Award: OCE-1737136

This award funded the successful collection, processing, and analysis of water column, particle, and aerosol samples for 'trace metals' and their isotopes from the US GEOTRACES GP15 Pacific Meridional Transect Cruise which sailed from Alaska to Tahiti. Overall, in collaboration with Seth John at the University of Southern Caliornia, high-resolution ocean sections of each of five bioactive trace metals (Fe, Ni, Cu, Zn, and Cd) and their isotopes (δ56Fe, δ60Ni, δ65Cu, δ66Zn, and δ114Cd) were completed (around 4000 data in total), representing a remarkable increase in the amount of data for these parameters in the ocean. Data was also collected on marine and atmospheric particle composition.These trace metal data were then used to address hypotheses and questions of oceanographic relevance in the North Pacific. Intellectual Merit Outcomes: The trace metals (Fe, Ni, Zn, Cu, and Cd) all play a vital bioactive role in the oceans, influening algal growth, marine biogeochemistry, primary productivity, and carbon cycling. They may also act as toxins, or as important geochemical tracers of biological activity, export processes, nutrient cycling and particle scavenging. Yet, fundamental questions remain about the processes which control their cycling. Answering these questions remain key to constaining the role of these elements in modern carbon cycling, but aso the application of elemental and isotopic tracers as paleo-proxies in the past. In this project, in adidtion to providing a high-resolution picture of these elements in the oldest ocean waters at the end of the global conveyerbelt (North Pacific Deep Water), we made a number of globally relevant findings, including: 1) Using the North Pacific as a case study, we show that oceanic Oxygen Minimum Zones do not act as removal locations for trace metals such as Cd or Zn, as had been previously hypothesized. Instead, we show that variable uptake of these elements into marine algae at thes surface relative to nutrients, and deeper release can explain their global distributions. This has implications for understanding how changing ocean oxgygenation in the past and future may impact these elements. 2) Using field data and modelling for the oldest waters in the ocean, we complete the global picture of Zn and Cd distributions through the oceans, and show that reversible particle exchange of Zn is likely to be important in setting distributions. We address questions that have been asked since the first Zn and Cd measurements were made in the North Pacific over 50 years ago. Our findings help groundtruth the use of these elements and their isotopes as proxies for paleo-oceanographers. 2) We show that a range of Fe sources are important to the North Pacific. At the surface, local sources supply Fe to the Alaskan coast, but these are prevented from reaching the open ocean by oceanographic currents. At depth, using a novel combination of Fe data, radionuclides, and other tracers, we show that iron plumes along the Alaskan Margin are actually sourced via long-distance transport from the Western subarctic Pacific. This suggests that previous global datasets of marginal Fe plumes may need more interpreation. We also show the importance of various hydrothermal vent locations on suppling iron throughout the intermediate and deep North Pacific (e.g. Loihi, East Pacific Rise, Juan de Fuca vents). 4) For the first time, we show that a remnant oceanic pool of dissolved Ni present in all surface waters is actually available to marine algae, and not unavailable as was thought. We also show how slow nutrient utilisation of Ni at high latitudes, together with slow regeneration (or reversible particle exchange) through the oceans explains global Ni distributions. Broader Impact Outcomes: This proposal included the professional development, education, and training of an early-career tenure-track PI, a postdoctoral fellow, two graduate students, and an undergraduate REU student from a Minority-Serving Institution, and led to three graduate student dissertations. The work also supported the USF Plasma Facility. Results were communicated to a range of scientific audiences at US Institutions, International Conferences, and to the local public in Florida (the St Petersburg Science Festival and the American Society of Chemical Engineers). The work addresses questions of broad oceanographic interest, with the results having the potential to transform understanding of metal cycling in the oceans, as well as the role of these metals in influencing carbon cycling and climate change. This work was carried out within the scope of the International GEOTRACES project, including rigorous intercomparison of data between NSF-funded US groups, and novel collaborations with Japanese GEOTRACES Groups. All data will be made available to the public, facilitating future synergistic and multidisciplinary approaches to understanding global biogeochemical cycling. Data from this project will be included in future GEOTRACES Data Product and electronic atlases (https://www.egeotraces.org/). Last Modified: 06/02/2023 Submitted by: Timothy M Conway