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

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

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

calculated greenschist facies mineral equilibria in the system cao feo mgo al 2 o 3 sio 2 co 2 h 2 o the kinetic problems associated with the experimental determination of reactions among complex solidsolution phases at low temperatures have hindered our understanding of the phase relations in greenschist facies rocks in the absence of reliable experimental data we have used the new expanded internally consistent thermodynamic dataset of holland and powell 1990 to present calculated phase equilibria for the system cao feo mgo al2o3 sio2 h2o co2 cafmasch with quartz in eccess in the range 400 500 c at low to intermediate pressures involving the minerals amphibole chlorite anorthite clinozoisite dolomite chloritoid garnet margarite andalusite and calcite by solving independent sets of non linear equations formed from equilibrium relationships we calculate not only the loci of reactions in pressuretemperature x co2 space but also the compositions of coexisting minerals in terms of the substitutions femg 1 and fe mg sial 1al 1 invariant univariant and divariant equilibria are calculated and discussed in relation to naturally occurring greenschist facies metabasic and siliceous dolomitic mineral assemblages we thus avoid the use of activity corrected curves so commonly presented in the literature as a substitute for genuine univariant phase diagram boundaries

holocene history of desertification along the woodland steppe border in northern china abstract the woodland steppe ecotone of the southeastern inner mongolian plateau in northern china is located at the northwestern limit of the pacific monsoon influence where the landscape may have been a sensitive recorder of past climatic changes physical chemical and biological analyses of ams 14 c dated sediment sequences from two lakes of this region were used to reconstruct the holocene vegetation and desertification history and distinguish four periods 1 a cold and humid period from 10000 to 8000 14 c yr b p 2 a warm and humid period from 8000 to 5900 14 c yr b p 3 a warm and dry period from 5900 to 2900 14 c yr b p and 4 a cool and dry period from 2900 14 c yr b p to the present the increased aridity during the middle holocene was likely caused by increased winter temperatures and enhanced winter evaporation the transition from a humid to an arid climate after 5900 14 c yr b p coincided with enhanced aeolian activity and deciduous woodlands were replaced by pine woodlands and then by steppes in response to the climatic deterioration these transitions led to the present desertification the records suggest that a simple association of thermal and moisture conditions such as warm wet or cold dry may be misleading

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

lateglacial and holocene dune evolution in the horqin dunefield of northeastern china based on luminescence dating abstract the horqin dunefield is located in the northern frontier of east asian monsoon eam zone and its activation and stabilization is sensitive to the ebb and flow of the eam however the activity of dunes in the horqin dunefield is still poorly understood due to limited numerical dating the purpose of the present study is to establish the chronology using luminescence dating in order to understand dune evolution of the horqin dunefield and to explore the relative role of climate and human activity eighteen samples were collected from seven sections following a southwest northeast transect through the dunefield and dated using quartz optically stimulated luminescence osl combining evidence from stratigraphy and the luminescence chronology dune evolution within the horqin dunefield since the lateglacial can be summarized as before 9 6 ka aeolian sand dunes were mobilized during the period 9 6 3 ka dunes were stabilized at around 3 ka dunes were mobilized again abruptly since 3 ka there were multiple phases of dune stabilization mobilization dune activity was dominated by climate before 3 ka however since 3 ka both climate variability and human impact have influenced dune evolution in the horqin dunefield

a 15 ka ph record from an alpine lake in north china derived from the cyclization ratio index of aquatic brgdgts and its paleoclimatic significance abstract a well dated sediment core from an alpine lake in north china gonghai lake was used for analysis of branched glycerol dialkyl glycerol tetraether lipids brgdgts based on the cyclization ratio index cbt of the brgdgts and using different terrestrial and lacustrine cbt ph empirical relationships the reconstructed ph records over the past ca 15 ka exhibited similar trends of variation although the absolute ph values were different in order to better understand the reconstructed ph record samples of surface soils from the dust source area and the catchment of gonghai lake as well as surface sediments from the lake were collected for instrumental ph measurements and modern brgdgt analysis the instrumental ph results demonstrated that the surface soils from the dust source area were alkaline while those from the catchment of gonghai lake were acidic in addition the instrumental ph results for the surface sediments from the lake were slightly alkaline and the corresponding ph values were intermediate between those of the two surface soil source groups this may reflect the effect of the input of material from different sources on the sedimentary ph record however the results from modern brgdgts in some of the surface soils and surface sediment samples demonstrate that brgdgts in the core sediments from gonghai lake are predominantly of aquatic origin therefore the cbt derived ph record over the past ca 15 ka from the lake can be interpreted as a record of the lake water ph history which is consistent with the carbonate content record from a parallel core from the same lake in addition using the modern lacustrine calibration the cbt derived ph values for surface sediments of gonghai lake are consistent with instrumental modern lake water ph values for the lake further comparison indicates that the lake water ph is controlled mainly by the degree of humidity of the local climate which is closely related to the intensity of the east asian summer monsoon easm therefore the ph record can be used as an indicator of easm intensity our results demonstrate that on the basis of careful analysis of its origins the cbt index of aquatic brgdgts can be used for lake water ph reconstruction and subsequent paleoclimate reconstruction and that in north china the lake water ph is controlled mainly by the degree of humidity of the local climate

climate change and human settlement as drivers of late holocene vegetational change in the faroe islands changes in faroese land surfaces during the late holocene reflect intimate interactions between cultural and environmental development analyses of fossil wood pollen and plant macrofossils indicate that the present open landscape replaced shrubby vegetation that was present from c 6000 bc up to c ad 660 conditions altered during the late holocene with loss of woody vegetation and increasing erosion trends that were initiated prior to human settlement ams dating of sub fossil betula salix and juniperus found buried in peat profiles from the islands of suouroy sandoy eysturoy vagar and streymoy revealed that the islands had at least partial woody vegetation cover up to the time of continuous settlement the settlement horizon identified in a lacustrine sequence on the island of eysturoy dated to c ad 570 it comprised pollen evidence for the cultivation of hordeum cultural macrofossil assemblages charcoal fragments diatom assemblage changes indicating lake nutrient enrichment and physical measurements showing increased sedimentation rates the pollen record showed that heathland development was initiated prior to anthropogenic impact the ecosystem impacts of settlement were therefore superimposed on landscape changes that began around ad 250 the earlier changes were most likely forced by increased storminess and declining atmospheric temperatures less

dry late glacial and early holocene climate in arid central asia indicated by lithological and palynological evidence from bosten lake china abstract stratigraphical and chronological investigations of four sediment cores from bosten lake the largest inland freshwater lake in china provide a reliable regional environmental evolution record since the late glacial the stratigraphy of the four cores has been well correlated according to their lithology and chronology osl and 14c dates pollen and grain size data from bosten lake show evidence for a dry regional climate during late glacial and early holocene 16 8 cal ka bp indicated by a thick layer of aeolian sand deposit 100 cm although the climate became humid after 8 cal ka bp analysis of pollen assemblages pollen a c ratio and ephedra percentage also indicates that the climate was relatively dry in the bosten lake area between 8 and 6 cal ka bp while afterwards more humid conditions ca 6 1 5 cal ka bp are assumed comparison with other lake records from arid central asia influenced by the westerly winds generally supports the assumption of late glacial to early holocene dry climates in westerly dominated regions hence they contrast the holocene climate development in monsoon asia relatively wet conditions during the late holocene 6 1 5 cal ka bp might be induced by stronger westerly circulation

the role of fire in the late holocene forest decline in semi arid north china based on a sediment core from lake hulun nuur in the semi arid forest steppe ecotone in north china we reconstructed the history of climate change vegetation development and fire frequency in this region during the mid to late holocene four stages were identified 1 6300 4900 cal yr bp a warm humid phase dominated by forest vegetation with moderate fire incidence and a gradual drying trend 2 4900 4250 cal yr bp a warm dry phase dominated by forest vegetation with increased aridity and high fire occurrence 3 4250 1750 cal yr bp a gradual drying phase with forest decline and low fire occurrence and 4 1750 cal yr bp present a cool dry phase dominated by steppe with some decrease in aridity building on previous studies in this region the successive timing of forest replacement by steppe along the precipitation gradient in the late holocene indicates a gradual retreat of the forest margin under climate drying vegetation succession was predominantly determined by climate but forests

three dimensional numerical modeling of upper crustal extensional systems 1 we focus on understanding the evolution and structural style of crustal extension in three dimensions using state of the art forward dynamic models to date few 3 d models exist that follow the evolution of tectonic processes into large deformation modes with sufficient resolution to resolve individual faults and shear zones we use an arbitrary lagrangian eulerian fully parallel finite element code that solves for viscoplastic flows in three dimensions plastic materials weaken with accumulating strain to localize deformation a weak seed region is introduced at the base of a plastic model extended by velocity boundary conditions controls on the geometry and spacing of three dimensional plastic shear zones are investigated the sensitivity of varying the offset between weak seeds and the sensitivity of strain weakening parameters on the linkage between offset rift zones and on the efficiency of rift propagation are tested the model results indicate the primary controls of strain dependent plastic rheology and rift offset on the efficiency of rift propagation and the style of rift segment interaction the amount and onset of strain weakening also play a large role in the degree to which the primary segments link and propagate toward each other resulting in a trade off effect between the amount of offset between the initial grabens and the strain weakening ratio the three dimensional models indicate three main rift modes for linkage between two upper crustal rift segments in three dimensions 1 small offset grabens with a single relay zone 2 intermediate offset grabens with one or more secondary step over graben segments and 3 large offset grabens with limited to no significant segment interaction

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

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

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

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

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

investigating the long term palaeoclimatic controls on the δd and δ18o of precipitation during the holocene in the indian and east asian monsoonal regions abstract this paper aims to achieve an improved understanding of the long term change trends of precipitation d and 18 o values d p and 18 o p in the asian monsoonal region and their relationship with the corresponding humidity trends during the holocene to do this we first review the observed modern spatial pattern of summer precipitation distribution in the east asian summer monsoon easm region under different easm intensities and the relationship between modern observed 18 o p values and corresponding precipitation amounts on monthly and inter annual timescales in the easm and indian summer monsoon ism regions second we compare holocene lacustrine and marine compound specific hydrogen isotopic records of n alkanes n alkanoic acid d n lacustrine authigenic carbonate and cave stalagmite oxygen isotopic records 18 o c and 18 o s from the asian monsoonal region all of which are closely related to d p and 18 o p variations the results demonstrate that in both the ism and easm regions all of these isotopic records exhibit roughly similar long term characteristics i e they were all more negative during the early holocene and early mid holocene ca 11 6 ka b p b p means before present present 1950 ad and then became more positive towards the late holocene third we compare representative paleo humidity records from the asian monsoonal region the results confirm that in the ism region a humid interval occurred in the early holocene and early mid holocene ca 11 6 ka b p and subsequently the climate became more arid towards the late holocene this indicates an enhanced ism during the early holocene and early mid holocene ca 11 6 ka b p and an ism of decreasing intensity towards the late holocene on a holocene orbital scale both 18 o p and d p appear to be controlled by an amount effect in the ism region consistent with the region s inter annual modern 18 o p data this evidence indicates that both 18 o p and d p paleo records are significantly related to paleo humidity in the ism region in contrast holocene humidity variations in the easm region exhibit clear spatial differences a humid mid holocene interval ca 8 3 ka b p occurred in southern and northern china but an arid interval from ca 7 3 ka b p occurred in central china in the middle reaches of the yangtze river based on precipitation distribution patterns under different easm intensities in the easm region over the past few decades we conclude that easm intensity was enhanced during the mid holocene ca 8 3 ka b p relative to the ism intensity the response of easm intensity to summer insolation was relatively slow in the easm region the relationship between climate and 18 o p and d p is more complex consistent with analyses of regional inter annual modern 18 o p data this evidence demonstrates that both 18 o p and d p paleo records cannot be used directly as paleo humidity i e precipitation amount or easm intensity indicators in the easm region further comparison and analyses demonstrate that the coupled variations in west east equatorial pacific temperature gradients and the west pacific subtropical high wpsh played an important role in determining easm intensity during the holocene

determinants of soil erosion during the last 1600 years in the forest steppe ecotone in northern china reconstructed from lacustrine sediments abstract wind erosion of soil in northern china contributes to the environment of east asia and even the northern hemisphere it is commonly thought that human induced grassland degradation determines soil erosion in the semi arid steppe region in this study we revealed determinants of soil erosion during the last 1600 years through analyzing lacustrine sediment from huangqihai lake in this region our results showed that soil erosion indicated by sediment particle size was enhanced during three periods 1570 1330 cal yr bp with warm and dry climate 1250 1000 cal yr bp with warm and wet climate and 470 150 cal yr bp with cold and dry climate the common feature of vegetation regimes for enhanced soil erosion was replacement of forest by steppe suggesting that decline in vegetation cover from forest to steppe which was attributed to climatic changes might lead to enhancement in soil erosion the trend of historical soil erosion did not match the steady increase in historical human population in china and the very short history of massive cultivation in southern inner mongolia in summary our results supported nature rather than human dominated soil erosion in the semi arid steppe region in north china during the last 1600 years

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

pollen detected altitudinal migration of forests during the holocene in the mountainous forest steppe ecotone in northern china abstract distributed on the margin of the influence of the asian monsoon the forest steppe ecotone in northern china is sensitive to climate change previous paleovegetation reconstructions in this region have led to inconsistent explanations of paleovegetation dynamics across sites we hypothesized that the patterns observed are related to altitudinal migration of forests across mountains in this region we combined eight lake sediment pollen records to explain how three forest types dominated by the tree genera pinus quercus and betula changed in response to temporal and spatial monsoon changes within the forest steppe ecotone during the holocene modern pollen assemblages showed that areas with large altitude range could support more forests which was further confirmed by the spatial patterns of late holocene forest distribution under dry climate our results confirmed that altitudinal migration of forests might exist in this region this kind of altitudinal migration of forests under different altitudinal ranges could help to explain the inconsistent patterns observed in arboreal pollen across sediment cores as well as the non linear response of horizontal forest distribution in relation to climate change

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

metamorphic equilibria in the siliceous dolomite system 6 kbar experimental data and geologic implications hydrothermal experiments with h2o co2 fluids at pfluid 6 kbar yielded the following quilibrium conditions for reactions important in metamorphosed siliceous dolomites t c x xco2 3 dolomite 2 quartz diopside 2 co2t 620 8x 0 73 0 03 5 5 dolomite 8 quartz h2o tremolite 3 calcite 7 co2t 600 5 550 5 540 5 500 5x 0 66 0 03 0 21 0 03 0 21 0 04 0 06 0 02 7 3 dolomite 4 quartz h2o talc 3 calcite 3 co2t 550 5 500 5 450 5x 0 25 0 05 0 07 0 02 0 03 0 02 8 2 dolomite talc 4 quartz tremolite 4 co2t 550 5 540 5 500 5x 0 22 0 03 0 21 0 02 0 06 0 02 a thermodynamically self consistent 6 kbar t xco2 topology results by extrapolating equilibria from experimental brackets using a modified redlich kwong equation for activities in h2o co2 mixtures this topology restricts the assemblage talc calcite to a narrow stability band in t xco2 space at xco2 0 55 and t 590 c accordingly the occurrence of talc calcite in pure siliceous dolomites metamorphosed at pfluid 6 kbar implies correspondingly water rich fluids

holocene environmental changes in the central inner mongolia based on single aliquot quartz optical dating and multi proxy study of dune sands abstract alternating units of dune sands and paleosols in the central inner mongolia imply multiple episodes of dune building and stabilization in response to the waxing and waning of the east asian monsoon such eolian deposits were dated by using the single aliquot quartz optical dating method combined with the multi proxy study on the deposits the past environmental changes during the holocene have been reconstructed our results indicate that widespread eolian sand mobilization occurred in the studied region during the beginning of the early holocene from 11 5 ka to 9 ka the climate became warm and humid during the period between 9 ka and 5 6 ka holocene optimum after 5 6 ka the region again became arid as inferred from dune building however the environmental changes during the late holocene have been affected by both climate and human impacts and the presence of desert environment in such semiarid region is not only the result of climatic drought of the late holocene but also related to poor land use practices

holocene moisture evolution in arid central asia and its out of phase relationship with asian monsoon history we synthesize palaeoclimate records from the mid latitude arid asian region dominated today by the westerlies arid central asia aca to evaluate spatial and temporal patterns of moisture changes during the holocene sediment records from i i takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200 year time slices the proxies used in these records include pollen and diatom assemblages sediment lithology lake levels and geochemistry mainly isotope data the results of our synthesis show that aca as a whole experienced synchronous and coherent moisture changes during the holocene namely a dry early holocene a wetter less dry early to mid holocene and a moderately wet late holocene during the early holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka 1 ka 1000cal a bp hence the effective moisture history in aca is out of phase with that in monsoonal asia as documented by numerous palaeoclimate records in monsoonal asia a strong summer monsoon and humid climate characterized the early holocene and a weakened summer monsoon and drier climate prevailed during the late holocene which were mainly controlled by changes in low latitude summer insolation in contrast we propose that the pattern of holocene effective moisture evolution in the westerly dominated aca was mainly determined by north atlantic sea surface temperatures ssts and high latitude air temperatures that affect the availability amount and transport of water vapor also topography of the tibetan plateau and adjacent asian highlands could have contributed to the intensification of dry climate in aca during the early holocene as a result of strengthening the subsidence of dry air masses associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation summer insolation might have played a key role in directly controlling moisture conditions in aca but only after the northern hemisphere ice sheets had disappeared in the mid and late holocene c 2007 elsevier ltd all rights reserved

late pleistocene record of cyclic eolian activity from tropical australia suggesting the younger dryas is not an unusual climatic event in the gulf of carpentaria northeastern australia 30 ka of lacustrine sedimentation provides a record of cyclic deposition of eolian dust 60 m just preceding the holocene adjacent layers containing eolian particles 60 m in a core from carpentaria relate to perhaps intermittent periods of eolian activity involving sediment deflation and thus aridity in northern australia each spanning at least 600 yr major peaks of dust deposition occurred about every 2 25 ka such amplitude of cyclicity has already been recognized elsewhere on the globe for other phenomena including waxing and waning of north american and european mountain glaciers oxygen isotope records from greenland and antarctic ice cores changes in deep sea benthic foraminiferal composition oxygen isotope records of deep sea foraminifera and atmospheric 14 c variations we propose that the cold younger dryas event that affected the northern hemisphere is matched by a significant dry event in the tropical region of northern australia and that the timing of this event fits well into the 2 25 ka cyclic pattern described here thus the younger dryas is a phenomenon of global significance and is not an odd event contrary to current belief in addition we propose that activation of dunes in northeastern australia over periods of 600 yr corresponds to perhaps intermittently stronger easterly trade winds during such periods the intertropical convergence zone may not have extended as far south as it does today

holocene environmental changes as recorded by mineral magnetism of sediments from anguli nuur lake southeastern inner mongolia plateau china abstract two cores one 1141 cm long an s and the other 885 cm long an a were retrieved from anguli nuur lake 41 18 24 n 114 20 27 e 1315 masl one of the largest lakes in the transition zone between a semi humid and semi arid climate parallel to the present limit of the southeast monsoon along the southeastern inner mongolia plateau in north china mineral magnetic parameters lf arm irm300mt sirm and irm 300mt were measured on an s and two additional parameters arm and hirm and four inter parametric ratios arm sirm irm300mt sirm irm 300mt sirm and sirm lf were calculated potential sources of these lake sediments catchment soils and dune materials close to the lake and in a distant sand plain were sampled and the magnetic properties of the surface material specimens were measured a chronological model was developed for an s by comparing and combining ams14c dates of an s with 137cs 210pb and ams14c dates of an a with the help of surface material magnetism the magnetic data of an s in combination with particle size toc and c n and pollen analyses indicate the environmental changes during the last 10 000 years around this lake conditions began to ameliorate at 10 900 cal yr bp 9600 14c yr bp and thus relatively wet and warm environments prevailed during 10 900 8900 cal yr bp 9600 8000 14c yr bp the holocene optimum or the wettest and warmest conditions was during 8900 7400 cal yr bp 8000 6500 14c yr bp the environment began to deteriorate from 7400 cal yr bp 6500 14c yr bp and the driest and coolest conditions occurred during 2200 480 cal yr bp there may have been a minor amelioration after 480 cal yr bp the inferred changes in palaeoenvironmental conditions around anguli nuur lake are broadly in agreement with those around most other sites on the inner mongolia plateau

annually laminated lake sediments and environmental changes in bashang plateau north china abstract angulinuo lake is the biggest lake on the bashang plateau north china and is 47 6 km2 in area and 2 6 m in depth a core from the inner part of angulinuo lake was sliced and the sediment was observed by scanning electronic microscope sem annual laminations characterized by variable color and grain size were found and interpreted as recording the cyclic deposition of lacustrine clay and aeolian dust the results of chemical analysis of coarse grains conducted by sem edax and grain size analysis of modern aeolian dust in the ice on angulinuo lake support an aeolian origin for the light coarse layers image analysis technique was used to calculate the size and number of coarse grains in each layer the coarse grains were fractionated into four classes 42 m 14 42 m 14 4 2 m and 1 4 4 2 m in general the abundance of the four classes shows similar temporal variation patterns around angulinuo lake the winter monsoon is strong and transports aeolian dust into the lake when the winter monsoon is strong the size and amount of coarse grains are expected to increase we infer that the winter monsoon was weaker during 8430 5440 year bp and was unstable in the later part of this period from 5440 year bp the winter monsoon became stronger and then weaker from 3250 to 2490 year bp during 2490 1170 year bp the winter monsoon was slightly stronger but since 1170 year bp it has become weaker again the changes of the winter monsoon intensity recorded in the annual laminations in angulinuo lake sediments correspond well to environmental changes in north china and to changes in sea level during the same period periods of weaker winter monsoon correspond to times of higher sea levels while the periods of stronger winter monsoon correspond to the neoglaciation stage in china and the periods of lower sea levels

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

isograds in internally buffered systems without solid solutions principles and examples internal buffering is recognised as an important end member process when considering the factors governing the composition of a fluid phase present in a rock during metamorphism in such processes the major isograd forming reactions take place at intersections in t xco2 space in p t space the trace of such intersections with changing pressure forms a univariant reaction along which the composition of the coexisting fluid phase changes in this paper it is demonstrated that the stoichiometry of these univariant reactions changes at singular points these singularities are controlled by divariant reactions which liberate co2 and or h2o and thus form degenerate univariant reactions in the complete chemical system a series of phase diagrams illustrating these points is presented for ultrabasic margarite kyanite clinozoisite and siliceous dolomite assemblages these diagrams provide a complete description of potential isograd forming reactions within each chemical system p t pseudosections are constructed for particular bulk compositions to illustrate the continuum between externally controlled and internally buffered conditions and the effects of changes in fluid and solid phases

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

holocene variability of the east asian summer monsoon from chinese cave records a re assessment oxygen isotope records from stalagmites in caves in southern china interpreted as proxy rainfall records reflecting the intensity of the east asian summer monsoon indicate gradual monsoon weakening for the last 9000 years as also documented for the indian monsoon coupled with high precision dating the speleothem proxy records have been used to test monsoon links with orbital forcing solar changes iceberg discharges in the north atlantic ocean currents and atmospheric methane however these benchmark cave records do not match other published dated e asian proxy rainfall record specifically here independently calibrated rainfall records from loess palaeosol magnetic properties and cave oxygen isotope intercomparisons which show variable e asian monsoon intensity through the entire holocene the strong correlation of the cave records with the extraregional indian monsoon record yet their mismatch with these other dated chinese rainfall records might be reconciled if the speleothem isotope variations reflect not changes in holocene rainfall amount but in rainfall source declining holocene influence of isotopically lighter indian monsoon sourced moisture over china would have resulted in increasing proportions of isotopically heavier rainfall sourced from the more oceanic e asian monsoon individual speleothems may thus regionally record holocene changes in indian monsoon intensity and isotopic influence conversely the other chinese proxy records described here reflect changes in rainfall amount and thus in e asian summer monsoon intensity for the holocene the e asian and the indian monsoon responses to orbital forcing are likely to have differed specifically due to e asian internal feedbacks and the seasonal contrasts between the two monsoon systems

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

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

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

orbital scale timing and mechanisms driving late pleistocene indo asian summer monsoons reinterpreting cave speleothem δ18o 1 southeast china cave 18o often interpreted as a pure east asian summer monsoon proxy lags maximum northern hemisphere summer insolation by 2 9 0 3 kyrs at the precession cycle the arabian sea summer monsoon stack lags by 8 1 kyr consistent with 13 other indian and east asian summer monsoon proxies from marine lake and terrestrial archives this 5 kyr phase difference cannot be attributed to age control inadequacies in the marine chronology it requires reconciliation in the context of proxy interpretation both of these lags are incompatible with a direct response to northern hemisphere summer insolation implicating additional forcing mechanisms analysis of heterodynes in the cave 18o spectrum demonstrates that variance contained in the arabian sea summer monsoon proxies also resides in the cave 18o record this variance is subtracted from the cave 18o record yielding a residual that is highly coherent and in phase with precession minima reflecting the impact of winter temperature change on cave 18o meteorological precipitation under cold conditions thus we argue that the timing of light cave 18o peaks cannot be interpreted as reflecting the timing of strong summer monsoons alone the 2 9 kyr precession band phase lag of cave 18o reflects the combined influence of summer monsoon forcing with a phase lag of 8 kyrs relative to precession minima and winter temperature forcing that is in phase with precession minima this interpretation is consistent with modern seasonality in the amount and isotopic composition of rainfall in southeast china

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

chinese stalagmite δ 18 o controlled by changes in the indian monsoon during a simulated heinrich event carbonate cave deposits in india and china are assumed to record the intensity of monsoon precipitation because the 18 o of the carbonate tracks the isotopic signature of precipitation these records show spatially coherent variability throughout the last ice age and suggest that monsoon strength was altered during the millennial scale climate variations known as dansgaard oeschger events and during the heinrich cooling events here we use a numerical climate model with an embedded oxygen isotope model to assess what caused the shifts in the oxygen isotope signature of precipitation during a climate perturbation designed to mimic a heinrich event our simulations show that a sudden increase in north atlantic sea ice extent during the last glacial period leads to cooling in the northern hemisphere reduced precipitation over the indian basin and weakening of the indian monsoon the precipitation is isotopically heavier over india and the water vapour exported to china is isotopically enriched our model broadly reproduces the enrichment of 18 o over northern india and east asia evident in speleothem records during heinrich events we therefore conclude that changes in the 18 o of cave carbonates associated with heinrich events reflect changes in the intensity of indian rather than east asian monsoon precipitation

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