RECENT PLANKTONIC FORAMINIFERS AND THEIR RELATIONSHIPS TO SURFACE OCEAN HYDROGRAPHY OF THE SOUTH CHINA SEA

The relative abundances of Recent planktonic foraminifers from surface sediments on the sea floor reveal relationships to hydrographic varia bles of the ocean surface. To investigate whether the effect of the ve rtical structure of oceanic upper-layer environments is important to t he changes in the abundance of planktonic foraminifers, a set of 173 c oretop faunal data from modern South China Sea (SCS) surface sediments was compiled for comparison with direct observations of sea-surface t emperature (SST) and the depth of thermocline (DOT). The coretops used in this study are distributed within the area of 25 degrees N and 105 degrees-125 degrees E, with water depths ranging from 68 to 3990 m. T he relationships between the abundances of planktonic foraminifer spec ies and hydrographic variables were examined using simple correlation analyses, In the analyses, four groups of planktonic foraminifers with different ecological preferences were identified: Group I - faunas pr imarily reliant on DOT, with positive correlations (N. dutertrei), Gro up II - faunas reliant on both SST and DOT, showing negative correlati ons with SST and positive correlations with DOT (G. glutinata, P. obli quiloculata, and G. bulloides, Group III - faunas reliant on both SST and DOT, showing positive correlations with SST and negative correlati ons with DOT (including G, sacculifer, G. menardii, and G. aequilatera lis), and Group IV - faunas reliant on both SST and DOT, with positive correlations (G. ruber,). Though each of these species displays selec tivity of ecological controls, these results indicate that in the SCS, correlations between faunal abundances of planktonic foraminifers and SST or DOT are about equally significant. This study also indicates a need for re-evaluating the relationships between planktonic foraminif er abundances and many other important hydrographic variables in the u pper-layer of oceans on a more regional scale. (C) 1998 Elsevier Scien ce B.V. All rights reserved.