Tracing the origins and recurrence of the South Atlantic Anomaly: A 2000-year absolute paleointensity record from central South America

Abstract

A robust characterization of geomagnetic field strength in the Southern Hemisphere over the past millennia is critical for understanding the (multi)centennial evolution of the South Atlantic Anomaly (SAA), one of the most prominent geomagnetic features at Earth’s surface. Yet, robust absolute paleointensity records remain scarce in this region, introducing significant uncertainty into geomagnetic field reconstructions. Here, we present 41 absolute archeointensity determinations obtained using the Thellier–Thellier method from central South America spanning the last two millennia. Combined with a selection of high-quality records from the same region, these new data yield virtual axial dipole moment values broadly consistent with the other few available Southern Hemisphere datasets but generally lower than those from Europe, indicating a persistent north–south asymmetry in geomagnetic field strength. A new global geomagnetic field model incorporating these new data suggests that the observed asymmetry reflects a persistently northward-shifted eccentric dipole. In addition, the model tentatively suggests a westward migration of a nondipolar low-intensity anomaly between 1 and 850 CE, from the Indian Ocean to northern South America, following a trajectory broadly similar to that of the modern SAA, which appears in the Indian Ocean after 1100 CE and progresses across Africa before reaching South America. These findings support the hypothesis of a recurrent large-scale geomagnetic pattern and highlight multiscale geodynamic control on geomagnetic field morphology, in which mantle and core processes interact to shape secular variation patterns on centennial to millennial timescales.