DISTRIBUTION OF PLANKTONIC FORAMINIFERA IN SURFACE SEDIMENTS FROM SEA AREA EAST OF THE RYUKYU ISLANDS AND THEIR INDICATIONS

123 surface sediment samples from sea area east of the Ryukyu Islands were quantitatively analyzed. On the basis of factor analysis for planktonic foraminifera, three faunal assemblages, G. ruber-G. glutinata, G. inflata-N. pachyderma (dex.) and N. dutertrei-P. obliquiloculata assemblages were identified in surface sediments from the study area. It's suggested that assemblage distributions are mainly controlled by carbonate dissolution, and as a result, distribution of G. ruber-G. glutinata assemblage is restricted to sub-area with water depth shallower than carbonate lysocline depth(CLD), but the distribution depth of G. inflata-N. pachyderma (dex.) assemblage is deeper than CLD. N. dutertrei-P. obliquiloculata assemblage is confined to the northwest of the study area due to the existence of overlying Kuroshio Current, and accordingly, the abundance of P. obliquiloculata, a indicator of the above warm current, is obviously high. To some extent, CLD and carbonate compensation depth (CCD) can be indicated by characteristics of abundance and assemblage distributions of the planktonic foraminifera in surface sediments. And it is revealed by carbonate preservation that the present CLD and CCD of the study area are about 3 100 m and 4 300 m respectively.