First‐order variations in sea level exhibit amplitudes of ∼200 m over periods that coincide with those of supercontinental cycles (∼300–500 Myr). Proposed mechanisms for this sea level change include processes that change the container volume of the ocean basins and the relative elevation of continents. Here we investigate how unbalanced rates of water exchange between Earth's surface and mantle interior, resulting from fluctuations in tectonic rates, can cause sea level changes. Previous modeling studies of subduction water fluxes suggest that the amount of water that reaches sub‐arc depths is well correlated with the velocity and age of the subducting plate. We use these models to calibrate a parameterization of the deep subduction water flux, which we together with a parameterization of mid‐ocean ridge outgassing, then apply to reconstructions of Earth's tectonic history. This allows us to estimate the global water fluxes between the oceans and mantle for the past 230 Myr and compute the associated sea level change. Our model suggests that a sea level drop of up to 130 m is possible over this period and that it was partly caused by the ∼150Ma rift pulse that opened the Atlantic and forced rapid subduction of old oceanic lithosphere. This indicates that deep water cycling may be one of the more important sea level changing mechanisms on supercontinental time scales and provides a more complete picture of the dynamic interplay between tectonics and sea level change.

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Earth's thermal evolution is largely controlled by the rate of heat loss through the oceanic lithosphere. This cooling rate is time-dependent because changes in tectonic rates (e.g., rates of seafloor creation and consumption) affect the seafloor age distribution (e.g., Becker et al., 2009), and thus prescribe intervals of Earth history with greater or lesser oceanic heat loss. The rate of cooling is also highly variable spatially, with mantle beneath young seafloor cooling much more rapidly than its counterpart beneath large insulating continents (Figure 1a). These variations in mantle cooling rate change with time as the plate tectonic configuration evolves, potentially inducing large spatial and temporal variations in the heat content of the mantle (e.g., Lenardic et al., 2011). It is important to understand such variations in order to better constrain Earth's thermal evolution back in time. Over the past decades, the relationship between mantle heat flow and the age of the oceanic lithosphere has been continuously refined to fit geophysical data (e.g.