Field examination of the oceanic carbonate ion effect on stable isotopes in planktonic foraminifera

We determined the delta(18)O and delta(13)C of individual Globigerinoides r uber and Pulleniatina obliquiloculata from sediment traps located from 5 de grees N to 12 degrees S along 140 degrees W in the Pacific Ocean to evaluat e the effects of varying [CO3=] on shell delta(18)O and delta(13)C. Variati ons in the offset between shell delta(13)C and delta(13)C(DIC) (Delta delta (13)C(S-DIC)) are attributed to differences in [CO3=], temperature, and she ll size between sample sites. When Delta delta(13)C(s-DIC) of G. ruber was corrected for variations in [CO3=] using the experimental slope of Bijma et al. [1998], the residual Delta delta(13)C(s-DIC) was correlated with mixed layer temperature (+0.10+/-0.04 parts per thousand degrees C-1). The slope of this temperature effect is consistent with experimental results. In P. obliquiloculata, Delta delta(13)C(s-DIC) and temperature were strongly anti correlated (-0.14+/-0.03 parts per thousand C-1). We are unable to separate the influences of [CO3=] and temperature in this species without independe nt experimental data. Correcting for [CO3=] variability on delta(18)O(s) of G. ruber improves the accuracy of estimated sea surface temperatures.