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An explanation for why changes to Earth’s magnetic field are weaker over the Pacific

New research may solve a mystery that has puzzled scientists for nearly a century.

Like winds in the atmosphere or currents in the ocean, there are fluid motions in the liquid core of the Earth. These core flows generate and maintain the Earth’s magnetic field, which gives us the Northern Lights and shields us from charged particles from space.

Core flows are weaker under the Pacific and also feature a planetary-scale current that hangs close to the equator in the Atlantic region, but then is deflected to higher latitude in the Pacific region. But why is that? That is the part that was not understood.

Now a new study by the University of Alberta has provided an explanation for why changes to Earth’s magnetic field over time are weaker over the Pacific region—a mystery scientists have been trying to solve for nearly a century.

Mathieu Dumberry, the lead author of the study, said, “Our explanation involves the electrical conductivity of the lowermost mantle. We show that if the conductance of the lowermost mantle is higher under the Pacific than elsewhere on the planet. This larger ‘magnetic friction’ weakens the local core flows; it also deflects the main planetary current flow away from the Pacific region as it avoids the region of higher conductance, leading to smaller changes in the Earth’s magnetic field in the region.”

Our study highlights that the core-mantle boundary region is quite heterogeneous. The conductance of the lowermost mantle is most probably not uniform around the globe,” he said.

“We hope that our results will motivate geophysicists to investigate further the possible differences between the Pacific region and elsewhere on the core-mantle boundary.”

Journal Reference:
  1. Dumberry et al., Weak magnetic field changes over the Pacific due to high conductance in the lowermost mantle. Nature Geoscience, (2020). DOI: 10.1038/s41561-020-0589-y

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