South Atlantic Anomaly recurrence revealed by 1500 yrs speleothem geomagnetic records

The Earth's magnetic field is rapidly decaying accompanying the growth of the South Atlantic Anomaly (SAA). The longevity and recurrence of this feature at millennial timescales is still elusive, mostly because of the scarcity of geomagnetic data in the region. Here we report a 1500 yrs geomagnetic record that combines the data of two well-dated stalagmites from the Pau d'Alho cave system, located close to the present-day minimum of the anomaly in central South America (western Brazil). Magnetic directions and relative paleointensity data (obtained with the pseudo-Thellier method) for both stalagmites are consistent throughout most of the interval analysed and agree with the available archeomagnetic data for the last 500 yrs. Before 1500 CE the data follow the ARCH3k.1 geomagnetic model that is based only on archeomagnetic data, and is markedly distinct from models that incorporate sediment data (e.g., HFM.OL1.A1, CALS3k.4e). Results reveal rapid directional variations (>0.1 deg.yr-1) at 860-960 CE and 1450-1750 CE, followed by stark decays in intensity (>0.05 mT.yr-1). Similarly rapid variations were reported for South Africa with a delay of 200 yrs relative to South America. These results suggest that fast geomagnetic field variations akin to those associated to the SAA are a recurrent feature in the region, the delay between continents probably reflecting the westward migration of the anomaly.