Award: OCE-2023456

The oceans shape Earth's climate by storing heat and moving carbon and nutrients around the planet. To understand how the ocean works -- and how it has changed over time -- scientists often rely on chemical 'fingerprints' preserved in seawater and seafloor sediments. This project focused on one such fingerprinting tool: the element barium. Although barium occurs in seawater at very low levels, its distribution and cycling are of particular interest because they are closely linked to the formation of a mineral called barite. Barite first forms as microscopic particles in the ocean through a process associated with the breakdown of organic material in the water column, then these particles sink. Because of this connection, measurements of barium and barite can be used to track how carbon and nutrients move through the ocean, both today and in the past.

A central outcome of the project was improving how reliably barium-based measurements can be interpreted. We showed that the stable isotope signature of barium -- small, measurable differences in the relative abundance of barium atoms -- changes in a consistent way when barite forms. This matters because isotope signatures are used to interpret environmental conditions, and those interpretations are most robust when the underlying chemical behavior is consistent across different settings. The project also identified an important process: the barium isotope signature preserved in seafloor minerals can be altered over time by chemical exchange with porewater, or seawater trapped within sediments. By combining laboratory experiments with modeling, we identified when this type of alteration is most likely to occur and provided practical guidance for recognizing sediment samples that best preserve original environmental information.

The project also produced new ways to describe barium in the modern ocean at a global scale. Using a data-driven modeling approach informed by recent GEOTRACES measurements, we created a three-dimensional picture of dissolved barium throughout the world's oceans and improved estimates of how much barium the ocean contains overall. Regional syntheses, including research in the Arctic Ocean, highlighted that coastal margins and sediment interactions can strongly influence barium chemistry, in addition to biological processes and ocean circulation. Beyond barium itself, the project developed methods and workflows that can be adapted to other ocean chemistry questions where observations are limited and measurements are difficult.

Results from this award have been shared primarily through peer-reviewed scientific publications and publicly accessible datasets. Measurements and derived products generated by the project were archived in established public repositories so that other researchers can reuse them. In addition, the project supported training through hands-on research experiences, including laboratory experiments, fieldwork, data analysis, and scientific writing. Finally, the project contributed to practical knowledge-sharing beyond the research literature by making openly available a set of 3D-printable laboratory designs developed during the course of the work.

Last Modified: 01/09/2026
Modified by: Tristan J Horner