Publications

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2017
Shaar, R, Tauxe L, Goguitchaichvili A, Devidze M, Licheli V.  2017.  Further evidence of the Levantine Iron Age geomagnetic anomaly from Georgian pottery. Geophysical Research Letters. 44:2229-2236.   10.1002/2016gl071494   AbstractWebsite

Recent archaeomagnetic data from ancient Israel revealed the existence of a so-called "Levantine Iron Age geomagnetic anomaly" (LIAA) which spanned the first 350years of the first millennium before the Common Era (B.C.E.) and was characterized by a high averaged geomagnetic field (virtual axial dipole moments, VADM>140ZAm(2), nearly twice of today's field), short decadal-scale geomagnetic spikes (VADM of 160-185ZAm(2)), fast field variations, and substantial deviation from dipole field direction. The geographic constraints of the LIAA have remained elusive due to limited high-quality paleointensity data in surrounding locations. Here we report archaeointensity data from Georgia showing high field values (VADM>150ZAm(2)) in the tenth or ninth century B.C.E., low field values (VADM<60 ZAm(2)) in the twelfth century B.C.E., and fast field variation in the fifth and fourth centuries B.C.E. High field values in the time frame of LIAA have been observed so far only in three localities near the Levant: Eastern Anatolia, Turkmenistan, and now Georgia, all located east of longitude 30 degrees E. West of this, in the Balkans, field values in the same time are moderate to low. These constraints put geographic limits on the extent of the LIAA and support the hypothesis of an unusually intense regional geomagnetic anomaly during the beginning of the first half of the first millennium B.C.E., comparable in area and magnitude (but of opposite sign) to the presently active South Atlantic anomaly.

2015
Cromwell, G, Tauxe L, Halldorsson SA.  2015.  New paleointensity results from rapidly cooled Icelandic lavas: Implications for Arctic geomagnetic field strength. Journal of Geophysical Research-Solid Earth. 120:2913-2934.   10.1002/2014jb011828   AbstractWebsite

The Earth's magnetic field is assumed to be a geocentric axial dipole (GAD) when averaged over sufficient time (10(5)-10(6)years). Recent investigations of global paleosecular variation and time-averaged field behavior on million year timescales generally support a predominantly dipole field in the Northern Hemisphere, but unique field structures at high southern latitudes suggest the presence of a substantial (g) over bar (0)(2) quadrupolar component. Average paleointensity results from Antarctica are approximately half the value predicted by a GAD field; this behavior has not been sufficiently investigated because there is a paucity of absolute paleointensity data from the high latitudes of the Arctic and Antarctic, so no adequate comparisons have been made between the two regions. We collected glassy volcanic material from 129 subaerial and subglacial volcanic units in Iceland in order to provide a suitable intensity data set at high northern latitudes. Forty-four sites met our very strict specimen and site level selection criteria. Four Holocene sites have a median intensity value of 55.8 +/- 15.6 mu T (virtual axial dipole moment=78.1 +/- 22.0ZAm(2)), consistent with the present-day field. Thirty-seven sites are between 11ka and 3.35Ma with a median intensity of 33.1 +/- 8.3 mu T (47.0 +/- 11.6ZAm(2)). This median intensity is indistinguishable from some long-term global field strength estimates. Reevaluation of existing high-latitude data suggests a general agreement with our Iceland results, but there are still too few Antarctic sites to adequately compare Arctic and Antarctic field behaviors.

2013
Shaar, R, Tauxe L.  2013.  Thellier GUI: An integrated tool for analyzing paleointensity data from Thellier-type experiments. Geochemistry Geophysics Geosystems. 14:677-692.   10.1002/ggge.20062   AbstractWebsite

Thellier-type experiments are a method used to estimate the intensity of the ancient geomagnetic field from samples carrying thermoremanent magnetization. The analysis of Thellier-type experimental data is conventionally done by manually interpreting data from each specimen individually. The main limitations of this approach are: (1) manual interpretation is highly subjective and can be biased by misleading concepts, (2) the procedure is time consuming, and (3) unless the measurement data are published, the final results cannot be reproduced by readers. These issues compound when trying to combine together paleointensity data from a collection of studies. Here, we address these problems by introducing the Thellier GUI: a comprehensive tool for interpreting Thellier-type experimental data. The tool presents a graphical user interface, which allows manual interpretation of the data, but also includes two new interpretation tools: (1) Thellier Auto Interpreter: an automatic interpretation procedure based on a given set of experimental requirements, and 2) Consistency Test: a self-test for the consistency of the results assuming groups of samples that should have the same paleointensity values. We apply the new tools to data from two case studies. These demonstrate that interpretation of non-ideal Arai plots is nonunique and different selection criteria can lead to significantly different conclusions. Hence, we recommend adopting the automatic interpretation approach, as it allows a more objective interpretation, which can be easily repeated or revised by others. When the analysis is combined with a Consistency Test, the credibility of the interpretations is enhanced. We also make the case that published paleointensity studies should include the measurement data (as supplementary files or as a contributions to the MagIC database) so that results based on a particular data set can be reproduced and assessed by others.

2011
Ziegler, LB, Constable CG, Johnson CL, Tauxe L.  2011.  PADM2M: a penalized maximum likelihood model of the 0-2 Ma palaeomagnetic axial dipole moment. Geophysical Journal International. 184:1069-1089.   10.1111/j.1365-246X.2010.04905.x   AbstractWebsite

P>We present a new time-varying model for palaeomagnetic axial dipole moment (PADM) for the past 2 Myr and compare it with earlier virtual axial dipole moment (VADM) reconstructions which have been based on stacking and averaging scaled relative palaeointensity records. The PADM is derived from both absolute and relative palaeointensity data and constructed using a new penalized maximum likelihood (PML) approach to recover a cubic B-spline representation of axial-dipole field variations on million year timescales. The PML method is explicitly intended to reduce bias in estimating the true axial dipole moment that arises in average VADM reconstructions. We apply the PML method to a set of 96 032 published data (1800 palaeointensities from igneous rocks, 3300 archaeointensities and 86 relative palaeointensity time-series of variable lengths and resolutions). Two models are discussed: PADM2Mp is a trial model based on a subset of the nine longest available sedimentary records; PADM2M uses a comprehensive data set (76 records, 81 446 data; 10 records were eliminated) and is our preferred model. PADM2M has a lower mean than existing VADM reconstructions but shows similarities in long-period variability. Some differences in timing, amplitude and resolution of certain features can be attributed to variations in age assignments. Others result from our more comprehensive data set and a reduction in bias attributable to PML modelling. PADM2M has an average axial dipole moment over 0-2 Ma of 5.3 x 1022 Am2 with a standard deviation of 1.5 x 1022 Am2. The Brunhes chron average (6.2 x 1022 Am2) is higher than for earlier epochs of Matuyama (4.8 x 1022 Am2), as seen in some previous studies. The power spectrum for our model agrees with previous estimates of the global palaeomagnetic power spectrum for frequencies up to about 102 Myr-1. We see no distinctive evidence in the power spectrum for orbital forcing of geodynamo behaviour.

2010
Shaar, R, Ron H, Tauxe L, Kessel R, Agnon A, Ben-Yosef E, Feinberg JM.  2010.  Testing the accuracy of absolute intensity estimates of the ancient geomagnetic field using copper slag material. Earth and Planetary Science Letters. 290:201-213.   10.1016/j.epsl.2009.12.022   AbstractWebsite

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 1721 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 submicronelongated 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 nonlinear 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 similar to 5% after applying the required corrections. (C) 2009 Elsevier B.V. All rights reserved.

2009
Sbarbori, E, Tauxe L, Goguitchaichvili A, Urrutia-Fucugauchi J, Bohrson WA.  2009.  Paleomagnetic behavior of volcanic rocks from Isla Socorro, Mexico. Earth Planets and Space. 61:191-204. AbstractWebsite

The direction and magnitude of the geomagnetic field vary both spatially and temporally and undergo significant departures from that of a geocentric axial dipole. In order to properly characterize persistent behaviors, time-averaged field models must be based oil the highest quality data. Here we present full-vector paleomagnetic data for volcanic units exposed in the southeast quadrant of the island of Socorro, Mexico. We carried out a joint expedition between the Scripps Institution of Oceanography and the Universidad Nacional Autonoma Mexico to Isla Socorro in January of 2005 during which we collected oriented paleomagnetic samples from 21 sites, representing as many as 10 different volcanic units (the oldest of which is similar to 540 ka). We subjected over 100 specimens to the most up-to-date paleointensity methods, and included the standard reliability checks. In all earlier study, Bohrson et al. (1996) proposed a series of widespread eruptive events, based on similarities of argon/argon dates. Paleointensity from specimens that conform to the strictest acceptance criteria are available from both the (unoriented) original sample collection and our fully oriented (but as yet undated) new collection. Correlation between the two collections is however problematic. The time-averaged direction from Socorro is consistent with that expected from a geocentric axial dipole, and the time-averaged intensity is 30.0 +/- 7.1 mu T, equivalent to a virtual axial dipole moment (VADM) of 67.6 +/- 16.0 ZAm(2).

2008
Ben-Yosef, E, Tauxe L, Ron H, Agnon A, Avner U, Najjar M, Levy TE.  2008.  A new approach for geomagnetic archaeointensity research: insights on ancient metallurgy in the Southern Levant. Journal of Archaeological Science. 35:2863-2879.   10.1016/j.jas.2008.05.016   AbstractWebsite

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. (C) 2008 Elsevier Ltd. All rights reserved.

Ben-Yosef, E, Ron H, Tauxe L, Agnon A, Genevey A, Levy TE, Avner U, Najjar M.  2008.  Application of copper slag in geomagnetic archaeointensity research. Journal of Geophysical Research-Solid Earth. 113   10.1029/2007jb005235   AbstractWebsite

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.

2006
Tauxe, L.  2006.  Long-term trends in paleointensity: The contribution of DSDP/ODP submarine basaltic glass collections. Physics of the Earth and Planetary Interiors. 156:223-241.   10.1016/j.pepi.2005.03.022   AbstractWebsite

The Deep Sea Drilling Project and the Ocean Drilling Program have been collecting fresh appearing submarine basaltic glass from the world's oceans for over three decades. This glass has proved nearly ideal for estimating paleointensity variations of the Earth's magnetic field. We compile here data for 726 paleointensity experiments from six publications on paleointensity using DSDP/ODP glass. We also include new data for an additional 225 specimens. These were obtained through the so-called "IZZI" paleointensity experiment of [Tauxe, L., Staudigel, H., 2004. Strength of the geomagnetic field in the cretaceous normal superchron: new data from submarine basaltic glass of the troodos ophiolite. Geochem. Geophys. Geosyst. 5 (2), Q02H06, doi: 10.1029/2003GCO00635] whereby infield-zerofield steps are alternated with the zerofield-infield steps to enhance quality assessment of the resulting data. The entire collection of data from 951 experiments was prepared for uploading to the MagIC data base (http://earthref.org), including original measurements, interpretations, and useful metadata. Excellent results were obtained throughout the depth (> 1400 mbsf) and age (0-160 Ma) range sampled. DSDP/ODP glass data are compared with published paleointensity data meeting minimal acceptance criteria from the time interval 1-160 Ma. Paleolatitudes were estimated for all cooling units in a self-consistent manner for use in calculating virtual axial dipole moments. We conclude: (1) There is about a 20% difference in mean values between the SBG and the lava flow data (48 +/- 36 and 57 +/- 29 ZAm(2) respectively). The difference is caused by the fact that there are more higher values in the lava flow data than in the SBG data set rather than a difference in the minimum values. Lava flows cooling over a periods of days to months can account for the discrepancy. (2) The positive relationship between polarity interval length and average paleofield intensity first hypothesized by [Cox, A.V, 1968. Lengths of geomagnetic polarity intervals. J. Geophys. Res. 73, 3247-3260] is supported by data compiled here. The Brunhes data (for which we have only a minimum estimate for polarity interval length) are consistent with a long polarity interval, suggesting that instead of racing toward reversal [Hulot, G., Eymin, C., Langlais, B., Mandea, M., Olsen, N., 2002. Small-scale structure of the geodynamo inferred from oersted and magsat satellite data. Nature 416, 620-623], we could instead be in the midst of a long stable polarity interval. (3) Because the average value appears to be a function of polarity interval length, it is probably not useful to calculate a mean value. Nonetheless, it appears that most of the time (apart from the Brunhes and the longest polarity intervals), the average dipole moment is substantially less than the present day value as suggested by [Juarez, T., Tauxe, L., Gee, J.S., Pick, T., 1998. The intensity of the earth's magnetic field over the past 160 million years. Nature 394, 878-881]. (c) 2006 Published by Elsevier B.V.

Yu, Y, Tauxe L.  2006.  Effect of multi-cycle heat treatment and pre-history dependence on partial thermoremanence (pTRM) and pTRM tails. Physics of the Earth and Planetary Interiors. 157:196-207.   10.1016/j.pepi.2006.04.006   AbstractWebsite

We test two fundamental assumptions embedded in Thellier experiments, the initial state dependence and the effect of multi-cycle heat treatment. We observe that the magnitude of partial thermoremanent magnetizations (pTRMs) imparted on an initial state of thermal demagnetization is larger than those of pTRMs in the presence of a TRM when the field used to impart pTRM is equal in magnitude and parallel to that used to produce TRM. A multi-cycle Thellier analysis on coarse-grained magnetites progressively produces more intense pTRMs and progressively erases more of the pTRM tails. Both pre-history and multi-cycle dependence will likely enhance the non-linear features of the Arai plot for coarse-grained magnetites. (c) 2006 Elsevier B.V. All rights reserved.

2004
Tauxe, L, Staudigel H.  2004.  Strength of the geomagnetic field in the Cretaceous Normal Superchron: New data from submarine basaltic glass of the Troodos Ophiolite. Geochemistry Geophysics Geosystems. 5   10.1029/2003gc000635   AbstractWebsite

[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.

2000
Selkin, PA, Tauxe L.  2000.  Long-term variations in palaeointensity. Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences. 358:1065-1088. AbstractWebsite

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 (Thellier method with pTRM checks) palaeointensity estimates available. Although the new data dramatically improve both spatial and temporal coverage, there is still a strong bias toward the most recent past. The last 0.3 Ma claim over half of the data in our combined database. We therefore divide the data into two groups, the densely sampled last 0.3 Myr and the more sparsely sampled period of time comprising roughly half of the data from 0.3 to 300 Ma. Separating them in this way, it is clear that the dipole moment of the Earth over the past 0.3 Myr (ca. 8 x 10(22) A m(2)) is dramatically higher than the average dipole moment over the preceding 300 Myr (ca. 5 x 10(22) A m(2)). Inclusion of poor-quality results leads to an overestimate of the average dipole moment. Interestingly, no other significant changes in the distribution of dipole moments are evident over the 300 million year span of the data.

Juarez, MT, Tauxe L.  2000.  The intensity of the time-averaged geomagnetic field: the last 5 Myr. Earth and Planetary Science Letters. 175:169-180.   10.1016/s0012-821x(99)00306-4   AbstractWebsite

The existing database for paleointensity estimates of the ancient geomagnetic field contains more than 1500 data points collected through decades of effort. Despite the huge amount of work put into obtaining these data, there remains a strong bias in the age and global distribution of the data reward very young results from a few locations. Also, few of the data meet strict criteria for reliability and most are of unknown quality. In order to improve the age and spatial distribution of the paleointensity database, we have carried out paleointensity experiments on submarine basaltic glasses from a number of DSDP sites. Of particular interest are the sites that provide paleointensity data spanning the time period 0.3-5 Ma, a time of relatively few high quality published data points. Our new data are concordant with contemporaneous data from the published literature that meet minimum acceptance criteria, and the combined data set yields an average dipole moment of 5.49 +/- 2.36 x 10(22) Am-2. This average value is comparable to the average paleofield for the period 5-160 Ma (4.2 +/- 2.3 x 10(22) Am-2) [T. Juarez, L. Tauxe, J.S. Gee and T. Pick (1998) Nature 394, 878-881] and is substantially less than the value of approximately 8 x 10(22) Am-2 often quoted for the last 5 Myr (e.g. [McFadden and McElhinny (1982) J. Geomagn. Geoelectr. 34, 163-189; A.T. Goguitchaichvili, M. Prevot and P. Camps (1999) Earth Planet. Sci. Lett. 167, 15-34]). (C) 2000 Elsevier Science B.V. All rights reserved.

1993
Pick, T, Tauxe L.  1993.  Holocene Paleointensities - Thellier Experiments on Submarine Basaltic Glass from the East Pacific Rise. Journal of Geophysical Research-Solid Earth. 98:17949-17964.   10.1029/93jb01160   AbstractWebsite

A complete description of the geomagnetic field requires both paleodirectional and paleointensity data. Although the paleointensity data base has grown steadily over the last three decades, it remains limited in time and space (the majority of data are of Holocene age and come from Europe). Furthermore, it has been difficult to assess the reliability of the paleointensity determinations. Here we present, paleointensity determinations on precisely dated Holocene (0 to 3500 years old) submarine basaltic glass from the East Pacific Rise (15-degrees-S to 22-degrees-S). Although hysteresis measurements and low-temperature isothermal remanent magnetization (IRM) acquisition experiments document a significant contribution of superparamagnetic grains, high blocking temperatures (above 400-degrees-C) and Curie temperatures between 490-degrees-C and 550-degrees-C indicate a single-domain low-Ti magnetite as the carrier of the remanent magnetization. This notion is further supported by the fact that saturation of remanence is achieved in moderate fields of about 200-300 mT. Submarine basaltic glass proves to be nearly ideal for paleointensity determinations in that it produces a high success rate for Thellier experiments. Twenty-six out of 30 samples resulted in acceptable paleointensity determinations. Multiple experiments on splits from the same sample show good reproducibility. The paleointensities for zero age glasses correspond precisely with the present field intensity at the site of recovery. The results of the remaining samples range from 16.7 to 53.9 muT with corresponding virtual axial dipole moments (VADM) of 3.61 X 10(22) to 11.9 X 10(22) A m2. The intensities vary rapidly with time excluding a westward drifting nondipole component as the source for these fluctuations. Basaltic glass is frequently recovered in both dredged and drilled material froin the ocean floor. The availability of submarine basaltic glass throughout the world oceans therefore holds great potential for a better distribution of paleointensity data through time and space.

1992
Tric, E, Valet JP, Tucholka P, Paterne M, Labeyrie L, Guichard F, Tauxe L, Fontugne M.  1992.  Paleointensity of the Geomagnetic-Field During the Last 80,000 Years. Journal of Geophysical Research-Solid Earth. 97:9337-9351.   10.1029/91jb01620   AbstractWebsite

High-resolution records of the relative paleointensity of the geomagnetic field have been obtained from five marine cores. Three duplicate records were used to estimate the regional coherency of the data within a single area (Tyrrhrenian Sea) while the two others document the field variations in the eastern Mediterranean and the southern Indian Ocean. Careful investigations of distinct rock magnetic parameters have established the downcore uniformity of the sediments in terms of magnetic mineralogy and grain sizes. The time-depth control was provided by oxygen isotopes, and small-scale variations in the deposition rates were constrained by means of tephrachronology. The synthetic curve calculated from the Mediterranean records provides a continuous record of the intensity variations during the last 80,000 years (80 kyr). which correlates well with the sparse volcanic data available for the period 0-40 kyr. The fact that identical behavior is seen in both data sets and that they also compare quite well with results from a core collected in the Pacific Ocean establishes the truly dipolar character of these variations. The dipole field moment is characterized by large-scale changes as shown by the existence of pronounced drops (at 39 and 60 kyr) alternating with periods of higher intensity. The record suggests a periodic nature for these intensity variations; however, the period studied is not sufficiently long to state this conclusively. These results demonstrate the potential of sediments for such studies and constitute a first step towards obtaining a global paleointensity record over a long period of time.