Magnetic Field Anomaly Probably Not Linked to Pole Reversal: Study

A map of the Earth showing the present-day deviation from expected magnetic field direction. Strong deviations are in yellow-orange, and little deviations are in blue. The star is Saint Helena, which is right in the anomaly. The gray line shows the outline of the seismic area that is warmer than the rest of the mantle. (Dr. Yael Engbers / University of Liverpool)

(CN) — Strange geomagnetic activity has occurred in the South Atlantic for millions of years and researchers say what is known as the South Atlantic Anomaly is a recurring event and unlikely to represent an impending reversal of Earth’s magnetic field.

The results of the study by University of Liverpool researchers extend the persistence of anomalous activity from thousands to millions of years and support the idea that the anomaly is linked to interactions at the interface of the mantle and core.

Liquid iron flowing in the Earth’s core generates a magnetic field that protects the atmosphere from solar wind — charged particles coming from the sun. The magnetic field allows us to navigate using a compass while also protecting our atmosphere from solar wind. The anomalous geomagnetic field increases solar particles in the atmosphere, potentially hindering satellites. Because is not stable, the magnetic field can and has throughout history become reversed.

The South Atlantic Anomaly is an area where Earth’s magnetic field is weakened, reducing protection from harmful space radiation. Signs of this include technical malfunctions aboard satellites and spacecraft.

“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,” said lead researcher Yael Engbers, a doctoral student at University of Liverpool, in a statement accompanying the study. “It suggests that the South Atlantic Anomaly is a recurring feature and probably not a sign of an impending reversal.”

Paleomagnetic researchers analyzed Earth’s magnetic record preserved in igneous rocks from the island of Saint Helena, in the heart of the anomaly. The geomagnetic records from 34 different volcanic eruptions that took place between 8 and 11 million years ago revealed that the direction of the magnetic field for St. Helena often pointed far from the North Pole, as it does today, according to a study published in the Proceedings of the National Academy of Sciences.

Engbers and colleagues analyzed volcanic rocks from Saint Helena, which was formed by two shield volcanoes, to determine whether the anomaly existed at the time of the eruptions. Because the basalt would reflect the orientation of the magnetic field at the time the lava cooled, the authors analyzed 225 core samples from 46 basalt flows on the island to determine the original magnetization direction of the samples. The results revealed variation in magnetic field directions that was higher than expected at the latitude.

Scientists debate the South Atlantic Anomaly, raising questions about where it comes from and whether it represents the start of a planet-wide weakening of the magnetic field and a possible upcoming pole reversal.

“Our study provides the first long-term analysis of the magnetic field in this region dating back millions of years,” Engbers said. “It reveals that the anomaly in the magnetic field in the South Atlantic is not a one-off, similar anomalies existed 8 to 11 million years ago.

“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 research was undertaken by the University of Liverpool’s DEEP (Determining Earth Evolution from Palaeomagnetism) research group and the Geomagnetism Laboratory.

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