The South Atlantic Anomaly: The Key for a Possible Geomagnetic Reversal

Abstract

The South Atlantic Anomaly is nowadays one of the most important features of the Earth's magnetic field. Its extent area at the Earth's surface is continuously growing since the intensity instrumental measurements are available covering part of the Southern Hemisphere and centered in South America. Several studies associate this anomaly as an indicator of an upcoming geomagnetic transition, such an excursion or reversal. In this paper we carry out a detailed study about this issue using the most recent models that also include data from the last ESA mission Swarm. Our results reveal that one of the reversed polarity patch located at the CMB under the South Atlantic Ocean is growing with a pronounced rate of −2.54·10 5 nT per century and with western drift. In addition, we demonstrate that the quadrupole field mainly controls this reversal patch along with the rapid decay of the dipolar field. The presence of the reversal patches at the CMB seems to be characteristic during the preparation phase of a geomagnetic transition. However, the current value of the dipolar moment (7.7 10 22 A 2 ·m ) is not so low when compared with recent paleomagnetic data for the Holocene (last 12 ka) and for the entire Brunhes geomagnetic normal polarity (last ∼0.8 Ma), although the rate of decay is similar to that given by previous documented geomagnetic reversals or excursions.

Latitudinal variation rate of geomagnetic cutoff rigidity in the active Chilean convergent margin

“…In the same line, Florindo and Alfonsi (1995), thought that seismic events could be linked to abrupt topographic changes at the CMB, which generated magnetic variations through the mantle. Another possible explanation of this apparent link between magnetic field, cutoff rigidity and geological systems arises from the instabilities in the CMB that are able to produce secular variations in the magnetic field on the Earth surface, and that corresponds to non-dipolar evolution of the geodynamo (Constable, 2007), since the topography of the CMB is significant in subduction zones, where the subducted slabs can generate downwelling or sinkholes in the deeper areas of the mantle and upwelling or outcrops in areas of divergence (Heirtzler, 2002;Koper, 2003;Hartmann and Pacca, 2009;Lassak et al, 2010;Calkins et al, 2012;Koelemeijer et al, 2012;Bayanjargal, 2013;Tarduno et al, 2015;Pavón-Carrasco and De Santis, 2016;Terra-Nova et al, 2016). However, the latest research on magnetic field and seismicity seems to come from the socalled lithosphere-atmosphere-ionosphere coupling (LAIC) (Hayakawa et al, 2015;De Santis et al, 2015Contoyiannis et al, 2016;Potirakis et al, 2016a, b;Oikonomou et al, 2017).…”

“…This extension of the Chilean flat slab trench towards the CMB is important because the latest research shows that the role played by CMB topography is closely related to the evolution of geodynamic and in particular to the existence of SAMA (Gubbins, 1988;Olsen et al, 2014;Tarduno et al, 2015;Pavón-Carrasco and De Santis, 2016). In addition, as the radial component of the Earth's magnetic field can be used as a measure of the variations in the CMB in periods of time of several months or years, we looked for significant variations in the geomagnetic spectra associated with other major geological events in the Chilean margin, as the latest research shows a statistically significant relation between geomagnetism and earthquakes (Hayakawa and Molchanov, 2002;Pulinets and Boyarchuk, 2004;Varotsos, 2005;Hayakawa et al, 2007Hayakawa et al, , 2015; Molchanov and Hayakawa, 2008;Liu, 2009;De Santis et al, 2015Contoyiannis et al, 2016;Potirakis et al, 2016a, b).…”

Extending Global Continuous Geomagnetic Field Reconstructions on Timescales Beyond Human Civilization

“…Ground and satellite observations reveal a decay of the geomagnetic axial dipole during the last 170 years (Finlay et al, ), an observation confirmed by recent measurements of the global geomagnetic field by the satellite mission Swarm (Olsen et al, ). It has been repeatedly suggested that this weakening of the geomagnetic field may indicate an impending excursion or reversal (Gubbins, ; Hulot et al, ; Laj & Kissel, ; Pavón‐Carrasco & De Santis, ). However, in general, decreases like the present one are followed by subsequent periods of recovery in field strength.…”

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

“…The rapid decay of Earth's dipole moment over the past two centuries (Gubbins et al, ; Jackson et al, ) is also associated with rapid changes in field morphology (Hulot et al, ). These observations have prompted speculation that the present behavior of the geodynamo is unusual (De Santis & Qamili, ; Laj & Kissel, ; Pavón‐Carrasco & De Santis, ) and provide motivation for improving our knowledge of the temporal evolution of the geodynamo further back in time. In particular, efforts have focused on improving the spatial and temporal coverage of archeomagnetic and paleomagnetic records over the past two millennia.…”