Middle eocene seawater pH and atmospheric carbon dioxide concentrations

The carbon dioxide content of the atmosphere [measured as the partial press ure of CO2 (pCO(2))] affects the content of the surface ocean, which in tur n affects seawater pH, The boron isotope composition (delta(11)B) of contem poraneous planktonic foraminifera that calcified their tests at different w ater depths can be used to reconstruct the pH-depth profile of ancient seaw ater. Construction of a pH profile for the middle Eocene tropical Pacific O cean shows that atmospheric pCO(2) was probably similar to modern concentra tions or slightly higher.