Geomagnetic field intensity in South America over the 500 years: New
archeointensity results from South Brazil
Abstract
Tracing the field in the past at the centennial and millennial timescale
(i.e., the archeomagnetic timescale) is important in improving
geomagnetic field models and also for field forecast analyses. The
distribution of archeomagnetic data across the globe is very
inhomogeneous with almost all data coming from the northern hemisphere,
particularly from Europe and Asia. Yet, the southern hemisphere is the
one presenting the highest variability for the past millennia and, it is
also the region comprising the South Atlantic Anomaly (SAA). The SAA is
characterized by the lowest total field intensity and it is presently
located in Southern Brazil. Some studies suggest that SAA is a
persistent field feature in South Atlantic for periods longer than
historical times, but the beginning of the influence of strong
non-dipole fields at the centennial-scale evolution in South Atlantic
region, could give important information about the recurrence of SAA at
longer timescales. Here, we report six new high-quality archeointensity
results for the Pelotas city region, in South Brazil with ages ranging
from 1790 to 1943 CE. Archeointensity measurements were performed with
the double heating technique, including partial termoremanent
magnetization (pTRM) checks and pTRM tail-checks. Measurements were
corrected from anisotropy of TRM and cooling-rate. Archeointensity
results vary from 36.4±0.6 μT to 27.8±2.0 μT. The new data complement
previous results obtained in South and Southeast Brazil, Argentina and
Chile and provide additional evidence for the rapid decay of the field
in the region. In addition, it demonstrates the gradual increase in the
contribution of non-dipolar components in the geomagnetic field of South
America since 1800 CE, therefore tracking the arrival of the South
Atlantic Anomaly to these times.