Constraining Global Dynamic Topography Using a Revised Observational Database

Earth’s topography is supported by both crustal and sub-crustal density variations. Dynamic topography results from the vertical displacement of the Earth’s surface due to processes operating within the mantle. Thus, isolating and quantifying observable dynamic topography can yield valuable information about mantle dynamics. An observationally-based approach can be used to investigate dynamic topography by calculating residual depth anomalies in the oceanic realm and residual topographic anomalies on the continents. To constrain the residual topographic contribution that arises from sub-crustal processes it is necessary to correct for crustal and sedimentary loading. We identify and correct for both forms of loading by exploiting a variety of seismologic datasets that include seismic reflection profiles, wide-angle/refraction surveys and receiver functions. We present a revised global compilation of oceanic residual depth measurements (n = 10,846) and continental residual topographic measurements (n = 3,897). This compilation represents a significant improvement in terms of the quantity and spatial distribution of measurements. In the oceanic realm, the correction methodology has been revised in two ways, which has improved resolution and accuracy. First, the crustal correction now accounts for variations in bulk density as a function of crustal thickness. Secondly, the quartz and clay content of the sedimentary column has been adjusted, which improves the quality of the sedimentary correction. The revised global compilation is used to generate a spherical harmonic representation of observable dynamic topography out to degree 40 (i.e. ~ 1000 km). The resultant power spectrum demonstrates that dynamic topography varies linearly with inverse wavenumber. Our global results are consistent with independent geologic markers of uplift and subsidence.