results of rock magnetic investigations and relative paleointensity determinations on lacustrine sediments from birkat ram golan heights israel i detailed rock magnetic investigations including the analysis of the laboratory installed magnetizations the measurement of hysteresis parameters and the high temperature dependency of the saturation magnetization were carried out on sediments from birkat ram golan heights israel the 550 cm long composite profile composed of three single cores is supposed to span the late holocene i e the last 4400 years at least titanomagnetites in the pseudo single domain range were identified as the main magnetic carrier minerals in the homogenous sediments the variations in concentration and grain size of the magnetic fraction are only partly reflected in the sediment lithology the relative paleointensity was estimated by normalizing the intensity of the natural remanent magnetization nrm after demagnetization at 20 mt j nrm 20 mt by different concentration parameters the median destructive field of the nrm mdf nrm is coherent with the relative paleointensity estimates indicating that a sedimentary effect has not sufficiently been removed by the normalization process the morphologies of these estimates however correspond to the archeomagnetic records from bulgaria and greece therefore a second normalization based on the linear relationship between the paleointensity estimates and the mdf nrm was applied resulting in an improvement of the records

high resolution palaeosecular variation in northern europe during the last 3200 years variations in the declination inclination and relative palaeointensity of earth s magnetic field during the last 3200 yr have been recorded from a sequence of annually laminated sediments in lake pohjajarvi lat 62 n central finland the magnetic mineralogy is uniform with only small variations in concentration of magnetite of pseudo single domain psd grain size the variations in direction were found to be very similar to records reconstructed from other lakes in finland and northwest russia while the relative palaeointensity curve can be correlated accurately with archaeomagnetic data from central europe

holocene palaeoecology of the golan heights near east investigation of lacustrine sediments from birkat ram crater lake abstract lacustrine deposits of the crater lake birkat ram located in the northern golan heights have been used as a paleoecological archive preliminary sedimentological and palynological investigations based on a composite profile allow the reconstruction of the environmental history of the last 6500 years fluctuations of the pollen composition trees and shrubs versus herbs values of oak and olive tree correspond to changes in different sediment parameters total organic carbon magnetic susceptibility which can be interpreted as the effects of human impact on the geo biosphere four phases with strong settlement activities can be identified for the northern golan heights 1 during the chalcolithic period early bronze age 2 during the hellenistic roman byzantine periods 3 during the crusader period and finally during modern time these periods were interrupted by wooded regeneration phases with low anthropogenic activities

sedimentary records of relative paleointensity of the geomagnetic field theory and practice sediments have proved irresistible targets for attempts at determining the relative variations in the earth s magnetic field because of the possibility of long and continuous sequences that are well dated and have a reasonable global distribution the assumption underlying paleointensity studies using sedimentary sequences is that sediments retain a record reflecting the strength of the magnetic field when they were deposited early theoretical work suggested that because the time required for an assemblage of magnetic particles in water to come into equilibrium with the ambient magnetic field was quite short no dependence on magnetic field was expected nonetheless a number of experiments showed that sedimentary magnetizations varied in accordance with the field albeit not always in a simple linear fashion experiments in which the sediments were stirred in the presence of a field to simulate bioturbation showed a reasonably linear relationship with the applied field and these results spurred the hope that variations in the earth s magnetic field might indeed be recoverable from appropriate sedimentary sequences examination of existing paleointensity data sets allows a few general conclusions to be drawn it appears that sedimentary sequences can and do provide a great deal of information about the variations in relative paleointensity of the earth s magnetic field the dynamic range of sedimentary data sets is comparable to those acquired from thermal remanences moreover when compared directly with such independent measures of magnetic field variations as beryllium isotopic ratios and thermally blocked remanences there is considerable agreement among the various records when viewed over timescales of hundreds to thousands of years relative paleointensity data sets from more than a few thousand kilometers apart bear little resemblance to one another suggesting that they are dominated by nondipole field behavior when viewed over timescales of a few tens of thousands to hundreds of thousands of years however the records show coherence over large distances at least thousands of kilometers and may reflect changes in the dipole field on the basis of a sequence spanning the brunhes and matuyama chrons the magnetic field has oscillated with a period of about 40 ka for the last few hundred thousand years but these oscillations are not clear in the record prior to about 300 ka thus they are probably not an inherent feature in the geomagnetic field and the correspondence of the period of oscillation to that of obliquity is probably coincidence

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

an 84 kyr paleomagnetic record from the sediments of lake baikal siberia we have conducted a paleomagnetic study of sediment cores obtained from the selenga prodelta region of lake baikal russia this record which spans approximately the last 84 kyr contributes to a better understanding of the nature of geomagnetic field behavior in siberia and is a useful correlation and dating tool we demonstrate that the lake baikal sediments are recording variations in the geomagnetic field the directional record displays secular variation behavior with a geomagnetic excursion at 20 ka and additional excursions appearing as large amplitude secular variation at 41 61 and 67 ka smoothing of the geomagnetic excursion behavior occurs in lake baikal sediments owing to the intermediate sedimentation rate 13 cm kyr 1 the lake baikal relative paleointensity record correlates to absolute paleointensity data for the last 10 kyr and to relative paleointensity records from the mediterranean sea and indian ocean for the last 84 kyr this correlation suggests a strong global i e dipole component to these records and further supports the reliability of sediments as recorders of relative geomagnetic paleointensity we show that a relative geomagnetic intensity stratigraphy has a potential resolution of 7 kyr by correlating continental and marine records the geomagnetic intensity stratigraphy helps constrain the age of the difficult to date lake baikal sediments

revised pacific antarctic plate motions and geophysics of the menard fracture zone a reconnaissance survey of multibeam bathymetry and magnetic anomaly data of the menard fracture zone allows for significant refinement of plate motion history of the south pacific over the last 44 million years the right stepping menard fracture zone developed at the northern end of the pacific antarctic ridge within a propagating rift system that generated the hudson microplate and formed the conjugate henry and hudson troughs as a response to a major plate reorganization 45 million years ago two splays originally about 30 to 35 km apart narrowed gradually to a corridor of 5 to 10 km width while lineation azimuths experienced an 8 counterclockwise reorientation owing to changes in spreading direction between chrons c13o and c6c 33 to 24 million years ago we use the improved pacific antarctic plate motions to analyze the development of the southwest end of the pacific antarctic ridge owing to a 45 counterclockwise reorientation between chrons c27 and c20 61 to 44 million years ago this section of the ridge became a long transform fault connected to the macquarie triple junction following a clockwise change starting around chron c13o 33 million years ago the transform fault opened a counterclockwise change starting around chron c10y 28 millions years ago again led to a long transform fault between chrons c6c and c5y 24 to 10 million years ago a second period of clockwise reorientation starting around chron c5y 10 million years ago put the transform fault into extension forming an array of 15 en echelon transform faults and short linking spreading centers

high resolution paleomagnetic records from holocene sediments from the palmer deep western antartic peninsula thick holocene sedimentary sections 45 m cored in the palmer deep by the united states antarctic program usap and during ocean drilling program odp leg 178 provide the first opportunity to examine past geomagnetic field behavior at high southern latitudes after removal of a low coercivity drilling overprint the sediments display a stable single component remanent magnetization two short cores that recovered the uppermost 2 6 m of sediment have inclinations that fluctuate about the present day inclination 57 measured at faraday station and several features with wavelengths of 10 to 20 cm appear to be correlative however shipboard measurements of inclination fluctuations on split core samples from three holes drilled at odp site 1098 do not correlate well with each other even though the intensity and susceptibility data correlate very well and the overall mean inclination for cores from each hole is consistent with the expected geocentric axial dipole gad inclination the correlation is improved dramatically by using inclinations measured on u channels taken from the pristine center of a split core consequently the anomalous directions and the resulting poor between hole correlation of inclinations obtained from shipboard data can be attributed to coring induced deformation which is common on the outer edge of odp piston cores and or measurement artifacts in the split core data our preferred inclination record is thus derived from u channel results the upper 25 m represents continuous sedimentation over the past 9000 yr with an average sedimentation rate exceeding 250 cm kyr 0 25 cm yr given that remanence measurements on u channels average over an interval 7 cm long we obtained independent measurements of the paleo geomagnetic field that average over only 30 yr this high resolution record is characterized by an inclination that fluctuates within 15 of the current gad inclination

on the use of calibrated relative paleointensity records to improve millennial scale geomagnetic field models current millennial scale time varying global geomagnetic field models suffer from a lack of intensity data compared to directional data because only thermoremanently magnetized material can provide absolute information about the past field strength the number of archeomagnetic artifacts that can provide such data diminishes rapidly prior to 3000 b c sediment cores provide time series of declination and inclination and of variations of magnetization the latter can reflect relative geomagnetic field variations if suitably normalized we propose a calibration technique based on predictions from global models and use the cals7k 2 model to calibrate relative paleointensity records from 22 globally distributed locations and assess whether they reflect actual field variations all except a few contain useful information for 0 to 7 ka and could be used to improve the existing models using synthetic data from a numerical dynamo simulation we show that with the existing directional data the distribution of intensity data has an important influence on model quality intensity data from a broad range of latitudes seem particularly important this study opens the possibility of extending global time varying geomagnetic field models further back in time than the current 7 kyr interval

palaeosecular variation of the earth s magnetic field during the last 10000 years based on the annually laminated sediment of lake nautajarvi central finland a palaeomagnetic study of the lake nautajarvi sediment sequence in central finland demonstrates that varved lake sediments can provideregionally applicable secular variations curves for holocene stratigraphic correlation and age control based on x ray radiography and digital image analysis techniques we constructed an inherent and continuous varve chronology for the lake nautajarvi varve sequence which covers nearly 10000 years with an estimated counting error of less than 1 and a mean sedimentation rate of 0 66 mm yr 1 we reconstructed a record of the palaeomagnetic secular variation psv of the earth s magnetic field in this nearly 7 m long section of clastic organic varves mineral magnetic measurements indicated that pseudosingle domain magnetite is the major carrier of the remanence psv shows many of the familiar features of declination and inclination that have previously been recorded in northern europe in addition the lake nautajarvi record contains a continuous record of relative palaeoi

global geomagnetic field models for the past 3000 years transient or permanent flux lobes psvmod1 0 is a compilation of globally distributed palaeodirectional data from archaeomagnetic artefacts lava flows and lake sediments at 24 sites evaluated at 100 year intervals from 1000 bc to ad 1800 we estimate uncertainty in these measures of declination and inclination by comparison with predictions from standard historical models in time intervals of overlap and use the 100 year samples and their associated uncertainties to construct a sequence of minimum structure global geomagnetic field models global predictions of radial magnetic field at the coremantle boundary cmb as well as inclination and declination anomalies at the earth9s surface provide an unprecedented view of geomagnetic secular variations over the past 3000 years and demonstrate a consistent evolution of the field with time resolution of the models is poorest in the southern hemisphere where only six of the 24 sites are located several with incomplete temporal coverage low flux regions seen in the historical field near the north pole are poorly resolved but the northern hemisphere flux lobes are clearly visible in the models these lobes are not fixed in position and intensity but they only rarely venture into the pacific hemisphere the pacific region is seen to have experienced significant secular variation a strong negative inclination anomaly in the region like that seen in 0 5 ma models persists from 1000 bc until ad 1000 and then gradually evolves into the smaller positive anomaly seen today on average between 1000 bc and ad 1800 the non axial dipole contribution to the radial magnetic field at the core mantle boundary is largest in the north central pacific and beneath central asia with clear non zonal contributions at the earth9s surface average inclination anomalies are large and negative in the central pacific and most positive slightly to the east of central africa inclination anomalies decrease with increasing latitude average declinations are smallest in equatorial regions again with strong longitudinal variations largest negative departures are centred over australia and eastern asia secular variation at the earth9s surface is quantified by standard deviation of inclination and declination about their average values and at the cmb by standard deviation in radial magnetic field all three show significant geographical variations but appear incompatible with the idea that secular variation in the pacific hemisphere is permanently attenuated by greatly enhanced conductivity in d 00 beneath the region

continuous geomagnetic field models for the past 7 millennia 2 cals7k 1 we present two continuous global geomagnetic field models for recent millennia cals3k 2 covering the past 3000 years and cals7k 2 covering 7000 years from 5000 bc to 1950 ad the models were determined by regularized least squares inversion of archeomagnetic and paleomagnetic data using spherical harmonics in space and cubic b splines in time they are derived from a greatly increased number of paleomagnetic directional data compared to previous efforts and for the first time a significant amount of archeointensity data is used in this kind of global model allowing the determination of evolution of geomagnetic dipole strength while data accuracy and dating uncertainties remain a limitation reliable low resolution global models can be obtained the results agree well with previous results from virtual axial dipole moment vadm studies from archeomagnetic intensity data apart from a systematic offset in strength a comparison of model predictions with the previous 3000 year model cals3k 1 gives general agreement but also some significant differences particularly for the early epochs the new models suggest that the prominent two northern hemisphere flux lobes are more stationary than cals3k 1 implied extending considerably the time span of stationary flux lobes observed in historical models between 5000 bc and 2000 bc there are time intervals of weak dipole moment where dipole power is exceeded by low degree nondipole power at the core mantle boundary model coefficients and evaluation code can be obtained from the earthref digital archive erda together with animations and snapshots plots for every 100 years at http www earthref org detailed urls for the different material are listed in appendix a

historic drought puts the brakes on earthflows in northern california california s ongoing unprecedented drought is having profound impacts on the state s resources here we assess its impact on 98 deep seated slow moving landslides in northern california we used aerial photograph analysis satellite interferometry and satellite pixel tracking to measure earthflow velocities spanning 1944 2015 and compared these trends with the palmer drought severity index a proxy for soil moisture and pore pressure that governs landslide motion we find that earthflow velocities reached a historical low in the 2012 2015 drought but that their deceleration began at the turn of the century in response to a longer term moisture deficit our analysis implies depth dependent sensitivity of earthflows to climate forcing with thicker earthflows reflecting longer term climate trends and thinner earthflows exhibiting less systematic velocity variations these findings have implications for mechanical hydrologic interactions that link landslide movement with climate change as well as sediment delivery in the region

eastern australian geomagnetic field intensity over the past 14000 yr summary two north eastern australian volcanic crater lake cores have been used to obtain relative intensity estimates for the geomagnetic field arm imparted in a low dc bias field has been used as a normalizing parameter the intensity fluctuations in the two lakes are in excellent agreement with each other and with south eastern australian archaeointensity data over their coeval time spans this strongly suggests that the same sources are influencing the geomagnetic secular variation throughout eastern australia at this time the relative intensity records go back to about 14000yr bp thereby extending currently available recent australian intensity records by some 7000 yr

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

continuous global geomagnetic field models for the past 3000 years abstract several global geomagnetic field models exist for recent decades but due to limited data availability models for several centuries to millennia are rare we present a continuous spherical harmonic model for almost 3 millennia from 1000 b c to 1800 a d based on a dataset of directional archaeo and paleomagnetic data and axial dipole constraints the model named continuous archaeomagnetic and lake sediment geomagnetic model for the last 3k years cals3k 1 can be used to predict both the field and secular variation comparisons and tests with synthetic data lead to the conclusion that cals3k 1 gives a good general large scale representation of the geomagnetic field but lacks small scale structure due to the limited resolution of the sparse dataset in future applications the model can be used for comparisons with additional new data for that time span for better resolved regions the agreement of data with cals3k 1 will provide an idea about the general compatibility of the data with the field and secular variation in that region of the world for poorly covered regions and time intervals we hope to iteratively improve the model by comparisons with and inclusion of new data animations and additional snapshot plots of model predictions as well as the model coefficients and a fortran code to evaluate them for any time can be accessed under http www mahi ucsd edu cathy holocene holocene html the whole package is also stored in the earthref digital archive at http www earthref org

relative geomagnetic paleointensity and δ18o at odp site 983 gardar drift north atlantic since 350 ka abstract at odp site 983 relative geomagnetic paleointensity and planktic and benthic 18o records have been acquired for the last 350 kyr the mean sedimentation rate in this interval is 11 3 cm kyr magnetic properties and hysteresis ratios indicate that pseudo single domain magnetite is the remanence carrier volume susceptibility k anhysteretic arm and isothermal irm remanence values vary by a factor of 3 4 well within the criteria usually cited for paleointensity studies natural remanent magnetization nrm is normalized by arm and irm to acquire the paleointensity proxy arithmetic means of nrm arm and nrm irm calculated for five demagnetization steps in the 25 45 mt range constitute the relative paleointensity estimates some paleointensity lows particularly those at 40 120 and 188 ka are associated with directional excursions of the field especially the event at 188 ka referred to here as the iceland basin event that constitutes a short lived polarity reversal for the last 200 kyr the records can be correlated with other high resolution paleointensity records such as those from the labrador sea mediterranean somali basin and sulu sea implying that the millennial scale features are globally synchronous a labeling system for paleointensity features is proposed that ties prominent highs and lows to oxygen isotope stages

a new high resolution geomagnetic relative paleointensity record for the north american holocene a comparison of sedimentary and absolute intensity data a new high resolution paleointensity record for north america has been constructed using holocene sediments from lake pepin minnesota lake pepin sediments yield the same holocene paleosecular variation curve as nearby lake st croix and satisfy all of the criteria recommended for paleointensity studies absolute paleointensity data for north america recorded by holocene volcanic and archeomagnetic samples provide an independent record of geomagnetic field paleointensity against which the relative intensity records from lake pepin and lake st croix can be compared since the absolute field paleointensity is known a priori the effects of the magnetic recording assemblage can be isolated anhysteretic remanent magnetization arm is the best choice among normalization parameters for the lake pepin sediments as the natural remanent magnetization nrm normalized by arm shows no coherence with magnetic grain size proxies and yields a record of relative paleointensity peaks and troughs whose amplitudes are very similar to those in the archeomagnetic arcmag and lake st croix data sets features with a wavelength of 1000 years are correlative between the three paleointensity records nrm normalized by saturation isothermal remanent magnetization sirm and by susceptibility shows grain size dependences that cause errors in the amplitudes of paleointensity features nrm sirm and nrm are not coherent with their normalizers but are both strongly coherent with independent grain size proxies such as the median destructive field of the nrm and hcr we successfully removed the grain size dependences from nrm sirm by applying a correction function based on the linear relationship between normalized intensity and the median destructive field of the nrm

continuous geomagnetic field models for the past 7 millennia 1 a new global data compilation 1 a global data set of archeomagnetic and paleomagnetic data covering the past 7000 years has been compiled it consists of 16 085 results of inclination 13 080 of declination and 3188 of intensity for the time span 5000 bc to 1950 ad declination and inclination data come partly from existing databases and partly from original literature a new global compilation of intensity data for the millennial scale is included data and dating uncertainties are discussed as we attempted to obtain an internally coherent data set the global distribution of the data is very inhomogeneous in both time and space all the data are compared to predictions from the previous 3000 year global model cals3k 1 this collection of data will be useful for global secular variation studies and geomagnetic field modeling although southern hemisphere data are still underrepresented in particular we will use it in a further study to update and extend the existing global model cals3k 1 the huge increase in data compared to the previous compilation will result in significant changes from current models as we might have missed some suitable data we encourage the reader to notify us about any data that have not been included yet and might fit in as improving our global millennial scale models remains our aim for the future the data files described in this paper are available from the earthref digital archive erda at http earthref org cgi bin erda cgi n 331

geomagnetic field variations in northern sweden during the holocene quantified from varved lake sediments and their implications for cosmogenic nuclide production rates palaeomagnetic analyses were conducted on two varved lake sediment sequences in northern sweden the magnetic properties of the sediment sequences are dominated by stable single domain magnetite with characteristics typical of bacterial magnetosomes alternating field demagnetization measurements indicate that the single domain magnetite is the dominant carrier of a stable natural remanent magnetization temporal variations in inclination and declination were obtained from a total of four cores and the data points were stacked according to their independent calendar year varve ages statistically significant patterns in inclination and declination form a regional palaeomagnetic secular variation psv curve which possesses features that are identical in form to the uk holocene psv master curve however the calibrated radiocarbon ages of uk features identified prior to 1500 bc are approximately 500 years older than their swedish varve dated equivalents which points to dating errors and or drifting of the geomagnetic field the sediments meet the uniformity criteria proposed for palaeointensity reconstruction and estimates of relative geomagnetic field intensity are calibrated against global dipole moment compilations a calculated nuclide production curve is derived from the reconstructed geomagnetic field intensity which empirically demonstrates the dominant modulation of cosmogenic nuclide production by dipole moment between 5000 bc and ad 1500

time dependent mapping of the magnetic field at the core mantle boundary we consider the problem of constructing a time dependent map of the magnetic field at the core mantle boundary we use almost all the available data from the last 300 years to produce two maps one for the period 1690 1840 and the other for 1840 1990 we represent the spatial dependency of the field using spherical harmonics the time dependency using a cubic b spline basis and seek the smoothest solutions compatible with the observations particular attention must be paid to the effects of the crustal field in the data we argue that for observations from permanent magnetic observatories the most efficient strategy is to use first differences of annual means for satellite data the most efficient strategy is simply to limit the number of data used so as to minimize any tendency to map the crustal field into the core field the resulting model fits the observatory data better than any previous model yet has less power in the secular variation than previous models demonstrating that very simple models fit the data the resulting time dependent field map exhibits much of the same structure in the field and its secular variation identified in earlier studies

third generation of the potsdam magnetic model of the earth pomme the potsdam magnetic model of the earth pomme is a geomagnetic field model providing an estimate of the earth s core crustal magnetospheric and induced magnetic fields the internal field is represented to spherical harmonic sh degree 90 while the secular variation and acceleration are given to sh degree 16 static and time varying magnetospheric fields are parameterized in geocentric solar magnetospheric gsm and solar magnetic sm coordinates and include disturbance storm time dst index and interplanetary magnetic field imf by dependent contributions the model was estimated from five years of champ satellite magnetic data all measurements were corrected for ocean tidal induction and night side ionospheric f region currents the model is validated using an independent model from a combined data set of orsted and sac c satellite measurements for the core field to sh degree 13 the root mean square rms vector difference between the two models at the center of the model period is smaller than 4 nt at the earth s surface the rms uncertainty increases to about 100 nt for the predicted field in 2010 as inferred from the difference between the two models

paleointensity studies on holocene pleistocene sediments from lake escondido argentina abstract relative changes in geomagnetic field intensity over the last 16 000 years bp were recovered from the study of four cores obtained from lake escondido south argentina rock magnetic analysis shows that the main magnetic mineral is magnetite the concentrations being mainly between 0 01 and 0 1 and the grain size between 1 and 8 m in order to fulfil the criteria for assessing the reliability of paleointensity data derived from sediments rev geophys 31 1993 319 the samples whose concentrations and size are beyond this range were rejected the remanent magnetisation at 20 mt nrm20 mt was normalised using the anhysteric remanent magnetisation arm100 mt the saturation of the isothermal remanent magnetisation sirm and the low field magnetic susceptibility k coherence function analysis indicates that the records are not significantly affected by local environmental conditions this suggests that the variations in normalised remanence are mostly likely due to geomagnetic paleointensity fluctuations arm100 mt is the best normaliser for the lake escondido sediments the record of relative paleointensity nrm20 mt arm100 mt shows peaks and troughs whose amplitudes are similar to those in the st lawrence estuary lake baikal lake pepin and larsen a ice shelf data set and a stack of archeomagnetic data given as virtual axial dipole moment vadm

palaeointensity in the pelagic realm marine sediment data compared with archaeomagnetic and lake sediment records summary four box cores collected from the ontong java plateau during the eurydice expedition have been used to make relative geomagnetic palaeointensity measurements rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy and that they are suitable for relative intensity estimates these are obtained by normalizing the nrm by an arm imparted in a low dc bias field the palaeoceanographic event known as the preservation spike is used to establish a crude time scale for the record so that it may be compared with other data from the same region and also with global palaeointensity estimates the marine sediment data are quite similar to australian intensity data from lake sediments and archaeomagnetic sources but as might be expected exhibit some obvious differences from the global record