Flament et al. (2026) identify a statistically significant correlation between inertia-corrected equatorial core-mantle boundary (CMB) heat flux heterogeneity and geomagnetic reversal frequency over the past 170 million years. “While a link has been proposed between geomagnetic reversal frequencies and the history of subduction, mantle convection, and an equatorial CMB heat flux minimum during superchrons, a statistically significant relationship between CMB heat flux and reversal frequency in mantle flow models remains to be established. Importantly, most previous studies (1) used mantle flow models in reference frames with significant lithospheric net rotation, which is problematic (Flament et al., 2022), (2) did not place results in the reference frame of the core by removing inertia, and (3) did not investigate the relative difference between equatorial and polar heat flux.”
This new study addresses those gaps, finding that geomagnetic reversal frequency correlates closely with changes in CMB heat flux heterogeneity — but only once that heat flux is corrected for Earth's inertia. This correction accounts for shifts in the planet's mass distribution, which cause the spin axis and rotational axis to realign through True Polar Wander (TPW).
Figure 1 illustrates this mechanism: (a) a schematic of TPW (green arrows), driven by the distribution of mass within Earth via global mantle convection, with dashed black lines denoting the magnetic field and eddy currents in the outer core shown as thick grey coils. The thickness of sinuous white arrows indicates heat flux amplitude, ranging from low heat flux beneath BLOBS (basal mantle structures) to large heat flux beneath subducted material. (b) shows present-day CMB heat flux for case C2, with present-day coastlines in solid white.
The key driver behind this correlation is the equatorial migration of BLOBS — large thermochemical piles at the base of the mantle. When these structures spread wider around the equator (over 70% coverage), as happened during the Jurassic reversal hyperactivity period, the resulting heat flux variability appears to destabilize the geomagnetic field and trigger frequent reversals. Conversely, when BLOBS coverage contracted (below 60%), as during the Cretaceous Normal Superchron, heat could transfer out of the core more efficiently, stabilizing outer core convection and suppressing reversals for tens of millions of years. Notably, the relationship between equatorial BLOBS area and heat flux heterogeneity is remarkably strong once inertia-corrected (r = 0.99 for the preferred model case, up from r = 0.64 uncorrected), making BLOBS migration the most robust statistical driver identified in the study.
Critically, this effect is specific to the equatorial region.
Polar CMB heat flux followed an opposite trajectory — increasing steadily toward the present rather than tracking the JHP/CNS pattern — and showed no consistent relationship with reversal frequency across model cases. Likewise, global CMB heat flux magnitude and global heat flux heterogeneity showed no significant correlation with reversals at all. It is specifically the amplitude of equatorial heat flux heterogeneity, once corrected for inertia, that tracks the reversal record — underscoring that reversal frequency is governed by regional, not global, patterns of core-mantle heat exchange.
Crucially, the team shows this pattern emerges at finer spatial detail (spherical harmonic degrees 2–4) than earlier models considered, and that correcting for inertia and removing spurious lithospheric net rotation from tectonic reconstructions was essential to uncovering the relationship — without these corrections, earlier studies found the opposite (and incorrect) relationship. The findings open new directions for exploring how CMB heat flux heterogeneity influences outer core stratification and, in turn, the stability of Earth's magnetic field.
Geomagnetic reversals are modulated by the motion of basal mantle structures
Nicolas Flament et al. (20216)
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