Abstract Mantle viscosity remains one of the largest outstanding uncertainties in global geodynamics. Time-dependent mantle circulation models that assimilate tectonic histories (MCMs) provide a way to test viscosity by assessing their present-day predictions against observations. This approach allows for the influence of viscosity on mantle density structure to be accounted for, which is not possible using instantaneous modelling approaches. Here we present the first systematic test of lower mantle viscosity against dynamic topography, the geoid, and seismic heterogeneity using high-resolution MCMs. Model density structure depends strongly on the assumed viscosity profile, which in turn controls the fit to seismic heterogeneity. The fit to dynamic topography and the geoid is further influenced by the instantaneous transmission of stresses to the surface. These two effects can either reinforce or counteract each other at different depths, which must be considered when attempting to match dynamic topography and geoid amplitudes. MCMs typically overestimate dynamic topography amplitudes. We find that it is possible to reduce these amplitudes by lowering viscosity in the upper lower mantle (≈660-2000 km), though this comes at the expense of a reduced fit to the geoid and/or seismic heterogeneity. Our preferred viscosity profile provides an excellent fit to observed geoid amplitudes and the seismic heterogeneity of S40RTS. We also tested an alternate tectonic reconstruction with tomography-based refinements around the Pacific which improved the correlation with the observed geoid by ≈20%. Our results show that MCMs can now reach a level of resolution and realism sufficient for comparison to multiple independent data sets, opening the door to systematic assessment of uncertain parameters which govern convection in the mantle.
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