Publications

2019
Shemer M, Crouvi O, Shaar R, Ebert Y, Matmon A, Horwitz LK, Eisenmann V, Enzel Y, Barzilai O, Team ASTER, et al. Geochronology, paleogeography, and archaeology of the Acheulian locality of ‘Evron Landfill in the western Galilee, Israel. Quaternary Research. 2019;91 (2) :729–750.
Behar N, Shaar R, Tauxe L, Asefaw H, Ebert Y, Heimann A, Koppers AAP, Ron H. Paleomagnetism and paleosecular variations from the Plio-Pleistocene Golan Heights volcanic plateau, Israel. Geochemistry, Geophysics, Geosystems. 2019.
Zeigen C, Shaar R, Ebert Y, Hovers E. Archaeomagnetism of burnt cherts and hearths from Middle Palaeolithic Amud Cave, Israel: Tools for reconstructing site formations processes and occupation history. Journal of Archaeological Science. 2019;107 :71–86.
2018
Stillinger MD, Feinberg J, Ben-Yosef E, Shaar, R., Hardin JW, Blakely JA. A Rejoinder on the Value of Archaeomagnetic Dating: Integrative Methodology Is the Key to Addressing Levantine Iron Age Chronology. Near Eastern Archaeology [Internet]. 2018;81 (2) :141–144. Publisher's Version
Shaar R, Hassul E, Raphael K, Ebert Y, Segal, Y, Eden I, Vaknin Y, S. M, Nowaczyk N, Chauvin A, et al. The First Catalog of Archaeomagnetic Directions From Israel With 4,000 Years of Geomagnetic Secular Variations. Frontiers in Earth Sciences [Internet]. 2018;164. Publisher's Version
Ebert Y, Shaar R, Emmanuel S, Nowaczyk N, Stein M. Overwriting of sedimentary magnetism by bacterially mediated mineral alteration. geology [Internet]. 2018;46 (4) :291-294. Publisher's Version
Shahack-Gross R, Shaar R, Hassul E, Ebert Y, Forget M, Nowaczyk N, Marco S, Finkelstein I, Agnon A. Fire and collapse: Untangling the formation of destruction layers using archeomagnetism. Geoarchaeology [Internet]. 2018;33 :513-528. Publisher's Version
2017
Farchi E, Ebert Y, Farfurnik D, Haim G, Shaar R, Bar-Gill N. Quantitative vectorial magnetic imaging of multi domain rock forming minerals using nitrogen-vacancy centers in diamond. Spin [Internet]. 2017;7 (3). Publisher's Version
Shaar R, Tauxe L, Goguitchaichvili A, Devidze M, Licheli V. Further evidence of the Levantine Iron Age geomagnetic anomaly from Georgian pottery. Geophysical Research Letters [Internet]. 2017;44. Publisher's Version
Ben-Yosef E, Milman M, Shaar R, Tauxe L, Lipschits O. Six centuries of geomagnetic intensity variations recorded by royal Judean stamped jar handles. Proceedings of the National Academy of Sciences [Internet]. 2017. Publisher's Version
Shaar R, Tauxe L, Ron H, Agnon A, Ebert Y, Finkelstein I. The Tel Megiddo paleointensity project: toward a high resolution reference curve for archaeomagnetic dating. In: Megiddo VI. Tel Aviv: Tel-Aviv University ; 2017. shaar_etal_megiddo_vi.pdf
Shaar R, Ben-Yosef E. paleomagnetic geochronology of Quaternary sequences in the Levant. In: Quaternary Environments, Climate Change, and Humans in the Levant. ; 2017. paleomagnetic_quaternary_levant_4_0_withfigures.pdf
2016
Tauxe L, Shaar R, Jonestrask L, Swanson‐Hysell NL, Minnett R, Koppers AAP, Constable CG, Jarboe N, Gaastra K. PmagPy: Software package for paleomagnetic data analysis and a bridge to the Magnetics Information Consortium (MagIC) Database." Geochemistry, Geophysics, Geosystems (2016). eochemistry, Geophysics, Geosystems [Internet]. 2016. Publisher's Version
Shaar R, Tauxe L, Ron H, Ebert Y, Zuckerman S, Finkelstein I, Agnon A. Large geomagnetic field anomalies revealed in Bronze to Iron Age archeomagnetic data from Tel Megiddo and Tel Hazor, Israel. Earth and Planetray Science Letters [Internet]. 2016;442 :173-85. Publisher's Version
2015
Shaar R, Tauxe L. Instability of thermoremanence and the problem of estimating the ancient geomagnetic field strength from non-single-domain recorders. Proceedings of the National Academy of Sciences of the United States of America [Internet]. 2015. Publisher's VersionAbstract

Data on the past intensity of Earth’s magnetic field (paleointensity) are essential for understanding Earth’s deep interior, climatic modeling, and geochronology applications, among other items. Here we demonstrate the possibility that much of available paleointensity data could be biased by instability of thermoremanent magnetization (TRM) associated with non-single-domain (SD) particles. Paleointensity data are derived from experiments in which an ancient TRM, acquired in an unknown field, is replaced by a laboratory-controlled TRM. This procedure is built on the assumption that the process of ancient TRM acquisition is entirely reproducible in the laboratory. Here we show experimental results violating this assumption in a manner not expected from standard theory. We show that the demagnetization−remagnetization relationship of non-SD specimens that were kept in a controlled field for only 2 y show a small but systematic bias relative to sister specimens that were given a fresh TRM. This effect, likely caused by irreversible changes in micromagnetic structures, leads to a bias in paleointensity estimates.

Shaar R, Tauxe L, Ben-Yosef E, Kassianidou V, Lorentzen B, Feinberg JM, Levy TE. Decadal-scale variations in geomagnetic field intensity from ancient Cypriot slag mounds. Geochemistry Geophysics Geosystems [Internet]. 2015;16 :195-214. Publisher's VersionAbstract
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.
2014
Ben-Yosef E, Shaar R, Tauxe L, Levy TE, Kassianidou V, Lorentzen B. Archaeomagnetic investigations of copper slag deposits in Cyprus. In: Kassianidou V, Papasavvas G Studies in Mediterranean Archaeology, Introduction to the Archaeometallurgy of Cyprus. Uppsala: Astrom Editions ; 2014.
Paterson GA, Tauxe L, Biggin AJ, Shaar R, Jonestrask LC. On improving the selection of Thellier-type paleointensity data. Geochemistry Geophysics Geosystems [Internet]. 2014;15 :1180-1192. Publisher's VersionAbstract
The selection of paleointensity data is a challenging, but essential step for establishing data reliability. There is, however, no consensus as to how best to quantify paleointensity data and which data selection processes are most effective. To address these issues, we begin to lay the foundations for a more unified and theoretically justified approach to the selection of paleointensity data. We present a new compilation of standard definitions for paleointensity statistics to help remove ambiguities in their calculation. We also compile the largest-to-date data set of raw paleointensity data from historical locations and laboratory control experiments with which to test the effectiveness of commonly used sets of selection criteria. Although most currently used criteria are capable of increasing the proportion of accurate results accepted, criteria that are better at excluding inaccurate results tend to perform poorly at including accurate results and vice versa. In the extreme case, one widely used set of criteria, which is used by default in the ThellierTool software (v4.22), excludes so many accurate results that it is often statistically indistinguishable from randomly selecting data. We demonstrate that, when modified according to recent single domain paleointensity predictions, criteria sets that are no better than a random selector can produce statistically significant increases in the acceptance of accurate results and represent effective selection criteria. The use of such theoretically derived modifications places the selection of paleointensity data on a more justifiable theoretical foundation and we encourage the use of the modified criteria over their original forms.
2013
Shaar R, Feinberg JM. Rock magnetic properties of dendrites: insights from MFM imaging and implications for paleomagnetic studies. Geochemistry Geophysics Geosystems [Internet]. 2013;14 :407-421. Publisher's VersionAbstract
Dendrites are crystals that grow in branches that diverge along crystallographically defined directions. Despite the importance of dendrites in paleomagnetic research, little is known about how dendrites act as magnetic recorders, because they exhibit complicated magnetic domain structures. In this study, we experimentally examine how textures and sizes of dendrites affect their magnetic domain structure and magnetic properties. We study two basaltic glass samples and three synthetic slag samples, which collectively define a wide range of dendritic morphologies. We use electron microscopy to characterize the morphology of the dendrites and magnetic force microscopy (MFM) to observe their magnetic domain structure. We characterize the dendrites' bulk properties by firs-order reversal curve distributions, Thellier-style paleointensity experiments, anisotropy of remanence, and anisotropy of susceptibility. The samples with the thinnest dendrites have high coercivity, stable single-domain (SD) - pseudo single-domain magnetization, and yield ideal Arai plots. By contrast, the sample with the thickest dendrites has the lowest coercivity and shows the most extreme multidomain (MD) behavior. All samples except one, exhibit significant remanence and susceptibility anisotropy. MFM observations show that dendrites built from branches of interconnected octahedra, typical for basaltic glass, have a stable, high coercivity, SD-like magnetization despite the fact that their overall dimensions exceed the SD-MD threshold. Their stability is likely due to interactions between the octahedra and their narrow rod-like interconnections. Dendrites that crystallize in faster cooling environments, such as in archaeological slag, display finer branch thicknesses (< 1 mu m) and few, if any, octahedra. The tips of these dendrites consist of closely intergrown, rounded, acicular branches that behave as pseudo single-domain grains due to interactions between the branches. The largest, thickest dendrites show MD behavior and MFM images show their magnetic domain walls to be arranged in crystallographically controlled, geometrically repetitive patterns within elongated branches, which give rise to their anisotropy characteristics.
Shaar R, Tauxe L. Thellier GUI: An integrated tool for analyzing paleointensity data from Thellier-type experiments. Geochemistry Geophysics Geosystems [Internet]. 2013;14 :677-692. Publisher's VersionAbstract
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.

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