Electrical conductivity of the suboceanic upper mantle constrained by satellite-derived tidal magnetic fields: 3-D inversion, validation and interpretation

We present the first three-dimensional (3-D) upper-mantle conductivity models obtained by an inversion of the satellite-derived tidally-induced magnetic fields (TIMFs). We primarily use the M2 period, but the potential benefit of the O1 period is also inspected. The inverse-problem solution is found using the recently developed frequency-domain, spherical harmonic-finite element method based on the adjoint approach. We tested two different TIMF data sets derived from the satellite measurements of the Swarm mission and two different regularizations; the solution is either required to be sufficiently smooth or reasonably close to the a-priori 3-D conductivity model WINTERC-e Wd-emax. The reconstructed conductivity models are locally compared with the 1-D conductivity profiles from other studies. If we use one of the available TIMF data sets, the smooth reconstructed model gravitates towards Wd-emax and the TIMF-adjusted Wd-emax model is closer to the reference conductivity profiles than the original Wd-emax model. Finally, we use the obtained 3-D conductivity distributions to calculate the corresponding 3-D water distribution in the upper mantle using thermodynamical and compositional models coupled to the electrical-conductivity laboratory measurement of individual mantle constituents.