Reconstruction of Cenozoic δ¹¹Bsw Using a Gaussian Process

The boron isotope ratio of seawater ( δ 11 B sw ) is a parameter which must be known to reconstruct palaeo pH and CO 2 from boron isotope measurements of marine carbonates. Beyond a few million years ago, δ 11 B sw is likely to have been different to modern. Palaeo δ 11 B sw can be estimated by simultaneously constraining the vertical gradients in foraminiferal δ 11 B (Δ δ 11 B) and pH (ΔpH). A number of subtly different techniques have been used to estimate ΔpH in the past, all broadly based on assumptions about vertical gradients in oxygen, and/or carbon, or other carbonate system constraints. In this work we pull together existing data from previous studies, alongside a constraint on the rate of change of δ 11 B sw from modeling. We combine this information in an overarching statistical framework called a Gaussian Process. The Gaussian Process technique allows us to bring together data and constraints on the rate of change in δ 11 B sw to generate random plausible evolutions of δ 11 B sw . We reconstruct δ 11 B sw , and by extension palaeo pH, across the last 65Myr using this novel methodology. Reconstructed δ 11 B sw is compared to other seawater isotope ratios, namely , , and δ 7 Li, which we also reconstruct with Gaussian Processes. Our method provides a template for incorporation of future δ 11 B sw constraints, and a mechanism for propagation of uncertainty in δ 11 B sw into future studies.