Oxygen and carbon isotope records of calcareous nannofossils for the past 1 Ma in the southern South China Sea

Oxygen and carbon isotopic analyses have been carried out on calcareous nannofossils from ODP Site 1143 in the southern South China Sea. The results demonstrate that the δ¹⁸O values of calcareous nannofossils for the past 1 Ma vary systematically with those of planktonic and benthic foraminifera from the same site. But the average δ¹⁸O value of nannofossils is 1.869‰ higher than that of planktonic foraminifera, and is 3.855‰ lower than that of benthic foarminifera. There are systematic differences between the δ¹³C values of nannofossils, planktonic foarminifera and benthic foraminifera. The average δ¹³C of nannofossils is 0.756‰ higher than that of benthic foraminifera, and is 0.460‰ lower than that of planktonic foraminifera. The δ¹³C values of nannofossils exhibit a significant positive shift beginning near isotope stage 14 and lasting until stage 8. This study also finds that there is a close ralationship between the δ¹³C of nannofossils and the percentage of Florisphaera profunda. This implies that the δ¹³C of nannofossils can be used as an indicator of sea water surface paleoproductivity.