Can we resolve 3D density heterogeneity in the lower mantle?

We reexamine the possibility of resolving 3D density structure in the mantle, by performing test inversions using a dataset of well constrained degree 2 splitting coefficients. We show that degree 2 in V s and V p can be resolved, and confirm that dlnV s /dlnV p > 2.5 at depths >2000km, indicating a chemical component to large scale heterogeneity. Models with ρ positively correlated with V s in the deepest mantle fit the data at least as well as those in which density and velocities are anti‐correlated. However, some rough bounds on dlnρ/dlnV s can be inferred. Models obtained from geodynamic considerations are acceptable, in contrast to models with large negative (<−0.3) or positive (>0.6) dlnρ/dlnV s throughout the lower mantle. The most robust feature is a marked increase in dlnρ/dlnV s at the top of the lower mantle reaching a maximum around 1500 km.