Two studies published by Jule Middleton documenting the rates, sensitivities, and barium-isotopic consequences of ion exchange in barite. The first paper investigated how fast and how much ion exchange affected the isotope composition of barium in barite–fluid systems. We did this by performing laboratory experiments under marine-relevant conditions. The main findings are that ion exchange occurs rapidly and results in a small-but-significant net Ba-isotopic fractionation of ≈−0.1 ‰. The results are published in Chemical Geology and can be accessed here for free until May 30th, 2023. (After that date, please contact one of the authors for a PDF if you cannot access.)
The second study takes these insights and applies them to the marine realm, specifically seawater, sediments, and porewaters from the Equatorial Pacific. Here we found that the barium isotope composition of porewaters was the same as bottom waters, whereas the porewaters were offset from co-located barites. Rather than reflecting seawater intrusion in sediments, we show that the porewaters are in isotopic equilibrium with the barites and that the slight barium isotope offset between the two phases is consistent with ion exchange. The results are described in Earth and Planetary Science Letters and can and can be accessed here for free until June 9th, 2023. (After that date, please contact one of the authors for a PDF if you cannot access.)
These studies show that ion exchange changes the barium isotope composition of barites that remain in contact with a fluid. Under some conditions, this process will affect the long-term fidelity of barite-hosted barium isotope records, and we encourage barium isotope practitioners to consider ion exchange when interpreting their data.
Middleton, J. T., Hong, W. L., Paytan, A., Auro, M. E., Griffith, E. M., & Horner, T. J. (2023). Barium isotope fractionation in barite–fluid systems at chemical equilibrium. Chemical Geology, 627, 121453, doi:10.1016/j.chemgeo.2023.121453.
Middleton, J. T., Paytan, A., Auro, M. E., Saito, M.A., & Horner, T. J. (2023). Barium isotope signatures of barite–fluid ion exchange in Equatorial Pacific sediments. Earth and Planetary Science Letters, 612, 118150, doi:10.1016/j.epsl.2023.118150.