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

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

vertical and horizontal distribution of sedimentary facies and hydromorphic paleosols around paleo lake in the pliocene sediments in southwest japan abstract the collaborative study between descriptive paleopedology and sedimentology for the pliocene sediments in southwest japan clarified the paleo groundwater table at lake margins and the change of the paleoclimatic conditions in the coastal region of eastern asia during the pliocene period 3 4 ma some hydromorphic paleosols were formed in the proximal floodplain and the natural levee which are generally located in a high topographic position and these paleosols finally reached a similar maturity to ultisol and inceptisol the vertical variation of the sedimentary facies suggests the increased sedimentation rates and increased volume of sediment supply during this period the stratigraphic distribution of the hydromorphic paleosols in the pliocene formation implies the rising of the paleo groundwater table and to become considerably fluctuating of the paleo groundwater table the temporal change in weathering conditions implies that precipitation increased during the middle pliocene warm period

the paleoclimatic record provided by eolian deposition in the deep sea the geologic history of wind the mineral component of pelagic sediment is brought to the deep sea by transport in the wind extraction and analysis of this dust allows estimation of the past aridity of the eolian source region via flux determinations and of the intensity of the transporting winds from grain size data these two parameters the grain size and mass flux of dust vary independently there are three significant sources of modern dust eastern and central asia northwest africa and arabia all in the northern hemisphere as the rainfall associated with the intertropical convergence zone is an effective barrier to southerly transport of dust the northern hemisphere is an order of magnitude more dusty than is the southern an asymmetry that has characterized most of the cenozoic eolian flux data show that most of the northern hemisphere was more arid during glacial maxima with 3 to 5 times as much dust transported during glacial stages than during interglacials only northwestern south america varied in the opposite sense the periodicity of quaternary variation in both eolian flux and eolian grain size data is strongly influenced by the milankovitch cycles of orbital variability wind intensities vary on a shorter time scale than the general 100 kyr cycles of glaciation and general aridity eolian grain sizes display forcing at precessional 19 and 23 kyr tilt 41 kyr and at approximately 30 kyr periodicities as a result the generalization that winds are uniformly stronger during glacial times is not valid whole cenozoic records show that the largest change in dust flux an order of magnitude increase occurred in the northern hemisphere and reflects continental drying associated with the late pliocene onset of northern hemisphere glaciation southern hemisphere eolian records show no sign of paleoclimatic changes in the late pliocene the most important change in cenozoic atmospheric circulation was a severalfold reduction in wind intensity that occurred at the time of the paleocene eocene boundary before then latest cretaceous and paleocene winds were essentially as strong as those of the late cenozoic this shift appears to be one of several climatic responses to a change in the nature and amount of global heat transport at about 55 ma

vegetation and climate changes during the last two glacial interglacial cycles in the western mediterranean a new long pollen record from padul southern iberian peninsula abstract a new sediment core from padul padul 15 05 provides a long and continuous sedimentary and paleoenvironmental record of the last 200 kyr here we present a detailed palynological study from this sedimentary sequence with new vegetation and paleoenvironmental data and a climatic interpretation for the last two climatic cycles from the southern iberian peninsula in the western mediterranean region pollen analysis from this core shows orbital scale vegetation oscillations mainly forced by precession and eccentricity pointing into insolation as the principal factor controlling vegetation changes at this latitude the last two glacial interglacial cycles from mis 6 to the present as well as stadial and interstadial phases are well represented and characterized by significant oscillations in mediterranean forest in the area but several differences with respect to other mediterranean long pollen records can be recognized some of these disparities between regions seem to be more related to different precipitation rates linked to the specific geographical features e g strong topographic relief than to latitudinal differences between the sites in addition a lake level reconstruction based on palynological data was developed and compared with the previous reconstruction from this record representing local environmental changes in the padul wetland that seems to be related to precipitation evapotranspiration balance and therefore to changes in regional climate conditions during glacial stadial conditions recorded by maxima in xerophytes the p e increased due to very low evapotranspiration resulting in high lake levels while during warmer interglacial interstadial phases except for the mis 5e mainly represented in this record by maxima in the mediterranean forest water level decreased as a result of high evapotranspiration exceeding precipitation input the comparison of the new padul 15 05 pollen record with the two previous palynological studies from padul shows significant differences mainly due to disagreements in the age control of the sequences this study shows that an accurate age depth model becomes essential when interpreting long paleoenvironmental and paleoclimate records

major element and ree compositions of pliocene sediments in southwest japan implications for paleoweathering and paleoclimate abstract the history of the east asian monsoon and the relationship between the development of the monsoon climate tectonics and global climate are complicated and controversial earlier studies have indicated that the east asian monsoon fluctuated in the asian interior during the pliocene thus the chemical weathering record in coastal regions of east asia can be the key to elucidating its evolution as well as the kuroshio current variability the present study clarifies the chemical weathering conditions in southwest japan based on the concentrations of major elements and rare earth elements rees in lacustrine muddy sediments the chemical weathering was moderate between 4 4 and 3 8 ma between 3 8 and 3 4 ma chemical weathering significantly intensified as indicated by the high values of the chemical index of alteration that reached a maximum of 98 as well as the high concentrations of rees and light rees against heavy rees and kaolinite rich clay mineral compositions despite the wide variation in source rock compositions and grain sizes the degree of chemical weathering remained moderate during the early pleistocene the intense chemical weathering on land in southwest japan from 3 8 to 3 4 ma may have been regulated by alternating periods of warm and humid climate brought by the invasion of the kuroshio current and the intensification of the east asian summer monsoon

late pliocene quaternary evolution of redox conditions in the western qaidam paleolake ne tibetan plateau deduced from mn geochemistry in the drilling core sg 1 abstract manganese mn in lake sediments reacts strongly to changes of redox conditions this study analyzed mn concentrations in oxides carbonates and bulk phases of the calcareous lacustrine sediments of a 938 5 m long core sg 1 taken from the western qaidam basin well dated from 2 77 ma to 0 1 ma comparisons of extractions from diluted hydrochloric acid acetic acid and citrate bicarbonate dithionite demonstrate that variations of mn concentrations from acetic acid leaching mnhoac are mostly responsible for mn ii fluctuations in the carbonate phase taking into account the relevant processes during weathering transportation deposition and post deposition of mn bearing rocks we conclude that mn input from catchment weathering and paleolake redox condition provide the primary controls on variations in the mn records of carbonate and oxide phases we propose mnhoac as a new sensitive indicator of paleolake redox evolution and catchment scale climate change the mnhoac variations show a long term upward decreasing trend indicating a long term decrease of mn input from catchment weathering associated with increasing oxygen content in the paleolake bottom water the great similarities of the mnhoac record with other regional and global records suggest that paleolake redox changes and climatic drying in the qaidam basin may be largely related to global cooling

high resolution ammonium ice core record covering a complete glacial interglacial cycle high resolution ammonium measurements were performed along the greenland ice core program grip deep ice core covering a complete climatic cycle no overall anthropogenic increase is observed over the last 300 years however springtime concentrations have roughly doubled since 1950 biomass burning is estimated to be a major source for ammonia emissions for preindustrial times it contributes between 10 to 40 to the total ammonium deposited on the central greenland ice sheet during the holocene no correlation is found between the ammonium summer concentrations recorded over the last 100 years and the area burned in northern north america which is considered to be the main source area for ammonium deposited on the central greenland ice sheet this suggests that the meteorological factor is predominant for the pattern of ammonium spikes observed in the ice core if unchanged meteorological conditions are assumed for the holocene as indicated by the 18o ice record a decreasing biomass burning activity toward present time can be derived from the ammonium ice record soil and vegetation emissions are responsible for the ammonium background concentrations in the ice the record therefore may be used to trace back the biomass history of the north american continent a pronounced decreasing trend in background ammonium is found during the holocene reflecting decreasing temperature and therefore lower nh3 emissions in the source region variations in the ammonium concentration during the glacial age are discussed in terms of changes in transport and deposition mechanisms and changes in source strength which can be related to the extent of the laurentide ice sheet the data suggest that the laurentide ice sheet was built up immediately after the last interglacial and went through several large fluctuations during the last ice age

late pliocene pleistocene changes in mass accumulation rates of eolian deposits on the central chinese loess plateau 1 late pliocene pleistocene changes in the mass accumulation rates mars of eolian deposits on the central chinese loess plateau clp are reconstructed from measured bulk sediment densities combined with sedimentation rates calculated for two loess red clay sequences the reconstructed mars demonstrate that over the past 3600 kyr distinct aridity humidity fluctuations occurred over glacial interglacial timescales and these were superimposed on a gradual long term drying trend comparisons of the clp mar record with the mar and 18o records for marine sediments suggest that the development of northern hemisphere ice sheets since the late pliocene has played a part in increasing the aridity of central asia in addition the phased uplift of the himalaya tibetan plateau evidently had a profound influence on the aridity of central asia this was mediated by variations in the east asian monsoonal circulation correlations among dust records from ice cores marine sediments and terrestrial loess over the last several glacial cycles provide compelling evidence that glacial periods are characterized by higher and more variable dust fluxes than interglacial intervals synchronous changes in the mar grain size and 18o records reveal dynamic linkages between asian interior aridity paleowind intensity and ice volume after the onset of major northern hemisphere glaciations

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

contribution of asian dust and volcanic material to the western philippine sea over the last 220 kyr as inferred from grain size and sr nd isotopes asian dust and volcanogenic materials are two major components in the northwestern pacific quantitatively distinguishing them and estimating their mass accumulation rates mars are very important for understanding regional and global climate change here we present the grain size composition of detrital sediments and the radiogenic strontium sr and neodymium nd isotopic compositions of different grain size fractions of detrital sediments that were recovered from the western philippine sea these new records show that the different grain size distributions can be associated with 1 asian dust from the western and central chinese deserts and chinese loess and 2 volcanogenic materials that were derived from the luzon islands the mars of this asian dust and volcanic materials are obtained by using weibull function fitting the mars of asian dust and volcanic materials are coupled with the glacial interglacial cycle these values are found to have been higher and more variable during the glacial period than during the interglacial period we argue that the strengthening aridity of the asian continent which is connected to solar insolation and ice volume variations from orbital eccentricity constitutes an important mechanism that drives the high mars of glacial dust in the western philippine sea the internal positive feedback of dust may be another important mechanism the significant increase in volcanic material during the glacial period was caused by sea level changes which were driven by the ice volume and solar insolation at high latitudes and by strengthened precipitation from the el nino southern oscillation enso which is driven by orbital eccentricity and precession cycles on the luzon islands

paleoclimatic record from the clay mineralogy of quaternary sediments of drill core dwj from jiudong subbasin western hexi corridor nw china the thick sedimentary deposits of the jiudong subbasin in the western hexi corridor of nw china can potentially provide important records of climate change in arid and semiarid areas subject to the interaction of the east asian summer monsoon easm and the westerlies here we present the results of a study of the clay mineralogy of the sediments of drill core dwj from the jiudong subbasin the clay minerals consist mainly of illite followed by chlorite kaolinite and smectite the clay mineral assemblages are used to define four paleoclimatic stages since 1 8 ma 1 during 1 8 1 2 ma the climate was relatively cold and arid 2 during 1 2 0 9 ma it was relatively warm and wet with strongly seasonal precipitation 3 during 0 9 0 3 ma there was a long term trend of cooling and drying and 4 during 0 3 0 1 ma the climate was warmer and wetter than during the previous period with strongly seasonal precipitation the paleoclimatic record of the jiudong subbasin since 1 8 ma is consistent with records from the tengger desert and typical monsoonal areas this suggests that the easm penetrated into the central regions of the north qilian shan and zhangye jiudong subbasin during 1 2 0 9 and 0 3 0 1 ma

orbital scale benthic foraminiferal oxygen isotope stratigraphy at the northern bering sea slope site u1343 iodp expedition 323 and its pleistocene paleoceanographic significance abstract a continuous composite oxygen isotope 18o stratigraphy from benthic foraminifera in the bering sea was reconstructed in order to provide insight into understanding sea ice evolution in response to northern hemisphere glaciation oxygen isotope records from multiple species of benthic foraminifera at integrated ocean drilling program iodp expedition 323 site u1343 54 33 4 n 176 49 0 e water depth 1950 m yield a highly refined orbital scale age model spanning the last 1 2 ma and a refined age model between 1 2 and 2 4 ma an inter species calibration was used to define species offsets and to successfully obtain a continuous composite benthic 18o record correlated with the global composite benthic 18o stack curve lr04 to construct an orbital scale age model the consistency of the benthic 18o stratigraphy with biostratigraphy and magnetostratigraphy confirms the reliability of both methods for constraining age the time difference between cyclic changes in sedimentary physical properties and glacial interglacial cycles since 0 8 ma is notable and suggests that physical properties alone cannot be used to construct an orbital scale age model amplitude changes in physical properties and a significant drop in the linear sedimentation rate during glacials after 0 9 ma indicate that the glacial sea ice edge extended beyond the bering sea slope site u1343 at this time

stacked 2 6 ma grain size record from the chinese loess based on five sections and correlation with the deep sea δ18o record 1 this study aims to establish a stacked climate record of the quaternary period from the chinese loess sequence and to address the forcing mechanisms for the regional climate history of the loess plateau by correlating the stacked record with a composite 18o record in deep sea sediments a total of 18 352 samples were obtained from five loess sections located at baoji lingtai jingchuan puxian and pingliang in the southern and middle loess plateau these yielded high resolution grain size records between section correlation of these shows that although small depositional hiatuses are present in places within a single section most parts of the sections display near continuous dust deposition throughout the quaternary the grain size records were tuned simultaneously to the theoretical variations in obliquity and precession of the earth s orbit the grain size records plotted on their orbital timescales were then averaged to form a stacked loess grain size time series termed the chiloparts record this resolves most of the orbital timescale paleoclimate events buried in the loess soil sequences of the southern and middle loess plateau and can be used as a regional archive of the pleistocene climate history in the loess plateau comparison of the chiloparts record with a composite marine 18o record shows that for the past 1 8 ma the loess paleosol record can be correlated almost cycle by cycle with the marine record several discrepancies in the climatic events between the two records have also been identified implying that regional forcing mechanisms may have played a part in the climatic evolution of the chinese loess plateau

atmospheric dust loadings and their relationship to rapid oscillations of the asian winter monsoon climate two 250 kyr loess records abstract similar to records extracted from marine sediments paleoceanography 6 1991 349 rev geophys 32 1994 159 and ice cores nature 399 1999 429 estimates of dust inputs to the chinese loess plateau indicate that the dust fluxes during periods of extensive glaciation were higher than those in interglacial times catena 18 1991 125 quat res 41 1994 35 prior studies nature 375 1995 305 quat sci rev 18 1999 811 indicating that millennial scale oscillations of asian dust occurred during glacial times have raised questions about the conditions that govern the generation and transport of dust particularly those operating during the winter monsoon we present here atmospheric dust loadings reconstructed from two central loess plateau sections these extended our present day observations to cover the last two glacial cycles and thus provided a unique perspective on the relationships between asian dust and climate the reconstructed loadings indicate that higher and more variable dust concentrations occurred during glacials compared with interglacials and the high dust loadings frequently preceded decreases in winter sea surface temperature of the north pacific ocean during glacials a mechanism was proposed to explain how the thermal contrasts between the eurasian continent and the surrounding oceans induced by the high dust loadings could either trigger or modulate millennial scale variations in the winter monsoon climate and thus rapid transitions of glacial dust loadings

origin and weathering properties of loess paleosol sequence in the goseong area on the east coast of south korea abstract this study aims to investigate the origin and weathering properties of the loess paleosol sequence in the goseong area on the east coast of south korea and to discuss the local sediment inputs and their paleoclimatic implications the geochemical properties suggest that the largest proportion of the sequence originated from the chinese loess plateau and or its source areas with a smaller quantity originating from the weathering products of the bedrock around the section although its origin can be regarded as the chinese loess plateau and or its source areas the sequence shows more weathered features than the chinese loess plateau moreover the weathering environments in south korea were different from those in the chinese loess plateau the difference in weathering properties may be attributed to the more humid climatic conditions in south korea the abundance of local sediment input to the sequence was controlled by sea level fluctuations in the east sea of korea and the global ice sheet developments during the glacial and interglacial cycles in the quaternary because local sediment occupies only minor proportions in the sequence the monsoon and westerly circulations in northeast asia played an important role in the loess formations in south korea as well as in the chinese loess plateau

the chinese loess in xifeng i the primary study on magnetostratigraphy of a loess profile in xifeng area gansu province summary 1848 specimens were collected systematically from about 900 horizons in the loess profile of xifeng gansu province china the magnetostratigraphy is established on the basis of the palaeomagnetic results after thermal cleaning usually at 300 c this result has been found to be generally consistent with previous work in luochuan the susceptibility varies regularly with the appearance of loess and palaeosol in the profile and thus could be used as a criterion to classify the loess and palaeosol sequence

eight glacial cycles from an antarctic ice core the antarctic vostok ice core provided compelling evidence of the nature of climate and of climate feedbacks over the past 420 000 years marine records suggest that the amplitude of climate variability was smaller before that time but such records are often poorly resolved moreover it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records here we report the recovery of a deep ice core from dome c antarctica that provides a climate record for the past 740 000 years for the four most recent glacial cycles the data agree well with the record from vostok the earlier period between 740 000 and 430 000 years ago was characterized by less pronounced warmth in interglacial periods in antarctica but a higher proportion of each cycle was spent in the warm mode the transition from glacial to interglacial conditions about 430 000 years ago termination v resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases but there are significant differences in the patterns of change the interglacial stage following termination v was exceptionally long 28 000 years compared to for example the 12 000 years recorded so far in the present interglacial period given the similarities between this earlier warm period and today our results may imply that without human intervention a climate similar to the present one would extend well into the future

salinity changes in the north west pacific ocean during the late pliocene early quaternary from 2 73 ma to 2 52 ma recent research has increasingly advocated a role for the north pacific ocean in modulating global climatic changes over both the last glacial cycle and further back into the geological record here a diatom 18o record is presented from ocean drilling program site 882 over the pliocene quaternary boundary from 2 73 ma to 2 52 ma mis g6 mis 99 large changes in 18odiatom of c 4 from 2 73 ma onwards are documented to occur on a timeframe broadly coinciding with glacial interglacial cycles these changes are primarily attributed to large scale inputs of meltwater from glacials surrounding the north pacific basin and the bering sea despite these inputs and associated change in surface water salinity on the basis of existing opal and uk37 temperature data and new modelled water column densities no evidence exists to suggests a removal of the halocline stratification or a resumption of the high productivity system similar to that which prevailed prior to 2 73 ma the permanence of the halocline suggests that the region played a key role in driving global climatic changes over the early glacial interglacial cycles that followed the onset of major northern hemisphere glaciation by inhibiting deep water upwelling and ventilation of co2 to the atmosphere

magnetostratigraphy and its paleoclimatic significance of the pl02 borehole in the yinchuan basin abstract the basin sediment provides an important means of studying regional tectonic actives however regional climate factors overlaying tectonic actives affect the sedimentary process in the basin because of the lack of long term scales data the research on climate change in the arid and semi arid region is limited the pl02 core located in the center area of deposition in the yinchuan basin has a thick deposit with a higher resolution and sedimentation rate making itself practical for the reconstruction of the paleoclimate and the coupling relationship between regional tectonic activities and climate change the study of the 720 m borehole near pingluo county is presented in this paper the chronostratigraphic sequence of the core is established by palaeomagnetic dating the magnetostratigraphic correlation to the geomagnetic polarity timescale shows that the pl02 core recorded the brunhes matuyama gauss jaramillo olduvai kaena and mammoth polarity chron or subchron the sedimentation rate and the magnetostratigraphic of the core indicate that the onset of the pl02 core in this section occurred at 3 4 ma bp the analysis of the core established a detailed chronological framework for regional geological research at the stage of 3 22 3 04 ma 2 581 1 95 ma and after 0 012 ma the sedimentation rate increases gradually which archive three regional tectonic subsidence events the frequency dependent susceptibility of the sediment is used to reconstruct the paleoclimatic change the frequency dependent susceptibility is more effective than the magnetic susceptibility on reflecting regional climate change in the basin from 3 4 to 0 467 ma the gradual decrease of frequency dependent susceptibility reflects the regional climate change from warm and humid to cold and dry since 0 467 ma the gradual increase of the frequency dependent susceptibility corresponds to the climate becoming warm and humid again

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

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

a rock magnetic study of loess from the west kunlun mountains west kunlun mountains have continuous loess deposits however very few papers have explored the rock magnetic characteristics of loess deposited there thus although kunlun mountains loess is one of the useful paleoclimate archives its importance has not been emphasized here we present detailed rock magnetic and bulk grain size studies on a 207 m loess core on the northern slope of the west kunlun mountains we find that magnetic susceptibility of loess from the northern slope of the west kunlun mountains is not controlled by changes in the concentration of ultrafine pedogenic magnetite and maghemite but instead controlled by changes in the concentration of aeolian multidomain magnetite and maghemite this is unsurprising given the low rainfall of the kunlun region and the lack of postdepositional weathering and soil formation in these aeolian sequences in addition we find that magnetic susceptibility values increase dramatically at 111 m corresponding to an age of similar to 0 5 ma the magnetic susceptibility increase is accompanied by coarsening of both bulk and magnetic grain size and softening of magnetic mineralogy we tentatively tie these changes in rock magnetic and grain size parameter records to an expansion of desert environment

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

aeolian dust supply from the yellow river floodplain to the pleistocene loess deposits of the mangshan plateau central china evidence from zircon u pb age spectra the thick loess palaeosol sequences in the mangshan loess plateau mlp central china along the south bank of the lower reach of the yellow river provide high resolution records of quaternary climate change in addition substantial increases in grain size and accumulation rate have been inferred in the upper part of the loess sequence above palaeosol layer s2 this study investigates the sources of the long term dust supply to the mlp and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since s2 240 ka by using end member modelling of the loess grain size dataset and single grain zircon u pb dating our results indicate that the lower yellow river floodplain directly north of the mlp served as a major dust supply for the plateau at least since the deposition of loess unit l9 and indirectly suggest that the integration of the yellow river and the disappearance of the sanmen palaeolake took place before l9 900 ka the sudden change in sedimentology of the mangshan sequence above palaeosol unit s2 may result from an increased fluvial sediment flux being transported to the lower reaches of the yellow river because of tectonic movements initiated in the weihe basin around 240 ka furthermore sediment coarsening can be explained by the gradual southward migration of the lower yellow river floodplain towards the mlp since the deposition of palaeosol s2 the migration is evidenced by the formation of an impressive scarp and is likely caused by tectonic tilting of the floodplain area 2018 elsevier ltd

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

magnetostratigraphy and palaeoclimatic significance of late tertiary aeolian sequences in the chinese loess plateau summary the aeolian red clay sequence in the central part of the chinese loess plateau was investigated in an attempt to obtain magnetostratigraphic and palaeoclimatic records from the results we deduce that aeolian dust accumulation and the related east asia palaeomonsoon system began at least 7 6 myr ago and that the tibetan plateau had reached a significant elevation by that time the late tertiary palaeoclimatic history of the red clay as reflected by magnetic susceptibility is reconstructed for the time period 7 6 2 5 ma increases in aeolian dust accumulation for the last 7 6 myr appear to have a close relation with the uplift processes of the tibetan plateau the remarkable increase of aeolian dust accumulation beginning at 3 2 ma appears to reflect the influence of an increasing global ice volume on the east asian monsoon and aeolian dust accumulation

loess and the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap database abstract mineral dust is an important constituent of the solid load in earth s atmosphere the total atmospheric aerosol loading being both a function of and a factor affecting climatic change human actions have progressively enhanced atmospheric dust loading especially in the past century so that both natural and human induced effects of atmospheric dust on climatic change require more detailed research records of changing climate are preserved in cores from the ocean floors glaciers and ice sheets as well as in terrestrial sedimentary sections quantitative data on the present day distribution of atmospheric dust are sparse but simulation of dust transport and deposition has been modelled with some success the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap database was designed to serve as a global validation data set for use with earth system models of the palaeo dust cycle loess a wind borne silt deposited on the continents particularly in the past 2 6 myr is an important potential source of information on past atmospheric dust accumulation a recent initiative sought to improve the terrestrial data coverage within the existing dirtmap database by involving representatives from key loess regions in coordinating the data synthesis process so as to facilitate interaction between the dust modelling and the data collection communities the results are presented in this issue in order to compare past minerogenic dust records loess with those in ice and ocean cores mass accumulation rates mars have been calculated as fluxes in g m2 yr the loess regions covered include north and south america europe siberia eastern asia and australasia it is acknowledged that provision of age models for the calculation of realistic mar values depends upon a number of conditions most notably sound chronostratigraphy and realistic values of loess dry bulk densities the mar data sets presented here show some notable variation both within and between the studied regions regional mar coverage also varies reflecting differences in the availability of key data on loess from one world region to another loess facies vary according to specific site and source conditions as well as in response to post depositional re working of primary wind lain loess by surface geomorphic processes mean particle size consistently declines downwind and terrace valley and upland sites generally yield the highest mar values characteristics noted in all regions discussed here the loess accumulations in two major world regions central and eastern asia and the great plains region of north america differ in some important respects from loess elsewhere in that they lie peripheral to deserts and are remote from the former sites of major quaternary ice sheets it is concluded that the mars for terrestrial sites obtained from loess are consistently higher than those obtained from ocean and ice cores so that future climatic models designed to study the role of global atmospheric dust will have to take full account of the present and past dust records over the continents

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

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

a direct link between the china loess and marine δ 18 o records aeolian flux to the north pacific most studies of quaternary climates conducted during the past 150 years have focused on glacial sequences and for the past 25 years marine sediments have provided significant further understanding of glacial and interglacial palaeoclimates an important goal of palaeoclimatology however to link the well known detailed continental records to marine records of similar resolution has yet to be realized the classic loess sequences of china provide an apparently continuous record of continental climate over the past 2 4 million years1 2 the oxygen isotope 18o timescale developed from the marine record3 gives us a global chrono stratigraphy of late pleistocene climates previously it has been suggested in studies of the aeolian component in pelagic sediments that it may be possible to link these two records directly by finding a suitable core from the north west pacific downwind from china4 5 here we report the results of such an effort for core v21 146 fig 1 and tie the last 500 000 years of the chinese loess soil sequence directly to the 18o timescale and in so doing refine the dating of regional loess and soil horizons

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

magnetostratigraphy and authigenic 10be 9be dating of plio pleistocene abyssal surficial sediments on the southern slope of mariana trench and sedimentary processes during the mid pleistocene transition

mid pliocene global land monsoon from pliomip1 simulations abstract the mid piacenzian pliocene warm period approximately 3 3 3 0 ma monsoon not only provides us with a useful insight into the future monsoon under a warming scenario with high atmospheric co2 concentration but is also hypothesized to play a key role in climate feedback through impact on the carbon cycle on a geological timescale the monsoon evolution over time is one key to test this hypothesis in this sense we examine the mid piacenzian global land monsoon area glma precipitation glmp and glmp intensity glmpi using all available model data from the pliocene model intercomparison project phase 1 pliomip1 relative to the pre industrial period both the glma and glmp increase in the mid piacenzian and by an average of 7 3 and 5 8 respectively on a large scale the increased glmp comes mainly from northern africa asia and northern australia quantitatively it is the variation of glma not of glmpi that makes a major contribution to the glmp change further analysis reveals that anomalous inland water vapor transportation due to the reduced large scale meridional thermal contrast in the mid to upper troposphere together with the variation of vertical moisture advection and evaporation explains most of the global land monsoon changes a model data comparison shows that the simulated monsoon precipitation variations are roughly consistent with the reconstructions in northern africa asia northern australia central america and eastern south america moreover the intensified mid piacenzian asian monsoon which is supported by both simulations and reconstructions or an overall intensified global land monsoon is hypothesized to contribute to the lowering of atmospheric co2 concentration and the subsequent onset of the sustained major northern hemisphere glaciation

glacial and interglacial patterns for asian dust transport abstract particle size distributions and depositional fluxes were investigated for present day asian dust and for the late quaternary loess palaeosol sequences from central china the regional scale transport of asian dust during interglacial stages is mainly attributable to non dust storm processes and is dominated by northwesterly surface winds conversely during glacial stages the impact of dust storms on the accumulation of loess is enhanced these regional effects are in contrast to the global dispersal of dust which is associated with transport by upper level westerly winds and is mainly the result of desert dust storms during both glacial and interglacial conditions temporal differences in the dust transport patterns to the loess plateau suggest that the variability in the coarse particle fraction 20 m during interglacial times is not directly attributable to the strong dust storms and dust fall events that have been linked to a strengthening of east asian winter monsoonal winds this is in contrast to the dust deposition rates which are strongly influenced by the monsoonal circulation

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

evolution of a deep water ferromanganese nodule in the south china sea in response to pacific deep water circulation and continental weathering during the plio pleistocene abstract the south china sea scs is connected to the west pacific through a deep channel in the luzon strait thus the scs deep water is sensitive to the evolution of pacific ocean circulation which significantly influences the global climate system geochemical data pb isotope and redox sensitive elements data and magnetic data were determined for a fe mn nodule obtained from jiaolong seamount in the central scs these records reflect interactions between changes in ice sheets deep pacific circulation and weathering inputs to the deep scs during the pliocene and quaternary our results show that the scs deep water environment can be divided into three major stages stages 1 3 stage 1 4 8 1 4 ma was characterized by a well oxygenated pacific deep water pdw and lower dust inputs then moderate stable deep water ventilation and greater inputs of asian dust occurred during stage 2 1 4 0 9 ma during stage 3

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

reinterpreting climate proxy records from late quaternary chinese loess a detailed osl investigation abstract numerous authors have utilised physical properties of chinese loess and red clay deposits to develop apparently detailed and continuous past climate records from the miocene into the holocene many of these studies have further suggested that the principal climatic agent responsible for the aeolian emplacement and diagenesis of chinese loess the east asian monsoon has fluctuated rapidly on millennial to sub millennial timescales in concert with dramatic changes in the north atlantic dansgaard oeschger cycles and heinrich events and the western pacific el nino southern oscillation much of this evidence is based on reconstructions and age models that are tied to assumptions concerning the nature of loess sedimentation and diagenesis for example the belief that loess sedimentation can be viewed as essentially continuous some authors have however cast doubt on these assumptions and suggest that the application of radiometric techniques may be required to determine their validity recent studies utilising optically stimulated luminescence osl methods have reinforced these doubts and here osl dates obtained at 10 cm intervals from three sites along a transect across the chinese loess plateau have been used in combination with climate proxy evidence to test the existing assumptions that underpin many palaeoclimatic reconstructions from loess in this way the first time continuous and independently dated late quaternary climate reconstruction is developed from loess the data indicate that sedimentation is episodic and that once emplaced loess is prone to pedogenic disturbance diagenetic modification and in some cases erosion the relationships between proxies and sedimentation rates are also assessed and climatic interpretations based on different age models compared the implications of these findings for reconstructions of climate from loess are explored and comparisons are made between the developed palaeoclimate records and evidence from ice and ocean cores this exercise also highlights important information concerning the relative influence of forcing mechanisms behind east asian monsoon change over the late quaternary

three large shifts in east asian monsoon circulation indicated by loess paleosol sequences in china and late cenozoic deposits in japan abstract correlations between loess paleosol sequences in china and late cenozoic deposits in japan suggest that the east asian monsoon circulation experienced three large shifts during the late cenozoic about 2 5 ma ago the onset of loess accumulation in north central china accompanied by a dramatic increase in eolian dust flux to the sea of japan marked a pronounced development of the east asian winter monsoon winds since ca 1 2 to 1 1 ma ago the obvious alternation of loess and paleosols in the chinese loess sequence with increased coarse grain size fraction in the loess units and higher than average magnetic susceptibility values in the paleosols and the repeated occurrence of interstratified marine clay layers in the osaka group of central japan indicate that the east asian monsoon circulation strengthened and the contrast between the summer and winter monsoons increased the paleosols of the chinese loess sequence were more strongly developed from ca 550 ka ago and loess started to accumulate in areas of the mid lower reaches of the yangtze river and in lake biwa of central japan from ca 450 ka ago reflecting more vigorous summer and winter monsoon circulations since ca 550 to 450 ka ago these large changes in east asian monsoon circulation were not only related to the changing solar radiation global glacial interglacial cycles and the changing configuration of land and sea but were also directly controlled by the uplift of the tibetan plateau

retreat of the cold halocline layer in the arctic ocean we present a comparison of arctic ocean hydrographic data sets from the 1990s with a focus on changes in the upper few hundred meters of the eurasian basin the most recent observations discussed here were collected during the spring 1995 scientific ice expedition scicex 95 the second in a series of scientific cruises to the arctic ocean aboard u s navy nuclear submarines although the 1990s have seen an abundance of synoptic cruises to the arctic this was the only one to take place in winter spring conditions other data considered here were collected during the first scicex cruise in summer 1993 scicex 93 and during an icebreaker cruise to the eurasian basin in summer 1991 oden 91 a new russian american winter climatology is also used as a reference these comparisons reveal that the eurasian basin cold halocline layer has retreated during the 1990s to cover significantly less area than in previous years specifically we find a retreat from the amundsen basin back into the makarov basin the latter is the only region with a true cold halocline layer during scicex 95 changes are also seen in other halocline types and in the atlantic water layer heat content and depth since the cold halocline layer insulates the surface layer and thus the overlying sea ice from the heat contained in the atlantic water layer this should have profound effects on the surface energy and mass balance of sea ice in this region using a simple mixing model we calculate maximum ice ocean heat fluxes of 1 3 w m 2 in the eurasian basin where during scicex 95 the surface layer lay in direct contact with the underlying atlantic water layer the overall cause of water mass changes in the 1990s might have been a shift in the atmospheric wind forcing and resulting sea ice motion during the late 1980s which we speculate influenced the location where fresh shelf waters flow into the deeper basins of the arctic ocean finally we discuss two different mechanisms that have been proposed for cold halocline water formation and we propose a compromise that best fits these data

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

pleistocene climate change inferred from multi proxy analyses of a loess paleosol sequence in china abstract the aeolian loess blanketing the chinese loess plateau clp is sensitive to climate change in monsoonal east asia here we present a multi proxy climatic record from a pleistocene loess paleosol sequence from the lantian basin on the southern margin of the clp the measurements include magnetic susceptibility and related magnetic properties bulk median grain size color reflectance and the color inferred hematite versus goethite ratio hm gt a long term aridification and cooling trend during the interval from ca 2 22 0 43 ma is indicated by two magnetic grain size proxies corresponding to the global climatic cooling of the late cenozoic in addition at least four intervals of climatic extremes are evident in the record of hm gt ratio at 1 71 1 65 ma 1 26 1 24 ma 0 94 0 86 ma and 0 62 0 48 ma these intervals are characterized by distinct regional climates which contrast with the global climatic conditions represented in marine sediments for example a relatively arid climate is documented from 1 71 to 1 65 ma which was rapidly succeeded by a relatively humid climate which is associated with the earliest hominin with an age of ca 1 63 ma in the lantian basin

nonstationary phase of the plio pleistocene asian monsoon paleoclimate records indicate that the strength of the asian summer monsoon is sensitive to orbital forcing at the obliquity and precession periods 41 000 and 23 000 years respectively and the extent of northern hemisphere glaciation over the past 2 6 million years the timing phase of strong monsoons has changed by 83 degrees in the precession and 124 degrees in the obliquity bands relative to the phase of maximum global ice volume inferred from the marine oxygen isotope record these results suggest that one or both of these systems is nonstationary relative to orbital forcing

magnetostratigraphy and paleoclimatic interpretation of a continuous 7 2 ma late cenozoic eolian sediments from the chinese loess plateau an almost 300m thick eolian sequence of late cenozoic sediments which includes 162 5m of quaternary loess paleosols and 126m of late tertiary eolian red clay from the central part of the chinese loess plateau was investigated to determine the magnetostratigraphy the results show that eolian dust accumulation and by inference the related east asia paleomonsoon had begun by 7 2ma as paleomonsoon are largely controlled by the tibetan plateau this implies that the plateau had reached some critical elevation by 7 2ma the section also documents a rapid increase in eolian dust accumulation in the late cenozoic at 3 2ma that is probably due to the influence of global ice volume on the east asian monsoon

aeolian n alkane isotopic evidence from north pacific for a late miocene decline of c4 plant in the arid asian interior abstract aeolian deposition in the central north pacific has been well recognized to originate from arid asian interior while there is no doubt about the transport of organic matters along with the mineral dust from the source region little is known about the nature and changes of the terrestrial organic compounds preserved in the deep sea sediments in this study higher plant leaf wax n alkanes from odp site 1208 and site 886 in the north pacific since the middle miocene were analyzed to explore long term changes in vegetation and climate in the source region accumulation rates of leaf wax n alkanes show an increasing trend consistent with the documented climatic drying of the asian interior since the late miocene the records of carbon isotopic enrichment factors of c29 n alkane relative to atmospheric co2 ec29 co2 show a prominent decrease from 12 to 8 ma the average ec29 co2 value prior to 8 ma is 0 8 heavier than after 8 ma although almost all values of ec29 co2 25 3 to 21 3 are well within the range of c3 plants adjustment of isotope discrimination by c3 plants is not considered as the main cause of the observed variations instead changes in relative abundance of c3 vs c4 plants are invoked to interpret the ec29 co2 records higher c4 contribution 17 7 5 3 to the local vegetation is inferred for the period prior to 8 ma implying a slightly warmer climate in the source region a marked decline in c4 plants from 12 to 8 ma interpreted as a result of regional temperature drop coincides with the prominent growth of northern tibetan plateau around 8 ma along with the global cooling climate our results therefore point to apparently close links among plateau uplift development of drying and cooling climates and vegetation changes in the asian interior

formation and evolution of the badain jaran desert north china as revealed by a drill core from the desert centre and by geological survey abstract the deserts in north china are regarded as direct records of the process of inland asian aridification amongst these deserts those proximal to the chinese loess plateau clp are especially important because of their role as sediment source areas in order to investigate the formation history of the badain jaran desert the largest desert proximal to the clp a 310 m long drill core was obtained from the desert centre which reached the underlying basement rock the lithology of the core consists of an upper layer of aeolian sand with three intercalated layers of lacustrine sediments overlying alluvial fluvial deposits which are developed unconformably over red coloured basement rock a geological survey indicates that the lower red coloured basement rock is of late cretaceous age and is cut by a mesozoic erosion surface widely developed over the badain jaran area on the basis of optically stimulated luminescence and electron spin resonance dating and stratigraphic correlation a preliminary chronological framework was established which was improved by tuning the aeolian sand proportion of the drill core to earth orbital obliquity and precession this final chronology suggests that 1 the basal age of the desert strata is at least 1100 ka corresponding to the formation of the badain jaran desert and 2 that the formation of the erosion surface terminated and the surface had begun to subside by at least 1200 ka the formation of the desert can be summarized as follows the alluvial fluvial fan formed by the heihe river draining the qilian mountains provided sufficient sedimentary material to form the desert under an arid climate while the asian winter monsoon and the westerlies entrained the clastic sediments from the fan area which finally accumulated downwind more distant sediment transport was prevented by the intervening mountainous terrain these coupled processes were driven by tibetan plateau uplift and ongoing global climatic cooling after initial formation of the desert three humid phases occurred in mis 13 15 mis 5 and the holocene during which extensive lakes developed the sequential drying out of the lakes may reflect inter relationships between global climate and the intensity of the asian summer monsoon and the westerlies

evolving sources of eolian detritus on the chinese loess plateau since early miocene tectonic and climatic controls abstract the thick deposits of eolian dust on the chinese loess plateau provide a rare opportunity to explore the past changes of surface processes in response to climatic and tectonic oscillations here we report a 22 ma long nd and sr isotopic records of the eolian sources decreasing e nd values and increasing 86 sr 87 sr ratios of the eolian deposits has been observed from early miocene to about 7 ma which indicates growing material contribution from qilian mountains relative to the gobi altay mountains the source shift during 22 7 ma is interpreted to reflect the erosional response of the qilian mountains to its surface uplift between 7 ma and 1 2 ma the results show relative constant nd and sr isotopic compositions of the eolian deposits and thus suggest a constant source contribution between qilian mountains and gobi altay mountains synchronized uplift of the two mountain ranges during this period may explain the constant ratio of source contribution since 1 2 ma nd and sr isotopic records indicate that the relative debris input from qilian mountains drops rapidly as large scale topographic changes would not be expected in such a short time period the source shift since 1 2 ma might be by the differing erosional responses in qilian mountains and gobi altay mountains to the development of full glacial climate after the middle pleistocene transition this work shows that combined nd and sr isotopic signatures of the dust records are valuable proxies to monitoring past surface processes on the million years time scale

coeval changes in grain size and sedimentation rate of eolian loess the chinese loess plateau to determine the temporal spatial relationship between strength of the winds transporting the chinese loess and aridity conditions of the loess source area six loess sections located respectively in the northern middle and southern loess plateau were studied grain size distributions were analyzed on loess paleosol samples that are closely spaced in the sections time scales were established by tuning each of the grain size records to theoretical changes in the earth s orbital parameters results obtained show that during the last two glacial cycles particle size of the loess co varies with apparent sedimentation rates suggesting that variations in winter monsoon intensity and the aridity of the loess source area are tightly coupled this proximal relationship is in striking contrast with the observation of distal eolian clays in north pacific sediments we propose that this phenomenon may result from the proximity of the loess plateau to the source area and from the significant control of the winter monsoon on the expansion retreat changes of the deserts in the northern and northwestern china

history of asian eolian input to the west philippine sea over the last one million years the eolian component in pacific ocean sediments has been recognized as providing a direct link between the continental loess and marine delta o 18 climate records over orbital timescales since 500 ka here we extend this eolian record over the past one million years we constructed high resolution clay mineral stratigraphies based on delta o 18 chronology in sediments from the international marine past global change images core md06 3050 from the west philippine sea in order to trace the sources of clay minerals and reconstruct proxy records of past changes in the asian eolian input to the basin since 1 0 ma the clay mineral assemblage in core md06 3050 mainly consists of smectite similar to 65 and illite similar to 25 with minor kaolinite similar to 5 and chlorite similar to 5 provenance analysis suggests that smectite was derived mainly from the weathering of volcanic rocks on luzon island whereas illite chlorite and kaolinite were mainly transported as eolian dust by the east asian winter monsoon from central asia illite smectite values in core md06 3050 are generally higher and more variable during glacial periods and lower during interglacials suggesting that higher eolian input to the west philippine sea generally co varied with east asian winter monsoon intensity and more aridity in continental asia since 1 0 ma spectral analysis further reveals the close link between the extent of high latitude glaciation east asian winter monsoon intensity and eolian input to the west philippine sea at eccentricity 100 ka obliquity 41 ka and precession 23 ka bands since 1 0 ma c 2012 elsevier b v all rights reserved

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

orbital scale environmental and climatic changes recorded in a new 200 000 year long multiproxy sedimentary record from padul southern iberian peninsula abstract padul is one of the few wetland sites in southern europe and the mediterranean region that exhibits an unusually large temporal span 100 kyr and continuous quaternary sedimentary record previous core based studies from padul yielded paleoecological datasets i e pollen and organic geochemistry but with a poor age control that resulted in rather arbitrary climate inferences therefore precise age control and a multidisciplinary approach is necessary to understand long term regional environmental and climate change and the associated local response of the padul wetland environment here we present a new long sediment record padul 15 05 from this wetland in the southern iberian peninsula with the aim of improving the age control of the sedimentary sequence and carrying out up to date high resolution multiproxy analyses in this study the age control is based on 61 ams radiocarbon dates for the last ca 50 kyr bp and on the extent of amino acid racemization aar in mollusc shells extending back 118 kyr bp no numerical ages are available for the bottom part of the core but the sediment accumulation rates sar and the cyclostratigraphic analysis of the multiproxy data suggest that the core preserves a continuous record of the last 197 kyr from late mis 7 to present with millennial scale time resolution sedimentological lithology magnetic susceptibility xrd color geochemical xrf toc c n carbonate content and paleontological pollen charophytes gastropods data show co varying cyclical paleoenvironmental changes linked to orbital scale climatic variability silicon magnetic susceptibility ms and total organic carbon toc data show periodicities between 26 2 19 6 kyr linked to insolation which is strongly dominated by precession cycles at this latitude high values of si and ms data have been related to high siliciclastic detrital input from sierra nevada range during minima in insolation due to enhanced soil weathering erosion during regional aridity and lower forest cover recorded by the arboreal pollen which could also be favored by a minor biogenic productivity in addition warm climate conditions during maxima in insolation mostly resulted in negative precipitation evapotranspiration balance and low lake levels while cold glacial and stadial periods were mainly characterized by positive precipitation evapotranspiration balance and therefore high lake levels the improved chronology of the padul sedimentary sequence along with a multiproxy study permitted us to better relate environmental and vegetation changes to climatic events and to demonstrate how both local i e lake level sedimentation and regional i e vegetation environments responded to orbital scale climate changes

evolution of the arid climate in high asia since 1 ma evidence from loess deposits on the surface and rims of the tibetan plateau the formation and development of the arid climate in high asia remain controversial this is largely because of the scarcity of continuous high resolution geological records from the asian interior region thick loess sequences deposited on the surface of the tibetan plateau and its rims provide great potential to reconstruct a high resolution history of the formation and evolution of high asia arid climate based on detailed investigations of the grain size and carbonate content of representative loess sequences in high asia a persistent drying of high asia occurred in the past 1 ma and two major rapid drying events occurred at about 0 9 0 8 ma and 0 5 ma persistent and rapid stepwise uplifts of the tibetan plateau since the mid pleistocene might play a dominant role in the drying of high asia although the mid pleistocene global cooling may partially contribute to the event

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

on the interpretation of chinese loess as a paleoclimate indicator the records of wind blown dust i e loess in china are some of the most important terrestrial records of past climate changes stretching back over the last 10 ma in the paleoclimate literature intervals of increased dust generation have been almost always interpreted as being associated with more intense or prolonged wintertime conditions here it is shown that in accordance with modern observations dust outbreaks in asia are predominantly springtime phenomena during spring frequent cyclogenesis in the lee of the mongolian altai and the passage of strong cold fronts produce the intense windstorms that loft and entrain dust into the air the meteorology governing such outbreaks is likely robust in past climates contrary to the common paleoclimate presumption it is actually the breakdown of the siberian high that permits the dust producing windstorms to occur the importance of cold fronts in generating such windstorms suggests that cooling of high latitude climate during the miocene or during glacial intervals might play a significant role in the signal recorded in the loess deposits the unique springtime factors that generate dust storms are an example of why the common partitioning of asian climate into a winter and summer monsoon is oversimplified and can be misleading

simulated variations of eolian dust from inner asian deserts at the mid pliocene last glacial maximum and present day contributions from the regional tectonic uplift and global climate change northern tibetan plateau uplift and global climate change are regarded as two important factors responsible for a remarkable increase in dust concentration originating from inner asian deserts during the pliocene pleistocene period dust cycles during the mid pliocene last glacial maximum lgm and present day are simulated with a global climate model based on reconstructed dust source scenarios to evaluate the relative contributions of the two factors to the increment of dust sedimentation fluxes in the focused downwind regions of the chinese loess plateau north pacific the model generally produces a light eolian dust mass accumulation rate mar of 7 1 0 28 g cm2 kyr during the mid pliocene a heavier mar of 11 6 0 87 g cm2 kyr at present and the heaviest mar of 24 5 1 15 g cm2 kyr during the lgm our results are in good agreement with marine and terrestrial observations these mar increases can be attributed to both regional tectonic uplift and global climate change comparatively the climatic factors including the ice sheet and sea surface temperature changes have modulated the regional surface wind field and controlled the intensity of sedimentation flux over the loess plateau the impact of the tibetan plateau uplift which increased the areas of inland deserts is more important over the north pacific the dust mar has been widely used in previous studies as an indicator of inland asian aridity however based on the present results the interpretation needs to be considered with greater caution that the mar is actually not only controlled by the source areas but the surface wind velocity

pedostratigraphy and paleomagnetism of a 7 0 ma eolian loess red clay sequence at lingtai loess plateau north central china and the implications for paleomonsoon evolution abstract a 305 m thick loess red clay sequence was discovered recently at lingtai which is located in the middle part of the chinese loess plateau it consists of a complete pleistocene loess soil sequence with a thickness of about 175 m and 130 m of tertiary red clay deposits the red clay sequence at lingtai is the thickest one presently known in the loess plateau field observations show that the lingtai red clay contains over 110 couplets of pedogenic b horizons and horizontal carbonate nodule horizons and that it can be regarded as an extremely thick soil complex paleomagnetic studies of 680 samples suggest that the basal age of the lingtai loess red clay sequence is about 7 05 ma grain size analysis of samples taken at 3 3 cm intervals indicates that the red clay has the same sedimentological characteristics as those observed in the loess thus suggesting a wind blown origin of the tertiary red clay and continuous atmospheric dust deposition in the loess plateau during the last 7 05 ma the pedogenic characteristics of the paleosols within the pleistocene loess and the b horizons in the red clay suggest that the east asia summer monsoon in the latest miocene may have already been slightly stronger than that during the holocene this implies that at about 7 5 ma bp the tibetan plateau could have been uplifted to a critical height in maintaining the east asia summer monsoon system observations of the loess red clay sequence also suggest that the long term changes in the east asia summer monsoon strength have been nonlinear since the latest miocene

fine grained quartz osl dating chronology of loess sequence from southern tajikistan implications for climate change in arid central asia during mis 2 abstract the desert and semi desert region of arid central asia is one of the most important areas of middle latitude dust emission and deposition in the northern hemisphere marine isotope stage 2 mis 2 was the latest and one of the most representative intervals of dust emission from the region and it is especially important for research into processes of dust transportation and deposition here we report the results of an optically stimulated luminescence study of the hoalin section in southern tajikistan which was deposited during mis 2 the fine grained quartz single aliquot regeneration sar approach was used and its reliability was verified by internal checks in addition grain size analyses calculated dust accumulation rates dars and mass accumulation rates mars were used to reconstruct the pattern of climate change during mis 2 the mean dar for southern tajikistan during mis 2 was 0 43 m ka and the corresponding average mar was 673 g cm2 a for a non river terrace site which is higher than the average mars estimated for the central and southern chinese loess plateau clp in contrast to previous suggestions the high dust dars and mars during the lgm indicate a cold dry climatic pattern rather than a cold humid pattern our results also confirm that the patterns of high dust emission and deposition during the lgm in the mid latitude arid zone of asia were synchronous

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

glacial interglacial changes in dust deposition on the chinese loess plateau the chinese loess plateau clp contains an extensive record of aeolian deposition through multiple glacial interglacial cycles independent chronologies based on pedostratigraphy magnetic susceptibility radiocarbon and luminescence dating were developed for 79 sites and used to estimate aeolian mass accumulation rates mars for marine isotope stages 1 5 the regional median value of mar for stage 2 is 310 g m2 yr compared to an estimate of 65 g m2 yr for stage 5 estimated mars from individual sites for stage 2 are approximately 4 3 times greater than mars for stage 5 and 2 1 times greater than for stage 1 mar values at individual sites are consistently highest in the northwest and lowest in the southwest of the clp during all marine isotope stages mars estimated on sections through loess terraces are consistently higher than mar estimates at other sites indicating that local recycling of loess material from exposed river valley deposits has been significant throughout the last 130 kyr although the spatial and temporal patterns in mar are robust there are uncertainties about the magnitude of these changes due to a lack of bulk density measurements and uncertainties in the chronologies for individual sites b site and chronological biases in the sampling used to derive regional estimates and c the unquantified nature of human impact on accumulation rates during the late holocene nevertheless the records from the clp pose a number of challenges which could be addressed by numerical models of the palaeo dust cycle

impact of climate change on the magnetic mineral assemblage in marine sediments from izu rear arc nw pacific ocean over the last 1 myr abstract a rock magnetic study was conducted on upper pleistocene marine sediments from international ocean discovery program expedition 350 site u1437 in order to highlight the paleoenvironmental changes in the nw pacific ocean influenced by the east asian monsoon regime remanent magnetization analyses hysteresis properties first order reversal curves and low temperature magnetic measurements were carried out along with electron microscope observations the results indicate that coarse grained titano magnetite is the dominant magnetic phase in the magnetic mineral assemblage time series analysis supports that this assemblage is modulated by global climate changes over the last 1 myr during the interglacial stages magnetic minerals are more abundant and are dominated by coarse grained titano magnetite of both terrigenous likely from mainland china and volcanic izu arc front japan origin during the glacial stages the magnetic mineral content is lower probably reflecting partial dissolution of ti magnetite and the magnetic assemblage is composed of terrigenous coarse grained titano magnetite and of higher coercivity presumably finer eolian particles likely hematite as a result of the enhancement of the winter monsoon in continental asia the magnetic mineral assemblage reflects a superimposition of volcanic and global climate signals bulk organic geochemical analyses for total and organic carbon as well as nitrogen and sulfur contents confirm a climatic signature in the composition of the sediments with more oxygenated water masses being present during glacial periods additional x ray fluorescence measurements on bulk samples indicate various origins of the sediment particles with both proximal and distal sources

tracking eolian dust with helium and thorium impacts of grain size and provenance reconstructions of the deposition rate of windblown mineral dust in ocean sediments offer an important means of tracking past climate changes and of assessing the radiative and biogeochemical impacts of dust in past climates dust flux estimates in ocean sediments have commonly been based on the operationally defined lithogenic fraction of sediment samples more recently dust fluxes have been estimated from measurements of helium and thorium as rare isotopes of these elements he 3 and th 230 allow estimates of sediment flux and the dominant isotopes he 4 and th 232 are uniquely associated with the lithogenic fraction of marine sediments in order to improve the fidelity of dust flux reconstructions based on he and th we present a survey of he and th concentrations in sediments from dust source areas in east asia australia and south america our data show systematic relationships between he and th concentrations and grain size with he concentrations decreasing and th concentrations increasing with decreasing grain size we find consistent he and th concentrations in the fine fraction 5 m of samples from east asia australia and central south america puna central west argentina with th concentrations averaging 14 g g and he concentrations averaging 2 cc stp g we recommend use of these values for estimating dust fluxes in sediments where dust is dominantly fine grained and suggest that previous studies may have systematically overestimated th based dust fluxes by 30 source areas in patagonia appear to have lower he and th contents than other regions as fine fraction concentrations average 0 8 cc stp g and 9 g g for 4he and 232th respectively the impact of grain size on lithogenic he and th concentrations should be taken into account in sediments proximal to dust sources where dust grain size may vary considerably our data also have important implications for the hosts of he in long traveled dust and for the 3he 4he ratio used for terrigenous he in studies of extraterrestrial he in sediments and ice we also investigate the use of he th ratios as a provenance tracer our results suggest differences in fine fraction he th ratios between east asia australia central south america and patagonia with ratios showing a positive relationship with the geological age of source rocks he th ratios may thus provide useful provenance information for example allowing separation of patagonian sources from puna central west argentina or australian dust sources he th ratios in open ocean marine sediments are similar to ratios in the fine fraction of upwind dust source areas he th ratios in mid latitude south atlantic sediments suggest that dust in this region primarily derives from the puna central west argentina region 23 32 s rather than patagonia 38 s in the equatorial pacific he th ratios are much lower than in extratropical pacific sediments or potential source areas measured as a part of this study east asia south america australia for reasons that are at present unclear complicating their use as provenance tracers in this region

litho and biofacies of early cretaceous rudist bearing carbonate sediments in northeastern japan abstract carbonate blocks of late aptian lower cretaceous age occur in the lower yezo group of central hokkaido in northeast japan the shallow water carbonates were emplaced by gravity sliding and rock fall into a deep water flysch basin various lithofacies can be distinguished within the blocks including massive wackestone bedded packstone and micro oncoid grainstone containing corals rudists an oyster gastropods calcareous algae and an orbitolinid foraminifer facies and palaeoecological analyses suggest deposition of low energy biostromes and sand banks in open lagoonal and restricted environments with local higher energy shoals and beaches the presence of calcareous sandstones and abundant insoluble residues in limestones suggest deposition in an attached carbonate platform close to a supply of terrigenous material rather than deposition upon seamounts within an oceanic setting a narrow rimmed shelf in tropical subtropical conditions would have been the depositional environment for these carbonates which were subsequently deformed into blocks and transported into deep water as a result of the tectonic collapse of the platform