The blue region represents the anomaly of the South Atlantic.
Geomagnetism Division, DTU Space / ESA
Earth’s magnetic field has been acting a little awkward. A region in the southern Atlantic Ocean, from Africa to South America, has experienced a severe weakening since the 1950s and in the past five years, the anomaly appears to be ready to split in two. This has caused some concern, because the magnetic field acts as a protective blanket for the planet, protecting us from charged particles circulating through space. Some have suggested that the anomaly may presage a reversal of our magnetic poles, wreaking havoc on electricity and navigation systems.
But a new study, published in the Proceedings of the National Academy of Sciences on Monday, suggests that the anomaly may not be as unusual as it seems; in fact it can happen regularly, if you are in the universe clock.
Researchers from the University of Liverpool analyzed rocks from volcanic eruptions that took place between eight and 11 million years ago. Previous research has shown that the anomaly has been around for a thousand years or more, but the Liverpool team was able to look even further back in time.
The team collected 225 samples from 46 different locations on Saint Helena, an island in the South Atlantic that lies beneath the magnetic field anomaly and is home to two volcanoes that formed during the same time period.
Volcanic rock provides a window through time, allowing researchers to understand what the magnetic field was like eons ago. When the lava flows cool and harden, the minerals “trapped” inside record the intensity and direction of the magnetic field at that time.
“Our study provides the first long-term analysis of the magnetic field in this region that dates back millions of years,” said Yael Engbers, a doctoral student at the University of Liverpool. “It suggests that the South Atlantic Anomaly is a recurring feature and is probably not a sign of an impending reversal.”
The researchers hypothesize that their finding also supports the idea that interactions in Earth’s innermost layers are likely responsible for the strange weakening of the field. Scientists have discovered a large region of rock in Earth’s mantle below the anomaly, called the African Low-Shear High-Speed Province (ALLSVP). Changes in the geochemical composition of this ALLSVP may be causing the weakening.
“This brings us closer to linking the behavior of the geomagnetic field directly to the characteristics of the Earth’s interior,” Engbers said.
Understanding the anomaly will be important for space-based research and satellite security in the future. A spacecraft from the Japanese space agency known as Hitomi is believed to have been affected by the anomaly. Because the magnetic field is weaker, spacecraft that traverse the region are more exposed to the dangers of space radiation. In 2016, when Hitomi went through the SAA, he suffered a communication problem. Soon after, he lost altitude and separated.
