climate instability during the last interglacial period recorded in the grip ice core isotope and chemical analyses of the grip ice core from summit central greenland reveal that climate in greenland during the last interglacial period was characterized by a series of severe cold periods which began extremely rapidly and lasted from decades to centuries as the last interglacial seems to have been slightly warmer than the present one its unstable climate raises questions about the effects of future global warming

east asian monsoon variations during oxygen isotope stage 5 evidence from the northwestern margin of the chinese loess plateau abstract we present the results of high resolution multi proxy climate studies of the s1 palaeosol corresponding to oxygen isotope stage ois 5 from the northwestern margin of the chinese loess plateau area here s1 is much thicker ca 6 8 m than in the central loess plateau areas ca 2 m where most previous studies have been conducted hence much higher resolution stratigraphic studies are possible yielding more insight into the temporal variations of the east asian monsoon during mis 5 the frequency dependent magnetic susceptibility as well as the concentration of secondary carbonate is used as an indicator of the summer monsoon intensity and the median particle size as an indicator of the winter monsoon intensity the results suggest that the northwestern margin of the chinese loess plateau experienced the strongest summer monsoon intensity in sub stage oiss 5e and the weakest in oiss 5a among the three warmer periods during stage 5 the summer monsoon was weaker in oiss 5b than in oiss 5d a dusty interval interrupted the second warmer period 5c and a soil forming event interrupted the first colder period 5d the results also suggest that the directions of changes in the intensities of summer and winter monsoons may not always have been proportionately opposite for example the weakest summer monsoon occurred in oiss 5a during which the winter monsoon was not the strongest we further conclude that the winter monsoon during the last interglacial was probably driven by global ice volume fluctuations while the summer monsoon was primarily controlled by the northern hemisphere solar insolation and was probably modified by a feedback mechanism that is the climatic buffering effect of low latitudinal oceans may have distorted the response of the summer monsoon to insolation variations finally our results do not show the degree of climatic instability comparable to that recorded in the grip ice core for the last interglacial oiss 5e even though the study area is situated in a region which has been sensitive to climatic changes

soil geomorphic research a selective overview abstract much soil geomorphologic research involves tracking the development of soils with time otherwise known as soil chronosequences most of these have been undertaken on landforms underlain by quaternary depsits of varying ages in general there is a predictable variation in both soil horizon sequence and amounts of constituents such as clay fe and caco 3 with time the rate at which these constituents accumulate in the soil is a function of parent material bioclimate and atmospheric dust influx and because of the latter soils in aridic regions can form at rapid rates profile properties can be used to estimate the ages of deposits and faulting events but the error on the estimated age can be 50 or greater the position of salt accumulations in soil profiles is one of the best indications of climatic change and these can be modelled to compare with various climatic parameters present and past profile characteristics due to pedogenic thresholds however can mimic those due to climatic change so close dating is necessary to differentiate the effects of both soil geomorphic data are essential to understand the origin of ancient paleosols in the sedimentary rock records but a major problem still is one of recognition of these features as soils and to separate the effects of pedogenesis from those of diagenesis

chronological discord between the last interglacial paleosol s1 and its parent material in the chinese loess plateau abstract an and porter geology 25 1997 603 reported six high dust influx events of millennial timescales recovered from the last interglacial paleosol s1 and correlated them to six cool events of millennial timescale in the north atlantic however the complexity of soil forming processes may have made the chronological correlation with the north atlantic records inadequate to examine the complexity of the s1 formation the s1 paleosol was traced laterally and identified based on the preserved characteristics observed in the field and analyzed in the laboratory our data show that from the northwest to the southeast the s1 paleosol gradually converges from three distinctive soil profiles into a single welded profile because the net rate of loess accumulation was attenuated to the southeast and pedogenic development intensified southeastward during the last interglacial three soil forming events within the s1 paleosol s1s1 s1s2 and s1s3 separated by two loess units s1l1 and s1l2 in the northwestern part of the loess plateau are stratigraphically coeval with a single soil profile in the southeastern margin of the loess plateau in the southeast the s1 paleosol developed into underlying older loess l2 e g at the lantian section the three paleosols s1s1 s1s2 and s1s3 are partially welded in the central part of the chinese loess plateau e g at the tianshui section where the lower portion of s1 paleosol developed in the underlying older loess unit l2 in the northwestern margin of the chinese loess plateau e g at the lanzhou section the preservation of the repeating soil loess sequence s1s1 s1l1 s1s2 s1l2 and s1s3 continuously documented the climatic events of the last interglacial our data also show that the magnetic signatures and particle size information are more or less acceptable climatic proxies only for the northwestern sections where the degree of pedogenesis was lower and the rate of eolian influx was greater during the last interglacial it appears that in all cases investigated the median grain size and the coarse fraction 63 m content define the upper and lower boundaries of the s1 paleosol reasonably well and can be used to estimate the time transgressive nature of the s1 paleosol relative to its parent material soil welding bioturbation and material translocation within the s1 soil profiles make it impossible to preserve the detailed and high resolution information of climate changes in those s1 profiles in the southeastern part including the popularly called central part of the chinese loess plateau

the depositional architecture and facies variability of shelf deltas in the eocene battfjellet formation nathorst land spitsbergen deltas are commonly classified according to their plan view morphology as either river dominated tide dominated or wave dominated however most deltas form under the mixed influence of these processes commonly with laterally varying process regimes it has also become clear that there is a mismatch between the plan view morphology and internal facies composition in some deltas combined outcrop and subsurface data from the eocene battfjellet formation spitsbergen provide an example of ancient shelf deltas that formed under mixed influence internally these shelf deltas are characterized by wave dominated facies that are normally associated with strike extensive nearly linear shoreline sandstones however the formation comprises partially overlapping sandstone bodies of limited lateral extent 20 km in any direction this stacking pattern is attributed to frequent autogenic lobe switching that caused localized and rapid transgressions such processes typify fluvial dominated deltas and occur less commonly in wave dominated ones thus there is an apparent mismatch between inferred plan view morphology and internal facies composition it is argued that the battfjellet deltas were flood dominated and prograded mainly during periods of high fluvial discharge however reworking of the fluvial flood facies by fair weather and storm waves as well as longshore currents resulted in a wave dominated facies character delta lobes undergoing auto retreat were particularly prone to reworking by basinal processes including tidal currents it is suggested that repeated delta progradation from inner shelf settings towards the outer shelf and shelf edge was aided by high sediment supply rather than relative falls in sea level as previously suggested this interpretation is supported by i the lack of major facies dislocations and extensive sub aerial unconformities and ii an overall relative rise in sea level as evidenced by an overall low angle 0 8 to 1 2 ascending shoreline trajectory the latter results from the combined effect of basin subsidence eustatic highstand and sediment compaction

paleosols and the effects of alteration abstract alteration of paleosols following development and burial is common chemical physical and mechanical processes can weld younger to older soil profiles and affect the accumulation dissolution and reprecipitation of mineral material in soils soil properties most affected include texture and porosity and the content and distribution of soluble salts amorphous silica gypsum carbonate and clay organic matter retention is highly dependent on post burial biologically controlled oxidation reduction and ph conditions processes such as erosion and deposition can truncate profiles or bury them either rapidly or extremely slowly effects of these and other processes on soil properties must be examined with care in paleosols that have been buried even for a short interval this study presents several examples of soil properties which should be evaluated carefully and possibly avoided as indicators in paleoenvironmental reconstruction paleosol classification and regional stratigraphic correlation

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

comparison of soils in midwestern united states and western europe with the interglacial record abstract paleosols that formed primarily before the last glaciation cannot be adequately explained by a model of holocene like interglacial periods of about 10 000 yr in length which has been inferred from the marine 18 o 16 o record geological and palynological evidence from terrestrial midlatitude sites suggests that temperate conditions conducive to soil formation existed for periods greatly in excess of 10 000 yr during the middle and late pleistocene available data on soils formed during this interval from western europe and midwestern united states are best explained by relatively long interglaciations or the development of composite soils over a number of temperate periods climatic contrasts between the interglaciations appear to have been overemphasized widespread assumptions regarding greater warmth in interglaciations prior to the present one are generally unproven in the absence of precise dating progress in relating paleosols to fragmentary local records of quaternary climatic changes will be achieved by detailed analytical techniques such as soil micromorphology

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

distribution and genesis of calcitic pedofeatures within a rapidly aggrading loess paleosol sequence in china abstract the distribution of calcitic pedofeatures within part of a buried paleosol complex on gaolanshan mountain near lanzhou in the western semi arid part of the loess plateau of china is interpreted in terms of a pedosedimentary model controlled by changes in dominance of regional climatic monsoonal forces during periods of moderate loess accumulation rates and moisture availability accretionary pedogenesis was characterised by localised dissolution and redistribution of calcite and development of compound calcitic depletion concentration pedofeatures these took one of two forms i equigranular hypidiotopic calcitic coatings or infillings 100 350 m and calcitic depletion hypocoatings the reconstruction provides the basis for explaining the ubiquitous occurrence of high concentrations of sand size grains and nodules of calcite within weakly leached horizons of other paleosols in the western part of the loess plateau of china their presence reflects not only the influence of semi arid conditions prevailing during the main stable soil forming intervals but also preceding drier periods of accretionary pedogenesis associated with transitional changes in relative dominance of dry northwesterly winter monsoons responsible for the transport of the dust to that of moist southwesterly and southeasterly monsoons the study emphasises the general need for a pedosedimentary approach when attempting to interpret loess paleosol sequences

paleosol classification problems and solutions abstract paleosols are soils that formed on landscapes of the geologic past three kinds exist buried exhumed and relict to help reconstruct paleoenvironments and for ease of comparison we suggest a property based classification system linked to genetic processes we use enduring properties because alteration of paleosols following burial is common morphological properties such as horizonation soil fabric root and worm casts and redoximorphic features are resistant to alteration and thus are valuable as criteria field observable and micromorphological properties degree of weathering and proportion of resistant minerals are also useful as criteria for paleosol orders total chemical analysis provides a proxy measure for base saturation and clay mineralogy we use proxy criteria to help classify paleosols that have changed markedly or have been lithified during or after burial to an earlier version of the system we add two new orders and include buried relict lithified and exhumed units at the suborder level our system clearly separates paleosol taxon names from those of all ground soils we use the prescript paleo at the order level and kryptic to designate the buried enduric to designate the relict lithic to designate the lithified and emergent to designate the exhumed paleosol suborders we use prescript modifiers to describe the physical characteristics of the paleosols and postscripts for parent material origin and the extensiveness of the paleosol landscape we present data and classify a number of paleosols as examples of the system

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

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

late quaternary dust flow on the chinese loess plateau abstract the dust flux of over 25 g cm2 103yr was reached in the central part of the chinese loess plateau during the last glacial maximum this is more than three times higher than during the last interglacial and early glacial time the grain size of the pleniglacial dust reached a peak shortly after 20 000 years ago and testifies to the occurrence of strong winds and frequent dust storms

pedogenesis and paleoclimate interpretation of the magnetic susceptibility record of chinese loess paleosol sequences in the chinese loess paleosol sequences from luochuan haanxi province china variations in the magnetic susceptibility have been accepted as an excellent proxy for paleoclimate and the standard interpretation is that climatic processes have enhanced the magnetic susceptibility of the paleosols beyond the base line level of the loess by using mineral magnetic properties and a soil chemistry extraction procedure we show that most of the magnetic susceptibility signal in both the paleosols and the loess is due to pedogenesis in effect loess deposition and pedogenesis are competing processes at all times and the presence of a paleosol simply indicates that the latter process was predominant these results imply that any interpretation of the paleoclimate record of loess paleosol sequences must recognize the pedogenic nature of the magnetic susceptibility signal and that the focus of future research must be on the critical role of climate in the development of the paleosols

soil climate system across the prairies in midwestern u s a abstract among mollisols across the prairie plains from eastern iowa to western kansas coincident systems of loess stratigraphy and sedimentology climate and soils are separated at 96 to 97 w longitude to the east udolls are formed peopeoria loess that dates back 14 000 radiocarbon years and are currently in a subhumid climate to the west ustrols are cormed in bignell loess that dates back to

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

climatic signals from loess soil sequences in the central great plains usa abstract late quaternary eolian deposits and buried soils in the central great plains are interpreted to reflect the fluctuation of climatic conditions under which they formed the loveland loess was deposited approximately between 500 and 100 ka within the loess are four zones of pedogenic carbonate accumulation after 416 35 ka before 260 25 ka around 193 22 ka and before 92 7 0 ka the pedogenic carbonate zones were probably formed under warm and dry conditions the moderately weathered barton sand at the barton section and the equivalent sandy silt ii at other sections deposited between 92 7 0 and 69 6 4 ka suggest windy probably warm and fluctuating moisture consitions a reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very low rate of loess deposition overlying the reddish pedocomplex is the sandy silt i probably a stratigraphic equivalent to the roxana silt dated at 40 30 ka in the central lowlands the gilman canyon formation 35 20 ka a thick cumulic loessial and organic matter rich pedocomplex developed under relatively moist and probably cool conditions the peoria loess was deposited at a very rapid rate under dry and cold conditions the brady soil 10 5 8 5 ka was formed under relatively warm and moist conditions the poorly weathered bignell loess was deposited during the warm and dry altithermal period 9 5 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

micromorphology and genesis of paleosols in the luochuan loess section china pedostratigraphic and environmental implications the loess paleosol sequence in the well known potou section near luochuan covers the entire pleistocene back to 2 5 ma in a much more complete sequence than any known from europe or north america to deduce a record of the pleistocene climatic history an understanding of the genesis of the paleosols is important main diagnostic features normally observable in surface soils have disappeared in the case of fossil soils therefore micromorphology is of outstanding importance because it enables the reconstruction of original properties and polygenetic soil development especially in pedocomplexes the upper part of the loess paleosol sequence can well be compared with the 18o record shown in the specmap curve of the brunhes epoch although the sequence of paleosols shows partly an even more detailed record of cold and warm stages and allows more specific informations regarding the paleoclimate of the interglacial periods cf fig 2 the last four paleosols represented by the s1 pedocomplex the upper part of the s2 and the s3 are genetically well comparable with the natural holocene soil indicating a similar climate with a tall grass steppe vegetation the s6 is a steppe soil also whereas the five soils of the s4 the s5 complex and the s7 are forest soils indicating more moist and partly warmer interglaciations than the holocene the loess paleosol sequence of the matuyama epoch seems to give more paleoclimatic informations than the deep sea cores known so far the lishi loess below the b m boundary down to 84 m in the section contains two more soils s11 and s13 which are developed under steppe vegetation in interglaciations similar to the present one and four forest soils the s8 complex the upper soil of the s9 and the s10 indicating again more moist interglaciations than the holocene most of the numerous soils in the wusheng loess are probably formed synsedimentarily as alternation of soil formation and addition of loess the red clay at the basis consists of four intensively developed but truncated paleosols the parent material of at least the lower part must be regarded as pliocene loess