An international team led by the Institute of Geosciences (IGEO, CSIC-UCM) demonstrated that 2,000 years ago there were already low-intensity geomagnetic anomalies similar to the current South Atlantic Anomaly (SAA).
The study, published in the journal PNAS, confirms that this phenomenon is not exclusive to the present but is part of a recurring process that operates on millennial scales.
What is the South Atlantic Anomaly
The SAA is an area where the Earth’s geomagnetic field is especially weak, allowing greater penetration of cosmic radiation. This weakening represents an increasing risk for:
- Satellites and space missions, which may suffer electronic failures.
- Technological systems, vulnerable to radiation.
Reconstruction of the magnetic field
The study reconstructed the evolution of the magnetic field in the southern hemisphere over the last two millennia. For this, 41 new absolute intensity determinations were obtained from archaeological materials from northwestern Argentina, close to the current center of the SAA.
- These materials, heated in ancient processes such as cooking, preserved signals of the magnetic field of their time.
- The measurements were carried out in archaeomagnetism laboratories with great precision.
By integrating these data with previous records, scientists developed a new global geomagnetic model, which allows analyzing the dynamics of the Earth’s outer core, where the magnetic field is generated.
Anomaly migration
The model confirms that the anomaly associated with the SAA originated under the Indian Ocean around the year 1000 and then migrated westward, crossing Africa and reaching America. It also reveals a similar episode during the first millennium, with a comparable trajectory.
According to CSIC researcher Miriam Gómez-Paccard, this indicates that the SAA is the most recent expression of a recurring geomagnetic process.
Complexity of the internal “engine”
Co-author F.J. Pavón-Carrasco highlighted that the lack of data in the southern hemisphere generated uncertainties. By incorporating new high-quality records, the model shows coherent and recurring patterns.
The results suggest a multiscale geodynamic control, conditioned by:
- Influences of the deep mantle beneath Africa.
- Dynamics of the Earth’s outer and inner core.
This confirms that the internal engine generating the magnetic field is much more complex than it seemed and that its future evolution, including the SAA, remains difficult to predict.
Implications and future
Although anomalies may weaken or disappear, the mechanisms and time scales are still unpredictable. Therefore, the authors emphasize the importance of expanding the archaeomagnetic records in the southern hemisphere, which will allow improving models and projecting the behavior of the Earth’s magnetic field more accurately.
The finding shows that the South Atlantic Anomaly is not an isolated phenomenon but part of a geomagnetic cycle that repeats over millennia. Understanding these processes is vital to anticipate technological and space risks and to deepen the knowledge of the internal “engine” of our planet.
