Estimating tectonic coastal uplift requires accounting for sea-level variations caused by rapid sediment redistribution

Information about past sea-level change is crucial for understanding coastal tectonic movements and seismic hazards. Locally, sediment isostatic adjustment (SIA) induced by erosional unloading and depositional loading could play an important role in sea-level change. However, such effects are commonly neglected, potentially leading to biased estimates of vertical tectonic deformation rate. Here we constructed a new sediment transfer history for Taiwan, where erosion and deposition are among the fastest on Earth, and used it to drive the numerical sea-level model to quantify SIA effects on the sea-level change and tectonic uplift estimates. Our simulations revealed that SIA could cause substantial spatial variation in sea-level change along Taiwan’s coasts, producing local relative sea-level change of >200 meters since 122 ka. We found that neglecting SIA effects can result in overestimation and underestimation of tectonic coastal uplift rates by up to 90% or more. Our results highlight the global importance of considering spatially varying SIA-driven sea-level changes when using paleo-sea-level indicators to characterize coastal tectonic movements. Along Taiwan’s coasts, rapid sediment redistribution can drive sea-level changes with large spatial variability, leading to substantial errors in tectonic uplift estimates, according to a numerical sea-level model simulation.