The influence of sediment isostatic adjustment on sea-level change and its records along the coast of Taiwan

Information of sea-level change history is crucial for the understanding of tectonic movements along coastal areas.  Locally, changes in sea-level may be influenced by sediment isostatic adjustment (SIA) that results from erosion and deposition and perturbs crustal elevation and the Earth’s gravitational field.  However, many previous studies on coastal uplifts neglected such effects.  In this study, we utilized gravitationally self-consistent sea-level model to quantitatively analyze how SIA affected the sea-level during the last glacial-interglacial cycle around Taiwan, where erosion and deposition are among the fastest in the world.  We constructed a time-variant sediment transfer history for Taiwan and used it, together with published ice loading history over the past 122 kyr, as input to drive the sea-level model.  To build a comprehensive sediment model, we combined erosion and exhumation rate data derived from cosmogenic nuclides, detrital zircon fission-track, and fully reset apatite fission track ages to construct the erosion rate map.  In addition, we compiled age data from both on-land and offshore sediment cores, and isopach map derived from submarine seismic profiles to generate the deposition rate map.  The modeling results show that SIA would cause significant spatial variations in sea-level history along the coast of Taiwan.  For example, along the eastern coast, isostatic uplift due to the high rate of erosion of nearby mountains induces sea-level fall, whereas isostatic subsidence resulting from deposition may surpass the effect of erosion and lead to sea-level rise along the southwestern coast.  This may be the first observation of completely different isostatic patterns of coastlines occurring in such a short distance, likely owing to the extremely rapid sediment redistribution and the relatively thin elastic lithosphere of Taiwan.  Furthermore, the effects of SIA may produce sea-level variations in the order of meters to tens of meters since 10 ka, and up to tens to more than two hundred meters since 122 ka along Taiwan’s coast.  Without the consideration of SIA effects, the estimation of tectonic coastal uplift rates may be overestimated or underestimated by up to 60% and 90%, respectively, along some coast of Taiwan.  Our results highlight the importance of considering SIA processes when using paleo-sea-level indicators to characterize tectonic movements along the coast, especially in regions with rapid erosion or deposition.