... axis with respect to an earth-fixed system: the true polar wander (TPW) and the duration of a single rotation: the length of day (LOD). Mass redistributions within and on the earth change the inertia tensor of the earth, which is visible as TPW. The LOD is proportional to the moment of inertia about the earth's spin axis, which, in turn, is proportional to the zonal harmonic of degree two of the geopotential. At present, this results in an acceleration of the earth's rotation, i.e. a shortening of the LOD (e.g. Nakada & Okuno, 2003). However, GIA-induced variations of the earth's rotation parameters are masked by other processes, e.g. the convective flow in the mantle, the direct effect of the present redistribution of ice and water masses and changes in the pressure fields at the core-mantle boundary (z.B. Mitrovica & Vermeersen, 2002).