Geomagnetic intensity variation during the last 4000 years

doi:10.1016/0031-9201(89)90035-6

Physics of the Earth and Planetary Interiors

Volume 56, Issues 1–2, July 1989, Pages 49-58

https://doi.org/10.1016/0031-9201(89)90035-6 Get rights and content

Abstract

Thellier-type determinations of the ancient geomagnetic intensity are reported for a large number of samples from Greece, comprising ancient pottery and other archaeologically dated forms of baked clay. Comparison is made with results for other parts of the world of about the same latitude: the Near East, China and the western U.S.A. These data indicate that, in the time-range studied, variation of the geomagnetic dipole moment is unlikely to have been the dominant influence; it is suggested that the westward drift of a non-dipole disturbance could have been responsible.

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Cited by (36)

Global archaeomagnetic data: The state of the art and future challenges
2021, Physics of the Earth and Planetary Interiors
Citation Excerpt :
Such regional data sets have been used to develop secular variation (or reference) curves (see Section 4.1), using evermore sophisticated mathematical approaches (recent examples include Lodge and Holme, 2009; Thébault and Gallet, 2010; Hellio et al., 2014; Batt et al., 2017; Livermore et al., 2018; Genevey et al., 2021; Kapper et al., 2020). Compilations of global archaeointensity data have also been used to infer global dipole moment evolution (e.g., McElhinny and Senanayake, 1982; Aitken et al., 1989; Yang et al., 2000; Genevey et al., 2008; Knudsen et al., 2008; Usoskin et al., 2016). Over the past 20 years (alongside the construction of direction and intensity curves), has been the development of temporally continuous global palaeomagnetic field models (see Section 4.2).
Archaeomagnetic data are fundamental for our understanding of the evolution of Earth's magnetic field on centennial to millennial timescales. From the earliest studies of the Thelliers, Aitken, Nagata and others in the 1950s and 1960s, archaeomagnetic data have been vital for extending our knowledge of the field to times prior to observational measurements. Today, many thousands of archaeomagnetic data allow us to explore the geomagnetic field in more detail than ever before. Both regional time series of archaeomagnetic data and the inclusion of archaeomagnetic data in time-varying global spherical harmonic field models have revealed a range of newly discovered field behaviour. More sophisticated approaches to developing regional curves and global models have allowed us to resolve the field in certain regions more robustly and with greater resolution than previously possible. In this review we give an overview of the widely used global archaeomagnetic database GEOMAGIA50, discuss the methods used to obtain archaeomagnetic data, their challenges, and explore progress over the past twenty years in developing regional secular variation curves and global spherical harmonic models of the archaeomagnetic field. We end the review by covering what we see as the “grand challenges” in archaeomagnetism, including which regions of the world should be focussed on with regards to data acquisition.
Full-vector paleomagnetic secular variation records from latest quaternary sediments of Lake Malawi (10.0°S, 34.3°E)
2016, Quaternary Science Reviews
Citation Excerpt :
We can compare that record with a number of paleointensity studies from farther to the North. The closest four paleointensity studies are Egypt (EGY-26°N; Aitken and Allsop, 1984; Hussain, 1983, 1987; Odah et al., 1995; Odah, 1999), Central Asia (CAS-38°N; Nachasova and Burakov, 2000), Greece (GRE-37°N; Aitkin et al., 1989), and Georgia (GEO-42°N; Nachesova and Burakov, 1987, 1996, 1997). All of these are paleointensity records developed from archeological/archeomagnetic studies and can be considered absolute records in their intensity estimates and high-resolution in their age control.
We have conducted a paleomagnetic study of Late Quaternary sediments from Lake Malawi, East Africa, in order to develop a high-resolution record of paleomagnetic secular variation (PSV). This study has recovered PSV records from two cores (3P, 6P) in northern Lake Malawi (10.0°S, 34.3°E). The PSV appears to be recorded in fine-grained detrital magnetite/titanomagnetite grains. Detailed af demagnetization of the natural remanence (NRM) shows that a distinctive characteristic remanence (ChRM) is demagnetized from ∼20 to 80 mT, which decreases simply toward the origin. The resulting directional PSV records for 3P and 6P are easily correlatable with 29 distinct inclination features and 29 declination features. The statistical character of the PSV in both cores is consistent with Holocene PSV noted at other Holocene equatorial sites. Radiocarbon dating of the cores is based on 18 independent radiocarbon dates and four dated stratigraphic horizons that can be correlated into each core. The final directional PSV time series cover the last 24,000 years with an average sediment accumulation rate of ∼30 cm/kyr. We have also developed a relative paleointensity estimate for these PSV records based on normalizing the NRM (after 20 mT af demagnetization) by the SIRM (after 20 mT af demagnetization). Changing sedimentation patterns complicate any attempt to develop a single paleointensity record for the entire core lengths. We have developed a relative paleointensity record for the last 6000 years that has 14 correlatable features including 5 notable peaks in intensity. Three of these peaks are synchronous with paleointensity highs farther north in SE Europe/SW Asia/Egypt but two of the peaks are at times of low paleointensity farther north. We interpret this to indicate that Lake Malawi (10°S) is at least partly under the influence of a different flux-regeneration region of the outer-core dynamo. A relative paleointensity record was also developed for ∼11,000–24,000 YBP; the general pattern appears to be consistent with other published records, but our confidence in the correlations is more limited.
Archeointensities in Greece during the Neolithic period: New insights into material selection and secular variation curve
2013, Physics of the Earth and Planetary Interiors
Citation Excerpt :
Numerous studies have provided high quality data for both the direction and intensity of the geomagnetic field in Europe e.g., compilations of (Genevey and Gallet, 2002, 2003, 2009, 2011). In particular, Greece owns a substantial number of suitable archeological materials and volcanic fields, so that numerous data are available from such artefacts (Aitken et al., 1984, 1989; DeMarco, 2007, 2008,; Spatharas et al., 2011; Aidona and Kondopoulou, 2012; Tema et al., 2012) or historical lava flows (Spassov et al., 2010). The most recent Greek secular variation curves (SVCs) are available for the last 8 millennia for the intensity and the last 6 millennia for the direction (DeMarco et al., 2008).
Numerous archeomagnetic studies have provided high quality data for both the direction and the intensity of the geomagnetic field, essentially in Europe for the last 10 millennia. In particular, Greece supplies a lot of archeological materials due to its impressive cultural heritage and volcanic activity, so that numerous data have been obtained from burnt clays or historical lava flows. The most recent Greek secular variation curves are available for the last 8 millennia for the intensity and the last 6 millennia for the direction. Nevertheless, the coverage still presents several gaps for periods older than 2500 BC. In an effort to complete the Greek curve and extend it to older times, we present the archeointensity results from three Neolithic settlements in Northern Greece. The samples are of two different natures: burnt structures from Avgi (5250 ± 150 BC) and Vasili (4800 ± 200 BC), as well as ceramics from Dikili Tash (4830 ± 80 BC) and Vasili (4750 ± 250 BC). The samples have been subjected to standard rock magnetic analyses in order to estimate the thermal stability and the domain state of the magnetic carriers before archeointensity measurements. Surprisingly, very few ceramic samples provided reliable archeointensities whereas samples from burnt structures presented a very good success rate. Complementary studies showed that a detailed examination of the matrix color, following archeological information and classification standards can be a decisive test for pre-selection of sherds. In spite of these unsuccessful measurements from ceramics, we obtained an intensity value of 73.5 ± 1.1 $μ$ T for Dikili Tash, a higher value than the other data obtained in the same area, during the same period. However we do not have evidences for a technical artefact during the experiment. The burnt structures yielded two reliable archeointensities of 36.1 ± 1.8 $μ$ T and 46.6 ± 3.4 $μ$ T for Avgi and Vasili, respectively. Finally, we achieved a new archeomagnetic dating for these sites by comparing these new archeointensity values, combined to the directional measurements already published, with the Bulgarian secular variation curve. These new results contribute to extend the Greek secular variation reference curve towards older periods.
New archaeointensity results from archaeological sites and variation of the geomagnetic field intensity for the last 7 millennia in Greece
2008, Physics and Chemistry of the Earth
In this study six new intensity determinations are presented, obtained from five well dated archaeological sites, located in northern Greece and in Paros, Cyclades Islands. The fired structures consisted of ceramic and pottery kilns belonging to the Hellenistic, Roman and Byzantine periods. Between 8 and 21 samples of highly fired baked clays, tiles and bricks were taken, homogeneously distributed over the structures. The samples were analysed using the classical Thellier method, providing the past intensities and directions of the geomagnetic field recorded at each site. The intensity values have been corrected for anisotropy of thermal remanent magnetisation and cooling rate effects. Differences in the mean archaeointensities per site ranging from 1% to 11%, before and after TRM anisotropy and cooling rate corrections, were obtained. The new results indicate a decrease of 20% of the geomagnetic field strength in Greece, during the last four centuries BC. In order to compare our results with previously published data, a catalogue of archaeo- and palaeointensity results for the Aegean area has been established, covering the last 7 millennia. It consists of 336 data from Greece, western Turkey and Former Yugoslavia, collected from various authors. Weighting factors have been applied to these data, that then have been treated with a hierarchical Bayesian modelling, and a geomagnetic field intensity variation curve for Greece was constructed. A good agreement is observed when comparing the curve for Greece with the Bulgarian secular variation curve (SVC) for intensity. Satisfactory coincidence is also found with the archaeointensity data from Mesopotamia. Despite the presence of some time gaps, a more precise secular variation intensity curve has been constructed for Greece which, combined with a forthcoming directional SVC, will help for dating purposes.
On the possible occurrence of 'archaeomagnetic jerks' in the geomagnetic field over the past three millennia
2003, Earth and Planetary Science Letters
Archaeomagnetism can provide a high-resolution full-vector description of the Earth’s magnetic field for the past several thousand years. We analyse the bulk of archaeomagnetic data (both direction and intensity) obtained recently in Western Europe and the Eastern Mediterranean covering the past three millennia. We demonstrate a remarkable coincidence between sharp cusps in geomagnetic field direction and intensity maxima (two clear ones at ∼AD 200 and 1400; two presently less well constrained at ∼800 BC and AD 800). These sharp changes may constitute a new feature of geomagnetic secular variation (‘archaeomagnetic jerks’) with time characteristics intermediate between ‘geomagnetic jerks’ and ‘magnetic excursions’.
An attempt to determine the absolute geomagnetic field intensity in Southwestern Iceland during the Gauss-Matuyama reversal
1999, Physics of the Earth and Planetary Interiors
We have measured the variation in the intensity of the geomagnetic field during the Gauss–Matuyama (N4–R3) polarity reversal by application of the Thelliers' method to specimens of lava flows from Hvalfjördur district in Western Iceland (Reynivallahals Mts.). Eleven lava flows all show very similar directions corresponding to an equatorial VGP (Plat=2.9°N, Plong=81.9°E, A₉₅=4.2, K=119). Twenty-nine specimens from nine of the flows were pre-selected for palaeointensity determination on the basis that specimens from the same drill cores showed a single component of magnetisation upon thermal or AF demagnetisation, and possessed low magnetic viscosity and reversible susceptibility curves upon heating at 600–650°C. Observation that the directional data obtained in the course of the palaeointensity experiments occasionally showed substantial non-linearity indicates that a significant chemical remanent magnetization (CRM) can be acquired in the direction of the laboratory field during heating at T. For each double heating step we calculated the ratio of CRM(T) to the magnitude of the natural remanent magnetization (NRM(T)) in the direction of characteristic remanence (obtained independently from another specimen from the same core). When this ratio exceeded 15%, the paleointensity data was rejected. In addition, specimens for which the quality factor was less than 5 were rejected. Twelve reliable palaeointensity values were obtained from specimens representing five lava flows. The results confirm that the palaeointensity was substantially reduced during the N4–R3 reversal. The range of mean palaeointensity values obtained for the five flows is 8.8 to 20.5 and the overall mean is 14.8±4.6 μT. This corresponds to an equivalent VDM of 3.81±1.19 (10²² A m²). A comparison of all Thellier palaeointensity data from the R3 magnetozone in the Rayinivallahals Mts. area reveals a progressive although irregular increase in the palaeointensity between the Gauss–Matuyama and Matuyama–Réunion reversals. This trend is opposite to that expected from the saw tooth model of palaeointensity variations.

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Geomagnetic intensity variation during the last 4000 years

Abstract

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

Phys. Earth Planet. Inter.

Recent archaeomagnetic results in England

J. Geomagn. Geoelectr.

Palaeointensity studies on archaeological material from the Near East

Geomagnetic intensity in Egypt and western Asia during the second millennium BC

Nature

Paleointensity determination using the Thellier technique: reliability criteria

J. Geomagn. Geoelectr.

Geomagnetic intensity measurements using bricks from Greek churches of the first and second millennia AD

Archaeometry

Extension of the Holocene dendrochronology by the preboreal pine series, 8800 to 10 100 BP

Radiocarbon

Information on past solar activity and geomagnetism from 10Be in the Camp Century ice core

Nature

Dating the Aegean Late Bronze Age with radiocarbon

Archaeometry

Influence of the Earth's magnetic field on radiocarbon dating

The westward drift of the Earth's magnetic field

Philos. Trans. R. Soc. London

Archaeomagnetic investigations in the USSR

Holocene geomagnetic secular variation in the western United States: implications for the global geomagnetic field

U.S. Geol. Surv. Open-File Rep. 80–824

Geomagnetic paleointensities from radiocarbon-dated lava flows on Hawaii and the question of the Pacific nondipole low

J. Geophys. Res.

Lengths of geomagnetic polarity intervals

J. Geophys. Res.

Information on past solar activity and geomagnetism from ¹⁰Be in the Camp Century ice core