pronounced changes in atmospheric circulation and dust source area during the mid pleistocene as indicated by the caotan loess soil sequence in north china the quaternary loess soil sequence in north china is of significant value for tracing variations in atmospheric circulation in this study we measured the anisotropy of magnetic susceptibility ams of the caotan ct loess soil sequence from the northeastern margin of the tibetan plateau tp and analyzed the surface textural features of quartz grains of representative samples the ams results indicate a primary sedimentary magnetic fabric without significant disturbance by pedogenesis the dec kmax values indicate a significant shift of the dominant surface wind direction from nearly n s to w e since 300 ka while the surface textural features of the quartz grains indicate an increase in the contribution from fluvioglacial sediments derived from the tp at the same time as there is no evidence of significant climatic changes around 300 ka we attribute the coeval changes of atmospheric circulation and dust source area to the uplift of the tp during the mid pleistocene and the resulting climatic cooling cooling of the tp may have led not only to the enhancement of the plateau monsoon but also to the significant accumulation of plateau glaciers which would have resulted in accelerated physical erosion of the underlying rocks thus increasing the quantity of fine grained fluvioglacial sediments to be transported to the study site

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

climate instability during the penultimate glaciation evidence from two high resolution loess records china the xinzhuangyuan and lijiayuan loess sections in the northwestern part of the chinese loess plateau were studied down to paleosol unit s2 which probably formed during marine oxygen isotopic stage 7 200 000 years b p the thickness of the loess soil sequence above s2 is 63 m at xinzhuangyuan and 43 m at lijiayuan a 2 cm sample spacing yields a mean depositional resolution of 50 80 years for the last and penultimate glacial loess units l1 and l2 and 200 years for the last interglacial soil unit sl thus enabling us to reconstruct high resolution climatic changes during the last two glacial interglacial cycles the grain size records of the two sections are regarded as a proxy for changes in the monsoon desert system over northern china results show that frequent large amplitude climatic oscillations on millennial timescales occurred during the penultimate glaciation in a manner similar to that during the last glaciation suggesting that suborbital scale climatic variations may be a common feature of the climate system during glacial periods of the pleistocene the last interglacial soil s1 is composed of three individual soils and two thin intervening loess horizons in both of the sections short term variations in grain size are not prominent within the soil complex implying the absence of strong millennial scale climatic oscillations during the last interglaciation in northern china

spatial variations of magnetic susceptibility of chinese loess for the last 600 kyr implications for monsoon evolution 1 we examine spatial variations in magnetic susceptibility ms over the loess plateau in china based on 50 sections in order to identify spatial changes in monsoon climate at key glacial interglacial and interstadial intervals for the last 600 kyr the results indicate strong coherence between ms variations during the interglacial periods and present day precipitation and temperature patterns this suggests that the strength of the summer monsoon had a dominant influence on the ms signals in soils through modulating pedogenic intensity the distribution of ms during glacial periods is characterized by weak s n gradients and rough w e zonal patterns indicating a negligible effect of the summer monsoon interstadial patterns are intermediate between the glacial and interglacial ones interglacial patterns for the last 600 kyr are essentially similar suggesting that the climate regime during these periods has not undergone significant changes and that the east asian summer monsoon has remained the main moisture carrier our estimates of the relative amplitudes of climate oscillations during these time slices are consistent with earlier paleoclimate studies these data associated with the available susceptibility based climofunctions may be used to estimate spatial changes of paleorainfall and paleotemperature for these key periods and hence to test climate models

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

stratigraphy and spatial and temporal paleoclimatic trends in southeastern eastern european loess paleosol sequences abstract the loess paleosol sections batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine are presently located in areas of different types of steppe and are highly sensitive for recording climatic changes a stratigraphy for these three southeastern eastern european sections is presented based on pedostratigraphy and correlation of recently obtained susceptibility records with susceptibility data of other sections of the area koriten mostistea vyazivok of the chinese loess plateau and with the benthic 18o record of odp 677 six pedocomplexes were studied at the serbian and romanian sections and five at the ukrainian section the oldest are related to marine isotope stage mis 17 batajnica stari slankamen and mircea voda and mis 13 15 stary kaydaky some points concerning the existing loess chronostratigraphies of bulgaria ukraine and china are discussed comparative study of the profiles allows the tracing of paleoclimatic and paleoenvironmental changes in southeastern eastern europe in time and space reconstruction of paleoprecipitation based on susceptibility rainfall relationships and calculations of sedimentation rates are evaluated

miocene climate change on the chinese loess plateau possible links to the growth of the northern tibetan plateau and global cooling the evolution of the asian monsoon arid environmental system during the cenozoic was closely related to the growth of the himalayan tibetan plateau and global climate change however due to inconsistencies in paleoclimatic reconstructions and to various constraints on the timing of the growth of the tibetan plateau the relative impacts of regional uplift and global cooling on asian climate change remain controversial here we investigate the mineralogical composition of a miocene red clay deposit on the western chinese loess plateau in order to infer changes in chemical weathering and monsoon intensity variations of four mineralogical ratios chlorite quartz illite quartz calcite quartz and protodolomite quartz reveal that the summer monsoon intensity was relatively strong during the early miocene 23 5 18 5 ma weakened gradually until 9 5 ma and strengthened again in the late miocene we synthesized previously published thermochronological data from the northeastern tibetan plateau and surrounding mountains and the results suggest that two phases of the rapid growth of northern tibet occurred around 24 17 and 13 7 ma comparison of paleoclimatic proxies and thermochronological data suggests that the gradual weakening of the summer monsoon intensity from 18 5 to 9 5 ma paralleled global cooling whereas two intervals of strengthened monsoon in the early and late miocene were possibly related to the rapid growth of northern tibet our combination of paleoenvironmental proxies and thermochronological data reveals possible links between miocene asian monsoon evolution phased growth of the tibetan plateau and global climate change and confirms the interconnection of geodynamic and atmospheric processes in the geological past

evidence for tibetan plateau uplift before 14 myr ago from a new minimum age for east west extension important changes in south asian climate occurred in the late miocene epoch 8 myr ago 1 2 and these have been attributed by some researchers to uplift of the tibetan plateau at about the same time3 5 unfortunately this link has been difficult to test because the timing of plateau uplift remains poorly constrained by independent evidence one way to determine the minimum age of uplift is to establish the initiation age of the north striking normal fault systems in southern tibet that are widely regarded6 10 as being related to gravitational collapse of the tibetan plateau here we report an40ar 39ar age of 14 myr for hydrothermal mica from an extensional fracture belonging to such a fault system in north central nepal this age implies that east west extension began before 14 myr ago in at least some parts of the tibetan plateau suggesting that the plateau attained its high mean elevation well before late miocene time

stepwise expansion of desert environment across northern china in the past 3 5 ma and implications for monsoon evolution abstract a systematic study of the last glacial cycle along three transects across the chinese loess plateau shows that sand sized particle content within loess decreases rapidly from north to south and that markedly high sand particle contents in loess horizons occur only in the northern part of the plateau this suggests that variation in the sand sized particle fraction within loess near the desert margin is closely linked to migration of the southern desert border in northern china where sand grains move mainly in saltation or modified saltation mode near the ground surface as desert margin shift is essentially controlled by the amount of monsoon precipitation the sand sized particle content within loess near desert margin is regarded as a new and readily applied proxy for variations in the strength of the east asian summer monsoon a continuous record of sand content in loess along the loess desert transitional zone shows that the mu us desert migrated southward at 2 6 1 2 0 7 and 0 2 ma suggesting a stepwise weakening of the east asian summer monsoon during the past 3 5 ma this evolutionary pattern is significantly different from that previously inferred from loess magnetic susceptibility records a widely used monsoon proxy our results further suggest that changes in global ice volume may have been an essential factor in controlling plio pleistocene monsoon evolution and that the anticipated future melting of polar ice cover may lead to a northward migration of the monsoon rainfall belt in northern china

sst and ice sheet impacts on the mis 13 climate as a first qualitative assessment tool loveclim has been used to investigate the interactions between insolation ice sheets and the east asian monsoon at the marine isotopic stage 13 mis 13 in work by yin et al clim past 4 79 90 2008 clim past 5 229 243 2009 the results are in need of validation with a more sophisticated model which is done in this work with the arpege atmospheric general circulation model as in the earth system model of intermediate complexity loveclim arpege shows that the northern hemispheric high insolation in summer leads to strong mis 13 monsoon precipitation data from the chinese loess plateau indicate that mis 13 was locally a warm and humid period guo et al in clim past 5 21 31 2009 yin and guo in chin sci bull 51 2 213 220 2006 this is confirmed by these general circulation model gcm results where the mis 13 climate is found to be hotter and more humid both in the presence and absence of any added ice sheets loveclim found that the combined effects of the ice sheets and their accompanying ssts contribute to more precipitation in eastern china whilst in arpege the impact is significant in northeastern china nonetheless the results of arpege confirm the counter intuitive results of loveclim where ice sheets contribute to enhance monsoon precipitation this happens through a topography induced wave propagating through eurasia with an ascending branch over northeastern china a feature which is also seen in loveclim the sst forcing in arpege results in a strong zonal temperature gradient between the north atlantic and east eurasia which in turn triggers an atmospheric gravity wave this wave induces a blocking okhotskian high preventing the northwards penetration of the meiyu monsoon front the synergism between the ice sheets and sst is found through the factor separation method yielding an increase in the meiyu precipitation though a reduction of the changma precipitation the synergism between the ice sheets and sst play a non negligible role and should be taken into consideration in gcm studies preliminary fully coupled aogcm results presented here further substantiate the finding of stronger mis 13 monsoons and a reinforcement from ice sheets this work increases our understanding of the signals found in the paleo observations and the dynamics of the complex east asian summer monsoon

east asian summer monsoon intensity inferred from iron oxide mineralogy in the xiashu loess in southern china abstract the xiashu loess in comparison to the well studied loess sequences in the chinese loess plateau clp provides a good opportunity for studying east asian monsoon variations from a southern china perspective here we present a study of the iron oxide mineralogy of the xiashu loess using integrated geochemical and diffuse reflectance spectroscopy drs measurements as well as magnetic data our results show that the free iron oxide fe d to total iron fe t ratio fe d fe t hematite hm to goethite gt ratio hm gt and saturation isothermal remanent magnetization sirm to magnetic susceptibility ratio sirm all indicate particularly strong summer monsoons during the formation of paleosols ps5 and ps4 equivalent to marine isotope stage 13 and 11 respectively however magnetic susceptibility and fe d fe t are not consistently reliable indicators of summer monsoon intensity for the whole section our results indicate that a multi proxy approach can give a more reliable summer monsoon intensity reconstruction the summer monsoon shows a cooling trend and a declining of precipitation from 0 5 to 0 3 ma after which it becomes warmer and wetter towards the top of paleosol ps1 equivalent to mis 5 however ps1 was formed under a relatively cooler temperature and wetter soil conditions in comparison to ps5 and ps4 such supra orbital variations in the east asian summer monsoon superimposed on the effects of glacial interglacial cycles in southern china are also reflected in the 0 4 0 5 ma cycle of marine carbon isotopes in the global ocean possibly indicating a strong link between terrestrial weathering and the global carbon cycle

magnetostratigraphic age and monsoonal evolution recorded by the thickest quaternary loess deposit of the lanzhou region western chinese loess plateau abstract the loess paleosol sequences of the chinese loess plateau clp are major paleoclimatic archives which document the evolution of the east asian monsoon eam and changes in the northern hemisphere ice sheets during the quaternary glacial interglacial cycles however the mechanisms regulating the trend of eam variations on a tectonic scale are unclear the loess deposits of the western clp which have a close relationship with tectonics and climate are much better suited to exploring these mechanisms than those of the central clp however studies of long term eam evolution from the western clp have been hindered by the lack of long accurately dated sequences with high sediment accumulation rates here we address this problem via high resolution magnetostratigraphic magnetic susceptibility and grain size analyses of a 416 2 m long drill core located at xijin village near lanzhou paleomagnetic dating indicates that the basal age of the xijin loess is 2 2 ma the and grain size records reveal that the east asian summer monsoon easm and east asian winter monsoon eawm strengthened synchronously at 1 24 ma subsequently during interglacial periods the easm began to penetrate and then dominate in the lanzhou region this was followed by two stepwise uptrends commencing at 0 87 and 0 62 ma which resulted in an increasingly moist interglacial climate in the region we suggest that the uplift of the tibetan plateau was largely responsible for these three stepwise enhancements of the easm overall however the long term trend of strengthening in eawm in the area may have been primarily caused by long term global cooling from the late pliocene onwards

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

simulating pliocene warmth and a permanent el nino like state the role of cloud albedo available evidence suggests that during the early pliocene 4 5 ma the mean east west sea surface temperature sst gradient in the equatorial pacific ocean was significantly smaller than today possibly reaching only 1 2 c the meridional sst gradients were also substantially weaker implying an expanded ocean warm pool in low latitudes subsequent global cooling led to the establishment of the stronger modern temperature gradients given our understanding of the physical processes that maintain the present day cold tongue in the east warm pool in the west and hence sharp temperature contrasts determining the key factors that maintained early pliocene climate still presents a challenge for climate theories and models this study demonstrates how different cloud properties could provide a solution we show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal sst gradients an expanded warm pool and warmer thermal stratification in the ocean and weaker hadley and walker circulations in the atmosphere having conducted a range of hypothetical modified cloud albedo experiments we arrive at our pliocene simulation which shows good agreement with proxy sst data from major equatorial and coastal upwelling regions the tropical warm pool middle and high latitudes and available subsurface temperature data as suggested by the observations the simulated pliocene like climate sustains a robust el nino southern oscillation despite the reduced mean east west sst gradient our results demonstrate that cloud albedo changes may be a critical element of pliocene climate and that simulating the meridional sst gradient correctly is central to replicating the geographical patterns of pliocene warmth

seismic structure and the active hellenic subduction in the ionian islands in the region of the ionian islands of western greece the active margin of the hellenic domain passes from oceanic subduction in the south to continental collision in the north linked by the right lateral cephalonia transform fault a slightly landward dipping interface revealed at 13 km depth by a single previous line in the channel between cephalonia and zante has been suggested as the interplate subduction boundary new marine multichannel reflection profiles and obs refraction and wide angle reflection data confirm the reflector as a regional feature these data evidence its extension to the south where large low angle thrust earthquakes occur offshore to zante the new profiles establish a coincidence between the focal depths of these large subduction events and the imaged bright reflective level confirming its tentative interpretation as the interplate boundary which generally appears with a positive reflection polarity in this context the ionian islands outcrop corresponds to a shallowing of the interplate boudary from south to north in the south offshore zante the interplate boundary comprises a stratified zone that may be considered as the sedimentary cover of the ionian basin oceanic like crust which forms the lower plate here the shallower position and single cycle reflection character of the interplate further north suggest that the lower plate could there be the apulian paleomargin to that basin

east asian monsoon variability over the last seven glacial cycles recorded by a loess sequence from the northwestern chinese loess plateau a 180 m thick loess paleosol sequence from the northwestern chinese loess plateau was investigated to construct a high resolution record of the east asian monsoon variability over the last seven glacial interglacial cycles the low field magnetic susceptibility mass specific and the mean grain size are used as proxies for changes in the intensity of the east asian summer and winter monsoon respectively because of the weaker pedogenesis at the northwestern chinese loess plateau compared to the central chinese loess plateau our and mean grain size records show a muted glacial interglacial contrast for the asian summer monsoon but an enhanced contrast for the asian winter monsoon although better resolved most orbital scale east asian monsoon variations captured by our and grain size records are similar to those reported from the central chinese loess plateau nevertheless variations in exhibit clear precessional cycles in three paleosol layers i e s1 s2 and s3 corresponding with solar insolation maxima furthermore unlike records at the central chinese loess plateau where is dramatically enhanced at paleosol s5ss1 corresponding to marine isotope stage 13 our new record shows a major enhancement at paleosol s4 corresponding to marine isotope stage 11 which indicates geographic differences in the timing of local monsoon precipitation in the two regions

an 800 ky proxy record of climate from lake sediments of the zoige basin eastern tibetan plateau abstract we present the results of magnetic susceptibility geochemical and pollen analyses of a 120 m long core of lacustrine and fluvial sediments from the zoige basin eastern tibetan plateau palaeomagnetic dating indicates that the sediment sequence spans the last ca 800 ky the magnetic susceptibility record appears to be related to global ice volume over this period and this relationship is used to produce a tentative revised chronology for the sediment sequence the various climate proxies show a pattern of periodic variations over the last 800 ky bp the date of 500 ky bp is a significant boundary prior to this date the climate proxies show a pattern of more frequent variability after 500 ky bp the variations are of lower frequency and higher amplitude the results also indicate that marine oxygen isotope stage 13 was an unusually intense interglacial in the eastern tibetan plateau and chinese loess plateau areas

tibet forcing of mid pleistocene synchronous enhancement of east asian winter and summer monsoons revealed by chinese loess record the mid pleistocene transition mpt of the global climate system marked by a shift of previously dominant 41 ka cycles to lately dominant 100 ka cycles roughly in the mid pleistocene is one of the fundamental enigma in the quaternary climate evolution the process and origin of the mpt remain of persistent interest and conjecture here we present high resolution astronomically tuned magnetic susceptibility ms and grain size records from a complete loess paleosol sequence at chaona on the central chinese loess plateau these two proxies are well known sensitive indicators to the east asian summer and winter monsoons respectively the records reveal a remarkable two step simultaneous enhancement of the east asian summer and winter monsoons at 0 9 ma and 0 64 ma respectively accompanied with an onset of a clear 100 ka cycle at 0 9 ma and of a final predominant 100 ka cycle starting at 0 64 ma the mid pleistocene stepwise rapid uplift of the tibetan plateau could be the mechanism driving the simultaneous enhancement of east asian summer and winter monsoons and the shift of the periodicities during the mpt by complex positive feedbacks 2012 university of washington

the climate of the mis 13 interglacial according to hadcm3 the climate of the marine isotopic stage 13 mis 13 is explored in the fully coupled atmosphere ocean general circulation model the hadley centre coupled model version 3 hadcm3 it is found that the strong insolation forcing at the time imposed a strengthened land ocean thermal contrast resulting in an intensified summer monsoon over asia the addition of land ice over north america and eurasia results in a stationary wave feature across the eurasian continent this leads to a high pressure anomaly over the sea of japan with increased advection of warm moist air onto the chinese landmasses this in turn reinforces the east asian summer monsoon easm highlighting the counterintuitive notion that depending on the background insolation and its size ice can indeed contribute to strengthening the easm the modeling results support the geological record indication of a strong easm 500 000 years ago furthermore arctic oscillation el nino southern oscillation and indian ocean dipole like teleconnection features are discussed in the mis 13 environment it is shown that the change in the tropical pacific sea surface temperature has the potential to impact the north atlantic climate through an atmospheric bridge

orbital and millennial antarctic climate variability over the past 800 000 years a high resolution deuterium profile is now available along the entire european project for ice coring in antarctica dome c ice core extending this climate record back to marine isotope stage 20 2 800 000 years ago experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation we assessed the general correspondence between dansgaard oeschger events and their smoothed antarctic counterparts for this dome c record which reveals the presence of such features with similar amplitudes during previous glacial periods we suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records

high resolution hematite and goethite records from odp 1143 south china sea co evolution of monsoonal precipitation and el nino over the past 600 000 years abstract precipitation has a larger variability than temperature in tropical monsoon regions thus it is an important climate variable however reconstructions of long term rainfall histories are scarce because of the lack of reliable proxies here we document that iron oxide minerals specifically the ratio of hematite to goethite hm gt is a reasonable precipitation proxy using diffuse reflectance spectrophotometry we measured samples from ocean drilling program odp 1143 drilling site 9 21 72 n 113 17 11 e 2777 m water depth for hematite and goethite whose formation processes are favored by opposing climate conditions in order to determine the content of hematite and goethite we produced a set of calibration samples by removing the iron oxides to generate the natural matrix to which hematite and goethite in known percentages were added from these calibration samples we developed a transfer function for determining hematite and goethite concentration from a sample s spectral reflectance applying this method to odp 1143 sediments top 34 m of a 510 m core with sampling interval of 10 cm we were able to reconstruct a continuous precipitation history for se asia of the past 600 kyr using the hm gt ratio as a proxy of the precipitation variability of asian monsoon the reliability of this hm gt proxy is corroborated by its consistency with the stalagmite 18o data from south china comparing long term hm gt records with the surface temperature gradient of equatorial pacific ocean we found that monsoon precipitation and el nino are correlated for the last 600 kyr the development of el nino like conditions decreased se asia precipitation whereas precipitation increases in response to la nina intensification

impact of ice sheet induced north atlantic oscillation on east asian summer monsoon during an interglacial 500 000 years ago marine isotope stage mis 13 an interglacial about 500 000 years ago is unique due to an exceptionally strong east asia summer monsoon easm occurring in a relatively cool climate with low greenhouse gas concentrations ghg this paper attempts to find one of the possible mechanisms for this seeming paradox simulations with an earth system model loveclim show that the presence of ice sheets over north america and eurasia during mis 13 induces a positive phase of the winter north atlantic oscillation nao like feature the ocean having a longer memory than the atmosphere the oceanic anomalies associated with nao persists until summer the signals of summer nao are transmitted to east asia to reinforce the monsoon there through the stationary waves excited at the asian jet entrance the geopotential height shows clearly a mid latitude wave train with positive anomalies over the eastern mediterranean caspian sea and the okhotsk sea and a negative anomaly over lake baikal this reinforces the effect of the high latitude wave train induced independently by the eurasian ice sheet topography as shown in previous study these features reinforce the meiyu front and enhance the precipitation over east asia the results obtained from loveclim are further confirmed by an atmospheric general circulation model arpege

magnetic properties and geochemistry of the xiashu loess in the present subtropical area of china and their implications for pedogenic intensity variations in the magnetic susceptibility of chinese loess have been used to indicate pedogenic intensity and therefore past climate across the chinese loess plateau clp however the relationship between climate and magnetic properties has not been fully resolved and therefore a study of loess sections distributed over a wider climatic region is timely in this study we have investigated a 22 1 m loess section named the xiashu loess at dagang china by integrating both rock magnetic and geochemical proxies this loess profile is situated in a modern subtropical climate region with annual mean precipitation and temperature of 1100 mm and 15 4 c respectively and therefore has experienced a stronger weathering intensity due to its lower latitude higher temperature and rainfall geochemical and magnetic evidence indicate the same source area for the xiashu loess as for loess in northern china the magnetic mineral assemblage of the xiashu loess is dominated by a higher concentration of superparamagnetic sp single domain sd magnetite maghemite grains in strongly weathered paleosols than in the loess layers consistent with the production of fine grained ferrimagnetic minerals during pedogenic processes nevertheless compared to loess in the clp the xiashu loess shows 1 reduced contrasts in magnetic susceptibility hard isothermal remanent magnetization hirm and remanence of coercivity bcr between loess and paleosols units which indicates that the loess units have undergone stronger pedogenic alterations 2 lower peak values of hirm and in paleosols in addition the ratios sirm arm sirm where sirm and arm are saturation isothermal remanent magnetization and the susceptibility of anhysteretic remanent magnetization respectively and bcr are found to be significantly correlated with the quotient cao na2o mgo tio2 a geochemical indicator of pedogenic intensity overall it seems that pedogenic processes in the xiashu loess lead to a relative increase in fine grained ferrimagnetic sp sd grains but depletion of anti ferromagnetic minerals magnetic and geochemical proxies indicate strengthened east asia summer monsoon during marine isotope stages 13 11 and 5 which is in good agreement with the records from the clp and the south china sea 2007 elsevier b v all rights reserved

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

palaeoclimatic changes in northeastern qinghai tibetan plateau revealed by magnetostratigraphy and magnetic susceptibility analysis of thick loess deposits reconstruction of a complete quaternary record of climatic changes in the northeastern qinghai tibetan plateau is not well obtained because of high relief and extensive surface erosion in this study two long cores obtained from thick loess deposits in the region both contain clear alternations of loess and paleosols indicating distinct climate changes during the quaternary the palaeomagnetic stratigraphy and optically stimulated luminescence dating indicate that the loess deposition began approximately 2 0 ma ago with continuous accumulation until the holocene dust accumulation rates in this region are much higher than those in the central chinese loess plateau suggesting an extended dust source and or robust transport agent variations of magnetic susceptibility of the loess are a good proxy index of warm wet and cold dry alternations and are correlated with the intensity of pedogensis the magnetic susceptibility record reveals that a relatively cold dry climate dominated the northeastern qinghai tibetan plateau in the quaternary punctuated by warm wet phases a stepwise strengthening of the plateau summer monsoon with a significant strengthening at around 1200 1000 ka and at least 7 phases of strengthening of the plateau summer monsoon in the past 800 ka are interpreted from the core data the cores provide evidence that strengthened warm wet climates occurred at around 80 130 190 250 290 340 385 420 500 625 690 720 and 755 780 ka which may correlate to warm wet phases in the qinghai tibetan plateau the palaeoclimate changes probably were regulated by the glacial interglacial alternations

contrasting crustal production and rapid mantle transitions beneath back arc ridges the eastern lau spreading centre located on the lau back arc basin hydrothermal vent system between fiji and tonga is a focus site of the ridge 2000 research programme of the us national science foundation the first large scale seismic study of the area reveals large and abrupt across and along strike changes in crustal properties implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes the authors conclude that stable broad triangular upwelling regions as inferred for mid ocean ridges cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which the material is rapidly released resulting in rapid changes in the character of the crust formed at the ridge this study shows that across strike and along strike changes in crustal properties at the eastern lau spreading centre are large and abrupt implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes it is concluded that stable broad triangular upwelling regions as inferred for mid ocean ridges cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which that material is rapidly released resulting in rapid changes in the character of the crust formed at the ridge the opening of back arc basins behind subduction zones progresses from initial rifting near the volcanic arc to seafloor spreading1 during this process the spreading ridge and the volcanic arc separate and lavas erupted at the ridge are predicted to evolve away from being heavily subduction influenced with high volatile contents derived from the subducting plate 2 3 4 5 current models4 6 7 8 predict gradational rather than abrupt changes in the crust formed along the ridge as the inferred broad melting region beneath it migrates away from heavily subduction influenced mantle in contrast here we show that across strike and along strike changes in crustal properties at the eastern lau spreading centre are large and abrupt implying correspondingly large discontinuities in the nature of the mantle supplying melt to the ridge axes with incremental separation of the ridge axis from the volcanic front of as little as 5 km seafloor morphology changes from shallower complex volcanic landforms to deeper flat sea floor dominated by linear abyssal hills upper crustal seismic velocities abruptly increase by over 20 and gravity anomalies and isostasy indicate crustal thinning of more than 1 9 km we infer that the abrupt changes in crustal properties reflect rapid evolution of the mantle entrained by the ridge such that stable broad triangular upwelling regions as inferred for mid ocean ridges9 10 cannot form near the mantle wedge corner instead the observations imply a dynamic process in which the ridge upwelling zone preferentially captures water rich low viscosity mantle when it is near the arc as the ridge moves away from the arc a tipping point is reached at which that material is rapidly released from the upwelling zone resulting in rapid changes in the character of the crust formed at the ridge

the asian monsoon over the past 640 000 years and ice age terminations oxygen isotope records from chinese caves characterize changes in both the asian monsoon and global climate here using our new speleothem data we extend the chinese record to cover the full uranium thorium dating range that is the past 640 000 years the record s length and temporal precision allow us to test the idea that insolation changes caused by the earth s precession drove the terminations of each of the last seven ice ages as well as the millennia long intervals of reduced monsoon rainfall associated with each of the terminations on the basis of our record s timing the terminations are separated by four or five precession cycles supporting the idea that the 100 000 year ice age cycle is an average of discrete numbers of precession cycles furthermore the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands and is nearly in anti phase with summer boreal insolation these observations indicate that insolation in part sets the pace of the occurrence of millennial scale events including those associated with terminations and unfinished terminations records of the asian monsoon have been extended to 640 000 years ago and confirm both that the 100 000 year ice age cycle results from integral numbers of precessional cycles and that insolation influences the pacing of major millennial scale climate events prior records of the asian monsoon have revealed cyclic variations over hundreds of thousands of years probably driven by variations in insolation caused by the precession of earth s orbit hai cheng and colleagues now provide a speleothem record from chinese cave samples that extends earlier records to 640 000 years ago close to the maximum age possible with uranium thorium dating this spectacular record confirms that the characteristic 100 000 year ice age cycle corresponds to an integral number four or five of precession cycles and that insolation influences millennial scale variations in monsoon strength

climatic implications of loess deposits from the beijing region variations in magnetostratigraphy pedostratigraphy grain size and magnetic suscep tibility of the loess deposits near beijing have been studied at two sections the sections are about 400 km east of the main loess deposits in china have a maximum thickness of 100 m and extend back to 1 1 ma the sequence consists of 14 loess palaeosol couplets s0 s14 which correlate well with sequences in the loess plateau susceptibility records from the sites near beijing are comparable to the xifeng luochuan and baoji sections located in the middle part of the loess plateau however the down core variations in the grain size in the upper lishi formation exhibit some differences the median grain size increases by about 25 30 m from l4 to l2 with the sandy grains 63 m increasing from 10 20 wt to 40 50 wt this implies that the depositional environment of the dust sources in the beijing loess section is different in some aspects from the loess plateau the beijing loess may have had a different dust source than the loess plateau copyright 2001 john wiley sons ltd journal of quaternary science

580 000 year environmental reconstruction from aeolian deposits at the mu us desert margin china abstract a 76 7 m thick section of aeolian sediment is exposed in the transition zone between the mu us desert and the loess plateau of northern china the aeolian sediments contain sand beds loess layers and palaeosols the particle size distribution data and the sem examination of quartz grains suggest the sand beds are wind blown origin palaeomagnetic measuring combined with thermoluminescence tl dating and pedostratigraphic correlation suggests the studied aeolian sequences were deposited within about 580 kyr the sand layers appear to reflect the episodic extensions of mu us desert during phases of active dune formation and intensified winter monsoon both the stratigraphy and the proxy climatic curves such as bulk magnetic susceptibility and grain size indicate that large amplitude second order climatic oscillations occur during both glacial and interglacial periods it is worth noting that nearly all the interglacial soils can be sub divided by the intercalated sand or loess beds this second order climatic oscillations are on the order of 10 000 of years which may reflect the precession scale variations of southeast summer monsoon driven by the orbital pacing of insolation in low latitudes

the loess record in southern tajikistan and correlation with chinese loess in the present study the chashmanigar loess soil sequence in southern tajikistan is studied this loess section has a paleomagnetic basal age of about 1 77 myr magnetic susceptibility color reflectance and grain size were systematically measured for closely spaced samples from the section paleosols consistently have a finer grain size distribution higher magnetic susceptibility redder color reflectance and lower dust sedimentation rate than loess horizons suggesting a colder drier and dustier environment during glacial periods than in interglacial periods the grain size record was tuned to variations in obliquity and precession of the earth s orbit the resulting magnetic susceptibility grain size and color reflectance time series all show well expressed astronomical periodicities during the pleistocene the mid pleistocene climate transition characterized by a shift of dominant climatic periods from 41 kyr to 100 kyr at about 1 0 0 8 myr is clearly documented in these proxy records comparison of the chashmanigar loess record with the lingtai loess section in china and the odp site 677 n 18 o record shows that during the entire pleistocene the climate cycles recorded by the central asian loess can be well correlated to the chinese loess and deep sea oxygen isotope records it is suggested that alternations of loess and soil horizons both in central asia and china could be basically forced by global ice volume variations although different wind systems have controlled the pleistocene loess transport and sedimentation in the two areas 2002 elsevier science b v all rights reserved

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

variability of monsoon climate in east asia at the end of the last glaciation abstract high resolution paleomonsoon proxy records from peat and eolian sand paleosol sequences at the desert loess transition zone in china denote a rapid oscillation from cold dry conditions 11 200 10 60014c yr b p to cool humid conditions 10 600 10 20014c yr b p followed by a return to cold dry climate 10 200 10 00014c yr b p variations in precipitation proxies suggest that significant climatic variability occurred in monsoonal eastern asia during the younger dryas interval late glacial climate in the chinese desert loess belt that lies downwind from europe was strongly influenced by cold air from high latitudes and from the north atlantic via the westerlies the inferred precipitation variations were likely caused by variations in the strength of the siberian high which influenced the pressure gradient between land and ocean and therefore influenced the position of the east asian monsoon front

danube loess stratigraphy towards a pan european loess stratigraphic model abstract the danube river drainage basin is the second largest river catchment in europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments indeed the danube river and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment however this vast loess province lacks a unified stratigraphic scheme european loess research started in the late 17th century in the danube basin with the work of count luigi ferdinand marsigli since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by kukla 1970 1977 in his correlations of loess with deep sea sediments loess palaeosol sequences in the middle and lower reaches of the danube river basin were a key part of this framework and contain some of the longest and most complete continental climate records in europe covering more than the last million years however the very size of the danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits local loess palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes which often change significantly with advances in age dating have limited the number of basin wide studies a unified basin wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records therefore we review the existing stratigraphic schemes and define a new danube basin wide loess stratigraphy based around a synthetic type section of the mosorin and stari slankamen sites in serbia we present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the chinese loess plateau with the oxygen isotope records from deep sea sediments and with classic european pleistocene stratigraphic subdivisions the hierarchy of danubian stratigraphic units is determined by climatically controlled environmental shifts in a similar way to the chinese loess stratigraphic scheme a new unified danube loess stratigraphic model has a number of advantages including preventing confusion resulting from the use of multiple national schemes a more transparent basis and the potential to set pleistocene palaeoenvironmental changes recorded in the danube catchment area into a global context the use of a very simple labelling system based on the well established chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the danube basin loess sites in a wider more accessible context that can be readily correlated world wide this stratigraphic approach also provides for the first time an appropriate framework for the development of an integrated pan european and potentially pan eurasian loess stratigraphic scheme

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record

the long term paleomonsoon variation recorded by the loess paleosol sequence in central china abstract the loess paleosol sequence in central china during the last 2 5 ma is a good record of the asian monsoon variation which could be considered as the concrete realization of global paleoclimatic cycles the geological and biological evidence of the loess paleosol sequence indicates that the loess was mainly the dust deposits transported by the northerly wind of winter monsoons and also suffered to some extent from pedogenesis caused by weakened summer monsoons and that the paleosol accreted by the rather slow dust accumulation was closely related to strengthened summer monsoons an alternating occurrence of loess and paleosol in the luochuan section implies the variation history of warm humid climate with a summer monsoon dominance and cold dry climate with a winter monsoon dominance the magnetic susceptibility of loess and paleosol can be regarded as a proxy index of asian monsoon variation an analysis of the susceptibility curve and structure characters of luochuan section shows that the asian monsoon circulation was strengthened from early pleistocene to late pleistocene and the 500 ka bp point and 1200 ka bp point seem to be a threshold and a turning point respectively in terms of the long term paleomonsoon variation in asia

possible link of an exceptionally strong east asian summer monsoon to a la nina like condition during the interglacial mis 13 abstract previous studies from the central and eastern chinese loess plateau clp showed that the s5 1 paleosol which corresponding to marine isotope stage mis 13 was the strongest developed during the last million years suggesting extremely strong east asian summer monsoon easm however evidence shows that regional diversity exists in the relative intensity of the s5 1 soil formation in this study we first verify systematically the s5 1 soil development across the whole clp by using numerous loess records we then examine the spatial variation of the magnetic susceptibility of different loess paleosol sections to identify the spatial change of the easm intensity during mis 13 we also compare the loess records with other monsoon records in china our results show that in central clp s5 1 is indeed the strongest developed as suggested by previous studies whereas in the western clp it is weakly developed and the s4 paleosol developed during mis 11 is the strongest as compared to mis 11 the northern front of the easm during mis 13 didn t penetrate into western clp but was located more northerly and eastward based on sea surface temperature records in the tropical pacific we suggest that the temporal and spatial abnormal variation of the easm during mis 13 could be related to a strong la nina or la nina like climate condition under such condition the western pacific subtropical high wpsh becomes weaker and retreats more northeastward leading to more precipitation in the mid east region of northern china but less rainfall in the western inland

paleomagnetic chronology and paleoenvironmental records from drill cores from the hetao basin and their implications for the formation of the hobq desert and the yellow river abstract reconstructing the cenozoic environmental history of hetao basin in the northern part of the ordos plateau in north china is important not only for revealing the evolution of the yellow river but also for understanding the formation of the hobq desert here we present the stratigraphic framework of drill core dr01 with length of 2503 18 m and the results of magnetostratigraphic and esr dating and multi proxy analyses of drill core wedp05 with length of 274 60 m from the hetao basin the magnetostratigraphic and esr results indicate that core wedp05 spans the last 1 68 ma stratigraphic sequence of core dr01 indicates that the hetao area was uplifted and eroded during the early cenozoic before subsiding to form a sedimentary basin subsequently the basin was a fluvio lacustrine environment during the pliocene and then experienced alternating desert and fluvio lacustrine conditions during the quaternary sedimentary facies and multi environmental proxy analyses of core wedp05 indicate that the basin was occupied by a fluvio lacustrine system during the following intervals 1 47 1 30 ma 1 17 1 07 ma 0 68 0 60 ma and from 0 47 ma to the last interglacial and that a desert environment developed during the lake regression phases of 1 30 1 17 ma 1 07 0 68 ma and 0 60 0 47 ma the presence of aeolian sand at the base of core wedp05 suggests that the origin of the hobq desert can be traced back to the early pleistocene and resulted from the erosion and transportation of exposed fluvio lacustrine sediments by near surface winds associated with the asian winter monsoon a large river channel in the hetao basin may have existed as early as the pliocene which was occupied by the yellow river when its upper reaches formed by at least 1 6 ma subsequently at least since 1 2 ma the yellow river formed its drainage system around the hetao basin and controlled the paleoenvironment evolution of the basin

northwestward decline of magnetic susceptibility for the red clay deposit in the chinese loess plateau 1 the loess paleosol red clay sequence in the chinese loess plateau has attracted attention for its potential in recording late cenozoic climatic changes over northern china although the details of the climatic implications of the proxies for example magnetic susceptibility and the reconstructed summer monsoon changes remain unclear here we report on a new section from baishui in gansu province and compare it with the lingtai and jingchuan sections by correlating the magnetic susceptibility from these sections we show that there is a clear systematic decrease of the magnetic susceptibility in the red clay deposits from the southeast lingtai section to the northwest baishui section this result suggests that the climatic parameters probably precipitation had a decreasing northwestward gradient during the red clay deposition this climatic pattern is similar to the present condition implying that the influence of the east asian summer monsoon on the chinese loess plateau has persisted from at least 6 ma

magnetostratigraphy and sedimentology of the jingchuan red clay section and correlation of the tertiary eolian red clay sediments of the chinese loess plateau a 325 m thick loess and red clay sequence was recently discovered at jingchuan which is situated about 45 km north of the previously studied lingtai section in the middle part of the chinese loess plateau the jingchuan section is composed of 199 m of pleistocene loess and 126 m of tertiary red clay deposits paleomagnetic studies show that the jingchuan red clay has a basal age of at least 7 7 ma which represents the oldest red clay deposits presently known in the loess plateau field observations and grain size analyses both suggest an eolian origin of the red clay thus extending available records of the eolian deposits in the loess plateau from about 7 0 ma to 7 7 ma correlation of both pedostratigraphy and magnetic susceptibility records suggests that the late cenozoic red clay records in the loess plateau have a general continuous nature thereby providing potential for deriving long term climatic evolution signals from this eolian loess and red clay sequence

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

correlation of loess paleosol sequences in east and central asia with se central europe towards a continental quaternary pedostratigraphy and paleoclimatic history abstract as recent small climatic fluctuations on a 102 103 year time scale can be correlated worldwide and represent a decline of mean annual temperature of only 1 c major climatic changes on at least a 105 year scale glacial interglacial cycles and probably a 104 year scale the approximate length of an interglacial must be of similar ages throughout the temperate climatic belt of the northern hemisphere this concept allows continental pedostratigraphical correlations detailed knowledge of the genesis of paleosols is needed to establish loess paleosol stratigraphies that can be used for paleoclimatic reconstruction most paleosols however are truncated and largely recalcified from overlying loess micromorphological studies allow primary and secondary carbonates to be distinguished and provide unequivocal evidence of clay illuviation this enables the recognition of typical loess weathered loess and the recognition of different genetic soil horizons such as cb bc ah bw and bt horizons for the brunhes epoch the sequence at karamaydan tadjikistan is more detailed than the corresponding section in luochuan china and even more than in se central europe except for the last glaciation the very good correlation with the deep sea oxygen isotope record which includes the development of an accurate astronomical time scale allows a detailed chronostratigraphical subdivision of the loess paleosol sequence in karamaydan which therefore should be regarded as a key sequence for reconstructing the climatic history of the brunhes epoch this implies that the loess paleosol sequences in se central europe are less complete than thought earlier pedocomplexes in karamaydan correspond with single paleosols in se central europe e g the f6 paleosol in stari slankamen correlates with pedocomplexes pk vi and v at karamaydan which were formed over a period of about 140 ka although pedogenesis was interrupted several times by loess deposition the f6 soil is therefore an example of a welded paleosol as are the f5 the f4 and the f2 paleosols in se central europe for most of the matuyama epoch the central and lower parts of the sequence at chashmanigar show more pronounced paleosols than the equivalent parts at luochuan in se central europe only at stari slankamen are three strongly developed though truncated paleosols f9 f11 above neogene sediments mineralogical investigations of the silt and clay subfractions show that there is little difference in the type and amount of pedogenic clay mineral formation between the holocene soils and the paleosols of the brunhes epoch at karamaydan and of the matuyama epoch at chashmanigar this suggests that the interglacial climates represented by the b or bt horizons of the buried paleosols of late middle and early pleistocene age were similar to that of the holocene

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

late pleistocene paleoclimatology of the central equatorial pacific sea surface response to the southeast trade winds proxy indicators of sea surface temperature and equatorial divergence based on radiolarian assemblage data and of trade wind intensity based on eolian grain size data show similar aspects of variability during the late pleistocene all indicators fluctuate at higher frequencies than the 100 000 year glacial interglacial cycle display reduced amplitude variations since 300 000 years ago exhibit a change in the record character at about 300 000 years ago the mid brunhes climatic event and have higher amplitude variations in sediments 300 000 850 000 years old time series analyses were conducted to determine the spectral character of each record 18o of planktonic foraminifer sea surface temperature values equatorial divergence indicators and wind intensity indicators and to quantify interrecord coherence and phase relationships the record was divided at the 300 000 year clear change in climatic variability nonstationarity the 18o based time scale is better lower in the core so our spectral analyses concentrated on the interval from 402 000 774 000 years the 18o spectra show 100 000 and 41 000 year power in the younger portion 0 300 000 years and 100 000 41 000 and 23 000 year power in the older interval all highly coherent and in phase with the specmap average stacked isotope record unlike the isotope record the dominant period in both the eolian grain size and equatorial divergence indicators is 31 000 years this period is also important in the sea surface temperature signal where the dominant spectral peak is 100 000 years the 31 000 year spectral component is coherent and in phase between the eolian and divergence records confirming the link between atmospheric and ocean surface circulation for the first time in the paleoclimate record since the 31 000 year power appears in independent data sets within this core and also appears in other equatorial records j imbrie personal communication 1987 we assume it to be real and representative of both a nonlinear response to orbital forcing possibly a combination of orbital tilt and eccentricity and some resonance phenomenon required to amplify the response at this period so that it appears as a dominant frequency component the mid brunhes climatic event is an important aspect of these records but its cause remains unknown

clay mineralogy and geochemistry and their palaeoclimatic interpretation of the pleistocene deposits in the xuancheng section southern china a red soil profile in xuancheng anhui province southern china in the middle to lower reaches of the yangtze river was investigated using x ray diffraction x ray fluorescence spec trometer and scanning electron microscopy the mobile components k2o and na2o and trace elements ba and sr of the xuancheng section exhibit a general trend of decrease downward along the red soil profile together with an increase downward of chemical index of alteration cia values suggesting more intense depletion in the lower portion than in the upper portion the major components sio2 a l 2o3 and fe2o3 as well as sio2 al2o3 sio2 fe2o3 and al2o3 fe2o3 ratios show notable fluctuations along the soil profile indicating intense climatic oscillations in the area during the pleistocene age the clay mineral assemblage of the xuancheng section can be generally subdivided into three groups suggesting a general trend of three stages of climate changes the lower portion of 10 4 6 3 m depth has a lower illite content and higher abundance of kaolinite and illite smectite i s clays indicating that a warm and wet climate prevailed over the episode of ca 600 350 ka bp a decrease in abundance of kaolinite and i s clays and increase in illite content at a depth of 6 3 2 2 m probably indicate a transition stage of climate change from warm humid to cool dry in the period ca 350 80 ka bp the higher illite content and lower abundance of kaolinite and i s clays in the upper portion of 2 2 0 m depth suggest that a relatively cool and dry climate dominated since ca 80 ka bp based on changes in clay mineralogy and chemical indices of the sediments seven warm cold fluctuations were determined in the area since the middle pleistocene climate changes documented in the xuancheng section are in agreement with the d 18 o records of sediments from the equatorial pacific core v28 238 and the loess palaeosol sequences in the loess plateau of northwestern china correlated to the episode of s4 and s5 soil units in the loess plateau the period of ca 600 350 ka bp in the xuancheng area was dominated by the particularly strong east asia summer monsoon as indicated by its most abundant kaolinite and i s clays fluctuations in clay mineralogy along the xuancheng soil profile were mainly controlled by both the east asia summer and winter monsoons in response to the global changes in the middle late pleistocene copyright 2009 john wiley sons ltd

loess particle size data indicative of stable winter monsoons during the last interglacial in the western part of the chinese loess plateau abstract particle size data from the western part of the chinese loess plateau do not support the last interglacial correlation suggested by the data from the central part of the loess plateau between the high dust influx events in the loess plateau and the cool events in the high northern latitudes the lack of marked oscillations in the particle size of the last interglacial paleosol s1 in the western part of the plateau is interpreted as an indication of stable winter monsoons it is thus inferred that the teleconnection between the northern high latitudes and the chinese loess plateau evident in the last glacial might not have existed during the last interglacial it is argued that the western part of the plateau is a better place to establish synchroneity between parent material eolian deposition and s1 paleosol formation 6 8 m thick under such cooler and drier conditions however to assume synchroneity between parent material eolian deposition and s1 paleosol formation only 2 5 m thick under the warmer and moister interglacial conditions in the central part of the plateau is a questionable practice thus the high resolution correlation with the data from the north atlantic area remains problematic

middle and late pleistocene loess sequences at batajnica vojvodina serbia abstract loess sequences in the vojvodina region northern serbia reveal a continuous record of paleoclimatic variations during the middle and late pleistocene the most detailed stratigraphic information comes from remarkable exposures on the cliffs of the right danube bank from vukovar to belgrade the batajnica loess section has been recognized as one of the most complete middle and late pleistocene records in this region a more than 40 m thick loess paleosol succession represents environmental transition from relative thin loess layers and rubified soils in lower part of profile to thick loess and fossil chernozems characterizing the last three glacial interglacial cycles the proposed stratigraphic model is based on a detailed magnetic susceptibility ms record which is related to the deep sea isotope stratigraphy and on correlation with other eurasian loess records using the distinct ms pattern of selected loess paleosol couplets this new stratigraphic model suggests serious revision of previous chronological interpretations ms as function of depth shows a well known pattern of low values in loess and high values in paleosols indicating strong enhancement of magnetic minerals during soil formation with the exception of the recent soil v s0 which is strongly contaminated by archaeological artifacts the third paleosol v s3 reveals the highest values in ms and a very distinct double peak the rock magnetic signal at batajnica resembles the typical pattern of the enviromagnetic records determined from other eurasian loess sites the paleopedological interpretations rubification index values and rock magnetic record at batajnica yield valuable data for the reconstruction of paleoclimatic fluctuations for the last 5 glacial interglacial cycles at least moreover the record provides an important link between the classical central european loess sites and the central asian and chinese loess provinces

iron geochemistry of loess and red clay deposits in the chinese loess plateau and implications for long term asian monsoon evolution in the last 7 0 ma abstract recently some groups of authors have demonstrated that the tertiary red clay deposits underlying the pleistocene loess paleosol sequence in the chinese loess plateau are wind blown in origin thus extending the eolian record in the plateau from 2 6 ma back to about 7 0 ma and providing a good opportunity to reconstruct long term monsoon changes as magnetic susceptibility the widely used paleomonsoon proxy of loess deposits is problematic in reconstructing the monsoon history recorded in the red clay the development of other proxies is urgently needed in this study we analyzed the ratios of citrate bicarbonate dithionite cbd extractable fe2o3 to total fe2o3 concentrations in four loess sections along a north south transect of the loess plateau and in the lingtai loess red clay sequence of 305 m thick the fe2o3 ratio in the loess sections clearly shows higher values in soil units than in loess horizons and a southward increase in this ratio is also remarkable along the transect these are in good agreement with the temporal spatial variations in the east asia summer monsoon intensity identified by other monsoon proxies and soil development observations the fe2o3 ratio thus attests to being a good proxy indicator of the summer monsoon evolution the lingtai fe2o3 ratio record shows high values over three time intervals 4 8 4 1 ma 3 4 2 6 ma and during the interglacial periods of the past 0 8 ma the increase in summer monsoon intensity over the three intervals also coincides with the well developed soil characteristics it is therefore concluded that the east asia summer monsoon has experienced a non linear evolution since the late miocene the occurrence of a monsoon prime at about 4 8 4 1 ma implies that the tibetan plateau one of the most important boundary conditions in maintaining the monsoon circulation must have been uplifted to a critical height at that time

co evolution of monsoonal precipitation in east asia and the tropical pacific enso system since 2 36 ma new insights from high resolution clay mineral records in the west philippine sea clay mineralogical analysis and scanning electron microscope sem analysis were performed on deep sea sediments cored on the benham rise core md06 3050 in order to reconstruct long term evolution of east asian summer monsoon easm rainfall in the period since 2 36 ma clay mineralogical variations are due to changes in the ratios of smectite which derive from weathering of volcanic rocks in luzon island during intervals of intensive monsoon rainfall and illite and chlorite rich dusts which are transported from east asia by winds associated with the east asian winter monsoon eawm since luzon is the main source of smectite to the benham rise long term consistent variations in the smectite illite chlorite ratio in core md06 3050 as well as odp site 1146 in the northern south china sea suggest that minor contributions of eolian dust played a role in the variability of this mineralogical ratio and indicate strengthening easm precipitation in se asia during time intervals from 2360 to 1900 kyr 1200 to 600 kyr and after 200 kyr the easm rainfall record displays a 30 kyr periodicity suggesting the influence of el nino southern oscillation enso these intervals of rainfall intensification on luzon island are coeval with a reduction in precipitation over central china and an increase in zonal sst gradient in the equatorial pacific ocean implying a reinforcement of la nina like conditions in contrast periods of reduced rainfall on luzon island are associated with higher precipitation in central china and a weakening zonal sst gradient in the equatorial pacific ocean thereby suggesting the development of dominant el nino like conditions our study therefore highlights for the first time a long term temporal and spatial co evolution of monsoonal precipitation in east asia and of the tropical pacific enso system over the past 2 36 ma

loess record of climatic changes during mis 12 10 in the jingyuan section northwestern chinese loess plateau abstract marine isotope stage 11 mis 11 has been considered as a potential analog for the present interglacial based on orbital scale solar insolation variations therefore increasing attention has been paid to mis 11 and the contiguous stages in recent studies of marine and terrestrial records as they may provide clues for predictions of future climate change in the chinese loess palaeosol sequences s4 soil interpreted as corresponding to mis 11 yields a precise terrestrial palaeoclimate record for this period in this study a loess palaeosol sequence l4 l5 from the jingyuan section on the northwestern margin of the chinese loess plateau clp was investigated to reconstruct the climatic variability during the periods mis 12 10 using proxies of grain size magnetic susceptibility total organic carbon and soil color index the results suggest that the l4 l5 sequence in the jingyuan section is much thicker 40 m than those in the central loess plateau areas 12 m the l5 loess equivalent to mis 12 developed under relatively cold and dry conditions climate evolution during this period was not as severe as that indicated in the marine isotopic records an episode of warmer and more humid conditions occurred during the middle stages of mis 12 reflecting a strengthened summer monsoon during the glacial period a similar scenario has been observed in the middle part of mis 10 high resolution multi proxy records for mis 11 suggest that a general warm humid climate was dominant during the formation of s4 soil however at least four fluctuations occurred reflecting unstable climate conditions and regional climate differences within the northwestern margin of the clp during this period the study also shows that the early part of s4 spanning over 30 ky was very warm and humid while the later part was characterized by mild cool conditions

high frequency pulses of east asian monsoon climate in the last two glaciations link with the north atlantic three loess sections in the loess plateau of china have been studied to characterize the variations of the east asian monsoon climate in the late quaternary period paleo weathering profiles based on two weathering indices reveal a series of spatially correlative intervals of lower weathering intensity lw in the last glacial and late penultimate glacial loess indicating significantly cooler or and drier conditions most of them are identified at or near the transitional boundaries between loess and soil units suggesting that climatic conditions favorable for lw events tended to occur at or near major climatic boundaries twenty eight radiocarbon and thermoluminescence measurements combined with kukla s magnetic susceptibility age model date these events at 14 21 29 38 52 71 135 and 145 ka bp with 5 10 ka frequency inlaid within the orbitally induced 20 ka periodicity the ages of the first six events in the last glacial period are therefore close to those of the coarse grained heinrich layers in the north atlantic ocean which resulted from massive discharges of icebergs the results indicate that the climate in the area affected by the east asian monsoon has experienced high frequency changes more or less synchronous with the heinrich events these high frequency changes have been reported by porter and an based on the grain size time series from the luochuan loess section our data also reveal that similar events also occurred during the penultimate glaciation the mechanisms linking the heinrich events and the east asian monsoon climate may be similar to that driving the younger dryas event which has been identified in a large number of records in china and in the surrounding oceans

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

regional distribution of the quaternary red clay with aeolian dust characteristics in subtropical china and its paleoclimatic implications abstract grain size and geochemical characteristics of 18 quaternary red clay qrc profiles mainly located in the lower and middle reaches of the yangtze river in subtropical china were studied the results showed that all the qrc profiles can be classified into three types type a mainly distributed between 29 n and 31 n share the similar characteristics with the xiashu loess with the uniformity of grain size and elemental compositions and the enrichment of the basic dust fraction 10 m 63 m which may originate from aeolian dust deposits and is hence called a loess like qrc type b mainly distributed between 25 n and 28 n shows alluvial features with many coarse grains and large scale vertical variation of grain size and chemical compositions type ab distributed between type a and type b approximately 28 n 29 n shows double unit structure the upper part is similar to type a the lower however shows alluvial features like type b the loess like qrc is mainly distributed along the yangtze river but gradually declines southwards and is rarely seen south of 28 n the existence of the loess like qrc is strong evidence for the occurrence of heavy dustfalls in the modern red soil areas in subtropical china during the quaternary glacial periods the region distributed with the loess like qrc is at least 3 latitude south of the xiashu loess implying that the loess red clay boundary in the yangtze valley had once oscillated with the alternations between glacial and interglacial climates during the quaternary period the loess like qrc actually includes both glacial and interglacial paleoclimatic information we suggest that the yellow brown earth ybe in the upper qrc was formed during the last glacial period the underlying red clay with the aeolian dust characteristics but being strongly weathered was initially deposited during the second last glacial or earlier glacial stages but heavily weathered and rubefied in the subsequent interglacial events no multi cyclical paleoclimatic records were found in the qrc profiles due to the overlapped information but the weathering degree of the profiles clearly show a trend of decreasing upwards which suggests that the climate in the yangtze valley has become colder and drier since the late quaternary period

pleistocene climatic history of east and central asia based on paleopedological indicators in loess paleosol sequences a micromorphological comparison of the loess paleosol sequence of the karamaydan section central asia with the upper part of the luochuan section china clearly indicates that for the brunhes chron the sequence at karamaydan is more detailed than the corresponding section at luochuan single paleosols at luochuan correspond to pedocomplexes at karamaydan for example s 3 at luochuan corresponds to pk iii and s 4 to pk iv and both pks developed in a period longer than one interglacial about 104 years some pedocomplexes at luochuan are represented by more detailed successions at karamaydan for example the s 5 complex at luochuan corresponds to pedocomplexes v and vi the loess paleosol sequence at karamaydan should therefore be regarded as a key sequence for reconstructing the climatic history of the brunhes epoch correlation with the deep sea oxygen isotope record of bassinot et al which includes an accurate astronomical time scale allows a detailed chronostratigraphical subdivision of the loess paleosol sequence in karamaydan for the brunhes epoch the sequence in the central and lower parts of the chashmanigar section also in central asia shows much more pronounced paleosols than the equivalent sequence at luochuan although some ck or ckm horizons indicate the presence of hiatuses nevertheless for this part of the sequence it provides more paleoclimatic detail with cold dry stages represented by loess and warm humid stages interglacials by paleosols than even the deep sea cores

the magnetic mechanism of paleosol s5 in the baoji section of the southern chinese loess plateau abstract in the central chinese loess plateau clp the magnetic susceptibility has the highest value in the s5 paleosol unit however at the southern of the clp such as in baoji the magnetic susceptibility value in the s5 paleosol unit is on the lower range of the top 6 paleosols s0 s1 s5 the studies of rock magnetism and geochemistry showed that the baoji s5 experienced a stronger pedogenesis and chemical weathering than the s3 the paleosol s3 was formed under an oxidizing environment where the maghemite and hematite are formed simultaneously maghemite is the main contributor to magnetic enhancement however the concentrations of maghemite in the s5 are lower than in the s3 with the development of pedogenesis the proportion of the maghemite component decreased in the s5 while the concentrations of anti ferromagnetic minerals mainly goethite increased in the field measurable amounts of dark brown iron manganese cutans can be observed on the cranny surface of s5 these indicate that the iron manganese elements in the s5 were assembled and pedogenesis occurred intermittently between wet and dry and strong leaching soil conditions this may have led to fine grained magnetite maghemite and hematite which were gradually converted into weak magnetic goethite therefore resulting in the lower magnetic susceptibility of s5

rock magnetic and grain size evidence for intensified asian atmospheric circulation since 800 000 years b p related to tibetan uplift abstract paleomagnetic rock magnetic and grain size studies of a thick loess sequence in the west qin ling mountain range show that loess deposition there began about 800 ka the data reveal a progressively increasing coarse grain size fraction upwards into the holocene the averages of these coarse size fractions are higher than in the central loess plateau which was apparently farther from the source area and slightly lower than those of the western loess plateau and the eastern tibetan plateau which were therefore closer to the source area the coarsening and source area location suggest 1 that asian air circulation may have changed and intensified at about 800 ka resulting in dust deposition in west qin ling 2 that dust carrying winds were driven not only by the asian winter monsoon but included also the westerlies and a winter monsoon caused by the tibetan plateau high and 3 that intensification of all these air circulation systems continues to the present increased elevation of the tibetan plateau so that it reached into the cryosphere by about 800 ka and a subsequent persistent uplift of the plateau may have been the mechanisms to trigger a change and intensify the air circulation system moreover this circulation shift and intensification simultaneous with a shift in milankovitch periodicity may have contributed to large global climate changes such as the 15 increase in global ice volume at ca 800 ka

high latitude influence on the eastern equatorial pacific climate in the early pleistocene epoch many records of tropical sea surface temperature and marine productivity exhibit cycles of 23 kyr orbital precession and 100 kyr during the past 0 5 myr refs 1 5 whereas high latitude sea surface temperature records display much more pronounced obliquity cycles at a period of about 41 kyr ref 6 little is known however about tropical climate variability before the mid pleistocene transition about 900 kyr ago which marks the change from a climate dominated by 41 kyr cycles7 when ice age cycles and high latitude sea surface temperature variations were dictated by changes in the earth s obliquity8 9 to the more recent 100 kyr cycles of ice ages here we analyse alkenones from marine sediments in the eastern equatorial pacific ocean to reconstruct sea surface temperatures and marine productivity over the past 1 8 myr we find that both records are dominated by the 41 kyr obliquity cycles between 1 8 and 1 2 myr ago with a relatively small contribution from orbital precession and that early pleistocene sea surface temperatures varied in the opposite sense to local annual insolation in the eastern equatorial pacific ocean we conclude that during the early pleistocene epoch climate variability at our study site must have been determined by high latitude processes that were driven by orbital obliquity forcing

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

separation of pedogenic and lithogenic components of magnetic susceptibility in the chinese loess palaeosol sequence as determined by the cbd procedure and a mixing analysis summary magnetic susceptibility variations in the chinese loess palaeosol sequences have been used extensively for palaeoclimatic interpretations the magnetic signal of these sequences must be divided into lithogenic and pedogenic components because the palaeoclimatic record is primarily reflected in the pedogenic component in this paper we compare two methods for separating the pedogenic and lithogenic components of the magnetic susceptibility signal the citrate bicarbonate dithionite cbd extraction procedure and a mixing analysis both methods yield good estimates of the pedogenic component especially for the palaeosols the cbd procedure underestimates the lithogenic component and overestimates the pedogenic component the magnitude of this eect is moderately high in loess layers but almost negligible in palaeosols the mixing model overestimates the lithogenic component and underestimates the pedogenic component both methods can be adjusted to yield better estimates of both components the lithogenic susceptibility as determined by either method suggests that palaeoclimatic interpretations based only on total susceptibility will be in error and that a single estimate of the average lithogenic susceptibility is not an accurate basis for adjusting the total susceptibility a long term decline in lithogenic susceptibility with depth in the section suggests more intense or prolonged periods of weathering associated with the formation of the older palaeosols the cbd procedure provides the most comprehensive information on the magnitude of the components and magnetic mineralogy of loess and palaeosols however the mixing analysis provides a sensitive rapid and easily applied alternative to the cbd procedure a combination of the two approaches provides the most powerful and perhaps the most accurate way of separating the magnetic susceptibility components