Can Correcting for Mantle Dynamics Reconcile Divergent Plio-Pleistocene Sea-Level Estimates?

Abstract

Estimates of global mean sea level (GMSL) during past warm periods provide a key constraint on ice-sheet sensitivity to future climate change and inform projections of long-term sea-level rise. Measurements from the most recent periods of enhanced warmth are especially valuable since these intervals represent the closest climatic analogues to near-future conditions. Considerable focus has therefore been placed on reconstructing sea-level during the Mid-Pliocene Warm Period (MPWP; 3.3–3.0 Ma) and the Last Interglacial (~129–116 ka), periods characterised by mean temperatures 2­–3 °C and ~1 °C above preindustrial levels, respectively. Many GMSL estimates have been obtained from palaeoshoreline deposits since these geomorphic proxies provide a more direct and potentially more precise constraint on past sea-level than stable isotope records. However, estimates from different sites differ by several metres due to spatially variable vertical crustal motions caused by geodynamic processes, including glacial isostatic adjustment and dynamic topography.To tackle this issue, we integrate a suite of Australian sea-level markers and geodynamic simulations into a probabilistic inverse framework to quantify and remove the effect of vertical crustal motions at a continental scale. We find that dynamic topography accounts for most of the observed MPWP sea-level marker deflection and is also significant for the LIG. After correcting for this process and glacial isostatic adjustment, we obtain a revised MPWP GMSL estimate of +16.0/10.4–21.5 m (50th/16th–84th percentiles). We also find that post-LIG dynamic topography may account for several metres of relative displacement across the Great Barrier Reef, potentially reconciling discrepant GMSL estimates from this region. Recalibration of sea-level projections with these revised estimates suggests a more stable Antarctic Ice Sheet under future warming scenarios and appears to rule out recent high-end forecasts.