Based on the quantitative analyses of abundance of planktonic foraminifera, benthic foraminifera, calcareous nannofossils, the ratios of calcareous to siliceous microfossils,and the determination of carbonate contents in the surface sediments of the northeastern South China Sea, it has been found that the carbonate contents, the abundance of planktonic foraminifera and calcareous nannoplankton, and the ratio of calcareous microfossils decrease rapidly while the ratio of the benthic foraminifera to the total foraminiferal fauna, specific value of siliceous microfossils, and the percentage of the agglutinated tests in the benthic foraminiferal fauna increase with the water depth. The results indicate that the microfossils abundance and ratio, and the carbonate content are closely related to the carbonate lysocline and carbonate compensation depth (CCD) in the study area. In addition, the carbonate lysocline and the CCD are different between the southern and northern parts of the South China Sea. Both the lysocline and the CCD are deeper in the south with 2?600 and 3?600 m than in the north with 2?200 and 3?400 m, respectively.
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