The issue is not really the source of the long-period "decade" fluctuations in the length of the day (LOD). It has been known for decades that these have to be caused by "weather" (fluid magnetohydrodynamics) in the liquid outer core. Has to be, as there is no other suitable source of angular momentum. The atmosphere and oceans up here on the surface simply fall short, by as much as an order of magnitude, and nothing else (ice, groundwater, tectonics, etc.) can even match them. The "weather" in the core is dynamically rather different than the weather up here - the heat source is radioactivity and precipitation of solid iron, while the core is quite conductive, and so the dynamics are MHD, not just HD. We don't know much about fluid motions in the core, but we do know that they have to exist, to drive the observed LOD variations (and also drive the observed changes in the geomagnetic field).
What the real question is is the nature of the torque between the mantle and the core. The two leading contenders are pressure torques (differences in pressure across whatever inverse mountains there are at the core mantle boundary) and electromagnetic torques. The E&M torques would be enhanced if the mantle is conducting.
So, this is a plus for the E&M torque theorists, but I wouldn't expect this issue to be really resolved for some centuries, if not longer. The core is not that far away, but it's hard to see through thousands of kilometers of rock...
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