Emergence and evolution of the South Atlantic Anomaly revealed by the new paleomagnetic reconstruction SHAWQ2k

The South Atlantic Anomaly (SAA) is one of the most outstanding features of the present geomagnetic
field. Thus, a good knowledge of the SAA is clue for a better understanding of the dynamical behavior
of the geomagnetic field. To achieve this goal, paleomagnetic data are crucial since they provide the
unique way to investigate past changes in the Earth’s magnetic field. Here, we present a new global
geomagnetic field reconstruction, the SHAWQ2k model, which is based on a critical revision of the
global archeomagnetic and volcanic dataset. The new model provides an improved description of the
geomagnetic field during the last 2 millennia, and yields surprising outcomes about the emergence and
development of the SAA. It shows that the reversed flux patch observed at the core-mantle boundary
and linked to the SAA, emerged in the Southern Hemisphere from at least 950 AD. This patch moved
westward from the equator to southern latitudes, being clearly isolated after 1400 AD. In addition, since
1550 AD a second reversed flux patch moving northeastward is observed in the North Atlantic. The new
data now available for the Southern Hemisphere coming from Africa and South America together with
the use of an appropriated weighting scheme in the modeling process have improved our understanding
of past geomagnetic field behavior and showed new evolutionary aspects of the SAA.