Oceanic <i>p</i>H control on the boron isotopic composition of foraminifera: Evidence from culture experiments

Abstract

Culture experiments were carried out with the species Orbulina universa at four different p H values (7.70±0.05, 8.15±0.05, 8.60±0.05, and 9.00±0.10) in order to establish the p H‐dependence of boron isotope fractionation between seawater and foraminifera. A clear relationship between the boron isotopic composition of the foraminifera and the p H of the seawater culture solutions was found, showing heavier boron isotopic composition at higher p H. This finding supports the viability of boron isotopes as a paleo‐ p H tool. It is important to note that Orbulina universa cultured in natural seawater, as well as those obtained from coretop samples, have a significantly lighter boron isotopic ratio than Globigerinoides sacculifer from coretop samples, suggesting that at least for this species, a vital effect is active.