Rapid mass redistributions in the deep mantle from satellite gravity and interactions with core flows

Constraining the transport of mass in the Earth’s mantle over a broad range of timescales is a key step in order to understand the mantle convection and its dynamic interactions with tectonic plates and core flows. Mapped with high accuracy all over the globe from GRACE and GRACE Follow-On satellite missions, the temporal variations of the gravity field can provide unique information on potential rapid mass redistributions within the Earth’s deep interior, even if their separation with the signals from the Earth’s fluid enveloppe is challenging. In the present study, we focus on the base of the mantle and the boundary with the core (CMB). Applying dedicated methods of space-time patterns recognition in the gravity field, we identify a rapid, anomalous north-south oriented gravity signal at large spatial scales across the Eastern Atlantic ocean in January 2007, which evolves over months to years. We show that this signal likely originates, at least partly, from the solid Earth ; it appears concomittant, both spatially and temporally, with the 2007 geomagnetic jerk. We hypothesize that it may be induced by vertical displacements of the perovskite to post-perovskite phase transition, caused by moving thermal anomalies near the base of the African Large Low Shear Velocity Province. This may result in the creation of a decimetric dynamic CMB topography over a timespan of a few years. To assess a potential link with the 2007 geomagnetic jerk, we finally investigate the impact of these changes in core-mantle boundary topography on the flow and the geomagnetic field in a thin layer at the top of the core. These results stress the interest of satellite gravimetry for providing novel insights into the dynamical interactions between the mantle and the core.