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Ben-Yosef, E, Millman M, Shaar R, Tauxe L, Lipschits O.  2017.  Six centuries of geomagnetic intensity variations recorded by royal Judean stamped jar handles. Proceedings of the National Academy of Sciences.   10.1073/pnas.1615797114   Abstract

Earth’s magnetic field, one of the most enigmatic physical phenomena of the planet, is constantly changing on various time scales, from decades to millennia and longer. The reconstruction of geomagnetic field behavior in periods predating direct observations with modern instrumentation is based on geological and archaeological materials and has the twin challenges of (i) the accuracy of ancient paleomagnetic estimates and (ii) the dating of the archaeological material. Here we address the latter by using a set of storage jar handles (fired clay) stamped by royal seals as part of the ancient administrative system in Judah (Jerusalem and its vicinity). The typology of the stamp impressions, which corresponds to changes in the political entities ruling this area, provides excellent age constraints for the firing event of these artifacts. Together with rigorous paleomagnetic experimental procedures, this study yielded an unparalleled record of the geomagnetic field intensity during the eighth to second centuries BCE. The new record constitutes a substantial advance in our knowledge of past geomagnetic field variations in the southern Levant. Although it demonstrates a relatively stable and gradually declining field during the sixth to second centuries BCE, the new record provides further support for a short interval of extreme high values during the late eighth century BCE. The rate of change during this “geomagnetic spike” [defined as virtual axial dipole moment > 160 ZAm2 (1021 Am2)] is further constrained by the new data, which indicate an extremely rapid weakening of the field (losing ∼27% of its strength over ca. 30 y).

Cai, SH, Tauxe L, Deng CL, Qin HF, Pan YX, Jin GY, Chen XX, Chen W, Xie F, Zhu RX.  2016.  New archaeomagnetic direction results from China and their constraints on palaeosecular variation of the geomagnetic field in Eastern Asia. Geophysical Journal International. 207:1332-1342.   10.1093/gji/ggw351   AbstractWebsite

We carried out an archaeomagnetic directional study on 38 oriented samples (bricks and baked clays) collected from four archaeological locations at three provinces in China. The ages of our samples, spanning from similar to 3000 BCE to similar to 1300 CE, were constrained using a combination of archaeological context, radiocarbon dating and stratigraphic information. Rock magnetic results demonstrate that the main magnetic minerals of the studied samples are magnetite and/or hematite in single domain and superparamagnetic states. A total of 20 new reliable archaeodirectional data from 12 independent sites are obtained after thermal demagnetization experiments. These are the first set of archaeodirectional data in China produced since the 1990s. The published data are largely from the past 2 kyr and data from older time periods are rare. Our new data, especially those from period older than 3 ka, fill many gaps of the presently published dataset and will provide strong constraints on palaeosecular variation of the geomagnetic field in Eastern Asia and on the improvement of global models. Quite a few inflection points in the direction of the geomagnetic field are recorded in Eastern Asia over the past 10 kyr and some of them synchronize with the maximums or minimums of the palaeointensity. The palaeosecular variation rates are very low (based on present data distribution) before 2000 BCE and then start to increase and fluctuate afterward, which is generally consistent with the pattern of palaeointensity variations in this area.

Dallanave, E, Bachtadse V, Crouch EM, Tauxe L, Shepherd CL, Morgans HEG, Hollis CJ, Hines BR, Sugisaki S.  2016.  Constraining early to middle Eocene climate evolution of the southwest Pacific and Southern Ocean. Earth and Planetary Science Letters. 433:380-392.   10.1016/j.epsl.2015.11.010   AbstractWebsite

Studies of early Paleogene climate suffer from the scarcity of well-dated sedimentary records from the southern Pacific Ocean, the largest ocean basin during this time. We present a new magnetostratigraphic record from marine sediments that outcrop along the mid-Waipara River, South Island, New Zealand. Fully oriented samples for paleomagnetic analyses were collected along 45 m of stratigraphic section, which encompasses magnetic polarity Chrons from C23n to C21n (similar to 51.5-47 Ma). These results are integrated with foraminiferal, calcareous nannofossil, and dinoflagellate cyst (dinocyst) biostratigraphy from samples collected in three different expeditions along a total of similar to 80 m of section. Biostratigraphic data indicates relatively continuous sedimentation from the lower Waipawan to the upper Heretaungan New Zealand stages (i.e., lower Ypresian to lower Lutetian, 55.5 to 46 Ma). We provide the first magnetostratigraphically-calibrated age of 48.88 Ma for the base of the Heretaungan New Zealand stage (latest early Eocene). To improve the correlation of the climate record in this section with other Southern Ocean records, we reviewed the magnetostratigraphy of Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau) and Integrated Ocean Drilling Program (IODP) Site 131356 (Wilkes Land Margin, Antarctica). A paleomagnetic study of discrete samples could not confirm any reliable magnetic polarity reversals in the early Eocene at Site 1172. We use the robust magneto-biochronology of a succession of dinocyst bioevents that are common to mid-Waipara, Site 1172, and Site U1356 to assist correlation between the three records. A new integrated chronology offers new insights into the nature and completeness of the southern high-latitude climate histories derived from these sites. (C) 2015 Elsevier B.V. All rights reserved.

Shaar, R, Tauxe L, Ron H, Ebert Y, Finkelstein I, Agnon A.  2016.  Large geomagnetic field anomalies revealed in Bronze to Iron Age archeomagnetic data from Tel Megiddo and Tel Hazor, Israel. Earth and Planetary Science Letters. 442:173-185.   10.1016/j.epsl.2016.02.038   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.

Tauxe, L, Shaar R, Jonestrask L, Swanson-Hysell N, Minnett R, Koppers AAP, Constable CG, Jarboe N, Gaastra K, Fairchild L.  2016.  PmagPy: Software package for paleomagnetic data analysis and a bridge to the Magnetics Information Consortium (MagIC) Database. Geochemistry, Geophysics, Geosystems. 17   10.1002/2016GC006307  
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.

Shaar, R, Tauxe L, Ben-Yosef E, Kassianidou V, Lorentzen B, Feinberg JM, Levy TE.  2015.  Decadal-scale variations in geomagnetic field intensity from ancient Cypriot slag mounds. Geochemistry Geophysics Geosystems. 16:195-214.   10.1002/2014gc005455   AbstractWebsite

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.

Tauxe, L, Sugisaki S, Jiménez-Espejo F, Escutia C, Cook CP, van de Flierdt T, Iwai M.  2015.  Geology of the Wilkes land sub-basin and stability of the East Antarctic Ice Sheet: Insights from rock magnetism at IODP Site U1361. Earth and Planetary Science Letters. 412:61-69.   10.1016/j.epsl.2014.12.034   AbstractWebsite

IODP Expedition 318 drilled Site U1361 on the continental rise offshore of Adélie Land and the Wilkes subglacial basin. The objective was to reconstruct the stability of the East Antarctic Ice Sheet (EAIS) during Neogene warm periods, such as the late Miocene and the early Pliocene. The sedimentary record tells a complex story of compaction, and erosion (thus hiatuses). Teasing out the paleoenvironmental implications is essential for understanding the evolution of the EAIS. Anisotropy of magnetic susceptibility (AMS) is sensitive to differential compaction and other rock magnetic parameters like isothermal remanence and anhysteretic remanence are very sensitive to changes in the terrestrial source region. In general, highly anisotropic layers correspond with laminated clay-rich units, while more isotropic layers are bioturbated and have less clay. Layers enriched in diatoms are associated with the latter, which also have higher Ba/Al ratios consistent with higher productivity. Higher anisotropy layers have lower porosity and moisture contents and have fine grained magnetic mineralogy dominated by maghemite, the more oxidized form of iron oxide, while the lower anisotropy layers have magnetic mineralogies dominated by magnetite. The different magnetic mineralogies support the suggestion based on isotopic signatures by Cook et al. (2013) of different source regions during low productivity (cooler) and high productivity (warmer) times. These two facies were tied to the coastal outcrops of the Lower Paleozoic granitic terranes and the Ferrar Large Igneous Province in the more inland Wilkes Subglacial Basin respectively. Here we present evidence for a third geological unit, one eroded at the boundaries between the high and low clay zone with a “hard” (mostly hematite) dominated magnetic mineralogy. This unit likely outcrops in the Wilkes subglacial basin and could be hydrothermally altered Beacon sandstone similar to that detected by Craw and Findlay (1984) in Taylor Valley or the equivalent to the Elatina Formation in the Adelaide Geosyncline in Southern Australia (Schmidt and Williams, 2013). Correlation of the “hard” events with global oxygen isotope stacks of Zachos et al. (2001) and Lisiecki and Raymo (2005) suggest that the source region was eroded during times with higher global ice volume.

Jiang, Z, Qin H, Liu Q, Dekkers MJ, Tauxe L, Barron V, Torrent J.  2015.  Acquisition of chemical remanent magnetization during experimental ferrihydrite-hematite conversion - implications for paleomagnetic studies of red beds,. Earth Planet. Sci. Let. . 428:1-10.   10.1016/j.epsl.2015.07.024  
Shaar, R, Tauxe L.  2015.  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. 112:11187-11192.   10.1073/pnas.1507986112  
Cromwell, G, Tauxe L, Halldorsson SA.  2015.  New paleointensity results from rapidly cooled Icelandic lavas: Implications for Arctic geomagnetic field strength. J. Geophys. Res.. 120 :2913-2934.   10.1002/2014JB011828.  
Biggin, A, Piipsa E, Pesonen L, Holme R, Paterson G, Veikkolainen T, Tauxe L.  2015.  Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation. Nature. 526:245-248.   10.1038/nature15523  
Tauxe, L, Yamazaki T.  2015.  Paleointensities. Treatise on Geophysics. 5, Amsterdam: Elsevier   10.1016/B978-0-444-53802-4.00107-X  
Cromwell, G, Tauxe L, Staudigel H, Ron H.  2015.  Paleointensity estimates from historic and modern Hawaiian lava flows using volcanic glass as a primary source material. Phys. Earth Planet. Int.. 241:44-56.   10.1016/j.pepi.2014.12.007  
Shaar, R, Tauxe L, Ben-Yosef E, Kassianidou V, Lorentzen B, Feinberg JM, Levy TE.  2014.  Decadal-scale variations in geomagnetic field intensity from ancient Cypriot slag mounds. Geochemistry, Geophysics, Geosystems.   10.1002/2014GC005455   AbstractWebsite

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, 4th - 5th centuries CE, 21 meter in height), and Mitsero Kokkinoyia (MK1, 7th - 5th BCE, 8 meter in height). The mounds are multi-layered 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 non-linear 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 sub-century 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. This article is protected by copyright. All rights reserved.

Patterson, MO, McKay R, Naish T, Escutia C, Jimenez-Espejo FJ, Raymo ME, Meyers SR, Tauxe L, Brinkhuis H, Scientists IE318.  2014.  Orbital forcing of the East Antarctic ice sheet during the Pliocene and Early Pleistocene. Nature Geoscience. 7:841-847.   10.1038/ngeo2273   AbstractWebsite

The Pliocene and Early Pleistocene, between 5.3 and 0.8 million years ago, span a transition from a global climate state that was 2-3 degrees C warmer than present with limited ice sheets in the Northern Hemisphere to one that was characterized by continental-scale glaciations at both poles. Growth and decay of these ice sheets was paced by variations in the Earth's orbit around the Sun. However, the nature of the influence of orbital forcing on the ice sheets is unclear, particularly in light of the absence of a strong 20,000-year precession signal in geologic records of global ice volume and sea level. Here we present a record of the rate of accumulation of iceberg-rafted debris offshore from the East Antarctic ice sheet, adjacent to the Wilkes Subglacial Basin, between 4.3 and 2.2 million years ago. We infer that maximum iceberg debris accumulation is associated with the enhanced calving of icebergs during ice-sheet margin retreat. In the warmer part of the record, between 4.3 and 3.5 million years ago, spectral analyses show a dominant periodicity of about 40,000 years. Subsequently, the powers of the 100,000-year and 20,000-year signals strengthen. We suggest that, as the Southern Ocean cooled between 3.5 and 2.5 million years ago, the development of a perennial sea-ice field limited the oceanic forcing of the ice sheet. After this threshold was crossed, substantial retreat of the East Antarctic ice sheet occurred only during austral summer insolation maxima, as controlled by the precession cycle.

Paterson, GA, Tauxe L, Biggin AJ, Shaar R, Jonestrask LC.  2014.  On improving the selection of Thellier-type paleointensity data. Geochemistry Geophysics Geosystems. 15:1180-1192.   10.1002/2013gc005135   AbstractWebsite

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.

Escutia, C, Brinkhuis H, Scientists E318.  2014.  From Greenhouse to Icehouse at the Wilkes Land Antarctic Margin: IODP Expedition 318 Synthesis of Results. Developments in Marine Geology. 7, Amsterdam: Elsevier   10.1016/B978-0-444-62617-2.00012-8  
Cai, S, Tauxe L, Deng C, Pan Y, Zheng J, Xie F, Qin H, Zhu R.  2014.  Geomagnetic intensity variations for the past 8 kyr: New archaeointensity results from Eastern China. Earth and Planetary Science Letters. 392:217-229.   10.1016/j.epsl.2014.02.030  
Di Chiara, A, Tauxe L, Speranza F.  2014.  Paleointensity determination from Sao Miguel (Azores Archipelago) over the last 3 ka. Physics of the Earth and Planetary Interiors.   10.1016/j.pepi.2014.06.008   Abstract

Paleointensity data from the Atlantic Ocean are rare. We present new paleointensity data from Sao Miguel (Azores Islands, Portugal) based on 20 paleomagnetic sites from 13 lava flows emplaced over the last 3000 years. Ten lava flows are radiocarbon dated, whereas three flows were paleomagnetically dated and one site was dated using stratigraphic relations. All the samples, previously investigated to recover paleo-directions, were subjected to IZZI experiments. Importantly, the new data are internally consistent, agree with Moroccan and European datasets, and offer new constraints for global geomagnetic field models. Some of the ages of the paleomagnetically dated lava flows have been revised based on the intensity data presented here. The inferred Virtual Axial Dipole Moments (VADMs) range from 68.2 to 163.5 ZAm(2). A peak in field strength with an estimated age of around 600 BC is well supported by two sites from the same flow (Furna), and is comparable to the high intensity values found in Portugal for the same age and the earlier field peak at about 1000 BC in the Levant. A gradient in VADM values with latitude from northwestern Africa and across Europe between 100 and 1000 AD is confirmed as well as its absence from between 0 to 100 AD. (C) 2014 Elsevier B.V. All rights reserved.

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.

Mitra, R, Tauxe L, McIntosh SK.  2013.  Two thousand years of archeointensity from West Africa. Earth and Planetary Science Letters. 364:123-133.   10.1016/j.epsl.2012.12.027   AbstractWebsite

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 C-14 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 form!

Houben, AJP, Bijl PK, Pross J, Bohaty SM, Passchier S, Stickley CE, Rohl U, Sugisaki S, Tauxe L, van de Flierdt T, Olney M, Sangiorgi F, Sluijs A, Escutia C, Brinkhuis H.  2013.  Reorganization of Southern Ocean Plankton Ecosystem at the Onset of Antarctic Glaciation. Science. 340:341-344.   10.1126/science.1223646   AbstractWebsite

The circum-Antarctic Southern Ocean is an important region for global marine food webs and carbon cycling because of sea-ice formation and its unique plankton ecosystem. However, the mechanisms underlying the installation of this distinct ecosystem and the geological timing of its development remain unknown. Here, we show, on the basis of fossil marine dinoflagellate cyst records, that a major restructuring of the Southern Ocean plankton ecosystem occurred abruptly and concomitant with the first major Antarctic glaciation in the earliest Oligocene (similar to 33.6 million years ago). This turnover marks a regime shift in zooplankton-phytoplankton interactions and community structure, which indicates the appearance of eutrophic and seasonally productive environments on the Antarctic margin. We conclude that earliest Oligocene cooling, ice-sheet expansion, and subsequent sea-ice formation were important drivers of biotic evolution in the Southern Ocean.

Cook, CP, van de Flierdt T, Williams T, Hemming SR, Iwai M, Kobayashi M, Jimenez-Espejo FJ, Escutia C, Gonzalez JJ, Khim BK, McKay RM, Passchier S, Bohaty SM, Riesselman CR, Tauxe L, Sugisaki S, Galindo AL, Patterson MO, Sangiorgi F, Pierce EL, Brinkhuis H, Scientists IE318.  2013.  Dynamic behaviour of the East Antarctic ice sheet during Pliocene warmth. Nature Geoscience. 6:765-769.   10.1038/ngeo1889   AbstractWebsite

Warm intervals within the Pliocene epoch (5.33-2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century(1) and atmospheric CO2 concentrations similar to today(2-4). Estimates for global sea level highstands during these times(5) imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adelie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

Cromwell, G, Constable CG, Staudigel H, Tauxe L, Gans P.  2013.  Revised and updated paleomagnetic results from Costa Rica. Geochemistry Geophysics Geosystems. 14:3379-3388.   10.1002/ggge.20199   AbstractWebsite

Paleomagnetic results from globally distributed lava flows have been collected and analyzed under the time-averaged field initiative (TAFI), a multi-institutional collaboration started in 1996 and designed to improve the geographic and temporal coverage of the 0-5 Ma paleomagnetic database for studying both the time-averaged field and its very long-term secular variations. Paleomagnetic samples were collected from 35 volcanic units, either lava flows or ignimbrites, in Costa Rica in December 1998 and February 2000 from the Cordilleras Central and Guanacaste, the underlying Canas, Liberia and Bagaces formations and from Volcano Arenal. Age estimates range from approximately 40 ka to slightly over 6 Ma. Although initial results from these sites were used in a global synthesis of TAFI data by Johnson et al. (2008), a full description of methodology was not presented. This paper documents the definitive collection of results comprising 28 paleomagnetic directions (24 normal, 4 reversed), with enhanced precision and new geological interpretations, adding two paleointensity estimates and 19 correlated Ar-40/Ar-39 radiometric ages. The average field direction is consistent with that of a geocentric axial dipole and dispersion of virtual geomagnetic poles (17.34.6 degrees) is in general agreement with predictions from several statistical paleosecular variation models. Paleointensity estimates from two sites give an average field strength of 26.3 T and a virtual axial dipole moment of 65 ZAm(2). The definitive results provide a useful augmentation of the global database for the longer term goal of developing new statistical descriptions of paleomagnetic field behavior.

Cromwell, G, Tauxe L, Staudigel H, Constable CG, Koppers AAP, Pedersen RB.  2013.  In search of long-term hemispheric asymmetry in the geomagnetic field : Results from high northern latitudes. Geochemistry Geophysics Geosystems. 14:3234-3249.   10.1002/ggge.20174   AbstractWebsite

Investigations of the behavior of the geomagnetic field on geological timescales rely on globally distributed data sets from dated lava flows. We present the first suitable data from the Arctic region, comprising 37 paleomagnetic directions from Jan Mayen (71 degrees N, 0.2-461 ka) and Spitsbergen (79 degrees N, 1-9.2 Ma) and five paleointensity results. Dispersion of the Arctic virtual geomagnetic poles over the last 2 Ma (27.34.0 degrees) is significantly lower than that from published Antarctic data sets (32.15.0 degrees). Arctic average virtual axial dipole moment (76.824.3 ZAm(2)) is high in comparison to Antarctica over the same time interval (34.88.2 ZAm(2)), although the data are still too sparse in the Arctic to be definitive. These data support a long-lived hemispheric asymmetry of the magnetic field, contrasting higher, more stable fields in the north with lower average strength and more variable field directions in the south. Such features require significant non-axial-dipole contributions over 10(5)-10(6) years.

Bijl, PK, Bendle JAP, Bohaty SM, Pross J, Schouten S, Tauxe L, Stickley CE, McKay RM, Rohl U, Olney M, Sluijs A, Escutia C, Brinkhuis H.  2013.  Eocene cooling linked to early flow across the Tasmanian Gateway. Proceedings of the National Academy of Sciences of the United States of America. 110:9645-9650.   10.1073/pnas.1220872110   AbstractWebsite

The warmest global temperatures of the past 85 million years occurred during a prolonged greenhouse episode known as the Early Eocene Climatic Optimum (52-50 Ma). The Early Eocene Climatic Optimum terminated with a long-term cooling trend that culminated in continental-scale glaciation of Antarctica from 34 Ma onward. Whereas early studies attributed the Eocene transition from greenhouse to icehouse climates to the tectonic opening of Southern Ocean gateways, more recent investigations invoked a dominant role of declining atmospheric greenhouse gas concentrations (e.g., CO2). However, the scarcity of field data has prevented empirical evaluation of these hypotheses. We present marine microfossil and organic geochemical records spanning the early-to-middle Eocene transition from the Wilkes Land Margin, East Antarctica. Dinoflagellate biogeography and sea surface temperature paleothermometry reveal that the earliest throughflow of a westbound Antarctic Counter Current began similar to 49-50 Ma through a southern opening of the Tasmanian Gateway. This early opening occurs in conjunction with the simultaneous onset of regional surface water and continental cooling (2-4 degrees C), evidenced by biomarker- and pollen-based paleothermometry. We interpret that the westbound flowing current flow across the Tasmanian Gateway resulted in cooling of Antarctic surface waters and coasts, which was conveyed to global intermediate waters through invigorated deep convection in southern high latitudes. Although atmospheric CO2 forcing alone would provide a more uniform middle Eocene cooling, the opening of the Tasmanian Gateway better explains Southern Ocean surface water and global deep ocean cooling in the apparent absence of (sub-) equatorial cooling.

Roberts, AP, Tauxe L, Heslop D.  2013.  Magnetic paleointensity stratigraphy and high-resolution Quaternary geochronology: successes and future challenges. Quaternary Science Reviews. 61:1-16.   10.1016/j.quascirev.2012.10.036   AbstractWebsite

Magnetic paleointensity stratigraphy is used to detect variations in the strength of Earth's ancient magnetic field. Paleointensity studies have demonstrated that a dominantly dipolar geomagnetic signal can be recorded in a globally coherent manner in different types of sediments and in non-sedimentary archives, including ice core records and marine magnetic anomaly profiles. The dominantly dipolar nature of geomagnetic paleointensity variations provides a global geophysical signal that has come to be widely used to date Quaternary sediments. Despite the many successful applications of paleointensity-assisted chronology, the mechanisms by which sediments become magnetized remain poorly understood and there is no satisfactory theoretical foundation for paleointensity estimation. In this paper, we outline past successes of sedimentary paleointensity analysis as well as remaining challenges that need to be addressed to place such work on a more secure theoretical and empirical foundation. We illustrate how common concepts for explaining sedimentary remanence acquisition can give rise to centennial to millennial offsets between paleomagnetic and other signals, which is a key limitation for using paleointensity signals for geochronology. Our approach is intended to help non-specialists to better understand the legitimate uses and limitations of paleointensity stratigraphy, while pointing to outstanding problems that require concerted specialist efforts to resolve.

Tauxe, L, Gee JS, Steiner MB, Staudigel H.  2013.  Paleointensity results from the Jurassic : New constraints from submarine basaltic glasses of ODP Site 801C. Geochemistry, Geophysics, Geosystems. 8   10.1002/2013GC004704  
Pant, NC, Biswas P, Shrivastava PK, Verma K, Pandey M, Party IODPES318.  2013.  Provenance of Pleistocene sediments from Site U1359 of the Wilkes Land IODP Expedition-evidence for multiple sourcing from east Antarctic craton and Ross orogen. Geological Society of London, Special Publications. 318:277-297.   10.1144/SP381.11  
Stocchi, P, Escutia C, Houben AJP, Vermeersen BLA, Bijl PK, Brinkhuis H, DeConto RM, Galeotti S, Psschier S, scientists IODPE318.  2013.  Relative sea-level rise around East Antarctica during Oligocene glaciation. Nature Geoscience. 6:380-384.   10.1038/ngeo1783  
Dallanave, E, Muttoni G, Agnini C, Tauxe L, Rio D.  2012.  Is there a normal magnetic-polarity event during the Palaeocene-Eocene thermal maximum (similar to 55 Ma)? Insights from the palaeomagnetic record of the Belluno Basin (Italy) Geophysical Journal International. 191:517-529.   10.1111/j.1365-246X.2012.05627.x   Abstract

In the lowermost Eocene sedimentary record of Ocean Drilling Program Site 1262 (Leg 208, Walvis Ridge, South Atlantic Ocean), the presence of a similar to 53-kyr-long normal polarity event has been recorded within the similar to 2.55-Myr-long reverse polarity Chron C24r (similar to 53.355.9 Ma) and termed PalaeoceneEocene magnetic reversal (PEMR). The origin of the PEMR has been speculatively related to a change in the Earth's rotation rate that was in turn influenced by an abrupt overturning of the ocean-atmosphere circulation that occurred during the PalaeoceneEocene thermal maximum (PETM) at similar to 55 Ma. Such provocative genesis for a magnetic-polarity reversal demands the PEMR to be confirmed (or refuted) in additional PETM sections. Here, we present detailed palaeomagnetic and rock-magnetic data from the Forada and Cicogna sections of the Belluno Basin in NE Italy, which contain an expanded and continuous record of the PETM termed clay marl unit (CMU). Our data indicate that these sediments were deposited during a continuous interval of reverse geomagnetic field polarity. We therefore conclude that no magnetic-polarity reversals occurred throughout the PETM. In addition, we studied the origin of the high degree of flattening affecting the characteristic magnetic component directions of the sediments, which we interpret as due to a combination of depositional inclination shallowing typical of detrital haematite, and post-depositional compaction of clays, particularly abundant in the carbonate-depleted CMU.

Tauxe, L, Stickley CE, Sugisaki S, Bijl PK, Bohaty SM, Brinkhuis H, Escutia C, Flores JA, Houben AJP, Iwai M, Jimenez-Espejo F, McKay R, Passchier S, Pross J, Riesselman CR, Rohl U, Sangiorgi F, Welsh K, Klaus A, Fehr A, Bendle JAP, Dunbar R, Gonzalez J, Hayden T, Katsuki K, Olney MP, Pekar SF, Shrivastava PK, van de Flierdt T, Williams T, Yamane M.  2012.  Chronostratigraphic framework for the IODP Expedition 318 cores from the Wilkes Land Margin: Constraints for paleoceanographic reconstruction. Paleoceanography. 27   10.1029/2012pa002308   AbstractWebsite

The Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin of Antarctica recovered a sedimentary succession ranging in age from lower Eocene to the Holocene. Excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals. Drill sites recovered the lower and middle Eocene, nearly the entire Oligocene, the Miocene from about 17 Ma, the entire Pliocene and much of the Pleistocene. The paleomagnetic properties are generally suitable for magnetostratigraphic interpretation, with well-behaved demagnetization diagrams, uniform distribution of declinations, and a clear separation into two inclination modes. Although the sequences were discontinuously recovered with many gaps due to coring, and there are hiatuses from sedimentary and tectonic processes, the magnetostratigraphic patterns are in general readily interpretable. Our interpretations are integrated with the diatom, radiolarian, calcareous nannofossils and dinoflagellate cyst (dinocyst) biostratigraphy. The magnetostratigraphy significantly improves the resolution of the chronostratigraphy, particularly in intervals with poor biostratigraphic control. However, Southern Ocean records with reliable magnetostratigraphies are notably scarce, and the data reported here provide an opportunity for improved calibration of the biostratigraphic records. In particular, we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the Paleogene and a substantially improved diatom calibration for the Pliocene. This paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the Wilkes Land margin cores. It further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region.

Pross, J, Contreras L, Bijl PK, Greenwood DR, Bohaty SM, Schouten S, Bendle JA, Rohl U, Tauxe L, Raine IJ, Huck CE, van de Flierdt T, Jamieson SSR, Stickley CE, van de Schootbrugge B, Escutia C, Brinkhuis H.  2012.  Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch. Nature. 488:73-77.: Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.   10.1038/nature11300   AbstractWebsite

The warmest global climates of the past 65 million years occurred during the early Eocene epoch (about 55 to 48 million years ago), when the Equator-to-pole temperature gradients were much smaller than today1, 2 and atmospheric carbon dioxide levels were in excess of one thousand parts per million by volume3, 4. Recently the early Eocene has received considerable interest because it may provide insight into the response of Earth’s climate and biosphere to the high atmospheric carbon dioxide levels that are expected in the near future5 as a consequence of unabated anthropogenic carbon emissions4, 6. Climatic conditions of the early Eocene ‘greenhouse world’, however, are poorly constrained in critical regions, particularly Antarctica. Here we present a well-dated record of early Eocene climate on Antarctica from an ocean sediment core recovered off the Wilkes Land coast of East Antarctica. The information from biotic climate proxies (pollen and spores) and independent organic geochemical climate proxies (indices based on branched tetraether lipids) yields quantitative, seasonal temperature reconstructions for the early Eocene greenhouse world on Antarctica. We show that the climate in lowland settings along the Wilkes Land coast (at a palaeolatitude of about 70° south) supported the growth of highly diverse, near-tropical forests characterized by mesothermal to megathermal floral elements including palms and Bombacoideae. Notably, winters were extremely mild (warmer than 10 °C) and essentially frost-free despite polar darkness, which provides a critical new constraint for the validation of climate models and for understanding the response of high-latitude terrestrial ecosystems to increased carbon dioxide forcing.

Ben-Yosef, E, Shaar R, Tauxe L, Ron H.  2012.  A chronological framework for Iron Age copper production at Timna (Israel). Bulletin of the American Schools of Oriental Research. 367:31-71.   10.5615/bullamerschoorie.367.0031  
Liu, Q, Roberts AP, LarrasoaÒa JC, Banerjee SK, Guyodo Y, Tauxe L, Oldfield F.  2012.  Environmental magnetism: Principles and applications. Reviews of Geophysics. 50:RG4002.: AGU   10.1029/2012rg000393   AbstractWebsite

In environmental magnetism, rock and mineral magnetic techniques are used to investigate the formation, transportation, deposition, and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes. All materials respond in some way to an applied magnetic field, and iron-bearing minerals are sensitive to a range of environmental processes, which makes magnetic measurements extremely useful for detecting signals associated with environmental processes. Environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics, chemistry, and biology and environmental science, including research on climate change, pollution, iron biomineralization, and depositional and diagenetic processes in sediments to name a few applications. Magnetic parameters are used to routinely scan sediments, but interpretation is often difficult and requires understanding of the underlying physics and chemistry. Thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities, complexities, and limitations to interpretations. In this review, we evaluate environmental magnetic parameters based on theory and empirical results. We describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations. We also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology, chemistry, and physics. Finally, we discuss directions in which environmental magnetism is likely to develop in the future.

Donadini, F, Elming SA, Tauxe L, Halenius U.  2011.  Paleointensity determination on a 1.786 Ga old gabbro from Hoting, Central Sweden. Earth and Planetary Science Letters. 309:234-248.   10.1016/j.epsl.2011.07.005   AbstractWebsite

Paleointensities from Precambrian rocks are rare and might be biased by remagnetization processes. Here we present new analyses of samples from a 1.786 Ga gabbro near Hoting, Central Sweden. Rock magnetic and mineralogical analyses indicate that one of the sites (site 5) may be pristine, whereas the others exhibit evidence of alteration. Characteristic remanent magnetization was determined using principal component analysis for each sample and was compared with results obtained in a previous study of Elming et al. (2009). Intensity measurements from site 5 show higher values compared to those of the other sites, suggesting that alteration processes may lead to underestimation of the field intensity. After cooling rate and anisotropy correction, the field moment at 1.786 Ga was estimated to be 25.6 +/- 33 ZAm(2) and 15.2 +/- 6.1 ZAm(2) from site 5 only and from all sites respectively. We consider the result from site 5 to be more accurate owing to the lack of evidence for alteration: our estimates agree well with the Proterozoic VDM values suggested by Biggin et al. (2009). (C) 2011 Elsevier B.V. All rights reserved.

Shaar, R, Ron N, Tauxe L, Kessel R, Agnon A.  2011.  Paleomagnetic field intensity derived from non-SD: Testing the Thellier IZZI technique on MD slag and a new bootstrap procedure. Earth and Planetary Science Letters. 310:213-224.   10.1016/j.epsl.2011.08.024   AbstractWebsite

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 (B(TRM)) and the field in which the NRM was acquired (B(NRM)). 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 B(TRM) is parallel and significantly stronger than B(NRM). 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 B(TRM) and B(NRM). 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. (C) 2011 Elsevier BM. All rights reserved.

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.

Shaar, R, Ben-Yosef E, Ron H, Tauxe L, Agnon A, Kessel R.  2011.  Geomagnetic field intensity: How high can it get? How fast can it change? Constraints from Iron Age copper slag Earth and Planetary Science Letters. 301:297-306.   10.1016/j.epsl.2010.11.013   AbstractWebsite

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). The geomagnetic spikes rise and fall over a period of less than 30 years and are associated with VADM fluctuations of at least 70 ZAm2. Thus, the Levantine archaeomagnetic record places new constraints on maximum geomagnetic intensity as well as for its rate of change. Yet, it is not clear whether the geomagnetic spikes are local non-dipolar features or a geomagnetic dipolar phenomenon. (C) 2010 Elsevier B.V. All rights reserved.

Mitra, R, Tauxe L, Gee JS.  2011.  Detecting uniaxial single domain grains with a modified IRM technique. Geophysical Journal International. 187:1250-1258.   10.1111/j.1365-246X.2011.05224.x   AbstractWebsite

Mid-ocean ridge basalt (MORB) specimens have often been found to have high ratios of saturation remanence to saturation magnetization (M(rs)/M(s)). This has been attributed either to dominant cubic anisotropy or to insufficient saturating field leading to overestimation of M(rs)/M(s) of a dominantly uniaxial single domain (USD) assemblage. To resolve this debate, we develop an independent technique to detect USD assemblages. The experimental protocol involves subjecting the specimen to bidirectional impulse fields at each step. The experiment is similar to the conventional isothermal remanent magnetization (IRM) acquisition experiment but the field is applied twice, in antiparallel directions. We define a new parameter, IRAT, as the ratio of the remanences at each field step and show it to have characteristic behaviour for the two assemblages; IRAT similar to 1 at all field steps for USD and <1 with a strong field dependence for multi-axial single domain (MSD) grains. We verified the theoretical predictions experimentally with representative USD and MSD specimens. Experiments with MORBs gave low IRATs for specimens having high M(rs)/M(s). This argues for a dominant MSD assemblage in the MORBs, possibly cubic in nature. Although undersaturation of the samples can indeed be a contributing factor to the exceptionally high M(rs)/M(s), this study shows that the nature of the assemblage cannot be dominantly USD.

Ben-Yosef, E, Shaar R, Tauxe L, Levy TE, Kassianidou V.  2011.  The Cyprus Archaeomagnetic Project (CAMP): targeting the slag deposits of Cyprus and the Eastern Mediterranean. Antiquity. 85 AbstractWebsite
Ben-Yosef, E, Levy TE, Higham T, Najjar M, Tauxe L.  2010.  The beginning of Iron Age copper production in the southern Levant: new evidence from Khirbat al-Jariya, Faynan, Jordan. Antiquity. 84:724-746. AbstractWebsite

The authors have explored the workplace and house of copper workers of the early Iron Age (twelfth to tenth century BC) in Jordan's Wadi Faynan copper ore district, showing that it belongs in time between the collapse of the great Bronze Age states and the arrival of Egyptians in the area under Sheshong I. They attribute this production to local - tribes perhaps those engaged in building the biblical kingdom of Edom.

Dallanave, E, Tauxe L, Muttoni G, Rio D.  2010.  Silicate weathering machine at work: Rock magnetic data from the late Paleocene-early Eocene Cicogna section, Italy. Geochemistry Geophysics Geosystems. 11   10.1029/2010gc003142   AbstractWebsite

We describe a scenario of climate forcing on sedimentation recorded in the late Paleocene-early Eocene Cicogna marine section from the Belluno Basin ( NE Italy). Previously published magneto-biostratigraphic data revealed that the similar to 81 m Cicogna section extends from Chron C25r to Chron C23r spanning the NP7/NP8-NP12 nannofossil zones (similar to 52.2-56.6 Ma). Using previously published rock magnetic data, augmented by data from this study, we describe and thoroughly discuss a pronounced increase of hematite ( relative to maghemite or magnetite) between similar to 54.9 and 54.6 Ma immediately above the Paleocene-Eocene boundary, followed by a second, long-term increasing trend from similar to 54 Ma up to similar to 52.2 Ma in the early Eocene. This hematite is essentially of detrital origin, insofar as it is associated with a strong shallow bias of paleomagnetic inclinations, and is interpreted to have formed on land by the weathering of Fe-bearing silicates and other primary minerals. We speculate that the warm and humid climate typical of the Paleocene-Eocene thermal maximum (PETM, similar to 54.9 Ma) as well as of the warming trend leading to the early Eocene climatic optimum (EECO; similar to 52-50 Ma) enhanced continental weathering of silicate rocks with the consequent production, transport, and sedimentation of detrital hematite grains. This hypothesis is confirmed by a statistical correlation between the rock magnetic properties and global climate as revealed by a standard benthic oxygen isotope record from the literature. Our temporal coupling between oxidation state of sedimentary magnetic phases and global climate is therefore consistent with the existence in the Paleocene-Eocene of the silicate weathering negative feedback mechanism for the long-term stabilization of the Earth's surface temperature.

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.

Ben-Yosef, E, Tauxe L, Levy TE.  2010.  Archaeomagnetic Dating of Copper Smelting Site F2 in the Timna Valley (Israel) and Its Implications for the Modelling of Ancient Technological Developments. Archaeometry. 52:1110-1121.   10.1111/j.1475-4754.2010.00528.x   AbstractWebsite

Site F2 in the Timna Valley, Israel, is a small copper smelting site of 'primitive' technology, dated by its excavator to the Pottery Neolithic (sixth to fifth millennium bce). This early date challenges the common view of the beginning of smelting technology in the Levant and has been contested by various scholars since its publication. In this study, we present results of archaeointensity experiments conducted on slag fragments from the site. The slag yielded an excellent ancient geomagnetic value (64.1 +/- 1.1 mu T) that, when compared to the Levantine master curve, suggests an age not older than the second millennium and most probably between the 13th and 11th centuries bce. In addition to demonstrating the applicability of geomagnetic archaeointensity experiments to independent dating of slag, we discuss the implications of the current results for the socio-historical picture of the Timna Valley, and in particular for the way in which technological developments were previously modelled in the archaeometallurgical research on the region.

Tauxe, L.  2010.  Essentials of paleomagnetism. :xvi,489p.., Berkeley: University of California Press Abstract
Mitra, R, Tauxe L.  2009.  Full vector model for magnetization in sediments. Earth and Planetary Science Letters. 286:535-545.   10.1016/j.epsl.2009.07.019   AbstractWebsite

Sediments provide a continuous record of past geomagnetic field variations. Although it is theoretically possible to get both the direction and intensity of the geomagnetic field from sediment records the, mechanism is not fully understood. Previous workers have postulated that flocculation plays an important role in detrital remanent magnetism (DRM). Flocs are porous, loose and highly fragile aggregates of microscopic clay particles and their behavior in a viscous medium is likely to be different than single particles of magnetic minerals. In order to understand the role of flocculation in sediment magnetization, we carried out a set of redeposition experiments at different field intensities and a quasi-constant field inclination of 45 degrees. We present here a simple numerical model of flocculation, incorporating both magnetic and hydrodynamic torques to explain the experimental data. At small floc sizes DRM acquisition is likely to be non-linear in field strengths comparable to the Earth's, but the sediments may be able to record the directions accurately. With increasing floc sizes sediments may retain a record of the intensity that is linearly related to the applied field or a direction parallel to the applied field, but are unlikely to do both at the same time. Also, the majority of the magnetic particles in the sediments may not be contributing significantly towards the net DRM and any bulk normalizing parameter may be unsuitable if the depositional environment has changed over the depositional period. (C) 2009 Elsevier B.V. All rights reserved.