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SUMMARY Gaining insight into the centennial evolution of the geomagnetic field over the past 2000 yr requires the acquisition of reliable palaeomagnetic data from the study of well-dated archaeological materials or rocks. However, despite previous efforts, palaeointensity data from regions south of 30°S are still underrepresented, potentially limiting the accuracy of global geomagnetic field models and their applications. In addition, a comprehensive understanding of the geomagnetic field evolution in South America is particularly relevant, as the recent geomagnetic secular variation has been mainly characterized by the significant growth of the South Atlantic Anomaly over the past three centuries. The evolution of this low-intensity region, currently centred over central South America, is well understood in detail only during the last few centuries, thanks to the availability of direct measurements. For both the geomagnetic and palaeomagnetic communities, understanding its evolution prior to this period remains a challenge. This study presents new palaeointensity estimates from San Juan Province, central western Argentina, based on the analysis of 23 pottery samples dated between the 3rd and 17th centuries CE using radiocarbon and archaeological constraints. We employed the Thellier-Thellier method, incorporating partial thermoremanent magnetization (pTRM) checks, TRM anisotropy corrections and cooling rate adjustments, and obtained 11 mean palaeointensity values of good technical quality for central South America. The results are consistent with the limited number of previously reported high-quality palaeointensity data within an area 900 km in radius centred on San Juan, all showing intensity values ranging from approximately 40 to 55 T. The new data, combined with these previously published high-quality intensities, do not show anomalously low values in intensity in the region between 200 and 1750 CE, suggesting no significant impact of the South Atlantic Anomaly in the region before the past three centuries. Furthermore, the findings suggest the presence of rapid multidecadal variations between 800 and 1100 CE, a behaviour also observed in other regions worldwide, which may point to a global or dipolar origin for these variations. By enhancing the data set for this latitude range, this work provides new constraints on the geomagnetic field’s past behaviour south of 30°S over South America and contributes to improving future global geomagnetic reconstructions.
Gómez‐Paccard et al. (Thu,) studied this question.