Topography: a robust constraint on mantle fluxes

The topography of the sea floor provides direct, global and robust evidence for a large mass flux through the mantle transition zone over the past few hundred million years. This is incompatible with some recent interpretations of noble gas constraints. Reconciliation with other geochemical constraints requiring distinct deep-mantle reservoirs is more plausible, but has not yet been fully demonstrated. Seafloor topography also constrains the present mass flux transported by mantle plumes and implies that plumes come from the base of the mantle.