geochemical and mineralogical control of different genetic types of deep sea nodules from the pacific ocean deep sea nodules from the northeast pacific nodule belt and the southeast pacific sonne basin being formed in areas bordering the equatorial zone of high biological productivity accumulate by two basically different growth processes a early diagenetic growth by supply from pore water and b hydrogenetic growth by supply from near bottom sea water these growth processes lead to different genetic types of nodules early diagenetic type a hydrogenetic type b and mixed type ab a further type ac very rich in mn is being formed by increasing influence of early diagenesis these types can clearly be distinguished by their shapes surface textures mineral constituents of oxide fraction internal microstructures and geochemistry a genetical classification is being proposed on the basis of statistically computed interelement relationships todorokite very poor in fe is the main mn phase in the early diagenetic substance mno2 intimately intergrown with feooh xh2o is the main phase in the hydrogenetic substance consequently an important difference can be pointed out the metal supply for the growth of the early diagenetic nodules is based on an ionic solution of me2 e g mn2 ni2 cu2 zn2 whereas the supply for the hydrogenetic nodules is caused by transport of colloidal particles mobilization of mn2 and fractionation from fe is controlled by the amount of decomposing organic matter in the peneliquid layer of the sediments the main factor controlling the intensity of early diagenesis is the biological productivity in surface waters the crucial point of reversal at a mn fe ratio of about 5 obtained by hyperbolical regression of the analyses of nodules from the southeast pacific represents best concentrations in ni and cu mn fe quotients greater than 5 cause a decrease of ni and cu content nodules from the northeast pacific nodule belt generally contain higher concentrations in cu than nodules from the southeast pacific this can be explained by an additional supply of cu transported below ccd by siliceous plankton

metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

biogenic influence on the growth of ferromanganese micronodules in the central indian basin abstract in a 20 cm core collected from the central indian basin with increasing depth the abundance of ferromanganese micronodules decreases as their size increases and the surface texture changes from rough to smooth biological debris including radiolarian fragments diatom tests and bacterial cells were found associated with the micronodules dissolution of biological debris with increasing core depth was evident ferromanganese oxides are present as fine imprints and coarse lumpy growths on the biological debris they are also present in different crystal forms in vugs and cavities in the micronodules electron microprobe spot analyses indicate that the micronodules are particularly high in manganese and iron in the upper and lower levels of the sediment column respectively diagenetic effects may account for the metal enrichment it appears that biological debris play an important role in the growth of the micronodules

influence of sedimentation on enrichment of manganese and growth of ferromanganese micronodules bengal fan india abstract based upon down core variations in o mn ratio in sediment and in micronodules mn content organic carbon and abundance of micronodules in two box cores from high and low sedimentation regions of the bay of bengal 0 20 and 0 40 cm levels were identified as mn oxidation zone in the western and the eastern regions of the bay despite similarity in bottom water o 2 and organic carbon contents of the region a higher abundance of micronodules down to the deeper levels was observed in the area of low sedimentation but in the upper surfaces increased enrichment of mn was observed in core 1 located in the area of higher sediment accumulation rapid recycling of mn faster burial transfer to mn reduction zone mn dissolution and its upward diffusion re precipitation increasing upward flux of mn ii and associated higher consumption of o 2 limits the width of mn oxidation zone and appears to be responsible for enhanced enrichment of mn in the area of high sedimentation the results of the present study also suggest that though the availability of mn controls the formation of micronodules their resident time in mn oxic zone regulates their growth and influences their morphology

the oxidation state of manganese in marine sediments and ferromanganese nodules marine sediments and ferromanganese nodules from the pacific ocean have been analyzed for the omn ratio of solid manganese we tested six chemical methods and concluded that the iodometric and oxalate methods were equivalent and were the best choice in terms of accuracy and precision on natural samples we choose the iodometric method for most of our analyses because the oxalate procedure is a method of differences the ferromanganese nodules that we analyzed were all from manop site h and had mnfe ratios that ranged from 5 6 to 70 these nodules were invariably highly oxidized with omn values ranging from 1 90 to 2 00 our most precise analyses suggest that less than 1 of the total manganese is present as mn ii we also analyzed red clay and hemipelagic sediments from the eastern tropical pacific baja borderland and manop site h and carbonate ooze samples from the equatorial pacific these sediments are also highly oxidized omn 1 90 to 2 00 except when mn ii appears in the interstitial water as dissolved mn ii increases the value of the omn ratio in the solid phase decreases the omn ratio decreases to values as low as 1 40 this decrease appears to be due to a decrease in oxidized manganese by reduction however an increase in reduced manganese in the solid sediments by adsorption or mnco3 formation can not be ruled out in all cases

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

characterization of hematite α fe2o3 goethite α feooh greigite fe3s4 and pyrrhotite fe7s8 using first order reversal curve diagrams 1 first order reversal curve forc diagrams have become a standard tool in rock magnetism yet magnetite is the only magnetic mineral that is well characterized using forc diagrams we present forc diagrams for predominantly single domain sd synthetic aluminous hematite a fe2 xalxo3 and goethite a feal ooh and natural greigite fe3s4 and pyrrhotite fe7s8 to constrain interpretation of forc diagrams from natural samples hematite and goethite have low spontaneous magnetizations and negligible magnetic interactions while greigite and pyrrhotite have higher spontaneous magnetizations and can have strong magnetic interactions the coercivity of hematite systematically increases with al content only for samples produced using the same synthesis method but it is variable for samples produced with different methods even for similar al content this precludes use of magnetic coercivity alone to quantify the al content of natural hematites goethite has much higher coercivity than hematite for all measured samples sd and superparamagnetic sp behavior is common in natural greigite samples with peak coercivities ranging from

first order reversal curve forc diagrams of magnetic mixtures micromagnetic models and measurements first order reversal curve forc diagrams were modelled and experimentally measured for different assemblages of single domain sd magnetite particles with bimodal distributions of coercivities and varying concentrations when fitting end member forc diagrams to the forc diagrams of mixtures linear additivity is obeyed for the non interacting mixtures with predicted mixing ratios within the errorbars of the actual mixing ratios interacting mixtures are not always linearly additive experimental bimodal mixtures of magnetite particles sd pseudo single domain psd have forc diagrams that are usually linearly additive regardless of the magnetite concentration of the sample 10 or 1 measured forc diagrams of mixtures of sd magnetite and sd hematite again show that linear additivity of the two end members holds however the very small ms of hematite compared to that of magnetite makes it difficult to detect a contribution on a forc diagram from hematite unless it comprises at least 88 of the mixture

new late permian paleomagnetic data from argentina refinement of the apparent polar wander path of gondwana the late paleozoic early mesozoic apparent polar wander path of gondwana is largely constructed from relatively old paleomagnetic results many of which are considered unreliable by modern standards paleomagnetic results derived from sedimentary sequences which are generally poorly dated and prone to inclination shallowing are especially common here we report the results of a joint paleomagnetic geochronologic study of a volcanic complex in central argentina u pb dating of zircons has yielded a robust age estimate of 263 0 1 6 2 0 ma for the complex paleomagnetic analysis has revealed a pretilting primary permian magnetization with dual polarities rock magnetic experiments have identified pseudo single domain titano magnetite and hematite as the mineralogic carriers of the magnetization lightning induced isothermal remagnetizations are widespread in the low coercivity magnetic carriers the resulting paleomagnetic pole is 80 1 s 349 0 e a95 3 3 n 35 and it improves a late permian mean pole calculated from a filtered south american paleomagnetic data set more broadly this new high quality igneous based paleomagnetic pole falls between the previously distinct late permian segments of the laurussian and gondwanan apparent polar wander paths suggesting that the long recognized disparity between these large paleomagnetic data sets may be primarily due to the inclusion of low quality or systemically biased data

unmixing magnetic remanence curves without a priori knowledge summary many of the natural materials studied in rock and environmental magnetism contain a mixed assemblage of mineral grains with a variety of different origins mathematical decomposition of the bulk magnetic mineral assemblage into populations with different properties can therefore be a source of useful environmental information previous investigations have shown that such unmixing into component parts can provide insights concerning source materials transport processes diagenetic alteration authigenic mineral growth and a number of other processes a new approach will be presented that performs a linear unmixing of remanence data into coercivity based end members using only a minimal number of assumptions a non negative matrix factorization nmf algorithm for unmixing remanence data into constituent end members is described with case studies to demonstrate the utility of the approach the shape of the end members and their abundances obtained by nmf is based solely on the variation in the measured data set and there is no requirement for mathematical functions or type curves to represent individual components therefore in contrast to previous approaches that aimed to unmix curves into components corresponding to individual minerals and domain states nmf produces a genetically more meaningful decomposition showing how a data set can be represented as a linear sum of invariant parts it has been found that the nmf algorithm performs well for both absolute and normalized remanence curves with the capacity to process thousands of measured data points rapidly

assessing the ability of first order reversal curve forc diagrams to unravel complex magnetic signals 1 first order reversal curve forc diagrams for mixtures of different magnetic phases and bimodal distributions have been measured to examine the efficiency of the forc method at unraveling complex magnetic signals the forc distributions for various magnetic minerals including magnetite maghemite hematite and goethite and their linear additivity are assessed mixtures containing only hard magnetic minerals like hematite or goethite which have relatively small spontaneous magnetizations ms and large magnetocrystalline anisotropies can be adequately described by a linear addition of the two end members because there are virtually no magnetostatic interactions between the phases mixtures dominated by softer minerals like magnetite and maghemite are more susceptible to interactions and exhibit nonlinear behavior when a hard phase with low ms like hematite is mixed with a softer phase with high ms like magnetite it can still be identified using the forc technique whereas it is impossible to do so using standard magnetic hysteresis measurements when the weaker phase can be identified then weak strong mixes add linearly however beyond a certain critical concentration the mineral with high ms swamps the magnetic signal and linearity breaks down it is suggested that the forc method is highly suitable for identifying small traces of hard magnetic minerals like hematite and goethite in the presence of minerals with high ms such as magnetite

magnetic fingerprint of the late holocene inception of the rio de la plata plume onto the southeast brazilian shelf abstract measurement of changes in the assembly of magnetic particles in sediment records is useful both for paleoclimatic and paleoceanographic reconstructions and for assessing provenance and pathways of sediment transport in this study we provide detailed rock magnetic analysis along with scanning electron microscopy sem ti ca ratio and particle size distribution of the decarbonated fraction of sediments to trace terrigenous source changes during the last 6 cal kyr bp in core 7610 collected on the se brazilian continental shelf magnetic mineralogy data indicate a gradual shift between two distinct sources of sediments 1 dust from southern south america patagonia central western argentina and puna altiplano plateau and 2 sediments eroded from the weathered volcanics of parana basin these materials reached the continental margin off argentina and uruguay by different pathways and were transported northward by the brazilian coastal current bcc the chronology of events related to the environmental record of core 7610 indicates that between 6 and 4 7 cal kyr bp dry conditions over continental south america resulted in enhanced eastward eolian transport of the argentinean loess and a limited discharge of the rdlp river load into the atlantic ocean at this time the sedimentary magnetic fraction that reached the se brazilian shelf reflect predominantly loessic sources transported from the pampean terraces to the argentinean and uruguay shelves and then distributed northward by the shelf current system from 4 7 to 2 cal kyr bp the climate became gradually wetter over the continent and the contribution of oxidized phases from the weathered parana basin mainly from the basaltic and acidic volcanics started to become important this change in climate overlaps in time a with the late holocene sea level fall recorded along the se south american coast later from 2 up to 0 9 cal kyr bp even wetter conditions were prevalent in s and se south america and the rdlp sedimentary load became the main source of sediments transported to the se brazilian shelf by the bcc the magnetic record of core 7610 reported here together with other paleoenvironmental tracers palynology geochemistry and stable isotopes thus indicates that the inception of the rdlp plume onto the se brazilian shelf started as early as 4 7 cal kyr bp and has been strengthened since then mostly due to changes in precipitation over south america and to a smaller extent by sea level changes

separating multidomain and single domain like remanences in pseudo single domain magnetites 215 540 nm by low temperature demagnetization it has long been hypothesized that the pseudo single domain properties of submicron magnetites are a result of coexisting multidomain and single domain like remanences we have separated these two types of remanence by low temperature demagnetization ltd in which samples are cooled through the low temperature magnetite isotropic point and rewarmed to room temperature all in zero field at the isotropic point the first crystalline anisotropy constant vanishes and multidomain remanence due to displaced domain walls will be unpinned we measured stepwise alternating field af and thermal demagnetization curves of weak field thermoremanent magnetization trm and anhysteretic remanent magnetization and of saturation isothermal remanent magnetization irms both with and without prior ltd for magnetites with mean particle sizes of 215 390 and 540 nm the memory fraction of remanence recovered after ltd which represents the single domain like component decreased from 44 for 215 nm grains to 23 for 540 nm grains in the case of irms memory of trm was approximately twice as large af decay curves were soft and multidomain like before ltd but became harder and single domain like in shape after ltd ltd removed most low unblocking temperature trm and irms distributed low unblocking temperatures are therefore a multidomain phenomenon probably resulting from successive adjustments of domain walls to changing internal fields and pinning strengths during heating

volcanic iron fertilization of primary productivity at kerguelen plateau southern ocean through the middle miocene climate transition abstract odp site 747 central kerguelen plateau contains a nearly complete record of the middle miocene climate transition mmct its unusually well preserved and rich foraminiferal assemblages have resulted in the mmct interval at site 747 becoming a focus of high resolution paleoclimatic studies that have established this sequence as a southern ocean reference we combine x ray fluorescence xrf elemental counts of fe ti and al and concentration dependent magnetic parameters to trace volcanic ash input to sediments at odp hole 747a we observe systematic variations in al ti and fe ti ratios that are consistent with increased primary productivity at times of increased terrigenous input and therefore increased nutrient supply a spike in terrigenous material which we interpret as volcanic ash coincides with major changes in species abundance and stable oxygen and carbon isotopic shifts within the mmct interval this correlation suggests that nutrient flux associated with volcanic iron fertilization played a significant role in controlling phytoplankton communities at site 747 we demonstrate that rapidly obtained xrf and magnetic parameters can provide useful proxies for terrigenous input and therefore nutrient fluxes in pelagic marine settings that can help to resolve local versus global drivers of paleoenvironmental and paleoceanographic changes

a method for unmixing magnetic hysteresis loops 1 hysteresis loops provide essential information concerning both induced and remanent magnetizations and are an important tool for characterizing magnetic mineral assemblages although the hysteresis behavior of mixed natural magnetic assemblages has been a focal point of much recent work little progress has been made in unmixing of hysteresis loops into characteristic components unmixing strategies can act as cornerstones for interpretation of rock magnetic data and have become popular for characterizing isothermal remanent magnetization acquisition curves unmixing of hysteresis loops is however a challenging task because the individual component loops in the mixture must meet stringent shape constraints we present a new technique for decomposing an ensemble of hysteresis loops into a small number of end members based on linear mixing theory the end members are not based on type curves but instead are derived directly from the hysteresis data particular attention is paid to the form of the end members ensuring they meet the shape constraints expected for hysteresis loops of natural magnetic mineral assemblages marine sediments from the southern ocean and lake sediments from butte valley northern california provide case studies on which the proposed unmixing method is tested

rock magnetic record of core sg 3 since 1 ma in the western qaidam basin and its paleoclimate implications for the ne tibetan plateau abstract quaternary saline lake deposits are well formed and widely distributed in the qaidam basin on the northeastern tibetan plateau nw china studying these lacustrine salt mineral deposits can improve our understanding of tectonic deformation asian interior aridification and monsoon climate associated with global cooling and tibetan plateau uplift previous paleoclimate records in the qaidam basin are mostly documented by geochemical proxies pollen spectra and sedimentary characteristics however supporting evidence from the rock magnetic index of sediments with salt deposits in the basin has not been well studied here we present a continuous high resolution 1 0 myr rock magnetic record from the well dated drill core sg 3 for typical saline lake deposits in the western qaidam basin the results show that deposits with low magnetic susceptibility are caused by low contents of magnetic minerals with single domain sd grains while those with high have relatively high contents of magnetic minerals with sd and pseudo single domain psd grains in full consideration of the sedimentary environment weathering and erosion associated with the global climate since the middle pleistocene we propose that variations in the closed lake are mainly influenced by erosion intensity and precipitation by combining the changes with pollen and grain size records we infer that the drying process of central asia since 1 ma with intensified aridity at 0 6 ma and 0 13 ma was primarily induced by global cooling

experimental mixtures of superparamagnetic and single domain magnetite with respect to day dunlop plots day dunlop plots are widely used in paleomagnetic and environmental studies as a tool to determine the magnetic domain state of magnetite i e superparamagnetic sp stable single domain sd pseudosingle domain psd multidomain md and their mixtures the few experimental studies that have examined hysteresis properties of sd sp mixtures of magnetite found that the ratios of saturation remanent magnetization to saturation magnetization and the coercivity of remanence to coercivity are low when compared to expected theoretical mixing trends based on langevin theory this study reexamines day dunlop plots using experimentally controlled mixtures of sd and sp magnetite grains end members include magnetotactic bacteria msr 1 as the sd source and a commercial ferrofluid or magnetotactic bacteria a12 as the sp source each sp component was added incrementally to a sd sample experimental results from these mixing series show that the magnetization and coercivity ratios are lower than the theoretical prediction for bulk sp magnetic size although steric repulsion was present between the particles we cannot rule out interaction in the ferrofluid for higher concentrations the sp bacteria are noninteracting as the magnetite was enclosed by an organic bilipid membrane our results demonstrate that the magnetization and coercivity ratios of sd sp mixtures can lie in the psd range and that an unambiguous interpretation of particle size can only be made with information about the magnetic properties of the end members

nonlinear preisach maps detecting and characterizing separate remanent magnetic fractions in complex natural samples natural remanent magnetization carriers in rocks can contain mixtures of magnetic minerals that interact in complex ways and are challenging to characterize by current measurement techniques here a non linear mapping scheme is described that efficiently enhances sensitivity and the resolution power of remanent preisach maps using this scheme a large dynamic range of magnetic moments and coercivities can be reliably resolved the method is applied to synthetic and natural standard samples containing magnetite and hematite as well as to natural samples from remanent magnetic anomalies where complex microstructures are observed it is shown that certain offset high coercivity patterns in remanent preisach maps may serve as fingerprints for exsolution structures of ilmenite in hematite or hematite in ilmenite and that in some magnetite bearing remanent anomalies the magnetite coercivity is increased beyond its intrinsic coercivity range experimental results and theoretical considerations indicate a minimal coercivity of about 10 mt for sd magnetite such that observation of lower coercivities implies psd or md grain sizes a diagnostic hematite pattern with a peak downwards offset of 17 2 of the intrinsic coercivity is found that is stable over a large range of intrinsic coercivities and may be related to shielding of internal defect or lamellar moments by a spin canting response to the internal field

magnetic fingerprint of southern portuguese speleothems and implications for paleomagnetism and environmental magnetism environmental magnetism of speleothems is still in its early stage of development here we report on our investigation of the environmental and paleomagnetic information that has been recorded in speleothems and what are the factors that control its preservation and reliability to address these issues we used a multidisciplinary approach including rock magnetism petrography scanning electron microscopy stable carbon and oxygen isotope compositions and major and trace element concentrations we applied this to a set of samples from different stages of speleothem evolution present day dripwater glass plates a weathered stalactite a fresh stalagmite cave sediments and terra rossa soils these samples come from the penico and excentricas caves located in two distinct aquifers of the algarve region south portugal our results show that the main magnetic carriers of the speleothems under study are primary detrital and consist of maghemite and magnetite similarities in coercivity and temperature dependence of the studied set of samples suggest that iron oxides are inherited from the terra rossa soils that cap the cave and were transported to the speleothems by dripwater hence they represent a regional environmental signature interestingly a stable and probably detrital remanent magnetization could be isolated in the fresh stalagmite whereas the weathered stalactite yielded chaotic magnetic directions and very low remanent intensities we propose that these low intensities can be the result from i different remanence acquisition mechanisms between stalagmite and stalactite and or ii iron dissolution by fungal activity we also suggest that magnetic properties and color and the content in detrital elements in the fresh speleothem inform about environmental processes acting on the interface of rock soil atmosphere while oxygen isotope composition and alkaline earth element concentrations inform about calcite water interaction processes these results provide a better understanding of how environmental information is recorded in speleothems and what the factors are that control the reliability of the paleomagnetic and paleo environmental signal

low temperature first order reversal curve forc diagrams for synthetic and natural samples first order reversal curve forc diagrams were measured on a variety of synthetic and natural submarine basalts and potsherds samples as well as for a mixture between room temperature and 10 k measuring forc diagrams allowed us to examine the behavior of the coercivity field and interaction field distributions with decreasing temperature generally as the temperature is decreased forc contours were observed to expand in all directions e g the maximum coercivity peak migrates toward a higher coercivity for synthetic magnetite samples there were abrupt changes in the forc distribution at the verwey transition 120 k while in the more complex natural magnetite samples the forc distribution gradually progressed with temperature as the temperature decreased forc diagrams were found to display different domain state characteristics for example samples with dominant superparamagnetic signals became single domain sd like a sd like sample stayed sd like and a psd like sample became more sd like in addition to these general features we also observed some more specialized features first in both synthetic and natural magnetite samples a secondary higher coercivity peak is occasionally present below the verwey transition which we suggest is a twinning contribution second the coercivity increases by a factor 15 between 300 k and 20 k in some of the seamount samples third the effect of field cooling zero field cooling on forc diagrams is negligible with the hysteresis parameters hc and hcr displaying a greater dependency finally it is shown that in mixtures of magnetite and hematite the hematite contribution disappears on cooling below the morin transition leaving a strong well defined magnetite signal

manganese micronodules a possible indicator of sedimentary environments abstract manganese micronodule distribution size internal features and chemical composition as well as the composition of associated sediments have been determined in eight sediment cores taken from the siliceous ooze area of the central indian basin cib micronodule abundance expressed as the number of micronodules per gram of dried sediment 0 375 n g and size 75 1000 m show considerable variation with core depth and are directly related to each other the morphology surface texture and internal features of the micronodules are similar to those of surface macronodules from the same basin micronodules have high contents of mn 35 02 cu 1 6 ni 1 4 and zn 0 37 high mn fe ratios 5 101 and very low fe 1 8 al 2 o 3 1 3 tio 2 0 30 sio 2 2 7 and rare earth element 522 ppm contents compared to surface and buried macronodules micronodule abundance size and composition depend on the redox characteristics of the sedimentary environment and can therefore be used as indicators of the sedimentary environment

magnetic characteristics of cv chondrules with paleointensity implications 1 we have conducted a detailed magnetic study on 45 chondrules from two carbonaceous chondrites of the cv type 1 mokoia and 2 allende allende has been previously extensively studied and is thought to have a high potential of retaining an extra terrestrial paleofield few paleomagnetic studies of mokoia have previously been undertaken we report a range of magnetic measurements including hysteresis first order reversal curve analysis forcs demagnetization characteristics and isothermal remanent irm acquisition behavior on both mokoia and allende chondrules the mokoia chondrules displayed more single domain like behavior than the allende chondrules suggesting smaller grain sizes and higher magnetic stability the mokoia chondrules also had higher average concentrations of magnetic minerals and a larger range of magnetic characteristics than the allende chondrules irm acquisition analysis found that both sets of chondrules have the same dominant magnetic mineral likely to be a feni phase taenite kamacite and or awaruite contributing to 48 of the mokoia chondrules and 42 of the allende chondrule characteristics forc analysis revealed that generally the allende chondrules displayed low field coercivity distributions with little interactions and the mokoia chondrules show clear single domain like distributions paleointensity estimates for the two meteorites using the remc and preisach methods yielded estimates between 13 and 60 t and 3 56 t respectively for allende and 3 140 t and 1 110 t respectively for mokoia from the data we suggest that mokoia chondrules carry a non primary remagnetization and while allende is more likely than mokoia to retain its primary magnetization it also displays signs of post accretionary magnetization

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

on the occurrence of ferromanganese micronodules from the sediments of the bengal fan a high terrigenous sediment input region studies of 13 samples 10 surface sediments and 3 cores from across the middle fan region of the bay of bengal reveal the presence of micronodules area 0 22 million km2 over the entire bay these micronodules have two dominant morphological forms botryoidal in the eastern bay and spheroidal in the central and the western regions of the bay the abundance of the micronodules was found to be higher in the eastern region of the bay in the cores the micronodules were generally found to decrease in abundance down core the core from the eastern region had micronodules down to deeper levels than the western side todorokite is the manganese mineral present in the micronodules associated mineral phases are quartz feldspar and phillipsite these micronodules have high mn 19 20 32 13 rather low fe 1 20 1 83 ni 0 10 1 14 zn 0 10 0 30 and co 0 01 0 04 and their mnfe ratio ranges from 10 55 to 25 42 the contents of mn ni cu and zn and the mnfe ratio decrease down core based upon the variations in the abundance morphology mnfe ratio of the micronodules and the elemental distributions and the omn ratio in the sediments remobilization of mn from deeper levels and its precipitation at the upper surfaces of the sediment column in an oxic environment is suggested the results of the present study also suggest that a high rate of sedimentation is not a limiting factor for the formation of micronodules although it might affect their growth

partial anhysteretic remanent magnetization in magnetite 1 additivity 1 we have tested the additivity of partial anhysteretic remanent magnetization parm for suites of eight synthetic magnetites with mean grain sizes from 65 nm to 18 m and 18 natural samples including lake sediments oceanic and continental volcanic rocks gabbros and granites in both synthetic and natural sample suites domain states inferred from hysteresis and other magnetic properties vary from single domain sd through pseudosingle domain psd to multidomain md for each sample total arm intensity was compared with sums of partial arms of three different types four conjugate pairs of parallel parms four pairs of perpendicular parms and one set of five neighboring parallel parms in each case the intervals of alternating field af over which a steady field h was applied to produce the partial arms are nonoverlapping and cover the entire af range 0 100 mt used to produce the total arm additivity of partial arms was verified to better than 3 for all the samples whatever the domain state sd psd and md or composition ranging from pure magnetite to x 0 6 titanomagnetite the universality of parm additivity is unexpected because its analog partial thermoremanent magnetization ptrm deviates from ideal behavior as the grain size increases and the domain structure becomes md the different behaviors probably result from the fact that parm is produced at ordinary temperatures over short times whereas the most intense ptrm is produced at temperatures approaching the curie point with significant dwell times promoting such processes as isothermal remanence acquisition domain nucleation and domain wall reequilibration verification of the law of additivity of parms is an encouraging first step toward validating pseudo thellier and other methods of paleointensity determination that use arm in place of or in addition to trm

compositional variations in manganese micronodules a possible indicator of sedimentary environments manganese micronodules from various environments were analyzed with the electron microprobe chemical characteristics of marine manganese nodules were examined in relation with their depositional environments and compared with those of manganese macronodules the compositional variation has a connection with accumulation rates and chemical features of the associated sediments mg and ti tend to be enriched in micronodules relative to the host sediments these elements may produce authigenic mineral phases in micronodules these observations show that manganese micronodules are chemically formed under approximately the same condition as that for macronodules but coexisting pairs of micronodules and macronodules collected from the same sediments suggest that oxic diagenesis plays a more important role in the formation of micronodules than that of macronodules the chemical features of manganese micronodules collected from several marine environments such as a marginal sea hemipelagic regions and the cent

atypical ferromanganese nodules from pelagic areas of the central indian basin equatorial indian ocean abstract two box core samples one each from red clay and siliceous ooze sediment provinces from the central indian basin indian ocean were studied both cores contained ferromanganese nodules at their tops the red clay sediment also hosts buried nodules at a depth of 82 cm chemical characterization of the sediments indicates that early diagenetic remobilization of transitional metals is pronounced in the siliceous ooze sediment while in the red clay no such effect is discernible this is further corroborated by the abundance and dissolution patterns of microorganisms and ferromanganese micronodules occurring in the two sediment columns bulk chemical analyses indicate that all the nodules are of the hydrogenetic b type vernadite and todorokite are the major minerals both of which constitute laminated nondirectional colloform and cuspate microstructures petrographic studies yield evidence of recrystallization of todorokite and partial transformation of vernadite to todorokite the former process being more advanced in buried nodules microprobe analyses revealed that primary todorokite has a lower mn fe ratio and higher ni content than recrystallized todorokite in the same sample the mineralogical reconstitution in the nodules is attributed to postdepositional intranodule diagenesis the present study does not reveal the correlation between mineralogy and microstructure in the nodules which has been suggested for the nodules from the pacific neither can any mineral or microstructure be considered specific for any particular genetic model the studied nodules are therefore atypical the mineralogical and chemical reordering in these ferromanganese nodules raises the question of the viability of radiometric methods in determining growth rates of such nodules

early diagenetic processes affecting nutrients in the pore waters of central indian ocean cores abstract pore water nutrients nitrite nitrate phosphate silicate ph and solid phase organic carbon were analysed for one core from the arabian sea and three cores from the manganese nodule area in the central indian ocean basin possible denitrification and unoxidized organic carbon are observed in the arabian sea core while nitrification with intermediate low nitrate and high organic carbon are found in the mottled zones of the pelagic cores mobilization of iron host oxyhydroxides and peaked profiles of organic carbon are related to a gradual increase in the phosphate profiles the asymptotic silica values are less than the 100 saturation levels of amorphous silica and they fall outside the stability field of sepiolite

dissolution behaviour of fine grained magnetite and maghemite in the citrate bicarbonate dithionite extraction method mineral magnetic properties of soils and sediments are increasingly used as proxy parameters for environmental and palaeoclimate analysis to investigate which magnetic minerals contribute to the environmental signal in the samples chemical techniques such as the citrate bicarbonate dithionite cbd extraction method have been introduced in environmental magnetism studies this technique is assumed to distinguish lithogenic magnetite from pedogenic maghemite mineral content in soils and sediments unfortunately interpretation of the cbd extractions is not straightforward because the procedure is sometimes more suitable for distinction between grain size than for distinction between minerals the procedure of the cbd extraction technique was investigated to determine the influence of extraction temperature and iron oxide concentration on the dissolution behaviour of the samples synthetic samples were extracted at three different temperatures 60o 70o and 80oc at similar iron oxide concentration 5 wt and for three different concentrations 0 1 wt 1 wt and 5 wt at the same temperature 60oc our results show that a lower extraction temperature reduces the dissolution rate for all samples while decrease in iron oxide concentration increases the dissolution rate thus the parameters in the cbd procedure have a major influence on the dissolution behaviour of the samples in practice this means that when natural samples of differing iron oxide concentration are extracted with this technique the results of the extractions cannot be compared therefore the outcome of this type of extraction experiment can only be accurately interpreted when the effect of the procedure on the dissolution behaviour is taken into account 1999 elsevier science b v all rights reserved

geochemistry of ferromanganese micronodules and associated mn and trace metals diagenesis at high terrigenous depositional site of middle fan region bay of bengal abstract the influence of sedimentation on the morphology growth and geochemistry of the micronodules and on mn enrichment in the sediments of the bay of bengal has been evaluated mn accumulation is 307 219 mg cm2 kyr 1 in cores having 20 17 cm kyr 1 sedimentation rate but drops to 34 17 7 mg cm2 kyr 1 in cores with 3 4 cm kyr 1 sedimentation rates however mn enrichment zone becomes thinner with increased sedimentation the abundance of the micronodules increases and they have been observed down to the deeper levels with higher contents of mn ni cu and zn from the areas of the lower sedimentation the results of the present study reveal that though the higher sedimentation may be conducive for higher mn accumulation in the upper surfaces of the sediments the growth abundance and enrichment of mn ni cu and zn in the micronodules are mostly regulated by their residence time within mn oxidation zone the influence of residence time on the morphology and the internal structures of the micronodules are also evaluated

mineralogy and geochemistry of surface sediments from the bengal fan indian ocean abstract the mineralogy and composition of 75 sediment samples from the bengal fan andaman sea and the eastern flanks of the upper nicobar fan have been determined sediments from the upper and middle bengal fan are mainly terrigenous and derived from the ganges brahmaputra river system whereas sediments from the andaman sea and the eastern flank of the upper nicobar fan vary from terrigenous to largely biogenic for the terrigenous sediments the continental influence is illustrated by the distribution of the major elements excluding ca which decrease away from the source the ti al and fe al ratios of the sediments are higher in samples from the cast coast of india than from the fans indicating the influence of material from the deccan basalts as well as from mafic rocks of the indian peninsula in the clay mineral fraction of upper bengal fan sediments illite and chlorite are the dominant constituents with minor amounts of smectite and traces of kaolinite illite is mainly a weathering product of lithic material from the himalaya and is transported by the ganges brahmaputra river system smectite is the dominant constituent of the sediments adjacent to the indian peninsula

deccan volcanism induced high stress environment during the cretaceous paleogene transition at zumaia spain evidence from magnetic mineralogical and biostratigraphic records abstract we conducted detailed rock magnetic mineralogical and geochemical mercury analyses spanning the cretaceous paleogene boundary kpb at zumaia spain to unravel the signature of deccan induced climate and environmental changes in the marine sedimentary record our biostratigraphic results show that zumaia is not complete and lacks the typical boundary clay zone p0 and the base of zone p1a 1 in the basal danian presence of an unusual 1m thick interval spanning the kpb is characterized by very low detrital magnetite and magnetosome biogenic magnetite contents and by the occurrence of akaganeite a very rare mineral on earth in oxidizing acidic and hyper chlorinated environments compatible with volcanic settings these benchmarks correlate with higher abundance of the opportunist guembelitria cretacea species detrital magnetite depletion is not linked to significant lithological changes suggesting that iron oxide dissolution by acidification is the most probable explanation the concomitant decrease in magnetosomes produced by magnetotactic bacteria at the anoxic oxic boundary is interpreted as the result of changes in seawater chemistry induced by surficial ocean acidification mercury peaks up to 20 50 ppb are common during the last 100 kyr of the maastrichtian zone cf1 but only one significant anomaly is present in the early danian which is likely due to the missing interval absence of correlation between mercury content r2 0 009 and total organic carbon r2 0 006 suggest that the former originated from the deccan traps eruptions no clear relation between the stratigraphic position of the mercury peaks and the magnetite depleted interval is observed although the frequency of the mercury peaks tends to increase close to the kpg boundary in contrast to bidart france and gubbio italy where magnetite depletion and akaganeite feature within a 50cm thick interval located 5 cm below the kpg boundary the same benchmarks are observed in a 1m thick interval encompassing the kpg boundary at zumaia results reinforce the synchronism of the major eruptions of the deccan traps magmatic province with the cretaceous paleogene kpg mass extinction and provide new clues to better correlate the deccan imprint of the global sedimentary record

the oxidation state of manganese in surface sediments of the deep sea iodometric titration of deep sea sediment from cores at manop sites m and h indicate a particulate mn oxidation state between 3 3 and 3 9 in the top 5 cm results from site h show a minimum in the mn oxidation state at 1 5 cm depth indicating mn reduction is occurring above the zone of pore water mn oxidation using a simple box model the rate of reduction is calculated to be 19 mg cm2 kyr 77 mg cm2 kyr at least 5 times the flux of mn to nodules in this region although no mn oxidation state minimum is observed in site m sediments oxic reduction is inferred from a particulate mass balance indicating that a large fraction of the mn rain to this site is not preserved in the sediments and must be remobilized we suggest that the process of reduction in oxic or suboxic environments near the sediment water interface may be an important mechanism controlling the concentration of mn in sediments and provides a mechanism for supplying diagenetic mn to the nodules at site h

wasp waisted hysteresis loops mineral magnetic characteristics and discrimination of components in mixed magnetic systems rock magnetic studies of complex systems that contain mixtures of magnetic minerals or mixed grain size distributions have demonstrated the need for a better method of distinguishing between different magnetic components in geological materials hysteresis loops that are constricted in the middle section but are wider above and below the middle section are commonly observed in mixed magnetic assemblages such wasp waisted hysteresis loops have been widely documented particularly with respect to rare earth permanent magnets basaltic lava flows remagnetized paleozoic carbonate rocks and an increasingly wide range of other rocks our modelling combined with a review of previous work indicates that there are several conditions that give rise to as well as magnetic properties that are characteristic of wasp waisted hysteresis loops first at least two magnetic components with strongly contrasting coercivities must coexist this condition can arise from either mixtures of grain sizes of a single magnetic mineral or a combination of magnetic minerals with contrasting cocrcivities or a combination of these two situations second materials that give rise to wasp waisted hysteresis loops will have relatively high ratios of the coercivity of remanence to coercive force b cr b c because b0 is controlled by the soft low coercivity component whereas bcris controlled by the hard high coercivity component third values of b cr b c 10 usually only occur for strongly wasp waisted loops when the low coercivity component comprises an overwhelmingly large fraction of the total volume of magnetic grains fourth a given mixture of superparamagnetic and single domain sd grains is more likely to give rise to wasp waisted hysteresis loops than an equivalent mixture of sd and multidomain grains fifth our results provide empirical confirmation that the total magnetization of a material is the sum of the weighted contributions of each component in the absence of significant magnetic interaction between particles thus to contribute significantly to wasp waisted behavior a mineral magnetic component must give rise to a significant portion of the total magnetization of the rock as a result minerals with weak magnetic moments such as hematite need to occur in large concentrations to cause wasp waistedness in materials that also contain ferrimagnetic minerals we outline a method for determining the magnetic components that can give rise to wasp waisted hysteresis loops this method is based on high and low temperature magnetic measurements that are used to identify the dominant remanence bearing mineral s and on mineral magnetic techniques that are used to discriminate between different magnetic domain states the method is illustrated with several examples from archaeological geological and synthetic materials

the responses of cyclonic and anticyclonic eddies to typhoon forcing the vertical temperature salinity structure changes associated with the horizontal convergence divergence the responses of the cyclonic eddies ces and anti cyclonic eddies aes to typhoon forcing in the western north pacific ocean wnpo are analyzed using argo profiles both ces and aes have the primary cooling at the surface 0 10 m depth and deep upwelling from the top of thermocline 200 m depth down to deeper ocean shortly after typhoon forcing due to the deep upwelling part of warm and fresh water at the top of aes move out of the eddy which leads to a colder and saltier subsurface in the aes after the passage of the typhoon in contrast the inflow of warm and fresh water heats and freshens the subsurface in the ces to compensate the cooling induced by the typhoon this explains why the observed strong sst cooling were much less than modeled since the aes are more frequent than ces in the wnpo it indicates that there is divergence convergence of warm and fresh water in the surface of aes subsurface of ces the divergence convergence effects of the aes and ces lead to the secondary cooling center locate at a shallow layer of 100 m in the aes and a much deeper layer of 350 m in the ces this shallow divergence convergence flow could lead a shallow overturning flow in upper oceans which may potentially influences the large scale ocean circulations and climates

the distribution of rare earth elements in manganese micronodules and sediments from the equatorial and southwest pacific abstract thirty three manganese micronodules and 38 associated sediments from selected areas in the equatorial and southwest pacific have been analyzed for ree significant variations in composition of both micronodules and sediments between the areas are observed in general the avarage ree abundance in manganese modules in a given area is higher than that of the associated micronodules but the ce la ratio of the micronodules is in some cases higher than that of the nodules the avarage ce la ratio of the micronodules is always higher than that of the associated sediment but the ree abundance is lower in several cases the ce anomaly is dominantly positive for micronodules and negative for sediments negative ce anomalies are however found in micronodules from the crest of the east pacific rise epr where metallogenesis is taking place positive ce anomalies occur in sediments from the southwestern pacific basin between the epr and new zealand the highest ce la ratios of both micronodules and sediments are found in this region reflecting the well oxidized conditions prevailing there

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

a late diagenetic syn folding magnetization carried by pyrrhotite implications for paleomagnetic studies from magnetic iron sulphide bearing sediments paleomagnetic rock magnetic and sedimentary micro textural data from an early miocene mudstone sequence exposed in okhta river sakhalin russia indicate the presence of pyrrhotite and magnetite at different stratigraphic levels sites that contain only magnetite have a reversed polarity characteristic remanent magnetization chrm with a low coercivity overprint which coincides with the present day geomagnetic field direction pyrrhotite bearing sites have stable normal polarity chrms that are significantly different from the present day field direction after correction for bedding tilt the chrm data fail a reversals test however the normal polarity pyrrhotite chrm directions become antipodal to the tilt corrected magnetite chrm directions and are consistent with the expected geocentric axial dipole field direction at the site latitude after 40 partial unfolding these data suggest that the pyrrhotite magnetization was acquired during folding and after lock in of the magnetite remanences electron microscope observations of polished sections indicate that fluid associated halos surround iron sulphide nodules pyrrhotite is present in randomly oriented laths in and around the nodules and the nodules do not appear to have been deformed by sediment compaction this observation is consistent with a late diagenetic origin of pyrrhotite documentation of a late diagenetic magnetization in pyrrhotite bearing sediments here and in recent studies of greigite bearing sediments suggests that care should be taken to preclude a late origin of magnetic iron sulphides before using such sediments for geomagnetic studies where it is usually crucial to establish a syn depositional magnetization

impact of climate change on the magnetic mineral assemblage in marine sediments from izu rear arc nw pacific ocean over the last 1 myr abstract a rock magnetic study was conducted on upper pleistocene marine sediments from international ocean discovery program expedition 350 site u1437 in order to highlight the paleoenvironmental changes in the nw pacific ocean influenced by the east asian monsoon regime remanent magnetization analyses hysteresis properties first order reversal curves and low temperature magnetic measurements were carried out along with electron microscope observations the results indicate that coarse grained titano magnetite is the dominant magnetic phase in the magnetic mineral assemblage time series analysis supports that this assemblage is modulated by global climate changes over the last 1 myr during the interglacial stages magnetic minerals are more abundant and are dominated by coarse grained titano magnetite of both terrigenous likely from mainland china and volcanic izu arc front japan origin during the glacial stages the magnetic mineral content is lower probably reflecting partial dissolution of ti magnetite and the magnetic assemblage is composed of terrigenous coarse grained titano magnetite and of higher coercivity presumably finer eolian particles likely hematite as a result of the enhancement of the winter monsoon in continental asia the magnetic mineral assemblage reflects a superimposition of volcanic and global climate signals bulk organic geochemical analyses for total and organic carbon as well as nitrogen and sulfur contents confirm a climatic signature in the composition of the sediments with more oxygenated water masses being present during glacial periods additional x ray fluorescence measurements on bulk samples indicate various origins of the sediment particles with both proximal and distal sources