a seismic discontinuity in the upper mantle between the eastern alps and the western carpathians constraints from wide angle reflections and geological implications abstract seismic investigation of the lithosphere by means of active source experiments is mostly confined to the crust and the moho structures in the upper mantle are more likely to be discovered by analyses of teleseismic data although these methods are restricted in their resolution capabilities the relatively rare evidence for upper mantle refractors or reflectors in active source data enables challenging and interesting studies of the lower and not so well known part of the lithosphere we present such an example from the tectonically complex region between the eastern alps and the western carpathians this area was covered by several extensive 3d wide angle reflection refraction experiments within the last decade and their layout was designed to illuminate the crustal structure and in particular the moho discontinuity in some areas reflections from below the moho are also recorded these reflections occur at recording offsets between 200 and 500 km and they are particularly strong in cross line recordings we derive a set of travel times from the data and perform a tomographic inversion for the depth and shape of the reflecting interface the inversion makes use of an existing 3d crustal model which also includes the moho topography since the upper mantle velocities are poorly constrained and the azimuthal distribution of the rays is biassed several tests are applied to investigate the reliability of possible solutions the results from the tomographic inversion indicate an overall horizontal and radially dipping reflector the average depth of the reflector is 55 km which is about 25 km below the crust mantle transition and amplitude modelling suggests that the reflecting interface represents a velocity increase the investigated area is further characterised by deep sedimentary basins high heat flow high velocities in the lower crust diffuse moho signature and a strong positive bouguer anomaly nearby xenolith outcrops exhibit a pronounced change in anisotropy and indicate the presence of two distinct layers in the lithospheric mantle whereas the deeper layer is thought to present more juvenile lithosphere derived from thermal relaxation in the post extension phase most likely the upper mantle reflector also represents this change in anisotropy though other scenarios are also possible we conclude that the entire lithosphere is significantly shaped by extensional processes which affect the area since the late oligocene early miocene

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

holocene climate changes in the monsoon arid transition reflected by carbon concentration in daihai lake of inner mongolia two sediment cores recovered in the central part of daihai lake in north central china were analysed at 2 to 4 cm intervals for total inorganic and organic carbon tic and toc concentrations the tic concentration is inferred to reflect temperatures over the lake region and an increase in the tic concentration implies an increase in the temperature toc concentration is considered to reflect the precipitation in the lake basin and higher toc concentrations denote more precipitations thus ams 14c time series of the tic and toc records of daihai lake sediments uncovers a detailed history of changes in temperature and precipitation in north central china during the last c 12 000 yr the holocene an epoch of postglacial warmth started c 11 500 cal yr bp and can be subdivided into three stages the early c 11 500 8100 cal yr bp middle c 8100 3300 cal yr bp and the late holocene c 3300 0 cal yr bp the climate was warm and dry during the early holocene warm and wet during the middle holoce

late holocene monsoon climate as evidenced by proxy records from a lacustrine sediment sequence in western guangdong south china abstract the study of a 300 cm thick exposed lacustrine sediment section in the hedong village in zhaoqing area which is located in sub tropical west guangdong province in south china demonstrates that the lacustrine sedimentary sequence possibly contains evidence for exploring variation of asian monsoon climate multi proxy records including the humification intensity total organic carbon and grain size fractions reveal a general trend towards dry and cold conditions in the late holocene that this is because of a decrease in solar insolation on an orbital scale three intensified asian summer monsoon asm intervals 3300 3000 cal yr bp 2600 1600 cal yr bp and 900 600 cal yr bp and three weakened asm intervals 4000 3300 cal yr bp 3000 2600 cal yr bp and 1600 900 cal yr bp are identified our humification record hd cal shows a good correlation on multi centennial scale with the tree ring 14 c record a proxy of solar activity a spectral analysis of hd cal reveals four significant cycles i e 1250 yr 300 yr 110 yr and 70 yr and most of these cycles are related to the solar activity our findings indicate that solar output and oceanic atmospheric circulation probably have influenced the late holocene climate variability in the study region

quantification of holocene asian monsoon rainfall from spatially separated cave records abstract a reconstruction of holocene rainfall is presented for southwest china an area prone to drought and flooding due to variability in the east asian monsoon the reconstruction is derived by comparing a new high resolution stalagmite 18 o record with an existing record from the same moisture transport pathway the new record is from heshang cave 30 27 n 110 25 e 294 m and shows no sign of kinetic or evaporative effects so can be reliably interpreted as a record of local rainfall composition and temperature heshang lies 600 km downwind from dongge cave which has a published high resolution 18 o record wang y j cheng h edwards r l he y q kong x g an z s wu j y kelly m j dykoski c a li x d 2005 the holocene asian monsoon links to solar changes and north atlantic climate science 308 854 857 by differencing co eval 18 o values for the two caves secondary controls on 18 o e g moisture source moisture transport non local rainfall temperature are circumvented and the resulting 18 o signal is controlled directly by the amount of rain falling between the two sites this is confirmed by comparison with rainfall data from the instrumental record which also allows a calibration of the 18 o proxy the calibrated 18 o record provides a quantitative history of rainfall in southwest china which demonstrates that rainfall was 8 higher than today during the holocene climatic optimum 6 ka but only 3 higher during the early holocene significant multi centennial variability also occurred with notable dry periods at 8 2 ka 4 8 4 1 ka 3 7 3 1 ka 1 4 1 0 ka and during the little ice age this holocene rainfall record provides a good target with which to test climate models the approach used here of combining stalagmite records from more than one location will also allow quantification of rainfall patterns for past times in other regions

the impact of ancient civilization on the northeastern chinese landscape palaeoecological evidence from the western liaohe river basin inner mongolia the western liaohe river basin in northeastern china is one of the cradles of ancient chinese civilization archaeological records from this region indicate that human occupation began about 8000 y

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

the identification of mantle reflections below hungary from deep seismic profiling abstract in the 1970 s the eotvos lorand geophysical institute performed seismic reflection deep sounding experiments with multiple coverage in several parts of the pannonian basin posgay 1975 one of the most interesting results was that arrivals were received in the time range corresponding to the depth of the asthenosphere they were interpreted as reflections posgay et al 1981 conspicuous arrivals from the time range of the asthenosphere 15 20 s were also received along the pannonian geotraverse in 1987 in the majority of sections published in other countries the upper mantle seems to be transparent the present paper discusses investigations and preliminary results which lead to the conclusion that this apparent transparency is due to the frequency range below 10 hz being neglected in both signal generation and recording in most deep continental reflection surveys the seismogeological conditions of the pannonian basin are certainly favourable for reflection studies of the upper mantle the correctness of the assumption that arrivals from the time range of the asthenosphere are primary reflections is subjected to further investigation and conclusions are made concerning the structure of the asthenosphere

grain size of fine grained windblown sediment a powerful proxy for process identification abstract dust transport by the wind is not a uniform process but may occur in different modes according to source area conditions and transport height and distance subsequently these differences are expressed in terms of grain size and fluxes of the aeolian deposits transport distances may vary from several tens of meters to thousands of kilometers while the height accordingly may vary from meters to more than thousand meters a relation with grain size distributions may be established on the base of type occurrences of different loess facies three main loess populations and several subpopulations of primary windblown origin may be defined according to their grain size dominated by fine sand to very coarse silt silt and very fine silt to clay respectively each of them reflects a specific aeolian process and transport conditions it follows that the grain size distribution of a loess deposit is an excellent proxy for the reconstruction of aeolian processes and wind circulation patterns apart from primary pure wind deposition loess may also be affected by secondary post depositional processes examples are settling of loess particles in a lacustrine setting and reworking by rivers or surface runoff although the primary loess characteristics are maintained reworking processes leave also their imprint in the grain size distribution as a useful tool for secondary process identification

environmental changes in hunshandake otindag sandy land revealed by optical dating and multi proxy study of dune sands abstract a stabilized sand dune from the southern hunshandake otindag sandy land in northeastern china was studied for reconstructing past environmental changes by optically stimulated luminescence osl dating magnetic susceptibility and particle size analysis the osl dating results indicate that the sandy deposits at the bottom of the section formed at 11 8 ka ago corresponding to low magnetic susceptibility and low fractions of fine particles

sediment colour reflectance spectroscopy as a proxy for wet dry cycles at lake el gygytgyn far east russia during marine isotope stages 8 to 12 marine isotope stage 11 has been proposed as an analogue for the present interglacial interval yet terrestrial climate records from both this region and time interval are rare the sediments deposited at lake el gygytgyn 67 30 0 n 172 5 0 e in far east russia contain a 3 56 ma record of climate variability this study presents a high resolution record of sediment colour change from marine isotope stage 8 to 12 ca 275 to 475 ka and demonstrates the link between lake catchment processes and climate variability the hue colour parameter calculated from data collected via colour reflectance spectroscopy in the visible spectrum 380 to 720 nm exhibits correspondence with global climate records determining the source of sediment colour changes was achieved through detailed mineralogical and sedimentological methods and linked to colour changes through a series of colour sensitivity tests mineralogical data measured by x ray diffraction reveal fluctuations in concentrations of clay minerals corresponding to colour changes further analyses of the clay mineral assemblages show no change in relative clay mineral abundances yet demonstrate a lake catchment dominated by physical weathering processes using measured mineral abundances reconstructions of sediment colour based on colour reflectance mineral standards link mineral and clay mineral content to overall sediment colour colour sensitivity tests demonstrate the ability of iron oxide minerals to stain sediments red additionally colour sensitivity to organic matter content was tested suggesting that organic content drives variability in the red portion of the spectrum and darkens the overall colour signal sediment colour is then ultimately linked to physical weathering of bedrock minerals with small amounts of chemical weathering producing iron oxides during wet intervals fluctuations in the sediment colour reveal a high resolution record of wet dry cycles and provide new information about wet periods for the russian arctic region not yet understood from other lake proxy records

re examining the potential of using sensitive grain size of coastal muddy sediments as proxy of winter monsoon strength sensitive components of grain size in coastal muddy sediments of china have been widely used for reconstruction of the east asian winter monsoon strength however trends of the winter monsoon strength profiles reconstructed for the past 2000 years from different sediment cores tend to be inconsistent and even contradictory in the present study the grain size variation sequence of the sensitive components in a sediment core collected from the middle of the min zhe coastal mud with a time span of 2700 years is determined the striking correspondence between the reconstructed mean grain size of the sensitive component with northern hemisphere temperature in particular the medieval warm period and the little ice age showed that coastal muddy sediments of china can be used to reconstruct a high resolution profile of east asian winter monsoon strength the inconsistencies in the winter monsoon proxy sequences from different studies are most likely caused by low resolution of grain size standard deviation data and direct influence of the river input materials in some studies c 2013 elsevier ltd and inqua all rights reserved

neogene quaternary magmatism and geodynamics in the carpathian pannonian region a synthesis in the carpathian pannonian region in neogene times westward dipping subduction in a land locked basin caused collision of two lithospheric blocks alcapa and tisia with the southeastern border of the european plate calc alkaline and alkaline magmatism was closely related to subduction rollback collision and extension from the spatial distribution of the magmatic activity four segments can be defined western segment magmatism occurring on the alcapa block central segment magmatism occurring on both alcapa and the tisia blocks south eastern segment and interior segment both on the tisia block most calc alkaline magmatism in the region resulted from melting of a heterogeneous asthenospheric mantle source modified by addition of fluids and sediment assimilation and fractionation processes at shallow crustal levels occurred in most of the segments strongly masking the deeper source processes long term subduction rollback and or delamination led to contamination of the asthenosphere beneath the western segment here large volume partial melts of the contaminated mantle caused underplating and crustal anatexis leading to mixing of mantle derived calc alkaline magmas with crustal melts in the central segment calc alkaline magmas were formed by subduction and rollback followed by back arc extension and slab breakoff avariable mantle source is indicated in the back arc setting and larger amount of fluid induced metasomatism source enrichment and assimilation nearer to the trench in the interior segment evolution from typical calc alkaline magmas to adakite like ones was related to extension due to fast rotations and transtensional tectonics here calc alkaline magmas formed by decompression melting of a heterogeneous crust mantle lithosphere while adakite like melts resulted from fliud dominated melting of the lithosphere along the south eastern segment slab breakoff was responsible for the generation of typical calcalkaline magmas but in the extreme south of the segment shallow level tearing of the slab followed breakoff strike slip tectonics allowed the rise of hot asthenosphere and generation of adakite like magmas via slab melting along the torn edge of the east european plate alkalic basaltic volcanism with an oib like asthenosphere source followed the calc alkaline stage

cyanobacterial precipitation of gypsum calcite and magnesite from natural alkaline lake water results from transmission electron microscopy provide direct evidence for cyanobacterial biomineralization of gypsum and calcite in aquatic environments laboratory simulations using filter sterilized natural lake water inoculated with synechococcus sp isolated from fayette ville green lake new york revealed epicellular biomineralization of gypsum calcite and magnesite experimental electron microscopical and sedimentological evidence indicates that synechococcus is responsible for a major proportion of the marl sediment and carbonate bioherms in green lake the elucidated role of synechococcus in biomineralization and its ubiquitous distribution in nature have widespread implications for cyanobacterial mineralization in marine and freshwater environments since late archean time

unconfined alluvial flow processes recognition and interpretation of their deposits and the significance for palaeogeographic reconstruction abstract palaeogeographic interpretation of the sedimentary rock record depends on correct recognition from the preserved evidence of the processes responsible for transporting and depositing the sediment this in turn depends on robust knowledge transfer from previous workers and the successful exchange of ideas between workers requires consistent use of a well defined vocabulary we have identified serious breakdowns in all these interpretation steps in the case of terrestrial unconfined flow and its deposits and these failures are leading to unreliable environmental and climatic interpretation this is significant because such alluvial deposits commonly form a majority of the rock record of continental environments working from the basic principles of geomorphology and fluid dynamics we have undertaken a wide ranging analysis of the nature of out of channel flow and from this make predictions about the characteristics of its deposits we identify the range of possible locations and conditions that lead to the development of unconfined flow review the processes operating in each case and examine the range of lithological features that can be produced by these processes this allows us to evaluate the reliability of the criteria claimed for identification of out of channel flow deposits and examine how our new insights might alter palaeoclimatic and palaeogeographic reconstructions published previously by others the sedimentary record of unconfined flows is much more diverse and complex than usually portrayed the received wisdom that the record of unconfined flow consists solely of upwards fining thin beds produced from shallow waning flows is shown to be flawed a wide range of lithofacies are possible and the variation in both flow steadiness and uniformity needs to be taken into account the previously published criteria for recognition of flows of this type are not diagnostic of process or location unconfined flow deposits cannot reliably be identified from grain size or bed thickness similar lithofacies may develop in a wide range of geomorphic and climatic settings because the deposits solely reflect the local flow conditions and sediment availability we recommend that the terms sandflat and sheetflood should not be used in sedimentological accounts because there is no longer a safe informal usage for either contradictory application of these terms and lack of robust definitions is leading to significant misunderstanding of palaeogeography and process our analysis should improve reconstruction of past terrestrial environments because it reveals more clearly the true variety of possibilities for the occurrence of unconfined flow and the resultant deposits enhanced understanding of the inherent uncertainties and realisation of the wider range of plausible alternative explanations should help resolve apparent contradictions with independent indicators of climate or geographic position

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

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

varied responses of forest at its distribution margin to holocene monsoon development in northern china abstract based on pollen analysis and other evidence in a sediment profile from huangqihai lake located at the limit of asian monsoon influence the local vegetation development and climatic change were reconstructed for the past 8600 years from 8600 to 7200 cal yr bp the local vegetation was dominated by steppe and tree cover was low then pine increased gradually and the local vegetation was pine and oak mixed forest with variable ratios of the two dominant tree taxa from 7200 to 3600 cal yr bp from 3600 to 3000 cal yr bp the forest was replaced by shrubland which was attributed to a period of intense drought from 3000 to 600 cal yr bp the tree cover declined to its lowest levels probably due to long term further drought after 600 cal yr bp steppe has become dominant again we found that the changes of vegetation type indicated by pollen percentages did not match existing evidence for monsoon dynamics changes in tree pollen concentration however well captured the changes in the asian monsoon implying different sensitivity of vegetation cover and vegetation type e g replacement of steppe by forest to the monsoon development in addition a shrubland dominated stage which has not been evident in previous studies was also clear in our pollen sequences our study implied that the responses of marginal forest to drought were variable depending on the drought regime the different responses of forest to climate drying in this study provide insights into the reliable prediction of forest dynamics in the semi arid regions

seismic velocity structure of a large mafic intrusion in the crust of central denmark from project estrid abstract the origin of regional sedimentary basins is being investigated by the estrid project explosion seismic transects around a rift in denmark this project investigates the mechanisms of the formation of wide regional basins and their interrelation to previous rifting processes in the danish norwegian basin in the north sea region in may 2004 a 143 km long refraction seismic profile was acquired along the strike direction of a suspected major mafic intrusion in the crust in central denmark the data confirms the presence of a body with high seismic velocity 6 5 km s extending from a depth of 10 12 km depth into the lower crust there is a remarkable moho relief between 27 and 34 km depth along this new along strike profile as based on ray tracing modelling of pmp reflections the lack of pmp reflections at a zone of very high velocity in the lowest crust 7 3 7 5 km s suggests a possible location of a feeder channel to the batholith the presence of volcanic rocks of carboniferous permian age above the intrusion mafic batholith suggests a similar age of the intrusion an older obliquely crossing profile and two new fan profiles deployed perpendicular to the main estrid profile show that the batholith is about 30 40 km wide the existence of this large mafic batholith supports the hypothesis that the origin of the danish norwegian basin is related to cooling and contraction after intrusion of large amounts of mafic melts into the crust during the late carboniferous and early permian the data and interpretations from project estrid will form the basis for subsidence modelling tentatively we interpret the formation of the danish norwegian basin as a thermal subsidence basin which developed after widespread rifting of the region

crustal scale extension in the central pannonian basin abstract within the hungarian segment of the panonian basin a 100 km long seismic reflection profile images the sedimentary fill of two major depressions and their associated crustal signatures these deep 7000 m subbasins are asymmetric half grabens bounded along their western margins by low angle crust penetrating subparallel listric faults the hanging walls are intensely fractured and comprise pre tertiary basement and upper crustal rocks the footwalls are formed by uplifted and ductilely deformed middle to lower crust the crust is relatively thin 25 27 km and decoupled by well defined detachment faults the moho has a gentle northeasterly dip and a spatially variable seismic signature the seismic images imply that the present crustal setting of the area was developed contemporaneously through the northeastward extension of the pannonian basin

dynamics of the last four glacial terminations recorded in lake van turkey abstract a well dated suite of lake van climate proxy data covering the last 360 ka documents environmental changes over 4 glacial interglacial cycles in eastern anatolia turkey the picture of cold and dry glacials and warm and wet interglacials emerging from pollen organic carbon authigenic carbonate content elemental profiling by xrf and lithological analyses is inconsistent with classical interpretation of oxygen isotopic composition of carbonates pointing to a more complex pattern in lake van region detailed analysis of glacial terminations allows for the constraining of a depositional model explaining different patterns observed in all the proxies we hypothesize that variations in relative contribution of rainfall snowmelt and glacier meltwater recharging the basin have a very important role for all sedimentary processes in lake van lake level of glacial lake van predominantly fed by snowmelt was low the water column was oxic and carbonates precipitating in the epilimnion recorded the light isotopic signature of inflow during terminations increasing rainfall and significant supply of mountain glaciers meltwater contributed to lake level rise increased rainfall enhanced density gradients in the water column and hindered mixing leading to development of bottom water anoxia carbonates precipitating during terminations show large fluctuations in their isotopic composition full interglacial conditions in lake van are characterized by high or slowly falling lake level rainfall and snowmelt feed the lake but due to re established mixing the isotopic composition of authigenic carbonates is heavier and closer to that of evaporation influenced lake water than that of runoff representing snowmelt and atmospheric precipitation

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

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

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

characteristic grain size component a useful process related parameter for grain size analysis of lacustrine clastics abstract lacustrine sediments are important archives for paleoclimate reconstructions the application of grain size analysis as palaeoclimatic proxy in lacustrine clastics is valuable but also difficult because the typical polymodal grain size distribution in these clastics to better understand the grain size distribution of lacustrine clastics and to promote the application of grain size in paleoenvironmental interpretation this study investigates lacustrine clastics from northern and southern china the grain size distribution of these sediments was decomposed by log normal distribution function fitting method based on the results and drawing upon the concept of paleomagnetic demagnetization and characteristic remnant magnetization from paleomagnetism a conceptual system has been established and defined for grain size distribution analysis the system is composed of four components i characteristic grain size component chgsc ii affiliated grain size component iii meaningful grain size component and iv combination feature of grain size components cfgscs based on the proposed system chgsc and cfgscs were used to detect the grain size distribution of clastics from the different lake zones investigated our results show the number modal size and percentage of chgsc s in grain size distributions are sensitive to changes in the lacustrine environment the chgsc s mirrors the dominant depositional process and hydrodynamic conditions the modal size of chgsc s is more sensitive to hydrological conditions than the widely used mean grain size approach thus the chgsc s provide a useful process related parameter for paleoenvironmental reconstructions to test this promising application we applied this approach to a deep drill core from the qaidam basin in the northeastern tibetan plateau

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

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

hypersalinity flushing and transient salt wedges in a tidal gulf an inverse estuary abstract because of high evaporation and low rainfall gulfs and embayments in the arid coastal regions of australia are endowed with highly saline water masses with salinities ranging from oceanic values at their mouths to values as high as 60 at their heads this presents the case of an inverse estuary in gulf st vincent of south australia an example of such an inverse estuary the salinity at the head ranges from 39 in winter to 42 in summer in sympathy with the seasonal changes of the local excess of evaporation over precipitation the salient characteristics of temperature salinity and density distributions in the gulf are here described despite a seasonal reversal of spatial temperature gradients the salinity gradient maintains the same sign and is strong enough to control a persistent density gradient from mouth to head in parallel with the case of estuaries a flushing time for salt is defined and estimated for the northern regions of the gulf although the water mass was initially assumed to be vertically well mixed because of tidally induced turbulence the present observations reveal the striking feature that at neap tides the horizontal density gradient forces a salt wedge from the north below the fresher water in the south

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

geological control on the origin of fresh groundwater in the otindag desert china abstract the present study has explored the origin of fresh groundwater in the otindag desert china using environmental tracers the results characterize hydrochemical and isotopic properties of groundwater in this middle latitude desert of arid asia clarifying their spatial distribution and linkage with climatic topographic and geologic settings and interpreting the groundwater source and chemical evolution hydrogeochemical and isotopic signals suggest that groundwater recharge in the desert is isolated from seasonal and regional variations in meteorological forcing stable isotopic data 2h 18o and radioactive isotopic data 3h indicate that the desert aquifer is dominated by high altitude cold water originating from the highland mountains that border the desert to the east and south variography shows that the dip of the main xilamulun fault is a dominant control on the groundwater flow implying that the tectonic settings are more important than climatic and topographical settings to explain the origin of groundwater in the desert this means that the origin of fresh groundwater in the desert is maily controlled by geological structures this study provides a new perspective into the origin and evolution of groundwater resources in the middle latitude deserts of the arid asia

lake levels for the past 19 000 years from the tl05 4 cores tulare lake california usa geophysical and geochemical proxies abstract geochemical and geophysical proxy data from the tl05 4 lake plain cores of tulare lake california are reported on here representing most of the past 19 000 years the new record consists of carbon nitrogen ratios total organic carbon toc nitrogen n total inorganic carbon tic grain size and magnetic susceptibility analyses from samples taken at 1 cm intervals 45 yr sample age control is provided by 22 radiocarbon dates the first part of the record 19 0 14 5 cal ka bp consists of elevated sand and silt percentages and higher sedimentation rates interpreted as elevated runoff associated with melting of the tioga age sierra nevada ice cap the tic was undetectable and toc and n were low suggesting low productivity in a relatively sterile freshwater lake from 14 5 to 10 3 cal ka bp the deposits consisted of 50 clay and 50 silt with tic and toc extremely low which is consistent with a stable low productivity lake from 10 3 to 7 5 cal ka bp an initial pulse of fining upward sand gave way to increased clay deposition that suggests a lake transgression to a stable highstand coeval with the deep water event found in previously published records of tulare lake and other lakes from central and southern california including owens lake and lake elsinore a few hundred year duration spikes in tic centered at 8 0 cal ka bp is suggestive of evaporating lake conditions toward the end of this early holocene highstand tulare lake dropped quickly to a relative low at 7 5 cal ka bp but then lake level increased steadily until 3 0 cal ka bp high amplitude fluctuation in almost all proxies occurs from 2 5 to 1 8 cal ka bp at the end of the record suggesting that this time interval was characterized by rapid fluctuations in lake level tulare lake levels during the holocene vary in conjunction with sea surface temperature sst records from the ocean drilling program odp site 1017 located off the coast of central california which suggests that variations in ssts throughout the holocene drove changes in precipitation in the sierra nevada and hence tulare lake level since historic lake level histories have been shown to be directly related to stream discharge from the sierra nevada this observation will be integral in forecasting future decadal scale changes in southern san joaquin valley water supply due to anticipated climate change

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

birps deep seismic reflection studies of the british caledonides the western isles north channel winch traverse fig 1 an extension of the successful moist profile1 was recorded in 1982 at sea along the west coast of britain for birps british institutions reflection profiling syndicate by the geophysical company of norway geco the purpose of the winch traverse was to study crustal structure of the caledonian foreland to cross the caledonian orogen and to establish the three dimensional geometry of mantle reflectors originally seen on moist we describe here the data first emphasizing british caledonian structures and then discussing features of the deep crust of wider significance the data are of very good quality and contain clear moho and upper mantle reflections the lower crust is surprisingly reflective deeply penetrative thrusts are observed and there is firm evidence that several of the mesozoic basins round the shores of the united kingdom were formed by reactivation of older features

holocene east asian summer monsoon records in northern china and their inconsistency with chinese stalagmite δ18o records abstract monsoon precipitation over china exhibits large spatial differences it has been found that a significantly enhanced east asian summer monsoon easm is characterized by increased rainfall in northern china and by reduced rainfall in southern china and this relationship occurs on different time scales during the holocene this study presents results from a diverse range of proxy paleoclimatic records from northern china where precipitation variability is traditionally considered as an easm proxy our aim is to evaluate the evolution of the easm during the holocene and to compare it with all of the published stalagmite 18 o records from the asian monsoon region in order to explore the potential mechanism s controlling the chinese stalagmite 18 o we found that the intensity of the easm during the holocene recorded by the traditional easm proxy of moisture or precipitation records from northern china is significantly different from the chinese stalagmite 18 o records the easm maximum occurred during the mid holocene challenging the prevailing view of an early holocene easm maximum mainly inferred from stalagmite 18 o records in eastern china in addition all of the well dated holocene stalagmite 18 o records covering a broad geographical region exhibit a remarkably similar trend of variation and are statistically well correlated on different time scales thus indicating a common signal however in contrast with the clear consistency in the 18 o values in all of the cave records both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal to centennial time scales over eastern china in addition both paleoclimatic records and modeling results suggest that holocene east asian summer monsoon precipitation reached a maximum at different periods in different regions of china thus the stalagmite 18 o records from the easm region should not be regarded as a reliable indicator of the strength of the east asian summer monsoon furthermore modern observations indicate that the moisture for precipitation in the east asian monsoon region is mainly derived from the indian ocean the moisture transport route from the indian ocean to the east asian monsoon region during the holocene is almost identical to that of modern precipitation therefore the strong correlation of 18 o records in the easm and indian summer monsoon ism regions and the similarity of the pattern of latitudinal changes in 18 o values in stalagmites and in modern meteoric precipitation along the water vapor transport route further suggests that the stalagmite 18 o records from the easm region are essentially a signal of the isotopic composition of precipitation which is determined mainly by changes in the 18 o of atmospheric vapor in the upstream source region over the indian ocean and indian monsoon region via the upstream depletion mechanism finally the main trends of the stalagmite 18 o records are strongly correlated with the known evolution of the ism and therefore these records reflect the history of the ism rather than that of the easm our findings support the conclusion that easm variability is mainly controlled by northern hemisphere summer insolation and was strongly modulated by ice volume during the last deglaciation and early holocene which delayed the response of the easm maximum to peak insolation forcing

grain size in sediments from lake sugan a possible linkage to dust storm events at the northern margin of the qinghai tibetan plateau samples of surface deposits in the lake sugan catchment as well as surface lake sediments eolian materials occulted in the lake ice cover and airborne dust were collected for grain size analysis the results show that the coarse fraction of the lake sediments could be transported by ambient winds and to a lesser extent by river flow in the study area sediment cores were retrieved from lake sugan in december 2000 and 210pb and 137cs dating and grain size analyses were performed on these samples 210pb ages and the volume percentage of the fraction of lake sediments 63 m were used to reconstruct the dust storm history from 1957 to 2000 observational data for dust storm events collected at a local meteorological station largely agrees with the reconstructed trend for the past 44 years suggesting that lake sediments can be employed to trace the dust storm history of the northern qinghai tibetan plateau

formation and evolution of the badain jaran desert north china as revealed by a drill core from the desert centre and by geological survey abstract the deserts in north china are regarded as direct records of the process of inland asian aridification amongst these deserts those proximal to the chinese loess plateau clp are especially important because of their role as sediment source areas in order to investigate the formation history of the badain jaran desert the largest desert proximal to the clp a 310 m long drill core was obtained from the desert centre which reached the underlying basement rock the lithology of the core consists of an upper layer of aeolian sand with three intercalated layers of lacustrine sediments overlying alluvial fluvial deposits which are developed unconformably over red coloured basement rock a geological survey indicates that the lower red coloured basement rock is of late cretaceous age and is cut by a mesozoic erosion surface widely developed over the badain jaran area on the basis of optically stimulated luminescence and electron spin resonance dating and stratigraphic correlation a preliminary chronological framework was established which was improved by tuning the aeolian sand proportion of the drill core to earth orbital obliquity and precession this final chronology suggests that 1 the basal age of the desert strata is at least 1100 ka corresponding to the formation of the badain jaran desert and 2 that the formation of the erosion surface terminated and the surface had begun to subside by at least 1200 ka the formation of the desert can be summarized as follows the alluvial fluvial fan formed by the heihe river draining the qilian mountains provided sufficient sedimentary material to form the desert under an arid climate while the asian winter monsoon and the westerlies entrained the clastic sediments from the fan area which finally accumulated downwind more distant sediment transport was prevented by the intervening mountainous terrain these coupled processes were driven by tibetan plateau uplift and ongoing global climatic cooling after initial formation of the desert three humid phases occurred in mis 13 15 mis 5 and the holocene during which extensive lakes developed the sequential drying out of the lakes may reflect inter relationships between global climate and the intensity of the asian summer monsoon and the westerlies

sediment color record from the northeast atlantic reveals patterns of millennial scale climate variability during the past 500 000 years a 500 000 yr long deep sea sediment color record from the northeast atlantic was investigated to reconstruct the evolution of late pleistocene climate variability on millennial time scales variations of the red green color intensity are probably caused by climatically induced changes in the ice rafted input of red colored iron bearing terrigenous material to the core site the resolution of the age model impedes the detection of distinct spectral features at sub milankovitch periodicities hence millennial scale climate variability is quantified as time dependent variance of the high pass filtered color time series the course of the estimated variance shows distinct patterns which can be linked to continental ice mass during the past 500 000 yr large amplitude millennial scale climate variability occurs only if continental ice mass exceeds a threshold level equivalent to sea level at approximately 40 of the lowering during the last glacial maximum

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

pollen based quantitative reconstruction of holocene climate changes in the daihai lake area inner mongolia china vegetation around the daihai lake northern china is very sensitive to climate changes in this paper pollen based quantitative climate reconstructions using three methods weighted averaging partial least squares method wapls modern analog technique mat and pollen response surface method prs were conducted to obtain robust reconstructions of holocene climate changes in the daihai lake area the result obtained by the three methods all consistently show the annual precipitation to have been 50 100 mm lower in the early holocene 100 200 mm higher in the mid holocene and 50 100 mm lower again in the late holocene than at present the wapls and the mat methods also show quasi synchronous oscillations of the mean annual temperature ta 18 28c lower in the early holocene and 18 38c higher in the midholocene than today the time period from 6200 to 5100 cal yr bp was the wettest and the warmest interval with an annual precipitation pa greater than 550 mm and mean annual temperature ta higher than 6 58c several cold and dry events can be identified to occur about 8200 6000 and 4400 cal yr bp with an annual precipitation less than 400 mm and a mean annual temperature colder than 4 58c respectively the mean temperature of the warmest month tw as reconstructed using both wapls and mat methods was relatively stable during the holocene fluctuating about 628c relative to the present level but the prs method suggests more varied tw values in both amplitude and frequency after 1500 cal yr bp no consistent pattern can be observed from these three different analyses probably because of the impact of intensified human disturbances on the natural vegetation the fluctuations of annual precipitation pa correspond to that observed in dongge cave in southern china the differences might be linked to indian monsoon and east asia monsoon climates or caused by the different degree of dating precision different temporal resolution and different sensitive response of climate proxies to the climate variations

production sedimentation and isotopic composition of organic matter in lake ontario organic matter and its carbon and nitrogen isotopic composition were measured in sequential sediment trap and core samples from the rochester basin of lake ontario to evaluate their usefulness in reconstructing historic changes in lake productivity the greatest flux of organic matter from the epilimnion occurred during late summer and coincided with whiting events indicating that calcite precipitation is an effective mechanism for sedimenting organic matter carbon isotopes of organic matter were low prior to the onset of stratification increased to maximum values in late summer and then decreased following fall overturn this pattern is controlled mainly by the timing of stratification and primary productivity which preferentially removes 12co2 from the epilimnion the physiological effect of decreased carbon isotopic fractionation with decreasing supplies of co2 aq may have also contributed to increased 13corgc nitrogen isotopes showed a seasonal pattern opposite to that of carbon whereby 15n values were low during the summer stratified period and high for the remainder of the year seasonal variability in 15norgn probably reflects changes in the source of sedimented organic particles which is dominated by isotopically depleted phytodetritus during the stratified period and isotopically enriched organic matter from heterotrophic or detrital sources during the mixed period a comparison of organic carbon accumulation rates and 13corgc between sediment cores collected in 1987 and 1993 1994 confirms earlier predictions that diagenetic processes reduce the mass accumulation of organic carbon in the zone of oxic pore waters but will not change the 13corgc values all cores analyzed for 13corgc display the reproducible pattern of a progressive increase in the 19oos peaking in the early to mid 1970s and then decreasing to the present this pattern matches the historical trends of phosphorus loading to the basin suggesting that 13c of organic carbon is a reliable proxy for paleoproductivity and responds to spring phosphorus supplies in the water column the 15n of sedimentary organic matter increased linearly from 1840 to 1960 at a rate of 0 3ppt per decade and remained relatively constant thereafter except for an increase in the upper few centimeters of sediment the increase in 15norgn reflects a combination of factors including early forest clearance by europeans increased sewering by municipalities after 1940 and increased nitrate utilization as productivity increased in the lower great lakes increased rates of denitrification in the central basin of upstream lake erie from the 1930s to the early 1970s may have also contributed to the rise in 15norgn values

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

continental scale temperature variability during the past two millennia past global climate changes had strong regional expression to elucidate their spatio temporal pattern we reconstructed past temperatures for seven continental scale regions during the past one to two millennia the most coherent feature in nearly all of the regional temperature reconstructions is a long term cooling trend which ended late in the nineteenth century at multi decadal to centennial scales temperature variability shows distinctly different regional patterns with more similarity within each hemisphere than between them there were no globally synchronous multi decadal warm or cold intervals that define a worldwide medieval warm period or little ice age but all reconstructions show generally cold conditions between ad 1580 and 1880 punctuated in some regions by warm decades during the eighteenth century the transition to these colder conditions occurred earlier in the arctic europe and asia than in north america or the southern hemisphere regions recent warming reversed the long term cooling during the period ad 1971 2000 the area weighted average reconstructed temperature was higher than any other time in nearly 1 400 years

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

mid holocene climate change in the eastern xinjiang region indicated by the grain size and stable isotope record from lake barkol northwest china a sediment core from lake barkol located in the eastern xinjiang autonomous region northwest china provided a high resolution record of environmental change covering the last 8 6 cal ka bp three major climate stages 8 6 7 1 7 1 2 0 and from 2 0 cal ka bp to the present were divided by grain size and the authigenic carbonate stable isotope of the lake sediment climatic drought during the period 7 1 4 5 cal ka bp deduced from lake barkol prevailed in the mid holocene climate in northern xinjiang and northwest mongolia in contrast it was wet in central xinjiang northwest india and the middle east during the same period the climatic difference between northern and southern arid central asia demonstrates the southward shifting of the westerlies which indicates the potential contribution of the siberian high in the mid holocene

late holocene climate change inferred from a lacustrine sedimentary sequence in southern inner mongolia china abstract this study presents a series of paleoenvironmental results from a radiocarbon dated 154 cm long lacustrine sedimentary sequence from qrdin nuur 115 51 20 e 42 36 20 06 n elevation 1290 asl in southern inner mongolia china measurements of grain size magnetic susceptibility ms total nitrogen tn total organic carbon toc total inorganic carbon tic atomic toc tn c n and carbonate content were conducted in order to reconstruct the climate since 3700 cal a bp in addition to a regional drying trend in the late holocene closely related to the weakening of the east asian summer monsoon easm four distinct climatic stages can be identified i from 3700 to 2909 cal a bp a semi arid and cool climate dominated the lake area with a transitory climatic amelioration from 3300 to 3150 cal a bp ii the interval from 2909 to 2589 cal a bp was characterized by a rising temperature and the recovery from drought iii from 2589 to 1903 cal a bp drought conditions were renewed and significantly intensified in a cold environment iv after 1903 cal a bp a warm climate with severe evaporation accelerated the shrinking of qrdin nuur a comparison of our results with other paleoclimatic records mainly from southern inner mongolia reveals similar climatic trends and highlights the asynchronous nature of the regional climatic transition to increased aridity which was reflected by the activation of the otindag sandy land and by the dominance of steppe landscapes several multi centennial temperature oscillations are recognized over the last two millennia as inferred from fluctuations in tic and carbonate content we correlate the warm interval from 853 to 560 cal a bp 1097 1390 ad with the medieval warm period mwp and the consequent cold interval from 560 to 128 cal a bp 1390 1822 ad with the little ice age lia furthermore the climatic reconstruction shows that the lake area was generally drier during the lia than in the mwp

biogeochemical evidence of holocene east asian summer and winter monsoon variability from a tropical maar lake in southern china abstract lake huguangyan 21 9 n 110 17 e a maar lake located near the south china sea can provide valuable sedimentary data regarding past changes of the east asian monsoonal system here we used the proxies of toc 13corg 15n and leaf wax n alkane 13c values 13cwax to reconstruct the lake conditions which in turn revealed patterns in monsoonal changes during the holocene two distinct patterns of proxy changes were identified in the sedimentary profile a marked shift in the 13cwax value at 9 2 ka thousand years ago suggests the abrupt disappearance of c4 plants signaling the enhancement of east asian summer monsoon easm between 9 2 and 1 8 ka a nearly pure c3 terrestrial ecosystem was present with the climax at ca 7 6 ka after ca 3 ka fewer tropical species and a reappearance of c4 plants at 1 8 ka indicate a weakened easm in the late holocene the toc concentration and 15n value proxies appear to be associated with lake aquatic production and upwelled nutrient supply and utilization which are modulated by and thus indicative of the strength of the east asian winter monsoon eawm the two eawm records suggest a weakening trend from the early to late holocene with the most significant transition at 6 ka thus the eawm trend was broadly in phase with that of the easm however the marked easm intensification at 9 2 ka occurred within the period of a strong eawm between 10 5 and 6 ka and lagged the monsoonal enhancement as inferred from the dongge cave 18o values our easm records displays an overall arid wet arid pattern which is in phase with the hydrological variability in tropical australia and anti phase with that in the outer tropical andes these phase relationships might be linked to changes in the thermal state of the tropical pacific during the holocene

patterns of local and regional grain size distribution and their application to holocene climate reconstruction in semi arid inner mongolia china abstract the semi arid temperate steppe in northern central china is one of the main areas influenced by frequent dust and sand storms and is at the same time a primary source of dust from deteriorated grasslands thus the sediment grain size distribution of inland lakes in this region can be a particularly useful indicator of palaeoenvrionmental change the local pattern of grain size suggests that aeolian activity is the most important agent for sedimentation in the lake center in this region as strong northwesterly winds prevail for most of the year and the surface runoff is very weak meanwhile the regional pattern of topsoil grain size and its close association with mean annual precipitation map allows the establishment of a statistical model for palaeo moisture reconstruction from sediment grain size in this study we reconstructed a humidity time series based on the sediment grain size sequence from anguli nuur lake on the southern inner mongolian plateau in china and found that it coincides very closely with the c n ratio carbon to nitrogen ratio and other humidity indices revealed in previous studies of this temperate steppe region and from the 18 o values of stalagmite calcite in southern monsoon dominated china this close relationship suggests that climate change in the semi arid areas of asia is strongly influenced by the pacific summer monsoon and that it is reasonable to use sediment grain size as an indicator of humidity variability in the semi arid steppe region the reconstructed humidity increased during the early holocene and generally humid conditions lasted from about 10 400 until 7000 yr bp the period from around 7000 to 5200 yr bp was a transition phase from humid to semi arid conditions and the monsoon intensity of that time may have been at the threshold for a semi arid vegetation ecosystem finally since approximately 5200 yr bp to present the climate has become more arid with corresponding vegetation deterioration and strong aeolian activity

crustal structure and active tectonics in the eastern alps 1 during the last decade a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the eastern alps and their adjacent tectonic provinces a fragmentation of the lithosphere into three blocks europe eu adria ad and the new pannonian fragment pa was interpreted and a triple junction was inferred the goal of this study has been to relate these deep crustal structures to active tectonics we used elastic plate modeling to reconsider the moho fragmentation we interpret subduction of eu below ad and pa from north to south and underthusting of ad mantle below pa from southwest to northeast the moho fragmentation correlates well with major upper crustal structures and is supported by gravity seismic and geodetic data an analysis of crustal thickening suggests that active convergence is associated with continued thrusting and lateral extrusion in the central eastern alps and thickening of the adriatic indenter under the southern alps according to the velocity relations at the triple junction pa moves relative to eu and ad along ene and se striking faults mainly by strike slip an eastward directed extensional component is compensated by the lateral extrusion of the central eastern alps the periadriatic insubric line east of the triple junction and the mid hungarian fault zone have relatively recently lost their role as first order active structures we favor the idea that the pannonian fragment and the tisza block merged to a soft microplate surrounded by the eastern and southern alpine carpathian and dinaric orogens