Oxygen and carbon isotopes of Recent calcareous nannofossils as paleoceanographic indicators

Abstract

δ 18O and δ 13C values for several species of planktonic foraminifera and calcareous nannofossils from Recent deep-sea sediments have been studied in order to evaluate their paleoceanographic and paleotemperature potential. Nannofossils from Indian Ocean core-tops reflect isotopic temperatures as warm as, or warmer than, the temperatures reported by Williams et al. (1977) for shallow-dwelling planktonic foraminifera from the same samples. In general, deep-sea sediment samples from the world's major oceans indicate that nannofossil δ 18O values are from 0.5 to 1 ‰ heavier than shallow-dwelling planktonic foraminifera. Although nannofossil δ 18O values depart from thermodynamic equilibrium with oceanic surface water temperatures, the δ 18O temperature trend parallels that of surface-dwelling planktonic foraminifera. Nannofossil δ 13C values also depart from equilibrium with surface water δ 13C-ΣCO 2 values. A comparison of nannofossil δ 13C data with that from planktonic foraminifera suggests that the rate of primary productivity in different water masses may be influencing the δ 13C of carbonate-secreting phytoplankton and zooplankton.