Influence of rapid sediment erosion and deposition on sea-level change in Taiwan

Numerous studies have shown that sediment deposition can perturb sea level by several meters over millennial timescales by modifying the gravity field, crustal elevation, and sediment thickness. However, considerably fewer studies focus on the complementary role of erosion on sea level change despite being subject to the same physics, partly because many rapidly eroding mountains are far from shorelines. Taiwan, a relatively small island (37,000 km²) eroding as rapidly as 6 mm/yr in places, offers a unique opportunity to test the coupled influence of erosion and deposition on sea-level change over a single glacial-interglacial oscillation. Here we document changes in sediment loading in and around Taiwan since the previous interglacial (120 ka) by compiling previously published erosion rate measurements across the island and post-glacial deposition rates within the western coastal plain and Taiwan Strait. For locations where deposition rates are unknown, we use a river flow routing and geometric marine deposition model to simulate transport and distribution of sediments in the Pacific Ocean and Taiwan Strait. A compaction model is further applied to estimate transient changes in sediment density and thickness. We use this sediment redistribution history to drive sea-level responses in a global, gravitationally self-consistent model, which computes gravitational, crustal, and rotational responses to erosion and deposition of sediment. Results show that most of the negative RSL signal due to deposition is flexurally filtered by the positive RSL response to erosion, which is larger in magnitude in this study area. These results suggest that sediment redistribution could have generated sea-level changes of >10 meters on the east coast of Taiwan since 10 ka and > 100 m since 120 ka. This helps shrink the discrepancy between observed and modeled shoreline elevations (some as high as 50 meters) attributed to tectonic uplift in simulations that neglect sediment redistribution. This case study also reveals that erosion in Taiwan may influence sea-level estimates on islands located several tens of km outboard over glacial-interglaical time scales.