New archeointensity data from South Brazil and the influence of the South Atlantic Anomaly in South America

Abstract

We obtained 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 thermoremanent magnetization (pTRM) checks and pTRM tail-checks. Measurements were corrected from anisotropy of TRM and cooling-rate effects. Archeological sites providing successful results comprised: Charqueada Santa Bárbara (1790–1838 CE; 36.4 ± 0.6 μT), Chácara da Brigada Militar (1830–1851 CE; 32.6 ± 2.9 μT), Casa Número 08 (1878–1879 CE; 32.1 ± 3.1 μT), Colégio da Família de Eliseu Maciel (1881–1883 CE; 28.7 ± 2.7 μT), Fundação Simon Bolívar (1884–1889 CE; 30.1 ± 2.0 μT), Campus Porto UFPel (1942–1943 CE; 27.8 ± 2.0 μT). Two other sites did not provide meaningful results. 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 from about 1500 to 2000 CE. In addition, they show a gradual increase in the contribution of non-dipolar components in the geomagnetic field of South America since 1800 CE, likely indicating a strengthening of the South Atlantic Anomaly over the continent from this time onward.