A preliminary study of living planktonic foraminifera distribution and its affecting factors in southern South China Sea

Living planktonic foraminifera was quantitatively analyzed for 20 stratified plankton tow samples collected from 11 sites in the southern South China Sea(SCS) in May,2002.The assemblage and distributing pattern of planktonic foraminifera were preliminarily analyzed based on these data.The result showed that living planktonic foraminifera distributed wildly in the surface water of the studied area,and totally 20 species were identified,of which most were tropic warm water species,cold water species only distributed sporadically.Globorotalia menardii,originally considered as a deep water species,appeared abundantly in the upper 50m water layer of the southern SCS,with generally thin and small shells.The abundance of living planktonic foraminifera in the upper 50 m water layer ranged from 6 138 to 64 174 individuals per 1 000 m~3 sea-water and showed a decreasing trend from west to east.High abundance values occurred in the southwest shallow-water area and the northwest upwelling area,suggesting that the abundance of living planktonic foraminifera may have a close relationship with nutrition level of the surface water.By comparing the planktonic foraminifera in the water samples with that in the surface sediment samples at 23 sites in the southern SCS,it could be found that they had a close relationship with each other.Although there were obvious differences in the distribution pattern and relative abundance of species,they showed very similar assemblages of dominant species.The main differences between them were that the relative abundance of dominant species in the water samples fluctuated violently with sampling sites,while it showed small variations in the surface sediment samples;and Hastigerina pelagica,a species apt to be dissolved,was abundant in the water samples but disappeared in the sediment samples.Besides,the dilution of terrigenous matter may have an obvious influence on the abundance distribution of planktonic foraminifera in the surface sediments.