Variation in stable carbon and oxygen isotopes of individual benthic foraminifera: tracers for quantifying the magnitude of isotopic disequilibrium

摘要

Stable carbon and oxygen isotopic compositions (δ13C and δ18O) ofbenthic foraminiferal carbonate shells have been used to reconstruct pastbottom-water environments. However, the details of factors controlling theisotopic disequilibrium between the shells and the surrounding bottomseawater (so-called the "vital effect") are still ambiguous. In thisstudy, we analyzed the isotopic composition of individual benthicforaminifera of multiple species by using a customized high-precisionanalytical system, and found that the magnitude of the isotopicdisequilibrium between benthic foraminiferal shell and the surroundingbottom seawater (δ13C_DIC and δ18O_water) in differentspecies is correlated with inter-individual isotopic variations. As aresult, we can choose suitable species as bottom-water proxies by using theinter-individual isotopic variations. In addition, by using the simplifiedinterpretation of the inter-individual and inter-species isotopic variationsestablished in this study, we could reconstruct the δ13C values ofdissolved inorganic carbon in bottom water by correcting foraminiferalisotopic compositions for the isotopic shift resulting from the isotopiceffects (vital effect, microhabitat effect, and many other reported isotopiceffects). Our findings will allow the use of isotope data for benthicforaminifera as more reliable proxies for reconstructing past bottom-waterconditions and evaluating global carbon cycling.