Foraminiferal boron isotope ratio as a proxy for surface ocean pH over the past 21 Myr

Data on foraminiferal boron isotopes can be used to determine past ocean pH for the past 21 Myr. Analysis of samples from a deep-sea sediment core shows that seawater boron concentrations and isotopic composition were both constant for the past 21 Myr. Based on foraminiferal isotope data, ocean pH was found to be 7.4 +/- 0.2. This value increased to 8. 2 +/- 0.2 about 7.5 Myr ago, and is almost the same today.