Diatom response to changes in palaeoenvironments of the northern South China Sea during the last 15 000 years

Changes in palaeoenvironments over the last 15 000 years have been documented by a high-resolution diatom record of core 17940 from the northern slope of the South China Sea. Four diatom assemblage zones, each characterized by different diatom components, are distinguished by cluster analysis. T. nitzschioides var. parva/(T. nitzschioides + T. nitzschioides var. parva) (Tnp/(Tnp + Tn)) and the brackish-littoral species, used as the proxies for temperature and salinity, are compared with previously published sea-surface temperature (FP-12E-SSTw) and sea-surface salinity (SSS) data from the same core and with the Dongge Cave δ18O record. The Bølling-Allerød warm phase, the Younger Dryas cold event, the Holocene Climate Optimum and three Holocene cooling events (7150–6250, 4150–3450 and 1800–1350 cal. yr BP) are clearly distinguished by changes in the abundance of the brackish-littoral species and/or in Tnp/(Tnp + Tn) data. A marked increase in the abundance of the coastal species Paralia sulcata during the interval 11 150–8050 cal. yr BP indicates a strong coastal water influence, probably due to both enhanced freshwater discharge from the Pearl River and the opening of the Taiwan Strait. This palaeoceanographic change might be caused partly by climate-induced sea-level lowering during the late Pleistocene and the early Holocene. The palaeoceanography during most of the Holocene appears to be primarily controlled by fluctuations in the East Asian summer monsoon intensity.