High-resolution palynological record of Holocene climatic and oceanographic changes in the northern South China Sea

For the first time, palynological records of terrestrial palynomorphs and dinoflagellate cysts are investigated in a sediment core from the northern South China Sea (SCS) covering the last 12,500 years. Both terrestrial and marine palynomorph records show strong signals of the sea-level change during the studied interval. The highest herb pollen content was associated with extensive grasslands on the exposed shelf at the low sea-level stand during the Younger Dryas and early Holocene. The increase in fern spores and decrease in concentrations of dinoflagellate cysts and terrestrial palynomorphs was observed during the sea-level rise interval from 12,500 to ~ 6800 (or 6000) cal yr BP. Then, the sea level became stabilized and consistently low dinoflagellate cyst abundances and high abundances of fern spores were recorded. A high abundance of Impagidinium in the period ~ 12,000–10,400 cal yr BP possibly resulted from increased input of western Philippine Sea waters into the SCS and the branching of the Kuroshio Current. A short-term decrease of Impagidinium at ~ 11,700–11,000 cal yr BP corresponding to the MWP-1B event might be associated with input of the East China Sea waters through the Taiwan Strait. The relationship between the sedimentation rates and the concentrations of terrestrial palynomorphs indicates a water-dominant transport for pollen and spore dispersal prior to ~ 6300 cal yr BP, whereas wind transport became more prominent thereafter. The timing of this change corresponds to the highest sea-level stand at ~ 6800–6000 cal yr BP, when the present oceanographic setting was formed. The mid-Holocene Optimum can be seen by the highest abundance of subtropical-tropical broad-leaved arboreal pollen and by the highest abundances of Dapsilidinium pastielsii. Three strengthened winter monsoon intervals at ~ 5500 cal yr BP, 4000 cal yr BP, and 2500 cal yr BP are reflected by increases in Pinus pollen content after the present oceanographic condition formed.