stacking paleointensity and oxygen isotope data for the last 1 5 myr piso 1500 coupled relative geomagnetic paleointensity rpi and oxygen isotope records are used to construct rpi and oxygen isotope stacks for the last 1 5 myr the coupled correlations are accomplished using the match algorithm lisiecki l e and lisiecki p a 2002 application of dynamic programming to the correlation of paleoclimate records paleoceanography 17 1049 doi 10 1029 2001pa000733 to simultaneously correlate isotope and rpi records the simultaneous match reduces the degree of freedom associated with correlations using rpi or oxygen isotope records alone the overall compatibility of rpi and oxygen isotopes indicates a dominant global but independent component in both signals the local wavelet power spectrum lwps for the rpi stack indicates little significant orbital power although the accompanying oxygen isotope stack has all the lwps characteristics expected of a high resolution oxygen isotope record containing orbital frequencies the piso 1500 stack represents a new stratigraphic template that can be used to correlate among marine sediment records and link them to polar ice cores via variations in cosmogenic nuclide production scaling the stack to values for virtual axial dipole moment vadm indicate maxima at 15 1022 am2 and minima that imply a threshold of 2 5 1022 am2 below which values are associated with either polarity reversals or magnetic excursions

sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

10be evidence for delayed acquisition of remanent magnetization in marine sediments implication for a new age for the matuyama brunhes boundary abstract fluxes of the meteoric cosmogenic radionuclide 10 be vary with changes in the incoming cosmic rays modulated by geomagnetic field intensity variations the variability in the 10 be flux can be used to synchronize ice cores as well as marine sediments by comparison with the relative paleointensity variations of the geomagnetic field however lock in of the paleomagnetic signal at some depth below the sediment water interface in marine sediments through acquisition of a post depositional remanent magnetization pdrm adds uncertainty to synchronization despite the long history of such studies the magnitude of the pdrm lock in depth remains controversial in this article we present clear evidence for a downward offset of the paleointensity minimum relative to the 10 be flux anomaly at the matuyama brunhes m b geomagnetic polarity boundary which we interpret to result from a 15 cm pdrm lock in depth this lock in depth indicates that up to several tens of thousands years of age offset probably occurs when a paleomagnetic record is used for dating marine sediments and the age of the m b boundary should be revised to ca 10 kyr younger which is consistent with a younger ice core derived age of 770 6 ka 2 this cosmogenic age tuning strategy will contribute to refining paleomagnetic based age models for marine sediments and identifying of lead lag relationships for global abrupt environmental changes

paleointensity assisted chronostratigraphy of detrital layers on the eirik drift north atlantic since marine isotope stage 11 1 four piston cores collected in 1999 and 2002 from the eirik drift southern labrador sea off se greenland provide paleomagnetic environmental magnetic and oxygen isotope records back to marine isotope stage 11 age models for the cores are based on a combination of planktonic oxygen isotope data relative geomagnetic paleointensity proxies and the identification of geomagnetic excursions laschamp and iceland basin environmental magnetic data delineate two distinct detrital signals interpreted to reflect the behavior of the surrounding ice sheets greenland and laurentide to orbital and millennial scale climate forcing broad decimeter scale intervals of increased magnetic concentration and grain size occur during the early part of interglacial marine isotopic stages mis 1 5 7 9 and 11 discrete centimeter scale layers recognized by magnetic concentration and grain size sensitive parameters gamma ray attenuation gra bulk density and carbonate content are observed in glacial and interglacial stages as well as during terminations on the basis of glacial reconstructions on greenland during the last termination the broad decimeter scale coarser grained intervals can be attributed to detrital influx associated with the retreat of the terrestrial based greenland ice sheet in the early holocene a similar magnetic signal observed within interglacial mis 5 7 9 and 11 indicates similar greenland ice sheet behavior during these time intervals two types of centimeter scale detrital layers are also recognized back to mis 11 detrital carbonate dc layers reflect predominately ice rafted debris ird deposition while the low detrital carbonate ldc layers reflect mass movement as evidenced by sharp basal contacts graded bedding and traction structures likely from the greenland slope some detrital layers on eirik drift particularly the dc layers can be tentatively correlated to detrital layers observed in the central north atlantic and to those documented on the southern side of the labrador sea at orphan knoll

a composite record of late pleistocene relative geomagnetic paleointensity from the wilkes land basin antarctica abstract we report high resolution paleomagnetic records obtained from six piston cores recovered on the continental rise of the wilkes land basin wlb east antarctica in the frame of the italian australian wilkes land glacial history wega project the studied cores with a length of ca 4 m each were collected from the gentle and steep sides of sedimentary ridges present in the lower part of the continental rise and consist of very fine grained sediments paleomagnetic measurements were carried out on u channel samples apart from a low coercivity magnetic overprint removed after the first steps of alternating field demagnetization each core is characterized by a well defined characteristic remanent magnetization paleomagnetic inclinations fluctuate around the expected value of ca 77 for such high latitude sites and always indicate normal magnetic polarity short period oscillations to anomalously shallow paleomagnetic inclinations up to 20 were identified at different levels of the sampled sequences positive reverse inclination values were however not observed specific rock magnetic measurements indicate a substantial homogeneity of the magnetic mineralogy in the sampled sequences for each core we reconstructed curves of relative paleointensity rpi as computed by nrm 20 mt and nrm 20 mt arm 20 mt variation of the geomagnetic field an original age model was established by tuning the individual rpi curves with the available global and regional reference rpi stacks paleomagnetic results supported by other limited bio and chronostratigraphic constraints establish that all the cores are late pleistocene in age two provide an expanded record of the last ca 30 ka pc18 and pc19 three span the last ca 100 200 and 300 ka respectively pc25 pc27 and pc26 and one reaches back to ca 780 ka pc20 approaching the brunhes matuyama transition thus the wega paleomagnetic record provides the first experimental data documenting the dynamics and amplitude of the geomagnetic field variations at high southern latitudes during the brunhes chron the individual normalized rpi records were merged in a wega rpi stacking curve spanning the last 300 kyr the comparison of the wega rpi individual and stacked curves with the global references rpi stacks shows that geomagnetic paleointensity variations with periods longer than a few to tens kyr depending on the sedimentation rate can be safely recognized in this sector of the peri antarctic margins furthermore the stacking of the individual chrm inclination records indicates that the recurrent swings to shallow paleomagnetic inclinations may be correlated to the main known geomagnetic excursions of the brunhes chron supporting the validity of the age models the reconstructed average sediment accumulation rates for the individual cores range from 0 6 to 19 cm ka and are compatible with their position within the wlb with the lowest rates found close to the ridge of the sedimentary drifts moreover the high resolution age models obtained in this study provide original constraints to assess chronology rates and amplitudes of the climatic and environmental processes affecting this key area of the peri antarctic margins during the late pleistocene

orbital modulation of the earth s magnetic field intensity more than 20 years ago on the basis of data from a pacific sediment core it was suggested that geomagnetic field intensity may vary with the earth s orbital obliquity centred on a period of 41 kyr as a result of the effect of obliquity on precessional forces in the earth s core1 it had also been proposed that precession plays an important role in the energy budget of the earth s geodynamo2 but subsequent analyses indicated that the energy available from precession is at least an order of magnitude less than that required to drive the geodynamo3 here however we report a spectral analysis of sedimentary records of relative geomagnetic palaeointensity from two north atlantic sites which shows significant power both at orbital eccentricity 100 kyr and obliquity 41 kyr the eccentricity power is also present in bulk magnetic properties such as susceptibility and is therefore attributable to lithological variations controlled by eccentricity driven climate change the obliquity power however is not apparent in bulk magnetic properties and seems to be a property of the geomagnetic field itself thus providing evidence for the orbital forcing of geomagnetic field intensity

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

mean mixed depth of sediments the wherefore and the why the activities and consequently the bioturbational effects of deposit feeding organisms are largely restricted to a narrow surficial zone of marine sediments with a worldwide environmentally invariant mean of 9 8 cm with a standard deviation of 4 5 cm currently available theories of infaunal behavior cannot predict quantitatively this observation a new simple model that accounts for the feedback between resource food abundance its reactivity and the intensity of bioturbation leads to a quantitative estimate of 9 7 cm this model constitutes a fundamental advance in our understanding bioturbation

detection of noninteracting single domain particles using first order reversal curve diagrams we present a highly sensitive and accurate method for quantitative detection and characterization of noninteracting or weakly interacting uniaxial single domain particles unisd in rocks and sediments the method is based on high resolution measurements of first order reversal curves forcs unisd particles have a unique forc signature that can be used to isolate their contribution among other magnetic components this signature has a narrow ridge along the hc axis of the forc diagram called the central ridge which is proportional to the switching field distribution of the particles therefore the central ridge is directly comparable with other magnetic measurements such as remanent magnetization curves with the advantage of being fully selective to sd particles rather than other magnetic components this selectivity is unmatched by other magnetic unmixing methods and offers useful applications ranging from characterization of sd particles for paleointensity studies to detecting magnetofossils and ultrafine authigenically precipitated minerals in sediments

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

variability of geophysical log data and the signature of crustal heterogeneities at the ktb summary small scale variations in geophysical borehole data re ect geological inhomogeneities in the earth s crust that is its petrological mineralogical and structural organization in this paper comprehensive geophysical log data from the boreholes of the german continental deep drilling program ktb are analysed they include electric radiogenic magnetic seismic and bulk properties of rocks the logs were recorded in crystalline basement down to 9 km depth with a sampling interval of 0 15 m we describe the vertical variability within the data series in order to relate their statistics to the small scale heterogeneities of the upper crust for each physical property spectral exponents b and hurst coe cients h were calculated power spectra indicate a scaling behaviour with b values mostly falling in the range 0 5 b 1 5 typical of 1 f noise however no particular values of b characterize the log data rescaled range analyses show long range correlations with persistence of the signals from metres to thousands of metres values of h ranging between 0 6 and 0 8 reveal the self a ne character of the data series all the log data present similar statistics suggesting a fractal variability of the physical properties of the earth s crust the inferred scale invariance helps to quantify the complexity of crustal heterogeneities

a precursor to the matuyama brunhes transition field instability as recorded in pelagic sediments abstract the period some 20 25 kyr just prior to the most recent generally recognized geomagnetic field polarity transition the matuyama to brunhes reversal appears to be marked by significant geomagnetic variability manifested as pronounced oscillations in intensity we compare several previously published paleomagnetic records with new high resolution paleomagnetic data obtained from five pelagic marine sites north atlantic dsdp hole 609b equatorial atlantic odp hole 665a and western equatorial pacific odp holes 803b 804c and 805b using standard rock magnetic normalization for all of the samples as well as a thellier thellier method on the sediments of hole 804c we consistently find a decrease in paleointensity dip of 1 approximately 15 kyr prior to the matuyama to brunhes transition in the five new records as well as in the previously published records despite sedimentation accumulation rates sar that range from 11 cm kyr to 1 cm kyr these sequences yield paleointensity curves that are broadly similar in form even at the lowest sars the intensity of the pre reversal low dip1 appears to be of the same magnitude as that of the transition itself dip2 of 1 in some of the records a directional excursion to nearly full normal polarity accompanies dip1 and remains after alternating field af and or thermal demagnetization whereas in other records the directional changes vanish with demagnetization and appear to be caused by overprinting a viscous remanent magnetization vrm contribution to nrm was identified in two of the records and until removed by af or thermal demagnetization was found to blur the double dip nature of the paleointensity profiles into an apparent single dip and also resulted in an apparent but erroneous sawtooth like post transitional sudden increase in paleointensity after appropriate normalization the magnitude of the post transitional recovery was much reduced the magnetic directions of three of the new records after cleaning and adjusting the stable declinations to either 0 normal or 180 reverse map to vgp positions lying in the pacific the directional variations however are far less consistent than the intensity variations the confirmed global existence of this dip so closely preceding a major reversal invites questions about its relation to the reversal itself the apparent normal character of this interval can also present problems for magnetostratigraphical interpretations based on coarse or incomplete sampling by mimicking the brunhes matuyama reversal some 15 kyr earlier in the section than its true location

is burial velocity a master parameter for bioturbation abstract the intensity of biological mixing in a marine sediment is widely believed to be related to the flux of labile organic matter at the same time this flux has been shown to be strongly correlated to the burial velocity one would then expect a significant correlation between biological mixing coefficient d b and burial velocity a nonlinear regression of existing data with a power law eqns 2 and 3 of the text produces a statistically significant correlation the statistical significance of the regression in no way implies causation and in fact it accounts for only about 22 of the total variance in the dataset thus reducing its physical significance a number of additional processes contribute to the large observed variance including timing of mixing events temporal and spatial heterogeneity differences in temporal scales sampling artifacts and specific particle associations with due care the d b relationship may prove useful in defining the likely range of d b values in a particular environment a similar analysis of the tracer identified surface mixed depth shows that it is essentially independent of burial velocity with a worldwide mean of 9 8 4 5 cm depth of mixing is probably more closely related to the energetic costs of deep burrowing

padm2m a penalized maximum likelihood model of the 0 2 ma palaeomagnetic axial dipole moment summary we present a new time varying model for palaeomagnetic axial dipole moment padm for the past 2 myr and compare it with earlier virtual axial dipole moment vadm reconstructions which have been based on stacking and averaging scaled relative palaeointensity records the padm is derived from both absolute and relative palaeointensity data and constructed using a new penalized maximum likelihood pml approach to recover a cubic b spline representation of axial dipole field variations on million year timescales the pml method is explicitly intended to reduce bias in estimating the true axial dipole moment that arises in average vadm reconstructions we apply the pml method to a set of 96 032 published data 1800 palaeointensities from igneous rocks 3300 archaeointensities and 86 relative palaeointensity time series of variable lengths and resolutions two models are discussed padm2mp is a trial model based on a subset of the nine longest available sedimentary records padm2m uses a comprehensive data set 76 records 81 446 data 10 records were eliminated and is our preferred model padm2m has a lower mean than existing vadm reconstructions but shows similarities in long period variability some differences in timing amplitude and resolution of certain features can be attributed to variations in age assignments others result from our more comprehensive data set and a reduction in bias attributable to pml modelling padm2m has an average axial dipole moment over 0 2 ma of 5 3 1022 am2 with a standard deviation of 1 5 1022 am2 the brunhes chron average 6 2 1022 am2 is higher than for earlier epochs of matuyama 4 8 1022 am2 as seen in some previous studies the power spectrum for our model agrees with previous estimates of the global palaeomagnetic power spectrum for frequencies up to about 102 myr 1 we see no distinctive evidence in the power spectrum for orbital forcing of geodynamo behaviour

a wavelet investigation of possible orbital influences on past geomagnetic field intensity 1 a number of sedimentary records of relative paleointensity have been reported to contain modes of variability that could have been driven by changes in the earth s orbital or climatic state proposed relationships are often based on visual correlation in the time domain or the presence of peaks in relative paleointensity frequency spectra close to those of the orbital components when discussing hypothesized connections it is not common for the phase relationship between paleointensity and orbital change to be addressed so a true mechanistic link cannot be confirmed the existence of a direct link between records of paleointensity and orbital climatic variation is tested using the cross wavelet transform and squared wavelet coherence it is found that while all the records show common power at certain periods the geomagnetic and orbital variations do not exhibit a consistent phase relationship suggesting there is no direct physical link between them this interpretation is supported by a lack of significant correlation in the time frequency plane between the studied records as measured by the squared wavelet coherence

measurement of the degree of smoothing in sediment paleomagnetic secular variation records an example from late quaternary deep sea sediments of the bermuda rise western north atlantic ocean abstract replicate paleomagnetic secular variation psv records for the last 15 000 yr have been recovered from two deep sea sediment gravity cores on the bermuda rise western north atlantic ocean the records have been correlated using several different parameters and dated by correlation to a nearby piston core which has a high resolution 14 c chronology the psv records are systematically subdued with respect to the expected local magnetic field variability during the holocene when sedimentation rates were about 10 cm kyr during the late pleistocene when sedimentation rates were a factor of 2 3 higher the psv variability was significantly larger we attribute this to smoothing of the psv records by a depositional post depositional remanence drm pdrm acquisition process with a 10 20 cm lock in interval the degree of psv smoothing was evaluated by comparing the vgp angular dispersion and vector spectral content of the bermuda rise cores with high resolution psv records from north america and great britain these results suggest a 50 reduction in the drm pdrm recording of vector variability during the holocene on the bermuda rise with most of the psv reduction occurring for features of less than 2000 yr in duration we can reproduce the subdued psv pattern with a mathematical model that simulates the site drm pdrm remanence acquisition process finally the replicate gravity cores document that psv records may be reproducible on a local scale even though they only retain a low pass filtered record of true magnetic field variability

brachiopod δ34scas microanalyses indicate a dynamic climate influenced permo carboniferous sulfur cycle abstract early isotopic studies of sulfate in carbonate minerals carbonate associated sulfate cas suggested that carbonates can provide a reliable well dated archive of the marine sulfur cycle through time however subsequent research has shown that diagenetic alteration can impose highly heterogeneous cas sulfur isotopic compositions 34 s cas among different carbonate phases within sediments such alteration necessitates targeted sampling of well preserved primary carbonate phases here we present a new record of carboniferous and early permian brachiopod 34 s cas generated from over 130 measurements of microsampled brachiopod shells our record refines existing brachiopod 34 s cas records and confirms a large 6 5 34 s cas decrease in the early carboniferous importantly the record also features a novel 3 5 increase in 34 s cas near the serpukhovian bashkirian boundary 323 4 ma that coincides with carbonate 13 c and 18 o increases variability in 34 s cas is minor both within 0 3 and among 2 individual co depositional brachiopod specimens a taxon specific 34 s cas offset is present one species composita subtilita that also exhibits a 13 c offset supporting the existence of biological vital effects on 34 s cas geologic evidence and mathematical modeling of the permo carboniferous carbon and sulfur cycles suggest that changes in the burial ratio of organic carbon to pyrite sulfur r c s are insufficient to explain the observed mid carboniferous 34 s cas record we find that changes in the 34s depletion of pyrite relative to seawater sulfate e 34 or in the 34 s of the input to the ocean 34 s in are also needed large additions of o2 from organic carbon burial during the permo carboniferous cannot be entirely compensated for with sulfur cycle changes lower than modern late visean po2 and or additional o2 sinks are needed to keep po2 at plausible levels based on the geologic context surrounding our record s mid carboniferous 34 s cas increase we advocate for simultaneous changes in pyrite burial e 34 and 34 s in driven by sea level or tectonically induced changes in environments of sulfur burial as a viable mechanism to produce rapid seawater 34 s changes

magnetostatic interactions in deep sea sediments inferred from first order reversal curve diagrams implications for relative paleointensity normalization 1 understanding magnetostatic interactions in sediments is important for paleomagnetism and rock magnetism magnetostatic interactions are known to affect significantly the efficiency of anhysteretic remanent magnetization arm acquisition and hence the ratio of arm susceptibility arm to saturation isothermal remanent magnetization sirm a magnetic grain size proxy widely used for environmental applications can be controlled by magnetostatic interactions relative paleointensity estimations may also be influenced by magnetostatic interactions because arm is often used as a normalizer to correct for the difference in magnetizability of sediments in this study characterization of magnetic grains in deep sea sediments from the north pacific ocean was conducted using first order reversal curve forc diagrams and irm acquisition curves the forc diagrams indicate that the magnetic grains consist mainly of a noninteracting single domain sd component and an interacting sd component and additionally of a multidomain md component the relative abundances of these components were semiquantitatively estimated by curve fitting of cross sections along a line parallel to the axis of local interaction fields hu and through a peak in the coercivity hc three components were fitted assuming a gaussian distribution of interaction fields hu the irm acquisition curves can be described by two dominant components assuming a log gaussian distribution the mean coercivities of the two components are 40 and 100 mt respectively it is estimated that the former component is carried by biogenic magnetite and roughly corresponds to the noninteracting sd component derived from the forc diagrams and that the latter component is carried by eolian maghemite corresponding to the interacting sd component the arm sirm ratio decreases with increasing concentration of the interacting sd component this implies that the arm sirm ratio is significantly affected by magnetostatic interactions and that it does not necessarily reflect magnetic grain size the effect of magnetostatic interactions on natural remanent magnetization acquisition in sediments is not well understood but if it is similarly sensitive to the sirm normalization by arm in relative paleointensity estimations would overcompensate for the concentration of magnetic grains and cause the significant coherence between the normalized intensity and the normalizer that has been reported in the literature

a geomagnetic paleointensity stack between 0 8 and 3 0 ma from equatorial pacific sediment cores 1 we have conducted a paleomagnetic study of six sediment cores taken from the equatorial pacific three from the west caroline basin and three from the manihiki plateau in order to make a relative paleointensity stack during the matuyama and late gauss chrons the age of the bottom of the cores ranges from 1 2 to 3 0 ma the sediments show little downcore changes in the proxies of magnetic grain size and mineralogy and are hence suitable for estimating relative paleointensity the age of the cores is controlled by correlating variations in magnetic concentration magnetic susceptibility and or anhysteretic remanent magnetization arm to target oxygen isotope 18o curves all cores from the manihiki plateau show an upward decrease of the natural remanent magnetization nrm intensity normalized by arm and isothermal remanent magnetization irm with a decrease in sedimentation rate such a trend was removed before being converted to relative paleointensity this observation implies that a sedimentation rate change can affect relative paleointensity estimation relative paleointensity records from the six cores coincide well with each other within uncertainty of age we constructed a stacked curve between 0 8 and 3 0 ma the equatorial pacific paleointensity stack epapis 3ma after adjusting age the number of cores stacked is three to four throughout the record quasiperiodic paleointensity lows occur in the epapis 3ma and corresponding paleointensity lows can be found in previously published records with some shifts in age at least parts of the paleointensity minima seem to be accompanied by geomagnetic excursions the asymmetric sawtooth pattern of paleointensity variations is not observed at the matuyama gauss boundary and thereafter in our record a spectral analysis shows that 100 kyr orbital eccentricity frequency may exist in paleointensity variations during the matuyama and late gauss chrons

correlation of paleointensity variation records in the brunhes matuyama polarity transition interval abstract paleomagnetic records of the 0 78 ma brunhes matuyama b m polarity reversal interval described from high resolution 8 11 cm kyr deep sea sediments from western equatorial pacific odp sites 767b and 769a show two successive and marked decreases in paleointensity of about 15 kyr wavelength each and a shift from full reversed to fuli normal polarity directions in only 2 kyr associated with the uppermost paleointensity decrease in contrast transition records from deep sea sediments with lower sedimentation rates tend to show simpler paleointensity variation with more complex patterns of directional change for example the b m transition record described from deep sea sediment core v16 58 from the southern indian ocean we suggest that the twin 10 be peaks reported in v16 58 correspond to increased production of this cosmogenic isotope associated with the double paleointensity dips recorded in odp 767b 769a the low resolution v16 58 paleomagnetic record can be accounted for by modeling of the geomagnetic field history in odp 767b at a nominal recording rate of 1 cm kyr and using an exponential lock in process filter with a half fixing depth of 16 cm the double paleointensity dips become a single broad magnetization low and the change in paleomagnetic directions is offset by about 16 cm below the actual level of the polarity transition similar to what we infer for v16 58 the low resultant magnetizations will be especially prone to overprinting which if in the present field will tend to give an americas vgp path the main features of the 10 be profile will be unaffected by the remanence lock in process and consequently retain their usefulness for correlation as a proxy of geomagnetic dipole intensity variation

origin of apparent magnetic excursions in deep sea sediments from mendeleev alpha ridge arctic ocean 1 arctic deep sea sediments often record intervals of negative inclination of natural remanence that are tens of centimeters thick implying magnetic excursions with durations of tens of thousand years that far exceed excursion durations estimated elsewhere and the lack of tight age control usually provides excessive freedom in the labeling of arctic excursions fortuitous variations in sedimentation rate have been invoked to explain the amplified excursions alternating field demagnetization of natural remanent magnetization nrm of sediment cores 08jpc 10jpc 11jpc and 13jpc recovered by the healy oden trans arctic expedition in august 2005 hotrax05 to the mendeleev alpha ridge yields apparent magnetic excursions in sediments deposited in the brunhes chron thermal demagnetization of the nrm however implies multiple magnetization components with negative inclination components usually unblocked below 350 c analysis of isothermal remanent magnetization acquisition curves from magnetic extracts indicates two magnetic coercivity components superimposed on one another magnetic experiments conducted under high and low temperatures show features that are characteristic for titano magnetite and titanomaghemite presence of the two magnetic phases is further confirmed by elemental mapping on a scanning electron microscope equipped for x ray energy dispersive spectroscopy eds and by high resolution x ray diffraction xrd it is unlikely that anomalously thick intervals of negative inclination in these brunhes aged sediments are caused by unusual behavior of the magnetic field in the arctic area we therefore attribute low and negative nrm inclinations in these cores to partially self reversed chemical remanent magnetizations apparently carried by titanomaghemite and acquired during the oxidation of detrital titano magnetite grains the high ti contents and high oxidation states indicated by eds and xrd data provide the conditions required for partial self reversal by ionic reordering during diagenetic maghemitization and this process appears to have affected all hotrax05 cores collected from the mendeleev alpha ridge

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

origin of orbital periods in the sedimentary relative paleointensity records abstract orbital cycles with 100 kyr and or 41 kyr periods detected in some sedimentary normalized remanence relative paleointensity records by power spectral analysis or wavelet analysis have been attributed either to orbital forcing of the geodynamo or to lithologic contamination in this study local wavelet power spectra lwps with significance tests have been calculated for seven relative paleointensity rpi records from different regions of the world the results indicate that orbital periods 100 kyr and or 41 kyr are significant in some rpi records during certain time intervals and are not significant in others time intervals where orbital periods are significant are not consistent among the rpi records implying that orbital periods in these rpi records may not have a common origin such as orbital forcing on the geodynamo cross wavelet power spectra xwt and squared wavelet coherence wtc between rpi records and orbital parameters further indicate that common power exists at orbital periods but is not significantly coherent and exhibits variable phase relationships implying that orbital periods in rpi records are not caused directly by orbital forcing similar analyses for rpi records and benthic oxygen isotope records from the same sites show significant coherence and constant in phase relationships during time intervals where orbital periods were significant in the rpi records indicating that orbital periods in the rpi records are most likely due to climatic contamination although common power exists at orbital periods for rpi records and their normalizers with significant coherence during certain time intervals phase relationships imply that contamination at orbital periods is not directly due to the normalizers orbital periods are also significant in the nrm intensity records and contamination in rpi records can be attributed to incomplete normalization of the nrm records further tests indicate that contamination is apparently not directly related to physical properties such as density or carbonate content or to the grain size proxy arm however wtc between rpi records and the grain size proxy arm irm implies that arm irm does reflect the contamination in some rpi records it appears that orbital periods were introduced into the nrm records and have not been normalized when calculating rpi records through magnetite grain size variations reflected in the arm irm grain size proxy the orbital power in arm irm for some north atlantic sites is probably derived from bottom current velocity variations that are orbitally modulated and are related to the vigor of thermohaline circulation and the production of north atlantic deep water nadw in the case of odp site 983 the orbital power in rpi appears to exhibit a shift from 41 kyr to 100 kyr period at the mid pleistocene climate transition 750 ka reinforcing the climatic origin of these orbital periods rpi records from the atlantic and pacific oceans and rpi records with orbital periods eliminated by band pass filters are highly comparable with each other in the time domain and are coherent and in phase in time frequency space especially at non orbital periods indicating that contamination although present at orbital periods is not debilitating to these rpi records as a global signal that is primarily of geomagnetic origin

relative paleointensity of the geomagnetic field during brunhes chron recorded in north pacific deep sea sediment cores orbital influence abstract relative paleointensity records of the geomagnetic field during the brunhes chron were obtained from two sediment cores in the north pacific near the hess rise the cores taken below the carbonate compensation depth ccd showed an oxidized environment and accompany little paleoclimatically induced lithological changes homogeneity of magnetic mineralogy and magnetic grain size which are prerequisites for sedimentary paleointensity were thoroughly examined using various techniques including low temperature magnetometry room temperature hysteresis parameters and s ratio isothermal remanent magnetization irm was used as a normalizer of the natural remanent magnetization nrm the appropriateness of the normalization was checked by the absence of correlation between the normalized intensity nrm irm and the normalizer irm the relative paleointensity records obtained are generally similar to the datasets from the east and central equatorial pacific spectral analysis showed significant power at the orbital eccentricity 100 kyr frequency in the relative intensity record but not for the normalizer this suggests orbital influence on the geomagnetic field intensity but the possibility of paleoclimatic contamination through rock magnetic changes should be examined further using cores from different sedimentary regime

a reassessment of post depositional remanent magnetism preliminary experiments with natural sediments abstract realignment of magnetic grains below the sediment water interface is thought to impart a post depositional remanent magnetization pdrm however there is little convincing evidence in the published literature that pdrm is the dominant mechanism by which sediments become magnetized we report here preliminary results from two kinds of laboratory experiments designed to investigate whether post depositional reorientation of magnetic particles is likely to occur in nature in the first experiment we monitored changes in the magnetization of natural sediments in response to changing laboratory fields our results are inconsistent with post depositional reorientation of magnetic particles in a second experiment we put live worms in a multi core tube with the original sediment water interface intact remagnetization was only observed in samples taken from a mound of fecal pellets formed at the surface these pellets had been suspended by a worm and redeposited in the laboratory field the other samples which were not resuspended but nonetheless bioturbated by the worms showed no change in magnetization our preliminary results do not support the hypothesis that post depositional reorientation occurs in natural undisturbed sediments below the sediment water interface

geomagnetic intensity variations over the past 780 kyr obtained from near seafloor magnetic anomalies knowledge of past variations in the intensity of the earth s magnetic field provides an important constraint on models of the geodynamo a record of absolute palaeointensity for the past 50 kyr has been compiled from archaeomagnetic and volcanic materials and relative palaeointensities over the past 800 kyr have been obtained from sedimentary sequences but a long term record of geomagnetic intensity should also be carried by the thermoremanence of the oceanic crust here we show that near seafloor magnetic anomalies recorded over the southern east pacific rise are well correlated with independent estimates of geomagnetic intensity during the past 780 kyr moreover the pattern of absolute palaeointensity of seafloor glass samples from the same area agrees with the well documented dipole intensity pattern for the past 50 kyr a comparison of palaeointensities derived from seafloor glass samples with global intensity variations thus allows us to estimate the ages of surficial lava flows in this region the record of geomagnetic intensity preserved in the oceanic crust should provide a higher time resolution record of crustal accretion processes at mid ocean ridges than has previously been obtainable

magnetic paleointensity stratigraphy and high resolution quaternary geochronology successes and future challenges abstract magnetic paleointensity stratigraphy is used to detect variations in the strength of earth s ancient magnetic field paleointensity studies have demonstrated that a dominantly dipolar geomagnetic signal can be recorded in a globally coherent manner in different types of sediments and in non sedimentary archives including ice core records and marine magnetic anomaly profiles the dominantly dipolar nature of geomagnetic paleointensity variations provides a global geophysical signal that has come to be widely used to date quaternary sediments despite the many successful applications of paleointensity assisted chronology the mechanisms by which sediments become magnetized remain poorly understood and there is no satisfactory theoretical foundation for paleointensity estimation in this paper we outline past successes of sedimentary paleointensity analysis as well as remaining challenges that need to be addressed to place such work on a more secure theoretical and empirical foundation we illustrate how common concepts for explaining sedimentary remanence acquisition can give rise to centennial to millennial offsets between paleomagnetic and other signals which is a key limitation for using paleointensity signals for geochronology our approach is intended to help non specialists to better understand the legitimate uses and limitations of paleointensity stratigraphy while pointing to outstanding problems that require concerted specialist efforts to resolve

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

effects of variable sedimentation rates and age errors on the resolution of sedimentary paleointensity records 1 synthetic u channel records of relative paleointensity have been generated with a numerical model simulating the recording process in sediments variable quality age control and variable sedimentation rates over a time interval of 500 ky simulation results indicate that paleointensity records with mean sedimentation rates up to 15 cm ky can reflect geomagnetic dipole intensity fluctuations with some amplitude differences between individual records of nongeomagnetic origin this study confirms that relative paleointensity records have great potential as a stratigraphic tool and that a stratigraphic precision of a few thousand years can be achieved with records characterized by high sedimentation rates spectral analyses suggest that caution should be used when interpreting the power spectra of individual records and that stacked records should be favored stacked u channel records with mean sedimentation rates of 1 cm ky do not provide reliable spectral information on the dipole intensity for wavelengths shorter than 25 50 ky and their utility is limited to long term trends in paleointensity for higher sedimentation rates the range of spectral information depends on the stack resolution sedimentation rates and the age model the best results are predictably obtained with high sedimentation rates and excellent age control in these cases the power spectra are reliable for wavelengths as short as 4 ky

dissolution and pyritization of magnetite in anoxie marine sediments concentrations of magnetite were determined with depth in sediments of varying h2s content taken from long island sound foam nwc and sachem sites and from a site in the rapidly depositing subaqueous portion of the mississippi delta for the three long island sound sites dissolution of magnetite during burial is clearly demonstrated and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide by combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide we find that magnetite dissolution is well described by the following rate law dcmagdt 1 1 10 5c0 5bcmagamag where cmag is the concentration of magnetite grams per gram of sediment cs is the concentration of dissolved sulfide mm and amag is the specific surface area of magnetite in the sediment cm2 per gram of magnetite this equation means that for a typical range of magnetite surface areas and dissolved sulfide concentrations the half life of magnetite in anoxic marine sediments ranges from about 50 to 1000 years sem observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite this only occurs if magnetite is in contact with high concentrations of h2s 1 mm for relatively long periods of time several hundred years with low concentrations of h2s 1 mm magnetite dissolution occurs without identifiable pyrite replacement we suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator

10 be evidence for the matuyama brunhes geomagnetic reversal in the epica dome c ice core every few hundred thousand years earth s north and south magnetic poles swap places for the first time a record of one of these geomagnetic reversals has been found in an ice core because the strength of the field is very low during a reversal the intensity of cosmic rays in the earth s atmosphere is increased this leads to an increase in the quantity of 10be which like 14c is formed by cosmic rays in the atmosphere deposited in the ice it is this 10be enhancement in the ice that has been detected an ice core drilled at dome c antarctica is the oldest ice core so far retrieved1 on the basis of ice flow modelling and a comparison between the deuterium signal in the ice with climate records from marine sediment cores the ice at a depth of 3 190 m in the dome c core is believed to have been deposited around 800 000 years ago2 offering a rare opportunity to study climatic and environmental conditions over this time period however an independent determination of this age is important because the deuterium profile below a depth of 3 190 m depth does not show the expected correlation with the marine record2 here we present evidence for enhanced 10be deposition in the ice at 3 160 3 170 m which we interpret as a result of the low dipole field strength during the matuyama brunhes geomagnetic reversal which occurred about 780 000 years ago if correct this provides a crucial tie point between ice cores marine cores and a radiometric timescale

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research