Calcareous nannofossils in surface sediments of the eastern and western South China Sea

A detailed interbasinal study of calcareous nannofossils in surface sediments and their environmental preferences was conducted across the South China Sea, from the upwelling area off Vietnam to the non-upwelling area off Luzon, Philippines. Emiliania huxleyi, Florisphaera profunda and Gephyrocapsa oceanica are the dominant taxa in all the stations, comprising 72%–100% of the total nannofossil assemblage. In the shallow coastal waters and nearshore environments in the western portion, the dominant taxa are E. huxleyi and G. oceanica. Offshore, towards the central (abyssal) portion of the SCS, F. profunda dominates the nannofossil assemblage. Distribution patterns observed in this study, as well as the results of the principal components analysis, confirmed and established environmental preferences not only of the three major taxa, but of several minor taxa as well. Based on these results and cluster analysis of the samples, three assemblages were recognized in the study area: (a) upwelling, (b) oceanic and (c) deep basin assemblages. The upwelling assemblage is associated with the Vietnam and Sunda Shelves upwelling areas and is dominated by E. huxleyi and G. oceanica. The oceanic assemblage encompasses the outer shelf to slope environments and is characterized by the common occurrence of F. profunda and E. huxleyi (western study area) and F. profunda and G. oceanica (eastern study area). The deep basin assemblage includes the abyssal portion of the SCS (below the inferred lysocline and calcite compensation depth) and is dominated by F. profunda (> 80%). It is proposed in the present study that F. profunda is resistant to dissolution.