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Abstract:
The South Atlantic geomagnetic Anomaly (SAA) is known as a region of the geomagnetic field that is approximately
25 T in intensity, compared to an expected value of 43 T. Geomagnetic field models do not find
evidence for the SAA being a persistent feature of the geomagnetic field, however these models are constructed
from paleomagnetic data that is sparse in the southern hemisphere. We present a full-vector paleomagnetic study
of 40Ar/39Ar dated Late Pleistocene lavas from Tristan da Cunha in the South Atlantic Ocean (Shah et al., 2016;
EPSL). Paleointensity estimations using the Thellier method of eight lava flows yield an average paleointensity of
the Tristan da Cunha lavas as 18 6 T and an average virtual axial dipole moment (VADM) of 3.1 1.2 1022
Am2. Comparing the VADM of the lava flows against the PADM2M, PINT and SINT-800 databases indicates that
the lava flows represent four distinct periods of anomalously weak intensity in the South Atlantic between 43 and
90 ka ago, constrained by newly obtained 40Ar/39Ar ages. This anomalously weak intensity in the Late Pleistocene
is similar to the present-day SAA and SAA-like anomalous behavior found in the recent archeomagnetic study by
Tarduno et al. (2015; Nat. Commun.). Our dataset provides evidence for the persistence or recurrence of geomagnetic
main field anomalies in the South Atlantic, and potentially indicates such anomalies are the geomagnetic field
manifestation of the long-existing core-mantle boundary heterogeneity seismically identified as the African Large
Low Velocity Shear Province (LLSVP).
