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

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

new estimates of oceanic tidal energy dissipation from satellite altimetry as a novel approach to computing the flux of tidal power into shelf areas tidal maps of an oceanic area near the patagonian shelf are derived from 11 months of altimetry records from the geosat satellite power fluxes are computed from the maps through laplace s tidal equations flux vectors for m sub 2 clearly show a convergence on to the southern portion of the shelf sea and their total is nearly twice the loss computed by miller for that area a decrease of quality factor with frequency from m sub 2 to s sub 2 is in keeping with webb s hypothesis of shelf resonances at frequencies a little higher than the tidal band

geomagnetic intensity spike recorded in high resolution slag deposit in southern jordan article i nfo in paleomagnetism periods of high field intensity have been largely ignored in favor of the more spectacular directional changes associated with low field intensity periods of excursions and reversals hence questions such as how strong the field can get and how fast changes occur are still open in this paper we report on data obtained from an archaeometallurgical excavation in the middle east designed specifically for archaeomagnetic sampling we measured 342 specimens from 72 samples collected from a 6 1 m mound of well stratified copper production debris at the early iron age 12th 9th centuries bce site of khirbat en nahas in southern jordan seventeen samples spanning 200 yr yielded excellent archaeointensity results that demonstrate rapid changes in field intensity in a period of overall high field values the results display a remarkable spike in field strength with sample mean values of over 120 t compared to the current field strength of 44 t a suite of 13 radiocarbon dates intimately associated with our samples tight control of sample location and relative stratigraphy provide tight constraints on the rate and magnitude of changes in archaeomagnetic field intensities

archeointensity in northeast brazil over the past five centuries abstract this study presents the first archeointensity results from northeast brazil obtained from 14 groups of architectural brick fragments sampled in the city of salvador bahia state 13 s 38 5 w and dated between the middle of the xvith century and the beginning of the xixth century the dating is ascertained by historical documents complemented by archeological constraints yielding in all cases age uncertainties of less than 50 years analyses were carried out using two experimental protocols 1 the zero field in field version of the classical thellier and thellier method as proposed by coe tt zi including partial thermoremanent magnetization ptrm and ptrm tail checks and 2 the triaxe procedure involving continuous high temperature magnetization measurements both trm anisotropy and cooling rate effects were taken into account for the intensity determinations the cooling rate effect was further explored for the tt zi protocol using three increasing slow cooling times 5 h 10 h and 25 h between 450 c and room temperature following archeological constraints the slowest cooling time was retained in our study yielding decreases of the raw intensity values by 4 to 14 for each fragment a mean intensity was computed and retained only when the data obtained from all specimens between 2 and 6 satisfied a coherence test at 5 a total of 57 fragments 183 specimens was considered for the computations of site mean intensity values with derived standard deviations of less than 8 of the corresponding means when separately computed using the two experimental techniques the site mean intensity values always agree to within 5 a good consistency is observed between intensity values of similar or close ages which strengthen their reliability our data principally show a significant and continuous decrease in geomagnetic field intensity in northeast brazil between the first half of the xviith century and the xxth century one result dated to the second half of the xvith century further suggests that the geomagnetic field intensity reached a maximum around 1600 ad this evolution is in good agreement with that expected in the city of salvador from the available global geomagnetic field models however the accuracy of these models appears less well constrained between 1550 ad and 1650 ad

long term variations in palaeointensity we compile a dataset of reliable palaeointensity estimates based both on published work and on new data from basaltic glass the basaltic glass data more than double the number of reliable thellie

new late neolithic c 7000 5000 bc archeointensity data from syria reconstructing 9000years of archeomagnetic field intensity variations in the middle east we present new archeomagnetic intensity data from two late neolithic archeological sites tell halula and tell masaikh in syria these data from 24 groups of potsherds encompassing 15 different time levels are obtained using the triaxe experimental protocol which takes into account both the thermoremanent magnetization anisotropy and cooling rate effects on intensity determinations they allow us to recover the geomagnetic intensity variations in the middle east between 7000 bc and 5000 bc i e during the so called pre halaf proto halaf halaf and halaf ubaid transitional cultural phases the data are compared with previous archeointensity results of similar ages from northern iraq yarim tepe ii and tell sotto and bulgaria we find that previous dating of the iraqi material was in error when corrected all northern mesopotamian data show a relatively good consistency and also reasonably match with the bulgarian archeointensity dataset using a compilation of available data we construct a geomagnetic field intensity variation curve for the middle east encompassing the past 9000 years which makes it presently the longest known regional archeomagnetic intensity record we further use this compilation to constrain variations in dipole field moment over most of the holocene in particular we discuss the possibility that a significant dipole moment maximum occurred during the third millennium bc which cannot easily be identified in available time varying global geomagnetic field reconstructions

a new three axis vibrating sample magnetometer for continuous high temperature magnetization measurements applications to paleo and archeo intensity determinations we have developed a new three axis vibrating sample magnetometer which allows continuous high temperature magnetization measurements of individual cylindrical 0 75 cm3 samples up to 650 c and the acquisition of thermoremanent magnetization trm in any direction and field intensity up to 200 t we propose a fast less than 2 5 h automated experimental procedure adapted from boyd s nature 319 1986 208 209 modified version of the thellier and thellier ann geophys 15 1959 285 376 method which provides continuous intensity determinations over a large typically 300 c temperature interval for each sample this procedure allows one to take into account both the cooling rate dependence of trm acquisition and anisotropy of trm several examples of analyses of ancient magnetization demonstrate the quality and reliability of the data and illustrate the promising potential of this new instrument in paleo and archeomagnetism

refining the archaeomagnetic dating curve for the near east new intensity data from bronze age ceramics at tell mozan syria abstract uncertainty in radiocarbon dates for the near east caused by a bimodal distribution of ages due to the natural fluctuations of 14 c in the atmosphere has demonstrated the need for an alternative absolute dating technique to aid in the construction of site chronologies here we present a new archaeointensity reference curve model for the first three millennia bce for the levant syria israel jordan for use in archaeomagnetic dating and contribute twelve new intensity results to an increasingly dense geomagnetic field record for the period between 2400 and 1200 bce in the near east archaeomagnetic analysis was conducted on ceramic samples i e pottery sherds from seven sequential and well constrained occupational layers at the site of tell mozan bronze age urkesh in northeastern syria resulting in a 90 success rate by specimen n 42 for archaeointensity determination and an 86 correspondence between the model and the archaeologically derived dates within one standard deviation 1 age standard deviations as low as 24 years were obtained after integration with stratigraphic constraints we also outline the techniques and sampling procedures of archaeomagnetic dating in a manner suitable for the non paleomagnetist while detailing methodology for archaeomagnetic researchers

toward an optimal geomagnetic field intensity determination technique 1 paleointensity determinations based on double heating techniques in field zero field cooling zero field in field cooling and two in field steps with opposite laboratory fields are generally considered to be functionally interchangeable producing equally reliable paleointensity estimates to investigate this premise we have developed a simple mathematical model we find that both the zero field first and in field first methods have a strong angular dependence on the laboratory field parallel orthogonal and anti parallel while the two in field steps method is independent of the direction of the laboratory produced field contrary to common practice each method yields quite different outcomes if the condition of reciprocity of blocking and unblocking temperatures is not met even with marginal 10 tails of partial thermoremanence our calculations suggest that the zero field first method with the laboratory produced field anti parallel to the natural remanence nrm is the most robust paleointensity determination technique when the intensity of the lab induced field is smaller than ancient field however the zero field first method with the laboratory field parallel to the nrm is the optimum approach when the intensity of the lab induced field is larger than the ancient field by far the best approach however is to alternatethe infield zerofield iz steps with zerofield infield zi steps

rapid sea level rise from a west antarctic ice sheet collapse a short term perspective will worldwide sea level soon rise rapidly because of a shrinkage of the west antarctic ice sheet wais here i give a personal perspective of that probability the crucial question is not whether large changes in ice mass can occur but how likely it is that a large rapid change say a several fold increase in the 20th century rate of about 2 mm a 1 will occur in the next century or two from awest antarctic cause twenty years ago weertman proposed that a marine ice sheet is inherently unstable but weertman s analysis was based on a simple model of a marine ice sheet that did not include fast flowing wet based ice streams which are now known to dominate the grounded ice sheet modern analyses do not definitively determine just how ice streams affect the stability of the wais but it can at least be said that there is no compelling theoretical reason to expect a rapid rise in sea level from the wais triggered by ice shelf thinning of the three main ice drainage systems in the wais the one that flows into pine island bay might be a particularly likely site for accelerated flow since there is no ice shelf to restrain the inflowing ice streams yet measurements show that this system is not significantly out of mass balance if the ross embayment system which has undergone several sudden glacial reorganizations in the last thousand years were unstable one might expect a history of large changes in the total outflow of ice into the ross ice shelf yet the total outflow in the ross embayment has remained relatively unchanged despite the large internal perturbations a fact that points to a stable not an unstable system study of the third major drainage from the wais into the ronne ice shelf also suggests that there is no gross discordance between the present velocity vectors and flow tracers in the ice shelf although the evidence is limited in the light of the evidence for recent stability it is difficult to see how climate warming whether anthropogenic or natural could trigger a collapse of the wais in the next century or two thus i believe that a rapid rise in sea level in the next century or two from a west antarctic cause could only occur if a natural not induced collapse of the wais were imminent based on a concept of pseudo random collapse once per major glacial cycle i estimate the chances of that to be on the order of one in a thousand

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

new historical archeointensity data from brazil evidence for a large regional non dipole field contribution over the past few centuries abstract we report new archeointensity data obtained from the analyses of baked clay elements architectural and kiln brick fragments sampled in southeast brazil and historically and or archeologically dated between the end of the xvith century and the beginning of the xxth century ad the results were determined using the classical thellier and thellier protocol as modified by coe including partial thermoremanent magnetization ptrm and ptrm tail checks and the triaxe protocol which involves continuous high temperature magnetization measurements in both protocols trm anisotropy and cooling rate trm dependence effects were taken into account for intensity determinations which were successfully performed for 150 specimens from 43 fragments with a good agreement between intensity results obtained from the two procedures nine site mean intensity values were derived from three to eight fragments and defined with standard deviations of less than 8 the site mean values vary from 25 t to 42 t and describe in southeast brazil a continuous decreasing trend by 5 t per century between 1600 ad and 1900 ad their comparison with recent archeointensity results obtained from northeast brazil and reduced at a same latitude shows that 1 the geocentric axial dipole approximation is not valid between these southeastern and northeastern regions of brazil whose latitudes differ by 10 and 2 the available global geomagnetic field models gufm1 models their recalibrated versions and the calsk3 models are not sufficiently precise to reliably reproduce the non dipole field effects which prevailed in brazil for at least the 1600 1750 period the large non dipole contribution thus highlighted is most probably linked to the evolution of the south atlantic magnetic anomaly sama during that period furthermore although our dataset is limited the brazilian archeointensity data appear to support the view of a rather oscillatory behavior of the axial dipole moment during the past three centuries that would have been marked in particular by a moderate increase between the end of the xviiith century and the middle of the xixth century followed by the well known decrease from 1840 ad attested by direct measurements

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

archaeomagnetic study of five mounds from upper mesopotamia between 2500 and 700 bce further evidence for an extremely strong geomagnetic field ca 3000 years ago the distribution of archaeomagnetic data in eastern europe and the near and middle east shows a remarkable gap in turkey this study presents the first archaeomagnetic results from five different mounds in southeast turkey the northern part of mesopotamia the rock magnetic experiments indicate that in the majority of the samples the dominant magnetic carrier is magnetite which is stable to heating to temperatures of 700 1c in general the demagnetization diagrams are single component and all five sets display well defined characteristic magnetizations and clustered directions for the period between 2500 and 700 bce the declinations are between 3501 and 201 while inclinations are in the range of 49 641 the directional results are compared with the global geomagnetic field models cals7k 2 arch3k cst 1 and cals3k 4 and the data from the archaeomagnetic database geomagia50v2 the results are coherent with both the data and the models except for two nearcontemporaneous sets dating 2000 bce which are offset to the east by more than 201 with respect to cals7k 2 archaeointensity measurements were made using the microwave and conventional thermal thellier methods applied to five sets of samples four furnaces and a mud brick wall these yielded comparable and intriguing results while those from the furnaces are slightly higher than the cals7k 2 model and in agreement with the geomagia50v2 and the middle east data the results from the mud brick wall suggest a high intensity of 100 8 mt 17 7 10 22 am 2 a t 1000 bce this result is

possible impact of the earth s magnetic field on the history of ancient civilizations we report new archeointensity results from iranian and syrian archeological excavations dated from the second millennium bc these high temperature magnetization data were obtained using a laboratory built triaxial vibrating sample magnetometer together with our previously published archeointensity results from mesopotamia we constructed a rather detailed geomagnetic field intensity variation curve for this region from 3000 bc to 0 bc four potential geomagnetic events archeomagnetic jerks marked by strong intensity increases are observed and appear to be synchronous with cooling episodes in the north atlantic this temporal coincidence strengthens the recent suggestion that the geomagnetic field influences climate change over multi decadal time scales possibly through the modulation of cosmic ray flux interacting with the atmosphere moreover the cooling periods in the north atlantic coincide with episodes of enhanced aridity in the middle east when abrupt societal changes occurred in the eastern mediterranean and mesopotamia although the coincidences discussed in this paper must be considered with caution they lead to the possibility that the geomagnetic field impacted the history of ancient civilizations through climatically driven environmental changes triggering economic social and political instability

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

a geomagnetic field model for the holocene based on archaeomagnetic and lava flow data abstract we propose a new geomagnetic field model for the holocene period based on archaeomagnetic and lava flow data avoiding the use of lake sediment data the source of data comes from the geomagia50v2 database which has been updated with the new archaeomagnetic and volcanic studies published during the last 3 yr the model called sha dif 14k allows us to analyse the behaviour of the geomagnetic field for the last 14 000 yr from 12 000 bc to 1900 ad for the model construction we use the spherical harmonic analysis in space and the penalized cubic b splines in time both spatial and temporal regularization norms are used to constrain the inversion problem and applied at the core mantle boundary cmb to assure the convergence of the model for the last 3 ka the model predictions agree with those given by the global model arch3k 1 and the european model scha dif 3k for older epochs the new model presents a clear improvement in field resolution with respect to other current models of the geomagnetic field for the holocene for the last 9 ka the time evolution of the dipolar moment obtained from the dipole field shows a clear minimum between 5500 bc and 3000 bc and the well known continuous decreasing trend of the geomagnetic field strength for the last millennium and a half a general view of the time average evolution of the geomagnetic field flux lobes at the cmb for the northern hemisphere suggests a marked lobe of positive magnetic flux when the dipole moment was maximum this lobe vanishes when the dipolar field is decreasing the north polar wander paths of both north magnetic dip and geomagnetic poles were obtained showing an average rate of motion of 5 1 km yr and 3 7 km yr respectively the model shows that the geomagnetic field can be averaged as axial dipolar in 2000 yr within an error of 5 the typical uncertainty of the palaeomagnetic studies finally and following the recent definition of archaeomagnetic jerks we found 8 critical events in the time evolution of the geomagnetic field for the last 8 ka characterized by a maximum in the hemispheric asymmetry of the proposed model the model is available in the earth ref digital archive at http earthref org erda 1897

the secular variation of the geomagnetic field in egypt in the last 5000 years the palaeo intensities fa of the geomagnetic field in egypt at some ages are determined by archaeomagnetic measurements and found to be fa 36 2 t at 3100 b c fa 46 8 t at 3000 b c fa 36 5 t at 2780 b c 49 0 t at 2500 b c 36 4 t at 2200 b c 57 5 t at 1990 b c 62 1 t atca 1400 b c 61 5 t at 1400 b c 69 9 t at 600 b c 59 3 t at 550 b c 79 9 t at 460 b c 73 7 t at 450 b c 69 7 t at 320 b c 56 2 t at a d 50 64 9 t at a d 400 54 4 t at a d 300 57 5 t at a d 700 and 43 0 t at a d 1975

high temperature archeointensity measurements from mesopotamia we present new archeointensity results obtained from 127 potsherds and baked brick fragments dated from the last four millennia bc which were collected from different syrian archeological excavations high temperature magnetization measurements were carried out using a laboratory built triaxial vibrating sample magnetometer triaxe and ancient field intensity determinations were derived from the experimental procedure described by le goff and gallet le goff and gallet earth planet sci lett 229 2004 31 43 as some of the studied samples were previously analyzed using the classical thellier and thellier thellier and thellier ann geophys 15 1959 285 376 method revised by coe coe j geophys res 72 1967 3247 3262 a comparison of the results is made from the two methods the differences both at the fragment and site levels are mostly within 5 which strengthens the validity of the experimental procedure developed for the triaxe the new data help to better constrain the geomagnetic field intensity variations in mesopotamia during archeological times with the probable occurrence of an archeomagnetic jerk around 2800 2600 bc

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

eight thousand years of geomagnetic field intensity variations in the eastern mediterranean 1 twenty new intensity determinations of the ancient geomagnetic field have been obtained from groups of potsherds and brick fragments from syria these artifacts archeologically well dated from 6000 b c to approximately a d 1200 have been analyzed using the thellier and thellier 1959 method as modified by coe 1967 intensity values have been corrected for the effects of anisotropy of thermal remanent magnetization and cooling rate our results indicate that field intensities were moderate in syria from 6000 b c to 3500 b c with values of 30 40 t there was a significant increase in intensity by a factor of 2 from 3500 b c to 700 b c which was interrupted by a moderate decrease between 2550 b c and 1750 b c during more recent periods our results show an intensity minimum approximately a d 200 and a maximum around the tenth century comparison with different data sets from the eastern mediterranean and central asia shows that geomagnetic field intensity variations were consistent at this large regional scale at least over the last 5 millennia

evidence for rapid geomagnetic field intensity variations in western europe over the past 800 years from new french archeointensity data abstract the number of reliable archeointensity determinations obtained from western europe for the past millennium remains limited moreover the large scatter between different datasets available is puzzling the present study analyzed 31 new groups of baked clay ceramic or brick fragments sampled in france 29 groups and in belgium 2 groups these groups contain several fragments collected from different artefacts and are precisely dated principally from historical constraints between the xiiith and the xixth centuries additionally we re evaluated 14 intensity values that we previously obtained from the same time period the fragments were analyzed using two different thermal methods 1 the in field zero field iz or the izzi version of the classical thellier and thellier method and 2 the triaxe protocol that involves high temperature magnetization measurements data were corrected for the anisotropy of thermoremanent magnetization trm and the dependence of trm acquisition on the cooling rate was taken into account in the different protocols archeointensity data obtained on twin specimens sampled from the same fragment and using both experimental techniques generally show a good agreement i e within 5 at the fragment and at the site level all retained site level averaged intensity results 43 of 45 groups have standard deviations of less than 5 t furthermore groups of approximately the same age have very consistent archeointensity altogether the data presented herein recover a detailed and smoothed geomagnetic field intensity variation curve characterized by two peaks in intensity the first during the second half of the xivth century and the second around ad 1600 followed by a significant decreasing trend in intensity during most the xviith and xviiith centuries this evolution does not satisfactorily fit with the expected intensity values for france derived from geomagnetic field models relying on a different evolution of the axial dipole moment our results lead us to propose that the axial dipole moment decreased from ad 1600 to the end of the xviiith century then slightly increased up to ad 1850 before decreasing again to present day

geomagnetic field intensity how high can it get how fast can it change constraints from iron age copper slag article the intensity of the geomagnetic field varies over different time scales yet constraints on the maximum intensity of the field as well as for its maximum rate of change are inadequate due to poor temporal resolution and large uncertainties in the geomagnetic record the purpose of this study is to place firm limits on these fundamental properties by constructing a high resolution archaeointensity record of the levant from the 11th century to the early 9th century bce a period over which the geomagnetic field reached its maximum intensity in eurasia over the past 50 000 years we investigate a 14 c dated sequence of ten layers of slag material which accumulated within an ancient industrial waste mound of an iron age copper smelting site in southern israel depositional stratigraphy constrains relative ages of samples analyzed for paleointensity and 14 c dates from different horizons of the mound constrain the age of the whole sequence the analysis yielded 35 paleointenisty data points with accuracy better than 94 and precision better than 6 covering a period of less than 350 years most probably 200 years we construct a new high resolution quasi continuous archaeointensity curve of the levant that displays two dramatic spikes in geomagnetic intensity each corresponding to virtual axial dipole moment vadm in excess of 200 zam 2