Whiteford, Ross, Heaton, Timothy J, Henehan, Michael James, Anagnostou, Eleni , Jurikova, Hana, Foster, Gavin L and Rae, James William Buchanan (2024) Reconstruction of Cenozoic δ11Bsw Using A Gaussian Process. Paleoceanography and Paleoclimatology, 39 (4). Art.Nr. e2023PA004769. DOI 10.1029/2023PA004769.

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Abstract

Key Points:
- We reconstruct the temporal evolution of seawater isotope ratios of boron, strontium, lithium, and osmium over the last 65 million years
- The evolution of seawater boron isotope ratio shows similarity to the evolution of strontium, lithium and osmium isotope ratios
- Randomly drawn, smooth time series are provided for use in uncertainty propagation in calculation of palaeo pH

The boron isotope ratio of seawater (δ11Bsw) is a parameter which must be known to reconstruct palaeo pH and CO2 from boron isotope measurements of marine carbonates. Beyond a few million years ago, δ11Bsw is likely to have been different to modern. Palaeo δ11Bsw can be estimated by simultaneously constraining the vertical gradients in foraminiferal δ11B (Δδ11B) 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 δ11Bsw 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 δ11Bsw to generate random plausible evolutions of δ11Bsw. We reconstruct δ11Bsw, and by extension palaeo pH, across the last 65Myr using this novel methodology. Reconstructed δ11Bsw is compared to other seawater isotope ratios, namely ,87/86 Sr, 187/188 Os , and δ7Li, which we also reconstruct with Gaussian Processes. Our method provides a template for incorporation of future δ11Bsw constraints, and a mechanism for propagation of uncertainty in δ11Bsw into future studies.

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