eolian deposition in the northeast pacific ocean cenozoic history of atmospheric circulation the mass accumulation rate and grain size distribution of the total eolian component of north pacific pelagic clays have been used to evaluate changes in eolian sedimentation and in the intensity of atmospheric circulation that have occurred during the past 70 m y eolian deposition was relatively low approximately 12 mg cm2 1 000 yr in the late cretaceous and paleocene reflecting an increasingly humid environment a peak in accumulation rates across the paleocene eocene boundary may be the result of episodic volcanism in mexico a sharp decrease in grain size across the paleocene eocene boundary is not readily interpreted fine eolian grain size and the low accumulation rates averaging 8 mg cm2 1 000 yr in the eocene and early oligocene are in agreement with low early tertiary thermal gradients and less vigorous atmospheric circulation large increases in grain size between 37 and 30 m y ago 20 and 10 m y ago and 5 m y ago to the present suggest that atmospheric circulation intensified by a factor of 1 5 1 8 and 1 4 respectively at these times eolian accumulation rates increased from 8 mg cm2 1 000 yr at the eocene oligocene boundary to approximately 25 mg cm2 1 000 yr at the end of the miocene with significant changes at 25 and 13 m y ago increased rates about 25 m y ago probably reflect movement of the core site into the influence of the westerlies and the increase 13 m y ago appears to be a response to steepening thermal gradients and intensifying atmospheric circulation resulting from major expansion of antarctic ice in the mid miocene along with a general increase in global aridity in the late cenozoic an order of magnitude increase in eolian accumulation rates 25 to 226 mg cm2 1 000 yr in pliocene pleistocene time coincides with the onset of northern hemisphere glaciation and consequent climatic deterioration the large increase in accumulation rates in pliocene pleistocene time coincides with a relatively smal increase in the intensity of atmospheric circulation compared to that in oligocene and miocene time suggesting that the increased deposition rates were the result of an increase in global aridity in glacial times rather than a further increase in the vigor of the global wind systems

sr nd isotope composition and clay mineral assemblages in eolian dust from the central philippine sea over the last 600 kyr implications for the transport mechanism of asian dust dust transport to the tropical subtropical northwestern pacific over the past 600 kyr was investigated using radiogenic isotopes 87sr 86sr and end together with the clay mineral composition of eolian dust preserved in a sediment core obtained from the philippine sea 12 30 n 134 60 e these data revealed the influence of two prevailing dust sources namely the asian deserts and nearby volcanic arcs e g the luzon arc with average contributions of around 70 and 30 respectively from each the clay mineral composition of the core resembled dust from the central asian deserts cads e g the taklimakan desert as in the north central pacific but published aerosol data collected near the study site during winter spring have the mineralogical signature of dust originating from the east asian deserts eads these data indicate that the relative contribution of ead dust increases with the northeasterly surface winds associated with the east asian winter monsoon eawm during winter spring but the prevailing westerlies and trade winds that carry dust from the cads is the dominant transport agent in the overall dust budget of the study site the results of this study contradict the prevailing view that direct dust transport by the eawm winds in spring dominates the annual flux of eolian dust in the northwest pacific

new absolute time scale for the quaternary climate in the chinese loess region by grain size analysis continuous loess sequences in china provide not only information for paleoclimatic reconstructions but also permit the establishment of a reliable absolute time scale for the quaternary an empirical relationship is developed between the grain size of the loess and the sedimentation rate in a short well dated reference section step 1 this relationship is extrapolated to the complete quaternary section step 2 after derivation of the sedimentation rate by measuring the grain size in all the layers of the sequence the duration of deposition of each layer is obtained by dividing thickness by sedimentation rate and subsequently the age of each point in the sequence is calculated by adding together all the duration values of the overlying layers the chronology of the extrapolated part of the section obtained in this way is independent of dates provided by other methods and may also be checked by them

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

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

differing controls over the cenozoic pb and nd isotope evolution of deepwater in the central north pacific ocean dissolved pb and nd isotope ratios of seawater as recorded by chemical marine precipitates such as hydrogenetic ferromanganese crusts have been used as paleoenvironmental proxy tracers for the north pacific however all ferromanganese crusts studied so far have either been subject to phosphatization or hydrothermal influence in their old part or only the young parts have been analyzed thus the pb and nd isotope compositions of north pacific deep waters prior to 20 ma are not well constrained we present new results for three ferromanganese crusts one of which cj01 shows no phosphatization and is located far away from the epr its age is inferred to be 75 ma and thus provides for the first time an opportunity to trace the nd and pb isotope evolution of central north pacific seawater back to the latest cretaceous the three crusts no matter whether phosphatized or not display very similar pb and nd isotope trends with age suggesting no modification of the pb and nd isotope distribution by post depositional phosphatization our data suggest that dissolved pb in deep waters of the central north pacific over the cenozoic and latest cretaceous has mainly been derived from eolian dust and only to a minor extent from weathering of island arcs for pb these trends broadly resemble the pb isotope evolution of the eolian silicate dust fraction of core ll44 gpc3 in the central north pacific we suggest that the isotope evolution of dissolved pb in central north pacific seawater has been mainly controlled by pb released from eolian dust from north america prior to 50 ma and after 40 ma from asia in contrast the nd isotope time series of the crusts are by no means similar to the nd isotope evolution of the silicate dust fraction in core gpc3 suggesting a decoupling from the pb and negligible contributions from dust to the dissolved nd in the central north pacific deep water the rise of nd isotope ratios of pacific seawater during the cenozoic has most likely been caused by the increasing volcanic activity and erosion of the volcanic arcs around the pacific

eolian quartz flux to lake biwa central japan over the past 145 000 years abstract eolian quartz flux eqf g cm 2 103yr 1 to lake biwa central japan provides direct information on variations of the east asian winter monsoon lake biwa sediments spanning the past ca 145 000 yr are characterized by two main periods when eqf values were significantly greater than 5 50 g cm 2 103yr 1 and two main intervals during which eqf values were lower two periods with eqf values 5 50 g cm 2 103yr 1occurred from ca 145 000 to 125 000 and 73 000 to 13 000 yr b p while times of lower eqf values occurred from ca 125 000 to 73 000 yr b p and around ca 5500 yr b p between ca 125 000 and 73 000 yr b p three minimum eqf values and two intervening peaks of slightly higher eqf values are recorded eqf increased markedly from ca 73 000 to 13 000 yr b p whereas between ca 53 000 and 20 000 yr b p the values recorded were relatively lower than those recorded during either the preceding or the subsequent episodes the data imply that the east asian winter monsoon strengthened during the periods when eqf values were high and weakened during the intervals with low eqf values the eqf record of lake biwa can be correlated with the grain size record of the quartz fraction in chinese loess and with the specmap marine 18o record however the eqf record apparently lags ca 5000 yr behind the loess and 18o records during stage 6 5 and 2 1 transitions and ca 10 000 yr during stage 5 4 transition these apparent lags could be due to problems with the chronology alternatively they may imply that the eolian quartz flux depended more on the extent of dust source regions than on wind intensity during these transitions

cenozoic evolution of asian climate and sources of pacific seawater pb and nd derived from eolian dust of sediment core ll44 gpc3 1 the large diameter piston core ll44 gpc3 from the central north pacific ocean records continuous sedimentation of eolian dust since the late cretaceous two intervals resolved by nd and pb isotopic data relate to dust coming from america prior to 40 ma and dust coming from asia since 40 ma the intertropical convergence zone itcz separates these depositional regimes today and may have been at a paleolatitude of 23 n prior to 40 ma such a northerly location of the itcz is consistent with sluggish atmospheric circulation and warm climate for the northern hemisphere of the early to middle eocene since 40 ma correlations between nd 7 55 end t 10 81 and pb 18 625 206 4pb 18 879 15 624 207 4pb 15 666 38 611 208 4pb 38 960 0 8294 207 6pb 0 8389 2 0539 208 6pb 2 0743 isotopes reflect the progressive drying of central asia triggered by the westward retreat of the paleo tethys comparisons between the changes with time in the isotopically well defined dust flux and nd and pb isotopic compositions of pacific deep water allow one to draw two major conclusions 1 dust bound nd became a resolvable contribution to pacific seawater only after the one order of magnitude increase in dust flux starting at 3 5 ma therefore eolian nd was unimportant for pacific seawater nd prior to 3 5 ma 2 the lack of a response of pacific deep water pb to this huge flux increase suggests that dust bound pb has never been important instead mobile pb associated with island arc volcanic exhalatives probably consists of a significant contribution to pacific deep water pb and possibly to seawater elsewhere far away from landmasses

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

southward shift of the intertropical convergence zone due to northern hemisphere cooling at the oligocene miocene boundary the mi 1 glaciation ca 23 ma which marks the oligocene miocene boundary was an aberrant cooling event that led to a build up of the antarctic ice sheet which reached the near modern volume or greater from its ephemeral or partial existence an increase of 1 in the 18o of benthic foraminifera during this interval has been attributed to the development of antarctic ice sheets and deep water cooling without definitive evidence northern hemisphere nh glaciation has not been a material consideration for the 18o increase here we investigate the interhemispheric temperature contrast during mi 1 with the movement of the intertropical convergence zone itcz at a site 10 31 n in the east pacific integrated ocean drilling program site u1333 to understand nh cooling and the possibility of nh glaciation the measured 143nd 144nd 87sr 86sr and clay mineral compositions of eolian dust fractions indicate unequivocally the deposition of asian dust during mi 1 and of central american and south american dust before and after mi 1 this is attributed to the southward displacement of the itcz over site u1333 during mi 1 the itcz shifts toward the warmer hemisphere thus our results suggest that the cooling during mi 1 was more significant in the nh than in the southern hemisphere which underwent a sudden expansion of continental ice sheets our data call for a forcing mechanism to drive significant nh cooling during this episode based on the available data we propose that the widespread growth of nh ice sheets and or changes in the production of north atlantic origin deep water could be possible causes of the nh cooling at that time

thermoluminescence dating of loess and palaeosols from the lantian section shaanxi province china abstract ten samples of loess and palaeosol collected from the upper part of lantian section shaanxi have been dated using the fine grain 4 11 m tl technique palaeodose values were determined by the regeneration method readhead 1982 the tl ages obtained ranged from 2 4 104 years for the upper malan loess l1 to 1 5 105 years for the upper part of loess l2 of the lishi loess fine grain tl dating does not seem to be suitable for the samples older than 150 ka the uncertainty of the tl age estimate especially for the palaeosol sample may be primarily an effect of disequilibrium of the 238u decay chain and of water content variations since deposition of sediments

east asia winter monsoon variations on a millennial time scale before the last glacial interglacial cycle grain size and magnetic susceptibility measurements on samples from a typical loess palaeosol sequence on the central chinese loess plateau are used to reconstruct the pleistocene east asian monsoon climate the coarse grained fraction i e the weight percentage 30 m of the bulk grain size distribution is used as a sensitive proxy index of the east asia winter monsoon strength on the basis of an absolute time scale time series variations of this proxy show that winter monsoon strengths varied on millennial time scales during the periods 145 165 240 280 320 350 390 440 600 640 860 890 900 930 and 1330 1400 kyr bp the wavelength of these climatic oscillations varied between 1 89 and 4 0 kyr as is shown by spectral analysis using the multitaper method although numerical simulation experiments show that high frequencies also can arise from measurement errors in the grain size analysis the frequencies prove to be sufficiently stable when the spectral analysis is repeated with a different number of tapers for the time being we do not correlate these climatic oscillations with palaeoclimatic records in the north atlantic deep sea sediments because both time scales need to be further improved our data however certainly demonstrate that millennial scale east asian winter monsoon variations in the last 1 4 million years can be detected from terrestrial loess records copyright 1999 john wiley sons ltd

quantitative resolution of eolian continental crustal material and volcanic detritus in north pacific surface sediment proxy records of continental climate and atmospheric circulation provided by analyses of eolian continental material extracted from marine sediment have resulted in significant new information concerning the behavior of these climate systems on various timescales these studies however currently are limited to certain geographic areas because no chemical or physical extraction procedure provides an unambiguous separation of eolian continental crustal material from other contaminants like volcanic detritus we employ a combined analytical and statistical procedure in an effort to extract a more refined eolian signal from areas that may be affected by volcanic detritus bulk surface sediment samples from 33 locations in the north pacific were treated using a conventional sequential extraction procedure to remove the carbonate silica and oxyhydroxide components and the residue was analyzed by instrumental neutron activation analysis inaa for la ce sm eu yb lu hf sc and th q mode factor analysis of these data shows that 99 of the variance is explained by two end members which we interpret to be continental crustal material and volcanic detritus five least squares normative analysis models were evaluated to estimate the relative amount of these end members in each sample the continental crustal component was approximated using a fine grained fraction of china loess and bulk loess the volcanic component was approximated using the compositions of average kurile kamchatka volcanic material a median ocean drilling program odp leg 145 ash and a median kurile basalt the model based on average kurile kamchatka volcanic material and the fine loess fraction gives the most accurate results central and east pacific samples typically contain up to 100 of the eolian continental crustal component while samples near japan kamchatka and the aleutians contain a majority of volcanic detritus however the highly variable composition of volcanic material can result in systematic errors up to 25 in samples dominated by volcanic detritus the geographic distribution of the compositional end members is consistent with a continental dust source originating in asia and being diluted by ash from the volcanic arcs of the pacific rim this improved identification and resolution of the eolian continental component realized in this approach should permit paleoclimatic reconstructions to be developed from sediments in significant portions of the world that were previously precluded from analysis because of limitations with chemical or physical extraction procedures

enhanced saharan dust input to the levant during heinrich stadials abstract the history of dust transport to the levant during the last glacial period is reconstructed using the isotope ratios of pb sr nd and hf in sediments of lake lisan the last glacial dead sea exposed marginal sections of the lisan formation were sampled near masada the perazim valley and from a core drilled at the deep floor of the modern lake bulk samples and size fractions display unique isotopic fingerprints the finest detritus fraction 87 sr 86 sr and lower end values 0 710 0 713 and 7 0 to 9 8 respectively relative to the coarser fractions 5 20 m and 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios 18 26 19 02 15 634 15 68 and 38 25 38 82 respectively are systematically higher in the finest detritus fraction relative to corresponding coarser fractions and bulk samples the 87 sr 86 sr and end values of the finest fraction correspond with those of atmospheric dust originating from the sahara desert while those of the coarse fractions are similar to loess deposits exposed in the sinai and negev deserts pronounced excursions in the sr nd pb isotope ratios toward more sahara like values coincide with the heinrich h stadials 6 5 and 1 reflecting significant increases in saharan dust fluxes during regionally arid intervals reflected by sharp lake level drops moreover during h6 the dust came from different saharan sources than during h1 and h5 while the relatively wet glacial climate in the levant suppressed the transport of dust to the lake watershed short term hyper arid spells during h stadial intervals were accompanied by enhanced supply of fine sahara dust to this region

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

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

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

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

flux and grain size variation of eolian dust as a proxy tool for the paleo position of the intertropical convergence zone in the northeast pacific abstract a 328 cm long piston core kodos 02 01 02 collected from the northeast equatorial pacific at 16 12 n 125 59 w was investigated for eolian mass fluxes and grain sizes to test these proxies as a tool for the paleo position of the intertropical convergence zone itcz the eolian mass fluxes of the lower interval below 250 cm 15 5 7 6 ma are very uniform at 5 1 mg cm2 103 yr while those of the upper interval above 250 cm from 7 6 ma are over 2 times higher than the lower interval at 12 1 mg cm2 103 yr the median grain size of the eolian dusts in the lower interval increases from 8 4 to 8 0 downward while that of the upper interval varies in a narrow range from 8 8 to 8 6 the determined values compare well in magnitude to those of central pacific sediments for the upper interval and equatorial and southeast pacific sediments for the lower interval this result suggests a possibility that the study site had been under the influence of southeast trade winds at its earlier depositional period due to the northerly position of the itcz and subsequently of the northeast trade winds for a later period when the upper sediments were deposited this interpretation is consistent with a mineralogical and geochemical study published elsewhere that assigned the provenance of the study core dust to central south america for the lower interval and to asia for the upper interval this study suggests that the distinct differences in eolian mass flux and grain size observed across the itcz can be used to trace the paleo latitude of the itcz

radiogenic isotopic mapping of late cenozoic eolian and hemipelagic sediment distribution in the east central pacific pelagic clay of the east central pacific province is shown to be a mixture of three primary detrital components reflecting continental source areas in asia north america and central and south america relative contributions from each source area are a function of geography and this distribution appears to have remained constant over the past five million years despite changing flux rates a q mode factor analysis of downcore records for pb sr and nd isotopes identified three factors that account for 98 of the total variance these factors represent the radiogenic isotopic signatures of 1 late cenozoic asian dust which dominates in the central north pacific 2 north american continental hemipelagic eolian sources restricted mainly to the easternmost north pacific at 30 n latitude and 3 central and south american sources restricted to areas east of 100 w longitude south of the intertropical convergence zone 6 n the asian dust signature diminishes abruptly we conclude that late cenozoic asian dust sources can be isotopically differentiated downcore from both north american and south and central american sources in the eastcentral pacific this approach has a utility for identifying changes in long term cenozoic atmospheric circulation patterns

asian continental nature of87sr 86sr ratios in north central pacific sediments strontium isotopic compositions were determined for silicate detritus in 152 deep sea and continental shelf surface sediment samples from the pacific ocean to trace their provenance the major characteristics of the spatial variation of the sr isotopes and the interpretation of this variation may be summarized as follows 1 sediments in the pacific have a lower average87sr 86sr ratio 0 7112 with a narrower range 0 703 0 724 than in the atlantic 0 7166 0 704 0 743 many western pacific volcanoes together with young continental crust supply material with low87sr 86sr ratios to the pacific in contrast to the large old cratonic crust that supplies material with high sr ratio to the atlantic 2 the87sr 86sr ratio is high in the north central pacific 0 711 0 719 the izu ogasawara and mariana arcs supply low87sr 86sr material to the western pacific but farther to east the abundant supply of loess carried by middle latitude westerlies from the asian continent 87sr 86sr ca 0 720 dominates the north central pacific

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

consistent trends in the true triaxial strength and deformability of cores extracted from icdp deep scientific holes on three continents abstract an extensive true triaxial testing program was carried out on core samples from three icdp sponsored deep scientific boreholes ktb germany safod united states and tcdp taiwan the three rocks differ in the processes that formed them and in many of their mechanical properties however all three rocks exhibited similar failure mechanism in which induced or reopened microcracks are primarily aligned with the 1 2 plane and the developed fault is steeply inclined in the 3 direction rock strength in all tested rocks increases with 2 when 3 is kept constant thus the common mohr type criteria which ignore the effect of 2 typically underestimate rock strength rather a 3d criterion that involves all three principal stresses represents well experimental results fracture plane slope for the same 3 steepens as 2 rises contrary to mohr type criteria with respect to deformation the onset of dilatancy increases with 2 in conclusion true triaxial tests conducted on cores from three scientific boreholes revealed important details of mechanical behavior not otherwise observed in conventional triaxial tests in addition they show mechanical behavior similarities as related to 2 effect regardless of rock type

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

dust production and deposition in asia and the north pacific ocean over the past 12 myr the silicate fractions of recent pelagic sediments in the central north pacific ocean are dominated by eolian dust derived from central asia an 11 myr sedimentary record at odp sites 885 886 at 44 7 n 168 3 w allows the evaluation of how such dust and its sources have changed in response to late cenozoic climate and tectonics the extracted eolian fraction contains variable amounts 70 of clay minerals with subordinate quartz and plagioclase uniform nd isotopic compositions nd 8 6 to 10 5 and sm nd ratios 0 170 0 192 for most of the 11 myr record demonstrate a well mixed provenance in the basins north of the tibetan plateau and the gobi desert that was a source of dust long before the oldest preserved asian loess formed nd values of up to 6 5 for samples 2 9 ma indicate 35 wt admixture of a young kamchatka like volcanic arc component the coherence of pb and nd in the erosional cycle allows us to constrain the pb isotopic composition of asian loess devoid of anthropogenic contamination to 206pb 204pb 18 97 0 06 207pb 204pb 15 67 0 02 208pb 204pb 39 19 0 11 87sr 86sr 0 711 0 721 and rb sr ratios 0 39 1 1 vary with dust mineralogy and provide an age indication of 250 ma 40ar 39ar ages of six dust samples are uniform around 200 ma and match the k ar ages of modern dust deposited on hawaii these data reflect the weighted age average of illite formation changes from illite smectite with significant kaolinite to illite and chlorite rich kaolinite free assemblages since the late pliocene document changes in the intensity of chemical weathering in the source region such weathering evidently did not disturb the k ar systematics and only induced scatter in the rb sr data we propose that when smectite forms at the expense of illite k and ar are quantitatively lost from what becomes smectite but are quantitatively retained in adjacent illite layers 40ar 39ar age data therefore are insensitive to smectite formation during chemical weathering but date the diagenetic growth of illite the major k bearing phase in the dust over the past 12 myr the dust flux to the north pacific increased by more than an order of magnitude documenting a substantial drying of central asia this climatic change however did not alter the ultimate source of the dust and neoformational products of chemical weathering always remained subordinate to assemblages reworked by mechanical erosion in dust deposited in eastern asia and the pacific ocean

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

neodymium isotopes as tracers in marine sediments and aerosols north atlantic nd and sm concentrations and nd isotopic compositions were measured on the detrital fraction of deep sea surface sediments and on aerosols sampled over the north atlantic and mediterranean sea the data expressed asend 0 and as model ages ranged from 14 5 end 0 4 9 and from 0 01 to 2 21 ga respectively two areas where the sediments contain relatively less radiogenic nd are to the west off north africa and eastward of the canadian shield this distribution is consistent with other tracers in suggesting that a significant fraction of the sediments are derived from aeolian material transported by major wind systems saharan dust transported in the equatorial trade winds belt and north american soil material transported in the latitudes of the westerlies between these aeolian dominated belts along an axis from the azores to gibraltar and the mediterranean lies a zone of more radiogenicend 0 values in sediments and aerosols influenced by the recent volcanism of this region previously reported distributions of nd isotopes in bottom formed iron manganese crusts and coatings are similar to distributions of nd isotope values in detrital sediments and aerosols this suggests that the detrital fraction has undergone partial dissolution and desorption in the water column and or in the pore waters of near surface sediments and that a significant proportion of nd in the authigenic ferromanganese phases is derived from this source and may therefore not represent strictly dissolved seawater nd isotope ratios useful as watermass tracers

interactive aggregation and sedimentation of diatoms and clay sized lithogenic material monospecific diatom cultures thalassiosira punctigera and skeletonema costatum were incubated in rotating cylinders together with clay suspensions present in a range of concentrations 5 100 mg kaolinite l 21 and as different minerals 50 mg l 21 kaolinite smectite illite and clay sized quartz powder the addition of lithogenic suspensions to diatom cultures accelerated the formation of visible aggregates in the roller tanks by a factor of 3 aggregate size decreased and density increased proportionally to the amount of kaolinite added to the diatom cultures in the presence of kaolinite and illite aggregate sizes were smaller and sinking rates lower than in the presence of smectite and quartz the influence of lithogenic matter on the sinking velocities of aggregates was ambiguous compound aggregates sank faster with increasing amounts of lithogenic matter present in cultures of t punctigera until a certain ratio between lithogenic and biogenic material was reached further increasing the amount of lithogenic matter did not increase sinking rates significantly in contrast increasing the concentration of kaolinite added to cultures of s costatum could decrease sinking velocities of the evolving compound aggregates this nonlinear behavior is argued to be primarily a function of aggregate composition on aggregate sizes and excess densities although the possibility of a mutual acceleration of vertical flux of algae and clay is confirmed the results show that the presence of lithogenic material could also decrease the downward flux of phytoplankton biomass rapid sinking of phytoplankton derived organic carbon via sedimentation of aggregates contributes significantly to the vertical transport of marine particulate organic carbon poc a process known as the biological pump volk and hoffert 1985 rapid sinking of clay sized lithogenic material can be inferred from sediment trap data wefer 1989 laboratory studies on marine aggregate formation and properties have focused on pure phytoplankton aggregates kiorboe et al 1990 riebesell et al 1991 kiorboe and hansen 1993 or on monomineralic clay aggregates kranck 1973 however coaggregation of phytoplankton and clay is a familiar phenomenon in aquatic environments first drawings of marine snow show sundry marine organisms and mineral grains embedded in a mucous matrix which dominates the aggregates by volume and appears to hold the solid compounds together tsujita 1953 avnimelech et al 1982 described enhanced floc formation and sedimentation of freshwater algae in the presence of clay and vice versa the fact that lithogenic and biogenic particles are often found in deep sediment traps during the same time interval in spite of independent occurrence in the surface water also suggests coaggregation and cosedimentation of these particles deuser et al 1983 wefer 1989 ittekkot 1993 while small amounts of both biogenic and lithogenic particles are present in all marine environments areas with elevated concentrations of lithogenic particles often show a high phytoplankton abundance at the same time and are thus particularly interesting in terms of interaction between phytoplankton and lithogenic material examples for marine en

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

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

cenozoic changes in atmospheric lead recorded in central pacific ferromanganese crusts the possible sources of pre anthropogenic pb contributed to the world s oceans have been the focus of considerable study the role of eolian dust versus riverine inputs has been of particular interest with better calibration of isotopic records from central pacific ferromanganese crusts using os isotope stratigraphy it now appears that deep water pb isotopic compositions were effectively homogeneous over a distance of 5000 km for the past 80 myr the composition shifted slightly from high 206pb 204pb ratios in the range of 18 87 0 02 before 65 ma to lower values of 18 62 0 02 by 45 ma and then gradually increased again very slightly to the present day ratio of 18 67 0 02 the regional homogeneity provides evidence of a dominant well mixed atmospheric source the most likely candidate for which is volcanic aerosols contributed either directly or as soluble condensates on eolian dust the slight shift in pb isotope composition of deep waters in the central pacific between 65 and 45 ma may be the result of a regional or perhaps global scale change in the sources of volcanic exhalations and volcanic activity caused by an increase in the importance of melting and assimilation of older continental crustal components over the cenozoic

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

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

lead nd and sr isotope records of pelagic dust source indication versus the effects of dust extraction procedures and authigenic mineral growth abstract eolian silicate dust of the 328 cm long piston core kodos 02 01 02 from the northeast equatorial pacific was analyzed for chemical compositions and nd sr and pb isotopic ratios to evaluate their use as hemispheric dust source discriminator and to examine the potential influence of authigenic smectite on these source signals neodymium and sr isotope ratios of the core determine a change from southern to northern hemisphere dust deposition at about 7 6 ma samples deposited between 15 5 and 7 6 ma resemble southeast equatorial pacific surface and down core dust values while younger samples correspond to signatures typical for dust derived from central asia the 15 5 to 7 6 ma lower interval of the core is smecite rich however previously proposed chemical fingerprints for authigenic smectite such as positive eu anomalies or high fe al ratios are not observed in the kodos samples the up to 40 smectite in the kodos core dust are thus interpreted to represent largely detrital smectite and no evidence is found for authigenic modification of nd sr isotopic or element ratio source signals of the dust records lead isotope results of the core lack prominent down core variation with changing source regimes as reported above a compilation of pacific pb isotope dust records reveals that pb isotope ratios vary as a function of silicate dust extraction procedures the step of removing biogenic silica thereby appears critical use of naoh appears most effective while minimally attacking eolian silicate material it is concluded that of the pb isotopic dust records published so far only a few are useful for dust source identification however once the silicate dust extraction procedure is further optimized for retrieving the pristine silicate dust pb isotopic composition specific source signatures should become well resolvable

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

high resolution paleoclimatic information from chinese eolian sediments based on grayscale intensity profiles abstract grayscale intensity profiles from photographic images offer a rapid means of obtaining paleoclimate proxy records from chinese loess dune sand and paleosols although the data can be obtained using conventional 35 mm film images a digital camera and laptop computer will produce a high resolution grayscale profile at a field site within minutes comparison of grayscale profiles with profiles of magnetic susceptibility measured down loess and dune sand sections at sites on the loess plateau and tibetan plateau in a range of altitudes and climatic regimes shows that the two parameters are highly correlated therefore grayscale intensity is a convenient alternative to magnetic susceptibility for generating paleoclimatic data in the loess and desert margin regions of china the resolution of both grayscale and susceptibility profiles ultimately is limited by bioturbation which is most pronounced in paleosols

true triaxial strength and deformability of the siltstone overlying the chelungpu fault chi chi earthquake taiwan 1 we conducted true triaxial compression tests to examine the effect of the intermediate principal stress 2 on brittle failure and deformability of the siltstone overlying the chelungpu fault taiwan for constant minimum stress 3 a pattern of increased strength 1 as a function of 2 unpredicted by common strength criteria was observed strength data are well fitted by a mogi modified nadai criterion relating the octahedral shear stress at failure to the mean normal stress on the induced shear fracture or fault the induced fault strikes subparallel to 2 and dips steeply in the direction of 3 significantly fault dip angle steadily increases as 2 rises for unchanged 3 sem inspection of tested specimens reveals only sporadic localized intergranular microcracks associated with the creation of the fault the modulus of elasticity and the onset of dilatancy exhibit a similar behavior to that of 1 as they increase with 2 when subjected to a constant 3

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

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

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

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

geochemistry of eolian dust in pacific pelagic sediments implications for paleoclimatic interpretations geochemical data rees th sc were determined for the operationally defined eolian dust oded fraction 63 m of late quaternary sediment samples n 57 from the north and equatorial pacific ocean paleoclimate studies commonly have assumed that this sediment fraction represents eolian materials from continental source regions this study shows on the basis of geochemical data published mineralogical data and mixing models that the oded fraction actually is a mixture of materials from two endmember sources the continental crust eolian transported weathering products and the oceanic crust primarily volcanogenic material mixing model results show that the average ash content is significant in the oded fraction equatorial pacific 43 north pacific 24 we have used this information to reconsider and refine the results of previous paleoclimate studies in the northwest pacific the flux of the eolian fraction is greater during glacial stages and shows a latitudinal maximum between 35 n and 42 n eolian fluxes are greatest during interglacial periods in the equatorial pacific these results are consistent with previous interpretations in contrast to previous assumptions eolian mass accumulation rates may not be a valid indicator of paleo aridity because they are correlated with grain size furthermore the relative abundance of the two endmembers is correlated with the average grain size of the dust fraction the continental crust component is associated with larger grains this compositional effect should be considered in future studies which commonly utilize grain size as a proxy indicator of paleo wind intensity

the effect of the intermediate principal stress on fault formation and fault angle in siltstone abstract we conducted true triaxial compression tests on specimens prepared from two siltstone core sections one above and one below the chelungpu fault taiwan for different constant 2 and 3 magnitudes the maximum principal stress 1 was raised until a post failure stage was reached and a through going fault had developed despite differences between the properties of the two cores in all tests peak 1 increased as 2 was set at higher levels than 3 in contrast to mohr coulomb condition predictions the fault normal vector was aligned with the 3 direction and made an angle with 1 direction the angle which corresponds to fault dip in case of normal faulting increased monotonically with 2 for fixed 3 a variation that is also inconsistent with mohr coulomb theory the results of shear band localization theory are used with fault angles observed for axisymmetric compression and deviatoric pure shear to infer properties of the inelastic constitutive behavior these properties are significantly different for the two cores using them to predict for other deviatoric stress states yields good agreement with the observations for core ii and acceptable agreement for core i the results are used to predict the angle variation for constant mean normal stress decreases as the deviatoric stress state varies from axisymmetric extension to axisymmetric compression and at fixed deviatoric stress state decreases monotonically with increasing mean normal stress

dependence of near surface magnetic susceptibility on dust accumulation rate and precipitation on the chinese loess plateau magnetic susceptibility ms of surface sediment varies systematically across the loess plateau in central china decreasing exponentially from 200 10 8 m3 kg at the northern margin of the qinling shan to 30 10 8 m3 kg near the southern margin of the mu us desert ms correlates highly with loess median grain size r2 0 79 which decreases south southeastward across the plateau it also correlates with mean annual temperature mat and mean annual precipitation map r2 0 58 and 0 60 respectively and with their product mat map r2 0 83 which is considered a measure of potential pedogenic activity because regional isopleths depicting grain size and the primary meteorological parameters are nearly parallel it is difficult to determine their relative influence on ms a simple ms model based on the observed spatial variation in loess thickness permits quantitative assessment of the effect of the dust accumulation rate on the ms signal of surface sediment and isolates the likely role of climate in the production of magnetic minerals the model suggests that 84 of the loess ms variance is dictated by the diluting effect of dust and 10 11 is associated with meteorological factors primarily precipitation the observed and modeled relationships support hypotheses that attribute variations in ms in the loess paleosol succession to varying rates of dust deposition and in situ production of magnetic minerals in the accretionary soils both of which are controlled by monsoon climate

variability of monsoon climate in east asia at the end of the last glaciation abstract high resolution paleomonsoon proxy records from peat and eolian sand paleosol sequences at the desert loess transition zone in china denote a rapid oscillation from cold dry conditions 11 200 10 60014c yr b p to cool humid conditions 10 600 10 20014c yr b p followed by a return to cold dry climate 10 200 10 00014c yr b p variations in precipitation proxies suggest that significant climatic variability occurred in monsoonal eastern asia during the younger dryas interval late glacial climate in the chinese desert loess belt that lies downwind from europe was strongly influenced by cold air from high latitudes and from the north atlantic via the westerlies the inferred precipitation variations were likely caused by variations in the strength of the siberian high which influenced the pressure gradient between land and ocean and therefore influenced the position of the east asian monsoon front

piston core record of late paleogene 31 ma to recent seafloor hydrothermal activity in the southwest pacific basin a large diameter piston core containing 8 35 m of metalliferous sediment has been recovered from a small abyssal valley in the remote southwest pacific basin 31 42 194 s 143 30 331 w 5082 m water depth providing unique insight into hydrothermal activity and eolian sedimentation there since the early oligocene a combination of fish teeth sr isotope stratigraphy and inaa geochemical data reveals an exponentially decreasing hydrothermal flux 31 ma to the present although hydrothermal sedimentation related to seafloor spreading explains this trend a complex history of late eocene early oligocene ridge jumps propagating rifts and plate tectonic reorganization of south pacific seafloor could have also played a role a possible hiatus in deposition as recorded by changes in core composition just below 2 m depth is beyond the resolution of the fish teeth sr isotope dating method employed here however the timing of this interval may be coincident with extinction of the pacific farallon ridge at 20 ma a low flux eolian component accumulating at this site shows an increase relative to the hydrothermal component above 2 m depth consistent with dust generating continental sources far to the west australia new zealand this is the first long term paleoceanographic record obtained from within the south pacific bare zone rea et al 2006 an anomalous region where pacific seafloor has largely escaped sediment accumulation since the late cretaceous

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

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

mineralogical and geochemical compositions of the eolian dust from the northeast equatorial pacific and their implications on paleolocation of the intertropical convergence zone 1 eolian components of a 328 cm long piston core collected from the northeast equatorial pacific at 16 12 n and 125 59 w were investigated for mineral and geochemical compositions in order to constrain the sources of dust and determine the latitudinal position of the intertropical convergence zone itcz recorded in the core the eolian components below 250 cm are characterized by smectite and phillipsite rich mineral composition depleted rare earth elements rees and high eu sm ratios indicative of volcanic rich composition these characteristics are found in equatorial and south pacific surface sediments of which eolian particles are supplied from central and south america in contrast eolian components above 250 cm are characterized by quartz and illite rich mineralogy and more shale like ree and trace element compositions which are common in surface sediments of the central pacific north of the itcz where eolian particles are sourced from the asia and north america the observed changes are attributed to the shifting of its eolian sources from the central and south america to the china and north america across the hemispheric dust barrier of the itcz this result suggests that smectite illite transition a phenomenon that smectite amount increases over illite at a depth can be used as a tracking tool for the paleolocation of the itcz in the northeast and central pacific backtrack path construction of pacific plate indicates paleolocation of the itcz north of 12 n 2 prior to late miocene

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

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

high resolution multi proxy climate records from chinese loess evidence for rapid climatic changes over the last 75 kyr the loess paleosol sequence in loess layer l1 malan loess is investigated in three regions of the western chinese loess plateau nine pedogenic layers are found in l1 and three proxy climate indices magnetic susceptibility ms grain size gs and caco3 content are measured at intervals of 0 2 kyr in order to recover records of monsoon climate variations time series of ms gs and caco3 content document the high resolution history of summer and winter monsoon climate variations over the last 75 kyr the records show a high degree of similarity to the warm interstadials recorded in ice cores from greenland and the antarctic and with heinrich events in the north atlantic during the last glacial cycle bond cycles are also recorded by the chinese loess records overall our results indicate that numerous rapid changes in climate occurred in china during the last glacial cycle but that the range of climate variations was smaller than recorded in greenland

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

87sr 86sr variation in north pacific sediments a record of the milankovitch cycle in the past 3 million years abstract temporal variations of sr isotopic compositions in the detrital component of north pacific sediments have been precisely examined the sr isotopic composition is controlled by the flux of eolian material from the asian continent with a high 87 sr 86 sr ratio 0 724 0 726 relative to volcanic material with a low ratio 0 703 0 705 from the izu ogasawara mariana arc and oceanic islands such as the hawaiian islands assuming that the volcanic flux is constant the temporal variation in sr isotopic ratio reflects the amount of eolian input from the continent the major characteristics of the temporal variations and the interpretation of them are summarized as follows 1 the 87 sr 86 sr records show cyclic fluctuations of 400 ky and 100 ky periodicities which are associated with the eccentricity of the earth s orbit milankovitch cycle 2 between 3 and 0 8 ma the 87 sr 86 sr ratio in the north central pacific sediment increases gradually this reflects an increased eolian input from the arid region in east asia the increase must be related to aridification of the asian continent 3 the decreased 87 sr 86 sr ratio during the past 0 8 m y implies a decreased eolian input the age of 0 8 ma may relate to the climatic event known as the middle pleistocene shift all of these phenomena reflect a fluctuation of the eolian flux corresponding to the paleoclimatic cycle of aridity in the asian continent the sr isotopic composition of pelagic sediment in the north pacific is sensitive to changes in the eolian input reflecting to the aridity of the asian continent

ichthyolith strontium isotope stratigraphy of a neogene red clay sequence calibrating eolian dust accumulation rates in the central north pacific abstract cenozoic pelagic red clays of predominantly eolian and hydrogenous origin blanket much of the central north pacific ocean basin the eolian component is a key indicator of past paleoclimatic conditions thus cenozoic atmospheric circulation can potentially be reconstructed through provenance studies of pacific red clays provided there are precise age controls methods commonly employed in the past to date red clay cores have included cobalt accumulation rates ichthyolith biostratigraphy magnetostratigraphy and ichthyolith strontium isotope stratigraphy the first two dating methods yield ages with large uncertainties while magnetostratigraphy is only relevant to cores with accumulation rates in excess of 1 mm kyr ichthyolith strontium isotope stratigraphy has shown promise as a chronological tool in marine studies but has been only sparingly employed in the dating of marine red clay sequences in this study we present a complete age depth profile for a large diameter piston core from the central north pacific ocean ew9709 pc 01 32 5 n 141 2 w consisting of 11 m of primarily wind deposited dust to generate this age depth profile strontium isotopic compositions were determined on fish teeth ichthyoliths previously cleaned of contaminants using a newly modified reductive cleaning procedure ages were determined by reference to the recently refined sr isotope curve for neogene seawater comparison with nearby giant piston core ll44 gpc3 reinforces the accuracy of our methods the data for ew9709 pc 01 indicate a fairly constant sediment accumulation rate of 0 45 mm kyr over most of the 24 myr time period represented by this core

hydrothermal sedimentation adjacent to the propagating valu fa ridge lau basin sw pacific abstract the partition geochemistry and hydrothermal metal accumulation rates ar during the late quaternary 3 km from hydrothermally active areas still shows an enrichment of mn ag ba and zn when compared to regional 500 m depth lau basin sea water the elements ni zn cu co and mo are associated with mn oxides in the sediment and are thought to have been scavenged by hydrothermal oxides during the transport of hydrothermal oxides away from the spreading center only a low proportion of fe is bound to the hydrothermal oxide phase in the sediments and this element is mainly associated with silicate phases principal components analysis pca of geochemical data in the detrital free caco 3 free fraction of the sediments supports a geochemical hydrothermal oxide association between mn ni mo cu zn pb p be ba and la with fe associated with the silicate weathered detrital fraction iron manganese ratios in the oxide phase range between 1 2 and 2 8 these values are below those found in sediments at mid ocean ridges peaks in the downcore distribution in mn appear to be contemporaneous in the cores studied and are probably the result of hydrothermal discharges on the vfr hemipelagic sedimentation rates throughout the area average 2 3 cm ka 1 hydrothermal mn ar range between 3 and 82 mg cm 2 ka 1 during the 0 30 ka b p period and between 5 and 65 mg cm 2 ka 1 during the 30 120 ka b p period maximum mn ar adjacent to the vfr are comparable to the highest values previously reported for recent sediments proximal to the east pacific rise epr during the entire period 0 120 ka b p mn ar are highest in core so48 101 located about 90 km behind the propagating tip of the vfr recent hydrothermal input has also occurred about 33 km behind the propagator this is in accord with the suggested location of fully evolved steady state magma chambers occurring some distance tens of kilometers behind propagating rift tips

late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean rea d k and janecek t r 1981 late cretaceous history of eolian deposition in the mid pacific mountains central north pacific ocean palaeogeogr palaeoclimatol palaeoecol 36 55 67 eolian dust preserved in deep sea sediment can provide a direct historical record of global atmospheric circulation data from a reasonably complete upper cretaceous section of pelagic sediments recovered at dsdp site 463 in the central north pacific provides a good record of eolian activity during the time period between about 112 hnd 66 m y ago we have isolated the eolian component from these sediments determined its mass accumulation rate and combined these data with the mineralogy of the inorganic fraction determined by others to construct a record of eolian deposition volcanic input is significant during aptian albian and maastrichtian times otherwise continentally derived minerals dominate mass accumulation rates of the continental eolian component range from over 500 mg cm 103yr during the late albian to a low of 5 mg cm2 10 yr during coniacian time for comparison the upper miocene to pleistocene rate averages about 20 mg cm2 103yr the temporal pattern of late cretaceous eolian accumulation of site 463 generally matches known changes in sea level suggesting that source availability is the dominant control of eolian sedimentation during that time

mineralogy of aeolian dust reaching the north pacific ocean 1 sampling and analysis the mineral composition of the 2 m clay and 2 to 20 m silt size fractions of aerosol particles collected near the margins of the north pacific ocean was determined by x ray diffraction analysis although the same mineral phases are present in the two size fractions there are significant differences in the quartz plagioclase and kaolinite concentrations north pacific aerosols are primarily composed of illite in both size fractions in addition to kaolinite in the 2 m size class and quartz and plagioclase in the 2 to 20 m size class quartz and plagioclase are present in significantly higher amounts in the 2 to 20 m size fraction while kaolinite is greater in the 2 size class western north pacific aerosol particles contain significantly higher 2 m quartz than samples collected in the east and eastern north pacific aerosols have significantly higher concentrations of 2 m smectite than those from the west

mineral particles from asia found in volcanic loess on the island of hawaii abstract x ray diffraction studies of bulk samples energy dispersive analyses of single mineral grains and x ray mapping of particles in grain mounts show that quartz grains are present in late quaternary tephric loess deposits of the pahala formation found at pu u o mahana near ka lae south point on the island of hawaii these particles are as large as 40 60 m and make up as much as 1 3 of the deposit quartz is virtually unknown in the basalts of the hawaiian islands so these particles were evidently transported more than 10 000 km from asia by late quaternary wind storms

temporal changes in the lead isotopic composition of red clays comparison with ferromanganese crust records abstract a record of changes in pb and sr isotopic composition of two cores dsdp 86 576a and ll44 gpc3 from the red clay region of the central north pacific has been determined for the past 60 65 million years the isotope records of the eolian silicate fraction of the red clays reflect the change in source area as the core sites migrated under different wind systems the sr isotope compositions of eolian silicate material are consistent with asian loess and north american arc volcanism that has been recognized from mineralogical studies the silicate bound eolian pb isotopic compositions similarly reflect asian loess and arc volcanism the isotope records of three ferromanganese crusts from similar locations in the central pacific are similar to the eolian component of red clays but offset to less radiogenic values this may be due to two mechanisms 1 pb that can be removed from eolian material by seawater is much less radiogenic or less likely 2 hydrothermal pb can be transported further away from venting sites through particle exchange with seawater despite hydrothermal venting acting as a net sink of oceanic pb the temporal changes in pb isotopes in the ferromanganese crusts bulk red clays and eolian silicates are similar although offset from each other suggesting that eolian deposition is an important source of pb to seawater and to ferromanganese crusts this contrasts with the atlantic and southern ocean where more intense deep water flow leads to isotopic gradients in femn crusts that do not reflect surface water conditions immediately above the crust a mechanism is proposed which accounts for pacific deepwater pb being isotopically influenced by eolian deposition

evolution of nd and pb isotopes in central pacific seawater from ferromanganese crusts abstract hydrogenetic ferromanganese crusts incorporate elements from ambient seawater during their growth on seamounts by analysing nd pb and be isotope profiles within crusts it is possible to reconstruct seawater tracer histories depth profiles of 10be 9be ratios in three pacific ferromanganese crusts have been used to obtain growth rates which are between 1 4 and 3 8 mm ma nd and pb isotopes provide intact records of isotopic variations in pacific seawater over the last 20 ma or more there were only small changes in pb isotope composition in the last 20 ma this indicates a constant pb composition for the erosional sources and suggests further that erosional nd inputs may have been uniform too end values vary considerably with time and most probably reflect changes in ocean circulation the end values of the crusts not only vary as a function of age but also as a function of water depth from 25 to 0 ma crust va13 2 from 4 8 km water depth has a similar pattern of end variation to the two shallower crusts from 1 8 and 2 3 km but about 1 0 to 1 5 units more negative this suggests that end stratification in pacific seawater as demonstrated for the present day has been maintained for at least 20 ma each crust shows a decrease in end from 3 5 ma to the present which is interpreted in terms of an increase in the nadw component present in the pacific from 10 to 3 5 ma ago the crusts show an increase in end this suggests a decreasing role for a deep water source with end less than circum pacific sources in this regard the panamanian gateway restriction from 10 ma with final closure at 3 5 ma may have played an important role in reducing access of atlantic derived nd to the pacific

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

millennial scale climatic oscillations during the last interglaciation in central china repeated southward excursions of north atlantic polar water during the last interglaciation 18 o stage 5 130 74 ka are recorded by planktonic foraminifera and ice rafted detritus in north atlantic sediment cores and greenland ice sheet cores display quasi synchronous fluctuations comparable high frequency variations in the east asian winter monsoon climate are discernible in three loess paleosol profiles in central china that span the last interglaciation peak values of the 40 m quartz fraction and bulk sediment samples from the s1 last interglacial accretionary paleosol complex reflect major dust flux events when winter monsoon winds strengthened frequent oscillations of the dust flux and nine significant dust events are recorded six events falling between ca 110 and 70 ka are correlated with cold peaks c19 24 identified in north atlantic cores two comparable dust peaks occur within paleosol s1ss3 substage 5e the older of these dating to ca 121 ka may correlate with a brief cold event recently recognized in high resolution marine and terrestrial climate proxy records

eolian inputs of lead to the north pacific we evaluate the importance of natural eolian pb to the dissolved oceanic pb budget by measuring the isotopic composition of pb in 35 holocene and late quaternary sediment samples from the north pacific and in 10 samples of chinese loess when the pacific is divided into sediments provinces based on published end and sedimentological data pb from the central north pacific tends to be the most radiogenic and homogeneous due to the dominance of eolian chinese loess lead from the marginal north pacific and the sparsely sampled regions south of 5 n are less radiogenic and more variable owing to hemipelagic inputs from various volcanic arcs and older continental crust located around the pacific rim 208pb 204pb ratios provide the most distinctive provenance information due to the relatively high ratios in chinese loess the chinese loess samples come from 3 localities and span up to 2 myr of time acetic acid leachate bulk loess and loess silicate fractions were analyzed separately leachate pb is considerably less radiogenic than silicate pb the isotopic composition of the silicate component closely matches the sediment data from the central north pacific confirming the dominance of eolian loess in this region we divided up a suite of published hydrogenous pb isotope data from the pacific ocean according to their locations within the three independently defined sediment provinces these data define three distinct fields differentiated primarily by their 206pb 204pb ratios which increase going from the central to southern to marginal provinces this relationship with sediment province strongly suggests that natural eolian and probably hemipelagic inputs significantly impact the seawater pb budget direct support for the dominance of eolian chinese loess in the central north pacific dissolved pb budget comes from the close match between loess leachate pb and the central province hydrogenous pb data eolian inputs are likely to dominate local seawater pb budgets only where eolian pb fluxes are high relative to hemipelagic pb fluxes and where the flux of pb carried by deep water advection is low

climate forcing of the pb isotope record of terrigenous input into the equatorial atlantic abstract pb isotopic compositions of bulk sediment cores from the tropical atlantic are used here to infer variations in the provenance of terrigenous input to the tropical atlantic during pleistocene climate cycles the 200 ka high precision 2 100 ppm pb isotope records of the ceara rise western atlantic and sierra leone rise eastern atlantic cores show a clear glacial interglacial cyclicity reflected by alternating unradiogenic pb and radiogenic pb in both cores the glacial interglacial pb isotopic contrast is also observed in pb pb space and can be explained in terms of binary mixing variations along the mixing lines reflecting changes in the relative proportions of the glacial unradiogenic and interglacial radiogenic pb source s the pleistocene pb isotopic variability of the terrigenous input to the ceara rise can be linked to changes in the weathering styles in the amazon basin and as a result in the amazon river discharge these changes are reflected by a greater contribution from the highlands andes pb source during glacial times and strengthening of the lowlands shield pb source during interglacials on the other hand pb isotopic variations in the sierra leone rise core indicate increased pb inputs from the saharan dust plume during glacial times in agreement with the wind patterns over africa furthermore this result bears some implications on the cause of the enhanced glacial terrigenous fluxes to the tropical atlantic which we infer to be due to increase in winter wind transport rather than glacial hyperaridity the cyclicity of the ceara rise and sierra leone rise pb isotopic records together with changes in the proportions of mixing sources throughout the last 200 ka monitor changes in the hydrological cycle over south america and the wind systems over africa respectively both of which are linked to the seasonal latitudinal migration of the intertropical convergence zone the correlation found between pb isotope cycles and other paleoclimate proxies suggests that pb isotopes may be responding to variations in earth s orbital parameters

increasing nd isotopic ratio of asian dust indicates progressive uplift of the north tibetan plateau since the middle miocene the time and rate of tibetan uplift is critical in understanding both the geodynamics of plateau growth and the influence of mountain building on climate change models predict that the uplift of the north tibetan plateau ntp occurred later than uplift of the south and central tibetan plateau uplift of the ntp is believed to have initiated the aridity in the interior of asia and to have critically affected the evolution of asian monsoon and ultimately global climate the history of ntp uplift has remained uncertain however scenarios range from early miocene to the past million years this work provides new evidence by relating the nd isotopic evolution of asian dust to ntp uplift the sources of the asian dust are located in the arid lands between the ntp and the central asia orogen mass balance calculations indicate that the decreasing e nd values from 8 2 to 10 4 for pacific dust since 15 ma reflects increasing relative contribution of ntp materials 40 to 70 to the dust source as paleoelevation in the central asia orogen has largely remained constant the increasing relative ntp detritus contribution is interpreted to reflect the progressive surface uplift of the ntp at a rate of at least 0 12 mm yr 1 since 15 ma

resolving eolian volcanogenic and authigenic components in pelagic sediment from the pacific ocean abstract we measured major and trace element concentrations in the operationally defined chemically extracted residual aluminosilicate component of sediment from ocean drilling program sites 1215 and 1256 in the central and eastern equatorial pacific ocean and found that this residual component contains volcanogenic and authigenic aluminosilicates in addition to inferred eolian material while the residual component younger than 20 ma from the central pacific odp site 1215 is similar compositionally to upper continental crust and suggests an increase in the delivery of asian dust material since 20 ma the residual in sediment older than 20 ma indicates significant amounts of volcanogenic and authigenic materials volcanogenic debris comprises as much as 40 of the residual between 23 40 ma which coincides with the mid tertiary ignimbrite flare up that occurred in much of western north america the residual component extracted from the 50 ma biogenic sediment reflects authigenic signatures seawater like negative cerium anomalies and elevated fe si ratios the previously interpreted increase in an andesitic detrital source in north pacific locations may instead be authigenic material presenting significant challenges for many paleoclimate proxies additionally in the eastern pacific odp site 1256 the residual component contains 70 of volcanogenic material most likely originating from central america and also includes refractory barite the ability to separately identify eolian volcanogenic and authigenic materials in the aluminosilicate component of pelagic sediment allows resolution respectively of the climatic geologic and chemical processes contributing to the paleoceanographic archive in this critical oceanic region

comparison of isotope stages 1 61 with the baoji type pedostratigraphic section of north central china until now comparisons between terrestrial and marine proxy climatic records have been achieved successfully only for the last 1 2 ma or back to oxygen isotope stage 36 the baoji loess paleosol section of north central china possesses 37 field identifiable paleosols and 37 loess units representing a time span of about 2 5 ma the baoji section is judged by the authors to be the most complete pedostratigraphic sequence in north central china this section coupled with recent success in correlating isotope records back to stage 63 or approximately 1 88 ma has enabled a more detailed comparison over a longer time span using magnetic reversals as markers the records are shown to have nearly equal numbers of identifiable warm and cold periods during the last 1 8 ma in addition although there are exceptions data sets reveal similar patterns during the same time intervals indicating climatic events on a global scale

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

movement of the intertropical convergence zone during the mid pleistocene transition and the response of atmospheric and surface ocean circulations in the central equatorial pacific this paper investigates the causes of a brief but prominent cooling episode 1 1 0 8 ma that occurred in the equatorial upwelling region of the atlantic and pacific during the mid pleistocene transition mpt using temporal changes in dust provenance regional hydrology and surface productivity recorded in a deep sea sediment core from the central equatorial pacific the 87sr 86sr and nd values of the inorganic silicate fraction indicate deposition of dust from australia and central south america before 0 8 ma but a gradual increase in asian dust deposition after 0 8 ma the change in dust provenance was accompanied by an increased dust flux and a decrease in surface productivity and salinity these changes can be explained by the southward movement of the intertropical convergence zone itcz and north equatorial counter current necc and the direct influence of these features on the site after 0 8 ma our results together with previously published atlantic data suggest the northward position of the itcz between 1 1 and 0 9 ma and the southward position thereafter the meridional movement of the itcz is in phase with the cooling and warming trend in upwelling regions in the equatorial pacific and atlantic which suggests strengthening of southeast trades relative to its northern counterpart between 1 1 and 0 9 ma as a plausible cause of this brief cooling event the southward movement of the itcz from 0 9 to 0 8 ma indicates more significant cooling in the northern hemisphere nh than in the southern hemisphere which is supportive of the interpretation that the nh ice sheet expanded significantly and stabilized after 0 9 ma

age calibration of piston core ew9709 07 equatorial central pacific using fish teeth sr isotope stratigraphy abstract a high resolution age depth profile is presented for a 16 m deep sea piston core ew9709 pc07 using three different methods magnetostratigraphy fish teeth strontium isotope stratigraphy and radiolarian biostratigraphy fish teeth are abundant throughout the core allowing for precise age determinations by sr isotope stratigraphy magnetostratigraphic ages though not available for this core were determined by correlation with the drill core record from adjacent odp site 1218 biostratigraphic ages were independently assigned to the lower 12 m of the core which contains abundant radiolaria all three methods define an early miocene age 20 ma for the core base a linear sedimentation rate of 2 0 mm ky was calculated for the lower 10 m of the core which is dominated by siliceous clays and calcareous ooze all three methods yield concordant ages over this interval 20 to 15 ma tectonic migration of the pc 07 site away from the equatorial high productivity zone produced a significant decrease in sedimentation rates after 15 ma diminishing to just 0 30 mm ky in the uppermost 3 m of the core correlated magnetic reversal and fish teeth ages are concordant within this upper red clay interval 10 to 0 0 ma which is dominated by eolian dust accumulation however within the 15 to 10 ma interval fish teeth ages appear to show more scatter departing from the magnetic ages by as much as 2 3 million years age discrepancies in this dominantly siliceous clay interval are most likely due to uncertainties in magnetostratigraphic age correlations we conclude from this that the eolian dust component in red clay cores can be reliably dated by the fish teeth strontium technique for otherwise undatable red clay cores from the vast northern pacific pelagic clay province this may prove to be the only available method for developing a regional cenozoic chrono stratigraphy

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

multiproxy evidence of middle and late pleistocene environmental changes in the loess paleosol sequence of bůhzdař czech republic abstract loess paleosol sequences preserve information that can be used to reconstruct paleoenvironments a dense network of reliably analyzed sequences from different geographic locations is crucial to address ecological and climatic trends which occurred during the pleistocene this paper focuses on a loess paleosol sequence in b hzda situated 9 km nw of prague czech republic geochemical approaches total organic carbon xrf elemental analyses xrd mineralogy 13c and 18o stable isotopes are combined with grain size distributions and optically stimulated luminescence osl to assess the climatic conditions at the time of formation of the strata the oldest loess at this location was formed circa 200 ka ago mis 7 making it the oldest loess in central bohemia for now the b hzda loess paleosol sequence was highly affected by several erosion events eemian paleosols mis 5e being completely missing the partly relocated paleosols situated at the lower part of the b hzda sequence represent a period of increased humidity during late mis 7 and mis 6 despite the fact that the b hzda profile is not particularly thick 5 m significant changes in paleoclimate reconstructions have been detected

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