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

Abstract

We determined the δ18O and δ13C of individual Globigerinoides ruber and Pulleniatina obliqniloculata from sediment traps located from 5°N to 12°S along 140°W in the Pacific Ocean to evaluate the effects of varying [CO3=] on shell δ18O and δ13C. Variations in the offset between shell δ13C and δ13CDIC (Δ13Cs-DIC) are attributed to differences in [CO3=], temperature, and shell size between sample sites. When Δδ13Cs-DIC of G. ruber was corrected for variations in [CO3=] using the experimental slope of Bijma et al. [1998], the residual Δδ13Cs-DIC was correlated with mixed layer temperature (+0.10±0.04%0 °C-1). The slope of this temperature effect is consistent with experimental results. In P. obliquiloculata, Δδ13Cs-DIC and temperature were strongly anticorrelated (-0.14±0.03%0 C-1). We are unable to separate the influences of [CO3=] and temperature in this species without independent experimental data. Correcting for [CO3=] variability on δ18Os of G. ruber improves the accuracy of estimated sea surface temperatures. Copyright 2000 by the American Geophysical Union.