LATE QUATERNARY BENTHIC FORAMINIFERA AND DEEP-WATER PALEOCEANOGRAPHY IN THE SOUTH CHINA SEA

Recent and late Quaternary deep-sea benthic foraminifera in the South China Sea (SCS) have been quantitatively studied, in order to approach some disputable questions about the glacial deep circulation of the P acific from the paleoceanographic records of a marginal sea, for examp le, whether or not there existed the North Pacific Deep Water (NPDW) d uring glacials. Based on the quantitative data of deep-sea benthic for aminiferal faunas from sixty-six surface sediment samples of the SCS, a Q-mode factor analysis indicates that the Globocassidulina subglobos a assemblage, the Astrononion novozealandicum and Bulimina aculeata as semblages and the Eggerella bradyi assemblage are associated with the Intermediate Water Mass (IWM), Deep Water Mass (DWM) and the deep wate r below CCD in the SCS, respectively. The factor assemblages resulted from surface sample data were then applied to the quantitative analysi s of late Quaternary deep-sea benthic foraminifera in eight cores from thr SCS and western Pacific. The results show a generally increased c ontribution of the DWM assemblage relative to that of the IWM assembla ge during glacials, which implies that the influence of the DWM increa sed and that of the IWM decreased in the SCS and western Pacific. Howe ver, there were two major deep-water paleoceanographic changes during the late Quaternary: (1) The deep-sea carbonate dissolution of the SCS and western Pacific was intensified during delta(18)O stages 4-5, evi denced by the higher arenaceous/calcareous ratios of benthic foraminif era and relative abundance of Eggerella bradyi. (2) The influence of t he Pacific DWM above 2500 m greatly increased during the last glacial maximum (LGM), inferred from the increased abundances of the Pacific D WM benthic foraminiferal assemblage as compared to those of the Pacifi c IWM and Pacific Bottom Water Mass assemblages in the western Pacific . Particularly, the water in which Favocassidulina favus was distribut ed could not enter the SCS since the LGM. Meanwhile, the great changes had taken place in the DWM of the SCS during the LGM, reflected in th e occurrence of a clearly cooled and ventilated DWM and the replacemen t of A. novozealandicum and B. aculeata assemblages by B. aculeata-Mel onis barleeanum assemblage at water depths of 1000-2500 m. These signi ficant changes during the LGM may be related to the formation of the N PDW.