Separating tectonic and climate signals in Holocene sea-level records using marine terraces in central Chile

Field observations of past sea-level variations are needed to validate models predicting future sea-level rise. Along tectonically active coasts, separating tectonic and non-tectonic sea-level components is challenging as both have similar amplitudes but necessary to decipher sea-level histories driven by climate forcing. Here, we present a new framework to decipher Holocene sea-level changes using marine terraces-geomorphic features formed by wave erosion of bedrock-mapped with high-resolution LiDAR data and numerical modelling. Applied to 266 sites along 500 km of central Chilean coast, we found that Holocene terrace elevations linearly correlate with Late Pleistocene terrace elevations, evidencing steady-state tectonics over the past 125,000 years. This proof of steady-state uplift allows subtracting tectonic components from Holocene elevations using uplift rates from Pleistocene terraces. We find that during the mid-Holocene, sea level reached 3.18 ± 0.15 m above modern elevation, only 0.33 m below glacial isostatic model predictions with 2·10²⁰ Pa·s mantle viscosity. We validated this relationship by reproducing Holocene terrace elevations using a landscape evolution model and glacial isostatic sea-level curves. Our results suggest that accounting for millennial-scale vertical land motion rates that average many seismic cycles may improve future relative sea-level change projections, highlighting the potential of rocky-shore geomorphology for sea-level research along tectonically active coastlines.