iii Pearson , Foster and Wade ( 2009 )
Fig . 3 . Boron isotope pCO 2 estimates ( red and blue symbols involve different assumptions ) and below , oxygen isotopes for the interval 32.8-34.8 Ma from Pearson et al . ( 2009 ). Red line added .
This boron isotope study of the late Eocene and early Oligocene employed MC-ICPMS and the fractionation of Klochko et al . ( 2006 ) so the results cannot directly be compared with Pearson and Palmer ( 2000 ). There is some variability but all the values are well above 400 ppm ( red line ). The pCO 2 estimates are very sensitive to the assumed boron isotope composition of seawater and could be substantially higher or lower than indicated but are unlikely to be below 400 ppm using any reasonable value .