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:delta(18)O relationships at 15 degrees-25 degrees 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 parts per thousand C-1) with a HL-LL offset of -0.33 parts per thousand due to symbiont photosynthetic activity. The effect of [CO32-] on O. universa is -0.002 parts per thousand mu mol(-1) kg(-1) and is insensitive to temperature. For G. bulloides, ontogenetic effects produce size-related trends in temperature:delta(18)O, whereby larger shells are enriched in O-18 relative to smaller specimens. The O. universa temperature:delta(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 degrees C. Temperature:delta(18)O relationships for G. bulloides provide good agreement with field data for this species from the northeast Pacific.