Award: OCE-2045408

Understanding How Elements Move Through the Ocean

This project is a collaborative research effort designed to better understand how biologically, and chemically active elements move through the ocean and contribute to the global carbon and trace elements cycles. Using the naturally occurring radioactive isotope thorium-234 (²³⁴Th) as a tracer, the project focused on quantifying how particles form, sink, and are recycled in the ocean. The project investigated how oceanic processes govern the distribution of trace elements and isotopes (TEIs), shaping carbon storage, nutrient and metal cycling, and their sensitivity to environmental change.

To achieve these objectives, field sampling was conducted during two major oceanographic expeditions, covering some of the most remote and scientifically valuable regions of the world’s oceans. The first cruise, aboard the R/V Roger Revelle, took place from November 2022 to January 2023, running from Tahiti to Punta Arenas, Chile, across the South Pacific and Southern Ocean. This region is known for its clear, low-dust, and low productivity, providing insight into how trace elements behave in contrasting environments. The second cruise followed a year later from November 2023 to January 2024 across the biologically rich Amundsen Sea and Antarctica Coastal regions. Together, these sections represent two extremes of ocean biogeochemistry, from oligotrophic gyres to highly productive ecosystems, allowing researchers to compare how particle fluxes and trace element dynamics vary across these gradients.

Across both cruises, the team collected thousands of samples from depths ranging from the surface to over 1000 meters. An example of the thorium-234 results is shown in Figure 1, demonstrating great variability in the flux, or loss of this radionuclide from the surface ocean.  These results will be used to look at the transport of carbon and other trace elements from the surface ocean to the deep sea. 

This project also provided major training opportunities for early-career scientists. Dr. Wokil Bam advanced from WHOI postdoctoral researcher to Assistant Professor at the University of Southern Mississippi in 2025. He gained hands-on experience in oceanographic fieldwork, sample processing, and data interpretation, as well as leadership in cruise operations and international collaboration. The GEOTRACES community provided an excellent platform for professional networking, fostering collaboration between U.S. and international teams.  All data and results have been shared with GEOTRACES community and through their data management efforts, are readily available to all.

In terms of Broader Impacts and Contributions, this project makes several important contributions to science and society:

a)     Enhancing global ocean knowledge:
The results add to a growing international dataset on how trace elements and carbon move through different ocean regions, which is essential for improving global biogeochemical and climate models. The results show the variations in ²³⁴Th fluxes and particulate organic carbon fluxes across the different oceanic regimes.

b)     Supporting future climate research:
Understanding how particles and trace metals behave in contrasting ocean environments helps predict how the ocean will respond to changes in temperature, productivity, and dust input factors that influence the global carbon sink.

c)     Building scientific capacity:
Through mentoring, training, and collaboration, the project supported the development of new oceanographers, fostering diversity and continuity in the marine science community.

d)     Promoting open science:
By contributing high-quality, standardized data to GEOTRACES and BCO-DMO databases, the project ensures that results are freely available for future researchers, educators, and modelers worldwide.

e)     Engaging in Public:
Dr. Ken Buesseler and Dr. Wokil Bam hosted a dedicated booth at the WHOI Science Stroll in 2023 and 2024, where they shared insights into the marine carbon cycle and the pivotal role of organic matter (aka fecal pallets). This event was attended by more than 1000 individuals of different age groups and educational backgrounds. 

Overall, this project successfully achieved its core goals: completing extensive field sampling, producing high-quality 234Th datasets, contributing to international collaborations, and training the next generation of marine scientists. It has expanded our understanding of how biological and chemical processes move materials through the ocean and set the stage for new research into the links between particles, trace metals, and the global carbon cycle.

Last Modified: 11/06/2025
Modified by: Ken O Buesseler