Can we identify mantle influence in paleomagnetic field reconstructions with help from geodynamo simulations?

Abstract:

Geomagnetic excursions are traditionally defined by extreme directional field changes and are contemporaneous with intensity lows. Virtual geomagnetic poles (VGP) are often used to compare directional field variations from different locations. Several paleomagnetic sediment records have been used to suggest preferred longitudinal bands for VGPs during excursions and reversals, and these results appear to be supported by some numerical simulations that employ “tomographic boundary conditions”. New geomagnetic field models based on paleomagnetic data and spanning up to 100 kyr support some longitudinal preference in VGP paths during field excursions. Moreover, they contain indications of a recurring intensity low in positions similar to the present-day minimum intensity area known as the South Atlantic Anomaly. Preferred longitudinal structures in geomagnetic field characteristics might be linked to the influence of heterogeneous heat flow through the core-mantle boundary (CMB) on the geodynamo process in Earth’s outer core. Indications for laterally heterogeneous structures in the deep mantle that would lead to heterogeneous heat flow through the CMB are also found in seismology. Findings from seismic tomography can be used to impose plausible heat-flow patterns on numerical geodynamo simulations to study the influence on the magnetic field morphology. Numerical simulations allow a full exploration of potential biases arising from limited spatial and temproral resolution in paleofield models. We compare statistics of magnetic field properties like VGPs and intensity minima that might be indicative of mantle control on the geodynamo from paleomagnetic field models and from numerical simulations with both homogeneous and heterogeneous CMB boundary conditions and assess support for the hypothesis that processes in the lowermost mantle influence the geodynamo process.