Postglacial sea level rose to the present height in ice-sheet far-field regions around 7000 years ago, and this point of time has long been accepted as the time during which modern coastal deltas, estuaries and barrier-lagoon systems started to grow. However, recent scientific evidence from the low latitude western North Pacific region (WNP) suggests that important changes along this coast took place around 8000 and 4000 years ago respectively. Here, we examine the evidence of regional sea-level change, summer monsoon rainfall, stratigraphic and geomorphologic records from deltaic and non-deltaic coasts in this region and analyze the responses of these coastal landforms to the changing environments throughout the Holocene. The results reveal that (1) the rapid rising sea level resulted in the sea reaching its maximum landward limit around 8000 years ago; (2) the investigated deltas and coastal landforms had kept sedimentation rates broadly sufficient to track the creation of accommodation space driven by the relative sea-level rise at markedly reduced rates during c. 8000-4000 years ago; (3) by 5000-4000 years ago all these deltas and coastal systems had reached a near-zero accommodation state, with upper-delta or upper-estuarine plains established close to mean sea level, reflecting a long-term balance between sediment supply, aggradation, and minor relative sea-level rise; (4) as the accommodation space closed because the relative sea level ceased to rise (or slightly fall) over the past 4000 years, the sedimentary modes changed from dominant upward aggradation in upper deltas to dominant seaward progradation in lower deltas, as well as the development of fluvial landforms and herbaceous vegetation wetlands on upper delta plains, which provided land resources necessary for agricultural expansions in coastal regions. According to the new findings that coastal evolution is naturally highly sensitive to sea-level change, the future rapid sea-level rise may halt the land growth trend of the deltas and estuaries that happened over the past 4000 years and likely cause a retrogradation state in these coasts.

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