Late Pleistocene and Holocene ice mass fluctuations and the Earth's precession constant

We computed, using a set of previously published Maxwell visco-elastic Earth models, time-dependent variations in the Earth's precession constant, H, associated with glacial cycles of duration {reversed tilde equals} 10⁵ yr. We found peak perturbations which are approximately an order of magnitude less than previous upper bound estimates, which assumed that variations in H arose solely from the redistribution of the ice age surface mass (ice plus ocean) load; that is, these studies neglected the visco-elastic isostatic adjustment of the solid planet and assumed a rigid Earth. A number of subsequent studies have cited and/or adopted the 'rigid Earth' variation in H to argue for a series of potentially important effects on the Earth's orbital dynamics, rotation and palaeoclimate. The results presented herein suggest that these arguments require significant re-appraisal. We also compute variations in H associated with the documented retreat of small ice sheets and glaciers over the last century and potential (recent) mass variations in the Antarctic and Greenland ice complexes. We find (in the case of a net mass loss from the Antarctic and Greenland ice sheets) that these effects may contribute a perturbation to H which is approximately the same amplitude as, but has the opposite sign to, the contribution from ongoing glacial isostatic adjustment during the last century.