Award: OCE-2023493

Iron (Fe) is an essential nutrient that supports marine life over vast areas of the ocean. However, the sources, transport, and fate of iron in the ocean are complex and only partially understood. This project aimed to investigate how iron is supplied from coastal waters to the open ocean,  focusing on the Oregon/Washington continental margin. Our research combined numerical models with field observations to improve our understanding of iron transport processes and their impacts on marine biogeochemistry.

Key findings

Iron transport mechanisms. Using high-resolution models, we found that iron transport from the Oregon shelf to the open ocean primarily occurs through bottom ocean currents, rather than surface processes. Specific transport “hot-spots” are associated with meanders of the California Undercurrent and small-scale ocean eddies. These findings provide a new framework for understanding how iron and other materials move from the coast to the open ocean (Figure 1). 

Hypoxia and iron release. Coastal hypoxia (low oxygen) plays a critical role in iron release from the sediment. We characterized hypoxia “hotspots” along the U.S. West Coast (Figure 2), where low oxygen enhances release of iron from the seafloor. These hotspots correspond to region of enhanced offshore transport of iron. One such hotspot is the Santa Barbara Basin in Southern California. Here, in collaboration with researchers at UC Santa Barbara, we measured high iron fluxes (Figure 3) and low oxygen concentrations (Figure 4), providing a comprehensive characterization of oxygen variability in the basin, and investigating the consequenes for marine productivity. This work provides insights on how coastal ecosystem may respond to declines in oxygen.

Deep iron plumes. As part of our collaboration with field researchers at University of Southern California, we identified unexpected deep plumes of particulate iron emanating from the Oregon margin (Figure 5). These plumes are connected to hypoxic waters along the continental slope, which likely alter the buoyancy of iron-rich particles and allow them to be transported offshore by the oceanic circulation. 

Coastal iron database. We compiled a new dataset of iron and organic ligand concentrations along the U.S. West Coast, providing a new resource to improve models and expand our understanding of Fe cycle processes along continental margins.

Advancing ocean biogeochemical modeling. We improved the iron cycling component of UCLA’s ROMS-BEC model, improving iron sources and refining the model’s ability to track particulate and dissolved iron forms. 

Broader Impacts

Improving predictions of ocean productivity. Understanding how iron and other nutrients moves through the ocean is essential for predicting changes in marine ecosystems. Our findings contribute to efforts to model ocean productivity, particularly in regions where iron is a limiting nutrient.

Supporting field research and collaboration. Our modeling work directly informed the design of oceanographic field campaigns, ensuring that sampling efforts targeted key locations for iron transport. This collaborative approach strengthened connections between modeling and observational oceanography.

Training the next generation of scientists. The project provided training for students and postdoctoral researchers. Two graduate students completed their Ph.D.s based on research supported by this project and have moved on to postdoctoral positions. Findings from this research were integrated into UCLA’s undergraduate oceanography courses.

Engaging with the scientific community. We shared our results through peer-reviewed publications, presentations at major scientific conferences (including Ocean Sciences, AGU, and GEOTRACES meetings), and participation in international working groups focused on ocean biogeochemistry.

Future Directions. The insights gained from this project have led to new research questions and follow-up investigations, including a new NSF-funded project on the transport and protection of iron along continental margins. We continue to work with the oceanographic community to improve models and support field research efforts focused on iron cycling.

Last Modified: 03/05/2025
Modified by: Daniele Bianchi