slaking and deformation behaviour slaking is a mechanical hydraulic process in which geomaterials disintegrate or crumble when subjected to wetting and drying cycles mudstone is particularly susceptible to this process this paper explores the slaking behaviour of geomaterials derived from several kinds of mudstone and the mechanical consequences using a comprehensive set of experimental data obtained through accelerated slaking tests and newly developed one dimensional compression slaking tests these data confirm that slaking in crushed mudstone is accompanied by a variation in the particle size distribution during wetting and drying cycles and a variation in grading results in an irreversible change in mechanical characteristics such as the reference packing density significant compression is also found to occur without any change in effective confining stress the results of x ray fluorescence analysis x ray diffraction analysis and scanning electron microscopy are also used to elucidate the effects of mineralogy and particle tex

magnetic parameter variations in the chaona loess paleosol sequences in the central chinese loess plateau and their significance for the middle pleistocene climate transition abstract a high resolution rock magnetic investigation was performed on the chaona quaternary loess paleosol sequences in the central chinese loess plateau based on a newly developed independent unturned time scale and magnetic records we reconstructed the history of the east asia monsoons during the last 3 ma and explored the middle pleistocene climate transition mpt rock magnetic results show that the loess layers are characterized by relatively high coercivity and remanent coercivity lower magnetic susceptibility ms and that the paleosol layers are characterized by relatively high ms saturation magnetization and remanent saturation magnetization spectrum analyses indicate that there are various periods in addition to orbital periodicities according to the onset and stable appearance of 100 kyr period we consider that the mpt recorded in this section began at 1 26 ma and was completed by 0 53 ma which differs from previous investigations based on orbitally tuned time scales the forcing mechanism for the mpt was more complicated than just the orbital forcing we conclude that the rapid uplift of the tibetan plateau may have played an important role in the shift of periodicities during the middle pleistocene

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

magnetism of loess palaeosol sequences recent developments abstract investigation of the global loess record primarily as a palaeoclimatic archive continues unabated one important aspect of this research effort is the determination of the magnetic properties of the loess itself and of the palaeosols developed within it in earlier work these have provided a record of major long term past climatic changes however recent studies are now revealing sub milankovitch signals with teleconnections from the chinese loess plateau clp to the greenland and antarctic ice caps as well as to climate related events in sediments recovered from the north atlantic these high resolution profiles cover to the last 130 000 years however progress is also being made in extending the record down below the loess sensu stricto of the clp into the so called red clay so that the aeolian record can now be carried back beyond 7 ma bp several authors have attempted to obtain quantitative estimates of palaeoprecipitation by comparing magnetic susceptibility of palaeosols with values for modern soils although the broad picture is qualitatively clear wetter interglacials dryer glacials the actual quantitative values provided by the various techniques differ significantly in the classic chinese sites palaeosols are always magnetically enhanced due to in situ pedogenic processes however evidence is now emerging to indicate that this is not the only magnetoclimatological model in cases such as siberia where wind vigour dominates over pedogenesis the opposite pattern is found with magnetic susceptibility minima in palaeosols this also occurs in situations where the sediments are water logged for significant amounts of time leading to gleying and concomitant loss of magnetic minerals the use of magnetic remanence as a geomagnetic polarity clock requires caution early interpretations were acceptable for establishing broad chronological control however recent scrutiny suggests that remanence lock in may be delayed by as much as 20 000 years furthermore synthetic magnetostratigraphies modelled on the basis of realistic sediment characteristics indicate that there are limits to the amount of geomagnetic detail likely to be resolved this seems to be the case for the blake event which manifests itself in a very variable way at different sites in the clp

enhancement mechanisms of magnetic susceptibility in the chinese red clay sequence 1 little is known about the mechanisms of magnetic susceptibility enhancement for the red clay sequence on the chinese loess plateau clp in comparison to the overlying loess paleosol sequence here we present a rock magnetic study of the red clay sediments from the central clp our results show that frequency dependence of fd lf hf where lf and hf are measured at 470 hz and 4700 hz respectively lf and susceptibility of anhysteretic remanent magnetization arm are linearly correlated within the red clay sequence this linear correlation indicates that the pedogenic magnetic minerals of the red clay have a rather uniform grain size distribution as in the loess paleosol sequence and the grain size is independent of the degree of pedogenesis nevertheless red clay sediments are slightly more enriched in superparamagnetic magnetic particles than the overlying loess paleosol sediments as indicated by the higher slope of the regression line between fd and lf

lead isotopes as a provenance tool for quartz examples from plutons and quartzite northeastern minnesota usa abstract the u pb isotope system in plutonic quartz samples approximates the crystallization age of the host granitoid and thus provides a useful provenance tool for detrital quartz grains we present lead isotopic data and u and pb concentrations of quartz from three late archean granitoids and from the early proterozoic pokegama quartzite all in northeastern minnesota lead in granitic quartz is considerably more radiogenic than in its associated whole rock host but it is similar or only slightly more thorogenic than its host pb pb ages obtained from quartz whole rock leached feldspar from the late archean granitic plutons are consistent with existing geochronology suggesting that the u pb system in quartz remained closed since crystallization u pb isotopic data for detrital clear quartz populations in the pokegama quartzite record late archean ages 2550 2650 consistent with a source from the superior province lead isotopic compositions of detrital k feldspar populations and lead and neodymium isotopic compositions of whole rocks samples from the pokegama quartzite also support a superior province source this study highlights the potential of the lead isotope system in detrital quartz k feldspar and whole rocks in provenance studies of sandstones

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

the record of changing hematite and goethite accumulation over the past 22 myr on the chinese loess plateau from magnetic measurements and diffuse reflectance spectroscopy 1 high field isothermal remanence hirm and diffuse reflectance spectroscopy drs wereusedto characterize hematite and goethite in a suite of bulkand particle sized fractioned samples from the chinese loess plateau representing the main changes in magnetic mineralogy over the past 22 myr the record of drs defined hematite largely reflects variations in the pedogenic fraction 8 mm makes the main contribution to goethite concentrations in the bulk samples pedogenic goethite concentrations generally vary inversely with those of hematite the lack of consistent correlations between hirm inferred mineral content and drs measurements casts doubt on the validity of using hirm to characterize the concentrations and relative proportions of hematite and goethite in sediments representing a long time span or a wide grain size distribution the progressive decline in the coercivity of the antiferromagnetic minerals in bulk samples throughout the whole period is mainly an expression of changes in the detrital fraction reflecting changes in the source region possibly involving increased aluminum substitution the good correlation between drs defined hematite and frequency dependent magnetic susceptibility in several chronologically defined subgroups of samples is consistent with the hypothesis that maghemite forms a transitional phase in a weathering sequence from ferrihydrite to hematite the results shed new light on using hirm to characterize hematite and goethite in sediments and on the history of weathering and climate change over the past 22 myr in the dust source regions and on the loess plateau

quantitative estimates of pedogenic ferromagnetic mineral formation in chinese loess and palaeoclimatic implications abstract the quasi continuously deposited loess sediments of the central chinese loess plateau constitute one of the most complete and long lasting records of quaternary palaeoclimate on land much of this record has been uncovered by measurement and interpretation of the magnetic properties of the loess the polarity of natural remanent magnetization has provided absolute age dates by correlation with the geomagnetic polarity time scale magnetic low field susceptibility has been used to reconstruct the cyclic changes of pleistocene palaeoclimates although the origin of the signal is still poorly understood from comparison with the 10 be concentration throughout the sequence we are able to determine the contributions to susceptibility from inherited and authigenic sources for the last 130 ky since the production of authigenic magnetite is directly related to regional precipitation annual palaeoprecipitation rates can be calculated palaeoprecipitation rates similar to present day rates are derived for oxygen isotope stage 5 including the last interglacial in contrast cold periods corresponding to oxygen isotope stages 2 and 4 experienced negligible precipitation the beginning and end of the time interval represented by oxygen isotope stage 3 however was characterized by short episodes when precipitation exceeded the holocene average

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

rock magnetism and geochemistry of two plio pleistocene chinese loess palaeosol sequences implications for quantitative palaeoprecipitation reconstruction abstract stratigraphic and spatial variations in the magnetic properties of chinese loess are widely accepted as reflecting changes in the intensity of soil forming processes over time and space recently several workers have used statistical correlations between the magnetic susceptibility and related parameters of modern loess plateau soils and modern climate to generate transfer functions to reconstruct past temporal and spatial trends in precipitation here we try to assess the viability of this approach by conducting magnetic and geochemical measurements of two long 2 5 my loess palaeosol sequences from different locations on the modern precipitation gradient across the loess plateau one site duanjiapo is located on the southern humid margin of the plateau and the other site luochuan is located in a drier modern environment some 160 km further north our results indicate discrepancies between magnetic and geochemical indicators of weathering and soil forming intensity and that any attempt to predict palaeoprecipitation at duanjiapo using published approaches would be significantly in error overall our results indicate a complex response of magnetic mineral transformations to climate including the production of both ferrimagnetic and antiferromagnetic minerals within the same climatic interval together with the destruction of magnetic material within some of the palaeosols therefore we suggest considerable caution should be exercised in generating quantitative climatic reconstructions from a single magnetic parameter

paleorainfall reconstructions from pedogenic magnetic susceptibility variations in the chinese loess and paleosols the rock magnetic properties of the chinese loess and paleosols constitute a unique and sensitive record of east asian paleoclimate through the quaternary period systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal which can be easily and rapidly measured at many sites across the loess plateau variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages as well as glaciations and interglaciations past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations the susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the loess plateau our rainfall reconstructions identify enhanced summer monsoonal activity in the chinese loess plateau region in the early holocene and the last interglaciation in the presently semiarid western area of the plateau annual precipitation in interglacial times was up to 80 higher than at present in the more humid southern and eastern areas values were up to 20 higher than today s levels during the last glaciation precipitation decreased across the entire plateau typically by 25 the relationship between pedogenic susceptibility climate and weathering age was examined over the northern hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate rather than soil age is the predominant factor that controls pedogenic susceptibility enhancement in loess soils

link between benthic oxygen isotopes and magnetic susceptibility in the red clay sequence on the chinese loess plateau 1 recent rock magnetic work on the red clay sequence on the chinese loess plateau clp convincingly demonstrates that the enhancement mechanisms of low frequency magnetic susceptibility i e measured at 470 hz lf in the red clay sequence are similar to those in the loess paleosol sequence therefore lf in the red clay sequence should indicate precipitation intensity received by the clp as is the case in the overlying loess paleosol sequence based on this result we compared lf in the red clay sequence with benthic oxygen isotope records we infer that the primary precipitation source on the clp varies over time in three phases during 8 1 4 5 ma the east asian summer monsoon dominates during 4 5 4 ma the polar westerlies dominate during 4 0 ma the east asian summer monsoon dominates we attribute these precipitation source shifts on the clp to the closure of the panama seaway around 4 5 ma and the tibetan uplift during the interval 4 2 6 ma

a new astronomical timescale for the loess deposits of northern china here we present a refined timescale for the entire sequence of quaternary chinese loess which relies upon the correlation of detailed monsoon records to the astronomical solution of laskar 1990 and the oceanic odp677 18o record of shackleton et al 1990 the chronological scheme considers in detail the relative structures of the palaeoclimatic and palaeomagnetic records to produce an accurate timescale that is consistent with the current understanding of loess depositional and post depositional processes analysis of this chronological framework demonstrates downward displacement of the palaeomagnetic horizons with respect to the climatic record

paleoclimatic significance of the mineral magnetic record of the chinese loess and paleosols the origins of the magnetic susceptibility variations of the chinese loess and paleosols are explored by scanning and transmission electron microscopy of magnetic extracts and by magnetic modeling of magnetic hysteresis data to provide quantified estimates of the major magnetic components microscopy identifies several distinct size and shape characteristics in the magnetic carriers lithogenic magnetites intact and abraded dominate the coarse grained magnetic fraction the smallest of the coarse grains is 2 i m the remaining magnetic materal is ultrafine in size with two types of magnetite particles present type a particles strongly resemble soil magnetites produced by inorganic precipitation type b particles which occur rarely are probably bacterial in origin quantitative modeling of these magnetic assemblages shows that over 90 of the susceptibility variations is accounted for by the superparamagnetic magnetite component compared to the loess units the paleosols are richer in magnetite particularly of superparamagnetic size and have a threefold higher ratio of magnetite to hematite we identify pedogenic formation of magnetite as the major contributor to the loess magnetic record matching this record against other paleoclimatic records we find an extremely high correlation with the standard 18o record the chinese loess sequences record a very high resolution magnetic stratigraphy directly related to changing climate

the environmental effects of the uplift of the qinghai xizang plateau the intense upheaval of the qinghai xizang plateau took place 2 ma bp the terraces of the yellow river in the lanzhou region and its upper sections provide a record of the uplift of the plateau the interaction of glaciation cycles resulting from climatic changes and pulsating tectonic upheavals are both involved in the record of environmental change across the plateau three tectonic climatic events which are termed respectively the qinghai xizang movement the huanghe yellow river movement and the gonghe movement occurred 2 1 5 1 0 and 0 15 ma bp the upheaval of the qinghai xizang plateau was the trigger mechanism of the asian monsoon the loess plateau was formed in the monsoon triangle of east asia human origins and human evolution may have been stimulated by the uplift of the qinghai xizang plateau

plio pleistocene climate evolution trends and transitions in glacial cycle dynamics abstract we describe the evolution of climate system dynamics by examining the climate response to changes in obliquity and precession over the last 5 3 myr in particular we examine changes in the shape of glacial cycles and the power of obliquity and precession response in benthic 18 o when the exponential trend in 18 o variance is removed its spectral power exhibits strong proportional responses to amplitude modulations in orbital forcing over most of the plio pleistocene precession responses correlate with modulations in forcing for the last 5 myr but 41 kyr response is sensitive to obliquity modulation only before 1 4 myr where responses are sensitive to modulations in forcing we demonstrate that glacial cycles are orbitally forced rather than being self sustained or paced by orbital changes the shapes of glacial cycles have several nonlinear properties which may be indicative of glacial interglacial differences in climate sensitivity or response time the saw tooth asymmetry of glacial cycles first appears shortly after the onset of major northern hemisphere glaciation and the relative duration of interglacial stages decreases at 1 4 myr collectively trends in the shape of glacial cycles and the sensitivity of 18 o to obliquity and precession are suggestive of major transitions in climate dynamics at approximately 2 5 and 1 4 myr but show no significant change associated with the appearance of strong 100 kyr cycles during the mid pleistocene transition

coupled 100 kyr cycles between 3 and 1 ma in terrestrial and marine paleoclimatic records earth s climate over the last one million years experienced several 100 kyr glacial cycles but no simple forcing mechanism has been identified numerous studies have tried to explain strong 100 kyr glacial cycles without recognizable forcing which has come to be known as the 100 kyr problem few studies have examined 100 kyr band paleoclimatic signals before 1 ma a recent study has demonstrated that benthic oxygen and carbon isotope records are phase locked and amplitude coupled at the 100 kyr band but that neither is phase locked to and amplitude coupled with the 100 kyr eccentricity signal between 3 and 1 ma this phasing and amplitude mismatch of the 100 kyr band between 3 and 1 ma between marine records and the eccentricity forcing signal has been called the late pliocene early pleistocene 100 kyr problem however it remains unknown whether terrestrial paleoclimate records are consistent with marine records at the 100 kyr band here i show that loess monsoon records from china are amplitude coupled with benthic oxygen and carbon isotope records at the 100 kyr band but not with the 100 kyr eccentricity forcing between 3 and 1 ma this observation provides further evidence in support of a free 100 kyr oscillation as the cause of the 100 kyr band amplitude variability in paleoclimatic records between 3 and 1 ma in contrast benthic oxygen isotope records and loess monsoon records at the 100 kyr band are not amplitude coupled with 100 kyr benthic carbon isotope records over the last 0 4 million years indicating that the late pleistocene 100 kyr climatic cycles may not result exclusively from a free oscillation

magnetoclimatology and paleoprecipitation evidence from a north south transect through the chinese loess plateau 1 magnetic measurements and grain size analyses are reported for eight sites along a 420 km north south transect across the chinese loess plateau with the goal of assessing the quantitative estimation of paleoprecipitation during the last interglacial oxygen isotope stage 5 130 kyr b p the climofunction of maher et al 1994 suggests that precipitation was generally elevated by about 150 mm yr over today s values but with the same north south gradient however in one area low precipitation values are found that suggest no significant increase

correlation between the magnetic susceptibility record of the chinese aeolian sequences and the marine benthic oxygen isotope record 1 it has been long known that the magnetic susceptibility record of the chinese loess correlates well with the marine benthic oxygen isotope record at the orbital bands during the last 0 8 ma suggesting that at the orbital scale the phasing and periodicity of the east asian summer monsoon easm are controlled by northern ice volume but not by northern summer insolation however during the interval 2 8 0 8 ma there is poor correlation between the easm record obtained from loess magnetic susceptibility and the global ice volume record obtained from marine benthic oxygen isotopes arguing against control of the phasing and periodicity of the easm by global ice volume here we show that during the interval 2 8 0 8 ma the magnetic susceptibility record of the chinese loess correlates well with the clipped and smoothed marine benthic oxygen isotope record from the eastern equatorial pacific ocean the data thus suggest that the orbital scale periodicity and phasing of the easm are controlled by northern ice sheets during the entire 2 8 ma not just the last 0 8 ma we have shown that tectonic events during the pliocene are the most plausible causes for the lack of correlation between the chinese red clay magnetic susceptibility record and the marine benthic oxygen isotope record during the interval 4 5 2 7 ma we have also shown that the correlation between chinese red clay magnetic susceptibility record and benthic oxygen isotope record between 6 and 4 5 ma is remarkable the work reported here is complementary to our previous work and indicate that the magnetic susceptibility record of the entire aeolian sequence on the chinese loess plateau can be correlated with the marine benthic oxygen isotope record

mechanism and effect of chemical weathering of sedimentary rocks the mineralogy geochemistry and physical and mechanical properties of rocks from four weathering profiles of miocene to pleistocene mudstones and sandstones in japan showed that chemical weathering of sedimentary rocks is characterized by sequential reaction between percolating groundwater and rock forming minerals pyrite a common mineral contained in sedimentary rocks is especially important in these sequential reactions pyrite is oxidized by oxygen coming from the ground surface and sulfuric acid is generated at the base of the oxidized zone the sulfuric acid in turn dissolves rock forming materials to make a dissolved zone if the fluxes of oxygen and water are in the same direction sulfuric acid generated at the oxidation front migrates farther and forms a dissolved zone if these fluxes are in opposite directions the oxidized and dissolved zones are not differentiated rocks in the dissolved zone are caused to deteriorate by the acid leaching and are acidic if buffering minerals such as calcite and zeolite are absent in the oxidized zone sandstone is strengthened because of cementation by iron oxide or hydroxide while mudstone is weakened because it has greater clay fractions and larger specific surface areas than sandstone

magnetostratigraphic dating of river terraces rapid and intermittent incision by the yellow river of the northeastern margin of the tibetan plateau during the quaternary up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of huang he the yellow river and daxia he in the linxia basin at the northeastern margin of the tibetan plateau the magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire quaternary it includes evidence for the jaramillo and olduvai normal polarity subchrons within the matuyama chron as well as the cobb mountain and stage 54 formerly gilsa events age constraints within the brunhes are provided by 14c and thermoluminescence optical stimulated luminescence dating the magnetostratigraphic chronology of the quaternary sediments indicates that terraces were formed at about 1 66 1 4 1 1 0 6 0 12 0 055 and 0 01 ma the terraces may represent climatically induced pauses in long term tectonically induced incision by the rivers on the basis of terrace heights and ages incision rates were highest from 1 66 to 1 4 ma 1 m kyr decreased from 1 4 to 0 12 ma 0 1 m kyr and increased from 0 12 ma to present 0 75 m kyr if river incision is attributed solely to uplift of the tibetan plateau then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of huang he in this area at about 1 75 ma however the effects of uplift cannot be fully separated from incision caused by changes in climate copyright 1997 by the american geophysical union

timing and structure of the mid pleistocene transition records from the loess deposits of northern china abstract the mid pleistocene transition mpt from obliquity to eccentricity forced climate variations has been extensively documented within the oceanic realm using a collection of orbitally tuned records of palaeoclimatic change from the loess sequences of northern china we have analysed terrestrial palaeomonsoon behaviour since 1 5 ma and characterised the structure of the mpt wavelet analysis of a stacked magnetic susceptibility record from the loess sequences indicates that the onset of 100 kyr cyclicity was synchronous in both global ice volume and the east asian monsoon system however analysis in the time domain reveals that during the mpt interim period the east asian winter monsoon appears to have weakened whilst global ice volume was increasing indicating that the palaeomonsoon was not the primary forcing mechanism responsible for driving the global climatic change

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

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

slaking behavior of clay bearing rocks during a one year exposure to natural climatic conditions abstract slaking of clay bearing rocks upon exposure to natural climatic conditions is a common problem at many engineering projects depending upon the regional climate clay bearing rocks slake in response to heating and cooling wetting and drying and freezing and thawing cycles however laboratory methods used for assessing the slaking behavior of clay bearing rocks including the standardized methods by the american society for testing and materials astm and the international society for rock mechanics isrm involve only wetting and drying treatments in this study we investigated the slaking behavior of clay bearing rocks by exposing them to natural climatic conditions for a period of one year twenty clay bearing rocks consisting of 5 claystones 5 mudstones 5 siltstones and 5 shales were selected for the study twelve replicate samples of each rock type were prepared so that each sample consisted of 10 pieces each piece weighing 40 60 g with a total weight of 450 to 550 g the samples were placed in separate metallic pans and exposed to natural climatic conditions from september 2009 to september 2010 each month one replicate sample of each rock type was removed from natural exposure and its grain size distribution was determined disintegration ratio d r defined as the ratio of the area under the grain size distribution curve of the slaked material for a given sample to the total area encompassing all grain size distributions was used to evaluate the extent of disintegration upon slaking d r can range from 0 to 1 with 0 indicating 100 slaking and 1 indicating no slaking after 3 months of exposure to natural climatic conditions claystones mudstones siltstones and shales exhibited d r values of 0 223 0 302 0 698 and 0 494 respectively these results suggest that over a given period of time claystones slake the most and siltstones the least relating d r to clay content of the rocks studied reveals that rocks with higher clay contents slake more rapidly and extensively under natural climatic conditions than those with lower clay contents

the mid pleistocene climate transition as documented in the deep south atlantic ocean initiation interim state and terminal event abstract the mid pleistocene transition mpt of the global climate system initiated by a shift towards much larger northern hemisphere ice shields at around 920 ka and ending with predominance of 100 kyr ice age cyclicity since about 640 ka is one of the fundamental enigmas in quaternary climate evolution climate proxy records not exclusively linked to global ice volume are necessary to advance understanding of the mpt here we present a high resolution pleistocene magnetic susceptibility time series of 12 sediment cores from the subtropical south atlantic essentially reflecting dissolution driven variations in carbonate accumulation controlled by changes in deep water circulation in addition to characteristics known from 18o records the data sets reveal three remarkable features intimately related to the mpt 1 an all pleistocene minimum of carbonate accumulation in the south atlantic at 920 ka 2 a mpt interim state of reduced carbonate deposition indicating that the mpt period may have been a discrete state of the pleistocene deep water circulation and climate system and 3 a terminal mpt event at around 540 530 ka documented in several peculiarities such as thick laminated layers of the giant diatom ethmodiscus rex

dating of erosion surface and terraces in the eastern qilian shan northwest china the actively deformed foreland of eastern qilian shan mountains contains well preserved geomorphic features such as erosion surfaces river terraces and tectonically uplifted alluvial fans providing suitable archives for research on regional tectonic activities and palaeoclimatic changes these geomorphic surfaces are well dated by using a combination of magnetostratigraphy electron spin resonance thermoluminescence infra red stimulated luminescence radiocarbon dating and correlation with the well established loess palaeosol sequences of china our results show that the erosion surface formed about 1 4 ma ago and the age of river terraces is 1 24 ma 820 860 ka 780 ka 420 440 ka 230 250 ka 140 ka 60 ka and 10 ka respectively valley incision rates of e 0 09 0 25 m ka 1 have been identified the repetitive stratigraphic and geomorphic pattern of these terraces indicates the fluvial sedimentation incision cycles are tightly associated with the 100 ka glacial interglacial climatic cycles copyright c 2006 john wiley sons ltd

re arrangement of atmospheric circulation at about 2 6 ma over northern china evidence from grain size records of loess palaeosol and red clay sequences abstract recent studies have shown that the red clay sequence underlying the quaternary loess of the chinese loess plateau is wind blown in origin continuous atmospheric dust deposition in the past 7 0 ma has been documented to address the wind system that transported the tertiary red clay two north south transects were studied in the chinese loess plateau one of the transects was designed to study spatial changes in grain size of the last glacial interglacial loess records and the other to observe particle changes of the tertiary red clay underlying the quaternary loess the loess transect consists of nine sections and the red clay transect of four sections analyses of closely spaced samples show that there is a strong southward decrease in grain size of both loess and palaeosol horizons of the late pleistocene which is consistent with the idea that the aeolian materials of the quaternary in the loess plateau are transported by the northerly winter monsoonal winds grain size distribution of the red clay sequences however does not show such a change from north to south along the red clay transect the particle size distribution is almost identical in the four sections suggesting that the winter monsoonal winds might have played a less important role in transporting the red clay material it is suggested that the red clay may have been transported by the westerlies from the dust source regions of northwestern china onto the loess plateau a remarkable re arrangement of atmospheric patterns at about 2 6 ma therefore has been recorded by the red clay loess shift it is speculated that this re arrangement of atmospheric patterns may have been caused by the onset of glaciation in the northern hemisphere

late cenozoic deformation and uplift of the ne tibetan plateau evidence from high resolution magnetostratigraphy of the guide basin qinghai province china the cenozoic intramontane gonghe guide basin in qinghai province china is tectonically controlled by the sinistral strike slip framework of the kunlun and altyn tagh south qilian faults in the northeastern tibetan plateau the basin is filled with thick cenozoic clastic sedimentary formations which provide important evidence of the deformation of this part of the plateau although they have long lacked good age constraints detailed magnetostratigraphic and paleontologic investigations of five sections in the guide basin and their lithologic and sedimentary characteristics allow us to divide a formerly undifferentiated unit the guide group into six formations where ages are now magnetostratigraphically well established they are given in parentheses the amigang 1 8 2 6 ma ganjia 2 6 3 6 ma and herjia formations 3 6 to ca 7 0 7 8 ma and the older miocene ashigong garang and guidemen formations these rocks document a generally upward coarsening sequence characterized by increasing accumulation rates increasing gravel content and sizes of its components changes of bedding dips and source rock types and marginal growth faults collectively reflect accelerated deformation and uplift of the ne tibetan plateau after 8 ma punctuated by a sharp increase in sedimentation rate at ca 3 2 ma that reflects the boulder conglomerates of the ganjia formation interestingly much of the vergence of the compressional deformation in the basin is to the south accommodated by a sequence of six thrusts f1 f6 which become active one by one progressively later toward the south undoubtedly contributing to the uplift of this part of the plateau f1 likely initiated the guide basin due to crustal flexure in the oligocene f2 was active in the early miocene f4 and f5 at ca 3 6 ma and f6 was active in the early pleistocene the detailed late miocene and younger magnetostratigraphy allows us to place much improved time constraints on the deformation and hence uplift of northeastern tibet which when compared with ages for events on other parts of the plateau provides important boundary conditions for the geodynamical evolution of tibet

astronomical calibration of loess paleosol deposits at luochuan central chinese loess plateau abstract the 140 m loess paleosol profile at luochuan in the central chinese loess plateau was sampled at 5 cm intervals in loess units and at 3 cm in paleosol units in order to obtain a high resolution climatic record covering the past 2 5 million years all samples were measured for magnetic susceptibility which is regarded as a good proxy index of the east asian summer monsoon strength on the basis of the astronomical theory of pleistocene climatic change an age model of the luochuan loess paleosol sequence was developed by tuning the magnetic susceptibility record to time series of insolation changes the results show that the ages of the boundaries between the malan and lishi and lishi and wucheng loess formations are 71 and 1320 kyr bp respectively the onset of loess accumulation is at 2470 kyr bp our age model was tested by comparing the orbitally derived ages with absolute age determinations of magnetic reversals and cross spectrum analyzing with solar radiation variations for summer at 65 n these indicate that the calibration provides a reliable time scale for the luochuan loess paleosol deposit

late neogene rock magnetic record of climatic variation from chinese eolian sediments related to uplift of the tibetan plateau abstract the late cenozoic red clay loess sequence in the chinese loess plateau provides a high resolution record of paleoclimatic and tectonic changes related to the phased uplift of the tibetan plateau detailed magnetostratigraphy of a recently recovered 125 m thick sediment sequence from the central chinese loess plateau shows that the red clay began to accumulate at ca 8 1 ma implying a marked drying in the interior of asian as well as the initial establishment of the east asian paleomonsoon regime prior to 3 8 ma the ferromagnetic mineral concentrations as revealed by both magnetic susceptibility and s ratios exhibit a cyclic pattern superimposed upon a linear trend this pattern collapsed immediately after 3 8 ma suggesting a change in source area this in turn may have resulted from the reorganization of atmospheric circulation and the onset of the modern asian monsoon probably associated with the accelerated uplift of the tibetan plateau to a certain threshold elevation

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

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

the effects of weathering on the physical and mechanical properties of a granitic saprolite less research has been carried out on the changes induced by weathering to the mechanical properties of reconstituted and intact soils that originate from chemical decomposition of rocks saprolite

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

mineral magnetic variation of the jiaodao chinese loess paleosol sequence and its bearing on long term climatic variability 1 to retrieve reliable long term paleoclimatic signals from the chinese loess paleosol sequences deposited over the past 2 6 myr multiparameter mineral magnetic investigations have been conducted on the jiaodao section on the chinese central loess plateau first the lithogenic magnetic components and the pedogenic overprinting were chemically separated by the citrate bicarbonate dithionite cbd method the magnetic properties of the least pedogenically altered loess units and post cbd loess paleosols are dominated by coarse grained lithogenic magnetite increasing degree of pedogenesis increases both the concentration and grain size of pedogenic magnetite maghemite long term changes of the pre cbd magnetic properties suggest a long term decrease in summer monsoon intensity and a long term increase in winter monsoon intensity from the late pliocene to the late pleistocene long term variations of the post cbd magnetic properties suggest an increase in both concentration and grain size of coarse grained lithogenic psd md magnetite grains and hence indicate a long term increase in winter monsoon intensity over that period the coercivity decrease of the lithogenic component for the loess unit l15 may be related to the accelerated uplift of the tibetan plateau and its adjacent regions during the period of l15 deposition from paleosol s5 to loess l1 higher values of coercivity of the lithogenic component occur in typical loess and paleosols and lower values are found at the loess paleosol transition these coercivity variations are thought to be related to significant changes in the source region as well as dust deposition in the loess plateau caused by changes in ice snow or vegetational cover these new results lead to a better understanding of the relationships between the effects of tectonic paleoclimatic and paleoenvironmental processes in northwestern china

stratigraphic evidence for the uplift of the tibetan plateau between 1 1 and 0 9 myr ago uplift of the tibetan plateau is manifest not only in widespread denudation but also by an increased deposition rate of sediment near or far from the exhumed regions our results indicate that the mass accumulation rate mar of eolian dust increased between 1 1 and 0 9 myr ago we associate this increase in mar and median grain size with uplift of the tibetan plateau and its adjacent regions during this period this middle pleistocene uplift can also be evidenced by the age of volcanism in the marginal region the existence of thick conglomerate deposits surrounding the uplifted plateau and the increased sedimentation rate of lacustrine deposits in the qaidam basin northeastern tibetan plateau between 1 1 and 0 9 myr ago the correlation between the loess and marine records indicates that after 0 9 myr ago these two records correlate well this good correlation probably suggest that the middle pleistocene upheaval event not only brought the plateau into the cryosphere but also enhanced the coupling of regional scale chinese loess transportation and deposition to the global ice volume variations through its effects on glacial grinding rock denudation and east asian monsoonal circulation

an astronomically tuned 8 1 ma eolian record from the chinese loess plateau and its implication on the evolution of asian monsoon the chinese loess paleosol sequences have led to a great understanding of the evolution of the east asian monsoon eam in the quaternary however evolution of the eam in the late miocene and pliocene is quite blurry hindering our understanding of the mechanisms driving the eam thus we obtained high resolution grain size records of 8 1 ma from the thickest eolian red clay sequence at chaona on the chinese central loess plateau and astronomically tuned the grain size records to the orbital variation with a time resolution of 1 5 ka to 5 8 ka the variability of coarse size fraction a recognized proxy for the east asian winter monsoon eawm indicates a persistent but stepwise intensification of the eawm at ca 5 5 ma 3 6 ma 2 6 ma and 1 ma filtering of this proxy record at 100 41 and 21 ka bands was conducted to trace the evolution of the eawm in a frequency domain over 8 1 ma temporal variations of these three cycles show a remarkable simultaneous enhancement at ca 5 5 ma indicating a synchronous intensification of high and low latitude signals in the eawm record we suggest that the closure of panama seaway to form the north atlantic thermohaline circulation and the high latitude cooling during this time might collectively trigger such a response copyright 2011 by the american geophysical union

palaeoclimatic and sedimentary history from magnetic susceptibility of loess in china the magnetostratigraphic age of the oldest loess sediments in the central chinese loess plateau investigated so far has recently been placed at ca 2 4 million years b p thus glaciations in central asia which are believed to provide the detritus for the formation of chinese loess commenced at the same time as the first ice rafted debris sank into the ocean basins of the northern hemisphere shackleton et al 1984 lithologic palaeontologic geochemical and especially rock magnetic variations throughout the loess column are indicative of palaeoclimatic fluctuations during loess deposition the variations of magnetic low field susceptibility in loess closely resemble those of the marine oxygen isotope record shackleton and opdyke 1976 and establish for the first time a continuous record of the pleistocene glacial and interglacial stages in a continental section spectral analysis of the rock magnetic time series indicates slow apparent sedimentation during interglacial periods which are characterized mainly by calcium dissolution and related compaction of the soils variable aeolic sediment influx as well as erosion and or polygenetic soil formation may also strongly influence the sedimentary history

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

modelling northern hemisphere ice volume over the last 3 ma the northern hemisphere ice sheet volumes over the last 3 ma were simulated using the lln 2 d model the forcings were both insolation and co2 concentration different atmospheric co2 scenarios were used because of a lack of co2 reconstruction over this remote past with constant co2 concentrations the simulated ice volume does not show any gradual increase as recorded in the marine sediments moreover its spectrum changes according to the chosen value of co2 when co2 is fixed at 220 ppmv the simulated ice volume is dominated by the similar to 100 ka period if a pre industrial co2 concentration of 280 ppmv is used the simulation is dominated by the similar to 41 ka period by using a linearly decreasing co2 concentration going from 320 ppmv at 3 ma bp to 200 ppmv at present the simulated changes in the power spectrum are in agreement with those obtained from the sedimentary records roughly before 1 ma bp the dominating period is similar to 41 ka afterwards the similar to 100 ka period becomes dominant this transition is accompanied by a gradual increase of the ice volume potential mechanisms for this transition are discussed using cyclic co2 fluctuations over the last 0 6 ma does not change significantly the spectral characteristics of the simulated ice volume but amplifies the amplitude of its variations c 1998 elsevier science ltd all rights reserved

a new osl chronology for dust accumulation in the last 130 000 yr for the chinese loess plateau abstract a sensitivity corrected multiple aliquot regenerative dose protocol has been developed for fine grained quartz osl dating of chinese loess its reliability has been assessed on the basis of the methodology and by dating reference samples of known age close to the transition from the last interglacial paleosol s 1 to the last glacial loess l 1 which corresponds to the marine oxygen isotope stage mis 5 4 transition on the basis of the fine grained quartz osl age estimates for 33 loess samples from the upper part of the luochuan profile a detailed chronostratigraphy of continuous dust accumulation in the past 130 ka has been proposed changes in the accumulation rate occurred during the last glacial period mis 4 to mis 2 unexpectedly high accumulation rates were found in the weakly developed l 1 2 s paleosol of the last interstadial mis 3 rather than in the classic l 1 1 and l 1 3 loess of the cold dry glacial condition mis 2 and 4 the osl ages show some disagreement with the previous numerical chronology for the loess paleosol sequence based on correlation of variations in grain size with sedimentation rate the latter method resulted in an almost constant accumulation rate from 72 to 12 ka

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

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

the mid pleistocene climate transition onset of 100 ka cycle lags ice volume build up by 280 ka the mid pleistocene climate transition mpt is the complex climatic change which brought the late pleistocene ice ages we explore the mpt in the time and frequency domains by new methods of time series analysis high resolution oxygen isotope records reveal that the ice volume related increase in 18o mean amplitude 0 29 0 05 1 transition midpoint 922 12 ka duration 40 9 ka significantly preceded the abrupt increase in the amplitude of the 100 ka cycle at 641 9 ka this finding can be quantitatively simulated using a simple ice bedrock model in which due to the additional ice the calving threshold is exceeded the simulated calving events prior to 650 ka are separated by 77 ka whereas after 650 ka they occur pseudo periodically with a mean period of nearly 100 ka the cause for the delay of the 100 ka calving cycle was not a slow bedrock relaxation rather the coincidental combination of insolation existing ice mass and bedrock depression