Thallner - The Influence of Mantle Convection on Earth’s Geomagnetic Field Observables

THURSDAY APRIL 25, 2024
Daniel Thallner, University of Florida
Studying the geomagnetic field and its variations over geological timescales provides insights into the geodynamo and deep Earth processes. Notably, a significant weak-field anomaly in the paleomagnetic record during the Precambrian-Cambrian transition suggests a shift from a thermally driven to a compositionally driven geodynamo upon inner core nucleation. However, a similar field behavior is indicated by weak geomagnetic field strengths observed during the Devonian period, that could be related to flow pattern changes in the outer core between small and large inner core regimes. These periods of weak field strength align with cyclic fluctuations observed in the long-term paleointensity record, which mirrors the time scale of convective overturn in Earth's mantle. While the mantle's cooling history dominates the core's heat transport, its full impact on the geodynamo is still not well understood.
To quantify the impact of mantle convection on the long-term geomagnetic field, we compared numerical geodynamo simulations with heterogeneous core-mantle boundary (CMB) heat flux. We conducted 270 numerical geodynamo simulations with CMB heat flux boundary conditions reflecting seismic tomography models of present-day Earth and plate-driven 3D global mantle convection models for both the present-day Earth and different states throughout a supercontinent cycle. By pairing these boundary conditions to simulations with identical geodynamo core parameters, we can directly compare the resulting geomagnetic fields at Earth's surface. Preliminary findings indicate that simulations with more detailed CMB flux from 3D mantle convection models show increased dipole-dominated geomagnetic fields with reduced secular variation and a lower likelihood of polarity reversals relative to their counterparts with CMB heat flux based on seismic tomography. This indicates that simulations using long wavelength spatial heterogeneities may overestimate the variability of the resulting magnetic field.
Contributors: Daniele Thallner, Courtney Sprain, Juliane Dannberg, Rene Gassmoeller, Richard Bono, Chris Davies, Domenico Meduri, Andy Biggin