Tectonic velocities, dynamic topography, and relative sea level

A simple dynamic model based on boundary layer theory shows that dynamic topography is unlikely to vary significantly in response to short term ( <= 20 Myr) variations in the mean tectonic velocity. 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 cannot 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.