environmental conditions for the presence of magnetofossils in the last glacial maximum inferred from magnetic parameters of sediments from the ulleung basin east sea abstract magnetic characterization of sediments from the ulleung basin in the east sea japan sea was carried out to decipher changes in environmental conditions over the last 39 000 years magnetic susceptibility intensities of natural remanent magnetization nrm anhysteretic remanent magnetization arm partial arm parm and saturation isothermal remanent magnetization sirm were measured for selected samples irm acquisition hysteresis and first order reversal curve forc measurements were made the ratios of rock magnetic parameters such as arm sirm arm and s ratio were determined to identify magnetic grain size and mineralogical variations along with electron microscope observations of magnetic mineral extracts down core variations in rock magnetic parameters for the 5 21 m long sediment core reveal distinct intervals with different grain size concentration and composition of magnetic minerals the uppermost portion and the high magnetic intensity zone hiz in marine isotope stage mis 2 are characterized by higher concentrations of fine grained magnetite whereas the mis 1 and 3 intervals contain lower concentrations of coarser grained magnetic minerals with increasing influence of hematite and or iron sulphide minerals the hiz interval is inferred to contain high occurrences of fine grained bacterial magnetosomes based on geochemical proxies east sea conditions for the hiz interval coincident with the last glacial maximum lgm can be summarized as having low total organic carbon toc enhanced eolian contributions from terrestrial organic particles and iron bearing minerals under the influence of an intensified east asian winter monsoon along with iron reducing but not sulphidic conditions that favoured growth and preservation of magnetotactic bacteria the delicate balance between reductive dissolution of magnetofossils under sulphidic conditions and production and preservation of magnetotactic bacteria in overlying iron reducing sediments for the hiz interval is responsible for the resultant abundance variations of magnetosomes in the studied sediments

sand dunes as a major proximal dust source for late pleistocene loess in the negev desert israel grain size analyses of three hilltop primary eolian loess sequences in the negev desert southern israel show a bimodal grain size distribution at 50 60 m and 3 8 m using analyses of mineralogy and osl ages we demonstrate that the coarse mode is composed mostly of quartz grains and its relative magnitude increases regionally with time suggesting an enhancement of a time transgressive proximal dust source compared to a distal saharan fine grain dust the only proximal dust source for large amount of coarse silt quartz grains is the sands that advanced into sinai and the negev concurrently with the loess accretion during the late pleistocene as a result of the exposure of the mediterranean shelf we therefore propose that the coarse silt quartz grains were formed through eolian abrasion within the margins of an advancing sand sea this relationship between desert sand seas as a source for proximal coarse dust and desert margin loess deposits can be applicable to other worldwide deserts such as northern africa china and australia

variation of rb sr ratios in the loess paleosol sequences of central china during the last 130 000 years and their implications for monsoon paleoclimatology abstract rb sr and magnetic susceptibility have been measured in the last interglacial glacial loess profiles at luochuan and huanxian central china a high degree of similarity between the parameters in both profiles suggests that variations of rb sr ratios in the sequence can be regarded as an indicator of east asian summer monsoon strength matching the rb sr record with the specmap 18o curve suggests that the rb sr ratio responds sensitively to changes of the east asian monsoon induced by global ice volume variation

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

cyclic quaternary alluviation and terracing in a nonglaciated drainage basin on the north flank of the qinling shan central china abstract pleistocene alluvial terraces of the nonglaciated ba river drainage basin on the north flank of the qinling shan are capped by a succession of loess units and paleosols that correlate with the standard marine isotope chronology and are used to date the subjacent alluvial gravels alluvial fills were deposited during isotope stages 2 6 8 12 and 16 whereas terracing occurred during interglacial stages 1 5 7 11 and 15 the apparent absence of terraces dating to stage 14 and stage 4 may be due to the lesser intensity of these glaciations compared to that of stage 2 although disruption of the alluvial regime by local tectonism is a likely alternative for the lack of a stage 4 terrace a stage 10 terrace was not positively identified from available exposures its possible absence could be related to post stage 12 uplift aggradational episodes correlate with glaciations and loess deposition whereas degradational episodes correlate with interglaciations or interstades and soil formation implying that climate is the primary control on quaternary paleohydrology this in turn points to variations in the earth s orbital geometry as the major factor that modulates both climate and ultimately the fluvial system in the qinling shan in this region glaciations were dominated by a cold dry winter monsoon climate whereas during interstades and interglaciations a warmer and wetter climate prevailed implying strengthening of the summer monsoon both the loess paleosol and the alluvial records are consistent with climate model simulations spanning the last 18 000 yr that show a change from cold dry conditions during the last glacial maximum to a climate warmer and wetter than present during the first half of the holocene

did an extensive forest ever develop on the chinese loess plateau during the past 130 ka a test using soil carbon isotopic signatures abstract pleistocene vegetation history on the chinese loess plateau has been traditionally investigated using palynological methods and questions remain regarding whether an extensive broadleaf deciduous forest ever developed on the loess table under favorable climatic conditions the authors have employed a c isotope approach to address this question by comparing 13 c values in soil organic matter from different loess ecological domains with known source vegetation to the c isotope values obtained from a paleosol section that can be dated back to 130 ka the c isotopic compositions of modern soils from the loess table and the loess desert transition gave 13 c values of 24 5 to 18 2 and 25 7 to 20 7 respectively these c isotopic ratios are consistent with the standing modern vegetation that is dominated by a mixture of c 3 and c 4 plants and can be distinguished from that in the patchy forest areas where exclusive c 3 trees yield a narrow 13 c value range from 26 9 to 25 average 26 1 obtained 13 c compositions from paleosols and loess sediments in the lantian and the luochuan profiles vary from 24 to 16 9 indicating a grass dominated steppe with shifting c 3 and c 4 contributions controlled mainly by paleoclimatic changes during the late pleistocene the present results suggest no extensive forest coverage on the loess table during the past 130 ka even under the most suitable conditions for forest development this conclusion supports the explanation of natural causes for the development of only patchy forests on the modern loess table and provides critical historical information toward the vegetation restoration project that is currently underway on the chinese loess plateau

estimation of aeolian dust flux on cheju island korea during the mid to late holocene abstract aeolian dust flux was estimated from a maar sediment with bimodal grain size distribution on cheju island korea during the mid to late holocene the bimodal grain size distributions of chemically isolated aeolian quartz and lithogenic minerals were partitioned into fine and coarse components by a weibull function fitting method and fine and coarse aeolian dust fluxes were estimated estimates of coarse dust flux ecdf during the last 6500 years varied from 2 to 14 mg cm 2 yr and averaged 7 mg cm 2 yr ecdf were low during the period 6500 4000 cal yr bp increased from 4000 to 2000 cal yr bp and decreased again from 2000 to 1000 cal yr bp indicating a millennial scale variation the estimates of fine dust flux efdf varied from 1 to 11 mg cm 2 yr with an average of 3 mg cm 2 yr the variation of efdf was characterized by centennial scale fluctuations these results demonstrate that aeolian dust sediments in downwind areas including korea and japan were a mixture of fine and coarse dust components transported by the westerlies and winter monsoon surface winds respectively this suggests that these aeolian dust sediments should be interpreted in view of two dust components and two transporting winds

hydrographic variability in the northern south china sea over the past 45 000 years new insights based on temperature reconstructions by uk 37 and texh86 proxies from a marine sediment core md972146 abstract millennial scale climate variability was persistent feature for greenland ice core and north atlantic marine records during the marine isotope stage mis 3 studying high quality climatic archives outside of the greenland and north atlantic with precise constraint of absolute dating and high resolution sampling is a prerequisite to understand how the millennial scale changes well expressed in north hemisphere nh high latitudes had been propagated out to the other regions here we generated the surface and subsurface hydrography u k 37 and tex h 86 temperatures and terrestrial material input n alkanes records with precise ams 14 c dated control for the 45 ka from a core md972146 retrieved from the northern south china sea scs then we compared our records to the oxygen isotope record from a greenland ngrip ice core and the mean grain size record from a loess sequence at gulang china we found that the millennial scale oscillations of hydrolography and terrestrial material inputs records during the time since the last deglaciation and of 33 45 ka share similar patterns in timing and amplitude of the nh high latitude climate however we found that a non nh pattern of millennial scale oscillations for the late mis 3 20 33 ka of our hydrography and terrestrial material inputs records our studies imply that the changes of obliquity also may be important in determining the timing and amplitude of millennial scale east asian monsoon eam variability expressed in the northern scs hydrography and terrestrial material inputs

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

the sr and nd isotopic variations of the chinese loess plateau during the past 7 ma implications for the east asian winter monsoon and source areas of loess abstract 143 nd 144 nd and 87 sr 86 sr ratios of the acid insoluble residues of the red clay and overlying loess paleosols from the lingtai profile of the loess plateau china were investigated the results show that variations of the 87 sr 86 sr ratios of the lingtai profile can be divided into two stages from 7 ma b p to 2 5 ma b p the acid insoluble residues in the red clay rc formation are characterized by higher 87 sr 86 sr ratios with an average of 0 7230 from 2 5 ma b p to the present the acid insoluble residues in the wuchen loess wl4 ws1 lishi loess l15 s1 malan loess l1 and holocene loess s0 have relatively lower 87 sr 86 sr ratios and display an overall descending trend from 0 7223 at 2 5 ma b p to 0 7182 at the present among three possible interpretations for the variations of 87 sr 86 sr ratios of acid insoluble residues of the loess provenance change chemical weathering change or grain size distribution change only grain size distribution change provides a satisfactory interpretation this implies that the east asian winter monsoon strength was weak and relatively stable from 7 ma b p to 2 5 ma b p but became continuously enhanced from 2 5 ma b p to the present all the red clay and the overlying loess paleosols in the lingtai profile have generally identical e nd 0 implying that the source regions of these eolian deposits of the chinese loess plateau may be relatively stable and has not changed since 7 ma b p

magnetostratigraphic dating of the linyi fauna and implications for sequencing the mammalian faunas on the chinese loess plateau the chinese loess plateau clp in north china is an important terrestrial archive that witnessed the environmental changes and mammal and early human evolution in asia over the past 2 6 ma establishing precise ages for the pleistocene faunas on the clp is critical for better understanding of these environmental biological and archaeological issues here we report a new magnetostratigraphic record that places age constraints on the linyi fauna on the southeastern clp our investigated 170 m thick linyi section mainly consists of two portions 1 an overlying eolian quaternary loess paleosol sequence and 2 underlying fluvial lacustrine sand and silty clay paleomagnetic results suggest that the composite section records the brunhes chron jaramillo and olduvai subchrons and successive reverse polarity portions of the intervening matuyama chron the linyi fauna is located between jaramillo and olduvai subchrons in the fluvial lacustrine interval with an estimated age of 1 5 1 6 ma combining previously dated faunas we establish a pleistocene magnetochronology spanning from 2 54 to 0 65 ma for the faunas on the clp

asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean rea d k and leinen m 1988 asian aridity and the zonal westerlies late pleistocene and holocene record of eolian deposition in the northwest pacific ocean palaeogeogr palaeoclimatol palaeoecol 66 1 8 a 30 000 year record of eolian deposition in the northwestern pacific ocean provides a history of the aridity of the asian source region and information on the changing latitude and intensity of the zonal westerlies the position of the maximum in eolian flux to the deep sea remained unchanged at 38 to 40 n during this entire time period but the dust flux record of aridity is greatest 6000 years ago at the holocene climatic optimum eolian grainsize data indicate that the northern margin of the westerly jet stream retreated northward during the holocene to a poleward extreme at about 6000 years ago and then moved back toward the equator the change in wind intensity across this margin was continually reduced throughout the holocene these sorts of data enhance our understanding of the behavior of the atmosphere during times of climate change and can be used to test computer generated models of past climatic conditions

late quaternary loess in northeastern colorado part ii pb isotopic evidence for the variability of loess sources a new application of the pb isotopic tracer technique has been used to determine the relative importance of different silt sources for late wisconsin loess in the central great plains of eastern colorado samples of the peoria loess collected throughout the study area contain k feldspar derived from two isotopically and genetically distinct sources 1 glaciogenic material from early and middle proterozoic crystalline rocks of the colorado province and 2 volcaniclastic material from the tertiary white river group exposed on the northern great plains pb isotopic compositions of k feldspar in loess from two dated vertical sections at beecher island and last chance colorado vary systematically implying climatic control of source availability we propose a model whereby relatively cold conditions promoted the advance of front range valley glaciers discharging relatively little glaciogenic silt but strong winds caused eolian erosion of white river group silt due to a decrease in vegetation cover during warmer periods valley glaciers receded and discharged abundant glaciogenic silt while surfaces underlain by the white river group were stabilized by vegetation isotopic data from eastern colorado loess sections record two warm cold warm cycles during late wisconsin time between about 21 000 and 11 000 radiocarbon yr b p similar to results from other studies in the united states and greenland

abrupt climatic events recorded by the ili loess during the last glaciation in central asia evidence from grain size and minerals abstract the loess record of central asia provides an important archive of regional climate and environmental changes in contrast to the widely investigated loess deposits in the chinese loess plateau central asian loess paleosol sequences remain poorly understood here we present an aeolian loess section in the southern ili basin based on granularity and mineralogical analyses we reconstruct climatic changes during the last glaciation the results indicated that most of the abrupt climatic events such as dansgaard oeschger events and heinrich events were imprinted in this loess section although their amplitudes and ages showed some differences compared with the millennial oscillations recoded in loess and stalagmites in east asia the arid central asia responded more sensitively to the warming events than to the cooling events the shifting trajectory of westerlies across central asia played an important role in dust deposition during the stadials the north atlantic climatic signals may have been transmitted from central asia to the east asian monsoon regions via the westerlies

climatic sub cycles recorded by the fourth paleosol layer at luochuan on the loess plateau the chinese loess paleosol succession deep sea sedimentary sequences and ice cores are the three types of paleoclimatic records measurements were made of the ancient climatic proxies of magnetic susceptibility median diameter of grain size and content 40 m and the caco3 content of samples collected at 1 cm depth intervals in the fourth paleosol layer of the luochuan loess paleosol section on the chinese loess plateau wavelet analysis of the data identified cycles of climate change which were compared to the marine 18o record of specmap the results showed that 1 when the fourth paleosol layer was forming the paleoclimate was relatively stable but five extreme climatic events were identifiable as occurring around 408 381 376 368 and 361 kabp 2 two of these regional events differed from the global trend 3 during marine isotope stage mis 11 the fourth paleosol layer of the luochuan loess section recorded a regional quasi 19 ka climatic sub cycle and 4 this sub cycle was also reflected globally in the specmap data indicating that during mis11 this sub cycle was regionally and globally synchronized

loess record of the aerodynamic environment in the east asia monsoon area since 60 000 years before present 1 the multimodal distribution of grains in loess and dust storm deposits has been widely reported in recent years our analysis demonstrates that the interaction of wind atmospheric turbulence and dust grain gravity along the dust transportation path results in a multimodal grain size distribution for suspended dust changes in the median sizes of the coarse and medium modes are related to variation in aerodynamic forcing lift force related to vertical wind and turbulence during dust entrainment in the source area and turbulence intensity in the depositional area on the basis of the numeric characteristics of the three modes of suspended particles a tentative model has been constructed which is used to study fluctuations of paleoaerodynamic environments from a time series of paleoatmospheric environmental changes of the loess plateau for the past 60 000 years we find that there are three patterns of aerodynamic environments in the dust source area stronger strong weak and 13 strong turbulence events since 60 000 years b p climatic variability in the dust depositional area is stronger than in the source area during the last glacial period the aerodynamic environment changed synchronously in the dust source and depositional areas over the entire trend however after 8000 years b p the aerodynamic force is strong in the dust source area while the turbulence intensity is weak in the dust depositional area differing from that of the last glacial period the strong turbulence periods correspond to the cooling events such as the heinrich events and the younger dryas cold event and may not be related to factors forcing the alternation between glacial and interglacial periods since 60 000 years b p the three patterns of aerodynamic environments are mainly controlled by the environmental changes in the dust source area and may be related to fluctuations of the winter monsoon in each pattern fluctuations of the turbulence intensity in the dust depositional area and the distance from dust source to dust depositional area are the major changes of the environment the summer monsoon recorded by magnetic susceptibility may vary prior to the winter monsoon since 50 000 years b p changes in the intensity of the summer monsoon may force changes in the advance retreat cycles of dust source areas in each winter monsoon pattern

optically stimulated luminescence dating of late quaternary loess deposits in the coastal region of north china provenance and paleoclimatic implications abstract the aeolian deposits in the coastal region of north china are important for reconstructing paleoclimate in this paper chronology climatic proxies and chemical compositions of four loess sections were studied optically stimulated luminescence osl dating results indicate that the coastal loess was accumulated during late quaternary with ages ranging from the penultimate glacial period to the latest holocene both granulometric characteristics and geochemical properties indicate that the dust provenance of the coastal loess is partially different from that of the chinese loess plateau characterized by more proximal contributions except distal dust transported by northwesterly winter winds from the inland gobi and sand deserts the coastal loess also contains proximal local coarse particles which were derived from the exposed shelf as well as neighboring hills multiple climatic proxies including color magnetic susceptibility and particle size parameters correlate well with the marine specmap 18o record indicating that climatic changes in the coastal region of north china during the late quaternary was mainly controlled by variations of the east asian monsoon driven by changes in global ice volumes

rapid and cyclic aeolian deposition during the last glacial in european loess a high resolution record from nussloch germany abstract this paper reports the results of an investigation of the weichselian upper pleniglacial loess sequences of nussloch rhine valley germany based on stratigraphy palaeopedology sedimentology palynology malacology and geochemistry 13 c supported by radiocarbon tl and osl dating grain size and magnetic susceptibility records are taken at 5 cm intervals from the upper pleniglacial upg loess the data indicate cyclic variations in loess deposition between ca 34 and 17 ka when the sedimentation rate is especially high 1 0 1 2 m per ka for more than 10 m the grain size index gsi ratio of coarse silt versus fine silt and clay shows variations which are assumed to be an indirect measurement of wind intensity the sedimentation rate interpreted from the profiles indicates high values in loess loess events le 1 to le 7 and low or negligible values in tundra gley horizons g1 to g8 osl ages from the loess and 14 c dates from organic matter in the loess show that loess deposition was rapid but was interrupted by shorter periods of reduced aeolian sedimentation comparison between the data from nussloch and other european sequences demonstrates a progressive coarsening of the loess deposits between ca 30 and 22 ka this coarsening trend ends with a short but major grain size decrease and is followed by an increase to a new maximum at 20 2 ka w shape correlation between the loess gsi and the greenland ice core dust records suggests a global connection between north atlantic and western european global atmospheric circulation and wind regimes in addition the typical upper pleniglacial loess deposition begins at ca 30 31 ka close to heinrich event he 3 and the main period of loess sedimentation at about 25 2 ka is coeval to he 2 correlation of magnetic susceptibility and grain size records shows that the periods characterised by high gsi coincide with an increase in the amount of ferromagnetic minerals reworked from the rhine alluvial plain they suggest enhancement in the frequency of the storms from n nw these results are integrated within a palaeogeographical model of dust transport and deposition in western europe for the weichselian upper pleniglacial or late pleniglacial

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

late quaternary loess like paleosols and pedocomplexes geochemistry provenance and source area weathering manasbal kashmir valley india abstract the late quaternary loess and loess like deposits in kashmir valley are natural archives that have preserved paleoclimate and paleoenvironmental records of the region we present a loess like paleosol located along the margin of the manasbal lake ganderbal which was studied in detail for understanding the pedological processes and reconstructing the late quaternary soil formation in this paper we present loess like paleosol formation of a nearly 10 6 m thick sequence exposed along the margin of manasbal lake ganderbal district srinagar kashmir geochemical and textural data of this loess like sedimentary sequence fluctuate reflecting the varied depositional processes operating in the valley differential intensity of weathering and processes of pedogenesis weathering indices such as chemical index of alteration chemical index of weathering and plagioclase index of alteration reveal weak to moderate weathering of the parent material provenance discrimination diagrams of the present study disclose that the manasbal loess like paleosol sediments are derived from the mixed source rocks suggesting a variety of provenance with variable geological settings which apparently have undergone weak to moderate recycling processes the manasbal paleosol horizons have been dated by the optically stimulated luminescence osl method to the marine isotope stages mid mis 3 41 7 8 0 ka and late mis 2 14 6 3 8 ka during the mis 3 period the climate was wetter forming a strong ahbtk paleosol as inferred from the geochemical data a steady increase in the caco 3 content and c n ratio in the paleosols from 6 50 m mis 3 indicates arid and drier climatic conditions the area around manasbal lake incised because of climate change and neotectonic activity since post 14 ka

mineralogical and pedogenetic evidence for palaeoenvironmental variations during the holocene on the loess plateau china abstract clay minerals in soils reflect successive stages of mineralogical evolution which depend on the environmental conditions that have prevailed during pedogenesis the objective of this research was to document the mineralogy of the clay fractions

coarse textured basal zones in thin loess deposits products of sediment mixing and or paleoenvironmental change abstract the purpose of this research was to characterize and interpret the coarse basal zones that are common in thin loess deposits that overlie coarser textured sediment to that end we sampled nine pedons in northeastern wisconsin and the upper peninsula of michigan each of which had formed in thin 55 cm loess over sandy glacial sediment at most of these sites the loess became noticeably coarser near the lithologic discontinuity the loess has a primary particle size mode in the coarse silt or fine very fine sand fraction 30 65 m and a secondary mode in the fine or medium sand fraction 200 400 m we attribute the secondary mode to mixing of underlying sands into the loess either during loess deposition or by post depositional pedoturbation in thin loess pedoturbation processes can penetrate into the underlying sediment facilitating mixing upward as far as 50 cm into the loess silt from the loess has also been mixed into the underlying sandy sediment alternatively in some pedons the loess itself coarsens with depth the particle size mode for the loess becomes increasingly coarser with depth this coarsening suggests that during loess deposition one or more of the following was occurring 1 wind velocities were decreasing over time 2 the textural character of the loess source area s were changing decreasing or 3 additional source areas with finer textured sediment became more dominant over time our research demonstrates the utility of detailed particle size data for detecting and interpreting the paleoenvironmental history of loess we also document the extent to which pedoturbation can impact the original textural characteristics of loess or any sediment that occurs as a thin surficial mantle

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

linking coarse silt production in asian sand deserts and quaternary accretion of the chinese loess plateau the chinese loess plateau clp is a large spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the east asian monsoon many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions although spatial and temporal variations in the grain sizes of clp sediments are fundamental to this effort controversy over the origin of the dominant coarse quartz silt has limited interpretations reexamination of the spatial pattern of grain size distribution across the clp and a field scale experiment conducted in the gobi desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal mu us tengger and badain jaran sandy deserts our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in central asia and identify this process as the most consistent with the well recognized systematic northwest southeast depositional pattern of the clp we suggest that only abraded coarse quartz grains transported short distances by long term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau these results decouple the production and transport of coarse silt and finer silt and clay particles which have a more distant and wider provenance changing the constraints on previous paleoclimatic reconstructions

10be and magnetic susceptibility in chinese loess 10be and magnetic susceptibility have been measured in the top 12 m of a loess profile from luochuan central china comparison of the 10be concentration record with the specmap 18o profile of the last 130 ka imbrie et al 1984 results in a new time scale which is in good agreement with that of kukla et al 1990 the calculated loess accumulation rates can be compared with existing records of dust falls in pacific deep sea sediments and antarctic ice cores a simple model for the 10be dust flux demonstrates that a significant part of the magnetic susceptibility signal in palaeosol horizons is due to in situ pedogenic production during times of high loess accumulation cold palaeoclimate this contribution is negligible

pleistocene paleoenvironmental changes in the high mountain ranges of central china and adjacent regions abstract during several joint chinese german expeditions the quaternary landscape and paleoclimatic evolution of the mountain ranges and grabens surrounding the loess plateau of central china was studied the results are compared with proxy data from the interior loess plateau to help reconstruct atmospheric circulation during late pleistocene times middle to late pleistocene alluvial terraces and fans capped with loess units and paleosols show that aggradational episodes correlate with periods of glaciation and increased loess accumulation in turn degradation correlates with interglacials or interstadials and increased soil formation this implies that climate is the primary control on quaternary paleohydrology and alluvial sedimentation and erosion the high mountains which barely reached the last glacial ela were only glaciated during the most favourable climatic period of glaciation the glaciation the glacial and alluvial forms point to a cool early to maximum glacial period with increased precipitation and to a maximum to final period with cold dry conditions during the last glaciation the maximum advance of the small glaciers took place towards the end of a relatively humid and cold period between ca 32 and 23 ka the following dry cold stage between ca 23 and 13 ka was rather unfavourable for glacial advance proxy data from the loess plateau supports the view that glaciations were more or less dominated by cold dry winter monsoon climate whereas during the interglacial interstadials a warmer and more humid climate prevailed implying a strengthening of the summer monsoon influence the results prove variations of the monsoon that in turn modulates paleohydrology periglacial dynamics glacier advances dust flux and soil formation

rift shear architecture and tectonic development of the ghana margin deduced from multichannel seismic reflection and potential field data abstract the ghana margin displays one of the best known transform margins studies of the margin have provided the framework for a number of conceptual models aimed at understanding transform margin development worldwide however the deep structure of the margin is poorly known as knowledge is based only on wide angle refraction measurements obtained from two separate localities on the margin consequently complexities in the rift shear margin architecture have been overlooked by current interpretations of margin development based on combined analysis of a detailed grid of 2710 km multichannel mcs lines and potential field data we provide new insights into the structural architecture and tectonic development of the ghana margin in particular we outline the deep structure of the entire margin using a series of 2d gravity modelled transects constrained by mcs and published wide angle data our study reveals more complex rift shear margin architecture than previously envisaged we demonstrate that the main transform boundary representing the continental extension of the romanche fracture zone is actually composed of two distinct margin segments i e the ene wsw trending sheared margin segment of the cote d ivoire ghana ridge and the ne sw trending rift influenced sheared margin segment of the ghana platform these segments evolved under varying stress regimes and during different time intervals west of the transform margin divergent rifting during the early cretaceous initiated the development of the deep ivorian basin essentially as a single major pull apart structure however east of the shear zone oblique rifting resulted in the development of the eastern ghana slope basin as a composite of at least two coalescing pull apart basins displaced along strike slip faults our structural interpretation of the transform boundary geometry shows that the ridge and platform margin segments were each subjected to separate thermal influences from two different migrating spreading centres tectonic uplift of the ridge began through transpression during mid albian time following a change in relative direction of plate motion from ne sw to ene wsw however the ridge uplift was amplified by thermal heating from a previously undocumented spreading centre whose progressive westward migration along the ridge followed closely after the albian transpressional phase the structural architecture of the ghana margin resulted from a combination of factors notably pre existing basement structure plate boundary geometry the relative direction of plate motion and thermal heating

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

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

comparison of late pleistocene and modern glacier extents in central nepal based on digital elevation data and satellite imagery abstract late pleistocene and modern ice extents in central nepal are compared to estimate equilibrium line altitude ela depressions new techniques are used for determining the former extent of glaciers based on quantitative objective geomorphic analyses of a 90 m resolution digital elevation model dem for every link of the drainage network valley form is classified as glacial or fluvial based on cross valley shape and slope statistics down valley transitions from glacial to fluvial form indicate the former limits of glaciation in each valley landsat multispectral scanner imagery for the same region is used to map current glacier extents for both full glacial and modern cases elas are computed from the glacier limits using the dem and a toe to headwall altitude ratio of 0 5 computed ela depressions range from 100 900 m with a modal value of 650 m and a mean of 500 m values consistent with previously published estimates for the central himalaya but markedly smaller than estimates for many other regions we suggest that this reflects reduced precipitation rather than a small temperature depression consistent with other evidence for a weaker monsoon under full glacial conditions

the paleolithic site of longwangchan in the middle yellow river china chronology paleoenvironment and implications the longwangchan paleolithic site situated on the yellow river terraces in the hukou area shaanxi province china was found in 2003e2004 and two areas localities 1 and 2 of the site were excavated in 2005e2008 abundant stone artifacts including microliths a grinding stone fragment and a shovel with some animal bones and shells were recovered from locality 1 in this study the cultural deposits from locality 1 were dated using radiocarbon and optical dating techniques and the sediment properties of the deposits were analyzed the results show that the age of the deposits ranges from 29 to 21 ka and most of them were deposited between 25 ka and 29 ka this indicates that corresponds to late marine isotope stage mis 3 and early mis 2 during the human occupation period the climate in this area became colder and drier sediments from beds where the grinding slab and the shovel were found were dated to w25 ka which is the oldest among the grinding stones found in china the microliths and the grinding stone are important evidence for an incipient socio economic process that eventually led to the regional transition from hunting foraging to farming

sedimentary responses to the pleistocene climatic variations recorded in the south china sea grain size analyses coupled with end member modelling have been performed on the terrigenous fraction of two leg 184 ocean drilling program sites 1144 and 1146 from the south china sea the grain size distributions over the last 1 8 ma enable a new interpretation of their connections to sea level variations and east asian monsoon strength previous investigations in this area have associated grain size variability with enhanced eolian input during glacial stages end member modelling downgrades the importance of this eolian contribution and indicates that the sediments can be described as a mixture of three end members fluvial mud inputs shelf reworking and river mouth migration grain size variations in the pleistocene section of the cores indicate a multiple stage evolution i from 1 8 to 1 25 ma the downcore grain size variations are low but show a correspondence between monsoon rainfall intensity and the fine grain sized fluvial inputs no link with sea level variations is noticeable ii from 1 25 to 0 9 ma there is an increase decrease in the intermediate fine end member 100 kyr cycle that is associated with the onset of a stronger summer monsoon and modest shelf reworking iii from 0 9 to 0 ma the grain size record is dominated by global sea level variations each glacial stage is associated with extensive shelf reworking and conveyance of coarse particles to the basin 2007 university of washington all rights reserved

late pleistocene chronology of loess deposition near luochuan china abstract loess near luochuan was sampled for thermoluminescence tl dating simultaneously with magnetic susceptibility measurements to provide the first independent age estimates on a susceptibility record from the loess plateau of china tl age estimates on late pleistocene loess l1 are stratigraphically consistent with no statistical difference in tl ages by the total or partial bleach techniques or by measuring ultraviolet or green wavelengths in the tl analysis loess below the last interglacial soil s1 yielded disparate results and is in many localities in central and eastern china unsuitable for tl dating because of complications of tl saturation and uncertainties in estimating the environmental radiation tl age estimates on the l1 loess are consistent with previously reported tl ages for sites near beijing and xian as well as in general agreement with age models for loess deposition based on paleomagnetics and magnetic susceptibility the convergence of a variety of geochronologic indices indicate that the last major period of loess deposition in central china began 70 000 10 000 yr b p and terminated

lake level and climate changes between 42 000 and 18 000 c 14 yr bp in the tengger desert northwestern china multiple lines of stratigraphic geochemical and fossil data suggest that fresh mesohaline paleolakes were widespread in the tengger desert of northwestern china and underwent major fluctuations during the late pleistocene the paleolakes started to develop at ca 42 000 c 14 yr b p the lake levels were the highest between 35 000 and 22 000 c 14 yr b p during which megalake tengger dominated the landscape the climatic conditions at this time were unique for this area and have no modem analogue after an episode of decline between 22 000 and 20 000 c 14 yr b p and an episode of rebound between 20 000 and 18 600 c 14 yr b p the paleolakes started to desiccate and completely disappeared around 18 000 c 14 yr b p the environmental proxy data indicate that the megalake tengger formed under warm humid climates the reconstructed climatic variations appear to be correlative with the abrupt climatic events reconstructed for the north atlantic c 2002 university of washington

fluctuations of eolian flux and ocean productivity in the mid latitude north pacific during the last 200 kyr abstract in order to understand fluctuations in terrestrial and marine environments a sedimentary core h3571 was investigated from the hess rise located in the mid latitude north pacific under the north westerly wind system the 18 o grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin good correlation between al and aerosol quartz in content and mass accumulation rate mar indicates that the alumino silicate minerals in the sediments are mainly transported by wind mar of mineral aerosol maraerosol varies from 156 to 732 mg cm 2 kyr 1 during the last 200 kyr the maraerosol maxima occur in oxygen isotope stage ois 4 to latest ois 5 middle ois 6 moderate maxima occur in early ois 1 2 late ois 3 and middle ois 3 these maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon the mean organic carbon total nitrogen atomic ratio is 7 2 suggesting that the organic matter in the core h3571 is also mainly of marine origin the mar of organic carbon marorganic exhibits two prominent maxima in ois 2 and 4 and relatively high values in middle and late ois 6 enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing pco2 in surface water during glacial times on the other hand the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments the effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the western pacific and equatorial atlantic as compared with that in the hess rise regime

abrupt change of sediment records in the southern south china sea during the last glacial period and its environment significance abstract chemical compositions of sediments at core ns07 25 6 39 945 n 113 32 936 e water depth 2006 m are analyzed to discuss abrupt change of sediment records in the southern south china sea scs during the last glacial period and its environmental implications major and trace elements experienced three significant changes which occurred at 31 9 26 1 and 18 5 ka bp respectively at 31 9 ka bp when sea surface temperature remained relatively low terrigenous sediment flux increased but biogenic activities weakened greatly at 26 1 ka bp both terrigenous sediment flux and biogenic fractions number were steady however some elemental ratios changed noticeably at that time before 26 1 ka bp core sediments with low nb ta but high zr hf ratios were mainly derived from the paleo mekong and or molengraaff rivers exposed on the sunda shelf at that time after 26 1 ka bp sediments with high nb ta but low zr hf ratios probably relate to strengthened impact of deep water current since 18 5 ka bp sea level ascended rapidly from 110 m below the present terrigenous sediment flux decreased and biogenic activities strengthened continuously probably related with the east asian monsoon evolution

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

pleistocene and holocene distribution of the radiolarian amphimelissa setosa cleve in the north pacific and north atlantic evidence for water mass movement abstract the radiolarian amphimelissa setosa is one of the prominent species of the pleistocene radiolarian assemblages in the sea of okhotsk below the marine isotope stage mis boundary 5 4 and it represents one of the most abundant radiolarian species in holocene and modern environments of the nordic seas we studied the a setosa distribution in six cores from the sea of okhotsk and established morphometric measurements on a setosa specimens from two cores of the sea of okhotsk and one core from the labrador sea we further compared our data with other available studies from the subarctic pacific the labrador sea the north atlantic the norwegian sea and the iceland greenland seas in order to discuss the possible settling of the species from the north pacific via the arctic ocean into the iceland greenland seas a setosa exhibits a stable abundant population in the sea of okhotsk during most of the last ca 0 7 m y and might repeatedly extend its population into the north atlantic through the arctic ocean during the pleistocene interglacial optima the species declines from the sea of okhotsk and from the subarctic pacific at the end of mis 5 its final documented settling into the north atlantic is during mis 5 when a setosa appears in low numbers in sediments of the labrador sea however reaching significant percentages at the boundary of mis 5 4 based on the available information we propose that a setosa could migrate from the north pacific into the arctic ocean during the interglacial optimum mis 5e and then through the channels of the canadian arctic archipelago into the baffin bay and labrador sea a further migration step of a setosa occurs at the boundary of mis 5 4 when a setosa migrated from the labrador sea into the north atlantic probably related to a southward expansion of cold waters at the end of the mis 5 during the warming at termination i a setosa moved from the north atlantic into the nordic seas the abundant occurrence of a setosa in sediments south of iceland the norwegian and north seas within the younger dryas period points to a marked cooling and a southward movement of polar water masses restricted to this time interval

regional climate driven c3 and c4 plant variation in the cheollipo area korea during the late pleistocene abstract marine isotope stage 3 mis3 spanning from 25 to 60 ka bp was a time of substantial environmental change that included changes in the global ice volume and atmospheric composition with resultant regional climate changes to understand past vegetation responses to such environmental changes in korea we estimated the abundance of c3 and c4 plants using the c n and carbon isotope ratios of sedimentary organic matter the mis3 sedimentary unit at the cheollipo site located in a western coastal area of korea is characterized by a dark to light gray colored sedimentary unit 3 05 to 5 05 m in elevation mis3 which is between an underlain oxidized yellowish sedimentary unit 5 05 m in elevation the estimated abundance of c4 plants varied between 60 and 10 during the mis3 the suborbital scale variation in the estimated percentage of c4 plants was similar to those reported in continental ice volume and the east asian monsoon intensity suggesting that c4 plants prevailed under colder and drier conditions intensified winter monsoon whereas c3 plants have favored a warmer and wetter climate intensified summer monsoon compared with high latitude regions e g chinese loess plateau and lake baikal where low summer temperature suppressed aridity and pco2 influences during the last glacial period vegetation change in cheollipo area may have more sensitively responded to aridity change which had been affected by the summer winter monsoon intensity the climate change in the western coastal area yellow sea side of korea during the late pleistocene may have been controlled by regional climate change coupled with continental ice volume change

grain size of loess palaeosol and red clay deposits on the chinese loess plateau significance for understanding pedogenic alteration and palaeomonsoon evolution abstract to assess pedogenic modification to grain size distributions of loess palaeosol and red clay deposits on the chinese loess plateau and to understand long term evolution of the east asian palaeomonsoon since the late miocene we investigate a continuous loess palaeosol red clay sequence at lingtai south chinese loess plateau and another parallel red clay sequence at zhaojiachuan central chinese loess plateau by analyzing the grain size distributions of bulk samples and chemically isolated quartz samples the relative intensity of pedogenic alteration of the loess palaeosol and red clay deposits can be quantified comparisons of the grain size distributions and contents of different grain size fractions between the bulk and the quartz samples suggest that pedogenic alteration is apparently stronger in the red clay sequence than in the overlying loess palaeosol deposits furthermore grain size parameters derived from the bulk and the quartz samples such as mean grain size coarse fraction content and u ratio exhibit similar variations in the loess palaeosol sequence quaternary 0 2 6 ma whereas these grain size parameters of quartz samples show different variability from those of bulk samples in the red clay sequence late miocene to pliocene 2 6 7 ma grain size of quartz from the loess palaeosol and red clay deposits exhibits distinct and persistent oscillations from the late miocene to the pleistocene implying that significant fluctuations of the palaeomonsoon climate in east asia might have occurred at least since late miocene time

spatial pattern of grain size in the late pliocene red clay deposits north china indicates transport by low level northerly winds abstract the confirmation of an eolian origin of the tertiary red clay from north china would make it a valuable terrestrial paleoclimatic record however it is still controversial as to which wind primarily transported the dust forming the red clay onto the loess plateau careful consideration of this question is a prerequisite for better understanding the history of atmospheric circulation in central and east asia during the miocene and pliocene epochs in this paper the grain size distributions of bulk samples and chemically isolated quartz grains of the late tertiary red clay were investigated to explore the potential transportation mechanisms of the dust as well as the atmospheric circulation at the time of deposition the samples were taken from six localities spanning across 550 km on the loess plateau the results show that the mean grain size of both bulk and quartz samples decreases southward as does the coarse fraction content 42 m these data not only give new evidence for the eolian origin of the red clay but also indicate that the red clay was probably transported mainly by northerly low level winds or the winds at least had a strong northerly component therefore the spatial distribution of grain size of the red clay is comparable to that of the overlying quaternary eolian loess which demonstrates a remarkable northwest southeast decrease in grain size sedimentation rate and thickness during the last glacial coinciding with the dominant wind direction of the northwesterly east asian winter monsoon however the grain size of the red clay is generally finer than the corresponding loess this indicates that the red clay may have been transported by a weaker winter monsoon associated with stronger pedogenic modification and or the dust source area was not extensive compared to that during the quaternary moreover the high content of grains coarser than 19 m transported mainly by energetic low level winds over short distances suggests that the dusts were not transported by upper level westerly

carbonate rhizoliths in loess and their implications for paleoenvironmental reconstruction revealed by isotopic composition δ13c 14c abstract loess paleosol sequences are important terrestrial archives for studying quaternary climate changes they often contain secondary carbonates including e g rhizoliths calcified roots these secondary carbonates are precipitated in isotopic equilibrium with root derived co2 and are therefore used to reconstruct the vegetation present during their formation based on stable carbon isotopic composition 13c usually the chronological context of secondary carbonates in general is not mentioned because it is assumed that they are formed synsedimentary with loess deposition the loess paleosol sequence at nussloch sw germany contains in its youngest part upper wurmian large carbonate rhizoliths with diameters of up to 5 cm and lengths of up to 1 m and more which have not been described in this profile so far we investigated rhizoliths as well as loess adjacent to and distant from rhizoliths for carbonatic carbon ccarb and organic carbon corg contents as well as their isotopic composition 13c radiocarbon dating to identify the rhizolith origin and the time frame of their formation considering the 13c fractionation by carbonate precipitation the 13ccarb values 10 9 0 1 revealed c3 plant origin of the rhizolith carbonate and the absence of large amounts of occluded primary loess carbonate similar 14c ages of rhizolith ccarb and corg 3788 59 years bp and 3150 59 years bp respectively argued for the absence of postsegregational alteration therefore they are suitable for the reconstruction of paleoenvironmental conditions after loess sedimentation the 14c ages clearly indicate that rhizoliths did not form synsedimentary roots penetrated the loess at nussloch after the deposition had ceased at 15 ka bp even in the loess adjacent to the rhizoliths up to a distance of 5 cm 13ccarb values indicate the presence of secondary carbonate deriving from postsedimentary organic matter of origin other than that of the reference loess material hence this postsedimentary input of younger root biomass might have masked the initial plant signal in loess paleosol sequences which could cause uncertainties for paleoenvironmental reconstructions based solely on loess organic matter

magnetism of chinese loess deposits summary the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene and ascertained a maximum loess age of about 1 2 myr a new collection of nearly 500 samples from a natural outcrop and a borehole section near lochuan lat 35 8 n long 109 2 e shaanxi province has been dated by magnetic stratigraphy thermal cleaning of the natural remanent magnetization nrm removes a strong secondary component of viscous origin along the present geomagnetic field which resides largely in magnetite the characteristic nrm component is due to haematite which is thought to be of chemical origin rhythmical intensity variations of nrm and initial susceptibility depend on the loess lithology and may reflect climatic changes during loess deposition the palaeomagnetic results are consistent between the two sections and yield a clearly defined magnetic polarity zonation the brunhes matuyama boundary and the jaramillo subchron have been positively identified in both outcrops at exactly the same stratigraphic level the olduvai subchron has been found in the borehole section which records the entire loess sequence most probably the formation of chinese loess began shortly after the matuyama gauss polarity transition therefore a late pliocene age of about 2 4 myr is assigned to the oldest loess sediments measured

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

high resolution record of the last climatic cycle in the southern carpathian basin surduk vojvodina serbia abstract high resolution study of the surduk loess palaeosols sequence in serbia vojvodina has been performed within a research project eole focusing on the impact of rapid climatic changes during the last climatic cycle in the european loess belt the methodology used for this multidisciplinary approach is based on a continuous sampling column that allows a very accurate correlation between all studied proxies magnetic susceptibility grain size and organic carbon and the dated samples irsl 14 c according to the stratigraphical and sedimentological data the surduk loess sequence appears as a very complete record of the last climatic cycle 19 m and exhibits a similar pattern than other contemporaneous loess sequences from western central and eastern europe the main difference is the evidence of a drier environment all over the last climatic cycle sedimentological and palaeopedological data the high resolution grain size record 5 cm is well correlated with stratigraphical boundaries and highlights a strong variability within the loess deposition especially during the upper pleniglacial between ca 33 and 15 ka during the upper pleniglacial a succession of millennial timescale events characterised by the deposition of coarser loess are particularly well evidenced by grain size data as in some west european records finally an attempt to correlate the variations of grain size parameters at surduk with the greenland grip dust record is proposed according to this study millennial timescale climatic events that characterise the north atlantic area during the last climatic cycle have thus been recorded in the environments located at the southern border of the european loess belt

tectonic and climatic controls on provenance changes of fine grained dust on the chinese loess plateau since the late oligocene abstract provenance variations of late cenozoic aeolian deposits on the chinese loess plateau clp were closely associated with regional tectonic activity and climatic change previous studies however have not reached a consensus regarding the nature and origin of past variations in source this study presents the results of oxygen isotope 18 o analyses of fine grained quartz 18 o variations exhibit distinct trends and patterns of variation over six time intervals i e 25 20 20 12 12 7 7 2 6 2 6 1 2 and 1 2 0 ma in comparison with quartz 18 o results from east asian dust sources and previous provenance studies of the same aeolian sequences we identify three significant composition changes of the dust source system at around 20 12 and 2 6 ma the dust source system was also rather unstable at 25 20 12 7 and 1 2 0 ma while three stable stages occurred at 20 12 7 2 6 and 2 6 1 2 ma the correlation between the provenance changes and paleoclimatic and tectonic evidence suggests that both tectonic and climatic factors were important in driving the observed stepwise provenance changes however the changes were mainly constrained by tibetan plateau uplift prior to the quaternary and by global climate change thereafter

magnetic mineralogy of chinese loess and its significance summary the topmost 16 metres of the loess section at xifeng central chinese loess plateau which cover the last 128000 years consist of two palaeosol beds interlayered by a loess horizon hysteresis parameters frequency dependent field and temperaturedependent susceptibility show very similar and stable magnetic mineral constituents in both loess and palaeosol samples the concentration and grain size of magnetite maghaemite and haematite control the magnetic properties of chinese loess susceptibility and loess thickness are closely related to geographic position and present climate across the loess plateau the loess and palaeosol magnetic properties are largely controlled by the fine grained magnetite formed in various quantities and grain sizes under the influence of pedogenesis during variable palaeoclimatic conditions therefore regional and global palaeoclimatic development during the last 2 5 myr can be reconstructed from susceptibility records in the loess plateau

evidence for a warm humid climate in arid northwestern china during 40 30 ka bp abstract former shorelines and sedimentary records from several lake basins in northwestern china xinjiang qinghai give evidence for warm and humid climatic conditions during 40 30 ka bp further indications of this favorable climate period are derived from palaeosols from the ili loess and from cemented calcareous layers on the terraces of the keriya river at the southern margin of the tarim basin and in the badain jaran desert in inner mongolia at that time annual mean temperature in the qaidam basin was 2 c higher and in the western part of inner mongolia even 2 3 c higher than today precipitation in most parts of northwestern china was between 60 300 mm greater than today these changes were probably a consequence of an increase in ocean surface temperature and evaporation resulting from a higher radiation input at middle and low latitudes caused by changes in the earth s precessional cycle as a result of these orbital changes it is suggested that the intensified westerly circulation was responsible for increased moisture over northwestern china

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

grain size of quartz as an indicator of winter monsoon strength on the loess plateau of central china during the last 130 000 yr the chinese loess paleosol sequence constitutes an important record of variations in asian monsoon climate over the past 2 4 myr magnetic susceptibility of loess and paleosols has been used as a proxy for summer monsoon intensity while median grain size has been regarded as a measure of the strength of winter monsoon winds that were responsible for most of the dust transport however median grain size is only an approximate index of winter monsoon strength because both paleosols and loess have been modified to various degrees by weathering processes that have produced pedogenic clay the quartz component of loess and paleosols is largely unaffected by weathering processes and therefore constitutes a more reliable proxy index of monsoon wind strength median grain size qmd and maximum grain size qmax values of monomineralic quartz isolated from the loess paleosol section at luochuan in the central loess plateau are characterized by two main intervals during the last ca 130 000 yr when these parameters were significantly greater than 9 and 85 m respectively and three main intervals when they were lower the data imply that the winter monsoon weakened during the intervals with low qmd and qmax values which coincide with marine oxygen isotope stages 5 3 and 1 and was strongest ca 67 000 and 20 000 yr ago during isotope stages 4 and 2 however both quartz grainsize records display second order high frequency high amplitude variations which are lacking in the magnetic susceptibility record that imply rapid and significant changes in atmospheric conditions that affect dust transport and deposition

the processes and mechanisms of severe sandstorm development in the eastern hexi corridor china during the last glacial period abstract dust transported by sandstorms has been an important feedback in climate change in the past and its environmental effects are predicted to have a great impact on future global climatic change investigating the grain size classes and the standard deviations of the modern sandstorm samples and the samples in the shagou section situated in the eastern hexi corridor lead us to suggest that the sand fraction within the range of 275 4 550 m in this section can be used as a sensitive indicator of severe sandstorms we selected the size range in the l1 stratum of the shagou loess section as indicative of temporal changes in sandstorm intensity in the eastern hexi corridor and found that during the last glacial period severe sandstorms in the eastern hexi corridor occurred with high frequency during these periods i 70 54 ka b p ii 51 48 ka b p iii 45 42 ka b p iv 38 33 ka b p v 31 28 ka b p and vi 26 12 ka b p in general the frequency and intensity of dust storms in the early mis 4 and late mis 2 periods were both high but they were reduced in the middle period mis 3 the primary factors controlling severe sandstorms are hydrology and wind power followed by the expansion of the source extent reduced precipitation caused the source region of sandstorms to expand in addition wind speeds also increased at this time these factors may have directly contributed to the abundance of severe sandstorms based on the grain size from a loess section the shagou section in the eastern hexi corridor we propose an evolutionary sequence of the severe sandstorms during the last glacial period this sequence is consistent with the dust records in the arctic the antarctic and low latitude the central equatorial pacific areas thus globally synchronous periods of high dust activity occurred in the last glacial period the strong winds proposed here provide a potential explanation for the global consistency of dust flux changes during the last glacial period

locating the boundary between the pleistocene and the holocene in chinese loess using luminescence a detailed chronology has been obtained for a loess section at yuanbao situated at the northwestern edge of the chinese loess plateau the ages were obtained by the measurement of the optically stimulated luminescence osl from coarse silt sized quartz grains these ages showed that deposition at this site was continuous from 17 ka to the present but that there was a decrease in the sedimentation rate from 0 60 to 0 10 m ka at 13 489 1 15 ka and this is proposed as the location of the pleistocene holocene p h boundary a change in osl sensitivity occurs at this depth the depth and sharpness of this boundary is compared with the change obtained in low field magnetic susceptibility ms measurements on 65 samples from the section the ms changes gradually over 1 9 m and thus does not provide an easily discernible boundary the new osl based sedimentation rates are used to calculate the mass accumulation rates for the holocene and the end of the pleistocene

lagrangian observations of the deep western boundary current in the north atlantic ocean abstract in this study the authors analyze the trajectories of 18 rafos floats launched in the deep western boundary current dwbc between the grand banks and cape hatteras to investigate the kinematics and dynamics in the region where the dwbc crosses under the gulf stream near 36 n the crossover region floats deployed in the chlorofluorocarbon cfc maximum associated with upper labrador sea water depth 800 m illustrate the entrainment process of this water mass into the gulf stream the behavior of the floats and fluid parcels in the crossover region is strongly dependent on the meandering of the gulf stream when the stream is close to its mean position fluid parcels entrained from the upper dwbc travel along the northern edge of the stream when a meander trough is present downstream of the entrainment location dwbc fluid parcels cross the gulf stream and sometimes are expelled on the south side this represents a previously unrecognized mechanism for transporting upper labrador sea w

palaeoclimatic records of the loess palaeosol sequences of the chinese loess plateau whether during past climate stages or into a progressively warming world changes in precipitation constitute a key component of climatic change quantitative proxies for palaeo precipitation are relatively rare the magnetic properties of the windblown loess units and interbedded palaeosols of the famous chinese loess plateau provide key palaeo precipitation data for this populous monsoon dominated region the loess palaeosol sediments record rainfall totals directly complementing the oxygen isotope records of chinese speleothems these isotopic records predominantly reflect moisture source and hence large scale atmospheric circulation changes the two major asian monsoon systems appear to display antiphase behaviour dominance of the indian summer monsoon system seems associated with minimum precession maximum northern hemisphere summer heating dominance of the east asian summer monsoons with maximum precession at 2 8 ma more intense development of the east asian winter monsoon initiated major increases in dust deposition rates and formation of relatively unweathered loess layers glacial stage loess units then interleaved with interglacial interstadial stage palaeosols throughout the quaternary period decoupling of the loess palaeosol rainfall records from the chinese cave records of moisture source shows that the indian and east asian monsoon winds were continuously driven by precessional forcing while summer monsoonal rainfall was greatly suppressed during cool glacial stages the timing of these east asian climatic transitions the subsequent intensification of northern hemisphere glaciations and the association between monsoon circulation changes and north atlantic temperatures indicates a possibly leading global role for these monsoonal changes via alterations in the poleward distribution of heat and moisture

east asian monsoon variation and climate changes in jeju island korea during the latest pleistocene to early holocene a 4 96 m long sediment core from the hanon paleo maar in jeju island korea was studied to investigate the paleoclimatic change and east asian monsoon variations during the latest pleistocene to early holocene 23 000 9000 cal yr bp high resolution toc content magnetic susceptibility and major element composition data indicate that jeju island experienced the coldest climate around 18 000 cal yr bp which corresponds to the last glacial maximum lgm further these multi proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14 000 cal yr bp which represents the commencement of the last major deglaciation after the last major deglaciation the toc content decreased from 13 300 to 12 000 cal yr bp and from 11 500 to 9800 cal yr bp thereby reflecting the weakening of the summer monsoon the lgm in jeju island occurred later in comparison with the chinese loess plateau such a disparity in climatic change events between central china and jeju island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central china and by the buffering effect of the pacific ocean

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

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

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

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

mid holocene climate change and its effect on prehistoric cultural evolution in eastern qinghai province china abstract we studied the mid holocene climate change in eastern qinghai province china and its impact on the evolution of majiayao 3980 2050 bc and qijia 2183 1635 bc cultures near the important neolithic site of changning the investigation focused on analyses of grain size magnetic susceptibility ratios of elemental contents and pollen assemblage from a loess paleosol sequence the results indicate that the climate was wet during 5830 4900 cal yr bp which promoted the development of early mid majiayao culture in eastern qinghai province however 4900 4700 cal yr bp were drought years in the region responsible for the decline and eastward movement of prehistoric culture during the period of transition from early mid to late majiayao culture the climate turned wet again during 4700 3940 cal yr bp which accelerated the spread of qijia culture to the middle reaches of the huangshui river including the changning site

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

orbital forcing of terrestrial mollusks and climatic changes from the loess plateau of china during the past 350 ka high resolution analyses of terrestrial mollusks from two loess sequences in the chinese loess plateau provide continuous evidence of paleoecosystem and paleoclimate processes through the recent three glacial interglacial cycles systematic fluctuations in thermal humidiphilous mollusk type punctum orphana indicate that the strength of the se asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 and 23 kyr respectively in contrast the cold aridiphilous mollusk vallonia tenera and pupilla aeoli variability displays a different pattern the strongest powers are centered at about 100 kyr and 41 kyr periods which drive the major period of winter monsoon variations in the chinese loess these different responses to winter and summer monsoon in the loess plateau of china suggest that both of these monsoon systems are tightly coupled in the 41 kyr cycle but are not coincident relative to the precession 19 23 kyr and 100 kyr cycles the relationship between the winter and summer monsoons is not a simple model reflecting a seesaw pattern

middle holocene environmental change in central korea and its linkage to summer and winter monsoon changes to trace the surficial responses of lowlands to past climate change we investigated 13c in total organic carbon toc c n ratios magnetic susceptibility ms and silicon si intensity directly proportional to concentration in wetland sediments collected from the gimpo area of central korea covering 6600 4600 cal yr bp two organic layers with high toc negatively depleted 13ctoc values 27 to 29 low ms values and low si intensities were found at 6200 5900 and 5200 4800 cal yr bp respectively these middle holocene wet periods corresponded to relatively intensified summer monsoon and solar activity periods the intervening dry period 5900 5200 cal yr bp with high ms high si and low toc corresponded to an intensified dust activity interval and stronger winter monsoon this multi centennial climatic fluctuation of wet periods 6200 5900 cal yr bp and 5200 4800 cal yr bp and an intervening dry period 5900 5200 cal yr bp in central korea was more synchronous with climate change in the arid inner part of china than with that in south china suggesting possible strong high latitude driven climatic influences e g north atlantic cooling events during the middle holocene

impacts of post depositional processes on rapid monsoon signals recorded by the last glacial loess deposits of northern china abstract rapid east asian monsoon oscillations recorded by chinese loess are thought to be dynamically linked to north atlantic climate however few efforts have been made to assess the effects of post depositional processes e g surface mixing and pedogenesis on loess paleoclimatic records here a detailed optically stimulated luminescence dating of a thick loess sequence from the western loess plateau is presented offering a reliable chronology for last glacial deposits magnetic susceptibility and mean grain size records from three loess paleosol sequences along a northwest southeast transect are investigated to evaluate impacts of post depositional processes on these loess based proxy records our results indicate that 1 loess sequences developed within the flat tableland of the central and western loess plateau are nearly continuous during the last glaciation and 2 post depositional processes have distinct impacts on rapid monsoon signals recorded in loess sequences from different regions in the central loess plateau rapid monsoon signals have been attenuated to various degrees depending on the sedimentation rate and pedogenic intensity in the northwestern loess plateau however due to high sedimentation rate and relatively weak pedogenesis high resolution grain size oscillations reliably record rapid monsoon changes and can be well correlated to rapid climate changes recorded in the greenland ice core and hulu cave stalagmite

shrinkage of east asia winter monsoon associated with increased enso events since the mid holocene instrumental records indicate a close relationship between the el nino southern oscillation and the east asian winter monsoon eawm on interannual to decadal time scales however few studies have examined possible links between them on centennial millennial time scales in northeast china modern observations show that the immigration of temperate forest trees such as pinus pine and quercus oak into cold temperate boreal forest is sensitive to changes in winter temperature here we present a continuous high resolution pollen record from lake moon in the central part of the great khingan mountain range northeast china the record reveals increasing contents of pinus and quercus pollen after similar to 6 0 ka cal bp which may indicate a gradual weakening of the eawm it is broadly coupled with an increasing el nino frequency since the middle holocene and we observe a statistically significant correlation between the percentages of pinus and quercus and a time series of el nino events on the centennial to millennial time scale the results of wavelet analysis and band pass filtering show that the occurrence and development of el nino have also promoted a weaker eawm after similar to 6 0 ka cal bp which is inversely correlated with the variation of the ca 500 year cycle originated from changes in solar output these results imply that the climate transition in the mid holocene is caused by the change of variations in solar activity and amplified by ocean circulation el nino southern oscillation to influence the east asian monsoon system especially the eawm and finally change the vegetation in great khingan mountain range

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

changes in mineralogy of loess paleosol sections across the chinese loess plateau quantitative mineralogical analysis of bulk samples and single particles was carried out on three loess sections of different local climate settings on the chinese loess plateau clp mineralogy geochemistry and single particle petrography of loess and paleosols are relatively uniform over the clp however in detail there are mineralogical changes related to eolian process and chemical weathering particle size sorting eastward from western sources led to an eastward increase of the total phyllosilicate contents enriched in fine illitic clay minerals after deposition detrital minerals susceptible to chemical weathering were sequentially altered in a progressive fashion with increasing precipitation in the order of calcite dolomite biotite illite chlorite amphibole and plagioclase the weathering of biotite chlorite and illite resulted in a significant increase of expandable phyllosilicate contents the sequential weathering of the minerals is reflected chemically in the decrease of na and mg and the increase of iron oxidation mineralogy of the chinese loess at individual sites reflects the effects of size fractionation during eolian transportation and progressive sequential weathering along the climatic gradient and it is essential to consider both effects when using mineralogical and dependent chemical data in the paleoclimatic reconstruction of the clp

bio climatic imprints on a holocene loess palaeosol from china micromorphology heavy minerals pollen and soil properties were examined in a typical holocene loess profile in the north of the loess plateau consisting of a palaeosol locally known as the ansai palaeosol underlain by the malan loess and overlain by modern loess the palaeosol consists of an upper humus rich ab horizon over a clay rich bt horizon the humus rich horizon is intensely weathered contains precipitated calcitic material derived from the overlying modern loess and has both high pollen content and diversity clay coatings in the clay rich horizon indicate formation by eluviation illuviation of clay pedogenetic characteristics and pollen analysis imply that the vegetation during the time of most intensive soil development is likely to have been a warm temperate forest a complex interpretation of the loess palaeosol sequence recognizes several development stages the phase of soil development maximum and minimum limiting ages for which are ca 8800 and 4400 c 14 years bp involved continuing but reduced loess deposition and successive holocene bio climatic environment overprinted new features on the palaeosol c 2003 elsevier ltd all rights reserved

last glacial pollen record from lanzhou northwestern china and possible forcing mechanisms for the mis 3 climate change in middle to east asia abstract the vegetation on the northeastern margin of the tibetan plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive pollen samples from the fanjiaping loess section in lanzhou on the western chinese loess plateau clp were analyzed in conjunction with osl dating the results indicate that pollen zone b 60 6 46 0 ka correlative to the early mis 3 had the greatest abundances of cupressaceae tsuga gramineae and cyperaceae of the entire section suggesting a warm phase during the last glacial period these pollen taxa decreased significantly in abundance in the zones c 46 0 39 0 ka and d 39 0 27 0 ka reflecting a substantial climate cooling from the middle mis 3 to mis 2 these results correlate with climate records from the south china sea the clp baikal lake north america north atlantic ocean and other regions and probably correspond with the decline of northern high latitude insolation and the increase of global ice volume from 50 to 20 ka in particular arboreal pollen fern spore and algae abundances declined sharply since 40 ka while shrub and herb pollen reached the highest abundances conifer pollen picea and abies abundance also rose markedly and increased up the section this implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since 40 ka the decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a snow ice albedo feedback which would result in less climate sensitivity to radiative forcing meanwhile vegetation decline in the northern hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling enhancing the growth of polar ice sheets since 40 ka the development of polar ice sheets increased the polar to equator temperature and pressure gradients strengthening the westerlies and supplying plenty of moisture to northwest china during 40 30 ka lake sediments developed widely on the tibetan plateau during 40 30 ka probably related to an increase in the seasonality of middle to low latitude insolation which caused an enhancement of glacier melting on the plateau

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

10be in chinese loess we report a first series of10be measurements on chinese loess covering the last 750 000 years the10be concentration shows a tendency to decrease with increasing grain size leaching experiments with acid solutions show that10be is strongly bound to particles and therefore mobility due to dissolution can be excluded the10be record in loess shows features similar to those observed in 180 records from deep sea sediments which strongly reflect climatic variations this allows one to correlate the10be loess records with 180 deep sea records and to establish a time scale based on this time scale accumulation rates of loess and10be fluxes can be calculated these reveal generally higher values for cold arid and windy periods than for warm humid and calmer intervals

comparison and implication of tex86 and u37k temperature records over the last 356kyr of odp site 1147 from the northern south china sea abstract proxy records from the south china sea scs have played an important role in understanding late quaternary scs environmental changes and the east asian monsoon eam variations but few long sea surface temperature sst records have been generated from the scs the recently established tex86 index provides an opportunity to generate long sst records especially for tropical oceans but the applicability and climatic interpretation of the tex86 index for the scs need further study we report and compare orbital scale resolution ca 5 3 kyr tex86 and u37k temperature records of the past 356 kyr for odp site 1147 from the northern scs both records display clear and similar glacial interglacial patterns the u37k sst fluctuated between 22 3 c and 28 3 c with a glacial interglacial difference of 4 5 c while the tex86 temperature fluctuated between 20 3 c and 25 4 c with a slightly smaller glacial interglacial difference of ca 4 c the tex86 temperature has been consistently lower than the u37k temperature over the past 356 kyr consistent with previous studies suggesting that the u37k index is a proxy for sst but the tex86 index is a proxy for subsurface temperature thus it is proposed that the temperature difference t between the u37k and tex86 records reflects mixed layer depth mld changes in the northern scs which fluctuated between 0 3 and 4 0 c with high values mostly during interglacials and lower values mostly during glacial stages mld changes in the northern scs are interpreted to be driven by eam changes with stronger winter monsoon resulting in a deeper mld and a smaller t thus the combination of u37k and tex86 records and their t can be used to reconstruct east asian winter monsoon variations as well as their influences on the hydrographic structure of the scs

high resolution climate record from the beijing area during the last glacial interglacial cycle the zhaitang loess section located in the western suburbs of beijing has yielded a very high resolution magnetic susceptibility record for the last glacial and interglacial period all substages can be clearly defined in marine isotope stage mis 5 s1 and even also in substage 5a demonstrating comparable detail with vostok and parts of the grip ice record rapid climate shifts during the eemian period may have extended to continental asia but exerted only a weak influence on the zhaitang record abrupt climate transitions 5b 5c 5d 5e recorded in this section from the ne edge of the plateau show more detrial than most other chinese loess records these three well defined peaks in substage 5a imply sensitivity of the east asian monsoon to rapid hemisphere scale climate change and the prospect of finding more information on orbital and non orbital events in the loess sequence

molluscan assemblages from the loess of north central china abstract although molluscan faunas are the most widespread fossil remains in the chinese loess there have been very few attempts to use their potential for climatic reconstruction or to develop ciimato stratigraphic schemes this paper reports assemblages of mollusca from three sites in the north and south central parts of the loess plateau and evaluates the uses of molluscan faunas as climatic proxies in the s 1 palaeosol the malan loess and s o palaeosol the molluscan sequence is compared with the record obtained from pedological and magnetic techniques the current study shows that major peaks in magnetic susceptibility thought to be due to pedogenesis under warm humid conditions can be matched by levels of high molluscan abundance the occurrence of a sharp molluscan peak within the malan loess otherwise only indicated by a slight increase in magnetic susceptibility is held to be due to the existence of a short lived humid episode and demonstrates the sensitivity of mollusca as indicators of relatively low magnitude climatic shifts not well indicated by other lines of evidence

records of late holocene east asian winter monsoon in the east china sea key grain size component of quartz versus bulk sediments abstract quartz isolated from bulk sediments taken from a core obtained from the distal mud area in the outer shelf of the east china sea was used as a proxy in order to determine the strength of the east asian winter monsoon eawm this data was compared with the grain size of bulk sediment from the same core it was found that the content of the key quartz based indicator fraction 15 2 65 6 m correlated well with the eawm strength with reference to current conditions high content of quartz in the selected fraction reflected strong eawm and vice versa the core record spanned 2100 years and three periods of change in eawm strength were identified a period of increased eawm strength prior to 1520 cal bp was followed by a period of weakened eawm strength from 1520 to 720 cal bp which is consistent with the sui tang warm period and the medieval warm period this is followed by a period of slightly increased eawm between 720 and 220 cal bp which corresponds to what is called the little ice age the history of eawm revealed by the quartz based proxy is in striking agreement with results from a previous study on bulk sediment based proxy however the quartz based proxy showed much higher sensitivity and resolution to the eawm strength and displayed much more distinct and sharper boundaries of transition across the three intervals of eawm change compared to the bulk sediment records eleven short eawm strengthening periods were found compared with four by the bulk sediment based proxy therefore this suggests that the quartz grain size proxy is a superior indicator of the winter monsoon strength in the study area