Deep Water Cycling and Sea Level Change Since the Breakup of Pangea. (24th June 2019) - Karlsen, Krister S.
Abstract: 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. Key Points: An imbalance between water fluxes into the mantle at trenches and out of the mantle at ridges may have changed sea level since Pangea time We estimate ocean mass change from tectonic reconstructions using parameterizations of subduction water flux based on slab age and velocity Faster slabs during Pangea breakup transported extra water to the mantle, contributing to a sea level drop of up to ∼130 m since 230 Ma