Scientists detect abrupt 2010 reversal in molten iron 2,200 km down—and still can’t explain it.
Deep beneath the Pacific, a vast current of liquid iron in Earth’s outer core quietly changed course. What had been a weak westward drift switched to a strong eastward surge around 2010. Researchers only pieced the shift together years later from satellite and ground data spanning 1997 to 2025.
The discovery, published in the Journal of Studies of Earth’s Deep Interior, challenges the long-held view that large-scale outer-core circulation stays relatively steady. Lead author Frederik Dahl Madsen of the University of Edinburgh’s School of GeoSciences said the reversal “raises new questions about the behavior of Earth’s deep interior.”
How satellites spotted the flip
Earth’s magnetic field is generated by the motion of electrically conducting molten iron and nickel in the outer core, roughly 2,200 kilometers below the surface. Tiny changes in that field, measured from space and ground observatories, let scientists reconstruct the flow at the core-mantle boundary.
Madsen’s team combined data from ESA’s Swarm and CryoSat missions with earlier records from Germany’s CHAMP and Denmark’s Ørsted satellites. Principal-component analysis showed that about 95 percent of the flow variance belongs to a relatively stable eccentric planetary gyre. A second component, accounting for roughly 4 percent, captures the Pacific anomaly: weak westward motion before 2010, then a clear shift to strong eastward flow after about 2012. The eastward current peaked and has weakened since 2020.
Links to the deeper core?
The Pacific region lies outside the main gyre that dominates flow under the Atlantic hemisphere. Scientists had long regarded it as comparatively quiet. The sudden, large-scale reversal—accounting for a noticeable fraction of surface flow—suggests the outer core can reorganize on timescales of a decade or less.
Madsen and colleagues note the timing coincides with changes in the solid inner core inferred from geodesy and seismology. They hypothesize that deeper processes may have triggered the surface-flow shift, though the exact mechanism remains unknown. ESA scientist Elisabetta Iorfida observed that the findings challenge assumptions of stable westward circulation and show regional changes can emerge rapidly.
No surface threat—yet new insight
The changes occur far below the crust and pose no immediate risk to people or climate. They do, however, refine models of the geodynamo that sustains Earth’s protective magnetic shield. Continued satellite monitoring will reveal whether the eastward flow is a temporary fluctuation, part of a longer oscillation, or a new equilibrium.
As Madsen put it, scientists now need to determine which of those possibilities is unfolding. The planet’s hidden engine, it turns out, is more restless than many expected.