An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids.

Oceanic residual depth varies on ≤ 5,000 km wavelengths with amplitudes of ±1 km. A component of this short-wavelength signal is dynamic topography caused by convective flow in the upper ∼300 km of the mantle. It exerts a significant influence on landscape evolution and sea level change, but its contribution is often excluded in geodynamic models of whole-mantle flow. Using seismic tomography to resolve buoyancy anomalies in the oceanic upper mantle is complicated by the dominant influence of lithospheric cooling on velocity structure. Here, we remove this cooling signal from global surface wave tomographic models, revealing a correlation between positive residual depth and slow residual velocity anomalies at depths <300 km. To investigate whether these anomalies are of sufficient amplitude to account for short-wavelength residual depth variations, we calibrate an experimentally derived parameterization of anelastic deformation at seismic frequencies to convert shear wave velocity into temperature, density, and diffusion creep viscosity. Asthenospheric temperature anomalies reach +150°C in the vicinity of major magmatic hot spots and correlate with geochemical and geophysical proxies for potential temperature along mid-ocean ridges. Locally, we find evidence for a ∼150 km-thick, low-viscosity asthenospheric channel. Incorporating our revised density structure into models of whole-mantle flow yields reasonable agreement with residual depth observations and suggests that ±30 km deviations in local lithospheric thickness account for a quarter of total amplitudes. These predictions remain compatible with geoid constraints and substantially improve the fit between power spectra of observed and predicted dynamic topography. This improvement should enable more accurate reconstruction of the spatiotemporal evolution of Cenozoic dynamic topography.

Growing evidence from a variety of geologic indicators points to significant topography maintained convectively by viscous stresses in the mantle. However, while gravity is sensitive to dynamically supported topography, there are only small free‐air gravity anomalies (<30 mGal) associated with Earth's long‐wavelength topography. This has been used to suggest that surface heights computed assuming a complete isostatic equilibrium provide a good approximation to observed topography. Here we show that the apparent paradox is resolved by the well‐established formalism of global, self‐gravitating, viscously stratified Earth models. The models predict a complex relation between dynamic topography, mass, and gravity anomalies that is not summarized by a constant admittance—i.e., ratio of gravity anomalies to surface deflections—as one would infer from analytic flow solutions formulated in a half‐space. Our results suggest that sizable dynamic topography may exist without a corresponding gravity signal.

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