The incorporation of boron into marine carbonates depends on the pH of seawater, so the isotopic composition of fossil carbonates can be used as an archive to investigate the past carbon cycle. Application of this proxy requires that the bulk isotopic composition of seawater is known, which is the case for the present-day ocean but becomes increasingly unclear in the distant geologic past.

Weathering processes at Earth’s surface liberate a wide array of elements and lead to the transformation of primary into secondary minerals with a large capacity for adsorption. These reaction products eventually enter the global ocean where they form some of the most important sources and sinks in the marine boron cycle. Changes in the amount or character of this continental export could have influenced the seawater composition over long timescales.