New archeointensity data from NW Argentina (1300–1500 CE)

Abstract

A good characterization of the geomagnetic field strength at centennial to millennial time scales in the Southern Hemisphere is particularly crucial to disentangle the long-term evolution of the South Atlantic Anomaly (SAA), an intriguing geomagnetic feature currently observed at the Earth’s surface. Here we present 59 new archeointensities obtained from four well-dated groups of potteries with ages ranging between 1300 and 1500 CE and collected in Northwest Argentina. The new data were obtained in accordance with the Thellier paleointensity method including partial thermoremanent magnetization (pTRM) checks and TRM anisotropy and cooling rate corrections. We have also performed a comparative study of the efficiency of magnetic susceptibility, ARM and TRM anisotropy tensors to correct the TRM anisotropy effect upon intensity estimates. Our results suggest that the magnetic susceptibility tensor systematically underestimates the TRM anisotropy effect by 10–30%. Our new data, together with selected archeointensities already published, confirm that the decrease of the geomagnetic field intensity in South America started around 1600–1650 CE, due to the arrival of the SAA.