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

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

magnetostratigraphical dating of loess deposits in china the age of chinese loess deposits has long been disputed biostratigraphical and earlier magnetostratigraphical investigations placed the entire loess formation within the pleistocene the new palaeomagnetic measurements reported here on a bore hole section near lochuan shaanxi province suggest a clearly defined magnetic polarity zonation which extends below the olduvai subchron a late pliocene age of 2 4 myr is assigned to the oldest loess sediments measured the intensity variations of natural remanent magnetization nrm and low field magnetic susceptibility are indicative of climatic changes during loess deposition

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

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

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

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

northern westerlies during the last glacial maximum results from cmip5 simulations abstractbased upon simulations from phase 5 of the coupled model intercomparison project cmip5 the vertical and regional characteristics of the northern westerlies during the last glacial maximum lgm are investigated in this study at the northern hemispheric scale all nine available models simulate a poleward shift of the 200 hpa jet and eight models simulate an equatorward shift of the 850 hpa jet compared to the preindustrial period these shifts are of approximately 2 3 latitude for the arithmetic multimodel mean the upper tropospheric cooling in the tropics possibly due to reduced latent heat release is expected to account for the poleward shift of the 200 hpa jet through the thermal wind relationship changes in the midlatitude baroclinic instability in response to the amplified polar cooling are associated with the jet stream in the lower troposphere through anomalous eddy activity in particular the types of predominant baroclinic eddies are regionally dependent the behavior of the 8

quaternary glacial history of the kanas valley chinese altai nw china constrained by electron spin resonance and optically stimulated luminescence datings abstract the chinese altai is located on the northern edge of central asia rich geological records of quaternary glaciations are preserved in this area however the glacial history in the chinese altai has hardly been investigated this study aims to rebuild the regional glacial history in the kanas valley of the chinese altai we present 14 electron spin resonance esr ages and 3 optically stimulated luminescence osl ages from glacial landforms by integrating with ages from previous studies five major glacial advances are identified during marine oxygen isotope stages mis 6 5 4 3 and 2 with ages of 167 0 16 0 123 0 18 0 ka 97 0 19 0 78 0 7 0 ka 76 0 16 0 73 1 6 6 ka 52 1 7 8 34 4 4 2 ka and 28 0 3 3 16 1 1 5 ka respectively the glacial advance during mis 5 is the local last glacial maximum and glaciers became successively more restricted from mis 5 to mis 2 in addition the extensive mis 3 glacial advance in the chinese altai contrasts with the absence of mis 3 glacial advance in the mongolia altai these glacial patterns reflect that precipitation brought by the westerlies might play a primary role on driving glacial advances during the last glacial in the chinese altai this glacial chronology is in reasonable agreement with existing glacial chronologies from other parts of the altai tian shan and pamir indicating similar climate controls on the patterns of quaternary glaciation across central asia highlands

the age and duration of the matuyama brunhes transition from new k ar data from la palma canary islands and revisited 40ar 39ar ages abstract paleomagnetic investigations conducted on lava sequences from la palma canary islands yielded several independent records of the matuyama brunhes transition mbt seven k ar ages of flows sampled across the mbt suggest a duration between 0 and 11 kyr and provide a weighted mean age of 786 3 ka analytical uncertainty only for the transition this value is significantly older than the previously admitted age of 779 2 ka derived from volcanic or sedimentary sequences when the 1 uncertainty on the calibration standard used in the present study is considered our age for the transition recorded at la palma becomes 786 8 ka we have recalculated the 40ar 39ar determinations from the previous studies using recent revisited ages for 40ar 39ar standards this yields a global dataset of 23 k ar and 40ar 39ar determinations our best estimate for the mbt age derived from this compilation is 789 2 ka analytical error or 789 8 ka total error within this 8 kyr uncertainty which could be considered as a minimum estimate this age remains compatible with recent determinations made by the astronomical time scale however the present study suggests that better control of the lock in depth as well as better quantification of uncertainties involved in the tuning of 18o records to orbital forcing models are needed to improve further the astronomical polarity time scale derived from sedimentary records in addition absolute dating by k ar and 40ar 39ar will gain in accuracy when uncertainty determinations on standards will be significantly improved

the contribution of loess magnetism in china to the retrieval of past global changes some problems abstract in the loess plateau of china the stratigraphical position of the brunhes matuyama boundary was not found in loess unit l8 at luochuan and jixian as is commonly accepted the interbedded palaeosols may be differentiated from the parent loess not only by their high magnetic susceptibility but also by their enhanced remanence properties these contrasts mainly result from concentration changes of the inherited magnetic minerals grain size changes and authigenic formation of magnetic minerals which are all linked to climate controlled soil formation processes

aeolian dust dynamics in central asia during the pleistocene driven by the long term migration seasonality and permanency of the asiatic polar front loess paleosol sequences preserve detailed archives of climate change reflecting the dynamics of aeolian dust sedimentation and the paleodust content of the atmosphere the detailed investigation of particle size distributions psds of windblown sediments is an increasingly used approach to assess the paleorecord of aeolian dust dynamics the central asian loess belt offers the potential to reconstruct pleistocene atmospheric circulation patterns along an adjacent west east transect within interior eurasia through granulometric studies in this study we present the aeolian dust record of the loess sequence at remisowka se kazakhstan which reflects a detailed signal of glacial interglacial climate and atmospheric dynamics in central asia on the basis of radiocarbon and amino acid geochronologic data long term semicontinuous trends in the aeolian dust record of the last glacial cycle are observed and interpreted to reveal their paleoclimate signal in consideration of the modern synoptical atmospheric circulation patterns and aeolian dust transport in central asia it is likely that the observed trends reflect the long term migration seasonal duration and permanency of the polar front during the late pleistocene previously published models which focused on the reciprocal glacial interglacial influence of the zonal westerlies and the asiatic high on the aeolian dust transport in central asia were overly simplified and should be modified to include the major influence of the asiatic polar front as the polar front activity is intimately connected with the development and position of the interhemispherically active high level planetary frontal zone hpfz the presented data give insight to long term aeolian dust dynamics and climate variability of interior eurasia which are linked with interhemispheric climates

late pleistocene continental climate and oceanic variability recorded in northwest pacific sediments core v21 146 provides a continuous record of northwest pacific pelagic sedimentation spanning the past 530 000 years downcore variations of 18o from benthic foraminiferal calcite were correlated to the specmap record to provide an age model for late pleistocene paleoclimatic and paleoceanographic variation fluxes of caco3 and eolian material have been determined by combining information about linear sedimentation rates bulk densities and component percentages the mass accumulation rate mar of caco3 varies from 58 to 1435 mg cm kyr 1 and exhibits the pacific ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record however the pattern of caco3 accumulation appears to shift during the mid brunhes so that prior to 350 000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods the flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loess soil stratigraphy in china dust fluxes range from 43 to 718 mg cm kyr 1 and are greater by a factor of about 4 during glacial times cross spectral analysis of the eolian flux and oxygen isotope records shows an inphase and coherent relationship at each of the major orbital periodicities of 100 41 and 19 kyr eolian grain sizes generally used as a proxy record of wind intensity range from 8 4 2 9 m to 6 2 13 6 m a change in grain size variability occurs near about 300 ka such that the older portion is characterized by lower frequency and higher amplitude fluctuations than the younger portion power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25 35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities the phase relationship for eccentricity between the eolian grain size and 18o records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions

a database for the matuyama brunhes magnetic reversal abstract we present a paleomagnetic database designated mbd97 comprising sedimentary and lava data for the matuyama brunhes reversal transition field using criteria regarding suitability of the rock samples measurement methods and temporal resolution of the data we consider 62 different studies of the matuyama brunhes reversal of these only 11 satisfy our selection criteria four lava sites one loess site three shallow marine sedimentary sites and three deep ocean sedimentary sites we discuss our reasons for accepting or disguarding each candidate data set we investigate the distribution of transitional virtual geomagnetic poles vgps they fall along american and asian australian longitudes the spatial and temporal complexity of the data indicate that the transitional field was almost certainly nonaxisymmetric and nondipolar the directional transition of the matuyama brunhes reversal took 2300 5000 years during which time the surface intensity fell to 10 20 of its pre and post transitional value we do not find any systematic bias due to site distribution or inclination shallowing although the errors in the data do vary over the duration of the reversal mbd97 is a small database but it has a fairly good geographic distribution and is suitable for studies of the matuyama brunhes transition nonetheless it is clear that further analysis of transitions will benefit from a continued program of data collection and analysis the data in mbd97 are listed

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

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

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

southern migration of westerlies in the northern hemisphere pep ii transect during the last glacial maximum abstract a southward shift of continuous and discontinuous permafrost zones and vegetation belts of taiga broad leaf deciduous and evergreen forests on the islands forming japan suggests a southern migration of the northern hemisphere nh summer westerly subtropical jet by around 3 5 of latitude at 135 140 e during the global last glacial maximum lgm since this jet induces the asian nh summer monsoon the southern shift caused a cooler and drier summer and the spread of deciduous forest in southern japan the expansion of mountain glaciers on the islands of japan also supports the southern migration of the subtropical westerly jet at present the ablation of snow occurs by heat and precipitation carried by the nh summer monsoon by comparison the position of the nh winter westerly subtropical jet remained unchanged presumably because its course was constrained by the himalayan tibetan plateau the northern limit of the kuroshio current corresponding to the boundary of the subtropical and subarctic water in the northwestern pacific ocean also migrated by around 3 during the global lgm the southern migration of the westerly subtropical jet suggests that the current situation where its location shifts during the nh summer to north of the tibetan plateau did not occur during the coldest phases of the global lgm although it did occur intermittently during marine isotope stage mis 3

postglacial environmental change of the pacific ocean off the coasts of central japan abstract downcore changes in microfossil assemblages and oxygen isotope ratios in three piston cores recovered from the northwestern pacific off central japan show that the subtropical kuroshio front was located to the south of c 4 core site lat 33 n during the last glacial the front then advanced northward passing over the c 4 site and the c 6 site 34 6 n at about 13 ka and 10 ka respectively and reached the c 1 core site 36 n at about 7 ka after 5 5 ka it retreated to the area between the c 1 and c 6 sites a brief but significant cold event the readvance of the cold oyashio current is recognized between 11 and 10 ka in the two northern cores but the current did not reach the southern c 4 site a contemporaneous cold event is known in the north atlantic and the cooling was probably a global phenomenon likely to be associated with lowering of sea level contamination of isotopically light water is apparent between 14 and 11 ka in the marked change in isotopic composition of benthic foraminifers oxygen isotope ratios of planktonic foraminifers show that prior to the advance of the kuroshio front the surface water at these core sites was isotopically lighter than the kuroshio water at that time

aspects of atmospheric circulation the late pleistocene 0 950 000 yr record of eolian deposition in the pacific ocean rea d k 1990 aspects of atmospheric circulation the late pleistocene 0 950 000 yr record of eolian deposition in the pacific ocean palaeogeogr palaeoclimatol palaeoecok 78 217 227 the eolian component of pelagic sediments provides a proxy record of atmospheric circulation intensity and of dust transport examination of those records indicates that the atmosphere responds to orbital forcing but that during the past 875 000 years the variability in atmospheric circulation is at much shorter periods than the 100 000 year variation in ice volume the mid brunhes climatic event is well characterized in the eolian grain size records and in records of sea surface phenomena it is not seen in proxy indicators of either deep water or ice volume variability the increase in the amplitude of paleoclimatic variability that denotes the early late pleistocene transition occurs suddenly about 875 000 years ago in the eolian grain size record which is about 20 000 to 25 000 years earlier than the transition in the deep sea caco3 dissolution record or in the 8180 proxy record of ice volume

are chinese loess deposits essentially continuous 1 we conducted a paleomagnetic examination of the last glacial loess of three representative profiles along an east west transect in the central loess plateau in order to assess the continuity of chinese loess the results show that the xifeng and luochuan profiles record the laschamp geomagnetic excursion but with different morphologies together with the published results from weinan southern plateau our results suggest that sedimentation of the last glacial loess in the central southern plateau was continuous at the time scale equivalent to the duration of the laschamp excursion 2 kyr but probably episodic at finer time scales 2 kyr no geomagnetic excursion was found at the yichuan profile near the yellow river valley where loess accumulation may be strongly affected by local environmental changes and thus may have been discontinuous both site location and time scale therefore need to be considered when considering continuity of chinese loess

magnetic enhancement and palaeoclimate study of a loess palaeosol couplet across the loess plateau of china summary the origin of the milankovitch palaeoclimatic signal so dramatically recorded in the chinese loess remains uncertain at least five hypotheses have been put forward to explain the well documented enhancement of magnetic susceptibility in palaeosols which formed when conditions were warmer and wetter we report here a magnetic study of a prominent loess soil couplet l4 s3 at three widely separated sites where present day mean annual rainfall and temperature range from 350mm to 700mm and from 6 c to 13 c the properties determined are laboratory remanences isothermal irm anhysteretic arm viscous vrm including viscous decay room temperature susceptibility and thermomagnetic behaviour at fields beyond 100 mt the irm spectra are all essentially identical both in shape and in absolute magnitude suggesting a uniform magnetic component widespread across the plateau subtracting the signal of this component isolates a second component the amount of which varies by an order of magnitude between sites the magnetic properties of this latter material are remarkably similar to those reported for bacterial magnetite in geological sediments and modern soils viscous decay of vrm takes place in two distinct stages one of which falls to zero in 10min we attribute magnetic enhancement which is the source of the palaeoclimatic signal to in situ pedogenetic formation of magnetite which we characterize in our interpretation as two separate forms of bacterial magnetofossils the most magnetic sample requires a mass fraction of about half of one per cent of this biogenic material

reliability of the natural remanent magnetization recorded in chinese loess 1 chinese loess paleosol sequences undoubtedly have recorded geomagnetic events both polarity reversals and excursions however the fidelity of the rapid paleomagnetic field oscillations during a polarity reversal remains uncertain to test the reliability and consistency of the natural remanent magnetization records in chinese loess 10 subsets of parallel samples across the matuyama brunhes mb reversal boundary were obtained from the luochuan region in the hinterland of the chinese loess plateau our paleomagnetic results show diversified virtual geomagnetic poles vgps during the mb transition but consistent vgps outside of the transitional zone the anisotropy of magnetic susceptibility and rock magnetism results indicate that the sampled interval is rather uniform and undisturbed the discrepancies of the characteristic remanent magnetization within the mb transition are probably due to the low efficiency in aligning magnetic grains mainly pseudo single domain magnetite associated with the low field intensity nevertheless the stratigraphic location of the mb boundary can be confidently defined therefore we conclude that chinese loess paleosol sequences can record geomagnetic reversal events but the morphology within the polarity transition is rather questionable

a magnetostratigraphic reassessment of correlation between chinese loess and marine oxygen isotope records over the last 1 1 ma abstract we present a magnetic polarity based paleoclimatic correlation between chinese loess and marine oxygen isotope stage mis records over the last 1 1 ma this revised land ocean comparison indicates that inconsistent occurrence of the matuyama brunhes boundary which lies in mis 19 in marine sediments and occurs either at the base lower part of loess l8 or the uppermost part of soil s8 in chinese loess is due to regional and or local climate variability across the chinese loess plateau and does not need to be attributed to lock in effects of loess remanence acquisition associated with pedogenesis this result implies that the geomagnetic polarity boundaries in chinese loess in general are reliable chronostratigraphic time markers therefore astronomically tuned timescales for chinese loess that presume a downward shift of polarity boundaries due to a time lag in remanence acquisition may have overestimated ages of certain loess paleosol units

chemical magnetization in chinese loess the relationship between the intensity of characteristic remanent magnetization chrm and pedogenesis is examined in the luochuan section the results show a consistent link between the intensity values of remanent magnetization after every thermal demagnetization step and magnetic susceptiblity and other indexes of pedogenesis moreover the intensity of chrm is also much higher in paleosols than in loess these results suggest that chemical remanent magnetization crm is the main mode of nrm acquisition in paleosols and is linked to pedogenesis pedogenic processes overprint the magnetic signal to a certain depth in the underlying loess so the interpretation of the high resolution paleomagnetic records from paleosols requires a degree of caution

sedimentation and diagenesis of chinese loess implications for the preservation of continuous high resolution climate records chinese loess has been extensively utilized to produce continuous and high resolution climate records of the late cenozoic such work assumes uninterrupted loess deposition and limited diagenesis here closely spaced optically stimulated luminescence osl dates are used to characterize the holocene and late pleistocene sedimentation histories of three sites across a nw se transect of the chinese loess plateau the results suggest that sedimentation is episodic at subglacial interglacial time scales with rates rapidly varying within units and between sites unconformities noneolian deposition and mixing of sediments also appear to be common existing understanding of loess deposition therefore requires reexamination while previous reconstructions of rapid climate change not dated using absolute methods should be regarded with caution loess deposits may still yield detailed climate records from specific high sedimentation rate strata and evidence for rapid climate change may yet be obtainable by targeting these units through absolute dating the rapid changes in sedimentation presented here indicate the east asian monsoon has the capacity to vary on millennial scales

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

evidence for the kamikatsura and santa rosa excursions recorded in eolian deposits from the southern chinese loess plateau 1 a detailed paleomagnetic investigation of a loess paleosol sequence in baoji southern chinese loess plateau reveals two distinct geomagnetic excursions accompanied by inferred relative paleointensity minima in the late matuyama chron rock magnetic experiments demonstrate that the sediments of the excursion intervals in loess unit l9 have the same magnetic properties as those from surrounding normal and reversed polarity intervals assuming constant sedimentation rate between the jaramillo matuyama and matuyama brunhes magnetic polarity boundaries the midpoint ages and durations for these two excursions are estimated at 0 89 ma and 16 kyr and 0 92 ma and 7 kyr respectively in addition these two events are separated by an interval with fully reversed polarity that had a duration of 16 kyr these estimates are supported by paleoclimatologically inferred age constraints the two excursions are probably correlated with the kamikatsura and santa rosa excursions respectively

the matuyama brunhes polarity reversal in four chinese loess records high fidelity recording of geomagnetic field behavior or a less than reliable chronostratigraphic marker abstract the paleomagnetic recording fidelity of chinese loess has been a matter of long term dispute to help shed light on the acquisition retention mechanisms of natural remanent magnetization in loess we report on high sampling resolution paleomagnetic constraints on the position of the matuyama brunhes boundary mbb in four typical loess sections in different marginal areas of the chinese loess plateau clp each of which has experienced different east asian winter summer monsoon strengths and pedogenic intensities detailed thermal demagnetization experiments for 1850 specimens reveal that none of the high accumulation rate loess with the weakest pedogenesis at caotan western clp the massive pedogenesis loess characterized by extensive development of thick calcareous nodule layers at jixian se clp and the moderately pedogenized loess at fanshan ne clp have preserved high fidelity geomagnetic records across the mbbs jiuzhoutai western clp one of the thickest loess profiles in the world contains the thickest and hitherto the most complex mbb that is too extensive to be regarded as rapid fluctuations of geomagnetic field during the m b reversal at jixian a predominance of pedogenesis induced chemical remanent magnetization overprinting has heavily obscured the original remanence the significant downward displacement of the mbb at fanshan and even its total absence at caotan together with extensive remagnetization of the coarse grained upper sandy loess layer l9 in both sections further suggest that the processes of remanence acquisition retention of chinese loess in the marginal areas of the clp are rather complicated thus interpretations of the fine structure of geomagnetic transitional field behavior and excursions especially in the matuyama chron should be regarded with caution

snowline elevation and eolian dust flux in the japanese islands during isotope stages 2 and 4 abstract changes in snowline elevation and dust flux clearly contrast the paleoenvironments of the japanese islands during isotope stages 2 and 4 a lower snowline elevation and a smaller dust flux during isotope stage 4 suggests a climate with a cold and dry summer dominated by winter monsoonal precipitation between 70 and 55 ka a higher snowline elevation and a larger dust flux during isotope stage 2 indicates a climate with a cold and very dry summer with a minimized winter monsoon precipitation especially around 18 ka a drier climate during stage 2 can be explained by 1 a lowering of sea surface temperature in the japan sea by blocking the warm tsushima current during a sea level lowering 2 the extension of sea ice over the northern part of the japan sea and the sea of okhotsk and 3 weakening of the summer monsoon and the southern migration of the polar front the increase in dust flux in both stages 2 and 4 suggests an intensification of westerlies and winter monsoon during these stages a bigger dust flux in stage 2 than stage 4 reflects 1 stronger westerlies and winter monsoon and 2 the emergence of continental shelf which became an important dust source

eolian deposits of the northern margin of the south china jianghan basin reconstruction of the late cretaceous east asian landscape in central china abstract the late cretaceous honghuatao formation includes a succession of thick clastic sedimentary sequences which are widely exposed in northwestern jianghan basin central china here detailed sedimentological and facies architectural analyses are performed allowing to re interpret and identify the controversy for sedimentary environment and to investigate the paleoclimatic condition the honghuatao stratigraphic sequence includes eolian dunes and dry interdunes deposits with fluvial channel deposits at the bottom and top the vertical change between fluvial and eolian systems indicates alternating wet and dry climate at the same time the provenance analysis combined with the paleocurrents from the w nw and ne indicates that huangling dome south qinling belt and dabie orogen supply the main detrital source for the honghuatao formation the late cretaceous first rifting subsidence in the jianghan basin provided accommodation space for the preservation of the aeolian accumulation moreover the existence of the mountain belts around the basin that is the orographic effect precluded the winds from transporting humidity to the interior of the jianghan basin generating the desert system this study shows that the formation of eolian deposits in the honghuatao formation and coeval strata in numerous adjacent basins was a sedimentary response to the prevailing desert climate in the mid to low latitude areas of the northern hemisphere during the late cretaceous which was predominately controlled by the subtropical high pressure system on a planetary scale

timing of the brunhes matuyama magnetic polarity reversal in chinese loess using 10be in chinese loess the brunhes matuyama b m geomagnetic reversal occurs 25 k y prior to the age found in marine sediments this offset has been attributed by some to post depositional magnetic overprinting of loess while others have argued it is due to errors in the loess time scale here we solve this long standing debate by exploiting a new method to extract reproducible records of geomagnetic field intensity from loess with 10 be a proxy for global average geomagnetic field intensity and using it to show that a pronounced minimum in field intensity a requirement for dipole field reversal is recorded in two separate loess records at ca 780 3 kyr b p this timing is synchronous with the b m reversal timing seen in marine records verifying the standard loess time scale as correct but it is 25 k y younger than the age depth of the magnetic polarity reversal recorded in these same chinese loess sediments demonstrating that loess magnetic overprinting has occurred

geomagnetic episodes of the last 1 2 myr recorded in chinese loess 1 the matuyama brunhes m b boundary termination of jaramillo normal subchron j m as well as three young geomagnetic excursions has been revealed in the weinan loess section zhu et al 1994 1998 1999 recently we carried out further paleomagnetic directional studies on the same section and recovered the onset of the jaramillo normal subchron m j and four geomagnetic excursions two in the brunhes and two in the late matuyama the fact that all seven excursions found in this section are in loess units and expected excursions in paleosols are not found suggests that short lived geomagnetic signals could be only recorded in loess units and may have been fully smoothed or wiped out in paleosol units by strong pedogenesis constrained by a new astronomical timescale hld00 ages of the geomagnetic excursions and reversal boundaries have been estimated we tentatively correlated these excursions with previous results indicating that a large lock in model may not be correct for the whole loess profile although some apparently big positive age discrepancies were observed for the main boundaries

misleading positions of geomagnetic reversal boundaries in eurasian loess and implications for correlation between continental and marine sedimentary sequences abstract the matuyama brunhes boundary mbb where the earth s magnetic field changed to its present orientation is one of the most frequently used time markers in continental quaternary stratigraphy although magnetic signals have been successfully recovered from loess deposits and an apparently coherent magnetostratigraphy seems to be in place a close examination of the published loess records from northern mid latitudes reveals significant uncertainty and variability for the position of the mbb in asia and part of central europe the mbb has been found in loess a glacial deposit this is in contrast to the well established palaeomagnetic records in deep sea sediments where the mbb is located in the interglacial oxygen isotope stage 19 this discrepancy has caused serious confusion in stratigraphic correlation between loess and marine sequences here we examine the causes of the discrepancy between the two sedimentary environments in their records of the mbb our approach includes a comparison of the mbb in loess and other continental records and an evaluation of the stratigraphic significance of the microtektites found around the mbb based on the occurrence of the mbb in an interglacial stage in lake and continental margin sequences and the correlative stratigraphic positions of the microtektites in marine sediments and loess we demonstrate that the measured positions of the mbb in loess are erroneous and misleading and its true occurrence was during the time of formation of the palaeosol corresponding to oxygen isotope stage 19 the most plausible cause for the apparent offset i e the mbb being found in the underlying loess instead is that the acquisition of remanent magnetisation in loess occurs at a certain depth substantially below the land surface the degree of such displacement is dependent on the lithology and structure of the deposits formed prior to the reversal and the time delay is estimated to be in the order of 103 104 years we show that other geomagnetic boundaries such as those of jaramillo and cobb mountain in loess have been similarly displaced though to a varying extent we suggest that the remanence acquisition in loess is closely related to the post depositional evolution in the structure of loessic materials which is in part influenced by regional climate conditions our conclusions on the displaced remanence acquisition have implications for loess chronology magnetostratigraphy as well as the geomagnetic interpretation of detailed magnetic signatures from loess

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

a detailed geomagnetic record from chinese loess abstract a collection of over 100 individually orientated hand samples was obtained from a 335 m loess section near lanzhou northern china previous studies defined the brunhes matuyama b m boundary and jaramillo normal subchron within the section the position of these magnetic markers led to the suggestion of a basal age for the section of 1 3 ma this disagrees significantly with a date of 2 45 ma for the onset of loess accumulation at lochuan 500 km to the east of lanzhou the present study considers the section in far greater detail and has derived a complex magnetostratigraphy isolating seven normal events within the lower 130 m of the section a simple interpretation of this magnetostratigraphy suggests a basal age for the section in the region of 2 4 ma however the relative chronology of the loess palaeosol sequence although appearing to confirm this basal age has revealed that this simple interpretation of the magnetostratigraphy may not be justified

the last two geomagnetic polarity reversals recorded in high deposition rate sediment drifts high resolution records of geomagnetic polarity transitions are rare owing to the difficulty of preserving in the geological record details of a process with a duration of only a few thousand years lavas can record the instantaneous field on cooling but lava records are themselves discontinuous and therefore polarity transition fields are seldom captured sedimentary records are more continuous but typical deep sea sedimentation rates of a few cm kyr 1are too low to record transition fields adequately here we report transition records from north atlantic drift deposits with high sedimentation rates 12 cm kyr 1 at the ocean drilling program sites 983 and 984 virtual geomagnetic polar vgp paths are similar within and between sites for the last two geomagnetic reversals attesting to a memory effect spanning back to back reversals the complex vgp paths feature two vgp clusters one located in northeastern asia and the other in the south atlantic ocean off south america and provide a link between the longitudinally constrained transitional vgps often recorded in sediments1 2 which represent highly smoothed renditions of transition fields and the scattered transitional vgps3 and vgp clusters4 observed in lava records

timing and lock in effect of the laschamp geomagnetic excursion in chinese loess 1 the laschamp geomagnetic excursion lge at 41 ka is a critical age control for hemispherical comparison of paleoclimate records from various kinds of geological archives e g ice core marine and lake sediments the timing of the lge in chinese loess however remains poorly constrained due to the lack of a reliable chronology and the complex acquisition processes of natural remanent magnetization here we systematically compare the paleomagnetic results of three optically stimulated luminescence dated loess sequences on the chinese loess plateau our results indicate that the timing of the lge in the northwestern loess plateau is slightly older than the absolute radiometric age determination and the timing inferred from greenland ice core 10be flux and marine i e relative paleointensity and authogenic 10be 9be stack records but younger than the counterparts in the central loess plateau we attribute the different timing of the lge in the three loess sections to a progressive southeastward increase in the lock in depth caused by the combined effects of postdepositional processes e g surface mixing chemical weathering and lock in delay on the remanence acquisition process we conclude that caution is needed to use the lge in chinese loess as a reliable tie event for high resolution chronological correlation to marine and ice core records only if the potential lock in effect can be precisely determined

age and palaeoclimatic significance of the loess of lanzhou north china extending in a broad arc that abuts the sandy non gobi deserts the loess plateau of northern china1 3 is one of the most massive accumulations of loess in the world the loess sequence is typically characterized by an alternation of silty or sandy loess with more clay rich palaeosols these alternations in conjunction with their enclosed faunas and distinctive mineralogies have been interpreted as reflecting pleistocene glacial interglacial cycles3 8 because it holds implications for the climatic and anthropological history of china9 10 the definition of a reliable chronological framework for loess deposition is of great interest recent palaeomagnetic studies4 5 have indicated that loess deposition in shaanxi province commenced 2 4 myr ago to assess the synchrony of loess accumulation across the loess plateau we have dated a 330 m thick loess sequence near lanzhou gansu province the magnetostrati graphical results reported here indicate that the base of this loess succession dates from 1 3 my r ago this young age in comparison to the shaanxi sequence is attributed to uplift along the northern fringe of the tibetan plateau11 that precluded early pleistocene loess preservation in this mountainous region palaeosols in the basal loess occur on average once every 25 kyr suggesting that climates conducive to soil forming events may have been modulated by orbital precession in the early pleistocene

in situ remagnetization experiments of loess on the chinese loess plateau evidence for localized post depositional remanent magnetization 1 inconsistent stratigraphic positions of reversal boundaries and spurious paleomagnetic variations associated with polarity reversals recorded by loess paleosols on the chinese loess plateau clp have in general been attributed to inferred delayed acquisition of magnetization and high frequency variations of the geomagnetic field respectively these conclusions are partly based on an incomplete knowledge of the magnetization acquisition process of loess recent laboratory experiments which demonstrate that dry deposited loess acquires a stable remanent magnetization after its first wetting precipitation resulted in significant inclination errors that are not generally encountered in chinese loess laboratory experiments only remotely mimic natural conditions and we have therefore performed in situ experiments at two sites on the clp separated by some 650 km to elucidate whether variations in natural conditions can impose secondary remanent magnetization components in loess l1 the experiments were performed by relocating blocks volume 5 10 3 m3 of last interglacial loess after being turned upside down inside loess exposures inverted blocks were retrieved and analyzed after 8 and 17 months respectively thermal demagnetization reveals that partial remagnetization has occurred within different parts of the loess blocks this secondary magnetization which is characterized by blocking temperatures that overlap with those of the primary component to above 450 c cannot be attributed to a viscous remanent magnetization and is therefore proposed to represent local and partial realignment of magnetic grains we tentatively propose that physical unlocking and realignment of magnetic grains may be assisted by pressure release caused by differential thermal expansion of the different mineral grains in loess localized remagnetization may account for a number of reported spurious paleomagnetic results from clp

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

glacial and interglacial eolian dust dispersal patterns across the chinese loess plateau inferred from decomposed loess grain size records previous studies have indicated that a genetically meaningful decomposition unmixing of loess grain size distributions can be accomplished with the end member modeling algorithm emma the independent decomposition of two series of loess grain size records from the ne tibetan plateau and loess plateau spanning the last glacial interglacial cycle indicates that the two data sets are described by very similar mixing models the average mixing model presented here is regarded as representative for the vast loess region in northern china and allows quantification of the contribution of three loess components to the loess grain size distributions a genetic interpretation and the paleoclimatic significance of the average mixing model have been provided by comparison of the modeled loess components with modern dust samples in terms of their grain size distribution and flux rates and by the distribution patterns of the loess components across the loess plateau reconstructed for the last two glacial interglacial cycles the sandy and silty loess components represent the coarse dust fraction supplied by saltation and short term suspension processes over the proximal part of the loess plateau during major dust outbreaks in spring and early summer the low level winter monsoon northwesterly wind system is the likely transporting agent for these dust events a clayey loess component represents the fine dust component supplied over the entire loess plateau by long term suspension processes during major dust outbreaks and as part of a background supply system the clayey loess component in the glacial loess deposits is dominantly supplied during major dust outbreaks by the northwesterly winter monsoon whereas the clayey loess component in the interglacial paleosols is mainly supplied by non dust storm processes possibly with a significant contribution by the high level subtropical jet stream westerly winds

an improved comparison of chinese loess with deep sea δ18o record over the interval 1 6 2 6 ma 1 based on a refined orbital timescale for the lower portion of pleistocene loess paleosol sequence at lingtai section we present an improved comparison of chinese loess with deep sea 18o record over the interval 1 6 2 6 ma unlike previous land ocean comparison our result suggests that each paleosol unit from s25 to s32 is approximately including two interglacial oxygen isotope stages the rationality of our revised comparison is supported by the well constrained ages of geomagnetic reversal boundaries in chinese loess and the almost cycle to cycle correlation between the grain size and deep sea 18o record spectral analyses demonstrate that variations of the magnetic susceptibility and grain size in the interval 1 6 2 6 ma were dominated by a prominent 410 ka periodicity implying a possible response of the east asian monsoon evolution to orbital eccentricity forcing

late pleistocene glacial advances in the western tibet interior it has long been observed that the timing of glacial advances is asynchronous across the himalaya karakoram tibet plateau hktp but the climatic implications if any remain unclear resolving this question requires additional glacial chronologies from unique spatial and climatic regimes as well as an analysis of how glaciers within different regimes are likely to have responded to past climate changes this study presents a 10be 21ne chronology from the mawang kangri range of western tibet 34 n 80 e an arid high elevation site we identify advances at 123 83 and 56 kyr which agree reasonably well with sites in the immediate vicinity but are asynchronous relative to sites across the entire hktp and relative to sites in the western hktp to evaluate hktp wide asynchroneity we compile dated glacial chronologies and classify them by the approximate timing of their maximum recent advance this result shows a strong spatial clustering of young mis 1 2 relative to older mis 3 5 maximum advances further comparison with modern precipitation temperature and topographic data show that the pattern of hktp wide asynchroneity is broadly independent of topography and can potentially be explained by local responses to changes in temperature at either very warm wet or cold dry sites sites that receive intermediate amounts of precipitation are more ambiguous although spatial clustering of mis 1 2 vs mis 3 5 advances is suggestive of past variations in precipitation at these sites in western tibet no spatial or climatic correlation is observed with the timing of maximum glacial advances we suggest this could arise from mis interpretation of disparate boulder ages generated by a prolonged mis 3 4 glacial advance in the western hktp

age and duration of the matuyama brunhes geomagnetic polarity reversal from 40ar39ar incremental heating analyses of lavas abstract constraints on the timing of geomagnetic polarity reversals have come mainly from k ar or more recently 40 ar 39 ar age determinations of lavas or their k rich phenocrysts that erupted prior or subsequent to particular geomagnetic events we have obtained 40 ar 39 ar isochron ages using incremental heating techniques on groundmass separates phenocryst poor whole rock samples or plagioclase from eight basaltic to andesitic lavas that erupted during the matuyama brunhes m b polarity transition at four geographically dispersed sites these eight lavas range from 784 6 7 1 ka to 770 8 5 2 ka 1 errors the weighted mean 778 7 1 9 ka gives a high precision age that is remarkably consistent with revised astronomical age estimates for the m b polarity transition 6 12 13 despite uncertainties in absolute calibration of 40 ar 39 ar ages relative to mineral standards used as neutron fluence monitors our age determinations are consistent with five other 40 ar 39 ar studies focused on the m b transition these results confirm that the earlier k ar based geomagnetic polarity time scale underestimated the age of the m b reversal by about 6 none of the eight isochron ages are distinguishable from one another at the 95 confidence level however we are tantalizingly close to testing for the duration of this reversal one lava at the base of a sequence of transitionally magnetized flows in chile and the uppermost lava in a similar sequence on maui are only just indistinguishable in age at the 95 confidence level and preserve different magnetic orientations we suggest that the 12 kyr difference in age represents an upper limit for the duration of the reversal and is similar to the period of low magnetic field intensity associated with records of the m b reversal from deep sea sediment cores together with the short duration 2 kyr of the directional reversal observed in several different marine sediment sections our data suggest that reversal of the field s direction could have occurred at slightly different times depending on the position of the recording site

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

subaerial and subaqueous deposition of loess experimental assessment of detrital remanent magnetization in chinese loess abstract loess and intercalated paleosols on the chinese loess plateau clp are the most extensive and continuous terrestrial archive of geomagnetic and paleoclimate variations covering the last 2 6 ma a first order time frame has been established for these sequences using paleomagnetic polarity boundaries major inconsistencies between the positioning of the matuyama brunhes polarity boundary in chinese loess paleosol sequences and marine records previously accounted for by assuming magnetization lock in depths in loess of up to 2 3 m have recently been resolved using a paleoclimatic indicator insensitive to pedogenesis that does require any major post depositional acquisition of a remanent magnetization this resolved controversy accentuates the lack of an adequate understanding of how chinese loess acquires and retains a stable remanent magnetization we report on laboratory re deposition experiments with subaerial and subaqueous simulations of natural loess to elucidate factors controlling the acquisition of magnetization in loess our work complements and extends recently published results from comparable laboratory experiments by zhao and roberts 2010 our major finding is that a stable magnetization is acquired and retained after initial wetting of dry deposited loess with no significant time lag in general accord with recent findings

quantifying ultrafine pedogenic magnetic particles in chinese loess by monitoring viscous decay of superparamagnetism we propose a new approach for quantifying pedogenically produced ultrafine nanometer scale magnetic particles in chinese loess we have recorded the viscous decay t 100 s of imposed isothermal remanent magnetization irm assumed to be selectively carried by superparamagnetic particles jv application of viscosity measurements relaxometry to loess paleosol sequences from the se extremity of the chinese loess plateau reveals that jv aptly reflects contributions of viscous superparamagnetic sp particles to the total remanence carried by an assemblage of magnetic particles time decay of jv can be determined with a higher resolution than the conventionally used frequency dependent susceptibility fd for characterizing the relative abundance of sp particles the nearly logarithmic time decay of irm implies a rather broad grain size distribution of pedogenic particles in chinese loess that may range from a lower size limit of 10 nm to an upper limit of 40 nm with a prevalent grain size maximum of 21 25 nm numerical calculations of the time dependence of irm decay demonstrate that the actual contribution of fine grained pedogenic magnetite maghemite to the total remanence is at least twice as large as that estimated by both fd and our proposed jv parameter we therefore propose that determination of superparamagnetic contributions by the time dependence of irm viscosity is a useful technique for tracking pedogenic processes and hence paleoclimatic conditions of chinese loess

magnetoclimatology teleconnection between the siberian loess record and north atlantic heinrich events new environmental magnetic data from loess and paleosol successions in outcrops in the upper reaches of the ob river drainage southern siberia track the major climatic variations over the last glacial interglacial cycle profiles of magnetic susceptibility and alternating deposition of loess and soil formation events correspond to oxygen isotope stages 1 5 the magnetic susceptibility data in association with the stratigraphic succession confirm that the wind vigor magnetoclimatological model is a viable alternative to the classic pedogenic model interpretation of magnetic susceptibility data from loess paleosol successions must therefore consider eolian dynamics available source materials and transport directions in addition to pedogenic processes rapid magnetic fluctuations are also observed these are identified for the first time in siberian records as the signature of the abrupt cold pulses responsible for the heinrich layers in north atlantic marine sediments the data thus form a component of climatic teleconnections across the northern hemisphere allowing correlations to be made among 1 siberian magnetic susceptibility stratigraphy 2 data recorded from other loess paleosol successions in china european russia europe and north america 3 north atlantic ice rafted detritus and 4 sea surface temperatures derived from molecular stratigraphy of marine sediments off the northwest coast of africa

timings and causes of glacial advances across the pep ii transect east asia to antarctica during the last glaciation cycle a comparison of glacial advances through the last glacial cycle between northern and southern hemispheres in the pep 2 transect east asia and australasia revealed 1 a relatively good synchrony of glacial advances during the lgm across the whole transect except antarctica 2 a rough synchrony in glacial advances in the karakorums himalayas japan and new zealand during marine isotope stages mis 3 and 4 although the age control is still poor and 1 a greater glacial extent in mis 3 and 4 than in mis 2 the lgm advances are driven by northern hemisphere temperature forcing but the mis 3 and or mis 4 advances appear to be dominantly controlled by the effects of moisture availability or lack of thereof in mainland australia and antarctica glaciers advanced only in the most humid phases in himalaya and karakorum where the moisture is supplied both by a summer monsoon and the westerlies timings of glacier advance coincide with both summer monsoon enhancement and westerly intensification in japan the glacier extent is controlled by monsoon changes sea surface temperatures ssts in the japan sea moisture source and by zonal shifts in westerly circulation in new zealand either insolalion changes or changes in the intensity of westerly circulation are invoked lis the main track of the westerlies did not change greatly during glacial times c 2003 elsevier ltd and inqua all rights reserved

the matuyama brunhes and upper jaramillo transitions recorded in a loess section at weinan north central china abstract the paleomagnetic records of the matuyama brunhes mb and upper jaramillo uj polarity reversals have been obtained from a loess section at weinan shaanxi province in china an investigation of the rock magnetic properties using stepwise irm acquisition hysteresis loops thermomagnetic analysis and x ray diffraction on magnetic extracts identifies pseudo single domain magnetite as the carrier of the main fraction of the remanence associated with maghemite and hematite the total duration of the directional change based upon independent loess accumulation rates is about 5000 yr for the mb reversal and about 3200 yr for the uj reversal these values are consistent with previous estimates obtained from marine or lacustrine sediments apart from a few intermediate points observed on north america mb and in the pacific uj the transitional virtual geomagnetic pole vgp paths are situated in two longitudinal bands over eastern asia and australia mb and the americas uj the bulk of the uj record and the part of the mb record over the americas are not consistent with the hypothesis of a record arising from smoothing of pre and post transitional directions 1 a reappraisal of the statistical approach of mcfadden et al 2 shows that the longitudinal distribution of the records of reversals is consistent with the hypothesis of genuine geographically preferred sectors for the paths independent of site longitude with a probability higher than 0 45 when the two weinan records are considered thus these results obtained from wind blown loess sustain the hypothesis of two preferential longitudinal bands for reversing transitional vgps suggested from the study of marine and lacustrine sediments

the dust provenance and transport mechanism for the chengdu clay in the sichuan basin china the chengdu clay in the sichuan basin china was named by thorp and dye in 1936 the genesis dust provenance and transport mechanism for the chengdu clay however are still debated in the present work the chengdu clay and adjacent loess from the eastern tibetan plateau the chinese loess plateau and the qinling mountains were investigated the content and grain size distribution of quartz quartz 18o sm nd isotopic system rare earth elements and other trace element concentrations for the chengdu clay and its adjacent loess were analyzed based on comparison and spatial variation analysis the results confirm that the chengdu clay is of aeolian origin the dust provenance of the chengdu clay differs from those of the adjacent loess the chengdu clay is possibly of local origin and is transported by an ancient katabatic wind over a short distance during glacial and stadial periods the alluvial sediments in the northwestern sichuan basin are possibly the major sources of the chengdu clay there is little possibility of an effective aeolian transport bringing dust from the tibetan plateau the arid area in northwestern china or inner mongolia into the sichuan basin where it may be deposited to form the chengdu clay thus long range dust transport by the east asian winter monsoon the westerly jet or the tibetan plateau winter monsoon possibly plays a minor role in controlling the magnitude of the dust flux of the chengdu clay in the sichuan basin

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

mountain glaciation in japan and taiwan at the global last glacial maximum abstract montane glaciation in japan and taiwan was maximal in mis 3 4 and glacier extent at the global last glacial maximum lgm was much more limited data from four areas in japan and two in taiwan where the topographical and chronological positions of the terminal moraines are well determined and the chronology is controlled by radiocarbon ams and 10be cosmogenic dates are presented in this paper equilibrium line altitudes elas at global lgm are around 1500 m in the hidaka range hokkaido 2500 m in the northern japanese alps 2700 m in the central japanese alps 2800 m in the southern japanese alps in japan and 3300 m in northern taiwan and 3500 m in central taiwan the elas are mostly determined by maximum discharge accumulation ablation area ratio aar and glacier toe and headwall ratio thar methods the pattern of contours of elas indicates a strong influence of precipitation control on glacier development in this region the ela depression at global lgm in japan was 1100 1300 m except in the northernmost part of the northern japanese alps only 400 m where the present hypothetical ela is extraordinarily low because of abundant snowfall the ela depression at global lgm in taiwan is estimated at about 1100 1300 m without consideration of uplift

dependence of the duration of geomagnetic polarity reversals on site latitude an important constraint on the processes governing the geodynamo the flow in the outer core responsible for generating earth s magnetic field is the duration of geomagnetic polarity reversals that is how long it takes for earth s magnetic field to reverse1 it is generally accepted that earth s magnetic field strength drops to low levels during polarity reversals and the field direction progresses through a 180 change while the field is weak1 the time it takes for this process to happen however remains uncertain with estimates ranging from a few thousand up to 28 000 years here i present an analysis of the available sediment records of the four most recent polarity reversals these records yield an average estimate of about 7 000 years for the time it takes for the directional change to occur the variation about this mean duration is not random but instead varies with site latitude with shorter durations observed at low latitude sites and longer durations observed at mid to high latitude sites such variation of duration with site latitude is predicted by simple geometrical reversal models in which non dipole fields are allowed to persist while the axial dipole decays through zero and then builds in the opposite direction and provides a constraint on numerical dynamo models

post depositional remanent magnetization lock in and the location of the matuyama brunhes geomagnetic reversal boundary in marine and chinese loess sequences article i nfo pdrm lock in loess paleosol bioturbation disturbs detrital magnetic particles after deposition so accurate recording of the ancient geomagnetic field in bioturbated sediments is widely attributed to acquisition of a post depositional remanent magnetization pdrm whereby the geomagnetic field exerts a torque on a magnetic particle and aligns it with the field after the final mixing event experienced by the particle the relationship between the matuyama brunhes boundary mbb and oxygen isotope age tie points in marine sediments has been widely used to determine the depth at which the paleomagnetic signal is locked in however such analyses can be badly affected by age discrepancies among different paleoclimatic proxies and by varying isotopic compositions of seawater in different locations and from the presence of different water masses at different depths at the same location it is therefore necessary to separately compare paleomagnetic data with respect to either benthic or planktonic foraminiferal oxygen isotope records for sites from the same water mass to avoid inadvertently introducing age differences to the analysis when the global data set is subjected to such a rigorous analysis few reliable data remain for the mbb using two complementary approaches we estimate that the mbb is on average shifted 20 cm below its true position in marine sediments this offset is the sum of the thickness of the bioturbated surface mixed layer which is possibly dominant and the pdrm lock in depth there is also controversy concerning observed differences in the position of the mbb relative to paleoclimatic proxies in marine sediments and chinese loess deposits for the chinese loess quartz grain size is insensitive to pedogenic alteration and is a useful parameter for determining the true position of the mbb with respect to paleoclimatic boundaries we conclude that the mbb occurs late in marine oxygen isotope stage 19 and in the upper part of chinese paleosol unit s8 rather than at the mid or lower part of loess unit l8 our results require adjustment of the generally accepted positions for the mbb and resolve a longstanding chronological conundrum for marine and chinese loess sequences

remagnetization of quaternary eolian deposits a case study from se chinese loess plateau 1 the loess paleosol succession in the southeastern margin of the chinese loess plateau retains high resolution archives of sedimentary and environmental change in this study we report a detailed paleomagnetic and rock magnetic investigation of loess paleosol sequences in the sanmenxia area spanning the last 1 1 myr the results demonstrate that the matuyama brunhes boundary occurs at the top of soil s8 and the upper and lower boundaries of the jaramillo normal subchron are encountered at the top of soil s10 and loess l13 respectively in agreement with the classic luochuan section loess l9 also referred to as the upper sand layer is the coarsest loess unit over the last 1 1 myr and carries an imperfect normal polarity magnetization although it is fully separated by a short reversed polarity interval this thick normal polarity zone is too extensive to represent excursions like kamikatsura and or santa rosa and is concluded to represent an artifact rather than a record of geomagnetic field directions precise multiparameter environmental magnetic determination reveals that the short reversed polarity interval within the middle of this thick normal polarity zone exactly corresponds to a thin pedogenic horizon detailed rock magnetic analyses show that there are no intrinsic differences in magnetomineralogical properties between this pedogenic interval and other parts of l9 although the composition of magnetically soft components magnetite maghemite in the short pedogenic interval is relatively higher than that of other parts of l9 thus it is proposed that extensive remagnetization of parts of l9 most likely reflects a lithology dependent process and the dramatic coarsening of particle size across l9 is the fundamental reason for pervasive remagnetization our magnetostratigraphic results strongly imply that we need to reconsider the remanence recording fidelity of coarse loess l9 and probably l15 and care should be taken to interpret excursions in future paleomagnetic investigations of the chinese loess

brief sea level fall event and centennial to millennial sea level variations during marine isotope stage 19 in osaka bay japan detailed sea level variation was investigated for marine isotope stage mis 19 based on diatom and grain size analyses of a marine sequence in a core of the osaka group diatom sea level proxies represent precession related signals correlated with highstands mis 19 3 and 19 1 and lowstand mis 19 2 astronomical tuning shows the marine sequence has a uniform accumulation rate of about 60 cm ka 1 a rapid sea level fall event was found in the earliest mis 19 demonstrated by several independent sea level proxies of diatom and grain size this event began with a rapid sea level drop followed by a gradual recovery at about 783 782 ka a maximum abundance of pelagic diatom taxa at a core depth of 402 20 m evidently shows the highest sea level peak in mis 19 supported by many other proxies based on the diatom data sea level change across mis 19 1 is characterized by centennial to millennial fluctuations the sea level fall event began just after the onset of a cooling event previously reported from the same core observations of a comparable sea level fall signal in many deep sea core records suggest the event is global

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

mineral magnetic variation of the jingbian loess paleosol sequence in the northern loess plateau of china implications for quaternary development of asian aridification and cooling a high resolution mineral magnetic investigation has been carried out on the jingbian loess paleosol sequence at the northern extremity of the chinese loess plateau results show that the magnetic assemblage is dominated by large pseudo single domain and multidomain like magnetite with associated maghemite and hematite variations in the ratios of sirm100mt sirm sirm100mt sirm30mt and sirm100mt sirm60mt sirm is the saturation isothermal remanent magnetization sirmnmt represents the residual sirm after an n mt alternating field demagnetization have been used to document regional paleoclimate change in the asian interior by correlating the mineral magnetic record with the composite 18o record in deep sea sediments the long term up section decreasing trend in those ratios in both loess and paleosol units has been attributed to a long term decrease in the relative contributions of eolian hematite during glacial extrema and of pedogenic hematite during interglacial extrema respectively which reveals a long term decreasing trend in chemical weathering intensity in both glacial stage source region the gobi and deserts in northwestern china and interglacial stage depositional area the loess plateau region we further relate this long timescale variation to long term increasing aridification and cooling during both glacial extrema in the dust source region and interglacial extrema in the depositional area over the quaternary period changes in those ratios are most likely due to quaternary aridification and cooling driven by ongoing global cooling expansion of the arctic ice sheet and progressive uplift of the himalayan tibetan complex during this period

small latitudinal shift in the kuroshio extension central pacific during glacial times evidence from pollen transport the mid latitude area of the central pacific is sensitive to ocean environmental change because latitudinal fluctuation in a transition zone between subtropical and subarctic waters has played an important role in climatic change in east asia the north pacific and north america higher amounts of pollen and spores were found in core h3571 on the hess rise during the glacials than during the interglacials pollen originating from broadleaf deciduous forest in warm and humid environments as well as from boreal conifers and tundra park tundra in cold and wet environments occurred during the glacials the boreal conifer pollen such as tsuga picea and haploxylon could originate from the central japanese archipelago that ephedra was supplied from the asian continent and that the main source regions for the rest of the pollen and spores were from the southern japanese archipelago to the area around the east china sea therefore ocean current transportation was important for the transportation of pollen and spores to the hess rise this evidence demonstrates a small southward shift in the kuroshio extension during the glacials it also suggests that terrestrial organic matter om deposited in the open sea may also be transported by ocean currents reflecting coastal terrestrial environments although it is widely believed that terrestrial om in open sea sediments is of aerosol origin

holocene treeline shifts and monsoon variability in the hengduan mountains southeastern tibetan plateau implications from palynological investigations abstract the upper 8 45 m of a sediment core from lake naleng were analysed for its pollen and charcoal content to detect vegetation climate and human activity changes on the southeastern tibetan plateau tp since the pleistocene holocene transition 11 7 cal kyr bp the application of pollen indicator taxa pollen sums biomisation and multivariate analysis helped to reconstruct environmental conditions during the holocene furthermore 64 surface samples from the southeastern tp and its foreland were analysed to investigate the relationship between modern pollen assemblages and vegetation the modern vegetation was recorded in the surface pollen assemblages by pollen indicator types although sediments also contain pollen spectra extra regional pollen transported from lower vegetation belts which is seen as a consequence of steep elevation gradients at the southeastern margin of the tp the relation between different vegetation belts and temperature from the modern sample sites was used to infer quantitative temperature trends for the holocene record spreading of forests at the beginning of the holocene marks the transition to warmer conditions from 10 7 to 4 4 cal kyr bp open abies betula forests were found at lake naleng probably reflecting a stronger than present summer monsoon temperature range reconstructions suggest a temperature that was about 2 3 c warmer and a treeline position that was 400 600 m higher than today a severe climate deterioration with temperatures about 1 2 c colder than before is documented by a retreating forest between 8 1 and 7 2 cal kyr bp forests retreated while subalpine rhododendron shrubs spread around lake naleng indicating colder conditions with temperatures 1 2 c below early and mid holocene level after 4 4 cal kyr bp the forest decline at 4 4 cal kyr bp is considered to reflect climatic conditions as low concentrations of charcoal particles found in this period exclude human induced fires as reason for the forest retreat however grazing indicators imply human influence on the environment since 3 4 cal kyr bp around lake naleng we therefore consider the rapid treeline shift seen at 3 4 cal kyr bp as partly generated by human activity and partly by climatic conditions

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

asian summer monsoon instability during the past 60 000 years magnetic susceptibility and pedogenic evidence from the western chinese loess plateau abstract the 28 m high resolution shajinping loess section in lanzhou on the western chinese loess plateau records a 60 ka millennial summer monsoon variation the record shows that asian summer monsoons have rapid episodic pulse enhancements spanning only ca 1 2 ka in high frequency domain and having sub milankovitch cycles of progressive weakening in low frequency domain in the last glaciation soil formation seems to occur with a surprisingly fast response to these summer monsoon enhancements resulting in weakly or moderately developed paleosol sequences both the pattern and timing of the summer monsoon enhancements show that they can be correlated to most major warm dansgaard oeschger episodes and long term cooling bond cycles of the north atlantic climatic records indicating a possible teleconnection between tropic oceanic air masses and the north atlantic climatic system but differences exist for the transition of mis 2 3 and the holocene where extraordinarily heavy dust input events and fairly variable climatic fluctuations occur for the former and latter respectively a westerlies swing model is proposed to interpret this link

land ocean linkages over orbital and millennial timescales recorded in late quaternary sediments of the japan sea late quaternary sediments of the japan sea are characterized by centimeter to meter scale alternations of dark and light layers which are synchronous basinwide high resolution analyses of the sediments from ocean drilling program site 797 reveal that deposition of the meter scale alternations reflect variations in paleoceanographic conditions which were closely associated with glacio eustatic sea level changes through the modulation of the volume and character of the influx to the sea through the tsushima strait the centimeter to decimeter scale alternations reflect millennial scale variations which are possibly associated with dansgaard oeschger d o cycles with each dark layer appearing to correspond to an interstadial this variability is attributed to the development of a humid climate in central to eastern asia and the consequent increase in discharge from the huanghe and changjiang rivers during interstadials this caused expansion of the east china sea coastal water ecscw which penetrated more strongly into the japan sea the increased influence of the lower salinity nutrient enriched ecscw reduced deep water ventilation and enhanced the surface productivity leading to the development of anoxic bottom waters and deposition of the dark layers thus the centimeter to decimeter scale alternations of the dark and light layers record wet and dry cycles in central to eastern asia possibly associated with d o cycles

how does chinese loess become magnetized despite nearly three decades of paleomagnetic research on the extensive chinese loess deposits a convincing explanation has yet to be developed for how chinese loess becomes magnetized to address this problem we conducted re deposition experiments using weakly consolidated holocene chinese loess that was disaggregated in the laboratory and compare our results with published paleomagnetic data we simulated a depositional remanent magnetization drm associated with dry deposition of eolian sediments and a post depositional remanent magnetization pdrm in which the sediment was water saturated after deposition the simulated drm faithfully records the declination of the applied field but with systematic inclination flattening addition of minor water slightly improves recording of the applied field but inclination flattening persists reliable recording of the applied field occurs for pdrm simulation in water saturated sediment our synthesis of paleomagnetic data from chinese loess indicates that time averaged paleomagnetic directions are often indistinguishable from the expected geocentric axial dipole gad field but in many cases inclinations are shallower than for a gad field we conclude that the chinese loess is magnetized by a combination of drm and pdrm mechanisms with water content providing the dominant control on which mechanism aligns the detrital mineral fraction where pedogenesis causes neoformation of magnetic minerals an additional chemical remanent magnetization crm will occur the magnetization of chinese loess therefore appears to be controlled by a complex time varying combination of drm pdrm and crm mechanisms

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

real time infrasonic monitoring of the eruption at a remote island volcano using seismoacoustic cross correlation s u m m a r y on 2013 november 20 a submarine eruption started close to nishinoshima island which lies 1000 km south of tokyo real time monitoring of the eruption is crucial for understanding the formation processes of the new volcano island and related disaster prevention in situ monitoring however is difficult in practice because the closest inhabited island chichijima is 130 km away from nishinoshima this study presents an infrasonic monitoring method that uses cross correlating records at a pair of online stations on chichijima one is the horizontal ground velocity recorded at a permanent seismic station operated by the japan meteorological agency jma the seismic records were corrected for atmospheric pressure using an empirical ground response to infrasound the other is the air pressure recorded at the jma meteorological observatory for each station we divided the whole records into 3600 s segments to suppress outliers each segment was normalized by the envelope function we then calculated cross correlation functions between the pair of stations using the fast fourier transform they present clear successive arrivals of infrasound coming from nishinoshima we also conducted an offline tripartite array observation using three low frequency microphones with a station spacing of 50 m installed in 2013 may the array analysis supports the results obtained from the online stations the typical root mean squared amplitude is on the order of 0 01 pa and the typical duration is several days the amplitudes were primarily controlled by the effective sound velocity structure from nishinoshima to chichijima the infrasonic observations together with the meteorological observation at chichijima suggest that infrasonic activity was not present in the first two weeks in 2015 january with the help of a more quantitative estimation of the meteorological effect we could infer eruptive activity in real time now many online seismic stations are available worldwide this study shows that installation of another infrasonic sensor close to the existing seismic station 1 km is useful for monitoring a remote island volcano in real time

glacial interglacial changes in the east australian current the east australian current eac is the western boundary current of the south pacific gyre transporting warm tropical waters to higher southern latitudes recent modelling shows that the partial separation of the eac 32 s and the coupled formation of the tasman front 34 s are caused by a steep gradient in the zonally integrated wind stress curl analysis of oxygen isotope ratios 18o in the planktonic foraminifer globigerinoides ruber from sediment cores from the coral sea and tasman sea indicates that the eac separation shifted northward to between 23 and 26 s during the last glacial we suggest these results indicate a significant change in the pacific wind stress curl during the glacial given recent evidence for el nino like conditions in the pacific during the last glacial with a reduction in the east west sea surface temperature sst gradient we suggest that weaker trade winds combined with more northerly stronger westerlies were associated with a change to the wind stress curl which repositioned the eac separation and tasman front in contrast by 11 ka bp the eac separation was forced south of 26 s this southward shift was synchronous with a rapid warming of tropical ssts and the onset of a la nina like sst configuration across the tropical pacific it appears that the south pacific trade winds strengthened accordingly causing the eac to readjust its flow this readjustment of the eac marks the onset of modern surface ocean circulation in the southwest pacific but the present eac transport was only achieved in the late holocene after 5 ka bp

millennial to submillennial scale features of the matuyama brunhes geomagnetic polarity transition from osaka bay southwestern japan 1 a high resolution magnetic record of the matuyama brunhes mb reversal transition was obtained from homogeneous marine clay in a 1700 m core from osaka bay the transition stretches over a core length of 6 4 m and yields four short reversal episodes two predate the main mb boundary mbb and two postdate it we made diatom analyses of sediments to estimate relative sea level changes and constructed an age model by correlation with the astronomically calibrated marine oxygen isotope curve the age model shows the short reversal episodes with durations of 1 kyr occurred at 4 5 kyr intervals within stage 19 and the mbb occurred about 5 kyr after the sea level highstand corresponding to isotopic event 19 3 it also shows the paleointensity minimum of 15 20 of the postreversal mean occurred at about 6 kyr before the mbb and another minimum at about 1 kyr after four virtual reverse to normal polarity boundaries found in this study suggest different ages for the mbb could be observed in lava flow studies some millennial to submillennial scale transition features found in this study are compatible with the previous numerical simulations of geomagnetic field reversal

can relative paleointensities be determined from the normalized magnetization of the wind blown loess of china although the wind blown loess and interbedded paleosol sequence in the loess plateau of china has been extensively studied and regarded as one of the most complete terrestrial records of both the geomagnetic field and climatic changes during the quaternary little attention has been paid to it as a source of relative paleointensity in this study we examine the malan loess l1 the last glacial sediments in the lingtai section to determine whether loess is able to reliably record the relative paleointensity toward that end both the conventional normalizing method as well as the pseudo thellier method tauxe et al 1995 were used in conjunction with the examination of the rock magnetic properties and natural remanent magnetization nrm rock magnetic properties of l1 show the uniformity in terms of magnetic mineralogy and grain size suggesting that they may be suitable for relative paleointensity studies normalized remanences derived from l1 show highs between both 72 66 ka and 62 51 ka and lows near 63 ka 42 ka and between 20 and 10 ka comparable results using different normalization parameters suggest that large amplitude variation of normalized magnetization may reflect the intensity variation of the geomagnetic field however comparisons of the normalized magnetization with contemporaneous marine records show some dissimilarities in particular the intensity low at 20 10 ka corresponding to the last glacial maximum is not compatible with the sint 800 composite record on the other hand spectral coherence analyses of middle and high frequency components of the normalized magnetizations suggest some climatic influence thus this apparent discrepancy may be explained by climatic changes in the loess plateau and the resulting effect on the nrm

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

10 be evidence for the matuyama brunhes geomagnetic reversal in the epica dome c ice core every few hundred thousand years earth s north and south magnetic poles swap places for the first time a record of one of these geomagnetic reversals has been found in an ice core because the strength of the field is very low during a reversal the intensity of cosmic rays in the earth s atmosphere is increased this leads to an increase in the quantity of 10be which like 14c is formed by cosmic rays in the atmosphere deposited in the ice it is this 10be enhancement in the ice that has been detected an ice core drilled at dome c antarctica is the oldest ice core so far retrieved1 on the basis of ice flow modelling and a comparison between the deuterium signal in the ice with climate records from marine sediment cores the ice at a depth of 3 190 m in the dome c core is believed to have been deposited around 800 000 years ago2 offering a rare opportunity to study climatic and environmental conditions over this time period however an independent determination of this age is important because the deuterium profile below a depth of 3 190 m depth does not show the expected correlation with the marine record2 here we present evidence for enhanced 10be deposition in the ice at 3 160 3 170 m which we interpret as a result of the low dipole field strength during the matuyama brunhes geomagnetic reversal which occurred about 780 000 years ago if correct this provides a crucial tie point between ice cores marine cores and a radiometric timescale