magnetic petrology of equatorial atlantic sediments electron microscopy results and their implications for environmental magnetic interpretation 1 the magnetic microparticle and nanoparticle inventories of marine sediments from equatorial atlantic sites were investigated by scanning and transmission electron microscopy to classify all present detrital and authigenic magnetic mineral species and to investigate their regional distribution origin transport and preservation this information is used to establish source to sink relations and to constrain environmental magnetic proxy interpretations for this area magnetic extracts were prepared from sediments of three supralysoclinal open ocean gravity cores located at the ceara rise geob 1523 1 3 49 9 n 41 37 3 w the mid atlantic ridge geob 4313 2 4 02 8 n 33 26 3 w and the sierra leone rise geob 2910 1 4 50 7 n 21 03 2 w sediments from two depths corresponding to marine isotope stages 4 and 5 5 were processed this selection represents glacial and interglacial conditions of sedimentation for the western central and eastern equatorial atlantic and avoids interferences from subsurface and anoxic processes crystallographic elemental morphological and granulometric data of more than 2000 magnetic particles were collected by scanning and transmission electron microscopy on basis of these properties nine particle classes could be defined detrital magnetite titanomagnetite fragmental and euhedral titanomagnetite hemoilmentite intergrowths silicates with magnetic inclusions microcrystalline hematite magnetite spherules bacterial magnetite goethite needles and nanoparticle clusters each class can be associated with fluvial eolian subaeric and submarine volcanic biogenic or chemogenic sources large scale sedimentation patterns are delineated as well detrital magnetite is typical of amazon discharge fragmental titanomagnetite is a submarine weathering product of mid ocean ridge basalts and titanomagnetite hemoilmenite intergrowths are common magnetic particles in west african dust this clear regionalization underlines that magnetic petrology is an excellent indicator of source to sink relations hematite encrustations magnetic spherules and nanoparticle clusters were found at all investigated sites while bacterial magnetite and authigenic hematite were only detected at the more oxic western site at the eastern site surface pits and crevices were seen on the crystal faces indicating subtle early diagenetic reductive dissolution it was observed that paleoclimatic signatures of magnetogranulometric parameters such as the ratio of anhysteretic and isothermal remanent magnetizations can be formed either by mixing of multiple sources with separate relatively narrow grain size ranges western site or by variable sorting of a single source with a broad grain size distribution eastern site hematite goethite and possibly ferrihydrite nanoparticles occur in all sediment cores studied and have either high coercive or superparamagnetic properties depending on their partly ultrafine grain sizes these two magnetic fractions are generally discussed as separate fractions but we suggest that they could actually be genetically linked

magnetic minerals as recorders of weathering diagenesis and paleoclimate a core outcrop comparison of paleocene eocene paleosols in the bighorn basin wy usa abstract magnetic minerals in paleosols hold important clues to the environmental conditions in which the original soil formed however efforts to quantify parameters such as mean annual precipitation map using magnetic properties are still in their infancy here we test the idea that diagenetic processes and surficial weathering affect the magnetic minerals preserved in paleosols particularly in pre quaternary systems that have received far less attention compared to more recent soils and paleosols we evaluate the magnetic properties of non loessic paleosols across the paleocene eocene thermal maximum a short term global warming episode that occurred at 55 5 ma in the bighorn basin wy we compare data from nine paleosol layers sampled from outcrop each of which has been exposed to surficial weathering to the equivalent paleosols sampled from drill core all of which are preserved below a pervasive surficial weathering front and are presumed to be unweathered comparisons reveal an increase in magnetization in outcrops compared with core equivalents which is principally driven by secondary hematite production authigenic hematite production in outcrops presents a complication for goethite hematite based paleoprecipitation proxies where estimates will be biased toward drier climate regimes the occurrence of low coercivity minerals is more consistent between core and outcrop however we propose an alteration process for pedogenic magnetite that is observed in both core and outcrop where pedogenic magnetite becomes progressively oxidized leading to higher mean coercivities and broader coercivity distributions compared to modern pedogenic magnetite this combination of diagenetic processes and surface weathering influences the magnetic properties of paleosols despite these changes magnetic enhancement ratios from b horizons correlate with independent map estimates from geochemical proxies which suggests that paleoprecipitation information is preserved future work should continue to address these complications by developing useful protocols that isolate the magnetic properties that are most resistant to alteration and remain strong indicators of map and climate

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

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

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

the low temperature besnus magnetic transition signals due to monoclinic and hexagonal pyrrhotite kung suan ho and wei teh jiang kindly supplied monoclinic pyrrhotite crystals from museum and ore mineral collections respectively c s h acknowledges funding from the central geological survey and ministry of science and technology r o c through grants 104 5226904000 02 01 and most 105 2116 m 001 018 respectively a p r acknowledges funding from the australian research council through grant dp160100805

magnetic mineral assemblages in soils and paleosols as the basis for paleoprecipitation proxies a review of magnetic methods and challenges abstract magnetic iron oxide minerals principally magnetite maghemite hematite and goethite are formed in well drained soils in response to a suite of physical chemical and biological factors despite a wide range of complexity in the pedogenic processes that lead to magnetic mineral formation dissolution and transformation there are well documented empirical relationships between various magnetic mineral assemblages in soils with environmental and climatic conditions recently there has been an increase in the number of quantitative magnetic paleoprecipitation proxies that have been developed and there is great potential for magnetic methods to be used in the geologic record to develop reconstructions of past climates magnetic paleoprecipitation proxies have been widely utilized in quaternary or younger loess paleosol systems however they have yet to be utilized in the pre quaternary fossil record future studies of magnetic mineralogy of soils and paleosols should aim to explore non loessic modern soils and pre quaternary paleosols with more focus on understanding the interaction between magnetic mineral assemblages and soil moisture applications of existing and novel magnetic paleoprecipitation proxies in the fossil record should prove to be a valuable resource for paleoclimatologists

a new method in mineral magnetism for the separation of weak antiferromagnetic signal from a strong ferrimagnetic background 1 this paper describes a new magnetic method for determining the contribution of weakly magnetic hematite against a strongly magnetic e g magnetite background the method involves measurements of mfr a residual or final remanence after hysteretic demagnetization of saturated isothermal remanent magnetization in terms of sensitivity and precision our proposed method is superior to the currently popular approach known as the hirm method compared to the latter mfr has no error amplification caused by subtraction of terms the method utilizes the available software for hysteretic demagnetization function on an automated vibrating sample magnetometer vsm this in turn automatically decreases some of the disturbing effects of the strong magnetic background e g magnetic viscosity initially non zero offset of hirm for partially oxidized magnetite etc

application and evaluation of biomagnetic and biochemical monitoring of the dispersion and deposition of volcanically derived particles at mt etna italy article i nfo article history received 6 august 2009 accepted 4 january 2010 available online xxxx biomagnetic monitoring using tree leaves as passive surfaces for particle collection has been shown to be a promising technique for assessing the dispersion and deposition of particles in the context of anthropogenic pollution by comparing leaves magnetic properties with trace metal levels measured in the leaves we here assess the utility of the biomagnetic technique as a sensitive fast and inexpensive method for assessment of volcanic plume deposition samples of sweet chestnut leaves castanea sativa were collected from the area surrounding mt etna volcano in sicily during the 2008 growing season when the volcano was displaying mild eruptive activity previous work has shown that the trace metal concentrations of these leaves show promise as a bio indicator of volcanic gas aerosol and ash deposition on the flanks of mt etna for 2008 icp ms analysis of the elemental abundances within the leaves showed that as cd cu mo tl k b al and co displayed elevated concentrations downwind of the volcanic source to the e ese but with overall reduced concentrations relative to 2007 less explosive activity than 2007 and a broader more easterly wind field may have distributed the volcanic plume over a wider area both of which would account for reduced trace element concentrations in 2008 correspondence of elevated concentrations in both years 2007 and 2008 with their respective wind fields suggests that plume deposition is the controlling factor rather than variability in the soils and that these leaves do indeed have potential as bio indicators of the plume s dispersion magnetic analysis of the leaves shows that the spatial distribution of saturation isothermal remanent magnetisation sirm and magnetic susceptibility lf values display a strong correlation with the wind influenced plume transport direction for 2008 with elevated concentrations of magnetic minerals on the eastern flanks in broad agreement with the icp ms data this spatial distribution provides further evidence of plume variability as the main control on the concentrations of magnetic particles on the leaf surfaces and on elemental uptake by the tree and suggests that biomagnetic monitoring may also hold promise as a method of assessing the dispersion and impacts of volcanic plumes the dominant magnetic mineral on the leaf surfaces is a magnetite like mineral contributing 90 of the sirm of coarse multi domain md grain size 5t o 15 m a volcanogenic source is most likely as magnetites from anthropogenic sources are typically an order of magnitude smaller in grain size 0 1 1 m these new results from the use of environmental magnetism on leaves in a volcanically affected region suggest that biomagnetic monitoring offers a new sensitive and rapid means for the assessment of volcanic plume deposition over wide areas

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

a rock magnetic study of loess from the west kunlun mountains west kunlun mountains have continuous loess deposits however very few papers have explored the rock magnetic characteristics of loess deposited there thus although kunlun mountains loess is one of the useful paleoclimate archives its importance has not been emphasized here we present detailed rock magnetic and bulk grain size studies on a 207 m loess core on the northern slope of the west kunlun mountains we find that magnetic susceptibility of loess from the northern slope of the west kunlun mountains is not controlled by changes in the concentration of ultrafine pedogenic magnetite and maghemite but instead controlled by changes in the concentration of aeolian multidomain magnetite and maghemite this is unsurprising given the low rainfall of the kunlun region and the lack of postdepositional weathering and soil formation in these aeolian sequences in addition we find that magnetic susceptibility values increase dramatically at 111 m corresponding to an age of similar to 0 5 ma the magnetic susceptibility increase is accompanied by coarsening of both bulk and magnetic grain size and softening of magnetic mineralogy we tentatively tie these changes in rock magnetic and grain size parameter records to an expansion of desert environment

source of the climate signal recorded by magnetic susceptibility variations in indian ocean sediments the origins of magnetic susceptibility variations in deep sea sediments from the indian ocean ocean drilling program odp leg 117 have been examined to identify the specific connections between climate shifts and sediment magnetic properties in a previous study the magnetic susceptibility variations in odp hole 722b were identified as an outstanding proxy paleoceanographic record despite evidence of postdepositional loss of magnetic minerals through reductive diagenesis this paradox is addressed by assessing the contributions of ferrimagnetic detrital iron oxides bacterial magnetosomes and paramagnetic detrital fe silicate minerals to the magnetic susceptibility signal in addition to detailed magnetic analyses mineralogical morphological and grain size data have been obtained from representative magnetic extracts for hole 722b we find that magnetic responses to climate change result from 1 fluctuations in the volume magnetic susceptibility which is primarily controlled by carbonate dilution 2 a ferrimagnetic signal which is restricted to the upper 7 meters below sea floor mbsf and which largely reflects source area aridity and 3 a paramagnetic susceptibility record below 7 mbsf which is coincident in frequency with variations in lithogenic grain size

fingerprinting upland sediment sources particle size specific magnetic linkages between soils lake sediments and suspended sediments accelerated erosion of fine grained sediment is an environmental problem of international dimensions erosion control strategies and targeting of mitigation measures require robust and quantitative identification of sediment sources here we use magnetic fingerprinting to characterize soils and examine their affinity with and contribution to suspended sediments transported within two subcatchments feeding bassenthwaite lake northwest england a high resolution soil magnetic susceptibility survey was made using a field susceptometer zh instruments sm400 probe combining the spatial and vertical down profile soil magnetic data a subset of soil profiles was selected for detailed laboratory based magnetic remanence analyses the magnetic properties of the catchment soils are highly particle size dependent magnetic analyses were performed on the 31 63 m fraction for particle size specific comparison both with the suspended sediments and lake sediments fuzzy cluster analysis groups the soil magnetic data into six clusters apparently reflecting variations in parent material and horizon type with three magnetically hard soils as unclassified outliers examination of the cluster affinity of the soils suspended sediments and lake sediments indicates that topsoils of the upper newlands valley and subsoils around keskadale beck are a major source of the newlands beck suspended load and the recent post nineteenth century sediments in the deep lake basin older lake sediments show strong affinity with a small number of the derwent suspended sediments and one of the glenderamackin soils a large number of derwent suspended sediments show no affinity with any of the soils or lake sediments instead forming a coherent discrete and statistically unclassified group possibly resulting from mixing between the magnetically hard subsoils of the medium to high altitude glenderamackin and troutbeck areas and softer lower altitude glenderamackin soils the lack of any affinity of these suspended sediments with the lake sediments may indicate deposition along the derwent flood plain and or in the shallow delta of lake bassenthwaite particle size specific magnetic fingerprinting is thus shown to be both highly discriminatory and quantitatively robust even within the homogeneous geological units of this catchment area such a methodological approach has important implications for small large scale catchment management where sources of sediment arising from areas with uniform geology have been difficult to determine using other approaches such as geochemical or radionuclide analyses

identifying goethite and hematite from rock magnetic measurements of soils and sediments we describe a sequence of experiments involving the acquisition of isothermal remanent magnetization irm in high 2 t fields followed by orthogonal demagnetization and the cooling and heating of remanent magnetization mr over the temperature range 196 c to 680 c the main aim of these experiments is to improve the basis for identifying the imperfect antiferromagnetic minerals contributing to the magnetic properties of natural soil and sediment samples which often contain complex mineral mixtures the procedures developed are first applied to a series of ore and synthetic samples of hematite and goethite each characterized by x ray diffraction xrd spectra and second to controlled mixtures of the two minerals the results confirm the mineral diagnostic nature of the experiments used they are subsequently used to identify goethite and hematite contributions to the rock magnetic properties of a variety of soils and recent sediments goethite can be unambiguously identified often accompanied by hematite in the majority of the samples studied despite indications from the synthetic mixtures that the ratio of goethite to hematite may have to exceed an order of magnitude before the goethite signatures are readily recognizable the rock magnetic tests are a much more sensitive basis for recognizing the presence of goethite in natural samples than are xrd analyses the results suggest that goethite s contribution to the rock magnetic properties of soil and sediment samples may often have been underestimated

distinguishing sediments from the yangtze and yellow rivers china a mineral magnetic approach the yellow river and the yangtze river contribute 10 of the global fluvial sediment flux to the oceans proper characterization of the sediments of the two rivers is critical to the knowledge of their fate in the marginal seas of the west pacific ocean magnetic measurements have been made on bulk sediments as well as on separated particle size fractions of representative samples from the yellow and yangtze river estuaries with the purpose of providing an efficient means of differentiating both groups of river sediments from each other we found that on average the yangtze river estuary sediments have relatively higher ferrimagnetic mineral contents and ferrimagnetic to antiferromagentic ratios compared with the yellow river estuary sediments a diagram of saturated isothermal remanent magnetization sirm versus the demagnetization parameter s 100 can clearly distinguish sediments from the two rivers detailed magnetic measurements carried out on particle size fractions provide additional confirmation

high field remanence properties of synthetic and natural submicrometre haematites and goethites significance for environmental contexts haematite and goethite are significant magnetic components both of marine and terrestrial sediments variable magnetic behaviour in haematite and goethite has been reported reflecting variations in grain size crystal defects nonstoichiometry and mode of formation here we provide new data first for a range of synthetic haematite and goethite powders of known grain size and second for a variety of haematite and goethite bearing natural samples including red bed samples and modern and fossil soils based on the synthetic data we identify two high field parameters which may be of value in identifying and characterizing the high coercivity components of natural environmental samples even when these are dominated magnetically by the presence of trace concentrations of ferrimagnets h indicates the proportion of the room temperature rt remanence acquired in fields from 2 tesla t up to 7 t and hcool indicates the increase or decrease in high field remanence upon cooling in zero field to 77 k lt used in tandem these parameters can differentiate between goethite dominated and haematite dominated samples and indicate differences in haematite grain size h values for the synthetic haematites vary between 27 and 38 with some apparent grain size dependence and for the goethites between 84 and 92 hcool values range from 130 to 157 for the goethites and 75 to 95 for those haematites of grain size 100 nm

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

hirm variations in the chinese red clay sequence insights into pedogenesis in the dust source area abstract although extensive rock magnetic studies have been performed on the chinese loess paleosol sediments few comparable studies have been applied to the underlying red clay sediments because of this paucity of data our understanding of the mineral magnetic properties of the red clay sequence and the paleoenvironmental information encoded in them is limited here we report hard isothermal remanent magnetization hirm variations from 8 1 to 1 2 ma in the lower part of the loess paleosol and the underlying red clay sequences of the chaona section on the chinese loess plateau the results indicate that there is a negative correlation between hirm and frequency dependence of magnetic susceptibility fd fd lf hf where lf and hf are magnetic susceptibility measured at 470 hz and 4700 hz respectively from 3 4 to 2 6 ma and a positive correlation between these two proxies from 8 1 to 3 4 ma and 2 6 to 1 2 ma we argue that the hirm variations from 8 1 to 3 4 ma and from 2 6 to 1 2 ma reflect hematite availability in the dust source region determined by the size of the area and climatic conditions of the dust source region the negative correlation between hirm and fd between 3 4 and 2 6 ma suggests that magnetic enhancement during this time interval may be related to the alteration of hematite goethite to magnetite maghemite we also find that hirm data between 8 1 and 3 4 ma show high coherence with the 100 kyr eccentricity signals suggesting eccentricity forcing of concentration variations of hematite in the dust source area higher resolution samples are needed to determine if concentration variations of hematite in the dust source area are coherent with the orbital obliquity and precession forcing signals

magnetic characterization of holocene sedimentation in the south atlantic surface sediment samples representative for the tropical and subtropical south atlantic 15 n to 40 s were investigated by isothermal magnetic methods to delineate magnetic mineral distribution patterns and to identify their predominant holocene climatic and oceanographic controls individual parameters reveal distinct yet frequently overlapping regional sedimentation characteristics a probabilistic fuzzy c means cluster analysis was applied to five concentration independent magnetic properties assessing magnetite to hematite ratios and diagnostic of bulk and fine particle magnetite grain size and coercivity spectra the resultant 10 cluster structures establish an oceanwide magnetic sediment classification scheme tracing the major terrigenous eolian and fluvial fluxes authigenic biogenic magnetite accumulation in high productivity areas transport by ocean current systems and effects of bottom water velocity on depositional regimes distinct dissimilarities in magnetic mineral inventories between the eastern and western basins of the south atlantic reflect prominent contrasts of both oceanic and continental influences

magnetic characterisation of present day deep sea sediments and sources in the north atlantic the north atlantic plays a key role in global climate through formation of north atlantic deep water which drives the thermohaline circulation to understand past and future climate change it is essential to understand the processes occurring within the present day north atlantic but ocean wide studies of present day sediment distribution and sources are relatively sparse here we use magnetic measurements to characterise the surface sediments of the north atlantic and identify the major climatic and oceanographic controls on their magnetic signatures the magnetic data and subsequent cluster analysis identify distinct spatial patterns of sediment sources and transport pathways much of the sedimentary magnetic signal appears to be controlled by detrital inputs especially of windblown dust and ice rafted debris ird with a range of different sources these sediment transport pathways can be validated by making direct comparison of the sediment magnetic properties with source rocks and soils and with iceberg trajectory and observation data the spatial distributions of the ird dominated sediments substantiate those mapped previously using lithological tracers provide additional spatial information on sediment sources and pathways and suggest that deep water currents are less significant than proposed in controlling present day sediment mineralogy and distribution the data form a present day basis for comparison with glacial stage ird and dust distributions and modes of ocean circulation

evidence against dust mediated control of glacial interglacial changes in atmospheric co2 the low concentration of atmospheric co2 inferred to have been present during glacial periods is thought to have been partly caused by an increased supply of iron bearing dust to the ocean surface1 this is supported by a recent model2 that attributes half of the co2 reduction during past glacial stages to iron stimulated uptake of co2 by phytoplankton in the southern ocean but atmospheric dust fluxes to the southern ocean even in glacial periods are thought to be relatively low and therefore it has been proposed that southern ocean productivity might be influenced by iron deposited elsewhere for example in the northern hemisphere3 4 which is then transported south via ocean circulation similar to the distal supply of iron to the equatorial pacific ocean5 6 7 here we examine the timing of dust fluxes to the north atlantic ocean in relation to climate records from the vostok ice core in antarctica around the time of the penultimate deglaciation about 130 kyr ago two main dust peaks occurred 155 kyr and 130 kyr ago but neither was associated with the co2 rise recorded in the vostok ice core this mismatch together with the low dust flux supplied to the southern ocean suggests that dust mediated iron fertilization of the southern ocean did not significantly influence atmospheric co2 at the termination of the penultimate glaciation

characterizing and quantifying iron oxides in chinese loess paleosols implications for pedogenesis to accurately decode the paleoclimatic and paleoenvironmental significance of magnetic properties in chinese loess paleosols neoformation of magnetic iron oxides via pedogenesis as well as the relationship between ferrimagnetic maghemite and magnetite and antiferromagnetic minerals hematite and goethite of both detrital and pedogenic origins should be well determined to resolve this problem magnetic iron oxides from a contiguous loess paleosol sequence lower part of the loess unit l1 paleosol unit s1 and the upper part of l2 at luochuan center of the chinese loess plateau were well characterized and quantified by using an integrated approach including chemical dissolution diffuse reflectance spectroscopy and rock magnetism methods results showed that these magnetic minerals have distinct coercivity and dissolution behavior which is highly grain size dependent more specifically the paleosol is enriched with nano sized pedogenic hematites with a medium coercivity of 130 mt which are also preferentially dissolved in a weak reductive environment in contrast the coarse grained micro sized detrital hematites with a medium coercivity of 1 t are dominant in loess in addition these coarse grained detrital hematites are more stoichiometric than their pedogenic counterparts as evidenced by the higher band position on the diffuse reflectance spectrum goethite can be well distinguished from hematite by its higher coercivity 4 7 t at low temperature 10 k the consistent dissolution behavior of goethite for both loess and paleosol samples in citrate bicarbonate dithionite solution indicates that goethite could be less relevant to the pedogenic processes the reductive dissolution of pedogenic maghemite lags the dissolution of pedogenic hematite and fine grained goethite which suggests that average grain size of pedogenic maghemite is relatively larger than those of pedogenic hematite and fine grained goethite detrital magnetite is hard to dissolve and 50 of its initial remanence survived after dissolution on the basis of these contrasting behaviors pedogenic hematite fine grained goethite and maghemite content was further quantified our results suggest that single domain pedogenic hematite was produced after initial formation of pedogenic maghemite this provides direct evidence for the recently proposed pathway in which ferrihydrite is transformed into a transient maghemite like phase before its final transformation into hematite

rock magnetic properties of a soil developed on an alluvial deposit at buttermilk creek texas usa 1 the evolution of magnetization within a floodplain soil begins with initial deposition of magnetic particles during sedimentation and continues via subsequent alteration and growth of iron bearing compounds by pedogenic and biologic processes measurements of soil magnetic properties capture information about the developmental history of the soil and are a convenient method by which to investigate environmental change and pedogenesis using a range of magnetic measurements a comprehensive scenario for soil development was constructed for floodplain sediments at the debra l friedkin site an important archeological site near buttermilk creek texas floodplain deposits have traditionally been avoided for soil magnetism studies because it is thought that the episodic input of sediment would form soils characterized by discrete sedimentary units rather than a continuous record of pedogenesis we demonstrate that alluvial deposits can sometimes carry a straightforwardly interpretable magnetic signal similar to those typically seen in loess deposits smooth variation of rock magnetic parameters as a function of depth also leads us to conclude that the soil at this site is largely undisturbed and that the age of lithic artifacts found within the soil may be interpreted within stratigraphic context

stable isotopes and debris in basal glacier ice south georgia southern ocean this paper combines a study of the rock debris and d 18 o isotopic characteristics of basal ice sequences in three representative glaciers in south georgia and concludes that the debris and ice has been entrained mainly by basal freezing the size distribution of the rock debris is typical of crushing and abrasion and reflects transport at the ice rock interface the d 18 o relationships show that clear ice associated with the debris has accreted through freezing he white bubbly glacier ice has d 18 o relationships typical of precipitation which demonstrates an altitudinal effect between glaciers

astrochronology of the mediterranean langhian between 15 29 and 14 17 ma an integrated high resolution magnetobiocyclostratigraphy including radioisotopic dating and astronomical tuning is presented for the interval between 15 29 and 14 17 ma in the marine la vedova section in northern italy the natural remanent magnetization is carried by the iron sulphide greigite and the resultant magnetostratigraphy can be correlated straightforwardly to the interval ranging from c5bn 2n to c5adn in the astronomically tuned neogene time scale atnts2004 spectral analysis on high resolution magnetic susceptibility and geochemical proxy records in the depth domain and using our magnetobiostratigraphic age model in the time domain demonstrate that the various scales of cyclicity in the section are related to astronomical climate forcing starting from our initial age model larger scale cycles were first tuned to eccentricity this first order tuning was followed by tuning the basic cycle to precession and boreal summer insolation using inferred phase relations between maxima in ca al redox sensitive elements and ba and minima in magnetic susceptibility and maxima in precession and minima in obliquity and boreal summer insolation our astronomical ages for reversal boundaries are supported by analysis of sea floor spreading rates and should replace the existing ages in the atnts2004 lacking direct astronomical control two major steps in the geochemical proxy records astronomically dated at 15 074 and 14 489 ma coincide with abrupt changes in sedimentation rate and are the result of the combined effect of the 400 kyr eccentricity cycle superimposed upon a longer term climatic or tectonic induced trend

iron oxide mineralogy in late miocene red beds from la gloria spain rock magnetic voltammetric and vis spectroscopy analyses abstract free ferric oxides of a red bed series were analyzed by rock magnetic techniques irm component analysis and by two less traditional methods visible spectroscopy and voltammetry all three methods have low limits of detection making them suited for this type of analysis the red bed samples studied contained clay minerals quartz and calcium carbonate as major constituents free fe oxides occurred at a concentration of 0 3 2 1 i e in the majority of the samples below the detection limit of x ray powder diffraction the combination of the employed analytical techniques enabled to characterize the mineralogy of free ferric oxides and to estimate the ratio of goethite and to hematite this ratio changes substantially within the section that probably indicates paleoclimatic changes

widespread occurrence of a novel high coercivity thermally stable low unblocking temperature magnetic phase in heated archeological material 1 the widespread occurrence of a novel high coercivity magnetic phase in well heated archeological material is reported its properties are defined when it represents the dominant magnetic phase although it is nearly always found as part of a mixture of magnetic phases they are as follows very high coercivity remanence coercivity 600 mt low unblocking temperatures 200 c and high degree of thermal stability this last property distinguishing it from goethite the phase shows striking similarities to magnetic phases produced by thermal decomposition of nontronite an fe rich clay where decomposition occurs after prolonged heating in air to high temperatures conditions suffered by well heated archeomagnetic material preliminary results of mossbauer and x ray diffraction spectroscopy suggest that the phase is more likely to be a substituted hematite rather than fe cristobalite or a variant of fe2o3

estimating the concentration of aluminum substituted hematite and goethite using diffuse reflectance spectrometry and rock magnetism feasibility and limitations this study was supported by the national natural science foundation of china 41374073 and 41430962 the national program on global changes and air sea interaction gasi 04 01 02 and the chinese continental shelf deep drilling program gzh201100202 pengxiang hu was further supported by the china scholarship council 2013 3009 david heslop and andrew roberts were supported by australian research council discovery project dp110105419

magnetic anisotropy of chloritoid 1 the magnetocrystalline anisotropy of monoclinic chloritoid a relatively common mineral in aluminum rich metapelitic rocks has been determined for the first time by measuring the high field anisotropy of magnetic susceptibility hf ams using two independent approaches i e a directional magnetic hysteresis measurements and b torque magnetometry on a collection of single crystals collected from different tectonometamorphic settings worldwide magnetic remanence experiments show that all specimens contain ferromagnetic s l impurities being mainly magnetite the determined hf ams ellipsoids have a highly oblate shape with the minimum susceptibility direction subparallel to the crystallographic c axis of chloritoid in the basal plane of chloritoid though the hf ams can be considered isotropic the degree of anisotropy is found to be 1 47 which is significantly higher than the anisotropy of most paramagnetic silicates and even well above the frequently used upper limit i e 1 35 for the paramagnetic contribution to the ams of siliciclastic rocks the obtained values for the paramagnetic curie temperature parallel and perpendicular to the basal plane indicate that this pronounced magnetocrystalline anisotropy is related to strong antiferromagnetic exchange interactions in the direction of the crystallographic c axis 0 as a consequence chloritoid bearing metapelites with a pronounced mineral alignment can have a high degree of anisotropy without the need of invoking a significant contribution of strongly anisotropic ferromagnetic s l minerals the newly discovered magnetocrystalline anisotropy of chloritoid thus calls for a revised approach of magnetic fabric interpretations in chloritoid bearing rocks

high coercivity remanence in baked clay materials used in archeomagnetism a study of the high coercivity remanence in archeological baked clays has been carried out more than 150 specimens from 46 sites across europe have been analyzed selected on the basis of the presence of a fraction of their natural remanence that was resistant to alternating field demagnetization to 100 mt the study was based on the stability of isothermal remanence to alternating field and thermal demagnetization and its variation on cooling to liquid nitrogen temperature results indicate that the high coercivity remanence may be carried by magnetite hematite and in isolated cases partially oxidized magnetite and goethite in addition a high coercivity thermally stable low unblocking temperature phase has been identified the unblocking temperatures of both the isothermal remanence and the alternating field resistant natural remanence exhibit similar unblocking temperatures suggesting that the same phases carry both signals the high coercivity low unblocking temperature phase contributes to the natural remanence sometimes carrying a stable direction and behaving ideally during palaeointensity experiments and sometimes not an unambiguous mineralogical identification of this phase is lacking although likely candidates include hemoilmentite related to clay source lithology and substituted hematite or magnetic ferri cristabolite both possible products of thermal transformation of iron bearing clays

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

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

influence of seawater exchanges across the bab el mandeb strait on sedimentation in the southern red sea during the last 60 ka 1 the location of core md92 1008 close to the southern edge of the red sea is ideal to study the evolution of seawater exchanges with the northern indian ocean through the bab el mandeb narrow strait the present study was aimed at documenting the paleoceanographic evolution of this area over the past 60 ka using high resolution magnetic sedimentological and geochemical indicators two modes of variability dominate the records i long term glacial interglacial variations and ii rapid millennial scale variability dansgaard oeschger type during the last glacial period changes in magnetic concentration were documented from natural and laboratory magnetizations after proper normalization they are inversely correlated to the total organic carbon toc content pointing out the key role played by reductive dissolution of magnetite on the evolution of magnetic concentration based on the temporal evolution of toc caco3 and planktonic 13c we suggest that past changes in the organic matter content i were closely linked to glacio eustatic variations which modulated long term seawater exchanges and nutrient supplies to the red sea through the narrow bab el mandeb strait and ii reflect millennial scale changes in productivity driven by monsoon wind intensity which controlled the amount of nutrient rich intermediate waters upwelled in the gulf of aden during the summer season and advected into the southern red sea the sea level rise following the onset of deglaciation generated a rapid flush of detrital material that was accumulated on the continental margins and on the previously emerged zones of the bab el mandeb area

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

isothermal remanence experiments at room and at liquid nitrogen temperature application to soil studies a simple magnetic mineral identification technique is proposed which measures isothermal remanent magnetisation irm acquired in different field strengths at 293 k and 77 k magnetic parameters are introduced that use these irms in order to distinguish concentration and type of ferromagnetic minerals in different magnetic states the method determines easily contributions of superparamagnetic ferrimagnetic minerals in environmental magnetism studies in addition high coercivity goethite and possibly superparamagnetic hematite are identified the analysis of the magnetic properties of a soil profile on a late pleistocene terrace from the jarama river in central spain is given as an example

the cause of extremely high magnetic susceptibility of the s5s1 paleosol in the central chinese loess plateau abstract the paleosol unit s5s1 which corresponds to marine isotope stage mis 13 is the most prominent paleosol layer in the central chinese loess plateau clp s5s1 has extremely high magnetic susceptibility but it remains uncertain whether this is related to climate or to time the duration of pedogenesis due to the anomalously low loess deposition rate to address this question we investigate the iron mineralogical properties of the s5s1 paleosol at the xifeng loess section located in the central clp we compare the results of s5s1 with other paleosol units yielding additional insights into the clp climatic changes during mis 13 the results show that magnetic enhancement of s5s1 paleosol is stronger than that of the other paleosol units which is mainly governed by pedogenic produce fine grained ferrimagnetic minerals the maximum value of the goethite concentration compared with hematite in the s5s1 paleosol unit is markedly higher than those in the other paleosol units the prolonged period of pedogenesis is not main controlling factor that leads to the magnetic enhancement of s5s1 because the concentration of sd sp has hardly changed compared with other paleosols as with the increasing of magnetic susceptibility changes in the ratio of pedogenic hematite to goethite as well as in magnetic enhancement indicate that the s5s1 paleosol developed under extremely humid conditions this extremely humid climate is a main cause that leads to the extremely high magnetic susceptibility