Reevaluation of the oxygen isotopic composition of planktonic foraminifera: Experimental results and revised paleotemperature equations

Cultured planktonic foraminifera, Orbulina universa (symbiotic) and Globigerina bulloides (nonsymbiotic), are used to reexamine temperature:δ 18 O relationships at 15°–25°C. Relationships for both species can be described by linear equations. Equations for O. universa grown under low light (LL) and high light (HL) share a slope of −4.80 (0.21‰ °C −1 ) with a HL‐LL offset of −0.33‰ due to symbiont photosynthetic activity. The effect of CO 3 2− on O. universa is −0.002‰ µmol −1 kg −1 and is insensitive to temperature. For G. bulloides , ontogenetic effects produce size‐related trends in temperature:δ 18 O, whereby larger shells are enriched in 18 O relative to smaller specimens. The O. universa temperature:δ 18 O relationships are more accurate than previously published equations for describing plankton tow data. Our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic Cibicidoides data below 10°C. Temperature:δ 18 O relationships for G. bulloides provide good agreement with field data for this species from the northeast Pacific.