Award: OCE-2046790

The transport of material from the surface ocean to depth plays a critical role in carbon storage, pollutant removal, and as a source of food for deep-sea organisms. This collaborative effort was designed to better understand the biological and chemical processes that influence the amount and timing of sinking particles and the trace elements and isotopes (TEIs) they carry from the ocean’s surface.  We used the radioactive isotope thorium-234 (234Th) as a naturally occurring tracer that integrates processes of particle formation, sinking, and recycling over monthly timescales. To achieve these objectives, field sampling was conducted during two major oceanographic expeditions that covered some of the most remote and complex 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. The second cruise occurred a year later, from November 2023 to January 2024, across the biologically rich Amundsen Sea and the Antarctic 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 the surface to depths of over 1000 meters. An example of our ²³⁴Th results is shown in Figure 1 and demonstrates the high variability in downward fluxes (sinking particles) across the regions sampled. These results will be pivotal for understanding the transport of carbon and other trace elements from the ocean surface to the deep sea and their role in the biogeochemical cycling of carbon and trace elements. 

This project also gave significant training opportunities to early-career scientists. Dr. Wokil Bam advanced from being a WHOI postdoctoral researcher to an 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 cooperation between U.S. and international partners.  All data and results have been shared with GEOTRACES community and are readily available to all through their data management efforts.

This project has made 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 are transformed, transported, and recycled in different ocean regions, information that is essential for improving global biogeochemical and climate models. The results show that variations in ²³⁴Th and particulate organic carbon fluxes vary significantly 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 inputs driven by a changing climate.

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 pellets) in ocean systems. This event was attended by more than 1,000 individuals from diverse age groups and educational backgrounds. 

Overall, this project successfully achieved its core goals: Completing extensive field sampling, producing high-quality ²³⁴Th datasets and particulate organic carbon export data, 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: 12/03/2025
Modified by: Claudia R Benitez-Nelson