Correcting for mantle dynamics reconciles Mid-Pliocene sea-level estimates

Estimates of global mean sea level during past warm periods provide an important constraint on ice sheet stability under prolonged warming and have been used to inform projections of future sea-level change. The Mid-Pliocene Warm Period (MPWP), ~3 million years ago, has been a particular focus since it represents the most recent interval in Earth history with inferred temperatures and atmospheric CO2 concentrations similar to those expected in the near future. Although several sea-level estimates for this period have been obtained from palaeoshoreline records, they differ by many metres due to spatially variable Pliocene-to-recent vertical motions of the crust, caused by geodynamic processes including sedimentary loading, tectonic activity, glacial isostatic adjustment, and mantle convection. To address this issue and place more robust bounds on the amplitude of MPWP sea level, we combine a continent-wide suite of Australian sea-level markers with geodynamic simulations to quantify and remove post-Pliocene vertical motions at the continental scale. We find that dynamic topography related to mantle convection is the dominant process responsible for deflecting Australian MPWP sea-level markers and that correcting for it and glacial isostatic adjustment yields a global mean sea-level estimate of +16.0^{+5.5}_{-5.6} m (50th/16th/84th percentiles). Although this range is consistent with other estimates from geomorphic sea-level indicators, the upper bound is lower than assumed in recent ice sheet modelling studies, suggesting a significantly more stable Antarctic Ice Sheet under future warming scenarios.