Boron Isotopes: A “Paleo-pH Meter” for Tracking Ancient Atmospheric CO2

The boron isotope composition of calcium carbonate shells of marine organisms has the unique potential to record surface ocean pH, allowing the calculation of atmospheric pCO2 due to the established relationship between pH and the partial pressure of (atmospheric) CO2 (pCO2). This “paleo-pH meter” allows scientists to produce a record of the natural fluctuations of atmospheric pCO2 over geologic time, which will help us better understand the impacts of the recent anthropogenic addition of CO2 to Earth’s atmosphere. Towards this end, a tremendous effort to understand the systematics of boron uptake in marine carbonates is underway. Here, we review the potential of boron isotopes to constrain ocean pH and, thus, atmospheric pCO2.