Anthony Osei Tutu , Christopher Harig

Past estimates of Earth’s mantle viscosity profile using the long-wavelength geoid suggest an increase in viscosity from the upper to lower mantle of roughly 2-3 orders of magnitude. We use a spatio-spectral localization technique with the geoid to estimate a series of locally constrained viscosity profiles covering two unique regions, the Pacific and Atlantic hemispheres. The Pacific region exhibits the conventional Earth's 1D rheology with a factor of roughly 80-100 increase in viscosity occurring at transition zone depths. The Atlantic region in contrast does not show significant viscosity jumps with depth, and instead has a near uniform viscosity in the top 1000 km. Our inferred viscosity variations between the two regions could be due to the prevalence of present-day subduction in the Pacific region and the relative infrequence of slabs in the Atlantic, combined with a possible hydrated transition zone and mid-mantle in the Atlantic region by ancient subduction.