Physicists explain why changes in Earth’s magnetic field are weaker in the Pacific

A new study by physicists at the University of Alberta provides an explanation for why changes in Earth’s magnetic field over time are weaker in the Pacific region, a mystery that scientists have been trying to solve for almost a century.

“This is something that has been a puzzle since the 1930s when it was first noticed,” said geophysicist Mathieu Dumberry, lead author of the study.

Like winds in the atmosphere or currents in the ocean, there are fluid movements in Earth’s liquid core, Dumberry explained. These core fluxes generate and maintain Earth’s magnetic field, giving us the Northern Lights and protecting us from charged particles in space. Scientists model the magnetic field for a variety of applications, including determining its orientation when looking at a map on your smartphone.

“Core flows are weaker in the Pacific and also have a planetary-scale current that hangs near the equator in the Atlantic region, but then drifts to a higher latitude in the Pacific region,” Dumberry said. “But why is that? That is the part that was not understood.”

Looking at the field can also give a new insight into the core flows that create it, Dumberry said.

“Our explanation involves the electrical conductivity of the lower mantle,” said Dumberry. “We show that if the lowest mantle conductance is higher under the Pacific than anywhere else on the planet, and this larger ‘magnetic friction’ weakens local core fluxes, it also diverts the main planetary current flux away from the region. Pacific as it avoids the region of highest conductance, leading to smaller changes in Earth’s magnetic field in the region. “

Dumberry noted that the model raises new questions about the composition of the core-mantle boundary region and what it can tell us about other regions of Earth.

“Our study highlights that the core-mantle boundary region is quite heterogeneous. The lowest mantle conductance is probably not uniform across the world,” he said.

“We hope that our results will motivate geophysicists to further investigate possible differences between the Pacific region and other locations at the central mantle boundary.”

The study, “Weak Changes in the Magnetic Field Over the Pacific Due to High Conductance in the Lower Mantle,” was published in Nature Geoscience.