geodynamo solar wind and magnetopause 3 4 to 3 45 billion years ago stellar wind standoff by a planetary magnetic field prevents atmospheric erosion and water loss although the early earth retained its water and atmosphere and thus evolved as a habitable planet little is known about earth s magnetic field strength during that time we report paleointensity results from single silicate crystals bearing magnetic inclusions that record a geodynamo 3 4 to 3 45 billion years ago the measured field strength is 50 to 70 that of the present day field when combined with a greater paleoarchean solar wind pressure the paleofield strength data suggest steady state magnetopause standoff distances of 5 earth radii similar to values observed during recent coronal mass ejection events the data also suggest lower latitude aurora and increases in polar cap area as well as heating expansion and volatile loss from the exosphere that would have affected long term atmospheric composition

intensity of the geomagnetic field in western europe over the past 2000 years new data from ancient french pottery 1 we studied 14 groups of french pottery fragments dated between the 4th and 16th centuries the potsherds were analyzed using the thellier and thellier 1959 method revised by coe 1967 intensity values were corrected for thermoremanent magnetization trm anisotropy and cooling rate dependence of trm acquisition we first analyzed modern ceramics produced following ancient techniques and fired in a wood burning kiln inside of which field intensity was measured the recovered mean intensity is within 3 of the expected value which proves the reliability of our experimental procedure thermal experiments carried out at rapid and slow cooling rates clearly indicate that the cooling rate correction is critical in archeointensity studies our data indicate that large variations in intensity occurred in france over the last 2000 years two relative maxima in intensity are observed one between the 8th and 10th centuries and the second between the 14th and 15th centuries similarities are observed between the archeointensity data from france and ukraine yielding some evidence for eastward drift of geomagnetic sources between western and eastern europe from a d 800 to a d 1700 we also show that the dipole moment evolution proposed by mcelhinny and senanayake 1982 and yang et al 2000 for the last two millennia is likely biased toward higher values mainly because of the absence of correction for the cooling rate dependence of trm acquisition in most published archeointensity studies we finally underline a possible relationship valid at least in western europe between changes in direction and intensity of the geomagnetic field

two thousand years of archeointensity from west africa this study presents 17 archeointensity estimates from senegal and mali two neighboring countries in west africa for the period 1000 bce to 1000 ce the archeological artifacts used in this study were collected during the course of two separate projects together spanning 22 years and across 8 separate excavations a primary objective of this study was to get accurate dates hence only samples with independent age constraints from pottery style detailed stratigraphy and 14c dates were used a total of 236 specimens from 63 samples were subjected to a double heating paleointensity experiment izzi method from which 95 specimens were selected using a set of very strict selection criteria the paleointensity results were corrected for differential cooling rate effects and remanence anisotropy additionally we demonstrate the equivalence of using tensors derived from anhysteretic and thermal remanences for correcting remanent anisotropy of the specimens and use the former for the anisotropy correction our data show good agreement with the most recent paleosecular variation model but are lower than the pre existing data which are mostly from egypt and morocco the presence of substantial non axial dipolar contributions in the region is evident when virtual axial dipole moments vadms from the published literature are calculated for 20 latitudinal bands and compared with our data the average vadm values show a distinct latitudinal gradient a prominent feature of this dataset is an intensity high observed prior to 700 ce in both senegal and mali comparing this peak with existing records from regions further to the north suggests a small but significant temporal offset and is interpreted to be additional evidence for a geomagnetic field with a significant and rapidly changing non axial dipolar contribution

geomagnetic field for 0 3 ka 2 a new series of time varying global models 1 steadily increasing numbers of archeomagnetic and paleomagnetic data for the holocene have allowed development of temporally continuous global spherical harmonic models of the geomagnetic field extending present and historical global descriptions of magnetic field evolution the current work uses various subsets of improved data compilations details of which are given in a companion paper by donadini et al 2009 and minor modifications of standard modeling strategies using temporally and spatially regularized inversion of the data and cubic spline parameterizations for temporal variations to produce five models with enhanced spatial and temporal resolution for 0 3 ka spurious end effects present in earlier models are eliminated by enforcing large scale agreement with the gufm1 historical model for 1650 1990 a d and by extending the model range to accommodate data older than 3 ka age errors are not considered as a contribution to data uncertainties but are included along with data uncertainties in an investigation of statistical uncertainty estimates for the models using parametric bootstrap resampling techniques we find common features but also significant differences among the various models indicating intrinsic uncertainties in global models based on the currently available holocene data model cals3k 3 based on all available archeomagnetic and sediment data without a priori quality selection currently constitutes the best global representation of the past field the new models have slightly higher dipole moments than our previous models virtual axial dipole moments vadms calculated directly from the data are in good agreement with all corresponding model predictions of vadms these are always higher than the spherical harmonic dipole moment indicating the limitations of using vadms as a measure of geomagnetic dipole moments

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

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

archaeomagnetism at ebla tell mardikh syria new data on geomagnetic field intensity variations in the near east during the bronze age abstract thanks to systematic excavations conducted at tell mardikh ebla syria during more than 40 years we collected eleven groups of bronze age ceramic fragments defining a series of seven time intervals dated to between 2300 bc and 1400 bc archaeointensity experiments were performed using the triaxe protocol that takes into account both anisotropy thermoremanent magnetization and cooling rate effects the results complemented by three other data previously obtained from ebla allow the recovery of geomagnetic field intensity variations over nearly 1000 years characterized by a v shape with a distinct relative intensity minimum around the 18th century bc they also permit to constrain the occurrence of an intensity maximum between 2300 and 2000 bc together with other archaeointensity data obtained from syrian levantine and anatolian regions the results from ebla help to make emerging a coherent pattern of geomagnetic field intensity variations in the near east over the entire bronze period this evolution was marked by distinct intensity maxima at 2600 2500 bc 2300 2000 bc 1550 1350 bc and at the very beginning of the first millennium bc iron age the latter showing a much higher magnitude than the three older ones we discuss the fact that the detected geomagnetic field intensity maxima could be associated with the occurrence of archaeomagnetic jerks that appear synchronous within age uncertainties with significant regional climatic fluctuations

palaeomagnetism of archaean rocks of the onverwacht group barberton greenstone belt southern africa evidence for a stable and potentially reversing geomagnetic field at ca 3 5 ga abstract palaeomagnetic data from the palaeoarchaean era 3 2 3 6 ga have the potential to provide us with a great deal of information about early conditions within and processes affecting the earth s core mantle and surface environment here we present new data obtained from some of the oldest palaeomagnetic recorders in the world igneous and sedimentary rocks from the onverwacht group of the barberton greenstone belt kaapvaal craton southern africa our palaeomagnetic measurements strengthen a recently published positive conglomerate test y usui j a tarduno m watkeys a hofmann and r d cottrell 2009 and our new u pb date constrains the conglomerate to older than 3455 8 ma the new palaeomagnetic data from other units are nontrivial to interpret and are of uncertain reliability when taken individually similar we argue to all other published palaeomagnetic data of this age nonetheless four poles two new two derived from published data produced from high temperature components of magnetisation recorded in the komati noisy and hooggenoeg formations exhibit considerably improved clustering when their directions are corrected for differences in attitude resulting from a large fold structure dated at 3 23 ga on the basis of this enhanced consistency in stratigraphic coordinates the positive conglomerate test and the absence of any clear indications of their remagnetisation from comparison with younger poles we argue that these are the most trustworthy palaeomagnetic results yet produced from any rocks of palaeoarchaean age when taken in conjunction with published data the new results present the most compelling evidence to date that the earth had a stable geomagnetic field at ca 3 5 ga in addition to presenting tentative evidence that it was undergoing polarity reversals the data do not appear to support a claim made previously from palaeoarchean palaeomagnetic data from the pilbara craton y suganuma y hamano s niitsuma m hoashi t hisamitsu n niitsuma k kodama and m nedachi 2006 of extremely rapid latitudinal plate motion during this period finally when compared with similarly aged data from the pilbara craton western australia the new data do not rule out the hypothesis that the two cratons were conjoined at this point in their history in the supercraton vaalbara

the time dependence of intense archeomagnetic flux patches 1 the long term temporal behavior of intense geomagnetic flux patches at the core mantle boundary and the relation with lower mantle lateral heterogeneity are under debate we apply an algorithm to detect centers of intense flux patches and track their time evolution in a recent archeomagnetic field model in order to study the kinematics of such intense magnetic flux patches on millennial timescale we find that most intense flux patches appear near the edge of the tangent cylinder quasi stationary periods with small oscillations of patches occur more than drifts detailed comparison of the archeomagnetic patches behavior with that seen in numerical dynamos with tomographic heat flux boundary conditions suggests that core mantle thermal coupling could be the cause of a statistical preference for some longitudes on the long term which does not exclude significant time spent away from the preferred longitudes this could explain the roughly coincident locations of high latitude patches in the historical geomagnetic field with that of the time average paleomagnetic field together with the much weaker patches intensity in the latter alternating eastward and westward drifts are also observed the drifts are more westward than eastward especially in the southern hemisphere indicating that the time average zonal core flow may also be driven by core mantle thermal coupling an average patch lifetime of 300 years is found which we hypothesize may indicate the vortex lifetime in the outer core

evidence for a 3 45 billion year old magnetic remanence hints of an ancient geodynamo from conglomerates of south africa 1 paleomagnetic and rock magnetic analyses of 3445 million year old dacite conglomerate clasts and parent body rocks from the barberton greenstone belt south africa define two dominant components of magnetization one component unblocked at low temperature is an overprint acquired 180 million years ago the other component is unblocked at high temperatures and passes a conglomerate test indicating that this component is older than the depositional age of the conglomerate 3416 ma the high unblocking temperature component shows scatter in the parent body rocks that can be explained by the effects of modern lightning strikes archean overprinting and the presence of multidomain magnetic grains that are conducive to carrying secondary magnetizations alternatively this scatter can be explained by exotic magnetization scenarios in the absence of a dynamo including magnetization by an external field related to solar wind interaction with the atmosphere such exotic mechanisms can be tested with the acquisition of paleointensity data while more scattered than paleomagnetic data recording the more recent geomagnetic field the high unblocking temperature component in the dacite parent body shows some consistency and the simplest explanation of the data is that they reflect a geodynamo 3445 million years ago

high fidelity paleointensity determination from historic volcanoes in japan 1 providing high fidelity paleointensity estimates is pivotal to identify temporal fluctuation of ancient geomagnetic field despite abundance of available paleointensity data in japan only dozen of them satisfy modern standards with systematic alteration checks high fidelity paleointensity estimates were obtained from historic andesitic lavas collected from mt aso ojodake 700 bc mt kirishima iwoyama ad 1768 ohachi ad 1235 and mt sakurajima an ei ad 1779 nabeyama ad 764 766 variation of geomagnetic field intensity is distinctively different from the prediction of global models arch3k 1 cals3k 3 cals3k 4 cals7k 2 and cals10k 1b for the past 4000 years in japan the compilation of high fidelity thellier data set in japan showed two obvious high intensities at ad 590 765 and ad 1330 1435 and one low intensity at 700 bc these time intervals with anomalous high low intensities are nearly identical to three of the four potential archeomagnetic jerks recognized from the european archeomagnetic data implying that the archeomagnetic jerks were global or at least northern hemispheric features to improve the poor representation of regional geomagnetic field variation with respect to the global model prediction more high fidelity paleointensity determinations are required in east asia

are there connections between the earth s magnetic field and climate understanding climate change is an active topic of research much of the observed increase in global surface temperature over the past 150 years occurred prior to the 1940s and after the 1980s the main causes invoked are solar variability changes in atmospheric greenhouse gas content or sulfur due to natural or anthropogenic action or internal variability of the coupled ocean atmosphere system magnetism has seldom been invoked and evidence for connections between climate and magnetic field variations have received little attention we review evidence for correlations which could suggest such causal or non causal connections at various time scales recent secular variation 10 100 yr historical and archeomagnetic change 100 5000 yr and excursions and reversals 10 3 10 6 yr and attempt to suggest mechanisms evidence for correlations which invoke milankovic forcing in the core either directly or through changes in ice distribution and moments of inertia of the earth is still tenuous correlation between decadal changes in amplitude of geomagnetic variations of external origin solar irradiance and global temperature is stronger it suggests that solar irradiance could have been a major forcing function of climate until the mid 1980s when anomalous warming becomes apparent the most intriguing feature may be the recently proposed archeomagnetic jerks i e fairly abrupt 100 yr long geomagneticfieldvariationsfoundatirregularintervalsoverthepastfewmillennia usingthearcheologicalrecordfromeuropetothe middle east these seem to correlate with significant climatic events in the eastern north atlantic region a proposed mechanism involves variations in the geometry of the geomagnetic field f i tilt ofthe dipole to lower latitudes resulting in enhanced cosmic ray induced nucleation of clouds no forcing factor be it changes in co2 concentration in the atmosphere or changes in cosmic ray flux modulatedbysolaractivityandgeomagnetism orpossiblyotherfactors canatpresentbeneglectedorshowntobetheoverwhelming single driver of climate change in past centuries intensive data acquisition is required to further probe indications that the earth s and sun s magnetic fields may have significant bearing on climate change at certain time scales 2006 elsevier b v all rights reserved

decadal scale variations in geomagnetic field intensity from ancient cypriot slag mounds geomagnetic models based on direct observations since the 1830s show that the averaged relative change in field intensity on earth s surface over the past 170 years is less than 4 8 per decade it is unknown if these rates represent the typical behavior of secular variations due to insufficient temporal resolution of archaeomagnetic records from earlier periods to address this question we investigate two ancient slag mounds in cyprus skouriotissa vouppes su1 fourth to fifth centuries ce 21 m in height and mitsero kokkinoyia mk1 seventh to fifth centuries bce 8 m in height the mounds are multilayered sequences of slag and charcoals that accumulated near ancient copper production sites we modeled the age height relation of the mounds using radiocarbon dates and estimated paleointensities using thellier type izzi experiments with additional anisotropy cooling rate and nonlinear trm assessments to screen out ambiguous paleointensity interpretations we applied strict selection criteria at the specimen sample levels to ensure objectivity consistency and robust error estimation we employed an automatic interpretation technique and put the data available in the magic database the analyses yielded two independent subcentury scale paleointensity time series the mk1 data indicate relatively stable field at the time the mound accumulated in contrast the su1 data demonstrate changes that are comparable in magnitude to the fastest changes inferred from geomagnetic models we suggest that fast changes observed in the published archaeomagnetic data from the levant are driven by two longitudinally paired regions the middle east and south africa that show unusual activity in geomagnetic models

comment on are there connections between the earth s magnetic field and climate by v courtillot y gallet j l le mouel f fluteau a genevey epsl 253 328 2007

reconstructing the holocene geomagnetic field abstract knowledge of the holocene evolution of earth s magnetic field is important for understanding geodynamo processes in the core is necessary for studying long term solar terrestrial relationships and can provide useful age constraints for archeologicaland stratigraphic applications continuous time varying global field models based on archeo and paleomagnetic data are useful tools in this regard we use a comprehensive data compilation and recently refined modelling strategies to produce cals10k 1b the first time varying spherical harmonic geomagnetic field model spanning 10 ky the model is an average obtained from bootstrap sampling to take account of uncertainties in magnetic components and ages in the data and hence has version number 1b instead of 1 this model shows less spatial and temporal resolution than earlier versions for 0 3 ka and particularly aims to provide a robust representation of the large scale field at the core mantle boundary cmb we discuss the geomagnetic dipole evolution and changes in holocene magnetic field morphology at the cmb as shown by the new reconstruction the results are compatible with earlier models cals3k 3 and cals3k 4 for 0 3 ka but reveal some clear deficiencies in the 0 7 ka cals7k 2 model prior to 3 ka cals10k 1b is able to resolve mobile and structurally evolving high latitude radial field flux lobes at the cmb in both hemispheres as well as persistent non zonal structure in the 10 ky average contributions to the average field from time varying structures in the equatorial indonesian australian region are particularly striking

a regional archeomagnetic model for europe for the last 3000 years scha dif 3k applications to archeomagnetic dating 1 the available european database of archeomagnetic field values and instrumental data has been used to produce a regional model for the geomagnetic field in europe for the last 3000 years from 1000 b c to 1900 a d connecting with the epoch covered by the igrf models this new model scha dif 3k constitutes an improvement with respect to the previous regional archeomagnetic model scha di 00 f which used relocated values and was only valid for the last 2000 years the new model has been obtained by least sums of absolute deviation inversion of paleomagnetic data using spherical cap harmonics for the spatial representation of the field and sliding windows in time an algorithm has been developed to jointly model the three archeomagnetic elements declination inclination and intensity the resulting model provides the direction and intensity of the earth s magnetic field over the european continent northern africa and western asia for the last 3000 years the fit to the european archeomagnetic database is more accurate than that provided by global archeomagnetic models in addition this model represents a step forward in archeomagnetic dating studies since the relocation error is avoided and can also be used to study the rapid changes of the geomagnetic field archeomagnetic jerks that have been recently proposed

possible links between long term geomagnetic variations and whole mantle convection processes the earth s internal magnetic field varies on timescales of months to billions of years the field is generated by convection in the liquid outer core which in turn is influenced by the heat flowing from the core into the base of the overlying mantle much of the magnetic field s variation is thought to be stochastic but over very long timescales this variability may be related to changes in heat flow associated with mantle convection processes over the past 500 myr correlations between palaeomagnetic behaviour and surface processes were particularly striking during the middle to late mesozoic era beginning about 180 myr ago simulations of the geodynamo suggest that transitions from periods of rapid polarity reversals to periods of prolonged stability such as occurred between the middle jurassic and middle cretaceous periods may have been triggered by a decrease in core mantle boundary heat flow either globally or in equatorial regions this decrease in heat flow could have been linked to reduced mantle plume head production at the core mantle boundary an episode of true polar wander or a combination of the two

improving geomagnetic field reconstructions for 0 3 ka global geomagnetic field reconstructions on millennial time scales can be based on comprehensive paleomagnetic data compilations but especially for older data these still suffer from limitations in data quality and age controls as well as poor temporal and spatial coverage here we present updated global models for the time interval 0 3 ka where additions to the data basis mainly impact the south east asian alaskan and siberian regions we summarize recent progress in millennial scale modelling documenting the cumulative results from incremental modifications to the standard algorithms used to produce regularized time varying spherical harmonic models spanning 1000 bc to 1990 ad from 1590 to 1990 ad gauss coefficients from the historical gufm1 model supplement the paleomagnetic information in addition to absolute paleointensities calibrated relative paleointensity data from sediments are now routinely included iterative data rejection and recalibration of relative intensity records from sediments ensure stable results bootstrap experiments to generate uncertainty estimates for the model take account of uncertainties in both age and magnetic elements and additionally assess the impact of sampling in both time and space based on averaged results from bootstrap experiments taking account of data and age uncertainties we distinguish more conservative model estimates cals3k nb representing robust field structure at the core mantle boundary from relatively high resolution models cals3k n for model versions n 3 and 4 we assess the impact of newly available data and modifications to the modelling method by comparing the previous cals3k 3 the new cals3k 4 and the conservative new model cals3k 4b we conclude that with presently available data it is not feasible to produce a model that is equally suitable for relatively high resolution field predictions at earth s surface and robust reconstruction of field evolution avoiding spurious structure at the core mantle boundary cmb we presently consider cals3k 4 the best high resolution model and recommend the more conservative lower resolution version for studies of field evolution at the cmb

a matlab tool for archaeomagnetic dating a matlab tool for archaeomagnetic dating has been developed in this work well dated palaeosecular variation curves psvcs can be used to date archaeological artefacts with unknown ages the archaeomagnetic direction declination and or inclination and the archaeointensity obtained from the archaeological artefact are compared with a master psvc in addition historical lava flows with controversial ages can be dated using this methodology the dating process follows the descriptions given by lanos 2004 which is based on the combination of temporal probability density functions of the three geomagnetic field elements here we develop an interactive tool in matlab code to carry out archaeomagnetic dating by comparing the undated archaeomagnetic or lava flow data with a master psvc the master psvcs included with the matlab tool are the different european bayesian curves and those generated using both regional and global geomagnetic field models a case study using all the psvcs available in europe and some undated archaeomagnetic data has been carried out to analyze how the different psvcs affect the dating process in addition the dating uncertainty and the relocation error have been analyzed in the european region results show that some regional bayesian psvcs and the regional scha dif 3k archaeomagnetic model are the best choices to obtain an accurate date in europe moreover when it is available the full geomagnetic field vector must be used for archaeomagnetic dating

core flow constraints on extreme archeomagnetic intensity changes abstract recent studies ben yosef et al 2009 shaar et al 2011 propose extreme archeomagnetic intensity changes termed spikes in the range 4 5 t year c a 1000 bc in the near east around 40 to 50 times larger than values typical of the present day in order to investigate whether such extreme changes are consistent with a model of the source region of the magnetic field namely the fluid flow at the surface of earth s core we construct upper bounds for instantaneous magnetic intensity change at an arbitrary site on the earth s surface these bounds are constrained by the amount of kinetic energy available to sustain the change taken here to be a prescribed value for the root mean squared surface velocity of 13 km yr as inferred from the current state of the core further we focus attention on two end members of optimised core surface flow structure unrestricted and purely toroidal as the derivation of the bounds demands complete knowledge of the geomagnetic field at the core surface we model the unknown field by means of a monte carlo approach extending to high degree the chaos 4 epoch 2010 ad and cals10k1 b epoch 1000 bc geomagnetic field models using 2000 realisations for each family of stochastic field models we find that optimised core flows are always large scale and that they tend to generate a non dipole quadrupole dominated secular variation at the earth s surface the dependence of the upper bounds as a function of site location reflects the large scale structure of the intensity itself stronger field permits more rapid change for the site in the near east purely toroidal flows have upper bounds of approximately 0 62 0 02 t year whereas unrestricted flows increase this bound to 1 20 0 02 t year we favour the former as more geophysically sound on the account of a large body of previous results from core surface flow inversions and consistency with the existence of a stratified layer at the top of the core even if we allow for a generous threefold increase in the prescribed rms velocity and a concomitant threefold increase in the bound we conclude that the reported occurrences of extreme intensity changes as suggested in the near east are not compatible with the commonly accepted structure of core surface flow however it may be that an explanation for spikes lies beyond our current perception of core dynamics and future work would be further motivated by seeking corroborative evidence of rapid intensity change from sites elsewhere on earth s surface we therefore also discuss the form that the secular variation would take in the case of simultanenous archeomagnetic spikes

geomagnetic intensity variations for the past 8 kyr new archaeointensity results from eastern china abstract in this study we have carried out paleointensity experiments on 918 specimens spanning the last 7 kyr including pottery fragments baked clay and slag collected from shandong liaoning zhejiang and hebei provinces in china approximately half of the specimens yielded results that passed strict data selection criteria and give high fidelity paleointensities the virtual axial dipole moments vadms of our sites range from 2 10 22 to 13 10 22 am 2 at 2250 bce our results suggest a paleointensity low of 2 10 22 am 2 which increases to a high of 13 10 22 am 2 by 1300 bce this rapid less than 1000 yrs six fold change in the paleointensity may have important implications for the dynamics of core flow at this time our data from the last 3 kyr are generally in good agreement with the arch3k 1 model but deviate significantly at certain time periods from the cals3k 4 and cals10k 1b model which is likely due to differences in the data used to constrain these models at ages older than 3 ka where only the cals10k 1b model is available for comparison our data deviate significantly from the model combining our new results with the published data from china and japan we provide greatly improved constraints for the regional model of eastern asia when comparing the variations of geomagnetic field in three global representative areas of eastern asia the middle east and southern europe a common general trend of sinusoidal variations since 8 ka is shown likely dominated by the dipole component however significant disparities are revealed as well which we attribute to non dipolar components caused by movement of magnetic flux patches at the core mantle boundary

an integrated archeomagnetic and c14 study on pre columbian potsherds and associated charcoals intercalated between holocene lacustrine sediments in western mexico geomagnetic implications 1 the firm relationship between archeomagnetic samples and their absolute ages which is usually determined or estimated using a variety of methods archaeological context thermoluminiscense c14 etc is crucial in any archaeomagnetic investigation in this paper we report 18 successful from 65 analyzed archaeointensity determinations of high technical quality performed on specimens obtained from three fragments of pre columbian potsherds these are unambiguously correlated with charcoal samples as they were found together in three thin lacustrine sedimentary layers in western mexico moreover new radiometric results were obtained in this study from all charcoal samples beta analytic yielding ages of 1490 40 1510 40 and 1580 40 bp in addition detailed magnetic measurements were carried out on all studied ceramic fragments these rock magnetic experiments which included low field susceptibility versus temperature hysteresis and first order reversal curve measurements indicate that the main magnetic carrier is ti poor titanomagnetite the average archeointensity values per ceramic fragments obtained in this study are very similar in all three cases 35 2 1 3 t n 5 36 8 1 6 t n 6 and 37 2 3 4 t n 7 this corresponds to an average intensity of 36 4 1 1 t and a virtual axial dipole moment value of 8 1 0 2 1022 am2 which is slightly lower than the present field strength corresponding at an age interval between 640 and 430 a d although we detected some relationship between the earth s magnetic field intensity and multidecadal climatic events such observations can only be considered tentative at this stage

eastward and westward drift of the earth s magnetic field for the last three millennia abstract we analyse the secular variation captured by the archaeomagnetic field model cals7k 2 in an effort to determine episodes of eastward and westward motions of earth s magnetic field at the core mantle boundary cmb over the past 3000 yr the direction amplitude and geographical distribution of these motions are described we find that the clearest azimuthal motions are observed at mid to high latitudes in the northern hemisphere where both eastward and westward motions occur these azimuthal motions correspond to displacements and distortions of the two main quasi stationary high latitude magnetic flux patches similar motions are not observed in the southern hemisphere although this may be a consequence of the poorer data coverage there the globally averaged drift for the past 1000 yr has been westward since 1400 ad but eastward between 1000 ad and 1400 ad in the broad region of the cmb under europe the times of transition in the direction of the mean azimuthal motion coincide with the times at which archaeomagnetic jerks have been reported our results suggest that these are caused by a relatively rapid

strength of the geomagnetic field in the cretaceous normal superchron new data from submarine basaltic glass of the troodos ophiolite 1 we present here new paleointensity data from 39 sampling sites collected from the quenched margins of pillow lavas and dikes exposed within the troodos ophiolite similar to 92 ma formed during the cretaceous normal superchron cns a period of approximately 40 million years when the geomagnetic field reversed extremely infrequently if at all monte carlo simulations suggest that a minimum of 25 estimates are necessary for a reasonably robust estimate for the average field strength our data suggest a dipole strength equivalent to the present field or nearly twice the post cns average the mean and standard deviation of the dipole moment 81 43 zam 2 z 10 21 from the 57 data points compiled here agree remarkably well with those predicted from the long paleointensity record derived from dsdp site 522 the new data set for the cns suggests a picture of a strong and stable field during the period of time when it stopped reversing moreover the similarity of the cns data with the present geomagnetic field suggests that it is presently in a state of unusual polarity stability

does earth s magnetic field secular variation control centennial climate change abstract we obtained new archeointensity data from french faience potsherds dated from the 17th to 19th century these results further document the occurrence of sharp changes in geomagnetic field secular variation in western europe over the past three millennia the intensity variation curve shows several maxima whose rising parts appear to coincide in time with the occurrence of cooling events documented in this region from natural and historical data this coincidence suggests a causal link between enhanced secular variation of the geomagnetic field and climate change over centennial time scales challenging the role of solar forcing as the sole factor provoking these climatic variations we propose that the archeomagnetic jerks described by gallet et al 1 y gallet a genevey v courtillot on the possible occurrence of archeomagnetic jerks in the geomagnetic field over the past three millennia earth planet sci lett 214 2003 237 242 may engage the mechanism for centennial climate change

rapidly changing flows in the earth s core variations in the earth s magnetic field over a span of a few months can be resolved despite the potential filtering effects of the electrically conducting mantle and are indicative of rapid flow in the earth s outer core

a new approach for geomagnetic archaeointensity research insights on ancient metallurgy in the southern levant we present results from an archaeointensity investigation based on a relatively unexploited recording medium copper slag deposits together with a recently improved experimental design for the archaeointensity experiment we demonstrate the applicability of this medium as well as other archaeometallurgical artifacts for the study of the ancient geomagnetic field intensity in addition to archaeointensity data from well dated archaeological contexts we obtained reliable archaeointensity results from poorly dated or contentious archaeometallurgical sites in the southern levant these results shed new light on the dating of these sites among them the copper smelting installation of timna 39b a site that has important implications for the beginning of metallurgy during the fifth millennium bce the paper also aims to introduce archaeointensity research to the archaeologist scholar and to encourage further collaboration between the disciplines in future research

new constraints on the variation of the geomagnetic field during the late neolithic period archaeointensity results from sichuan southwestern china we have carried out an archaeomagnetic study on a late neolithic locality liujiazhai in sichuan southwestern china we pull together various dating techniques including radiocarbon analysis optically stimulated luminescence dating stratigraphic information as well as archaeological and archaeomagnetic estimations to constrain the age of the studied samples rock magnetic results indicate thermally stable fine grained magnetite or titanomagnetite as the dominant magnetic carriers more than half of the specimens 141 246 in the paleointensity experiment pass the selection criteria and are considered to record robust intensity values the virtual axial dipole moments range from approximately 2 8 to 7 8 1022 am2 with an average of 5 9 1022 am2 indicating that the geomagnetic intensity around 3000 before the common era b c e is overall lower than the present field intensity 9 8 1022 am2 of this area the new results from liujiazhai are generally consistent with the published data of similar age but deviate from the only available model of cals10k 1b at certain time periods making them important for future improvements of the model those data are significant for constraining the variation of geomagnetic field intensity between 3100 and 2600 b c e and improving the regional model of eastern asia

styles of cenozoic collisions in the western and southwestern pacific and their applications to palaeozoic collisions in the tasmanides of eastern australia abstract the western and southwestern pacific preserve evidence of cenozoic collisions that guide our understanding of processes and geometries involved in collisions in ancient orogens in particular in this case the palaeozoic tasmanides of southeastern australia although several styles of collisions are present in the pacific ranging from arc arc collision to arc plateau collision the dominant two are oblique and strike slip collisions between island arcs and rifted continental fragments and collisions between forearc lithosphere and continental fragments the 58 ma collision along the northern margin of the australian plate in new guinea the 44 34 ma collision preserved in new caledonia and the 26 25 ma collision in the north island of new zealand may be parts of a single plate boundary collision that migrated southwards along the plate boundary they characterize the main style of deformation in which a collision between forearc crust and continental fragment produces subduction flip or rollback thereby avoiding a classic arc continent collision processes involved in and geometries that have developed from sw and w pacific style collisions have been applied to the interpretation of the evolution of the delamerian orogen and lachlan orogen in the southern tasmanides with varying degrees of success the ophiolite obduction model has been successfully applied to the western tasmania part of the delamerian orogen although there is discussion about its applicability to the mainland the best example of an arc accretion that of the ordovician macquarie arc in the eastern lachlan orogen developed from rare geometry in the western pacific wherein with the constraint that no forearc or subduction complex has been identified the arc lies on the continental plate above a continental dipping subduction zone the multiple subduction zone model of halmahera has been widely applied to the back arc of the lachlan orogen but evidence for clear subduction zones or arcs is not present

globally strong geomagnetic field intensity circa 3000 years ago abstract high fidelity geomagnetic field intensity determination was carried out using 191 baked fragments collected from 20 kilns or hearths with ages ranging between 1200 bc and ad 1725 in south korea geomagnetic field intensity variation displayed three narrow minima at 800 700 bc ad 700 and ad 1600 and two maxima at 1200 1100 bc and ad 1000 1100 in most time intervals virtual axial dipole moment vadm variation is confined within 20 of the present vadm however geomagnetic field intensity circa 3000 yr ago is nearly 40 larger than the present value such high vadms circa 3000 yr ago are in phase with those in other longitudinal bands in northern hemisphere centered at 5e france 30e the middle east and 200e hawaii although strong geomagnetic field intensity circa 3000 yr ago is globally synchronous the highest vadm occurs at slightly different time intervals in different locations hence it is possible that the globally strong geomagnetic field intensity circa 3000 yr ago reflects the migration of persistent hemispheric flux in northern hemisphere or an episode of geomagnetic field hemispheric asymmetry

initiation and long term instability of the east antarctic ice sheet antarctica s continental scale ice sheets have evolved over the past 50 million years however the dearth of ice proximal geological records limits our understanding of past east antarctic ice sheet eais behaviour and thus our ability to evaluate its response to ongoing environmental change the eais is marine terminating and grounded below sea level within the aurora subglacial basin indicating that this catchment which drains ice to the sabrina coast may be sensitive to climate perturbations here we show using marine geological and geophysical data from the continental shelf seaward of the aurora subglacial basin that marine terminating glaciers existed at the sabrina coast by the early to middle eocene epoch this finding implies the existence of substantial ice volume in the aurora subglacial basin before continental scale ice sheets were established about 34 million years ago subsequently ice advanced across and retreated from the sabrina coast continental shelf at least 11 times during the oligocene and miocene epochs tunnel valleys associated with half of these glaciations indicate that a surface meltwater rich sub polar glacial system existed under climate conditions similar to those anticipated with continued anthropogenic warming cooling since the late miocene resulted in an expanded polar eais and a limited glacial response to pliocene warmth in the aurora subglacial basin catchment geological records from the sabrina coast shelf indicate that in addition to ocean temperature atmospheric temperature and surface derived meltwater influenced east antarctic ice mass balance under warmer than present climate conditions our results imply a dynamic eais response with continued anthropogenic warming and suggest that the eais contribution to future global sea level projections may be under estimated