The Ediacaran Period was marked by significant shifts in carbon isotopes, rapid climatic changes, variations in sulphate concentrations, and notable transitions in Earth's redox state. The barium concentrations and isotopic compositions of seawater are closely linked with marine biogeochemical processes, for example redox conditions, sulphur cycling and primary productivity. As a continuous archive and without known fractionation, carbonates have begun to emerge as a more reliable record to reconstruct palaeoseawater Ba systematics. However, Ba exists in different phases within carbonate rocks, including as barite, e.g. at Jiulongwan Section [1], which could obscure interpretations of a primary seawater Ba signal. Therefore, it is important to extract Carbonate-Associated Barium (CABa) cleanly. Published studies show that sequential leaching can successfully extract strontium from carbonate [2] and barite [3]. In this study, we combine these two leaching techniques to extract Ba associated with different phases from carbonate rocks using reference limestones and artificial mixtures of barite and limestone, with the aim of extracting the least contaminated CABa from the carbonate fraction. This has been achieved using an ammonium acetate prewash to remove the exchangeable fraction, dilute acetic acid to target the CABa, before using nitric acid for the remaining phases. Comparing Ba concentrations of the different leachates, the prewash (~exchangeable fraction) and nitric acid (~oxide and silicate residue) leaches released more Ba than the carbonate phase. Additionally, this study demonstrates that the calculated solubility of pure barite in ammonium acetate and dilute acetic acid is approximately 1.13 × 10^-5 mol/L and 1.19 × 10^-5 mol/L, respectively, which is higher than the solubility of barite in pure water at 25℃, reported as 1.04 × 10^-5 mol/L[4]. We find that, at room temperature, the presence of Ca²⁺ ions in the solution further enhances barite dissolution, increasing Ba solubility to 1.75 × 10^-5 mol/L and 3.02 × 10^-5 mol/L in ammonium acetate and dilute acetic acid respectively. This means when barite is present within carbonate rocks, its increased solubility can interfere with CABa extraction during the leaching process, potentially contaminating the extracted signal. The new finding and the newly developed approach refine CABa extraction along with other Ba phases and will be tested using carbonate of Ediacaran age, helping to contribute to more robust and comprehensive interpretations of sedimentary Ba data.

1.          Cui, H., et al., Dynamic interplay of biogeochemical C, S and Ba cycles in response to the Shuram oxygenation event. Journal of the Geological Society, 2021. 179(2).
2.          Chen, X. and Y. Zhou, Effective Leaching of Argillaceous and Dolomitic Carbonate Rocks for Strontium Isotope Stratigraphy. Geostandards and Geoanalytical Research, 2024. 48(1): p. 57-75.
3.          Breit, G.N., E.C. Simmons, and M.B. Goldhaber, Dissolution of barite for the analysis of strontium isotopes and other chemical and isotopic variations using aqueous sodium carbonate. Chemical Geology: Isotope Geoscience section, 1985. 52(3-4): p. 333-336.
4.          Rosseinsky, D.R., The solubilities of sparingly soluble salts in water. Part 5.—The solubility of barium sulphate at 25° C. Transactions of the Faraday Society, 1958. 54(0): p. 116-118.

sequential leaching, barium, carbonate rocks, barite