Marine pollen records provide perspective on coastal wetlands through Quaternary sea-level changes

The response of coastal wetlands to future sea-level rise remains uncertain. Palaeoecological data are essential to constrain the still conflicting ecological models. However, obtaining detailed palaeo-coastal stratigraphic records before Holocene is often difficult due to repeated Quaternary marine transgression-regressions. Here we utilize pollen data from a deep-sea sedimentary archive in northern South China Sea to explore the historical behavior of coastal wetlands at a large river estuary over the last 140-kyr. A recurrent wetland (Cyperaceae)-pioneer species (Selaginella)-zonal forest (Pines) succession throughout the last glacial-interglacial cycle implies a coastal salt marsh origin of the Cyperaceae pollen. Comparing with global sea-level reconstructions, the increases in Cyperaceae pollen abundance, and hence the expansions of coastal salt marsh, were found to be closely linked with rapid large-scale sea-level rises. This finding indicates a resilience of coastal wetlands to future sea-level rise, and highlights the probable importance of conventionally ignored horizontal adaptability in long-term survival of coastal wetlands. Overall, marine pollen records provide an opportunity to supplement existing palaeoecological observations of coastal wetlands during the Quaternary.