Differential rotation of Earth’s inner core relative to the mantle is thought to occur under the effects of the geodynamo on core dynamics and gravitational core–mantle coupling. This rotation has been inferred from temporal changes between repeated seismic waves that should traverse the same path through the inner core. Here we analyse repeated seismic waves from the early 1990s and show that all of the paths that previously showed significant temporal changes have exhibited little change over the past decade. This globally consistent pattern suggests that inner-core rotation has recently paused. We compared this recent pattern to the Alaskan seismic records of South Sandwich Islands doublets going back to 1964 and it seems to be associated with a gradual turning-back of the inner core as a part of an approximately seven-decade oscillation, with another turning point in the early 1970s. This multidecadal periodicity coincides with changes in several other geophysical observations, especially the length of day and magnetic field. These observations provide evidence for dynamic interactions between the Earth’s layers, from the deepest interior to the surface, potentially due to gravitational coupling and the exchange of angular momentum from the core and mantle to the surface.
The digital waveform data in this study are openly available from the Incorporated Research Institutions for Seismology Data Management Center (http://iris.edu) and Canadian National Seismograph Network (http://earthquakescanada.nrcan.gc.ca/stndon/CNSN-RNSC/index-en.php). The analogue waveforms from the station COL were collected and manually digitized by ref. 7, and those of the SSI doublets are available at https://doi.org/10.6084/m9.figshare.21548679.v1. The yearly averaged LOD measurements and the daily Earth Orientation Parameters series (EOPC04) are freely downloaded from the International Earth Rotation and Reference Systems (https://www.iers.org/IERS/EN/Home/home_node.html).