Dinoflagellate cyst distribution in surface sediments from the South China Sea in relation to hydrographic conditions and primary productivity

The geographical distribution of dinoflagellate cysts was investigated in palynologically treated surface sediments from the South China Sea (SCS) to understand the driving environmental factors associated with specific taxa. The western SCS generally has higher total cyst concentrations (>300 cysts g⁻¹) than the eastern region (<200 cysts g⁻¹). The highest concentrations (>1000 cysts g⁻¹) occur off southern Vietnam, whereas the lowest cyst concentrations are off Luzon. The ratio of heterotrophic to autotrophic taxa has inverse distributional patterns to total cyst concentrations, and is likely to be related to an increase in relative abundances of autotrophic taxa when nutrient inputs increase. Brigantedinium spp., Selenopemphix nephroides, and Stelladinium reidii have their highest relative abundances and concentrations off Borneo. Their concentrations are significantly positively correlated with January sea-surface temperature (SST-Jan). In contrast, concentrations of Selenopemphix undulata, Spiniferites hyperacanthus, Dapsilidinium pastielsii and Operculodinium?longispinigerum are negatively correlated with SST-Jan. Lejeunecysta sabrina, cysts of Protoperidinium spp., Votadinium spp., Quinquecuspis concreta and Selenopemphix quanta are positively correlated with chlorophyll-a (chl-a) concentrations and are found in the high primary productivity regions of the SCS. Total Impagidinium, Impagidinium aculeatum, Impagidinium paradoxum, Impagidinium patulum, Nematosphaeropsis labyrinthus, and Polysphaeridium zoharyi are positively correlated with water depth. Their highest abundances are recorded in the northern slope-deep basin that is influenced by the Kuroshio Current, and this cyst assemblage indicates an open-ocean environment.