South Atlantic anomalies have appeared for millions of years

The South Atlantic Anomaly (SAA) is an important focus of research into the evolution of the Earth’s magnetic field. In this region between Africa and South America, the strength of the magnetic field is significantly weakened compared with areas at similar latitudes.

Some studies have suggested that the SAA is indicative of upcoming changes, such as a reversal of the magnetic field. But now, a new study shows that magnetic anomalies in the South Atlantic region are nothing new. 

Researchers at the University of Liverpool have found evidence that  anomalies appeared in the South Atlantic as far back as eight to 11 million years ago. According to the study authors, it is unlikely that the recurring activity signals an impending reversal of the Earth’s magnetic field.

The geomagnetic field protects the planet from harmful radiation by deflecting solar wind that would otherwise destroy the ozone layer. However, the field is not entirely stable and has the potential to reverse itself, as it has done many times in the past.

The most obvious impacts of the SAA are technical malfunctions on satellites and spacecraft as they are exposed to strong radiation in the region.

The Liverpool researchers focused their analysis on igneous rocks from Saint Helena, an island located within the South Atlantic Anomaly. The rocks preserve historical evidence of the behavior of Earth’s magnetic field.

The rocks were found to contain geological records of 34 different volcanic eruptions which occurred between eight and 11 million years ago. The analysis showed that at the time of these eruptions, the direction of the magnetic field for St. Helena often pointed far from the North pole – as it still does today.

“Our study provides the first long term analysis of the magnetic field in this region dating back millions of years. It reveals that the anomaly in the magnetic field in the South Atlantic is not a one-off, similar anomalies existed eight to 11 million years ago,” said study lead author PhD student Yael Engbers.

“This is the first time that the irregular behavior of the geomagnetic field in the South Atlantic region has been shown on such a long timescale. It suggests that the South Atlantic Anomaly is a recurring feature and probably not a sign of an impending reversal.”

“It also supports earlier studies that hint towards a link between the South Atlantic Anomaly and anomalous seismic features in the lowermost mantle and the outer core. This brings us closer to linking behavior of the geomagnetic field directly to features of the Earth’s interior.”

The study is published in the Proceedings of National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer