Continuous millennial decrease of the Earth’s magnetic axial dipole

Poletti, Wilbor; Biggin, Andrew J.; Trindade, R. I.; Hartmann, Gelvam A.; Terra-Nova, Filipe

doi:10.1016/j.pepi.2017.11.005

Cited by 29 publications

(40 citation statements)

References 131 publications

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“…One of the main consequences is the poor knowledge of dipole moment variation prior to 1840. Models disagree when to know if the dipole moment decreased regularly since~750 CE (Poletti et al, 2018) or since~1700 CE after seven centuries of stability (Hellio & Gillet, 2018). The lack of data also prevents a precise understanding of geomagnetic anomalies at the Earth's surface such as the present South Atlantic anomaly (e.g., Campuzano et al, 2019;Terra-Nova et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Secular Variation of the Intensity of the Geomagnetic Field in Mexico During the First Millennium BCE

Hervé

Perrin

Alva‐Valdivia

et al. 2019

Geochem Geophys Geosyst

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In Western Eurasia, the first millennium BCE is characterized by the fastest secular variation of the Earth Magnetic Field observed over the last millennia and by a geomagnetic anomaly centered on the Middle East. On the global scale, the variation of the dipolar field during this period remains poorly constrained because of the lack of data in other geographical areas. Here, we presented 23 new mean archaeointensity data on ceramic sherds dated between 1500 BCE and 200 CE from Chalcatzingo archaeological site in Central Mexico. Archaeointensities were determined using the classical Thellier-Thellier protocol with corrections for TRM anisotropy and cooling rate effects. Our work doubles the number of high-quality archaeointensity data in Mexico during the considered period. Using a Bayesian approach, a new secular variation curve was calculated at Mexico City between 1500 BCE and 200 CE after selection of Mexican archaeointensity data. After a period of oscillations of the intensity between 20 and 40 μT from 1500 to 300 BCE, the curve shows a large maximum`~65 μT in the second century BCE. The corresponding VADM varied between~4.0 and~11.0 × 10 22 Am 2 , which highlights further that the intensity of the geomagnetic field could vary at regional scale over a larger range as previously thought. However, this amplitude variation may be overestimated, as it does not take into account the fast directional variation observed at this time.Plain Language Summary Archaeological baked clays are the best material to reconstitute the past secular variation of the Earth magnetic field, because they acquired a generally stable thermoremanent magnetization usually parallel and proportional to the ambient field at the time of their baking. Global modeling of the geomagnetic field requires a spatial and temporal distribution of data as homogeneous as possible, which is still not the case yet. In spite of its rich archaeological heritage, high-quality archaeointensity data are still very few in Mexico. The present study focuses on pottery sherds dated between 1500 BCE and 200 CE from Chalcatzingo archaeological site in Central Mexico. We obtained 21 new mean archaeointensities, which almost doubles the high-quality Mexican dataset for this period. The new secular variation Mexican curve exhibits oscillations of the intensity between 20 and 40 μT from 1500 to 300 BCE, before a large maximum~65 μT in the second century BCE. This work will help to have a better knowledge of the variation of the dipolar geomagnetic field during the first millennium BCE, when the fastest secular variation over the last millennia was reported in the Middle East ("geomagnetic spikes").

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Section: Introductionmentioning

confidence: 99%

Secular Variation of the Intensity of the Geomagnetic Field in Mexico During the First Millennium BCE

Hervé

Perrin

Alva‐Valdivia

et al. 2019

Geochem Geophys Geosyst

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“…Extending the record using paleomagnetic observations offers insights, but the message is not always clear. Paleomagnetic intensity measurements support a lower rate of decline over the past 1 kyr (Poletti et al, ), but there are several instances in the past 7 kyr when larger trends did not persist for long enough to cause a reversal (Constable & Korte, ).…”

Section: Introductionmentioning

confidence: 99%

Variability of Millennial‐Scale Trends in the Geomagnetic Axial Dipole

Buffett

Davis

Avery

2019

Geophysical Research Letters

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The historical trend in the axial dipole is sufficient to reverse the field in less than 2 kyr.Assessing the prospect of an imminent polarity reversal depends on the probability of sustaining the historical trend for long enough to produce a reversal. We use a stochastic model to predict the variability of trends for arbitrary time windows. Our predictions agree well with the trends computed from paleomagnetic models. Applying these predictions to the historical record shows that the current trend is likely due to natural variability. Furthermore, an extrapolation of the current trend for the next 1 to 2 kyr is highly unlikely. Instead, we compute the trend and time window needed to reverse the field with a specified probability. We find that the dipole could reverse in the next 20 kyr with a probability of 2%.

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“…Geomagnetic records at the scale of billions to millions of years were fundamental to demonstrate the tectonic movements of lithospheric plates, providing a means for quantitatively assess the dynamic configuration of the upper layers of the planet (e.g., Pesonen et al, 2003;Kono, 2010). On the other hand, the geomagnetic record at the scale of thousands of years to years (and less) is the way to probe the geodynamic processes acting at the deepest layers of the Earth, at the core and its neighborhood, including heat-flow changes at the core-mantle boundary, movements of the conductive fluid in the outer core, and interactions between the inner and outer cores, and the lower mantle (e.g., Kono, 2010;Aubert et al, 2013;Finlay et al, 2016;Poletti et al, 2018).…”

Section: ____________________________________________________________mentioning

confidence: 99%

“…Although there is some speculation about the origin of the geomagnetic jerks (e.g., Bloxham et al, 2002;Mandea et al, 2010;Demetrescu and Dobrica, 2014;Feng et al, 2018) its physical mechanism is still not fully understood. Centennial to millennial variations are investigated through records of geological and archaeological materials, and are essential to understand most of the operant physical mechanisms in the outer core at these timescales (e.g., Brown et al, 2015;Constable et al, 2006;Poletti et al, 2018), as well as physical interactions between the mantle and the core (e.g., Tarduno et al, 2015, Terra-…”

Section: ____________________________________________________________mentioning

confidence: 99%

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Archaeomagnetic field intensity evolution during the last two millennia

Silva¹

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Paulo pelo espaço a mim concedido, e também a todos os seus funcionários. Em especial, agradeço às técnicas Daniele Brandt e Sônia Alonso e ao técnico Giovanni Moreira por todo o suporte. Agradeço a todos aqueles que de alguma forma fizeram, ou ainda fazem, parte do USPMag: alunos de iniciação científica, mestrandos, doutorandos, pós-doutorandos, técnicos e professores. Em especial, aos colegas: Agradeço aos meus colega de pós-graduação do Departamento de Geofísica (USP) pelo convívio e ambiente agradável. Agradeço também imensamente aos membros e aos agregados da Sala-E208 do Departamento de Geofísica (USP) por me aguentarem e, principalmente, por toda conversa! Ressalto meus agradecimentos à Karine Carvas, minha grande amiga e por muitas vezes "psicóloga"! Agradeço ao meu irmão e parceiro, Clodoaldo Poletti, por todo o incentivo e força durante meu doutorado. Foram inúmeras as vezes em que ele me impulsionou quando eu titubeei. Sem dúvidas, um dos pilares mais fortes desse caminho. Agradeço à minha mãe, Ivane Poletti, por nunca deixar de me apoiar nos momentos em que me faltaram forças. Por me transmitir segurança e me tranquilizar, mesmo no momento em que vivia sua maior adversidade. E também, pela sua garra e, principalmente, por todo seu amor. Agradeço à minha parceira no crime, Grasiane Mathias. A intensidade na qual eu desenvolvi o meu doutorado foi apenas um reflexo da intensidade de minha vida pessoal, proporcionada justamente pela Grá. No período de um doutorado, nós namoramos, casamos, tivemos uma filha (que, por sua vez, me mostrou o que realmente é a vida!), moramos em outro país, nos permitimos e evoluímos. Hoje somos um time de três (Grá, Alice e eu) e somos mais fortes, como consequência direta do que vivemos juntos. A ciência não seria para mim tão bela e reveladora se Grá e Alice não fossem o filtro delicado de parte de minha miopia!iii Abstract ______________________________________________________________________ Temporal variations of Earth's magnetic field provide a great range of geophysical information about the dynamics at different layers of the Earth. Since it is a planetary field, regional and global aspects can be explored, depending on the timescale of variations. In this thesis, the geomagnetic field variations for the last two millennia were investigated. For that, some improvement on the methods to recover the ancient magnetic field intensity from archeological material were done, new data was acquired and a critical assessment of the global archaeomagnetic database was performed. Two methodological advances are reported, comprising: i) the correction for microwave method of the cooling rate effect, which is associated to the difference between the cooling times during the manufactory of the material and that of the heating steps during the archaeointensity experiment; (ii) a test for thermoremanent anisotropy correction from the arithmetic mean of six orthogonal samples. The temporal variation of the magnetic intensity for South America was investigated from nine new data, three ...

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Continuous millennial decrease of the Earth’s magnetic axial dipole

Cited by 29 publications

References 131 publications

Secular Variation of the Intensity of the Geomagnetic Field in Mexico During the First Millennium BCE

Secular Variation of the Intensity of the Geomagnetic Field in Mexico During the First Millennium BCE

Variability of Millennial‐Scale Trends in the Geomagnetic Axial Dipole

Archaeomagnetic field intensity evolution during the last two millennia

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