Accurate relative sea-level projections require quantifying natural and anthropogenic processes, but are limited by sparse vertical land motion observations. Here, we compile a quality-controlled sea-level database since 16 ka in the Bohai and Yellow Seas, applying a spatio-temporal hierarchical model to quantify relative sea-level change and establish millennial-scale geologic vertical land motion baselines. Our reconstruction reveals rapid relative sea-level rise of 14.6 ± 1.5 mm a⁻¹ at 10.8 ± 0.2 ka, refining constraints on Meltwater Pulse 1B. Glacial isostatic adjustment, sediment compaction and loading, and tectonics govern late Holocene relative sea-level changes, establishing a baseline of -0.5–0.5 mm a^-1. Conversely, modern vertical land motion is dominated by land-use changes, with groundwater extraction driving subsidence of 15.1 mm a⁻¹ in northern China – magnitudes rivalling deglacial meltwater pulses. Along South Korea’s coast, discrepancies between modern observations and our baseline suggest interactions between compaction, groundwater depletion-driven rebound, and tectonics. Geologic baselines isolate natural from anthropogenic signals, providing a benchmark for coastal adaptation.
Accurate relative sea-level projections require quantifying natural and anthropogenic processes, but are limited by sparse vertical land motion observations. Here, we compile a quality-controlled sea-level database since 16 ka in the Bohai and Yellow Seas, applying a spatio-temporal hierarchical model to quantify relative sea-level change and establish millennial-scale geologic vertical land motion baselines. Our reconstruction reveals rapid relative sea-level rise of 14.6 ± 1.5 mm a⁻¹ at 10.8 ± 0.2 ka, refining constraints on Meltwater Pulse 1B. Glacial isostatic adjustment, sediment compaction and loading, and tectonics govern late Holocene relative sea-level changes, establishing a baseline of -0.5–0.5 mm a^-1. Conversely, modern vertical land motion is dominated by land-use changes, with groundwater extraction driving subsidence of 15.1 mm a⁻¹ in northern China – magnitudes rivalling deglacial meltwater pulses. Along South Korea’s coast, discrepancies between modern observations and our baseline suggest interactions between compaction, groundwater depletion-driven rebound, and tectonics. Geologic baselines isolate natural from anthropogenic signals, providing a benchmark for coastal adaptation.