Stratification at the Top of the Outer Core: Constraints from Smks and Pmkp Phases

Abstract:

Convection in the Earth's outer core is responsible for the generation of the planet's magnetic field and is strongly dependent on interactions between the mantle and inner core. However, despite undergoing vigorous convection, the outer core is not necessarily a single uniform, homogeneous layer of the Earth. Recent seismic and geomagnetic studies suggest that the uppermost outer core is comprised of a chemically distinct layer of stably stratified material. This layer is likely enriched in light elements, which may either be accumulating due to the release of light elements during the solidification of the inner core, or due to a flux of material across the core mantle boundary.

Here we compile a new dataset of SmKS and PmKP differential travel time data to investigate the vertical and geographical extent of stratification in the uppermost outer core. By jointly considering SmKS and PmKP phases, carefully correcting for known mantle structures, exploring the effect of core mantle boundary topography, and considering changes in the core over recent time, we are able to place new constraints on this stably stratified layer at the top of the outer core.