Effects of uncertainty in mantle viscosity structure inferred from seismic tomography on glacial isostatic adjustment

Accurate mantle viscosity structures are essential when modelling glacial isostatic adjustment (GIA). In principle there are two strategies to constrain the viscosity structure. The first one is to invert it from the GIA process itself, which results generally in a radial stratification into upper and lower mantle viscosities and an effective elastic thickness of the lithosphere. These values are usually obtained for the cratonic regions of Laurentide and Fennoscandia, or are further adjusted to represent regions of a different tectonic setting. The second one is to obtain such structures from seismological tomography models, where variations in velocity are transferred to temperature and then to viscosity variations. Whereas the conversion from velocity to temperature is constrained from geodynamics, the conversion of temperature to viscosity involves uncertainty parameters in the Arrhenius law, e.g., the activation enthalpy.

In this study we quantify the dependency of GIA signals on the choice of the activation enthalpy factor. We compute an ensemble of viscosity structures using different conversion factors and show to which extent the choice influences the resulting obtained deformation and relative sea-level changes. That way we link uncertainties in viscosity structure generation to uncertainties in the observables and identify regions that are most affected.

This work contributes to the German Climate Modeling Initiative PALMOD.