Tectonic velocities, dynamic topography, and relative sea level
Résumé
The competition between ocean volume and dynamic topography in response to variable tectonic velocities can be captured by a simple, yet dynamically consistent, analysis based on the boundary layer theory. Our model reveals that short-lived changes in plate velocity (""tectonic pulses") have a negligible impact on dynamic topography. Tectonic velocities essentially mirror variations in mantle viscosity, but are not indicative of substantial modification of dynamic topography, which primarily reflects mass anomalies in the mantle. This implies that relative sea level is unlikely to be affected by "tectonic pulses" and also that observed tilting of cratonic margins couldn't result from a pulse of increased tectonic velocities. Thus, relative sea level is primarily controlled by the seafloor age distribution, although long-term (>100 myrs) changes in tectonic velocity will produce dynamic topography that reinforces sea level changes associated with changing ridge volume. These results can be related to present day plate motion and trench migration and mantle flow inferred from mantle tomography, in order to characterize the current variation -either dynamic or isostatic- of the volume of the oceans.