Deep beneath the equatorial Pacific, a broad region of Earth's molten outer core abruptly reversed its direction of flow around 2010, according to satellite and ground-based magnetic data — and scientists say they don't yet know why.
The finding, led by Frederik Dahl Madsen of the University of Edinburgh's School of GeoSciences, draws on magnetic-field observations collected between 1997 and 2025 from the European Space Agency's Swarm and CryoSat missions, along with Germany's CHAMP and Denmark's Ørsted satellites, combined with data from ground-based magnetic observatories. The study found that a region of the liquid iron outer core roughly 2,200 kilometers below the surface flipped from a weak westward flow to a strong eastward flow around 2010 — and that the eastward flow has itself been weakening again since 2020.
"The large-scale flow reversal beneath the Pacific raises new questions about the behavior of Earth's deep interior," Madsen said. Notably, the timing of the reversal coincides with independently detected unusual behavior in Earth's solid inner core, identified through separate seismic and geodetic studies — a coincidence that suggests the planet's core layers may be more dynamically coupled to one another than scientists had previously assumed.
"The rise of the strong eastward flow in the Pacific is contemporary with a change in behavior in the inner core," Madsen said, though the research does not establish a causal link between the two phenomena. The study, published in the Journal of Studies of Earth's Deep Interior with co-authors Isobel Howard, William Brown and Kathryn Whaler, challenges the long-standing assumption that large-scale circulation in the outer core is stable over long timescales.
Researchers say they want more satellite magnetic data to determine whether the Pacific reversal was a one-off event or part of a recurring pattern in Earth's deep interior — a question with implications for understanding how the planet's magnetic field, which shields life on Earth from harmful solar radiation, is generated and maintained deep below the surface.