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

anhysteretic remanent magnetization of fine magnetic particles 1 various magnetic parameters are in common use for estimating the grain size of magnetic particles among these the ratio of the intensity of anhysteretic remanent magnetization arm to that of isothermal remanent magnetization as well as their alternating field af demagnetization curves are used as an indicator of the domain state of the particles several models have been proposed to describe physically the acquisition of arm in a biased af field jaep 1969 first developed a semiquantitative theory based entirely on the thermal fluctuation analysis developed by neel 1949 1954 1955 significant discrepancies were found between his model and experimental results on magnetite a new general theory of arm based on the work of jaep is presented here with particular regard to the influence of various parameters like grain size coercivity and mineralogy on arm intensity an analytical expression for arm intensity in the special case of very fine particles was derived from this theory and a good agreement with experimental results and data from the literature was found a new estimation of the atomic reorganization time was obtained from arm measurements on a sample of the yucca mountain tuff which has well known mineralogy and grain size distribution the results are in agreement with the value proposed by mcnab et al 1968 for magnetite some authors considered magnetic interactions as the key to understand the arm in fine particles and this is certainly true for strongly interacting samples in this case arm would be useless for the characterization of magnetic grains however many sediments have a very low concentration of well distributed magnetic grains for these samples the explanation of an arm in terms of intrinsic properties of the grains as qualitatively proposed by other authors is more suitable

iron oxide characteristics of the chinese loess red clay sequences and their implications for the evolution of the east asian summer monsoon since the late oligocene abstract the most significant climatic change in east asia involved the formation and evolution of the coupled monsoon arid environmental system during the cenozoic which was dynamically linked to global cooling and the growth of the qinghai tibet plateau however our understanding of monsoon evolution since the late oligocene remains controversial due to differences in the interpretation of various environmental proxies from loess archives in this study the composition and relative abundance of pedogenic iron oxides of two eolian sequences from the lingtai section and the zhuanglang drill core were investigated using rock magnetic optical spectroscopy and geochemical analyses the results indicate that while the composition of iron oxides in the mio pliocene red clay and quaternary loess paleosol sequences is similar the concentrations of magnetite maghemite hematite and goethite are quite different between loess paleosol and red clay the combination of magnetic proxies magnetic susceptibility fed fet and color a values reveals that precipitation and temperature played varying roles in driving pedogenesis and chemical weathering since the late oligocene during the late oligocene to early miocene the occurrence of relatively strong pedogenesis and chemical weathering was likely the result of high temperatures rather than high precipitation the east asian summer monsoon intensified during the middle miocene climate optimum 16 5 14 5 ma in response to global climatic warming subsequently during the middle to late miocene the monsoon intensity gradually weakened due to global cooling after 8 ma the summer monsoon strengthened substantially and reached a maximum during 4 5 2 6 ma possibly as a result of the uplift of the northeastern margin of the qinghai tibetan plateau during the late miocene the monsoon intensity then commenced a decreasing trend in the early pleistocene but then strengthened again after 1 0 ma

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

thermoremanence anhysteretic remanence and susceptibility of submicron magnetites nonlinear field dependence and variation with grain size we have measured initial susceptibility 0 and the dependence of anhysteretic remanent magnetization arm and thermoremanent magnetization trm on applied field for seven samples of magnetite with mean grain sizes from 40 to 540 nm trm acquisition is nonlinear in geomagnetically relevant weak fields contrary to the usual assumption made in paleointensity determination over the 40 540 nm range 0 varies with particle shape but only weakly with particle size d and can be used to correct for varying magnetite concentrations in sediment cores arm is strongly size dependent over the same range and is the best parameter for monitoring grain size variations in natural samples arm and trm have similar variations as d 1 for d 1 m suggesting a common source for this pseudo single domain psd dependence on grain size however trm is 10 20 times more intense than arm in grains around 0 2 m in size the trm microstate seems to be a two domain structure whereas the arm microstate may be a vortex structure which has never before been convincingly demonstrated by magnetic measurements independent evidence comes from theoretical fits to trm and arm field dependence data in moderate and strong fields trm in 215 540 nm magnetites is explained by two domain theory but arm is not in smaller grains d 0 1 m a psd theory predicts that trm is carried by single domain sd moments of entire grains but arm resides in moments 1 per grain 20 40 times weaker these remanence levels match those of metastable sd and vortex states respectively we therefore propose that magnetite grains in the 0 1 0 5 m size range can remain in metastable sd or two domain states following acquisition of trm but revert to a vortex ground state when field cycled for example in arm acquisition or alternating field demagnetization

particle size related mineral magnetic source sediment linkages in the rhode river catchment maryland usa characterization of both the source materials and the bottom sediments of an estuary by magnetic characters on a particle size basis allows the source of the bottom sediments to be determined and indicates a shift in sediment sources corresponding to changing land use patterns the major source of the sediments in the lower part of cores from the middle of the estuary is eroding shorelines soil derived particulates from the uplands dominate the upper part of the cores this change in source occurred in the early part of the 19th century the magnetic character of the most recent sediments suggests a progressive depletion through time of the upland soils in the finest fractions

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

the record of changing hematite and goethite accumulation over the past 22 myr on the chinese loess plateau from magnetic measurements and diffuse reflectance spectroscopy 1 high field isothermal remanence hirm and diffuse reflectance spectroscopy drs wereusedto characterize hematite and goethite in a suite of bulkand particle sized fractioned samples from the chinese loess plateau representing the main changes in magnetic mineralogy over the past 22 myr the record of drs defined hematite largely reflects variations in the pedogenic fraction 8 mm makes the main contribution to goethite concentrations in the bulk samples pedogenic goethite concentrations generally vary inversely with those of hematite the lack of consistent correlations between hirm inferred mineral content and drs measurements casts doubt on the validity of using hirm to characterize the concentrations and relative proportions of hematite and goethite in sediments representing a long time span or a wide grain size distribution the progressive decline in the coercivity of the antiferromagnetic minerals in bulk samples throughout the whole period is mainly an expression of changes in the detrital fraction reflecting changes in the source region possibly involving increased aluminum substitution the good correlation between drs defined hematite and frequency dependent magnetic susceptibility in several chronologically defined subgroups of samples is consistent with the hypothesis that maghemite forms a transitional phase in a weathering sequence from ferrihydrite to hematite the results shed new light on using hirm to characterize hematite and goethite in sediments and on the history of weathering and climate change over the past 22 myr in the dust source regions and on the loess plateau

an application of relative moment tensor inversion to the 26 december 2003 mw 6 6 iran bam earthquake abstract a relative moment tensor inversion technique is used to retrieve the focal mechanisms of teleseismic earthquakes the observed data consists of amplitude spectra of the direct p phase on vertical and the direct s phase on rotated horizontal components the effect of propagation paths is minimized using relative amplitude spectra of close lying earthquakes recorded by common stations the inversion is carried out for six components of the moment tensors the focal mechanisms are determined using a linear weighted least squares approach signed spectral moment the method is applied to seven earthquakes that occurred close to the 26 december 2003 m w 6 6 iran bam earthquake and were recorded at regional teleseismic distances with good azimuthal coverage most focal mechanisms obtained in this study show a predominantly right lateral strike slip component similar to those obtained by other independent estimates the application of the relative moment tensor inversion using spectral amplitudes combined with polarity data proves to be flexible and effective in estimating focal mechanisms of teleseismic data and the method is suitable for routine implementation in seismic networks

grain sizes of susceptibility and anhysteretic remanent magnetization carriers in chinese loess paleosol sequences detailed rock magnetic studies show that susceptibility mass specific and anhysteretic remanent magnetization arm of the chinese loess paleosol sequences are carried by almost identical magnetic carriers therefore the ratio arm or equivalently arm where is defined as 0 and 0 is the intercept susceptibility of the plot of versus arm and arm is field normalized arm can be used to quantify the grain size of and arm carriers by determining this ratio for three chinese loess paleosol profiles jiuzhoutai yuanbao and yichuan characterized by different degrees of environmentally controlled pedogenesis and sedimentation rates we show that the lower grain size limit of aeolian magnetic particles in the less pedogenically altered loess units is about 100 300 nm in the finer grained pseudosingle domain psd grain size range in contrast the grain sizes of pedogenically produced magnetic particles for mature paleosols dominantly cover both the superparamagnetic sp and single domain sd ranges on the basis of plots of arm against samples can be divided into four regions i ii iii and iv region i corresponds to the least pedogenically altered primary loess samples with arm of 0 165 0 24 samples in region ii a transition zone between the least altered loess and the onset of development of paleosols have values identical to those in region i but have lower arm of 0 09 0 165 with increasing susceptibility in zone iii arm is positively correlated with indicating the gradually increasing influence of sp particles finally in zone iv with higher than 6 5 10 7 m3 kg 1 arm is independent of the variations in suggesting that arm is totally controlled by the pedogenic finest grained particles and the size distribution of these particles remains almost constant the development of soils in the chinese loess revealed by these three profiles from three sites can be clearly explained by a continuous process of pedogenesis increasing from zone i to zone iv the definition of the pedogenic zones can help to improve our understanding of the underlying mechanisms and variability of pedogenesis and thus could enable more successful and accurate separation of the authentic pedogenic signals from the background signal of the aeolian inputs at different loess sites worldwide

grain size distribution of pedogenic magnetic particles in chinese loess paleosols 1 variations in magnetic parameters of the long chinese loess paleosol sequences reflect paleoclimatic fluctuations however there remain ambiguities whether the magnetic proxies are controlled by the concentration or by the distribution of magnetic grain sizes we systematically investigated the frequency dependence of low field magnetic susceptibility fd and the decay rate dr dependence of anhysteretic remanence magnetization arm susceptibility arm dr for a set of representative loess paleosol samples from the yuanbao section western chinese loess plateau after removing the effect of aeolian coarse grained magnetites both fd and arm dr are nearly independent of the degree of pedogenesis indicating a presence of fine grained magnetic particles ranging from superparamagnetic to single domain with an almost constant grain size distribution therefore the magnetic enhancement of magnetic susceptibility or arm is caused dominantly by changes in the concentration of these fine grained pedogenic grains

magnetic characteristics of loess paleosol sequences in tacheng northwestern china and their paleoenvironmental implications abstract systematic rock magnetic data including magnetic mineralogy and magnetic concentration magnetic susceptibility laboratory induced magnetic remanences are presented from the loess paleosol sequences in tacheng northwestern china to explore the specific paleoenvironmental significance of magnetic characteristics in the xinjiang loess results show that ferrimagnetic minerals such as magnetite and maghemite dominate the magnetic properties in the tacheng tc section similar to the magnetic mineralogy of loess deposits in the chinese loess plateau clp the magnetic particles in the tc section are characterized by multi domain md and pseudo single domain psd behavior representing the detrital primary mineral phase the absolute contents of pedogenic ultrafine superpara sp ferrimagnetic particles are very low in the tc section indicating that pedogenesis has a limited contribution this is quite different from the magnetic enhancement of loess deposits in the clp variation of magnetic susceptibility and median grain sizes could be interpreted by the predominance of paleowind intensity as well as provenance variation a similar pattern was also found in other places in xinjiang such as talede section in yili basin and bole section in the western tianshan our results suggest that variation of detrital inputs might have played a pivotal role in the enhancement of magnetic susceptibility while pedogenesis was probably responsible for the increase of finer single domain sd particles in paleosol units the arm sirm ratio could serve as an indicator for reflecting the degree of pedogenesis in xinjiang loess

determining the climatic boundary between the chinese loess and palaeosol evidence from aeolian coarse grained magnetite summary this paper proposes a new method to distinguish between interglacial deposits and pedogenically overprinted glacial loess based on the concentration variations of coarse grained aeolian magnetically pseudo single domain and multidomain magnetite we apply the method to a sequence from the upper part of the loess unit l2 marine isotope stage mis 6 to the sub loess unit s1l2 mis 5d at the yuanbo yb section in the chinese loess plateau the method is based on the differences in low temperature properties between the coarse grained multidomain and pseudo single domain detrital magnetite and the pedogenic magnetic particles including superparamagnetic sp particles and relatively larger sp maghemite particles the former is characterized by a crystallographic verwey transition around 120 k in contrast the magnetization of the latter continuously decreases in intensity with increasing temperatures the method involves two steps 1 calculating the first derivative of the low temperature thermal demagnetization of the saturated isothermal remanent magnetization acquired at 20 k lt sirm which enhances the behaviour related to the verwey transition and 2 fitting a third order polynomial background to the data between both 50 70 and 150 300 k and then subtracting this background from the total derivative curves the area under the background corrected derivative curves represents the absolute intensity drop associated with the verwey transition j tv this is caused by the aeolian coarse grained magnetite which is very sensitive to the changes in the intensity of the winter monsoon and in turn re

out of phase evolution between summer and winter east asian monsoons during the holocene as recorded by chinese loess deposits we analyzed climate proxies from loessic soil sections of the southern chinese loess plateau the early holocene paleosol s0 is 3 2 m thick and contains six sub soil units co eval soils from the central loess plateau are thinner 1 m consequently higher resolution stratigraphic analyses can be made on our new sections and provide more insight into holocene temporal variation of the east asian monsoon both summer and winter monsoon evolution signals are recorded in the same sections enabling the study of phase relationships between the signals our analyses consist of i measurements of magnetic properties sensitive to the production of fine grained magnetic minerals which reflect precipitation intensity and summer monsoon strength and ii grain size analyses which reflect winter monsoon strength our results indicate that the holocene precipitation maximum occurred in the mid holocene 7 8 3 5 cal ka bp with an arid interval at 6 3 5 3 cal ka bp the winter monsoon intensity declined to a minimum during 5 0 3 4 cal ka bp these results suggest that the east asian summer and winter monsoons were out of phase during the holocene possibly due to their different sensitivities to ice and snow coverage at high latitudes and to sea surface temperature at low latitudes

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

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

magnetic properties of loess deposits on the northeastern qinghai tibetan plateau palaeoclimatic implications for the late pleistocene summary the loess palaeosol deposit on the northeastern qinghai tibetan plateau is sensitive to environmental changes thus providing a good opportunity to investigate regional palaeoenvironmental evolution and its relationship with global climatic changes detailed rock magnetic investigations and grain size determination were carried out on a 35 m thick loess palaeosol sequence at dongchuan the northeastern qinghai tibetan plateau the principal ferrimagnetic minerals in both the loess and palaeosol units are large pseudo single domain magnetite maghemite palaeosol units are generally enriched in ultrafine grained magnetite maghemite of pedogenic origin variations of low field magnetic susceptibility and frequency dependent susceptibility in the loess and palaeosols can mainly be attributed to changes in the concentration of these minerals higher values of frequency dependent susceptibility occur in the palaeosol horizons except for the weakly developed palaeosol suggesting that higher concentrations of ultrafine magnetite maghemite particles occur in palaeosol units due to in situ pedogenesis the frequency dependent susceptibility of the loess units is very low and uniform indicating absence of the super paramagnetic grains and negligible pedogenically induced enhancement of magnetic susceptibility generally magnetic susceptibility combined with the frequency dependent susceptibility of the loess palaeosol sequences reflect the glacialinterglacial changes thus can be employed as a proxy measure of palaeoclimate in this region however the low field magnetic susceptibility record does not consistently correlate to the variations in stratigraphy of the dongchuan loess palaeosol sequence it is thus suggested that multiparameter rock magnetic investigations combined with non magnetic measurements such as grain size analysis represent a more powerful approach for palaeoclimatic research into the complex loess palaeosol record in the qinghai tibetan plateau

mineral magnetic properties of loess paleosol couplets of the central loess plateau of china over the last 1 2 myr 1 we have conducted a multiparameter investigation of 15 loess paleosol couplets s0 l1 to s14 l15 from the jiaodao section in the central loess plateau of china using environmental magnetic approaches coupled with soil science techniques the magnetic parameters display systematic variations that seem to be closely related to paleoclimate variations and intensity of pedogenesis high temperature susceptibility curves of paleosols show a generally decreasing trend in reversibility from the base of the lishi formation to the holocene black loam possibly indicating a decrease in weathering intensity this may reflect a long term increase in aridity and or a general long term cooling trend of the interior of the asian continent from 1 2 ma to the present several samples display wasp waisted hysteresis loops these are most pronounced in moderately enhanced paleosols less pronounced in the practically unaltered loess and subdued in the well developed paleosols but wasp waistedness reappears in the most developed paleosols this wasp waistedness sequence suggests that the composition concentration and grain size of magnetic minerals all contribute to the hysteresis behavior of samples from the studied loess paleosol sequence but each factor has a different effect at different stages of pedogenesis

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

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

detrital and early diagenetic processes in late pleistocene and holocene sediments from the sw galicia bank inferred from high resolution enviromagnetic and geochemical records abstract u channel based high resolution magnetic and geochemical measurements supported by scanning electron microscopy x ray diffraction and fluorescence and grain size analyses of discrete samples were carried out on six sediment cores recovered from the sw flank of the galicia bank at the prestige s wreck area five magnetochemical facies reflecting the different sedimentary environments i e hemipelagic contouritic turbiditic sediment provenances and early diagenetic redoxomorphic processes i e mn peaks are defined on the basis of a cluster analysis the records showed climatically forced detrital signatures of regional importance associated with continental slope sedimentary processes the chronostratigraphy and correlation of the cores is based on 20 14 c ams dating recognition of heinrich like events h1 to h3 and well documented holocene climatic features from a geochemical and enviromagnetic perspective the late pleistocene to holocene evolution of the area shows two different sedimentation contexts mis 2 is dominated by down slope depositional processes the highest sedimentation rates 9 1 cm ky were achieved during this interval the major turbidite activity is recorded between 31 000 yr bp and 13 500 yr bp successive arrivals of ird h1 to h3 are also identified during this period in contrast holocene sedimentation was dominated by a mixture of pelagic hemipelagic and along slope depositional processes and presented considerable lower sedimentation rates 3 cm ky bottom currents intensification at 7000 yr bp and 4500 yr bp coinciding with late holocene warm events are also recognised during this stage

contrasting behavior of hematite and goethite within paleosol s5 of the luochuan profile chinese loess plateau 1 the chinese loess paleosol sequence provides an excellent record of long term variations in the east asian paleomonsoon for representative loess profiles paleosol units have enhanced magnetic properties compared to loess units however at some depth intervals with special paleoenvironmental conditions selective depletion of antiferromagnetic afm minerals hematite and goethite could occur resulting in complexities in accurately linking variations in magnetic properties to long term fluctuations in paleoclimate to resolve this problem we directly measured the mass concentrations of these afm minerals using second order diffuse reflectance spectroscopy drs and then correlated the drs results to high field isothermal remanent magnetization hirm from paleosol unit s5 at the luochuan profile central chinese loess plateau our results suggest that a low hirm anomaly just below the sub paleosol unit s5s1 is caused by fluctuations specifically in goethite content while the hematite concentration exhibits a maximum over the same depth interval this appears to rule out significant loss of hematite to reductive dissolution and further indicates that hematite and goethite may respond differently to changes in the paleoclimate conditions

correlation of the magnetic susceptibility stratigraphy of chinese loess and the marine oxygen isotope record chronological and palaeoclimatic implications abstract the thick deposits of wind blown silt of the loess plateau in central china constitute arguably the most important terrestrial record of the late pliocene and pleistocene climate magnetic susceptibility stratigraphy has proven extremely useful for quantifying the palaeoclimatic record of chinese loess with intervals of high magnetic susceptibility corresponding to warm humid interglacials and intervals of low susceptibility to cooler drier glacials several workers have noted that the magnetic susceptibility stratigraphy strongly resembles the marine oxygen isotope record for which a high resolution chronology is available from tuning to the frequencies of earth orbital parameters attempts have been made to correlate the two records statistically and we use this approach to generate a new magnetic susceptibility time series for the central chinese loess plateau our results suggest that the two records are sufficiently similar over the interval ca 0 1 5 my bp for this approach to yield a useful age model for loess accumulation spectral analysis of the resulting magnetic susceptibility time series clearly shows that the growth of 100 ky variance which occurs in the marine oxygen isotope record after about 1 my bp also occurs synchronously in the magnetic susceptibility record reinforcing recent suggestions of a strong linkage between the high latitude northern hemisphere and the asian climate we also show that a significant improvement in the strength of the loess magnetic susceptibility marine oxygen isotope correlation occurs after about 1 5 my bp which corresponds to a significant increase in the rate of sediment accumulation across the loess plateau

cautionary note on magnetic grain size estimation using the ratio of arm to magnetic susceptibility the ratio of anhysteretic remanent magnetization arm to magnetic susceptibility is widely used for rapid estimation of magnetic grain size variations on interpreting arm variations no significant influence of interactions among magnetic grains on arm acquisition is usually assumed implicitly although some previous experiments using artificial sediments and biogenic magnetites opposed this assumption our rock magnetic study of deep sea surface sediments from the pacific ocean showed that arm depends strongly on the concentration of magnetic minerals and on the r value of cisowski 1981 an index of the strength of magnetic interactions this result demonstrates that arm can be influenced significantly by magnetic interactions in natural sediments we corrected for the influence of the magnetic interactions using the observed concentration dependence of arm regional variations of arm values before the correction were geologically unnatural in terms of magnetic grain size variations previous interpretations of arm variations on magnetic grain size without consideration of magnetic interactions may not be valid

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

sources of fine grained magnetic minerals in sediments a problem revisited progress in the discrimination of fine grained magnetic minerals in sediments and sediment sources using measurements of magnetic susceptibility at two frequencies and of magnetic remanence generated by a combination of direct and alternating currents is summarized the former measurements yield values for low field and frequency dependent susceptibility lf and fd respectively the latter generate an anhysteretic remanent magnetisation arm that when normalized to the dc bias field can be represented as the susceptibility of arm arm using quotients derived from lf fd and arm to generate bi logarithmic plots it is possible to discriminate between assemblages dominated by magnetic minerals formed through pedogenesis and those arising from the presence of magnetotactic bacteria that use chains of magnetic particles to seek optimum environments in surface sediments sediments to which both types of magnetic mineral contribute occupy positions between the envelopes of values typical of soil d

the superparamagnetism of yucca mountain tuff yucca mountain tuff contains small titanomagnetite grains with narrow size distributions in the superparamagnetic range schlinger et al 1988 magnetic measurements on three samples comprising hysteresis loops at low and ambient temperatures acquisition and demagnetization of isothermal remanent magnetization thermal demagnetization of the saturation remanence and of a low temperature thermoremanence and frequency and temperature dependent susceptibilities allow evaluation of the magnetic properties in terms of neel s 1949 single domain theory precise grain volume distributions have been obtained by applying the blocking volume concept to thermal demagnetization results in contrast an attempt to derive mean particle volumes by fitting a langevin curve to the room temperature magnetization curves fails probably because the precondition for the langevin function kv kt 1 is not met it is only for the sample with the smallest grains and in weak fields 20 mt that a langevin fit provides a reasonable volume estimate there is good agreement between the experimental results and the calculated frequency and temperature dependence of susceptibility thus verifying that neel s theory is sufficient for the magnetic description of single domain assemblages spanning the superparamagnetic stable single domain boundary however some deviations between modeled and measured susceptibilities exist and the physical causes may include size dependent anisotropy nonuniform magnetizations and also an uncertain preexponential time constant 0 while 0 10 11 s gives the best fit for the sample with the largest grains 0 10 9 s is more reasonable for the others thus 0 may indeed be size and temperature dependent as predicted by brown 1959 the commonly cited parameter fd frequency dependence of susceptibility reaches 30 at room temperature rt for one sample with a blocking temperatures just below rt while fd 0 at rt for a superparamagnetic sample with smaller grains these results thus exemplify that fd is not limited to 15 as a number of studies suggest and that fd 0 must not be taken to imply the absence of superparamagnetic grains

pedogenesis and paleoclimate interpretation of the magnetic susceptibility record of chinese loess paleosol sequences in the chinese loess paleosol sequences from luochuan haanxi province china variations in the magnetic susceptibility have been accepted as an excellent proxy for paleoclimate and the standard interpretation is that climatic processes have enhanced the magnetic susceptibility of the paleosols beyond the base line level of the loess by using mineral magnetic properties and a soil chemistry extraction procedure we show that most of the magnetic susceptibility signal in both the paleosols and the loess is due to pedogenesis in effect loess deposition and pedogenesis are competing processes at all times and the presence of a paleosol simply indicates that the latter process was predominant these results imply that any interpretation of the paleoclimate record of loess paleosol sequences must recognize the pedogenic nature of the magnetic susceptibility signal and that the focus of future research must be on the critical role of climate in the development of the paleosols

paleoclimatic significance of the temperature dependent susceptibility of holocene loess along a nw se transect in the chinese loess plateau we have conducted mineral magnetic investigations of samples of modern dune sand pristine loess and present day loess along a nw se transect from the northern to the central loess plateau in china the methods used include the temperature dependence of susceptibility tds before and after citrate bicarbonate dithionite cbd treatment as well as x ray diffraction xrd analysis the xrd analyses demonstrate that magnetite and hematite both exist in the chinese loess paleosol sequence and its modem source area but the tds measurements show that magnetite is the predominant contributor to magnetic susceptibility maghemite is present in the pristine loess and the present day loess due to pedogenesis the pedogenic processes that produce the maghemite are closely linked to paleoclimate and for this transect precipitation appears to be the most important climatic variable we suggest that tds can be used as a useful method for the analysis of pedogenesis and climatic change

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

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

physical properties governing groundwater flow in a glacial till catchment abstract hydraulic conductivity surface topography and sediment thickness influence the spatial and temporal pattern of groundwater flow and stream discharge in an unconfined aquifer in a 3 7ha headwater catchment in central ontario canada groundwater levels in the soils adjacent to the stream also significantly influence the magnitude and spatial distribution of stream discharge topographic convergence in plan and decreasing sediment thickness along flowpaths result in surface saturation and groundwater discharge hillslope gradients adjacent to discharge areas determination how fluctuating groundwater levels influence the extent of spatial variations in surface saturation and saturation within the soils as a result of spatial differences in hillslope gradients the spatial patterns of both groundwater and stream discharge change with fluctuating groundwater levels unsaturated sediment s in upslope locations store water infiltrating during wet periods such that groundwater flow from upslope sediments maintains high groundwater levels near the stream and supplies baseflow during dry periods the direction of horizontal groundwater flow in harp 4 21 is not perpendicular to topographic contours so that subcatchment boundaries based on topographic divides differ by as much as 57 from their true subcatchment boundaries based on groundwater divides therefore groundwater flow models based on surface topography may incorrectly predict the spatial pattern of stream discharge

magnetic proxy climate results from the duanjiapo loess section southernmost extremity of the chinese loess plateau we report mineral magnetic results from a 7 5 m loess sequence 150 samples from the southernmost extremity of the chinese loess plateau which includes the last two glacial cycles in this area the loess sediments experienced particularly intense weathering processes the magnetic assemblage is dominated by a mixture of pseudo single domain psd and multidomain md magnetite with associated superparamagnetic sp grains of either magnetite or maghemite in the paleosols and weathered loess horizons all the rock magnetic parameters fluctuate in parallel with marine sediment 18o data over the last 150 kyr thus reflecting changing global paleoclimatic conditions this relationship is also supported by the evidence of milankovitch cycles in the magnetic susceptibility record paleorainfall estimates when compared with other studies from the chinese loess plateau underline the more humid character of this region during the last 130 kyr

iron mineralogical proxies and quaternary climate change in se european loess paleosol sequences abstract the loess paleosol sequences batajnica stari slankamen serbia and mircea voda romania represent key archives for the climate and landscape development of the middle and lower danube basin during the last 700 000 years for deciphering the quaternary climate evolution in these regions the batajnica stari slankamen and mircea voda sites are for the first time studied by a multi proxy approach based on iron mineralogical parameters changes in the iron mineralogical composition are identified and characterized by rock magnetic investigations diffuse reflectance spectroscopy drs and munsell color based proxies the results show that environmental conditions during mid and early middle pleistocene interglacials were more favorable for hematite formation suggesting a more oxidizing pedoclimate as in the more recent interglacials this is also reflected in a gradual increase of the anhysteretic remanent magnetization vs saturation isothermal remanent magnetization arm sirm ratio in the studied profiles changes in this ratio can be linked to a preferential hematitization of coarse grained ferrimagnetica and relates to warmer climate conditions and a more extended estival dry period at the same time rock magnetic parameters indicate a preferential destruction of fine grained magnetic particles in older paleosols resulting from seasonal excess moisture a progressive cooling and decrease of rainfall during the middle and late pleistocene is evidenced not only for interglacial pedocomplexes but also for glacial loess layers this finding is in line with previously published proxy records of silicate weathering and clay formation at these sites and similar trends reported from other sites in the european steppe belt relating iron mineralogical proxies to paleopedological characteristics and proxies of silicate weathering additionally a change in the seasonal pattern of the interglacial temperature and precipitation regime from a mediterranean type to a steppe type climate is revealed highlighting the potential of such a multi proxy approach possible triggers for this paleoenvironmental evolution are discussed as well finally highlighting a quaternary uplift hypothesis which best could explain the inferred trend of cooling aridification and increasing continentality accordingly changes in atmospheric circulation and rain shadow effects induced by small scale uplift of european mountain belts alps carpathians dinaric alps would provide a driving mechanism for the westward extension of the eurasian steppe belt into central and se europe during the quaternary

quantitative relationships between magnetic enhancement of modern soils and climatic variables over the chinese loess plateau environmental magnetism has been widely employed to reconstruct past climate changes on the chinese loess plateau clp and several climofunctions based on the magnetic properties of loess have been developed however systematic investigation of the quantitative relationship between topsoil magnetic enhancement and modern climate remains uncommon in this study we obtained surface soil samples from 257 sites over the clp and adjacent regions from this set we used 180 samples from sites unaffected by potential contamination to investigate the relationship between the commonly measured magnetic properties of magnetic susceptibility and magnetic remanence and modern climatic variables the spatial distribution of the results demonstrates a strong nw se gradient of the magnetic enhancement of surface soils the results of more detailed magnetic parameters indicate that pedogenic viscous superparamagnetic and stable single domain particles are mainly responsible for the magnetic enhancement of the soils in the studied region and that the magnetic grain size distribution of the ferrimagnetic components of pedogenic origin remains almost constant independent of pedogenic intensity the uniform mechanism of magnetic enhancement mainly linked with the concentration of the pedogenic components rather than with variations in magnetic grain size decreases the level of ambiguity in climate reconstructions based on magnetic measurements of chinese loess statistical analyses including correlation principal component analysis pca and multiple regression analysis suggest that annual rainfall rather than temperature exerts the dominant effect on soil magnetic enhancement finally we used the results to develop several transfer functions to reconstruct mean annual precipitation map transfer functions based on frequency dependent susceptibility fd and anhysteretic remanent magnetization arm provide the most reliable estimates of map this study significantly improves the understanding of the relationship between soil magnetic properties and climate

decay rate dependence of anhysteretic remanence fundamental origin and paleomagnetic applications 1 we have measured the intensity of anhysteretic remanent magnetization arm as a function of alternating field af decay rate for synthetic and natural single domain sd and pseudo single domain psd magnetites arm intensity increases as decay rate decreases multidomain md magnetites have the opposite response arm increasing as the decay rate increases these are identical to the sd psd and md dependences of thermoremanent magnetization on cooling rate for all grain sizes and domain structures arm intensity increases as the af decay rate used to achieve an initial demagnetized state decreases decay rate differences in arm intensity are a property of low and medium coercivity grains as shown by annealing and by stepwise af demagnetizing samples we interpret the sd results to mean that increased af exposure time permits a closer approach to equilibrium magnetization an approximate thermal activation theory based on neel 1949 and an exact theory by egli and lowrie 2002 predict 6 11 increases in arm for an order of magnitude decrease in decay rate in reasonable accord with the observed 12 increase for 0 065 m sd grains for md grains we hypothesize that increased exposure time slower decay permits more efficient self demagnetization reducing arm low coercivity grains experience the largest self demagnetizing fields and therefore have the largest decay rate response initial state decay rate response is attributed to longer exposure times leaving domain walls more strongly pinned in deeper potential wells the net self demagnetizing field is zero in the demagnetized state acquisition decay rate annealing and initial state responses of psd grains are a blend of sd and md responses because arm is the most frequently used normalizer in relative paleointensity determination it is important either to use a standard decay rate or else to remove the decay rate dependence by demagnetizing the arm to 30 of its initial value arm0 3 a standard demagnetization level for the normalizing arm is particularly important when comparing paleointensity records from different laboratories