magnetic properties of coastal loess on the midao islands northern china implications for provenance and weathering intensity abstract loess deposits are widely distributed over the islands in the bohai gulf and neighboring regions of northern china the coastal loess located to the east of the chinese loess plateau clp is believed to have a local source from exposed marine sediments and a distant source from inner arid regions in asia in this study magnetic geochemical and diffuse reflectance spectroscopic analyses were conducted on the loess to explore its relationship with the loess on the clp and its paleoclimatic implications we find that the coastal loess shows similar geochemical composition background susceptibility and magnetic enhancement to loess on the clp magnetic minerals characteristic of pedogenesis are more important in the paleosol layer with fine ferrimagnetic minerals abundant in paleosol layer sb1 and hematite in paleosol layer sb2 geochemical evidence suggests that weathering intensity in paleosol sb2 is similar to or even stronger than in paleosol sb1 pedogenic enhancement of magnetic susceptibility in the study area is not so strong which may be due to enhanced hematite formation as opposed to ferrimagnetic mineral production and preservation

record of middle pleistocene climate change from buck lake cascade range southern oregon evidence from sediment magnetism trace element geochemistry and pollen comparison of systematic variations in sediment magnetic properties to changes in pollen assemblages in middle pleistocene lake sediments from buck lake indicates that the magnetic properties are sensitive to changes in climate buck lake is located in southern oregon just east of the crest of the cascade range lacustrine sediments from 5 2 to 19 4 m in depth in core contain tephra layers with ages of 300 400 ka at 9 5 m and 400 470 ka at 19 9 m in these sediments magnetic properties reflect the absolute amount and relative abundances of detrital fe oxide minerals titanomagnetite and hematite the lacustrine section is divided into four zones on the basis of magnetic properties two zones 19 4 17 4 m and 14 5 10 3 m of high magnetic susceptibility contain abundant fe oxides and correspond closely to pollen zones that are indicative of cold dry environments two low susceptibility zones 17 4 14 5 m and 10 3 5 3 m contain lesser amounts of fe oxides and largely coincide with zones of warm climate pollen transitions from cold to warm climate based on pollen are preceded by sharp changes in magnetic properties this relation suggests that land surface processes responded to these climate changes more rapidly than did changes in vegetation as indicated by pollen frequencies magnetic properties have been affected by three factors 1 dissolution of fe oxides 2 variation in heavy mineral content and 3 variation in abundance of fresh volcanic rock fragments trace element geochemistry employing fe and the immobile elements ti and zr is utilized to detect postdepositional dissolution of magnetic minerals that has affected the magnitude of magnetic properties with little effect on the pattern of magnetic property variation comparison of ti and zr values proxies for heavy mineral content to magnetic properties demonstrates that part of the variation in the amount of magnetite and nearly all of the variation in the amount of hematite are due to changes in heavy mineral content variation in the quantity of fresh volcanic rock fragments is the other source of change in magnetite content magnetic property variations probably arise primarily from changes in peak runoff at low to moderate flows magnetic properties reflect only the quantities of heavy minerals derived from soil and highly weathered rock in the catchment at high flows however fresh volcanic rock fragments may be produced by breaking of pebbles and cobbles and such fragments greatly increase the magnetite content of the resulting sediment climatically controlled factors that would affect peak runoff levels include the accumulation and subsequent melting of winter snow pack the seasonality of precipitation and the degree of vegetation cover of the land surface our results do not distinguish among the possible contributions of these disparate factors

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

the late pleistocene palaeoclimatic record of north atlantic deep sea sediments revealed by mineral magnetic measurements eight cores of north atlantic deep sea sediment are correlated using simple rapid and non destructive measurements of magnetic susceptibility and isothermal remanence this stratigraphy is demonstrably related to late pleistocene palaeoclimatic variations by comparison with the oxygen isotope and microfossil records of these cores fluctuations in the concentration dependent magnetic properties of the cores largely reflect their lithological composition consisting of climatically modulated cycles of marl glacial horizons and nannofossil chalk interglacial horizons high magnetic concentration characterises glacial horizons which correspond to periods when carbonate productivity was severely restricted and ice rafted detrital inputs were prolific coincident with the migration south of the north atlantic polar front to within 3 of latitude north of the coring site in contrast interglacial horizons are characterised by low magnetic concentration and high carbonate content of the sediment consequent on the retreat of the polar front and the re establishment of coccolith floras in its wake during these periods ratios formed between individual magnetic parameters are independent of magnetic concentration and are thus free of any climatic influences wrought by carbonate oscillations in this study however such ratios exhibit a definite response to palaeoclimatic variations attributable to differences in the composition and grain size of the magnetic mineral assemblage of glacial vis a vis interglacial horizons of the cores these differences in mineral magnetic composition are substantially confirmed by mossbauer effect studies of selected samples representing peak glacial and interglacial horizons of one core such glacial interglacial contrasts in the concentration mineralogy and grain size of the magnetic assemblage most probably result from variations in the source and flux density of detritral inputs induced by changes in climate x ray diffraction studies of the same core indicate that variations in the mineralogy of the detrital fraction of the sediment are consistent with those of the magnetic assemblage together these data point to the conclusion that a subsidiary low latitude possibly aeolian detrital flux supplements high latitude ice rafted input in glacial horizons of the cores the low latitude flux however is also identifiable in interglacial horizons independent evidence suggests that this low latitude aeolian flux may be derived from the sahel region of north africa and transported to the coring site by harmattan winds associated with saharan dust outbreaks

variation of magnetic properties in sediments from lake towuti indonesia and its paleoclimatic significance abstract we investigated the mineral magnetic behavior of sediments from lake towuti located in the eastern sulawesi ophiolite belt indonesia rock magnetic analysis supplemented by x ray diffraction and scanning electron microscopy analysis were performed on sediment core tow10 9b from the north basin of lake towuti to give insights on the environmental and sedimentary processes controlling the magnetic properties of the sediment and its paleoclimatic significance the results show that the core has three distinct zones of varying magnetic properties careful examination demonstrates that these zones correspond to varying levels of iron oxide dissolution and magnetite precipitation that are climatically and environmentally dependent the magnetically strongest zone is characterized by weak iron oxide dissolution and intense magnetite precipitation likely driven by changes in the stratification and or water level of the lake during dry conditions in marine isotope stage 2 mis2 period whereas the two magnetically weaker zones are characterized by signs of dissolution and correspond to relatively wet conditions respectively during marine isotope stage 3 mis3 and the holocene although our data show that major changes in concentration dependent parameters such as magnetic susceptibility and saturation isothermal remanent magnetization sirm in lake towuti sediment correlate with changes in regional rainfall many of the concentration changes are more strongly affected by in situ chemical processes than by changes in erosion and terrestrial sediment supply these findings urge caution in the interpretation of magnetic mineral concentration profiles as indicators of clastic sediment inputs

apparent correlation of palaeomagnetic intensity and climatic records in deep sea sediments most reports of a correlation between pleistocene climate and geomagnetic field intensity rely strongly on the assumption that sediment natural remanent magnetic nrm intensity provides a record of geomagnetic field strength and is not sensitive to local changes in properties of the sediment critical assessment of relevant data presented here and elsewhere1 2 from deep sea sediment cores shows that a pronounced dependence of nrm intensity on sediment composition can occur which implies that this assumption is unlikely to be generally valid as sediment composition often reflects varying depositional conditions induced by climatic change the significance of correlations proposed between pleistocene palaeomagnetism and climatic indicators in deep sea sediments may be less dramatic than sometimes supposed

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

climate change during the last deglaciation in antarctica greenland ice core records provide clear evidence of rapid changes in climate in a variety of climate indicators in this work rapid climate change events in the northern and southern hemispheres are compared on the basis of an examination of changes in atmospheric circulation developed from two ice cores high resolution glaciochemical series covering the period 10 000 to 16 000 years ago from a central greenland ice core and a new site in east antarctica display similar variability these findings suggest that rapid climate change events occur more frequently in antarctica than previously demonstrated

correlation between indian ocean summer monsoon and north atlantic climate during the holocene there has been a number of investigations for the correlation between the asia monsoon and the north atlantic climate for the last glacial however little research has been done for the present interglacial the holocene here we present for the first time a high resolution composite proxy record for the indian ocean summer monsoon spanning around 12 000 years based on the 13c time series of both a single plant species carex mulieensis remains cellulose and the total plant assemblage cellulose in the hongyuan peat bog from the tibet plateau the records show that the strength of the indian ocean summer monsoon had abrupt variations during the last 12 000 years the weakest monsoon occurred in the younger dryas period following rapid strengthening from around 11 200 to 10 800 a bp the monsoon kept a generally strong level for around 5300 years from around 5500 a bp onwards the monsoon strength tended to gradual decrease in addition there are a series of abrupt variation events of the monsoon strength on centennial to millennial time scales which superimpose the general tendency of the monsoon variation in every case when the ice rafted debris events in the north atlantic occurred the summer monsoon strength decreased correspondingly these evidences show that teleconnection between the indian ocean summer monsoon and the north atlantic climate is present not only in the last glacial but also in the holocene which may be linked to abrupt reorganizations of the ocean thermohaline circulation leading to redistribution of energy changing temperature and moisture gradient over the southern subtropical indian ocean and eventually controlling the variability of the indian ocean summer monsoon

magnetic mineral diagenesis in the river dominated inner shelf of the east china sea china the inner shelf of the east china sea is a river dominated margin characterized by fine grained mud deposits and a rapid sedimentation rate three short sediment cores 2 7 m in length were examined to characterize spatial variations in magnetic mineral diagenesis the sediment cores were analyzed for sedimentation rates magnetic properties particle size distribution organic carbon and total sulfur content the two more proximal cores with higher sedimentation rates 2 2 cm yr and 0 96 cm yr do not exhibit obvious effects of reductive dissolution of magnetite with increasing depth which is consistent with their lower total sulfur content the offshore core a12 4 which has a lower sedimentation rate contains clear evidence of magnetite dissolution and increasing total sulfur content with depth the three cores have a similar sediment source and organic matter input therefore we suggest that a higher sedimentation rate will lead to less reductive diagenesis of magnetite assuming that other factors are constant the iron to sulfate reduction boundary i e revealed by the onset of a rapid decline of magnetic susceptibility is located 1 0 m below seafloor in core a12 4 this is much deeper than is reported in many other coastal marine environments and can be explained by the higher sedimentation rate the presence of refractory terrestrial organic matter and an abundant input of detrital iron oxides this study demonstrates that analyses of the magnetic mineral zonation provide a straightforward approach to assess diagenetic organic carbon decomposition pathways in marine environments

mineral magnetic study of lacustrine sediments from lake pumoyum co southern tibet over the last 19 ka and paleoenvironmental significance abstract high resolution proxy records from tibetan plateau are essential to understand the past climatic and environmental changes in this work we conducted systematic environmental magnetic studies on lacustrine sediments from lake pumoyum co southern tibet spanning from the last deglaciation 19 ka to present we correlated the magnetic proxies in the lake core with environmental changes the magnetic proxies from the 3 units were studied both unit 3 19 13 2 ka and unit 2 13 2 8 4 ka contain evidences for an anoxic or sub anoxic environment fine grained greigite dominates the bulk magnetic properties of unit 3 while both magnetite and greigite coexist in unit 2 overall this reveals a transition from an anoxic environment to an oxic environment in contrast unit 1 8 4 ka present spans the holocene when the lake environment was oxic there is an increasing trend in the concentration of magnetic minerals which reflects an increasing transport of magnetic minerals from the catchment into the lake due to the increased post glacial melt water flow although different mechanisms affect the magnetic assemblage and associated magnetic properties in the different units our results suggest that the magnetic proxies of the local lake environment on southern tibet are sensitive to environmental changes

tectonic and sedimentary evolution of the late miocene pleistocene dali basin in the southeast margin of the tibetan plateau evidences from anisotropy of magnetic susceptibility and rock magnetic data abstract the cenozoic dali basin located at the northeast of diancang shan and south of the first bend of yangtze river is tectonically controlled by the dali fault system in the southeast margin of the tibetan plateau the basin is filled with late miocene to pleistocene fluviolacustrine sediments which provide invaluable information about the tectonic deformation and drainage network reorganization in this area in this study we discuss the anisotropy of magnetic susceptibility ams of the dasongping section in the dali basin which spans an interval from 7 6 to 1 8 ma although rock magnetic experiments indicate that magnetite and hematite are the main remanence carriers hysteresis loops low values of bulk susceptibility and low temperature susceptibility suggest that paramagnetic minerals are major contributors to low field ams the rock magnetic parameters indicate that the dali basin experienced four stages of infilling and the sediment sources may have changed at 4 2 ma the clustering of the minimum principle axes k min nearly perpendicular to the bedding plane and the pronounced n s magnetic lineation parallel to the bedding plane indicate that the ams of the dali basin is a superimposed fabric consisting of a sedimentary compaction and a mild initial deformation overprint the well defined n s magnetic lineation is likely due to the nnw and nne oblique shear caused by the heqing and red river faults

magnetic characteristics of sediments from a radial sand ridge field in the south yellow sea eastern china and environmental implications during the mid to late holocene abstract proxy records from radial sand ridge fields are essential for understanding sedimentary environmental changes forced by climate driven coast and sea level variations that affect large river inlets we conducted a systematic environmental magnetic study on sediments from a radial sand ridge field in the south yellow sea eastern china from 41 6 to 0 m the sediments of core yz07 derive from river mouth littoral and modern tidal flat environments magnetic measurements indicate that magnetite and hematite dominate the studied magnetic mineral assemblages magnetic mineral contents are highest in the river mouth environment and lowest in the modern tidal flat environment the magnetic minerals in the core yz07 sediments can be attributed primarily to detrital inputs rather than biogenic sources the highest and sirm values and lowest arm sirm and arm values reflect relatively warm and humid climate conditions respectively during the period 7000 to 2900 a b p 41 6 24 73 m compared with the period 7000 to 2900 a b p 41 6 24 73 m the period between 2900 and 870 a b p 24 73 5 14 m is characterized by lower arm and sirm values and higher arm sirm and arm values which indicate cool and dry climatic conditions our results reconfirm known regional climatic events that demonstrate holocene climatic instability gradual decreases in and sirm and increases in arm sirm arm and fd characterize the sediments after 870 a b p 5 14 0 m as indicated in previous studies these changes were influenced by diversion of the yellow river additionally spectral analysis of the and arm sirm records reveals rapid climatic fluctuations on millennial and centennial scales that coincide with those recorded in marine sedimentary records from adjacent regional seas these results are important for investigations into the interactions between regional systems and global change in monsoonal climatic regions thus providing an example of the evolution of a large scale geomorphic feature resulting from river sea interaction

velocity map of the thwaites glacier catchment west antarctica the two dimensional surface velocity of thwaites glacier west antarctica was mapped with 23 ascending and 22 descending orbit european remote sensing satellite synthetic aperture radar ers sar interferograms time range 1995 2000 the velocity map covers 175 500 square km from the amundsen coast to the southern turning point of the satellite orbit and comprises over 80 of the thwaites catchment

metal enrichment and magnetic properties of core sediments from the eastern yellow sea east asia implications for paleo depositional change during the late pleistocene holocene transition abstract to investigate the paleo depositional environments sediment cores yj1 and yj2 from a tidal flat of the eastern yellow sea were analyzed for the vertical variations of metal concentrations particle size clay mineralogy magnetic properties and total organic carbon content toc fe and mn concentrations determined by both partial and total acid extraction increased at 15 m depth in yj1 and 10 m in yj2 the layer directly below these fe rich brownish horizons showed dramatic decreases in clay mineral content and trace metals zn pb cu cr co ni and as but increases in sand fraction magnetic susceptibility and toc all results were inverse in the upper metal rich layer these dramatic changes in multi parameters are likely due to an environmental change during the late pleistocene holocene transition the rapid environmental change sand rich and oxic clay rich and anoxic resulted in aqueous dissolution of redox sensitive metals e g fe and mn from the lower sandy layer materials the dissolved metals diffused upward and concomitantly were immobilized within the upper clay rich layer the reprecipitated fe or mn hydro oxides then scavenged trace metals by coprecipitation and or adsorption this study suggests that metal distribution patterns can provide new insights into the paleo depositional processes during the pleistocene holocene period

paleoenvironmental implications of rock magnetic properties of late quaternary sediment cores from the eastern equatorial atlantic rapid and nondestructive rock magnetic measurements of late quaternary sediment cores from the senegal continental slope and the sierra leone rise in the eastern equatorial atlantic correlate strongly with the specmap oxygen isotope master curve and carbonate content the rock magnetic paleoclimatic relationship results from differences in the concentration accumulation rate grain size and composition of magnetic minerals between glacials and interglacials at both sites magnetic mineral assemblages of glacial episodes are characterized by higher concentrations and accumulation rates of magnetic minerals by coarser grained ferrimagnetic minerals e g magnetite and by a lower ratio of ferrimagnetic to antiferromagnetic e g goethite hematite minerals by serving as a sensitive tracer for various deep sea sedimentary components rock magnetic properties can provide insights into changing sediment sources and fluxes and therefore are a useful addition to more traditional chemically and mineralogically based paleoceanographic techniques

late pleistocene evolution of the rhine meuse system in the southern north sea basin imprints of climate change sea level oscillation and glacio isostacy high resolution continuous core material geophysical measurements and hundreds of archived core descriptions enabled to identify 13 late pleistocene rhine meuse sedimentary units in the infill of the southern part of the north sea basin the netherlands northwestern europe this sediment record and a large set of optical stimulated luminescence dates 14c dates and biostratigraphical data allowed to establish detailed relationships between climate change sea level oscillation glaciation history and the sedimentary development of the rhine fluvial system during the last glacial cycle marine isotope stages 5e 2 eemian weichselian a well preserved eemian sediment record was encountered as the infill of a late saalian mis6 subglacial basin part of this record reflects groundwater rise controlled fine grained sedimentation as a result of postglacial early eemian sea level rise it shows strong analogy to developments known from the holocene rhine meuse delta outside of the glacial depressions near coastal deposits are only fragmentarily preserved the early glacial rhine sediment record is dominated by organic debris and peat layers marking landscape stability and low fluvial activity part of this record may have been formed under near coastal conditions significant amounts of reworked marine biomarkers in the lag deposits of early pleniglacial mis4 fluvial systems indicate that this period is characterized by extensive reworking of older mis5 near coastal sediments despite the marked early pleniglacial climatic cooling input of new sediment from the drainage basin was relatively low a feature that is related to the presence of regolith protective relic soil complexes in the basin during the early middle pleniglacial a major rhine avulsion indicates the system was in an aggrading mode and that sediment supply into the lower reaches of the rhine had strongly increased this increase in sediment supply coincided with the timing of major climate cooling that occurred from 50 to 45 ka onwards the increase in sediment supply is related to final breakup of the soil complexes in the drainage basin after 24 ka a strong input of coarse grained gravelly sediments was observed which indicates a strong increase in physical weathering processes and periglacial controlled supply of bedload sediment in the catchment a time delay between climate change 30 ka and channel belt aggradation 24 ka is explained as a result of transport path length between source and sink and or effects of higher continental runoff rates after 22 ka the late middle pleniglacial late pleniglacial and lateglacial rhine meuse record testifies for strong influence of glacio isostatic controlled differential upwarping of the study area glacio isostatic controlled forebulge upwarping and lateral valley tilting is shown to have deflected rhine meuse channel belts after 35 ka glacio isostatic upwarping is seen as the main cause for strong incision during the first phase of the late pleniglacial 30 24 ka at later stage glacio isostatic controlled incision was overruled due to high climate controlled sediment input from the catchment and probably initial glacio isostatic subsidence migration of channel belts towards the direction of the former centre of glacio isostatic uplift indicates that glacio isostacy influenced rhine meuse paleogeography until far into the lateglacial 2007 elsevier ltd all rights reserved

the effect of sea level climate and shelf physiography on the development of incised valley complexes a modern example from the east china sea abstract analysis of high resolution seismic reflection and sonar data from the east china sea ecs continental shelf reveals the presence of an extremely broad 330 km and deep maximum incision of 72 m incised valley complex whose development and subsequent fill is constrained to the end of the last glacial cycle 20 000 yr bp to present results from this study indicate that sea level change climate controlled discharge and sediment supply and shelf physiography were important factors in the development and subsequent fill of the ecs incised valley complex for example wet climatic conditions during the initial marine oxygen isotope stage mis 2 fall of sea level promoted fluvial erosion of the exposed shelf however the trend toward drier conditions during the mis 2 fall of sea level slowed the overall development of the incised valley complex to the point where only minor incision occurred during the maximum lowstand furthermore the low gradient morphology of the exposed outer shelf diminished the ability of fluvial systems to incise instead fluvial systems migrated laterally creating a shallow 300 km incised valley system on the outer shelf during the late mis 2 rise of sea level accommodation was generated within the flooded reaches of the valley complex however arid climatic conditions that prevailed at this time resulted in minor sediment delivery to the transgressive shoreline via the incised valley complex thus the upper part of the drowned lowstand fluvial deposits were exposed at the sea floor and reworked into a valley wide tidal bar and tidal sheet complex wetter climatic conditions during middle to late mis 1 resulted in abundant sediment delivery to the drowned parts of the valley complex estuary and buried lowstand fluvial deposits below the depth of tidal ravinement where they remained undisturbed current sequence stratigraphic models can be applied to the late quaternary stratigraphic secession of the ecs however these models are too simplistic because they rely largely on rates and directions of sea level change to explain stratal architectures although the extent and rate of sea level change is extremely important this study shows that high frequency climate change and shelf physiography also play important roles in the development of stratigraphic architectures these factors are particularly important for the development of incised valleys where they directly influence incised valley morphology and facies distributions

magnetite diagenesis in marine sediments from the oregon continental margin the magnetochemistry of sediments from the oregon continental margin is examined to determine the effects of iron sulfur diagenesis on the paleomagnetic record magnetic mineral dissolution and transformation into iron sulfides are a common feature in these suboxic to anoxic lutites these processes are evidenced in rapid decreases in natural remanent magnetization intensities and stabilities systematic changes in other rock magnetic properties and increases in solid phase sulfur concentrations with depth hysteresis measurements are used to evaluate downcore changes in magnetite concentration and grain size magnetite abundances decrease downcore from initial values of about 0 1 and nominal grain diameters lie within a narrow pseudosingle domain range of 0 08 to 0 6 m a first order surface area reaction model da dt ka is proposed to explain the magnetite dissolution mechanism where a is the total magnetite surface area and k is the rate constant the solution of this equation predicts that the surface area and concentration decrease exponentially and the concentration in addition depends on grain size application of this model in two cores where grain size varies with depth successfully explains the downcore profiles of both concentration and surface area despite extensive magnetite destruction magnetic directions in such sediments appear to reliably record long wavelength trends of the geomagnetic field

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

rock magnetic properties related to thermal treatment of siderite behavior and interpretation detailed analyses of rock magnetic experiments were conducted on the oxidation products of high purity natural crystalline siderite that were thermally treated in air atmosphere susceptibilities increase sharply between 400 and 530 c indicative of some new ferrimagnetic mineral phase generation both a drop between 540 and 590 c on the heating cycle and a dramatic increase from 590 c to 520 c on the cooling cycle occurred and are well consistent with the characteristic of magnetite a distinct hopkinson type susceptibility peak indicates that hematite is the terminal product if siderite is heated to 700 c over and over it has been revealed in detail that the original inverse magnetic susceptibility fabric contributed by the crystalline anisotropy of siderite in siderite bearing specimens is changed to a normal magnetic fabric during incremental heating over 410 490 c this is a result of dominant contributions from the distribution anisotropy of newly transformed ferromagnetic minerals a strong chemical viscous remanent magnetization could be produced during siderite oxidation in an external field rock magnetic experimental results show that magnetite maghemite and hematite are the transformation products of high temperature oxidation of siderite in air maghemite was not completely inverted to hematite even at temperature as high as 690 c during incremental thermal treatments the mineral transformation processes were confirmed by conventional optical microscopic observation x ray diffractometry and mossbauer spectroscopic analyses these results indicate that the rock magnetic methods used here are reliable and highly sensitive in detecting very small magnetic phase changes in rocks we conclude that these temperaturedependent variations of magnetic properties can be used as criteria for identification of siderite in rocks and sediments furthermore it is clear that great care should be exercised in thermal demagnetization of siderite bearing rocks in paleomagnetic magnetic anisotropy and rock magnetic studies

magnetic properties of tidal flat sediments on the yangtze coast china early diagenetic alteration and implications measurements of magnetic properties total organic carbon toc and total sulphur ts were performed on recent tidal flat sediments from the feng xian fx and bei bu gang bbg areas of the yangt

low temperature behavior and memory of iron rich titanomagnetites mt haruna japan and mt pinatubo philippines we report low temperature remanence and memory of octahedral crystals of titanomagnetite from mt haruna japan and mt pinatubo philippines the crystals have curie temperatures of 460 490 c indicating a low ti content 0 11 x 0 16 saturation isothermal remanence sirm produced at 20 k decreased rapidly in warming through the isotropic temperature 42 k ti 55 k where the first magnetocrystalline anisotropy constant k1 changes sign and momentarily vanishes 96 99 of the original sirm was demagnetized at ti and none was recovered in recooling from 300 k to 20 k sirm produced at 300 k decreased continuously in the course of zero field cooling leveling out around ti on rewarming to 300 k 45 60 of the initial sirm was recovered this memory or recovered remanence is very large compared to that of magnetite and must be due to domain walls that are more strongly pinned probably magnetostrictively by crystal defects which are common in natural crystals the present low temperature experiments provide a quick non destructive method of identifying iron rich titanomagnetites in soils sediments and rocks

low temperature magnetic behavior of titanomagnetites titanium substitution has a significant effect on the temperature dependence 5 300 k of low temperature saturation remanence and of initial susceptibility in synthetic and natural titanomagnetite fe3 xtixo4 0 x 0 4 and electronic and lattice relaxation phenomena over the entire titanomagnetite compositional range these features produce diagnostic magnetic behavior useful for titanomagnetite identification in natural samples moreover the apparent similarities between the thermal decay of low temperature remanence of titanomagnetite with pyrrhotite pure magnetite and superparamagnetic phases can lead to complications in interpreting low temperature remanence data when titanomagnetite is present

the sand ridge field of the south yellow sea origin by river sea interaction abstract the origin of a large field of sand ridges offshore from the north jiangsu coast in the south yellow sea has been investigated on the basis of bathymetry seabed samples high resolution seismic profiles and 31 to 71 m deep boreholes sediment composition including heavy minerals and clay minerals sampled from surface sediments shows that most of the sand was derived from the changjiang yangtze river but in the northern part of the field particularly the clay came from the huanghe yellow river seismic profiles show late pleistocene distributary channels of the ancient changjiang river underlying much of the southern part of the sand ridge field the holocene transgression cut a widespread ravinement surface reworking abundant late pleistocene sandy sediment the available sand was reworked by tidal currents into large ridges the location of the ridges is strongly influenced by relict channels in the southern part of the field and by tidal currents in the northern and especially the northeastern part of the field resulting in a radiating ridge pattern these ridges provide an example of the evolution of a large scale geomorphic feature resulting from river sea interaction in which climatic and sea level changes played an important role

the f ratio on 20 w during the north atlantic bloom experiment abstract we have used data gathered during the north atlantic bloom experiment to model new and total production and the f ratio on 20 w the results imply that as much as half the spring bloom total production occurs well in advance of stratification however although new production potentially equals export production into the interior of the ocean observations during nabe and the model suggest that this export may not be fully realized during the bloom and may be trapped and recycled in the upper water column during the year

rapid coupling between ice volume and polar temperature over the past 150 000 years a new approach to dating a continuous sea level record using speleothem u th ages shows that past variations in global ice volume occurred within centuries of polar climate change with rates of sea level rise reaching at least 1 metre per century

magnetic properties of biogenic soil greigite fe3s4 magnetic measurements were performed on soil samples which contained bacterial greigite the greigite containing soil horizon is characterized by sirm 70 ka m 1 and by q factors 5 alternating field af demagnetization curves of the nrm gave stable directions according to irm acquisition and alternating field demagnetization of the irm and arm the greigite in bulk soil samples shows single domain behaviour this sd behaviour is also confirmed by hysteresis and by frequency dependent susceptibility measurements the thermomagnetic behaviour was checked on extracted greigite the magnetic parameters of soil greigite are compared with parameters of sedimentary greigite and of bacterial magnetite

thermal alteration of the magnetic mineralogy in ferruginous rocks the northampton ironstone contains the paramagnetic minerals siderite and berthierine and a trace of the ferrimagnetic mineral magnetite the magnetic fabric of this sedimentary rock as defined by the anisotropy of magnetic susceptibility is controlled by bedding compaction but is inverse i e the maximum susceptibility axes are normal to the bedding plane this inverse fabric is attributed to the dominating presence of siderite the rocks were incrementally heated to 600 c and the magnetic fabric was measured at room temperature and at near liquid nitrogen temperature after each heating step cooling the samples in liquid nitrogen enhances the paramagnetic contribution to the magnetic fabric after heating the samples above 250 c the room temperature magnetic fabric became normal with the minimum susceptibility axes perpendicular to the bedding plane the low temperature magnetic fabric remains inverse until the samples are heated to about 500 c after heating to higher temperatures a normal fabric was observed at both room temperature and low temperature rock magnetic evidence shows that magnetite is created during the heating the start of mineralogical changes in the rock was detected by electron spin resonance spectroscopy powder x ray diffraction and acquisition of isothermal remanence berthierine starts to break down at approximately 250 c and is totally oxidized by 500 c the creation of magnetite in the heating experiments corresponds with this mineralogical change the change in the room temperature magnetic fabric is associated with the decomposition of berthierine part of which alters to magnetite the new magnetite phase has a normal magnetic fabric which overprints the inverse magnetic fabric of siderite

magnetic and geochemical evidence of yellow and yangtze river influence on tidal flat deposits in northern jiangsu plain china abstract the formation of a broad tidal flat along the coast of the northern jiangsu province of china depends largely on the sediment supply from the yellow and yangtze rivers although the relative contributions from each of these two large rivers remain uncertain knowledge of sediment sources to the tidal flat is critical for understanding the evolution of this muddy coast impacted by the large rivers the present study focuses on tracking the sediment source of the tidal flat deposits based on sediment magnetic properties and geochemical analyses as well as statistical analysis the study shows that sediments to the north of yangkougang site 9 have lower values of saturation isothermal remanence magnetization sirm magnetic susceptibility demagnetization parameter s 100 ratios lower fe al values and higher ca concentrations while the opposite is true for samples south to haozhigang site 18 in addition sirm values of the 63 m fractions generally display increasing trend from north to south these results suggest that sediment sources rather than particle size variation are the dominant factors influencing the bulk magnetic properties in light of the sediment composition comparison between the yellow river and yangtze river factor analysis is used to identify sediment source of the tidal flat sediments it is indicated that the yellow river in its former course is the dominant supplier for sites to the north of yangkougang site 9 while the yangtze river is the dominant supplier for sites to the south of haozhigang site 18 the coast between yangkougang site 9 and haozhigang site 18 is a transition zone influenced by both rivers the inferred provenance contrasts are consistent with the pattern of coastal geomorphological evolution our data also suggest that sediments eroded from the former yellow river delta have contributed to the evolution of the yangtze estuary in historical time this study demonstrates that a combined magnetic and geochemical fingerprinting techniques in couple with statistical analysis is valuable for identifying sediment sources of tidal flats and deltas influenced by large rivers in the world

holocene variability of the kuroshio current in the okinawa trough northwestern pacific ocean abstract cores 255 and b 3gc from the southern and northern okinawa trough respectively were studied for determining the variability of the kuroshio current on centennial scales during the holocene based on detailed ams 14 c dates stable isotope and planktonic foraminiferal distribution the main flow of the kuroshio current was inferred to re enter the okinawa trough at 7 3 calendar cal kyr bp leading to abrupt changes in sedimentation rate remarkably increased abundance of the kuroshio current indicator pulleniatina obliquiloculata increased sea surface temperature sst and depth of thermocline dot during 4 6 2 7 cal kyr bp the abundance of p obliquiloculata sharply decreased corresponding to a decreases in sst and dot implying that the influence of the kuroshio current weakened at that time possibly as a result of the intensified winter monsoon significantly the kuroshio current proxies e g the difference in sst between the southern and northern okinawa trough display periodicities of 1500 yr and 700 800 yr ascribed to the second harmonic of the 1500 yr cycle in oceanic thermohaline circulation during the holocene the holocene events at 0 6 1 7 3 3 4 6 5 9 8 1 9 4 cal kyr bp in the okinawa trough appear to be the most recent manifestation of the millennial scale climate cycle recorded in the north atlantic arabian sea marine sediment cores and greenland ice cores suggesting global climatic tele connections

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

diagenetic formation of ferrimagnetic iron sulphide minerals in rapidly deposited marine sediments south island new zealand abstract detailed magnetostratigraphic studies of late neogene siliciclastic sediments of the awatere group south island new zealand 41 45 s 174 05 e have revealed a wide range of palaeomagnetic behaviour examination of rock magnetic properties was undertaken using conventional palaeomagnetic techniques and thermomagnetic x ray diffraction and electron microprobe analyses these analyses indicate that the ferrimagnetic iron sulphide minerals greigite and pyrrhotite are responsible for a stable and intense magnetic remanence in fine grained sediments whereas titanomagnetite is the only remanence bearing mineral identified in coarser grained sediments which are less strongly and less stably magnetised than the fine grained sediments detrital titanomagnetite grains are likely to have undergone dissolution during early diagenesis as a result of iron sulphide formation which occurs commonly in rapidly deposited anoxic sediments that support active sulphate reduction and h 2 s formation preservation of greigite and pyrrhotite is inferred to result from the arrest of the pyritisation process probably due to the low permeability of the fine grained sediments and consumption of available h 2 s before full reaction to pyrite occurred relative palaeomagnetic instability and weak remanence intensities in coarser grained sediments is likely to be due to low titanomagnetite concentrations resulting from titanomagnetite dissolution

magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern mediterranean sea summary magnetic properties irm arm xin s ratio at 0 3 t room temperature rt hysteresis and thermomagnetic curves and geochemical data fe s mn al ti organic c were studied in two eastern mediterranean boxcores abc26 and bc19 at a resolution of 3 5 mm the boxcores contain sapropel s1 9 6 kyr bp at a few decimetres below seafloor the magnetic fraction consists predominantly of single domain sd to pseudo singledomain psd magnetite in the entire cores the original input of magnetic grains comes from two sources aeolian dust both cores and volcanic ash from the minoan eruption of santorini core bc19 only non steady state diagenesis has changed the magnetic mineralogy considerably in these alternating organic rich organic poor sediments during deposition of sapropel s1 reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities coarser magnetic grain sizes and partial maghemitization in thermomagnetic curves two types of pyrite can be identified one oxidizes below 450 uc and the other above 450 uc the higher oxidation temperature is predominantly found below the sapropel this may be related to the microtexture of pyrite which is euhedral below sapropels and mainly framboidal within sapropels since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half c 5 cm of the sapropel the oxidized part of the sapropel is enriched in diagenetically formed fe oxides with relatively high coercivity and arm the maximum coercivity is found in a distinct layer between the present day mn and fe redox boundaries at the top of the unoxidized sapropel the freshly precipitated fe oxides in this centimetre thick layer contain a mixture of superparamagnetic sp grains and high coercivity sd magnetite higher in the oxidized zone the freshly precipitated fe oxides have aged into generally slightly lower coercivity sd grains with relatively high arm in addition to the diagenetic formation of fe oxides at the top of the sapropel formation of a ferrimagnetic fe monosulphide may have occurred within the sapropel during later stages of diagenesis which may have enhanced the arm signal in the organic rich interval in particular

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

field and temperature behavior of remanence in synthetic goethite paleomagnetic implications synthetic powders of pure goethite exhibit an antiferromagnetic behavior and negligible isothermal remanent magnetization up to 4 tesla however thermoremanence up to 0 3 am kg 1 can be imparted to the samples high field measurements show median acquisition field of 9 13 t and suggest saturation fields of the order of 10 t large increase in remanence at low temperature is an intrinsic feature of goethite the weak ferromagnetism observed is linked to a bulk origin for spin imbalance rather than to an effect of very fine grain size or surface defects the results are compared with properties of rocks bearing goethite and hematite

asian monsoon oscillations in the northeastern qinghai tibet plateau since the late glacial as interpreted from visible reflectance of qinghai lake sediments abstract qinghai lake is a large saline lake on the qinghai tibetan plateau of central asia that is effected by both the indian and asian monsoons we used reflectance spectroscopy to characterize the sediments in a 795 cm long core taken from the southeastern part of the lake sediment redness which is related to iron oxide content seems to monitor paleoclimatic changes in the core iron oxides appear to be eroded from nearby red beds or loess deposits and are transported by fluvial means into the lake thus redness increases at times of increased precipitation that is as monsoon strength increases our redness monsoon proxy shows climate changes on several times scales on a millennial scale it records humid conditions during the early and mid holocene from about 4200 to 2300 yr bp low redness values suggest a two millennial long dry period which in the late holocene is followed by a more humid period on a centennial scale the redness proxy records not only the little ice age but also the medieval warm period the dark ages cool period and the roman warm period time series analysis of the redness record indicates a 200 yr frequency which corresponds to the de vries solar cycle suggesting that in addition to insolation changes resulting from orbital variations solar forcing also results from cyclic changes in the sun s luminosity

toward the discrimination of fine grained ferrimagnets by magnetic measurements in lake and near shore marine sediments the magnetic properties of low field susceptibility frequency dependent susceptibility fd and susceptibility of anhysteretic remanent magnetisation arm are used to define sets of natural soil and sediment samples within which by the criteria of king et al 1982 and maher 1988 the modal ferrimagnetic grain diameter is less than 0 07 0 1 m within this sample set two distinct groups with low and high values respectively for the quotients arm and arm fd are defined the first group includes sediment samples from sites where published studies propose a detrital origin for the fine grained ferrimagnetic content where catchment samples are available for comparison they fall within the same envelope as do clays from palaeosol samples within chinese loess this envelope of low quotient values also overlaps with the values for the fine grained synthetic magnetite samples within maher s 1988 new mt series the high quotient envelope of values includes sediments from the adriatic sea and clays from saltmarsh and shallow water marine sediments in nw britain in these cases no catchment source is postulated for the fine grained magnetite the size range of magnetite in this set appears to be almost exclusively stable single domain ssd and a bacterial origin seems likely sample sets from estuarine environments between river inflow sites and the open sea show intermediate values which in the case of the potomac are ordered by distance down river although at this stage magnetic measurements alone cannot discriminate between bacterial and fine grained detrital ferrimagnets in sediments they hold out some promise of doing so provided the distinctions proposed here can be substantiated by transmission electron microscopy

sea level changes forced ice breakouts in the last glacial cycle new results from coral terraces abstract sea level cycles recorded by coral terraces at huon peninsula hp in papua new guinea match rapid climate changes that occurred between 30 000 and 65 000 years ago seen in greenland ice cores and marine sediments each cycle of 6000 7000 years ended with a sea level rise of 10 15 m lasting 1000 2000 years following a longer period of falling sea level precise dating shows that each rise corresponds to a heinrich episode of ice rafted detritus in north atlantic signalling massive ice outbreak from north america sea level may be the trigger that forced near synchronous breakouts of ice from north america and eastern greenland the hp sea level changes also correspond to similar cycles in benthic oxygen isotopes reported from the north atlantic which are too large to be explained entirely in terms of ice volumes jointly the sea level and isotope records suggest that the north atlantic deep ocean cooled as sea level fell and warmed as sea level rose in each 6000 year cycle

magnetic mineral dissolution in pleistocene fluvio lacustrine sediments nihewan basin north china abstract the nihewan fluvio lacustrine sequence north china has recorded late pliocene pleistocene climatic and environmental changes and contains valuable information on early human evolution in high latitude east asia we carried out a combined mineral magnetic and geochemical investigation on a sequence from the xiantai section eastern nihewan basin results suggest that large amplitude magnetic property variations between so called high magnetic and low magnetic units mainly result from preservation dissolution cycles of detrital magnetic minerals in alternating oxic and anoxic depositional environments in our preservation dissolution model the high and low magnetic units represent glacial and interglacial deposits respectively this contributes to a better understanding of the link between magnetic properties and climate in the xiantai fluvio lacustrine sequence based upon this relationship early humans may have occupied the xiantai and xiaochangliang sites during an interglacial period during both interglacial and glacial periods at the donggutuo site and during a glacial period at the maliang site our work provides a paleoenvironmental context for early human adaptation and occupation in mainland east asia during the early pleistocene

stratigraphic development during the late pleistocene and holocene offshore of the yellow river delta bohai sea abstract a 61 m long sediment core hb 1 and 690 km of high resolution seismic profiles from offshore of the yellow river delta bohai sea were analyzed to document the stratigraphy and sea level changes during the late pleistocene and holocene accelerator mass spectrometry 14c dating and analyses of benthic foraminifera ostracods the mineral composition and sedimentary characteristics were performed for core hb 1 and seven depositional units du 1 du 7 in descending order were identified the seismic reflection data were interpreted in light of the sedimentological data of the core and correlated with other well studied cores obtained previously in the bohai sea area seven seismic units su 1 to su 7 in descending order were distinguished and interpreted as follows su 7 corresponds to marine facies in marine isotopic stage mis 5 su 6 to terrestrial facies in mis 4 su 5 and su 4 to alternating terrestrial and marine facies du 7 du 5 in mis 3 su 3 to terrestrial facies du 4 in mis 2 su 2 to holocene marine facies du 3 and du 2 and su 1 to modern yellow river delta sediments deposited since 1855 du 1 the sedimentary facies from du 7 to du 5 reflect sea level fluctuations during mis 3 and the boundary between du 5 and du 6 which coincides with that between su 4 and su 5 is a distinctive laterally continuous undulating erosion surface with up to 20 m of relief this surface reflects subaerial exposure between transgressions during mis 3 estimated sea levels during mis 3 ranged from 35 5 to 60 5 m or lower with short term fluctuations of 20 m sedimentary environments in the bohai sea area were governed mainly by eustatic sea level changes and the bohai strait topography which controls the entry of sea water into the bohai sea area the mineral composition of the sediment core suggests that the yellow river did not discharge into the bohai sea or at least did not influence the study area significantly during parts of mis 3 and mis 2 to the early holocene 11 8 5 cal kyr bp

the yangtze river deposition in southern yellow sea during marine oxygen isotope stage 3 and its implications for sea level changes abstract the depositional history of the lower yangtze river and sea level changes during marine oxygen isotope stage mis 3 was established using three long drill cores from the northern yangtze deltaic plain and southern yellow sea by using sedimentary analysis and ams 14c dates voluminous channel deposits of the lower yangtze river in mis 3 were found from the northern deltaic plain and offshore area with a thickness of over 30 m the thick channel deposits are characterized by massive medium to fine sand deposits with sporadic tidal influence during mis 3 the yangtze river appears to have mainly migrated between the modern river mouth and middle jiangsu coastal plain and likely built a delta complex in the field of yangtze sand shoal in northern east china sea a large sediment supply and rapid sea level variations promoted rapid progradation of the delta onto the flat shelf the highest sea levels during mis 3 are estimated to have reached 25 5 m below the present sea level