Models of isostatic and dynamic topography, geoid anomalies, and their uncertainties

Abstract

Knowledge of the dynamic topography at Earth's surface caused by sublithospheric density contrasts would provide crucial constraints on models of mantle dynamics. We calculate global models of this dynamic topography by subtracting from the observed topography estimates of the topography caused by assumed isostatically compensated density variations in the crust, the oceanic lithosphere, and the continental tectosphere. We also calculate the isostatic geoid anomaly that would result from these compensated near‐surface density anomalies. Because there is controversy about the thermal structure of old oceanic lithosphere, we investigate two models of the cooling of the oceanic lithosphere (half‐space and plate) and calculate the effect of each on the inferred dynamic topography. Peak amplitudes of dynamic topography from sublithospheric sources expanded to spherical harmonic degree 6 are approximately ±1 km. We estimate the uncertainties in the calculated dynamic topography and geoid by combining the errors in the data and systematic errors. To obtain the spectral coefficients of the fields, we use weighted least squares inversions. The calculated dynamic topography arising from sublithospheric sources, residual geoid, and errors associated with these fields can be used in studies of mantle dynamics.