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Geomagnetic field intensity in South America over the 500 years: New archeointensity results from South Brazil
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  • Gelvam Hartmann,
  • Wilbor Poletti,
  • Ricardo Trindade,
  • Lucio Ferreira,
  • Pedro Sanches
Gelvam Hartmann
Universidade Estadual de Campinas, Campinas, Brazil

Corresponding Author:[email protected]

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Wilbor Poletti
Universidade de São Paulo, Geophysics, Sao Paulo, Brazil
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Ricardo Trindade
Universidade de São Paulo, Geophysics, Sao Paulo, Brazil
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Lucio Ferreira
Universidade Federal de Pelotas, Departamento de Antropologia e Arqueologia, Instituto de Ciências Humanas, Pelotas, Brazil
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Pedro Sanches
Universidade Federal de Pelotas, Departamento de Museologia, Conservação e Restauro, Instituto de Ciências Humanas, Pelotas, Brazil
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Abstract

Tracing the field in the past at the centennial and millennial timescale (i.e., the archeomagnetic timescale) is important in improving geomagnetic field models and also for field forecast analyses. The distribution of archeomagnetic data across the globe is very inhomogeneous with almost all data coming from the northern hemisphere, particularly from Europe and Asia. Yet, the southern hemisphere is the one presenting the highest variability for the past millennia and, it is also the region comprising the South Atlantic Anomaly (SAA). The SAA is characterized by the lowest total field intensity and it is presently located in Southern Brazil. Some studies suggest that SAA is a persistent field feature in South Atlantic for periods longer than historical times, but the beginning of the influence of strong non-dipole fields at the centennial-scale evolution in South Atlantic region, could give important information about the recurrence of SAA at longer timescales. Here, we report six new high-quality archeointensity results for the Pelotas city region, in South Brazil with ages ranging from 1790 to 1943 CE. Archeointensity measurements were performed with the double heating technique, including partial termoremanent magnetization (pTRM) checks and pTRM tail-checks. Measurements were corrected from anisotropy of TRM and cooling-rate. Archeointensity results vary from 36.4±0.6 μT to 27.8±2.0 μT. The new data complement previous results obtained in South and Southeast Brazil, Argentina and Chile and provide additional evidence for the rapid decay of the field in the region. In addition, it demonstrates the gradual increase in the contribution of non-dipolar components in the geomagnetic field of South America since 1800 CE, therefore tracking the arrival of the South Atlantic Anomaly to these times.