Eustasy, supercontinental insulation, and the temporal variability of terrestrial heat flux

Heat flux from convection in Earthʹs mantle has recently been suggested to vary substantially (20–30%) with the Wilson cycle of continental aggregation and dispersal, because of possible changes in the aspect ratio of convective cells, and the present-day heat flux may be at the maximum at such a temporal variation. This possibility of strong temporal fluctuations in heat flux has an important bearing on how we should model the thermal evolution of Earth in general. As most of convective heat flux appears as oceanic heat flux, and changes in oceanic heat flux can cause changes in the global sea-level, the likely amplitude of such a temporal variation can be quantified by long-term eustasy. Though this inference may be complicated by other processes that can affect the global sea level, most of them predict sea-level fall when Pangea was present, allowing to place a likely bound on the temporal variability of heat flux. Given the geologically plausible age–area distribution of seafloor, the present-day oceanic heat flux is likely at the minimum (not the maximum) of a possible temporal fluctuation, and the oceanic heat flux at ∼ 200 Ma cannot be lower than today by more than a few percent. I also suggest that mantle warming by supercontinental insulation is probably up to only ∼ 20 K, though it still has a nontrivial consequence for the global sea level.