paleoclimatic significance of magnetic properties on the red clay underlying the loess and paleosols in china abstract the red clay unit of northern china is a widespread miocene pliocene 7 2 2 5 ma aeolian deposit that underlies much of the quaternary loess paleosol sequence in the central loess plateau it comprises a sequence of highly developed soils and interbedded layers of less weathered loess like material here referred to as reddish loess in common with the loess paleosol alternations of the overlying quaternary deposits the soil reddish loess alternations are interpreted to represent climatic fluctuations in this case between warm humid and relatively dry cool conditions however while magnetic susceptibility variations in the quaternary deposits provide a good proxy for pedogenic intensity in the red clay the relationship is less clear and magnetic susceptibility data are in conflict with other measures of pedogenesis in an attempt to resolve this issue we have investigated a red clay section and overlying loess paleosol sequence at xifeng and have supplemented these data with samples from the red clay at lingtai our study indicates that the red clay and loess paleosol sequence have a common magnetic mineralogy comprising magnetite maghemite and hematite and possibly goethite and that both sequences show a good correlation between magnetic susceptibility and the magnitude of the superparamagnetic sp component this implies that susceptibility enhancement in the red clay is strongly related to the magnitude of the sp content a component that is widely recognised as having a pedogenic origin in quaternary deposits further support for a correlation between pedogenesis and magnetic susceptibility in the red clay is provided by a good correlation between magnetic susceptibility and the rb sr ratio an independent weathering index however differences in the magnetic mineralogy of the two units are also evident the minimum magnetic susceptibility of the red clay is less than half the value of the overlying quaternary deposits at locations such as xifeng and lingtai while the maximum sp content is relatively larger than for the quaternary deposits while we cannot discount the possibility that the former difference is a reflection of different parent materials for the two units climate may also be a contributory factor in explaining these differences precipitation is a major control on magnetic enhancement in paleosols maher and thompson 1995 quat res 44 383 391 liu et al 1995 palaeogeogr palaeoclimatol palaeoecol 113 243 248 but soil anoxia and iron oxide dissolution occur if moisture exceeds some critical level soil moisture is therefore a critical factor in determining whether the correlation between pedogenesis and magnetic susceptibility in loess deposits is positive central loess plateau china magnetic enhancement negative alaska siberia magnetic destruction or uncertain pakistan argentina new zealand cycles of enhancement and destruction while our results indicate a generally positive correlation between pedogenesis and magnetic susceptibility in the red clay they also imply that a more thorough paleoclimatic interpretation can only be achieved using complementary but independent techniques more work is required to deconvolve the climatic record of the red clay but the reward may be the extension of the record of paleomonsoon evolution back into the pliocene and late miocene

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

saharan wind regimes traced by the sr nd isotopic composition of subtropical atlantic sediments last glacial maximum vs today new nd sr isotopic data on the 30 m lithic particles of surface and last glacial maximum sediments recovered along the african margin between the equator and the gibraltar strait are presented in combination with grain size measurements this 30 m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions in the eolian fraction both sr and nd isotopic tracers reveal the same major northwestern origin mauritania mali southern algeria and morocco the archaean formations of the western saharan shield could be the source of the very unradiogenic ratios observed here the more southern regions senegal guinea act only as secondary sources a similar pattern is observed for the lgm lithic particles are mostly transported by both trade and saharan air layer sal winds along an approximate ne sw axis this main feature matches the southern plume characterizing the dust transport observed during winter no significant latitudinal shift of the belt winds is observed between the lgm and today at the lgm however dust fluxes were 2 4 times higher than today leading to a more archaean type imprint in the deposits we do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the lgm and the location of the major wind systems both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical africa during the last glacial period

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

the characterisation of saharan dusts and nile particulate matter in surface sediments from the levantine basin using sr isotopes abstract the provenance of sediments within the levantine basin of the eastern mediterranean was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on the detrital fraction of surface sediments and the two most important sources of detrital matter to the region saharan dust was characterised by an 87 sr 86 sr isotopic ratio in the range 0 7160 0 7192 there was a small systematic decrease in 87 sr 86 sr from west to east which is interpreted as due to a change in the balance of aeolian source material the nile particulate matter had a 87 sr 86 sr isotopic ratio in the range 0 7057 0 7071 87 sr 86 sr isotopic signatures together with sr concentration were used to calculate the contributions made by saharan dust and nile particulate matter to the surface sediments of the levantine basin it was shown that nile derived sediment was dispersed widely across the levantine basin enabling the area affected by retention of sediment behind the aswan dam to be determined

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

descending particles from the atmosphere to the deep ocean a time series study in the subtropical ne atlantic 1 the transport ways of organic matter into the deep ocean are still under debate lithogenic particles deliver nutrients to the surface boost biological production and impact on carbon export this study focuses on the transfer of lithogenic particles from the atmosphere to the deep ocean and its physical and biological interactions during their descent through the water column a clear coupling between atmospheric dust occurrence and deep sea lithogenic particle fluxes at 2000 m depth was observed in the subtropical ne atlantic 33 n 22 w this has never been demonstrated before for this site far away from the african continental slope and with no lateral influx of particles present the atmospheric signal transmission to the deep ocean lies in the range of one to two months the presented data demonstrate the dependence of lithogenic deep sea fluxes on the positioning in the ocean and on particle residence times in the water column

spatial variations in paleowind direction during the last glacial period in north china reconstructed from variations in the anisotropy of magnetic susceptibility of loess deposits abstract anisotropy of magnetic susceptibility ams of chinese loess is considered to be an effective tool for determining paleowind direction however the relationship between ams and the paleowind direction is still a matter of debate this study reports the results of ams measurements of chinese loess deposited during the last glacial period on slopes of varying slope angles and orientations the sites are located on the chinese loess plateau in west qinling and on the eastern margin of qilian mountain the results show that within the same region magnetic lineations are clustered along similar orientations despite differences in slope exposure and slope angle but that different regions exhibit different directions of magnetic lineation these results suggest that the alignment of the magnetic grains during deposition of the eolian deposits was determined by air circulation rather than by water flow on the surface of the slopes and therefore that the ams of chinese loess can be used to determine paleowind directions in addition our results indicate that the ams of chinese loess is determined mainly by the patterns of regional surface wind flow that occurred during dust accumulation rather than by the uniform pattern of large scale atmospheric circulation in addition since wind direction is influenced significantly by regional topography the ams of chinese loess may have the potential to detect significant changes in past regional topography

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

magnetic susceptibility of loess in china abstract the low field susceptibility of the loess deposits in the chinese loess plateau is due to both paramagnetic and ferromagnetic minerals paramagnetism can be seen in the less to unweathered loess horizons where superparamagnetic contributions which arise from ultrafine magnetite particles are not as strongly developed as in the heavily weathered palaeosols frequency dependent susceptibility and minimum unblocking temperatures of low temperature thermoremanent magnetization generally indicate finer grain sizes in the palaeosols as compared to the loess beds this grain size difference and the fact that susceptibilities of the same stratigraphic palaeosol layer vary by an order of magnitude between the western and central regions of the plateau are considered as strong evidence that the ultrafine magnetite is not of detrital aeolian origin but was formedin situ the pedogenetic processes are clearly related to palaeoclimatic changes therefore the various susceptibility properties may serve for a detailed reconstruction of the continental palaeoclimatic conditions for the last 2 5 ma since the palaeomagnetically dated beginning of loess sedimentation in china

hydrothermal sediments as a potential record of seawater nd isotope compositions the rainbow vent site 36 14 n mid atlantic ridge 1 geochemical compositions and sr and nd isotopes were measured in two cores collected 2 and 5 km from the rainbow hydrothermal vent site on the mid atlantic ridge overall the cores record enrichments in fe and other metals from hydrothermal fallout but sequential dissolution of the sediments allows discrimination between a leach phase easily leachable and a residue phase refractory the oxy anion and transition metal distribution combined with rare earth element ree patterns suggest that 1 the leach fraction is a mixture of biogenic carbonate and hydrothermal fe mn oxy hydroxide with no significant contribution from detrital material and 2 99 5 of the ree content of the leach fraction is of seawater origin in addition the leach fraction has an average 87sr 86sr ratio indistinguishable from modern seawater at 0 70916 although we lack the nd value of present day deep water at the rainbow vent site we believe that the ree budget of the leach fraction is predominantly of seawater origin we suggest therefore that the leach fraction provides a record of local seawater nd values nd isotope data from these cores span the period of 4 14 ka 14c ages and yield nd values for north east atlantic deep water neadw that are higher 9 3 to 11 1 than those observed in the nearby madeira abyssal plain from the same depth 12 4 0 9 this observation suggests that either the iceland scotland overflow water isow and lower deep water contributions to the formation of neadw are higher along the mid atlantic ridge than in the surrounding basins or that the relative proportion of isow was higher during this period than is observed today this study indicates that hydrothermal sediments have the potential to provide a higher resolution record of deep water nd values and hence deepwater circulation patterns in the oceans than is possible from other types of sediments

hydrothermal origin of devonian conical mounds kess kess of hamar lakhdad ridge anti atlas morocco various interpretations have been proposed for the origin of peculiar cone shaped finely crystalline devonian carbonate mounds of the hamar lakhdad ridge anti atlas morocco ranging from shallow water reefs to deep water mud mounds formed by biogenic and or hydrodynamic processes this study is the first integrated sedimentological and geochemical analysis of these structures the mounds are cone shaped steep sided circular to subelliptical in plan view and exhibit internal crude bedding parallel to the mound9s outer surface they occur in a cluster of 48 mounds on top of a volcanic massif stable isotope analyses of first stage isopachous nonluminescent cement have yielded marine values in contrast the finely crystalline carbonate that makes up the bulk of the mound and the internally sedimented mud between crusts of early marine cements have significantly lower 18 o values whereas values of 13 c are similar to those of the early marine cement strontium isotope ratios also clearly distinguish the nonluminescent early marine cements from the finely crystalline material the 87 sr 86 sr values for the former 0 707 934 0 709 392 are in or near the devonian marine range whereas the ratios for the latter 0 708 515 0 709 656 indicate a more radiogenic sr source on the basis of their lithology architecture isotope geochemistry and clustered occurrence on top of a volcanic pile we propose that the finely crystalline material that forms the mounds and the intermound beds was precipitated from hydrothermal fluids and that accretion of the material was driven by hydrothermal venting

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

anti atlas moroccan chain as the source of lithogenic derived micronutrient fluxes to the deep northeast atlantic ocean identifying the source of atmospheric dust is crucial to better understand the global marine biogeochemical cycle as phytoplankton growth relies on dissolved micronutrient elements available in the open ocean mineralogical geochemical and sr isotope analyses of a one year time series april 2003 april 2004 of deep ocean particle flux at the madeira abyssal plain in the subtropical northeast atlantic are presented the lithogenic fraction has a high occurrence of palygorskite and smectite and an absence of kaolinite together with sr isotopic compositions similar to the northeast atlantic aerosols this indicates the anti atlas moroccan chain of paleozoic age as the source region the lithogenic fraction supplies 4 times more fe during a dust event than during the spring summer aeolian input a continuous input of only 1 of the lithogenic iron made available over a year period could lead to an increase in primary productivity of 40 relative to today s value

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

clues from mis 11 to predict the future climate a modelling point of view simulations performed with the lln two dimensional northern hemisphere climate model have confirmed that climate is largely triggered by changes in insolation forcing although atmospheric co concentration also plays an important role in particular in the amplitude of the simulated variations marine isotope stage 11 mis 11 some 400 kyr ago and the future share a common feature related to climate forcing i e the insolation at these times displays small similar variations mis 11 can be considered an analogue for future natural climate changes different simulations were performed to identify the conditions constraining the length of the mis 11 simulated interglacial clearly its length strongly depends on the phase relationship between insolation and co2 variations it is only when insolation and co act together towards a cooling i e they both decrease together that the climate enters quickly into glaciation and that the interglacial may be short otherwise each forcing alone is not able to drive the system into glaciation and the climate remains in an interglacial state the same situation applies for the future however we already know that co2 and insolation do not play together indeed insolation has been decreasing since 11 kyr bp and co2 concentration remains above 260 ppmv with a general increasing trend over the last 8000 yr therefore we conclude that the long interglacial simulated for the future is a robust feature and the earth will not enter naturally into glaciation before 50 kyr ap c 2003 elsevier science b v all rights reserved

the ion chemistry of lakes and late holocene desiccation in the badain jaran desert inner mongolia china abstract in the markedly arid badain jaran desert one of the least studied areas in the world over a hundred permanent lakes exist among the dunes the geochemistry of water samples from nine lakes and from the groundwater in the desert and on its periphery was investigated ion chemistry of the water from these desert lakes changes considerably on a regional scale we argue that there is a positive correlation between the ages of these lakes and their totally dissolved solids tds varying between 1 2 and 398 2 g l tritium analysis of groundwater in wells gives an age generally older than four decades and younger than 100 years the lacustrine deposits freshwater fauna and shorelines indicate the existence of large water bodies with low salinities in the inter dune hollows of this desert during the early and middle holocene the precipitation in this desert during the early and middle holocene was estimated to be ca 200 mm year on average at least twice as high as at present on the basis of paleoecology tl and radiocarbon ages it was concluded that the huge enrichment of ions in the lakes and decrease of water availability originated from climatic desiccation during the last 4000 years the paleoclimate of the badain jaran desert reported here was remarkably consistent with the late quaternary climatic histories of the regions to the immediate north west east and south of the study area

origins of peri saharan dust deposits traced by their nd and sr isotopic composition abstract isotopic ratios of sr and nd can be used as very precise tracers in conjunction with mineralogical geochemical tracers and climatic models to identify the origins of dust deposit and to quantify their fluxes both today and throughout the last climati cycles this technique is useful for constraining aeolian transport and atmospheric circulation trajectories from desert sources and over the oceans the present work concerns dust deposits surrounding the saharan desert on the canary islands the african fraction of the dust deposits displays isotopic values which are typical of moroccan origin on the other hand tunisian loesses have been derived from the northern part of the sahara in this case tracers are sensitive enough to distinguish between center saharan shield origin and peri saharan secondary sources allowing us to distinguish between transport due to the trade winds vs the harmattan or mediterranean wind regimes

time dependence of magnetic susceptibility of soil chronosequences on the california coast abstract as the age of the soils in a chronosequence on the california coast increases the difference between the magnetic susceptibility of eluvial and illuvial horizons increases and the residual susceptibility after extraction with citrate bicarbonate dithionite cbd decreases enhanced susceptibility results from the conversion of nonferrimagnetic minerals to secondary ferrimagnetic forms most likely maghemite and the preferential accumulation of inherited and pedogenic magnetic minerals little enhancement occurs for pedons younger than 40 000 yr by 124 000 yr most of the magnetic susceptibility can be attributed to forms soluble in cbd magnetic susceptibility appears to vary systematically over time for three chronosequences from areas with mean annual precipitation ranging from 650 to 1500 mm yr 1 magnetic susceptibility enhancement may be a useful parameter for estimating soil age in certain climates

holocene saharan dust deposition on the cape verde islands sedimentological and nd sr isotopic evidence holocene aeolian silts deposited on the cape verde islands provide information about the origin of african palaeodusts that have fallen on the north eastern atlantic ocean over the last 10 000 years sedimentological composition indicates that most of these aeolian silts are unquestionably of continental origin their sr and nd isotopic composition identifies a saharan origin suggesting transport by harmattan winds we estimate that saharan dust comprises 75 95 of material in these holocene silts the rest coming from the weathering of local basaltic bedrock

pedogenic and lithogenic contributions to the magnetic susceptibility record of the chinese loess palaeosol sequence summary we have studied the magnetic properties of 69 loess and palaeosol samples from the loess plateau in china our methodology involves the combination of differential dissolution of secondary iron oxides and oxyhydroxides using citrate bicarbonatedithionite cbd with measurements of magnetic parameters because most of these parameters are additive we can use pre and post cbd values to determine the mineral magnetic properties of the cbd soluble material we can also calculatc the partitioning of iron atnong various phases approximately two thirds of the total iron in our samples exists as paramagnetic iron in silicate minerals antiferromagnetic material haematite constitutes almost all of the remainder however the magnetic susceptibility record of the loess palaeosol sequence arises primarily lrom a small amount of iron in ferrimagnetic phases this iron consists of a cbd resistant component which rcpresents multidomain grains inherited from the parent material of the loess and a cbd soluble component which represents grains near the superparamagnetic single domain boundary the first component appears in nearly uniform amounts throughout the loess column and is the dominant ferrimagnetic phase in the magnetically less enhanced loess accumulation of the second component in the palaeosols gives rise to the magnetic susceptibility enhancement of the loess column the magnetic properties of the cbd soluble component indicate that it formed as a result of in sitir pedogenesis which confirms our earlier conclusion that the palaeoclimate record of the loess palaeosol sequence at the sites that we have sampled is primarily a record of pedogenesis

rare earth elements in suspended particulate material of north atlantic surface waters on a transect between the northwest and northeast atlantic ocean 30 n 60 w to 60 n 2 w june july 1996 suspended particulate material spm in 24 near surface water samples 4 to 22 m3 with spm concentrations between 32 and 447 mg m 3 has been collected using a large volume centrifuge system the samples have been analyzed for y the rare earth elements rees and major inorganic and biogenic carrier phases such as al clay fe mn poc opal and caco3 the concentration pattern of particulate rees roughly follows the spm distribution average values pmol l 1 are for y 2 36 la 0 84 ce 0 82 pr 0 17 nd 0 67 sm 0 14 eu 0 030 gd 0 15 tb 0 024 dy 0 16 ho 0 036 er 0 12 tm 0 018 yb 0 13 and lu 0 022 extensive variability in negative ce anomalies have been observed along our transect with the strongest anomalies in areas of high poc abundances significant fractionation between lrees and hrees has been found for all major particulate phases these data are characterized by 1 strong relationships p 0 001 exist between concentrations of nonlithogenic excess hrees tb lu and poc values indicating that complexation with organic ligands promotes temporary hree enrichment on solid surfaces 2 the behavior of particulate fe and mn fractions is decoupled while fe and al clay phases exhibit preferential uptake of lrees la gd with crust like signatures particulate excess mn is strongly coupled to the poc phase r2 0 82 and to excess hrees we therefore suggest that the enrichment of rees in mn particles occurs via the formation of biogenic material probably mediated by bacteria and is not caused by adsorption onto mn oxihydroxides another result is that y in all studied relationships with the major inorganic and biogenic phases is very similar to ho implying their chemistries in surface ocean particulates are dominated by similar valency and ionic radii the y ho ratios average of 69 7 mol mol 1 have been very constant along our transect and lie in between the ratios for seawater 100 and continental crust 50

the long term paleomonsoon variation recorded by the loess paleosol sequence in central china abstract the loess paleosol sequence in central china during the last 2 5 ma is a good record of the asian monsoon variation which could be considered as the concrete realization of global paleoclimatic cycles the geological and biological evidence of the loess paleosol sequence indicates that the loess was mainly the dust deposits transported by the northerly wind of winter monsoons and also suffered to some extent from pedogenesis caused by weakened summer monsoons and that the paleosol accreted by the rather slow dust accumulation was closely related to strengthened summer monsoons an alternating occurrence of loess and paleosol in the luochuan section implies the variation history of warm humid climate with a summer monsoon dominance and cold dry climate with a winter monsoon dominance the magnetic susceptibility of loess and paleosol can be regarded as a proxy index of asian monsoon variation an analysis of the susceptibility curve and structure characters of luochuan section shows that the asian monsoon circulation was strengthened from early pleistocene to late pleistocene and the 500 ka bp point and 1200 ka bp point seem to be a threshold and a turning point respectively in terms of the long term paleomonsoon variation in asia

changes in the distribution of uvigerinidae species over the past 775 kyr implications for the paleoceanographic evolution of the japan sea abstract the distribution of benthic foraminifera of the uvigerinidae family which are abundant in middle to upper pleistocene samples from the yamoto basin in the japan sea have been analyzed quantitatively and used for paleoceanographic interpretations twenty three uvigerinidae species are reported from iodp site u1426 6 of which are present in at least three or more samples with 10 or more abundance and considered as dominant species the abundance and ecological preferences of dominant uvigerinidae species comprised of uvigerina mediterranea uvigerina yabei uvigerina sp 1 uvigerina peregrina suggest dysoxic conditions with high influx of organic matter between 775 and 475 ka in response to the enhanced flow of the tsushima warm current the end of mis 13 marked the onset of more extreme glacial interglacial climate cycles in the japan sea glacial interglacial alternations of uvigerina peregrina and trifarina angulosa from 475 ka to the holocene indicate major fluctuations in circulation and productivity within this semi enclosed basin both u peregrina and t angulosa respond to 100 kyr variability reflecting the paleoclimatic shift and global ice volume changes associated with the middle pleistocene transition

tracing dust input to the mid atlantic ridge between 14 45 n and 36 14 n geochemical and sr isotope study abstract a geochemical and sr isotope study was carried out on sediment cores collected from the logatchev hydrothermal vent site 14 45 n on the mid atlantic ridge with the aim of identifying aeolian inputs into the overlying water column the logatchev vent site lies beneath the ne trade winds which transport large amounts of detrital material across the north atlantic sequential dissolution of the sediments has been used to discriminate the detrital fraction from other types of sediment ree patterns for the acetic acid fraction at the logatchev site record contributions from biogenic carbonate seawater like ree pattern and oxy hydroxides which exhibit positive eu and negative ce anomalies typical of hydrothermal origin the logatchev site leach fractions have similar major element compositions to terrigenous al fe mn oxides whose ree patterns show strong positive ce and negative eu anomalies that are comparable to those of preformed fe mn oxides of continental origin based on major element and ree data and 87sr 86sr ratios 0 7197 0 7236 the residue fractions at the logatchev site contain a significant contribution from aeolian sources whose chemical composition is virtually identical to oligotrophic settling particles in the equatorial atlantic ocean in comparison residues from the rainbow hydrothermal site 36 14 n have geochemical composition controlled by hydrothermal anhydrite chavagnac v german c r milton j a palmer m r 2005 sources of ree in sediment cores from the rainbow vent site 36 14 n mar chem geol 216 329 352 they are characterised by 87sr 86sr ratios of 0 7087 0 7093 which are significantly less radiogenic than those of the saharan dust hence the data suggest 1 a significant contribution of aeolian material to the sediments at 14 45 n that is not present at 36 14 n 2 that this material is most likely of north african origin and 3 that this source of aeolian material has remained relatively constant over the last 13 kyr

summer monsoon variations over the last 1 2 ma from the weathering of loess soil sequences in china the loess soil sequence in northern china contains a near continuous record of quaternary paleoclimate magnetic susceptibility and grain size have so far been the only proxies available to address the long term changes of the east asian paleomonsoon extending back to more than one million years in this study the ratio of cbd citrate bicarbonate dithionite extractable free fe2o3 fed a measure of iron liberated by chemical weathering versus the total fe2o3 available fet was measured on samples at 10 cm intervals taken from two loess sections deposited over the last 1 2 ma variations of this index are highly consistent with other pedological indicators but in addition provide a quantitative measurement of the degree of pedogenesis in the loess plateau since chemical weathering in the region mainly depends upon summer precipitation and temperature weathering intensity primarily reflects changes in the east asian summer monsoon the new proxy has been used to document a series of summer monsoon changes of global significance which are not necessarily recorded by magnetic susceptibility

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

the mid pleistocene climate transition a deep sea carbon isotopic perspective five 13c records from the deep ocean extending back to 1 3 ma were examined in order to constrain changes in mean ocean carbon isotope composition and thermohaline circulation over the 41 to 100 ka climate transition these data show that significant perturbations in mean ocean carbon chemistry were associated with the mid pleistocene climate transition notable features of the last 1 3 myr are 1 a pronounced 0 3 decrease in mean ocean 13c between 0 9 and 1 0 myr followed by a return to pre 1 0 ma values by 400 ka b p which we propose was due to the onetime addition of isotopically depleted terrestrial carbon to the ocean possibly associated with an increase in global aridity and decrease in the size of the biosphere across the 41 to 100 ka transition 2 no change in the atlantic pacific a p 13c gradient over the last 1 3 myr suggesting no change in mean ocean nutrient content accompanied the addition of light carbon and 3 stronger vertical nutrient fractionation in the north atlantic in the middle pleistocene between sites 607 and 552 suggesting weaker north atlantic deep water formation at this time relative to the early and late pleistocene we also find evidence for a more pronounced deep recirculation gyre in the western north atlantic basin in the early brunhes as evidenced by aging of deep northern basin water site 607 relative to deep water in the equatorial atlantic site 664

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

rare earth elements and nd isotopes tracing water mass mixing and particle seawater interactions in the se atlantic abstract distributions of dissolved and particulate rare earth elements rees and seawater neodymium isotopic composition e nd were established in samples from the bonus goodhope bgh ipy geotraces cruise in the se atlantic sector of the southern ocean 36 s 13 e to 57 s 0 feb mar 2008 close to the south african continent in the subtropical domain particulate rees show the highest concentrations and flat paas normalized patterns clearly tracing their lithogenic origin active cerium oxidation onto suspended particles is evidenced by the mirror image relationship of the cerium anomaly between dissolved and particulate phases unradiogenic dissolved neodymium in surface waters e nd 17 1 traces the influence of old sedimentary material brought by the agulhas current and rings to the cape basin area a mass balance calculation suggests that the release of nd from dissolution of lithogenic material corresponds to a remobilization of 154 10 6 t of sediment per year i e 5 of the total sediment delivered to the southeast african coast annually at open ocean stations both dissolved and particulate rees present negative cerium anomalies indicating that particles have acquired a marine signature the increasing ree concentrations with depth and the strong linear correlations of dissolved ree with silica indicate that surface removal and deep re mineralisation of rees are partially related to the biogeochemical cycle of silicate which involves biogenic silica diatoms combined with marine carbonates these authigenic phases could explain the observed ree patterns in suspended particles except for la we suggest that the positive la anomalies in both phases are linked to the oceanic barium cycle and the partial dissolution of barite crystals especially in the polar frontal zone the e nd composition behaves conservatively in intermediate and deep waters while input processes affect the isotopic signal of subtropical surface waters and weddell gyre bottom waters an indian ocean and an atlantic variety of aaiw have been isotopically differentiated e nd 9 3 0 3 and e nd 8 0 0 5 respectively homogeneous signatures characterize circumpolar waters e nd from 8 2 to 8 4 for cdw a binary mixing model has been used to assess the contribution of undiluted nadw reaching southern latitudes

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