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

high paleointensities for the canary islands constrain the levant geomagnetic high understanding the behavior of enigmatic geomagnetic traits such as the levant intensity high is currently challenged by a lack of full vector records of regional variations in the geomagnetic field here we apply the recently proposed multi method paleointensity approach to a suite of 19 lavas from the canary islands dating between 4000 bc and 1909 ad our new record reveals high paleointensities vadms 120 zam2 coinciding with and shortly after the peak in geomagnetic intensity in the levant at 1000 bc furthermore our data suggests a westward movement of this geomagnetic phenomenon at a rate of 6 7 12 per century in addition to izzi thellier microwave thellier and the multi specimen method the calibrated pseudo thellier method is an important part of the multi method paleointensity approach the calibration of this relative paleointensity method was derived from a suite of hawaiian lavas it is improved with the results of the canarian cooling units pseudo thellier results from samples with very low curie temperature 150 c however cannot be reliably converted to absolute paleointensity estimates the multi method paleointensity approach yielded a reliable estimate for 60 of the flows sampled an unusually high success rate for a paleointensity study involving lavas

stochastic modelling of regional archaeomagnetic series summary we report a new method to infer continuous time series of the declination inclination and intensity of the magnetic field from archeomagnetic data adopting a bayesian perspective we need to specify a priori knowledge about the time evolution of the magnetic field it consists in a time correlation function that we choose to be compatible with present knowledge about the geomagnetic time spectra the results are presented as distributions of possible values for the declination inclination or intensity we find that the methodology can be adapted to account for the age uncertainties of archeological artefacts and we use markov chain monte carlo to explore the possible dates of observations we apply the method to intensity datasets from mari syria and to intensity and directional datasets from paris france our reconstructions display more rapid variations than previous studies and we find that the possible values of geomagnetic field elements are not necessarily normally distributed another output of the model is better age estimates of archeological artefacts

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

archaeomagnetism of burnt cherts and hearths from middle palaeolithic amud cave israel tools for reconstructing site formation processes and occupation history abstract apart from magnetostratigraphy archaeomagnetism is rarely used in middle and late pleistocene sites here we present detailed palaeomagnetic analyses of cemented hearths and burnt chert items from amud cave israel 68 55 ka two types of materials common in levantine middle palaeolithic cave sites both materials are shown to be recorders of the geomagnetic field and were used to reconstruct either the ancient field direction for cemented hearths or intensity palaeointensity for chert at the time of the last burning or shortly after we test the utility of palaeomagnetic data to further our understanding of temporal aspects of occupations in the cave by comparing the dispersion of the palaeomagnetic data to the known characteristics of geomagnetic secular variation in the holocene we show that divergent palaeointensities can help identify diachronic burning events suggesting different activity patterns in two areas of the cave additionally we used palaeomagnetic directional vectors to distinguish between a well preserved hearth and one that had been mixed prior to cementation using rock magnetic investigations we demonstrate that magnetic methods can be used as a relatively fast and inexpensive method to identify burning of cherts in antiquity above 500 c the palaeomagnetic results are in agreement with results of previous studies at amud cave obtained by other independent methods this study shows that palaeomagnetic methods can serve as a powerful tool in the study of palaeolithic sites

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

full vector archaeomagnetic records from anatolia between 2400 and 1350 bce implications for geomagnetic field models and the dating of fires in antiquity abstract anatolia as one of the busiest crossroads of ancient civilizations provides an ideal platform for archaeomagnetic studies previous results from the middle east have suggested the occurrence of a strong peak in geomagnetic intensity at 1000 bce associated with dramatic field strength variations that could require a radical rethinking of geodynamo theory the behavior of the field in the centuries preceding this peak remains poorly constrained however here we present the results of full vector archaeomagnetic experiments performed on 18 sets of samples from three archaeological sites belonging to assyrian trade colony and hittite periods associated rock magnetic analyses showed that the major magnetic carrier is magnetite chemically stable up to 700 c and the magnetic mineral assemblage is composed mostly of non interacting psd grains the directional results are compared with existing data and with the most recent global geomagnetic field models pfm9k 1b and sha dif 14k the directions are in remarkably good agreement with sha dif 14k which is based on archaeomagnetic and lava flow data together with our earlier results from anatolia we triple the existing database of directions for the 700 year long period 2200 1500 bce over a large region from greece to azerbaijan and from moldavia ukraine to egypt three archaeointensity methods thermal izzi thellier microwave thellier and the multi specimen protocol msp produced virtual axial dipole moment estimates 9 0 10 9 10 22 am 2 that are somewhat higher than contemporaneous regional and global data and model predictions suggesting that the field was already substantially stronger than today more than 800 years prior to the reported peak in addition to constraining geomagnetic variability our data also allow us to assign relative dates to inferred fire events in the assyrian trade colony period sites this allows us to conclude that the fire events at the largest site kultepe were not all contemporaneous with one another and with the abandonment of the site as has been previously hypothesized

depositional remanent magnetization toward an improved theoretical and experimental foundation the first theoretical predictions for the behavior of magnetic particles in water were that sedimentary magnetizations would be fully aligned with the ambient field yet redeposition experiments showed a strong and quasi linear dependence on the external field this empirically observed linearity has served as the fundamental assumption of sedimentary paleointensity studies for decades we present redeposition experiments which suggest instead that the relationship between depositional remanence drm and applied field may frequently be curved for magnetic fields in the range of the earth s numerical simulations using a flocculation model can explain the redeposition data and suggest that drm will be significantly non linear when the flocs are small several microns there is a strong dependence of floc size on salinity particularly in low salinity environments floc size has a profound influence on the efficiency of drm hence low salinity environment may give results with poor reproducibility the size of the floc in which magnetic particles are embedded is not accounted for in current methods of normalization yet is the most important parameter on the bright side however it now seems possible to quantitatively explain paleointensity in sedimentary systems opening the door to absolute paleointensity estimates from sediments whose key parameters of floc size distribution and settling times can be constrained

sound velocity of mgsio3 perovskite to mbar pressure abstract brillouin scattering measurements of the aggregate shear wave velocities in mgsio 3 perovskite were conducted at high pressure conditions relevant to the earth s lowermost mantle approaching 1 mbar infrared laser annealing of samples in a diamond anvil cell allowed us to obtain high quality brillouin spectra and to drastically extend the upper limit of pressure for brillouin measurements we found that the pressure derivative of the shear modulus d g d p g of mgsio 3 perovskite is 1 56 0 04 which is distinctly lower than that of previous lower pressure experiments below 9 gpa extrapolation of the high pressure shear velocities of perovskite to ambient pressure are in excellent agreement with earlier room pressure brillouin measurements the shear modulus shear velocity and longitudinal velocity at ambient pressure were determined to be g 0 172 9 15 gpa v s 6 49 3 and v p 10 85 3 km sec the mineralogical model that provides a best fit to global seismological 1 d velocity profiles is one that contains 85 90 vol perovskite in the lower mantle the results of this study are the first to demonstrate that the elastic wave velocities for a near adiabatic lower mantle with a bulk composition dominated by magnesium silicate perovskite are consistent with the average lower mantle seismic velocity structure the large pressure range over which acoustic measurements of mgsio 3 perovskite performed in this study has thus allowed us to put tighter constraints on compositional models of the earth s lower mantle

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

time variations in geomagnetic intensity 1 after many years spent by paleomagnetists studying the directional behavior of the earth s magnetic field at all possible timescales detailed measurements of field intensity are now needed to document the variations of the entire vector and to analyze the time evolution of the field components a significant step has been achieved by combining intensity records derived from archeological materials and from lava flows in order to extract the global field changes over the past 12 kyr a second significant step was due to the emergence of coherent records of relative paleointensity using the remanent magnetization of sediments to retrace the evolution of the dipole field a third step was the juxtaposition of these signals with those derived from cosmogenic isotopes contemporaneous with the acquisition of records new techniques have been developed to constrain the geomagnetic origin of the signals much activity has also been devoted to improving the quality of determinations of absolute paleointensity from volcanic rocks with new materials proper selection of samples and investigations of complex changes in magnetization during laboratory experiments altogether these developments brought us from a situation where the field changes were restricted to the past 40 kyr to the emergence of a coherent picture of the changes in the geomagnetic dipole moment for at least the past 1 myr on longer timescales the field variability and its average behavior is relatively well documented for the past 400 myr section 3 gives a summary of most methods and techniques that are presently used to track the field intensity changes in the past in each case current limits and potential promises are discussed the section 4 describes the field variations measured so far over various timescales covered by the archeomagnetic and the paleomagnetic records preference has always been given to composite records and databases in order to extract and discuss major and global geomagnetic features special attention has been devoted to discussing the degree of confidence to be put in the data by considering the integration of multiple data sets involving different techniques and or materials

testing the accuracy of absolute intensity estimates of the ancient geomagnetic field using copper slag material abstract the middle eastern copper slag is a promising new material for studying intensity variations in the geomagnetic field with high resolution and precision the purpose of this study is to test the accuracy of archaeointensity estimates determined using copper slag by addressing two questions 1 does slag material display the magnetic properties required for valid thellier experiments and 2 what is the accuracy of the archaeointensity estimates derived from thellier style experiments on optimal samples we address the first question through a comprehensive microscopic and magnetic study of representative archaeological slag samples in order to identify the properties responsible for optimal behavior in thellier experiments to address the second question we reproduced slag samples in the laboratory under controlled magnetic fields and analyzed them using the same izzi paleointensity technique used for the ancient slag microscopic analyses of the archaeological slag show that ferromagnetic phases occur as three dimensional dendritic structures whose branches consist of submicron elongated particles magnetic analyses show that these dendrites behave as an assemblage of shape controlled single domain like particles and that their magnetization is thermoremanent we conclude that slag material can be magnetically suitable for valid thellier experiments the laboratory produced slag material demonstrated similar magnetic and mineralogical properties as the archaeological slag izzi experiments showed that non linear trm acquisition even at field strengths similar to earth s and trm anisotropy are important factors to monitor during paleointensity studies of slag material anisotropy and non linearity are probably related to the dendritic shape of the oxide grains intensity estimates derived from three laboratory produced slag samples demonstrated accuracy to within 5 after applying the required corrections

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

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

pressure and temperature dependence of elastic wave velocity of mgsio3 perovskite and the composition of the lower mantle abstract simultaneous measurements of compressional p and shear s wave velocities and unit cell volume density have been conducted on mgsio 3 perovskite to 9 2 gpa and 873 k using ultrasonic interferometry in conjunction with x ray diffraction finite strain analysis of current data allowed us to determine the elastic moduli and their pressure derivatives independent of the pressure measurement the results are k s 253 2 gpa g 173 1 gpa k s p 4 4 1 and g p 2 0 1 the temperature derivatives of the bulk and shear moduli were tightly constrained from acoustic velocity measurements yielding k s t 0 021 2 gpa k and g t 0 028 2 gpa k p and s wave velocities and density profiles for a pyrolite compositional model consisting of magnesium silicate perovskite and magnesiowustite are calculated at lower mantle depths along a 1600 k adiabatic geotherm the results agree with those of seismic model prem within 0 5 0 5 and 0 3 respectively from 800 to 2600 km the effect of fe and mg partitioning between magnesium silicate perovskite and magnesiowustite on the calculated velocities and density is negligibly small compared to the effects of composition and temperature simultaneous constraints from p and s wave velocities and density support for a homogeneous lower mantle with pyrolitic composition

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

changes in the intensity of the geomagnetic field a new more reliable technique has been used to determine the ancient intensity of the earth s magnetic field using samples of baked clay from eight sites in the eastern mediterranean the resultant power spectrum reveals a single strong component with a period of 1430 years the reproducibility of the results obtained with the new method also makes limited archaeomagnetic dating with a precision of between about one and two hundred years between 900 bc and ad 400 possible

the effect of remanence anisotropy on paleointensity estimates a case study from the archean stillwater complex paleomagnetism of archean rocks potentially provides information about the early development of the earth and of the geodynamo precambrian layered intrusive rocks are good candidates for paleomagnetic studies such complexes are commonly relatively unaltered and may contain some single domain magnetite armored by silicate mineral grains however layered intrusives often have a strong petrofabric that may result in a strong remanence anisotropy magnetic anisotropy can have particularly disastrous consequences for paleointensity experiments if the anisotropy is unrecognized and if its effects remain uncorrected here we examine the magnetic anisotropy of an anorthosite sample with a well developed magmatic foliation the effect of the sample s remanence fabric on paleointensity determinations is significant paleointensities estimated by the method of thellier and thellier range from 17 to 55 t for specimens magnetized in a field of 25 t we describe a technique based on the remanence anisotropy tensor to correct paleointensity estimates for the effects of magnetic fabric and use it to estimate a paleointensity for the stillwater complex mt usa of 32 t adjusted for the effects of slow cooling

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

paleomagnetic field intensity derived from non sd testing the thellier izzi technique on md slag and a new bootstrap procedure abstract experimental techniques to determine paleomagnetic field intensity are based on a theoretical framework that is valid only for single domain sd ferromagnetic particles yet most of the available materials exhibit distinctly non sd properties designing the optimal paleointensity methodology for non sd is therefore a fundamental challenge in paleomagnetism the objective of this study is to experimentally test the izzi thellier absolute paleointensity method on small md recorders the test has two purposes 1 to describe the characteristic non sd patterns occurring in arai plots and 2 to identify the optimal approach in interpreting non sd behavior we carried out paleointensity experiments on 40 specimens from 4 synthetic re melted slag samples with identical magnetic properties mineralogy texture and non sd state produced under different field intensities we ran three batches of izzi experiments using different conditions that allow for a detailed characterization of the non sd behavior we find that the curvature of the arai plot is systematically dependent on the angle and the proportion between the field used in the paleointensity experiment btrm and the field in which the nrm was acquired bnrm straight line arai plot occur when the two fields are parallel and equal and seems to always give the true slope convex curves occur when btrm is parallel and significantly stronger than bnrm concave curves occur in all the other cases and yield two end case slopes that are always different than the true slope in addition zigzagged patterns increase with the angle the proportion between btrm and bnrm we test the accuracy of the best fitting line approach and conclude that best fitting line in curved plots cannot provide robust paleointensity estimates yet the two end case slopes in concave curves provide adequate constraints for the true value we introduce a new procedure to calculate a 95 confidence interval of the paleointensity from curved plots using bootstrap statistics we substantiate the new procedure by conducting two independent tests the first uses synthetic re melted slag produced under known field intensities 3 sd samples and 4 non sd samples the second compares paleointensity determinations from archeological slag samples of the same age 34 sd samples and 10 non sd samples the two tests demonstrate that the bootstrap technique may be the optimal approach for non ideal dataset

silicate perovskite analogue scalo3 temperature dependence of elastic moduli abstract the elastic moduli of scalo 3 perovskite a very close structural analogue for mgsio 3 perovskite have been measured between 300 and 600 k using high precision ultrasonic interferometry in an internally heated gas charged pressure vessel this new capability for high temperature measurement of elastic wave speeds has been demonstrated on polycrystalline alumina the temperature derivatives of elastic moduli of al 2 o 3 measured in this study agree within 15 with expectations based on published single crystal data for scalo 3 perovskite the value of k s t p is 0 033 gpa k 1 and g t p is 0 015 gpa k 1 the relative magnitudes of these derivatives agree with the observation in duffy and anderson duffy t s anderson d l 1989 seismic velocities in mantle minerals and the mineralogy of the upper mantle j geophys res 94 1895 1912 that k s t p is typically about twice g t p the value of k s t p for scalo 3 is intermediate between those inferred less directly from v p t studies of fe free and fe and al bearing mgsio 3 perovskites wang y weidner d j liebermann r c zhao y 1994 p v t equation of state of mg fe sio 3 perovskite constraints on composition of the lower mantle phys earth planet inter 83 13 40 mao h k hemley r j shu j chen l jephcoat a p wu y bassett w a 1991 effect of pressure temperature and composition on the lattice parameters and density of mg fe sio 3 perovskite to 30 gpa j geophys res 91 8069 8079 zhang weidner d 1999 thermal equation of state of aluminum enriched silicate perovskite science 284 782 784 the value of g t p for scalo 3 is similar to those of most other mantle silicate phases but lower than the recent determination for mgsio 3 perovskite sinelnikov y chen g neuville d r vaughan m t liebermann r c 1998 ultrasonic shear wave velocities of mgsio 3 perovskite at 8 gpa and 800k and lower mantle composition science 281 677 679 combining the results from the previous studies and current measurements on scalo 3 perovskite we extracted the parameters q and 0 needed to fully specify its mie gruneisen debye equation of state in this study we have demonstrated that acoustic measurements of k s t unlike v p t data tightly constrain the value of q it is concluded that scalo 3 has normal 0 1 3 and high q 3 6 the high value of q indicates that scalo 3 has very strong intrinsic temperature dependence of the bulk modulus similar behaviour has been observed in measurements on fe and al bearing silicate perovskites mao et al 1991 zhang and weidner 1999

assessment of the usefulness of lithic clasts from pyroclastic deposits for paleointensity determination 1 paleomagnetic and rock magnetic measurements were carried out on lithic clasts found within pyroclastic deposits to assess their potential for paleointensity determinations the use of multiple lithologies in a single paleointensity determination would provide confidence that the result is not biased by alteration within one lithology lithic clasts were sampled from three historically active volcanoes lascar in the chilean andes mt st helens united states and vesuvius italy at lascar triple heating paleointensity experiments allow development of new selection criteria for lithic clasts found within pyroclastic deposits using these criteria the lascar data yield a mean paleointensity of 24 3 1 3 t 1 n 26 which agrees well with the expected value of 24 0 t this indicates that pyroclastic rocks have promise for paleointensity determinations pyroclastics however still suffer from the range of problems associated with conventional paleointensity experiments on lava flows samples from mt st helens are strongly affected by multidomain md behavior which results in all samples failing to pass the paleointensity selection criteria at vesuvius md grains magnetic interactions and chemical remanent magnetizations contributed to failure of all paleointensity experiments rock magnetic analyses allow identification of the causes of failure of the paleointensity experiments however in this study they have not provided adequate preselection criteria for identifying pyroclastics that are suitable for paleointensity determination

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

the effects of secondary mineral formation on coe type paleointensity determinations theory and simulation thellier type experiments are the most widely applied approaches for determining the absolute paleointensities of earth s magnetic field one major problem however is that specimens are prone to thermal alteration due to the intensive thermal treatment during experiments linear arai plots with acceptable partial thermal remanent magnetization ptrm checks have been considered as evidence for the absence of or negligible effects of thermal alteration and as reliable indicators of high quality paleointensity estimates however by simulating the coe variant of the thellier method on assemblages of single domain sd magnetite particles it is demonstrated that new magnetic minerals which form during thermal treatments can result in linear concave up or concave down arai plots depending on the magnetic properties of both the primary and secondary magnetic phases among this range of behavior pseudoideal arai plots which are linear with acceptable ptrm check statistics would lead to paleointensity underestimates it is further demonstrated that ptrm checks are proportional to the degree of underestimate with a magnetic granulometry dependency for sd particles due to the complexity of this dependency ptrm check statistics are only comparable when specimens have similar magnetic properties this suggests that a universal threshold for ptrm check statistics is not likely to be effective since the criteria of linearity and low ptrm check statistics are insufficient to guarantee the fidelity of the estimates auxiliary rock magnetic methods such as temperature dependent hysteresis parameters and anhysteretic remanent magnetization are highly recommended to identify the presence of alteration

early bronze age copper production systems in the northern arabah valley new insights from archaeomagnetic study of slag deposits in jordan and israel this paper presents results of an archaeomagnetic study of slag from four early bronze eb age copper production sites in the faynan copper ore district and the northern arabah valley modern israel and jordan the results provide age constraints for metallurgical activities at these sites together with previously published data they indicate copper production around ca 2900 cal bce eb ii iii transition and between ca 2600 1950 cal bce spanning the later part of the eb iii and the entire eb iv period these data strongly suggest a direct link between faynan and the old kingdom of egypt which is reflected in the most significant phase of copper production and trade in the northern arabah prior to the iron age and in a settlement wave in the negev highlands in addition the results indicate that during the late eb ii copper was smelted up to 40 km away from the mines this is evident at the unique cultic site of ashalim located on the main road between faynan southeast of the dead sea and the settled areas in the core of canaan

large geomagnetic field anomalies revealed in bronze to iron age archeomagnetic data from tel megiddo and tel hazor israel abstract geomagnetic field measurements from the past few centuries show heightened secular variation activity in the southern hemisphere associated with the south atlantic anomaly saa it is uncertain whether geomagnetic anomalies at a similar scale have existed in the past owing to limited coverage and uncertainties in the paleomagnetic database here we provide new evidence from archaeological sources in the levant suggesting a large positive northern hemisphere anomaly similar in magnitude to the saa during the 9th 8th centuries bce called levantine iron age anomaly we also report an additional geomagnetic spike in the 8th century the new dataset comprises 73 high precision paleointensity estimates from ca 3000 bce to 732 bce and five directional measurements between the 14th and the 9th centuries bce well dated pottery and cooking ovens were collected from twenty archaeological strata in two large contemporaneous stratigraphical mounds tells in israel tel megiddo and tel hazor the new data are combined with previously published data and interpreted automatically using the pmagpy thellier gui program the tel megiddo and tel hazor data sets demonstrate excellent internal consistency and remarkable agreement with published data from mesopotamia syria the data illustrate the evolution of an extreme geomagnetic high that culminated in at least two spikes between the 11th and the 8th centuries bce iron age in the levant the paleomagnetic directional data of the 9th century bce show positive inclination anomalies and deviations of up to 22 from the averaged geocentric axial dipole gad direction from comparison of the levantine archaeomagnetic data with igrf model for 2015 we infer the levantine iron age anomaly between the 10th and the 8th centuries bce is a local positive anomaly the eastward extent of the anomaly is currently unknown

nonlinear thermoremanence acquisition and implications for paleointensity data abstract in paleointensity studies thermoremanence is generally regarded as a linear function of ambient magnetic field at low fields comparable to that of the present day earth we find pronounced nonlinearity at low fields for a class of materials with silicate hosted magnetite that otherwise perform well in paleointensity experiments we model this nonlinearity with narrow size ranges of large acicular single domain grains which are most likely in a vortex state i e nonuniformly magnetized sometimes labeled pseudosingle domain simple trm theory predicts that even certain single domain particles will also exhibit a nonlinear response saturating in fields as low as the earth s such behavior although likely to be rare may bias some paleointensity estimates the bias is especially pronounced when the laboratory field is higher than the ancient field fortunately the fundamental assumption that thermoremanence is proportional to applied field can and should be routinely checked at the end of successful paleointensity experiments by adding two extra heating steps

a paleointensity technique for multidomain igneous rocks 1 we developed a paleointensity technique to account for concave up arai diagrams due to multidomain md contributions to determine unbiased paleointensities for 24 trial samples from site ga x in pleistocene lavas from floreana island galapagos archipelago the main magnetization carrier is fine grained low titanium magnetite of variable grain size we used a comprehensive back zero forth bzf heating technique by adding an additional zero field heating between the thellier two opposite in field heating steps in order to estimate paleointensities in various standard protocols and provide internal self consistency checks after the first bzf experiment we gave each sample a total thermal remanent magnetization ttrm by cooling from the curie point in the presence of a low 15 t laboratory applied field then we repeated the bzf protocol with the laboratory applied ttrm as a synthetic natural remanent magnetization nrm using the same laboratory applied field and temperature steps to obtain the synthetic arai signatures which should only represent the domain state dependent properties of the samples we corrected the original arai diagrams from the first bzf experiment by using the arai signatures from the repeated bzf experiment which neutralizes the typical md concave up effect eleven samples meet the arai diagram post selection criteria and provide qualified paleointensity estimates with a mean value for site ga x of 4 23 1 29 t consistent with an excursional geomagnetic field direction reported for this site

small scale structure of the geodynamo inferred from oersted and magsat satellite data the geodynamo in the earth s liquid outer core produces a magnetic field that dominates the large and medium length scales of the magnetic field observed at the earth s surface1 2 here we use data from the currently operating danish oersted3 satellite and from the us magsat2 satellite that operated in 1979 80 to identify and interpret variations in the magnetic field over the past 20 years down to length scales previously inaccessible projected down to the surface of the earth s core we found these variations to be small below the pacific ocean and large at polar latitudes and in a region centred below southern africa the flow pattern at the surface of the core that we calculate to account for these changes is characterized by a westward flow concentrated in retrograde polar vortices and an asymmetric ring where prograde vortices are correlated with highs and retrograde vortices with lows in the historical 400 year average magnetic field4 5 this pattern is analogous to those seen in a large class of numerical dynamo simulations6 except for its longitudinal asymmetry if this asymmetric state was reached often in the past it might account for several persistent patterns observed in the palaeomagnetic field7 8 9 10 we postulate that it might also be a state in which the geodynamo operates before reversing

application of copper slag in geomagnetic archaeointensity research 1 paleointensity and archaeointensity studies since the 1950s have produced numerous geomagnetic intensity data for the last seven millennia as a consequence of different experiments and materials there is a complex and internally inconsistent picture of the geomagnetic field behavior in this study we present data using a recently developed experimental design on a heretofore unexploited recording medium copper slag deposits our results based on hundreds of specimens from various archaeometallurgical sites of the southern levant demonstrate the applicability of copper slag material for archaeointensity studies in addition to frequently exhibiting good experimental behavior slag has further advantages such as dense multilayer deposits and in cases embedded charcoals which open the door to data sets with excellent age control and resolution the data presented here augment the high quality database from the middle east and support previously observed periods of rapid change of the intensity of the geomagnetic field

geochemical and petrographic characteristics of impactites and cretaceous target rocks from the yaxcopoil 1 borehole chicxulub impact structure mexico implications for target composition we present major and trace element data as well as petrographic observations for impactites suevitic groundmass bulk suevite and melt rock particles and target lithologies including cretaceous anhydrite dolomite argillaceous limestone and oil shale from the yaxcopoil 1 borehole chixculub impact structure the suevitic groundmass and bulk suevite have similar compositions largely representing mixtures of carbonate and silicate components the latter are dominated by melt rock particles trace element data indicate that dolomitic rocks represented a significant target component that became incorporated into the suevites in contrast major elements indicate a strong calcitic component in the impactites the siliceous end member requires a mafic component in order to explain the low sio2 content multicomponent mixing of various target rocks the high alteration state and dilution by carbonate complicate the determination of primary melt particle compositions however two overlapping compositional groups can be discerned a high ba low ta group and a high fe high zn and high hf group cretaceous dolomitic rocks argillaceous limestone and shale are typically enriched in u as br and sb whereas anhydrite contains high sr contents the oil shale samples have abundances that are similar to the north american shale composite nasc but with a comparatively high u content clastic sedimentary rocks are characterized by relatively high th hf zr as and sb abundances petrographic observations indicate that the cretaceous rocks in the yaxcopoil 1 drill core likely register a multistage deformation history that spans the period from pre to post impact contrary to previous studies that claimed evidence for the presence of impact melt breccia injection veins we have found no evidence in our samples from a depth of 1347 1348 m for the presence of melt breccia we favor that clastic veinlets occur in a sheared and altered zone that underwent intense diagenetic overprint prior to the impact event

on the possible occurrence of archaeomagnetic jerks in the geomagnetic field over the past three millennia abstract archaeomagnetism can provide a high resolution full vector description of the earth s magnetic field for the past several thousand years we analyse the bulk of archaeomagnetic data both direction and intensity obtained recently in western europe and the eastern mediterranean covering the past three millennia we demonstrate a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima two clear ones at ad 200 and 1400 two presently less well constrained at 800 bc and ad 800 these sharp changes may constitute a new feature of geomagnetic secular variation archaeomagnetic jerks with time characteristics intermediate between geomagnetic jerks and magnetic excursions

thermoelastic behaviour of silicate perovskites insights from new high temperature ultrasonic data for scalo3 abstract mg fe al si al o 3 perovskite stable only at pressures 20 gpa is the dominant mineral of the earth s lower mantle and thus controls its physical properties including seismic wave speeds however the development of a thorough understanding of the thermoelastic behaviour of this silicate perovskite is compromised by its marginal metastability on recovery at ambient conditions study of the close structural analogue scalo 3 stable at much lower pressure has the potential to provide insight into the behaviour of its silicate cousin here previous exploratory ultrasonic measurements of the compressional and shear wave speeds on a fine grained polycrystalline specimen have been extended to 1000 k under 300 mpa confining pressure within an internally heated gas medium high pressure apparatus the wave speeds and derived bulk and shear moduli vary approximately linearly with temperature with derivatives k s t p 21 3 3 mpa k 1 and g t p 19 0 1 mpa k 1 respectively the new data along with previous measurements of thermal expansion and the pressure dependence of the elastic moduli have been assimilated into the comprehensive internally consistent finite strain model of thermoelastic behaviour proposed by stixrude l lithgow bertelloni c 2005 thermodynamics of mantle minerals i physical properties geophys j int 162 610 632 comparison of the newly constrained model for scalo 3 with emerging data for mgsio 3 perovskite provides guidance in the analysis of the chemical composition and temperature of the earth s lower mantle

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

ab initio elasticity and thermal equation of state of mgsio3 perovskite we have used high temperature ab initio molecular dynamic simulations to study the equation of state of orthorhombic mgsio3 perovskite under lower mantle pressure temperature conditions we have determined the gru neisen parameter q as a function of volume our state of the art simulations accurate to within 10 resolve the long standing controversy on thermal expansion k and gru neisen parameter of mgsio3 perovskite under ambient conditions we find the values for k and q of 1 86u10 35 k 31 and 1 51 respectively in excellent agreement with the latest experimental studies calculated elastic constants and the static equation of state at 0 k agree well with previous simulations we have found no evidence for the high temperature phase transitions of orthorhombic mgsio3 perovskite to cubic or tetragonal phases at mantle temperatures fl 2001 elsevier science b v all rights reserved

solar activity reconstructed over the last 7000 years the influence of geomagnetic field changes 1 the long term solar activity as manifested by sunspot number has been recently reconstructed on multi millennium time scales by s k solanki et al 2004 from the measured concentration of 14 c in tree rings the exact level of the reconstructed solar activity depends however on independently evaluated data of the geomagnetic dipole strength variations recently a new series of the palaeomagnetic dipole moment reconstruction for the last 7000 years has been presented by m korte and c g constable 2005a on the basis of a thorough analysis of global samples the new palaeomagnetic series yields a systematically lower dipole moment in the past compared to the earlier geomagnetic reconstructions we have revised the earlier sunspot activity reconstruction since 5000 bc using the new geomagnetic data series and found that it is roughly consistent with the previous results during most of the period although the revised sunspot number values are in general higher nonetheless it is confirmed with the new palaeomagnetic series that the sun spends only 2 3 of the time in a state of high activity similar to the modem episode this strengthens the conclusion that the modem high activity level is very unusual during the last 7000 years

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

thermal instability of the fluid column in a borehole application to the yaxcopoil hole mexico observational evidence proved that even when a borehole is in fully stabilized conditions temperature data may exhibit certain unrest resembling irregular oscillations in the order of hundredths or in the extreme case even tenths of degree temperature was monitored in complicated hydrogeological conditions in the yaxcopoil 1 hole chicxulub impact structure mexico two experiments are reported a 20 day monitoring when a logger was located in the center of the high temperature gradient anomaly produced by the cold wave slowly propagating downwards and b simultaneous three loggers 18 day monitoring with loggers located above in and below the anomaly all observed temperature time series displayed intermittent oscillations of temperature with sharp gradients and large fluctuations over all observed time scales while the upper and lower records revealed quasi periodic temperature variations the central record shows fast temperature oscillations with strong up and down reversals all with amplitudes up to a few tenths of degree the observed temperature time series were processed by recurrence and recurrence interval quantification as well as by spectral analyses it is shown that fluid in a borehole subject to thermal gradient is stable as far as the gradient remains below a certain critical value at higher rayleigh numbers the periodic character of oscillations typical for quiescent regime is superseded by stochastic features this oscillatory convection occurs due to instability of the horizontal boundary layers in the specific case of the yaxcopoil hole the time series above and below the cold wave characterized by relatively lower temperature gradients between 20 and 50 mk m contain a clear low frequency component produced by tidal forcing this component dominates over the high frequency domain periods from 10 15 to 1 min which exhibit a scaling behavior this pattern conspicuously changes in the center part of the cold wave where the local temperature gradient exceeds 200 mk m and where tidal forcing composes only 3 of the signal

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

extreme geomagnetic field variability indicated by eastern mediterranean full vector archaeomagnetic records the magnetic field of the earth can exhibit considerable variations at short time scales even as short as decades the archaeomagnetic studies of middle eastern artefacts mainly from israel and jordan show evidence for an exceptionally high intensity period from 1050 700 bc which displays two distinct spikes over the levant the levantine iron age anomaly liaa its exact duration and geographical extent are still poorly known despite the wealth of ancient settlements the extensive cultural heritage and a long history of trade and immigration the archaeomagnetism of turkey and cyprus remains largely unexplored this study presents a large data set of ancient directions and intensities from seven archaeological sites in the eastern mediterranean covering a time span of 2000 yrs the recorded directions from thirteen sets of samples are coherent with our earlier findings yet show significantly larger swings than existing field models in particular we confirm the very large swing in inclination we found earlier from 1910 1850 bc that is also captured by the greek psv curve and shallower by more than 10 than predicted by existing field models consequently these models require substantial revision in this region we were able to determine the archaeointensity from five sets of mud bricks from the thirteen attempted allowing us to provide the full field vector furthermore we present thirty one new archaeointensity results from potsherds and mud bricks that considerably enhance existing data especially when a set of strict selection criteria is applied fourteen sets of potsherds from a single site tell atchana provide the longest sequence recorded so far in turkey from 2100 to 1350 bc we find exceptionally high intensities of 145 and 175 zam2 around 700 bc in well dated mud bricks and potsherds from two different locations tell tayinat and kilise tepe supporting extreme geomagnetic field variability in the region moreover these two high intensities confirm the younger spike of the liaa in turkey

insights on the geomagnetic secular variation in the eastern mediterranean first directional data from cyprus abstract the first directional archaeomagnetic results from cyprus are presented based on the study of seven baked clay structures excavated at the copper smelting site of agia varvara almyras situated some 20 km south of nicosia this ancient copper working site represents a unique example of complete primary production of the copper metal in cyprus in total five furnaces one ore roasting pit and an oven were sampled in situ for an archaeomagnetic investigation all the studied structures are well dated based on pottery finds and radiocarbon dates with ages ranging from 600 bce to 50 bce several rock magnetic experiments were performed to determine the main magnetic carrier and to investigate the thermal stability of the studied material the direction of the characteristic remanent magnetization chrm for each structure has been determined by demagnetization of 7 15 specimens in alternating magnetic fields up to 100 120 mt mean directions were calculated assuming a fisherian distribution and are well defined for five out of the seven structures studied the new directions are compared with the directional data and the secular variation curves available from the surrounding area and with the predictions of global geomagnetic field models they are an important contribution to improving our knowledge of the geomagnetic field variations in the eastern mediterranean and offer new insights about fast geomagnetic directional changes during the first millennium bce that were not previously identified by the available geomagnetic field models predictions in this area

elasticity composition and temperature of the earth s lower mantle a reappraisal the interpretation of seismological models for the earth s lower mantle in terms of chemical composition and temperature is sensitive both to the details of the methodology employed and also to uncertainties in key thermoelastic parameters especially for the dominant mg fe sio3 perovskite phase here the alternative approaches adiabatic decompression of the lower mantle for comparison at zero pressure with laboratory data and the projection of laboratory data to lower mantle p t conditions for direct comparison with seismological observations are assessed along with the equations of state on which they are based it is argued that adiabatic decompression of the lower mantle is best effected by a strategy in which consistent third order finite strain expressions are required simultaneously to fit the strain dependence of both the seismic parameter and the density this procedure accords due weight to the most robust seismological observations namely the wave speeds and reduces to an acceptable level the otherwise very strong covariance among the fitted coefficients it is demonstrated that this approach can readily be adapted to include the effects of relaxation from the hill average to the reuss lower bound of the aggregate bulk modulus which governs the radial variation of density for the projection of laboratory thermoelastic data to lower mantle p t conditions the preferred equation of state is of the mie gruneisen type involving the addition at constant volume of the pressure along a finite strain principal 300 k isotherm and the thermal pressure calculated from the debye approximation to the lattice vibrational energy a high degree of consistency is demonstrated between these alternative equations of state possible departures of the lower mantle from conditions of adiabaticity and large scale homogeneity are assessed these are negligible for the prem model bullen parameter b 0 99 0 01 but significant for ak135 b 0 94 0 02 reviving the possibility of a substantially superadiabatic temperature gradient experimentally determined thermoelastic properties of the major mg fe sio3 perovskite and mg fe o magnesiowustite phases are used to constrain the equation of state parameters employed in the analysis of seismological information although the scarcity of information concerning the pressure and temperature dependence of the elastic moduli for the perovskite phase remains a serious impediment nevertheless it is demonstrated that the combination of a pyrolite composition simplified to the three component system sio2 mgo feo with molar xpv 0 67 and xmg 0 89 and a lower mantle adiabat with a potential temperature of 1600 k consistent with the preferred geotherm for the upper mantle and transition zone is compatible with the prem seismological model within the residual uncertainties of the thermoelastic parameters for the perovskite phase in particular such consistency requires values for the perovskite phase of ks ks p t and q ln ln v t of approximately 3 8 and 2 and g t near 0 022 gpa k 1 for the lower mantle assemblage more silicic models which have sometimes been advocated can also be reconciled with the seismological data but require lower mantle temperatures which are much higher by about 700 k for pyroxene stoichiometry however the absence of seismological and rheological evidence for the pair of thermal boundary layers separating convection above and below which is implied by such models remains a formidable difficulty under these circumstances the simplest possible model that of grossly uniform chemical composition throughout the mantle is preferred

detecting multidomain magnetic grains in thellier palaeointensity experiments the thellier technique is the most commonly used method for absolute palaeointensity studies it is based on thellier s laws stating that partial thermoremanent magnetisations ptrms are independent and additive which however only are true for non interacting single domain sd grains for multidomain md grains individual ptrms are not independent and thellier palaeointensity experiments on rocks with a significant proportion of md grains may therefore lead to erroneous palaeofield estimates by introducing a ptrm tail check in the coe version of the thellier technique j geophys res 72 1967 3247 we present a simple method to detect and discard such rocks the usefulness of the ptrm tail check is exemplified by thellier palaeointensity experiments performed on two palaeomagnetic sample collections with different magnetomineralogy miocene baked sediments from french massif central are shown to be ideal for thellier studies with the remanent magnetisation residing in thermally stable sd grains for palaeocene eocene basaltic lavas from faeroe islands 64 of otherwise acceptable palaeointensity estimates are discarded due to the failure of ptrm tail checks indicating the presence of significant concentrations of md grains 2001 elsevier science b v all rights reserved

interpretation and mathematical modeling of temporal changes of temperature observed in borehole yaxcopoil 1 within the chicxulub impact structure mexico summary geothermal research of the chicxulub impact structure on the yucatan peninsula mexico included repeated temperature logs following 0 3 0 8 15 24 34 and 50 months after shut in of drilling operations at the 1 5 km deep yaxcopoil 1 borehole a gradual distortion of the linear temperature profile by a cold wave propagating downward from 145 m to 317 m was detected within the observational period of 49 months march 2002 april 2006 the amplitude of the cold wave was increasing with depth and time in the range of 0 8 1 6 c as an explanation of this unusual phenomenon the hypothesis of downward migration of a large volume of drilling mud reported lost during drilling within the overlying and cooler highly porous and permeable karstic rocks has been proposed the thermal effects of the migrating fluid have been evaluated by solving numerically the heat conduction convection equation in appropriate geothermal models the best coincidence between the observed data and the simulations was yielded by the model of the drilling mud migrating as a large body parameters of this model are constrained by the measured temperature logs relatively tightly i the vertical extent of the downward migrating fluid body is about 5 10 m possibly increasing within the observational period of 49 months by a factor of 2 ii the horizontal extent of the body must be at least 15 20 m i e by order s of magnitude larger than the diameter of the borehole iii the average speed of the migration is about 5 metres per month and iv the fluid must migrate through a highly porous rock 80 porosity or more this high porosity which is necessary for the model to fit the observed data and the observed relatively stable velocity of the migration indicate the existence of a well developed system of interconnected cavities down to more than 300 m about 150 m more than the deepest cave system known in yucatan yet

hydrogeology of the south eastern yucatan peninsula new insights from water level measurements geochemistry geophysics and remote sensing summary the yucatan peninsula is one of the world s largest karstic aquifer systems it is the sole freshwater source for human users and ecosystems the region hosts internationally important groundwater dependent ecosystems gdes in the 5280 km2 sian ka an biosphere reserve the gdes are threatened by increasing groundwater abstractions and risks of pollution hydrogeological exploration work is needed as basis for sound groundwater management a multidisciplinary approach was used to study this data scarce region geochemical data and phreatic surface measurements showed distinct hydrogeological units in the groundwater catchment of sian ka an the hilly southwestern areas had a low hydraulic permeability likely caused by a geology containing gypsum whereas the transition zone and flat areas in the east and north had a high permeability in the latter areas the fresh groundwater could be described by a dupuit ghyben herzberg lens geophysical borehole logging and time domain electromagnetic soundings identified a shallow low resistive and high gamma radiation layer present throughout the hilly area and transition zone its thickness was 3 8 m apparent conductivity was 200 800 ms m and natural gamma radiation about 80 counts pr second the layer is proposed to be ejecta from the chicxulub impact cretaceous paleogene boundary spatial estimates of recharge were calculated from modis imagery using the triangle method average recharge constituted 17 of mean annual precipitation in the study area recharge was greatest in the hilly area and towards valladolid near the coast average actual evapotranspiration exceeded annual precipitation the multidisciplinary approach used in this study is applicable to other catchment scale studies

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

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

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

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

paleomagnetic field properties at high southern latitude 1 statistical analyses of paleomagnetic data from lava flows are used to study geomagnetic field behavior on million year timescales previous paleomagnetic studies have lacked high latitude measurements necessary to investigate the persistence of geomagnetic anomalies observed in the recent and historical field and replicated in some numerical geodynamo simulations these simulations suggest that reduced convective flow inside the tangent cylinder may affect the magnetic field at high latitude whereas lower latitude observations are expressions of columnar helical flow outside the tangent cylinder this paper presents new paleointensity and paleodirectional data from 100 volcanic sites in the erebus volcanic province evp antarctica and 21 new age determinations by the 40ar 39ar incremental heating method the new evp data are combined with previously published paleomagnetic and geochronological results providing 133 sites 91 having radioisotopic dates modified thellier thellier paleointensity estimates are reported for 47 sites 37 have dates ages for the combined data set span 0 03 to 13 42 ma the 125 high quality evp directional data selected from the merged data set have a non fisherian distribution and a mean direction with an inclination anomaly of 3 but 95 confidence limits include the prediction from a geocentric axial dipole virtual geomagnetic pole vgp dispersions for brunhes matuyama and the combined 0 5 ma data set are consistently high compared with values from middle to low latitude regions regardless of the criterion used to determine transitional fields with vgp latitude cut off at 45 the dispersion 23 9 2 1 for the combined 0 5 ma evp data set is consistent with earlier high latitude data and paleosecular variation psv in model g but not with some more recent statistical psv models mean evp paleointensity of 31 5 2 4 t derived from 41 high quality sites is about half the current value at mcmurdo 63 t the result is essentially independent of data selection criteria high vgp dispersion and low intensity values support the global observation of anticorrelation between directional variability and field strength simulations of time varying dipole strength show that uneven temporal sampling may bias the mean evp intensity estimate but the possibility of persistently anomalous field behavior at high latitude cannot be excluded

integrated interpretation of physical properties of rocks of the borehole yaxcopoil 1 chicxulub impact structure 1 the borehole yaxcopoil 1 drilled within the chicxulub meteoritic impact structure mexico was completely cored from 404 to 1511 m through postimpact tertiary limestones underlain by impactites the impactites comprise impact melt rich suevitic breccia followed by megablocks of cretaceous limestones calcarenites dolomites and anhydrites measurements of porosity density and thermal parameters on 450 samples equidistant sampling complete depth range and of ultrasonic velocities and electric resistivity on 80 representative samples are used to investigate the physical properties of carbonate rocks and to study the influence of the impact experiments under elevated pressure calculations using frequency dependent biot gassmann theory and cross checking with borehole logs where available show that ultrasonic laboratory and sonic in situ data correspond sonic and electric quasi continuous logs are obtained from empirical correlations with thermal conductivity density and porosity and consideration of mineralogical composition and microstructure these data give constraints on interpretation and geophysical modeling of e g seismic and gravity data in the tertiary postimpact limestone section the rock fabric porosity influences the physical properties the upper boundary of the impactites is distinctly determined by the high inhomogeneity factor and anisotropy coefficient of thermal conductivity and by the temperature gradient from high resolution borehole temperature measurements all physical properties indicate that the upper part of the suevitic breccia can be distinguished from the lower suevite unit in the cretaceous megablocks a high variability of all properties particularly thermal conductivity density of solid material and temperature gradient due to the high variability in the mineral composition calcite dolomite anhydrite is observed

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

integrated deep drilling coring downhole logging and data management in the chicxulub scientific drilling project csdp mexico impact structures in the solar system are mainly recognized and explored through remote sensing and on earth through geophysical deep sounding to date a continuous scientific sampling of large impact craters from cover rocks to target material has only seldom been performed the first project to deep drill and core into one of the largest and well preserved terrestrial impact structures was executed in the winter of 2001 2002 in the 65 myr old chicxulub crater in mexico using integrated coring sampling and in situ measurements the combined use of different techniques allows a three dimensional insight and a better understanding of impact processes here we report the integration of conventional rotary drilling techniques with wireline mining coring technology that was applied to drill the 1510 m deep yaxcopoil 1 yax 1 well about 40 km southwest of mrida yucatn mexico during the course of the project we recovered approximately 900 m of intact core samples including the transitions of reworked ejecta to post impact sediments and that one from large blocks of tilted target material to impact generated rocks i e impact melt breccias and suevites coring was complemented by wireline geophysical measurements to obtain a continuous set of in situ petrophysical data of the borehole walls the data acquired is comprised of contents of a natural radioactive element velocities of compressional sonic waves and electrical resistivity values all the digital data sets including technical drilling parameters initial scientific sample descriptions and 360 core pictures were distributed during the course of the operations via internet and were stored in the icdp drilling information system http www icdp online org serving the global community of cooperating scientists as a basic information service

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

physical interpretation of hysteresis loops micromagnetic modeling of fine particle magnetite 1 hysteresis measurements have become an important part of characterizing magnetic behavior of rocks in paleomagnetic studies theoretical interpretation is often difficult owing to the complexity of mineral magnetism and published data sets demonstrate remanence and coercivity behavior that is currently unexplained in the last decade numerical micromagnetic modeling has been used to simulate magnetic particles such simulations reveal the existence of nonuniform remanent states between single and multidomain known as the flower and vortex configurations these suggest plausible explanations for many hysteresis measurements yet fall short of explaining high saturation remanence high coercivity data such as those commonly observed in fine grained submarine basalts in this paper we review the theoretical and experimental progress to date in understanding hysteresis of geological materials we extend numerical simulations to a greater variety of shapes and sizes including random assemblages of particles and shapes more complex than simple rods and cubes our simulations provide plausible explanations for a wide range of hysteresis behavior

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

physical properties of the yaxcopoil 1 deep drill core chicxulub impact structure mexico abstract the chicxulub structure in mexico one of the largest impact structures on earth was formed 65 ma by a hypervelocity impact that led to the large mass extinction at the k pg boundary the chicxulub impact structure is well preserved but is buried beneath a sequence of carbonate sediments and thus requires drilling to obtain subsurface information the chicxulub scientific drilling program was carried out at hacienda yaxcopoil in the framework of the international continental scientific drilling program in 2001 2002 the structure was cored from 404 m down to 1511 m through three intervals 794 m of postimpact tertiary sediments a 100 m thick impactite sequence and 616 m of preimpact cretaceous rocks thought to represent a suite of megablocks physical property investigations show that the various lithologies including the impactite units and the k pg boundary layer can be characterized by their physical properties which depend on either changes in fabric or on mineralogical variations the magnetic properties show mostly dia or paramagnetic behavior with the exception of the impactite units that indicate the presence of ferromagnetic probably hydrothermally deposited magnetite and pyrrhotite the magnetic fraction contributes mainly to enhanced magnetization in the impactite lithologies and in this way to the observed magnetic anomalies the shape and orientation of the magnetic grains are varied and reflect inhomogeneous fabric development and the influence of impact related redeposition and hydrothermal activity the chicxulub impact occurred at the time of the reverse polarity geomagnetic chron 29r and this finding is consistent with the age of the k pg boundary

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