Manteldynamik, nacheiszeitliche Landhebung und das radiale Mantelviskositätsprofil

Georg Kaufmann (Universität Göttingen)

We infer the radial viscosity structure of the Earth's mantle from observations of
long-wavelength geoid, glacially-induced sea-level changes, and changes in the Earth's
rotation and gravitational field. We employ a combination of forward and formal inverse
modeling of long-term mantle circulation driven by large-scale density differences deduced
from seismic tomography. Based on the resulting unscaled mantle viscosity profiles, we
model the time-dependent glacial isostatic adjustment of the Earth related to past and
present changes in the ice-ocean mass imbalance and we deduce scaled mantle viscosity profiles,
which simultaneously fit the long-wavelength geoid constraint and glacially-induced changes
of the Earth's shape.

Three mantle viscosity profiles are fitting the observational data equally well. All profiles
are characterized by a two order of magnitude variation of viscosity within the Earth's
mantle. Variations of viscosity in the upper mantle are less than one order of magnitude.
In the lower mantle, the viscosity differs significantly with depth for all models.
Average viscosities in the upper and lower mantle are around $(2-5)\times 10^{20}$ and
$(1-3)\times 10^{22}$~Pa~s, respectively.