Oxygen and Carbon Isotope Records of Quaternary Calcareous Nannofossils from the Western Pacific Warm Pool and Their Palaeoceanographical Significance

Oxygen and carbon isotopic analyses have been carried out on calcareous nannofossils from core MD97-2140 in the Western Pacific warm pool. The results demonstrate that the δ¹⁸O values of calcareous nannofossils for the past 1.75 Ma vary systematically with δ¹⁸O values of planktonic foraminifer Globigerinoides ruber from the same core. The δ¹⁸O records of calcareous nannofossils show a dominant 41 ka peak between 1 478 and 900 ka and a 100 ka peak between 850 and 6 ka, and 59 isotope stages can be recognized. The similarity between δ¹⁸O records of planktonic foraminifera and nannofossils implies that calcareous nannofossil δ¹⁸O can also play an important role in stratigraphic and palaeoceanographic studies. The δ¹³C records of nannofossils can be divided into four major stages respectively at the boundaries 900 ka, 480 ka and 250 ka. The trends of the nannofossil δ¹³C records from MD97-2140 are similar to primary productivity variations at ODP site 807, also located in the Western Pacific warm pool, indicating that nannofossil δ¹³C can be used as an indicator of sea surface palaeoproductivity.