Award: OCE-2049639

Iron, manganese, zinc, copper, cobalt, cadmium, and nickel are present in seawater at vanishingly low concentrations, but they exert outsized control on ocean chemistry and biology as essential cofactors for the enzymes phytoplankton use to photosynthesize and respire. Lead, by contrast, is a contaminant that tracks human emissions into surface waters. Mapping these elements is the central charge of the international GEOTRACES program. This award supported the trace-metal component of the U.S. GEOTRACES GP17-OCE section, a 56-day expedition aboard the R/V Roger Revelle (RR2214) from Tahiti to Punta Arenas, Chile (1 December 2022 to 25 January 2023). The transect crossed the South Pacific subtropical gyre, the Antarctic Circumpolar Current, and the Pacific sector of the Southern Ocean: open ocean far from continents, rivers, and dust plumes, where almost no high-resolution trace-metal data existed before GP17-OCE.

Graduate student Phil Kong sailed as the John Lab super-tech on RR2214. At the University of Southern California, research associate Shun-Chung Yang and graduate students Cat Odendahl and Adam Ross then led sample analysis through the GEOTRACES analytical pipeline. By the close of the award, the lab had measured dissolved concentrations of twelve elements (Fe, Mn, Zn, Cu, Cd, Ni, Pb, Co, La, Ce, Pr, Nd) on 251 samples; dissolved nickel and copper stable isotopes on 279 and 256 samples; and total and ligand-leachable particulate iron and δ⁵⁶Fe on 122 samples.

One finding is methodological. Measuring total dissolved copper in seawater is surprisingly difficult: a fraction of dCu is held in tightly bound organic complexes that conventional acidification fails to recover. Yang and his collaborators developed an alternative to the community standard of UV irradiation: a brief hydrogen-peroxide oxidation followed by shortened acidification. Applied to GP17-OCE and to the earlier GP15 transect, the method revealed a refractory dissolved Cu pool that previous methods had missed. The pool is large, accounting for roughly 20% of total dissolved Cu across the Pacific and adding 0.5–1.5 nM to measured concentrations, and it carries an isotopically lighter δ⁶⁵Cu signature. Recognition of this pool requires a revision of the marine copper budget.

Combined with GP15, the GP17-OCE measurements yield the first basin-scale 60°N–60°S Pacific section of dissolved Cu, δ⁶⁵Cu, and δ⁶⁰Ni, and the first basin-scale view of total and ligand-leachable particulate Fe across the Pacific. Crossover-station agreement with the earlier GP16 East Pacific transect is excellent, supporting the combined dataset as a benchmark for the next generation of global iron and trace-metal models.

The award trained three graduate students across the full GEOTRACES analytical pipeline, with at-sea experience for one and leadership of in-preparation manuscripts for all three. Datasets generated under this award are being submitted to the Biological and Chemical Oceanography Data Management Office (BCO-DMO) for open community access. Beyond the immediate research community, the data products and methods developed here support a clearer understanding of how the open ocean delivers essential nutrients to phytoplankton, how toxic metals such as copper differ in the open ocean from polluted coastal waters, and how trace-metal cycling is likely to respond to projected change in the South Pacific and Southern Oceans.

Last Modified: 04/28/2026
Modified by: Seth G John