Award: OCE-2048604

The ocean moves heat, freshwater, and nearly all chemical elements around the planet. Some of those elements are nutrients that support marine life. However, tracking where nutrient elements originate, how they move, and where they are removed can be difficult because many ocean processes happen far from land, deep below the surface, or over long timescales. To address this challenge, this project used two chemical tracers, radium and barium, that help reveal how the ocean works. Radium is especially useful for tracing inputs from the edges of the ocean, including continental shelves, seafloor sediments, and hydrothermal vents. Barium is closely tied to internal ocean cycling, including the formation and dissolution of particles in seawater. Together, these tracers provide complementary ways to study both external inputs and internal transformations.

The project focused on samples collected as part of the U.S. GEOTRACES GP17-OCE expedition, which crossed the South Pacific and Southern Ocean. This region is important because waters formed or transformed near the Southern Ocean help supply nutrients to other parts of the ocean. One major outcome of the project was showing that boundary processes are more important for open-ocean chemistry than previously recognized. In particular, the results show that Subantarctic Mode Water formed near the Campbell Plateau and Chatham Rise can carry shelf-derived radium and associated trace-element nutrients into the subtropical South Pacific. This matters because these waters help connect shallow ocean boundaries to remote open-ocean ecosystems. The project also found evidence for recent hydrothermal input along the Pacific-Antarctic Ridge and used radium isotopes to estimate the age of the hydrothermal plume. These findings show how focused inputs at ocean boundaries can become connected to much larger-scale patterns of ocean chemistry.

The project also produced new global views of barium in seawater. Using recent GEOTRACES observations and machine learning, the project generated global estimates of dissolved barium distributions. This output was then used in a mechanistic model to test how barium distributions are shaped by multiple processes, including ocean circulation, particle formation and dissolution, and the chemical environment in which those transformations occur. This research shows how large community datasets can be converted into global chemical maps, and how those maps can then be used to test ideas about the processes that control ocean chemistry. In this way, the project connects modern ocean observations to broader questions about marine geochemical cycles and Earth history.

Results from this award have been shared through peer-reviewed publications, submitted manuscripts, public datasets, model outputs, conference presentations, seminars, and public-facing science communication. Data products and model outputs have been archived in public repositories so that other researchers can reuse them. The project also supported training through hands-on research experiences in fieldwork, isotope geochemistry, data analysis, data stewardship, modeling, scientific writing, and presentation of results. In addition, the project contributed to broader public engagement through participation in a Scientific American podcast about Southern Ocean research and by sharing open-source 3D-printable laboratory tools that can be used by other research and teaching laboratories.

Last Modified: 06/22/2026
Modified by: Tristan J Horner