New Archeomagnetic Directional Records From Iron Age Southern Africa (ca. 425–1550 CE) and Implications for the South Atlantic Anomaly

Abstract

The paucity of Southern Hemisphere archeomagnetic data limits the resolution of paleosecular variation models. At the same time, important changes in the modern and historical field, including the recent dipole decay, appear to originate in this region. Here a new directional record from southern Africa is presented from analysis of Iron Age (ca. 425–1550 CE) archeological materials, which extends the regional secular variation curve back to the first millennium. Previous studies have identified a period of rapid directional change between 1225 and ∼1550 CE. The new data allow us to identify an earlier period of relatively rapid change between the sixth and seventh centuries CE. Implications for models of recurrent flux expulsion at the core‐mantle boundary are discussed. In addition, we identify a possible relationship of changes recorded in these African data with archeomagnetic jerks.

Characterization of the South Atlantic Anomaly

“…There are a number of damages that spacecraft sustain while in orbit. These range from space debris, problems with the vacuum of space, various problems associated with the plasma environment, and various problems explicitly associated with the radiation environment (Heirtzler, 2002). One of the cases is that of the International Space Station, which needs additional shielding to deal with this sort of problem.…”

“…A research study on the future of the SAA in addition to implications for radiation harm in space was carried out by Heirtzler (2002). In this research, the SAA showed an important part of the harmful effects of radiation which happens close to the world's orbit.…”

Preferred locations of weak surface field in numerical dynamos with heterogeneous core–mantle boundary heat flux: consequences for the South Atlantic Anomaly

“…In addition, based on archeological materials from Africa and South America, it was argued that rapid local temporal geomagnetic field variations in these regions are attributed to the SAA time evolution (e.g. Hartmann et al 2010Hartmann et al , 2011Tarduno et al 2015;Poletti et al 2016;Shah et al 2016;Hare et al 2018;Trindade et al 2018). Accordingly, the SAA may be locked to the South Atlantic at the surface, perhaps alternating between Africa and South America.…”

Archaeomagnetic field intensity evolution during the last two millennia

“…Recent geodynamo models (e.g., Aubert et al, 2013) suggest that the secular variations observed in the surface geomagnetic field might be associated with compositional and thermal heterogeneities revealed by seismic tomography in the inner core and at the core-mantle boundary (e.g., Burke et al, 2008). For the southern hemisphere, a direct link between long-lived mantle heterogeneities and the SAA have been postulated, where a large low shear velocity province (LLSVP) at the core-mantle boundary beneath Africa would be a preferential site for the expulsion of reversed magnetic flux from the core (Tarduno et al, 2015;Hare et al, 2018). Since the LLSVP is a geographically fixed region with an age greater than >100 Ma (Burke et al, 2008), if the SAA generation is linked to it, then the SAA is expected to be a recurring (or persistent) feature.…”

“…In Africa, important results both from directional and intensity data were obtained last years (e.g. Casas et al, 2008;Goméz-Paccard et al, 2012;Neukirch et al, 2012;Mitra et al, 2013;Donadini et al, 2015;Osete et al, 2015;Tarduno et al, 2015;Kapper et al, 2017;Hare et al, 2018), in order to describe secular variation of SAA; most of them, indicate a rapidly westward drift accompanied to a decrease in field intensity for the past few centuries (e.g. Tarduno et al, 2015).…”