Compositions and Distribution of Living Planktonic Foraminifera in Autumn Waters of the Northern South China Sea

Living planktonic foraminifers have been quantitatively analyzed on 40 plankton tow samples which were collected from 19 sites in the northern South China Sea (SCS) in September, 2004. The affecting factors on the distribution and compositions of foraminiferal faunal are then discussed. The results indicate that most foraminifera occurred in the autumn northern SCS are tropical warm water species, which apparently shows a regional distribution. The abundance of living foraminifera forms a general pattern with high abundance occurring in the northwest and relatively low values in the southeast of the studied area. The relative abundances of shallow water species G. sacculifer and G. ruber show high values near the coast area, and N. dutertrei are mainly distributed on the outer shelf and slope, and the high percentage of G. menardii mainly appeared at the southeast deep water area. G. calida and G. aequilateralis show similar distribution pattern, with high percentage at the deep water sites. Both of them show especial high values at the southernmost site off Vietnam. Our study suggests that the regional distribution of living planktonic foraminifers in the autumn northern SCS is mainly controlled by the combined impacts of primary productivity and water depth. High abundance usually appeared under high primary productivity area, and water depth also plays an important role on the distribution of subsurface dwelling species. The thickness, temperature and salinity of the mixed layer have no significant relationship with the distribution of living foraminifers in the autumn northern SCS, but the temperature and salinity structure of the lysocline do show significant relationship with the distribution of some subsurface dwelling species such as N. dutertrei、G. glutinata、G. calida and G. aequilateralis, In addition, the abundance of foraminifera is apparently higher in the warm eddies, with particularly higher percentage of G. sacculifer, than its adjacent sites, which suggests that warm eddy also has a significant influence on the distribution of planktonic foraminifera. P. obliquiloculata is only abundant in the northeastern part of the studied area which is affected by the branches of Kuroshio.