 furthermore 13c values of most samples were lower than 3 0 indicating that c3 vegetation was the main vegetation in the tengger desert during the middle and late holocene moreover 18o values of the crts were ultimately inherited from summer precipitation influenced by the amount effect in summer and strong evaporation the lower 18o values of the crts revealed that relatively higher effective moisture occurred from 7 to 4 cal kyr bp while the higher 18o values indicated that relatively lower effective moisture occurred from 4 to 2 cal kyr bp in the tengger desert the holocene millennial scale moisture changes in the hinterland of the tengger desert suggest an arid early holocene 11 7 7 cal kyr bp a relatively humid mid holocene 7 4 cal kyr bp and a humid to arid late holocene 4 2 cal kyr bp the discrepancy of effective moisture change reconstruction based on the crts in the tengger desert and adjacent lake sediments during the early holocene demonstrated that the reliability of the reconstructed results from lake sediments during this period needs further investigation

carbonate rhizoliths in loess and their implications for paleoenvironmental reconstruction revealed by isotopic composition δ13c 14c abstract loess paleosol sequences are important terrestrial archives for studying quaternary climate changes they often contain secondary carbonates including e g rhizoliths calcified roots these secondary carbonates are precipitated in isotopic equilibrium with root derived co2 and are therefore used to reconstruct the vegetation present during their formation based on stable carbon isotopic composition 13c usually the chronological context of secondary carbonates in general is not mentioned because it is assumed that they are formed synsedimentary with loess deposition the loess paleosol sequence at nussloch sw germany contains in its youngest part upper wurmian large carbonate rhizoliths with diameters of up to 5 cm and lengths of up to 1 m and more which have not been described in this profile so far we investigated rhizoliths as well as loess adjacent to and distant from rhizoliths for carbonatic carbon ccarb and organic carbon corg contents as well as their isotopic composition 13c radiocarbon dating to identify the rhizolith origin and the time frame of their formation considering the 13c fractionation by carbonate precipitation the 13ccarb values 10 9 0 1 revealed c3 plant origin of the rhizolith carbonate and the absence of large amounts of occluded primary loess carbonate similar 14c ages of rhizolith ccarb and corg 3788 59 years bp and 3150 59 years bp respectively argued for the absence of postsegregational alteration therefore they are suitable for the reconstruction of paleoenvironmental conditions after loess sedimentation the 14c ages clearly indicate that rhizoliths did not form synsedimentary roots penetrated the loess at nussloch after the deposition had ceased at 15 ka bp even in the loess adjacent to the rhizoliths up to a distance of 5 cm 13ccarb values indicate the presence of secondary carbonate deriving from postsedimentary organic matter of origin other than that of the reference loess material hence this postsedimentary input of younger root biomass might have masked the initial plant signal in loess paleosol sequences which could cause uncertainties for paleoenvironmental reconstructions based solely on loess organic matter

oxygen and carbon isotopic composition of quaternary meteoric carbonates from western and southern europe their role in palaoenvironmental reconstruction abstract the relationship between environmental conditions and the 18 o and 13 c values of soil and groundwater carbonates in europe is poorly understood consequently the use of the isotopic composition of these carbonate palaeoclimatic indicators in european sedimentary sequences is restricted in this study we examine the 18 o and 13 c values of soil and groundwater carbonates from western and southern europe in western europe there is no relationship between carbonate 18 o values and carbonate 13 c values the 18 o values of soil carbonate appears to be driven by temperature whilst the 13 c value of soil and groundwater carbonate reflects the persistent dominance of c 3 vegetation in this region during the quaternary the 18 o and 13 c values of soil carbonates from spain and crete show a strong degree of co variance suggesting that they are being controlled by the same environmental factor this is suggested to be aridity 18 o values are controlled by soil moisture evaporation whilst 13 c value is controlled by soil moisture degassing vegetation abundance and possible c 3 c 4 vegetation inputs the paper concludes by highlighting the fact that although currently under utilised the 18 o and 13 c values of soil and groundwater carbonates have a huge potential for providing important palaeoenvironmental information from sites across europe

recharge to the inter dune lakes and holocene climatic changes in the badain jaran desert western china we present new estimates on evaporation and groundwater recharge in the badain jaran desert western inner mongolia of northwestern china based on a modified penman equation suitable for lakes in china geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake level variations in this desert environment should reflect palaeoclimatic changes the chronology of lake level change established by radiocarbon and u series disequilibrium dating methods indicates high lake levels and a wetter climate beginning at ca 10 ka and lasting until the late mid holocene in the badain jaran desert the greatest extension of lakes in the inter dune depressions indicates that the water availability was greatest during the mid holocene relicts of neolithic tools and pottery of qijia culture 2400 1900 bc suggest relatively intensive human activity in the badain jaran desert during the early and middle holocene supporting our interpretation of a less harsh environment wetter climates during the holocene were likely triggered by an intensified east asian summer monsoon associated with strong insolation

pedogenic carbonate cutans on clasts in soils as a record of history of grassland ecosystems pedogenic carbonate cutans coatings pendants rinds on coarse clasts are common in stony soils of arid and semiarid regions dominated by open vegetation this paper gives an overview of the potential of the carbonate cutans for paleograssland research using data from literature and personal observations carbonate coatings are stratified into distinct microlamina which can provide a record of local environmental changes lamina made of a rather pure calcium carbonate with better formed and parallel oriented crystals seem to be indicative of relatively dry phases that were less favorable for biological activity a high content of admixtures poorer formed and randomly oriented calcite crystals presumably mark wetter periods characterized by climatic amelioration at a most general level n 13 c of the cutan carbonate can provide information on the type of photosynthesis of local vegetation whereas n 18 o in carbonate material of the coatings correlates with oxygen isotopic composition of precipitation water at the site and is sensitive to fluctuations in temperature to obtain chronological evidence on cutan formation the 14 c and th u methods can be applied with certain limitations additionally cutan growth rates can be used to evaluate the age of these features fl 2002 elsevier science b v all rights reserved

characteristics of collisional orogens with low topographic build up an example from the carpathians sequence stratigraphy in the hinterland kinematic analysis of thin skinned thrusting in the foreland and thermochronological tracking of exhumation in the orogenic core are combined to quantify the mechanics of an orogen with low topographic build up the carpathian system demonstrates that collisional deformation can couple and thicken the lower orogenic plate along reverse faults that dip more steeply than the subduction zone defining a foreland coupling type of collision near the surface this is expressed by wide antiforms in the upper plate and the thin skinned orogenic wedge a sequence stratigraphic analysis of the back arc transylvanian basin demonstrates that the sedimentary architecture records orogenic uplift pulses with both short and long wavelengths these correspond to the activation of individual thrust sheets in the thin skinned wedge and to lower plate coupling events respectively

formation and environmental significance of late quaternary calcareous root tubes in the deserts of the alashan plateau northwest china calcareous root tubes are widely distributed across the badain jaran desert and the tengger desert of the alashan plateau in northwest china however the reliability of their 14 c dating results and their environmental significance remain unclear in this study the conventional 14 c ages of 31 calcareous root tube samples and one aquatic mollusc shell sample which were all collected from the badain jaran desert and the tengger desert were measured the results reveal that nine of the 14 calcareous root tube samples from the badain jaran desert were from marine isotope stage mis 3 while two samples were from mis 2 the other three samples were dated to the mid holocene one of which is consistent with the aquatic mollusc shell sample collected from the shoreline of zhunzhahanjilin lake in the badain jaran desert moreover the 17 calcareous root tube samples from the tengger desert were all dated to the mid and late holocene most of which were from the mid holocene the results demonstrate that calcareous root tubes can be used as

radiocarbon dating of thin pedogenic carbonate laminae from holocene archaeological sites radiocarbon dating has been previously suggested to be applicable to pedogenic carbonate however until now the validity of radiocarbon dates from pedogenic carbonate remained poorly understood because of the relatively low resolution of chronological controls in this study we compared the radiocarbon dates a total of 21 of thin 0 2 0 3 mm in thickness laminae of pedogenic carbonate coatings on clasts from holocene archaeological sites in the eastern mediterranean and south siberia with independently estimated age ranges for these sites we obtained a high correlation between the oldest laminae of coatings with the site ages the 14 c ages of pedogenic carbonate were systematically younger by c 0 3 1 6 ka mean c 0 75 ka compared with archaeological sites this finding suggests that pedogenic carbonate despite potential complicating factors can be dated more accurately with 14 c than has been generally appreciated

the ion chemistry of lakes and late holocene desiccation in the badain jaran desert inner mongolia china abstract in the markedly arid badain jaran desert one of the least studied areas in the world over a hundred permanent lakes exist among the dunes the geochemistry of water samples from nine lakes and from the groundwater in the desert and on its periphery was investigated ion chemistry of the water from these desert lakes changes considerably on a regional scale we argue that there is a positive correlation between the ages of these lakes and their totally dissolved solids tds varying between 1 2 and 398 2 g l tritium analysis of groundwater in wells gives an age generally older than four decades and younger than 100 years the lacustrine deposits freshwater fauna and shorelines indicate the existence of large water bodies with low salinities in the inter dune hollows of this desert during the early and middle holocene the precipitation in this desert during the early and middle holocene was estimated to be ca 200 mm year on average at least twice as high as at present on the basis of paleoecology tl and radiocarbon ages it was concluded that the huge enrichment of ions in the lakes and decrease of water availability originated from climatic desiccation during the last 4000 years the paleoclimate of the badain jaran desert reported here was remarkably consistent with the late quaternary climatic histories of the regions to the immediate north west east and south of the study area

evidence for holocene environmental changes in the northern fertile crescent provided by pedogenic carbonate coatings abstract holocene environmental changes in the northern fertile crescent remain poorly understood because of the scarcity of local proxy records in the region in this study we investigated pedogenic soil formed carbonate coatings on stones at the pre pottery neolithic site gobekli tepe as an indicator of local early mid holocene environmental changes the 14c ages and stable isotopic composition of carbon and oxygen in thin 0 2 0 3 mm thick pedogenic carbonate lamina indicate two main periods of coating formation the early holocene ca 10000 6000 cal yr bp and the mid holocene ca 6000 4000 cal yr bp during the first period there was an inverse relationship between 13c and 18o curves a decrease in 13c values coincide with an increase in 18o values for this period a trend towards higher temperatures is suggested in the mid holocene the mean rate of coating growth was 2 3 times higher than in the early holocene both 13c and 18o reached their maximum values during this time and the direction of changes of the 13c and 18o curves became similar the combination of data suggests that this period was the most humid in the holocene and on average warmer than the early holocene at ca 4000 cal yr bp secondary accumulation of carbonate ceased presumably reflecting a shift to a more arid climate

the tectonic evolution of a critical segment of the dinarides alps connection kinematic and geochronological inferences from the medvednica mountains ne croatia the transition zone between the alps and dinarides is a key area to investigate kinematic interactions of neighboring orogens with different subduction polarities a study combining field kinematic and sedimentary data microstructural observations thermochronological data rb sr and fission track and regional structures in the area of medvednica mountains has revealed a complex polyphase tectonic evolution we document two novel stages of extensional exhumation the first stage of extension took place along a late cretaceous detachment following the late early cretaceous nappe stacking burial and greenschist facies metamorphism two other shortening events that occurred during the latest cretaceous oligocene were followed by a second event of extensional exhumation characterized by asymmetric top ne extension during the miocene top nw thrusting took place subsequently during the pliocene inversion of the pannonian basin the cretaceous nappe burial late cretaceous extension and the oligocene earliest miocene contraction are events driven by the alps evolution in contrast the latest cretaceous eocene deformation reflects phases of dinaridic contraction furthermore the miocene extension and subsequent inversion display kinematics similar with observations elsewhere in the dinarides and eastern alps all these processes demonstrate that the medvednica mountains were affected by alpine phases of deformations to a much higher degree than previously thought similarly with what has been observed in other areas of contractional polarity changes such as the mediterranean black sea or new guinea systems the respective tectonic events are triggered by rheological weak zones which are critical for localizing the deformation created by both orogens

holocene shorelines and lake evolution in juyanze basin southern mongolian plateau revealed by luminescence dating holocene environment change in the gobi desert of mongolia and northwestern china is of global significance as it is one of the key dust source areas of the world the juyanze basin located in the central gobi desert of southern mongolian plateau is one of the three terminal basins of the heihe river that flows north from the qilian mountain a series of geomorphic shorelines at different elevations around the basin indicate that large lake levels fluctuated during the past in this study we measured the exact elevation of shorelines in the juyanze basin using digital global positioning system and found seven shorelines at 37 36 34 30 28 24 and 22 m above modern basin floor a m b f optically stimulated luminescence dating was employed to date the deposition of beach sand and gravel sequences at these shorelines results indicate a paleolake developed in the basin at 5 ka when lake levels reached 26 m a m b f the lake level then gradually increased to 29 m a m b f at 3 3 ka and r

dolomite as a tracer for the source regions of asian dust 1 the possibility of using dolomite as a source tracer for asian dust was assessed samples of potential dust sources were systematically collected from the arid semiarid areas in north china dolomite of detrital origin was detected only in samples taken from the regions on the north margin of tibetan plateau nmtp thus the nmtp originated dust can be detected by the presence of detrital dolomite and applications are performed for the modern dust in beijing and the ancient dust deposits of loess in north china contribution of the nmtp originated particles to the spring dust in beijing and the loess in chinese loess plateau and eastern tibetan plateau are suggested however dolomite cannot be detected in the studied dust storm dust and the loess in northeast china indicating their sources other than the nmtp regions

primary and secondary carbonate in chinese loess discriminated by trace element composition abstract carbonate in the eolian deposits on the chinese loess plateau carries a significant amount of information on the evolution of paleo environment however the paleo proxies based on total carbonate are largely complicated by the coexistence of primary and secondary carbonate this work provides a new method to quantify the relative proportion of primary and secondary carbonate in these eolian deposits according to the mn ca and mg ca ratios of bulk carbonate the carbonate associated mg and mn which can be extracted by selective dissolution using diluted weak acid are mostly derived from primary carbonate because the secondary carbonate contains very little mg and mn the amounts of mg and mn associated with carbonate could thus serve as proxies for the pedogenic dissolution of primary carbonate which reflect clear glacial interglacial changes of summer monsoon a positive correlation between the mn ca and mg ca ratios of bulk carbonate has been observed indicating binary mixing between secondary carbonate with the low mn ca and mg ca ratios and primary carbonate with high mn ca and mg ca ratios the high mn ca and mg ca ratios of primary carbonate endmember also indicate alxa arid lands as the main source of eolian deposits on chinese loess plateau the mn ca and mg ca ratios of carbonate could be employed as a quick method to check the purity of the secondary carbonate used for paleo environmental studies and help to interpret the paleo proxies based on the bulk carbonate the results reveal significant amount of primary carbonate included in the traditionally believed pure authigenic carbonate phases such as carbonate concretion rhizolith and the fine grain sized carbonate the new method also helps to appraise the control of the relative portion of primary and secondary carbonates on the stable carbon and oxygen isotopes of bulk carbonate high mg ca ratio and low mn ca ratio of the carbonate in red clay formation is observed which confirms the existence of authigenic dolomite

oxygen and carbon stable isotope composition of authigenic carbonates in loess sequences from the carpathian margin and podolia as a palaeoclimatic record abstract samples were collected from the outcrops situated in the north and east of the carpathian margin in the transition zone between the area of loess covers of eastern and western europe the chosen localities include two zones of temperate climate with slightly different prevailing wind directions these loess palaeosol sequences formed and develop in different time intervals early quaternary epoch podolia ukraine and late quaternary epoch carpathian foothills poland the isotopic analysis was carried out on many types of authigenic soil carbonates including nodules rhizoliths rhizocretions calcified root cells and bioclasts the carbon isotopic compositions 13 c of different types vary markedly these differences seem to be more important than the variations within one type of carbonate at a particular section the 13 c values for authigenic carbonate cements rhizoliths rhizocretions and nodules vary in a narrow range from about 11 to 8 suggesting that calcite cements were precipitated under roughly similar conditions with a considerable supply of co 2 derived from biomineralization of organic matter predominantly from c 3 plants the 18 o record of the calcite cements within the upper quaternary deposits exhibits relatively slight variability suggesting that 18 o values in soil water were homogeneous the significant depletion of 13 c as well as 18 o in calcite from calcified root cells 12 and 7 respectively and to a lesser extent from calcitic globules with respect to calcite cements points to different environments of formation the morphology of calcite crystals replacing root cells and their carbon and oxygen isotopic composition indicate that they may precipitate inside the root cells from fluids with organic compounds in general the temperature reconstructions yield an average mat about 11 c for the upper quaternary sediments deposited during mis 2 the estimated mat for sediments of mis 3 5 range from 12 to 14 c mean annual temperatures estimated for the lower quaternary of podolia fall in the range from 9 to 11 c with two single minimums about 7 c probably corresponding to short lived environmental changes the mat curve throughout the lower part of lower quaternary is more variable and shows several local shifts up to 3 c

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

developing inorganic carbon based radiocarbon chronologies for holocene lake sediments in arid nw china abstract inorganic carbonates are often used to establish radiocarbon 14c chronologies for lake sediments when terrestrial plant remains tpr are rare or when bulk organic matter is insufficient for dating a problem that is common for many lakes in arid regions however the reservoir effect re as well as old carbon contributed from the lakes catchment make it difficult to establish reliable chronologies here we present a systematic study of inorganic 14c ages of two lake sediment sequences one from a small enclosed saline lake lake gahai in qaidam basin and the other from a large freshwater lake lake bosten in xinjiang modern dissolved inorganic carbon dic of the lakes paleo lake sediments exposed in the catchment and mollusk shells in core sediments from lake gahai were dated to assess the re and the contribution of pre aged carbon to the old ages in the cores we propose a statistical regression to assess more than one re for the 14c carbonate ages within our sedimentary sequences old radiocarbon ages contributed by detrital carbonates were assessed by comparing the ages of mollusk shells with those of carbonates at the same sediment depths we established the re of the authigenic component and assessed detrital old carbon contributions to our two sites and this was used to correct the 14c ages based on this approach we developed age models for both cores and tested them using 210pb ages in both cores and tpr based 14c ages recovered from lake bosten we further tested our age models by comparing carbonate based oxygen isotope 18o records from both lakes to an independently dated regional speleothem 18o record our results suggest if sedimentary sequences are densely dated and the re and the contribution of old carbon from detrital carbonates can be ascertained robust chronological frameworks based on carbonate based 14c determinations can be established

quantitative reconstruction of holocene millennial scale precipitation in the asian monsoon margin of northwest china revealed by phytolith assemblages from calcareous root tubes in the tengger desert the spatio temporal characteristics and driving mechanisms of the asian summer monsoon asm during the early and middle holocene remain unclear moreover the timing of maximum monsoon precipitation in the asian monsoon margin of northwest china during this period is also a subject of considerable debate herein we analyzed phytolith assemblages within 55 calcareous root tube crt samples from the hinterland of the tengger desert to quantitatively reconstruct holocene millennial scale precipitation changes and discuss the potential forcing mechanisms our results revealed that the mean annual precipitation map was 138 53 to 149 18 mm during 10 0 7 0 cal kyr bp 179 26 to 192 26 mm during 7 0 5 0 cal kyr bp and 129 20 to 161 13 mm during 5 0 1 0 cal kyr bp the quantitative reconstruction results suggested that precipitation in this area was low in the early holocene then increased to a maximum in the middle holocene 30 higher precipitation than present and gradually decreased in the late holocene maximum monsoon precipitation did not occur until the middle holocene in this area because the northernmost margin of the asm reached its northernmost latitude lagging behind its maximum monsoon intensity suppressed by high northern latitude ice volume forcing during the early holocene despite high summer insolation in addition to quantifying the holocene millennial scale precipitation changes in the northwestern margin of the asm this study also provides new evidence for spatial and temporal variations of the asm during the holocene

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

the role of climate and aeolian dust input in calcrete formation in volcanic islands lanzarote and fuerteventura spain calcretes are widely described in non marine settings with carbonates in their catchment or vicinity areas but in volcanic islands without carbonates in their substrate calcretes are not very common in lanzarote and fuerteventura canary islands characterized by impressive volcanic landscapes the sedimentary carbonate rocks are rare except for some recent marine and aeolian deposits in these settings very well developed calcretes cover large areas of the present landscape the source of calcium required for the formation of these calcretes has not been discussed in much detail till now although its role is critical to an understanding of the climatic conditions in which calcium was transported and fixed and of the calcrete formation processes the petrological and geochemical studies 87sr 86sr ratios 13c 18o major trace and ree carried out in this paper do confirm the important role of aeolian dust input in the formation of these calcretes canarian calcretes were mainly generated by pedogenic processes and are composed of various irregular carbonate lamina interbedded with fine clastic deposits our study indicates that these interbeddings were the result of several stages in which during dry periods aeolian dust deposition alternated with leaching and calcite precipitation during wetter periods when plants insects and bacteria played an important role in carbonate precipitation the 18o 2 70 to 2 22 vpdb and 13c 8 21 to 0 24 vpdb values indicate that calcretes were formed by pedogenic processes comparison of calculated 18o values for the canary calcretes with continental mid latitude calcrete values reflects the more homogeneous temperature regimes of calcrete formation in island oceanic settings calcrete87sr 86sr ratios 0 706357 to 0 709208 show strong affinity with those obtained in aeolian carbonate dust and marine deposits and are relatively different from those obtained in basalts ree major and trace element concentrations show that ca bearing minerals from volcanic host rock contributed little to calcrete formation and most of the calcium was supplied by aeolian deposits such as the aeolian dust coming from the sahara and sahel or sand dunes

aeolian activity in the south margin of the tengger desert in northern china since the late glacial period revealed by luminescence chronology abstract aeolian sediments from deserts in northern china have been widely used in the study of aeolian sedimentology and its dynamic association with past climate conditions the tengger desert the fourth largest desert in china is sensitive to the waxing and waning of the asian monsoonal system previous attempts to date aeolian deposits in the tengger desert concentrated solely on local scales and only a limited number of dates have subsequently been made available accordingly past sand dune activity in this desert remains poorly understood the aim of this study was to conduct a detailed historical investigation of aeolian activity in this region since the late glacial period and potential forcing mechanisms that governed the desert s evolution for this purpose we collected and dated eighteen samples from different geological sections along a west east transect in the desert s southern margin using optically stimulated luminescence osl our results in combination with previous aeolian sediment chronologies show that sand dune accumulation occurred before 10 ka sandy loess developed between 10 and 6 ka when sand dunes stabilized as a result of increased effective moisture levels and sand dunes again mobilized from 3 ka onwards as a result of increased aridity findings indicate that aeolian activity at the southern margin of the tengger desert was closely associated with asian monsoon circulation moreover the transition between mobilization and stabilization of sand dunes demonstrates the significance of effective moisture which is influenced by both monsoon precipitation and local convection and evaporation effects interacting together to control aeolian activity

hydrological conditions over the western mediterranean basin during the deposition of the cold sapropel 6 ca 175 kyr bp a new oxygen isotope record is reported from a stalagmite collected in the argentarola cave located on the tyrrhenian coast of italy as shown from observations and numerical modeling of n 18 o in modern precipitation the recorded n 18 o variability for this zone is dominated by the amount of precipitation so called amount effect the n 18 o profile measured in the stalagmite is characterized by a prominent negative excursion ca 2 3x between 180 and 170 kyr bp this paleoclimatic feature is interpreted as being due to a relatively wet period which occurred during the penultimate glacial period more precisely during marine isotope stage 6 5 this pluvial phase is shown to correspond chronologically to the deposition of the sapropel event 6 s6 although this particular sapropel event occurred during a cold phase the n 18 o excursion is similar to those corresponding to other sapropels s4 s3 and s2 the evidence for humid conditions during s6 in the western mediterranean basin agrees with previous studies based on deep sea sediment cores taken collectively the data suggest that during sapropel events dilution of ocean surface waters was not restricted to the output of the river nile but was rather widespread over the entire mediterranean sea due to increased rainfall 2002 elsevier science b v all rights reserved

soils at the hyperarid margin the isotopic composition of soil carbonate from the atacama desert northern chile we evaluate the impact of exceptionally sparse plant cover 0 20 and rainfall 2 114 mm yr on the stable carbon and oxygen composition of soil carbonate along elevation transects in what is among the driest places on the planet the atacama desert in northern chile d 13 c and d 18 o values of carbonates from the atacama are the highest of any desert in the world d 13 c vpdb values from soil carbonate range from 8 2 at the wettest sites to 7 9 at the driest we measured plant composition and modeled respiration rates required to form these carbonate isotopic values using a modified version of the soil diffusion model of cerling 1984 earth planet sci lett 71 229 240 in which we assumed an exponential form of the soil co2 production function and relatively shallow 20 30 cm average production depths overall we find that respiration rates are the main predictor of the d 13 c value of soil carbonate in the atacama whereas the fraction c3 to c4 biomass at individual sites has a subordinate influence the high average d 13 c value 4 1 of carbonate from the driest study sites indicates it formed perhaps abiotically in the presence of pure atmospheric co2 d 18 o vpdb values from soil carbonate range from 5 9 at the wettest sites to 7 3 at the driest and show much less regular variation with elevation change than d 13 c values d 18 o values for soil carbonate predicted from local temperature and d 18 o values of rainfall values suggest that extreme 80 in some cases soil dewatering by evaporation occurs at most sites prior to carbonate formation the effects of evaporation compromise the use of d 18 o values from ancient soil carbonate to

reflections of surface water seasonality and climate in stable oxygen isotopes from tyrannosaurid tooth enamel abstract patterns of isotopic variation in enamel of eight albertosaurus teeth from the campanian maastrichtian horseshoe canyon formation alberta were measured by serial sampling along the growth axis cycles in the isotopic values appear to correlate to published tooth growth rates for tyrannosaurids tyrannosaurid dinosaur teeth of 50 mm in length provide ideal repositories of terrestrial climatic information as each records a full annual cycle of body water isotopic variation the relatively thin enamel precludes problems associated with time averaging associated with complex growth patterns found in thick mammalian enamel the most consistent and striking pattern associated with all of the teeth are two relatively closely spaced subequal maxima these appear to be associated with onset of a seasonal episode of high humidity after the activation of the amount effect where the influence of ambient temperature on surface water and body water 18 o ends while temperatures remain above 20 c teeth within a single fossiliferous horizon show the same general isotopic pattern and range a notable difference in pattern shape and magnitude of isotopic variation between tyrannosaurid teeth from several stratigraphic intervals of the lower horseshoe canyon formation section indicates a climatic changes from strong seasonality high annual temperature range with distinct precipitation and humidity maxima during each year at the base of the section to milder seasonality at the top

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

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

millennial scale environmental changes in the asian monsoon margin during the holocene implicated by the lake evolution of huahai lake in the hexi corridor of northwest china the pattern of holocene environmental changes in the asian monsoon margin on a millennial timescale remains controversial based on lithological characteristics and sedimentological proxies we reconstructed holocene effective humidity changes and the lake evolution of huahai lake in the marginal area of the asian monsoon in the hexi corridor of nw china our results show that alluvial and aeolian deposition before 10 4 cal ka bp indicate an arid environment that lacustrine deposition from 10 4 to 8 8 cal ka bp indicates a transition from an arid to a humid environment and that lacustrine deposition from 8 8 to 5 5 cal ka bp occurred during the most humid conditions indicated by proxy records grain size carbonate toc and c n after 5 5 cal ka bp a depositional hiatus implicates an arid environment in the late holocene holocene environmental changes on millennial timescales in huahai lake imply that climate was arid to humid in the early holocene most humid in the mid holocene and arid in the late holocene these moisture changes were influenced by the asian monsoon particularly the transportation of water vapor by the indian monsoon in addition these moisture changes could have been affected by westerly winds that could have contributed to the water vapor supply to this region during the mid holocene the most humid conditions that occurred in the study area during the mid holocene may have been caused by strong westerlies and low levels of evaporation

using petrography and geochemistry to determine the origin and formation mechanism of calcitic plant molds rhizolith or tufa rhizoliths root casts and rhizocretions are prolific in the geologic record and their morphology and isotopic signatures can be important indicators of paleoenvironment and paleoclimate in a semiarid playa in nevada the calcite plant encrustations preserved at the playa surface resemble rhizoliths morphologically and would seem to indicate pedogenesis and root activity the features are preserved as short thin upright and or overturned tubes that often exhibit an apron at the base branching is rare and the tubes can be filled with sediment or calcite or left open however detailed macroscopic microscopic and geochemical analyses of these features reveal that they are instead macrophyte stem encrustations that form in standing water while these features form in a manner similar to paludal tufa they do not resemble typical tufa deposits e g barrages mounds cascades instead they mimic rhizoliths this study describes the macroscopic and microscopic characteristics of these features and distinguishes them from rhizoliths so that they can be accurately identified in the geologic record furthermore this study identifies a more appropriate method of interpreting the stable isotope values of these tufa like plant molds these types of carbonates are faithful recorders of ambient aquatic conditions e g geochemistry as well as local hydrologic parameters e g water depth when the playa surface is flooded but their geological application is restricted to a partial annual signal e g plant growing season presence of standing water on the playa it is important to correctly identify these types of plant encrustations in the geologic record since 1 their presence indicates a shallow standing body of water rather than a paleosol and 2 their isotopic composition records not only an ambient aquatic signal but an extremely restricted climatic signal that should not be interpreted with models for pedogenic carbonates

indication of millennial scale moisture changes by the temporal distribution of holocene calcareous root tubes in the deserts of the alashan plateau northwest china abstract calcareous root tubes or rhizoliths have a strong potential for paleoenvironmental studies especially in reconstructing paleoenvironmental conditions and paleovegetation previous studies suggested that the effectivity of the moisture level affects the formation of calcareous root tubes in the deserts of the alashan plateau northwest china however it remains unclear whether the temporal distribution of calcareous root tubes can be used to reconstruct paleo effective moisture in this area in this study based on conventional 14c dating results of 34 holocene calcareous root tube samples collected from the badain jaran desert the tengger desert and the ulan buh desert in the alashan plateau of northwestern china millennial scale changes in paleo effective moisture during the holocene in this area were reconstructed the frequency of the 14c dating results demonstrates that 62 of the holocene samples were dated to 7 5 cal kyr bp and 38 of the holocene samples were dated to 4 2 cal kyr bp indicating an arid period during the early holocene before 8 0 cal kyr bp a humid period during the mid holocene 8 0 5 0 cal kyr bp and a humid to arid period during the late holocene after 5 0 cal kyr bp the reconstruction results were consistent with other previous reconstruction results from lake sediments and aeolian sand lacustrine sequences which indicated that temporal distribution of calcareous root tubes can reflect millennial scale changes in paleo effective moisture in this area however a single sample could indicate local environmental changes that may differ from the overall desert environmental changes hence the relatively humid environmental record obtained from the presence of calcareous root tubes is a local signal or a regional signal that should be noted

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

a holocene climatic record from arid northwestern china abstract the history of climatic changes during the interval 8500 3000 cal yr b p has been reconstructed from stratigraphical and chronological studies and the results of total organic carbon toc total inorganic carbon tic element composition pollen and stable isotope analyses of a section along the hongshui river in the southern tengger desert nw china the record suggests that from 8450 bottom of the studied section to 7500 yr b p the climate was characterized by instability from 7500 to 5070 yr b p the climatic conditions improved and can be divided into two parts a warm humid spell between 7290 and 6380 yr b p during which the average temperature was 3 4 c higher than that of today and a warm dry spell lasting from 5950 to 5720 yr b p the climate deteriorated between 6380 and 5950 yr b p from 5720 to 5070 yr b p the temperature decreased but humidity increased an abrupt temperature drop occurred between 5340 and 5290 yr b p that indicated the decline of the warmer and humid mid holocene climate from 5070 yr b p onward the climate oscillated significantly and there were three large temperature decreases coinciding with high mountain glacier advances between 5070 4670 yr b p 4300 3740 yr b p and 3410 3230 yr b p top of the section respectively the climatic fluctuations recorded in the southern tengger desert appear in phase with climatic changes recognized in the tibetan plateau suggesting that the period between 7290 and 6380 yr b p was the most warm humid spell one extremely dry event occurred at ca 3000 yr b p and subsequently the fluvial lacustrine depositional process terminated and wind action prevailed in the area both of these features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation which are closely connected with global changes

pedogenic carbonates as a proxy for palaeo co2 in the palaeozoic atmosphere abstract according to a model by cerling cerling t e 1991 carbon dioxide in the paleoatmosphere evidence from cenozoic and mesozoic paleosols am j sci 291 377 400 cerling t e 1999 stable carbon isotopes in palaeosol carbonates in thiry m simon coincon r eds palaeoweathering palaeosurfaces and related continental deposits vol 27 of spec publ int assoc sediment pp 43 60 the carbon isotope composition of calcretes should depend on the soil type and the co 2 concentration in the atmosphere we have tested cerling s model by investigating 14 palaeozoic sections with soil profiles a large number of carbonate types of different genetic origin exist in the localities examined comparing the palaeozoic samples with recent and subrecent calcretes it can be demonstrated that anhedral cryptocrystalline 2 concentration

reconstructing the response of c3 and c4 plants to decadal scale climate change during the late pleistocene in southern illinois using isotopic analyses of calcified rootlets abstract the 13c and 18o values of well preserved carbonate rhizoliths crs provide detailed insights into changes in the abundance of c3 and c4 plants in response to approximately decadal scale changes in growing season climate we performed stable isotope analyses on 35 40 crs sampled at 1 cm intervals from an 18 cm thick paleosol formed in southern illinois during wisconsin interstadial 2 minimum 13c values show little variation with depth whereas maximum values vary dramatically and average values show noticeable variability maximum 18o values vary less than the minimum 18o values these findings indicate that a diverse and stable c3 flora with a limited number of c4 grass species prevailed during this interval and suggest that the maximum growing season temperatures were relatively stable but minimum growing season temperatures varied considerably two general patterns characterize the relationships between the 13c and 18o values obtained from the 1 cm samples in some cases low 13c values correspond to low 18o values and high 13c values correspond to high 18o values suggesting that cooler growing season temperatures favored c3 and warmer growing season temperatures favored c4 plants in other cases low 13c values correspond to high 18o values likely suggesting that wetter growing season conditions were favorable to c3 plants the high density of well preserved crs in this paleosol provides a unique opportunity to study detailed ecological responses to high resolution variability in growing season climate