Iron supply from the Oregon margin to the ocean dominated by hypoxia-dependent particles

• 成果类型: Article
• 署名作者: Floback, Alexis E.; Pham, Anh Le-Duy; Damien, Pierre; Odendahl, Catherine E.; Weiske, Jennifer; Thomas, Katherine E.; Gaffney, Justin; John, Seth G.; Bianchi, Daniele; Moffett, James W.
• 署名单位: University of Southern California; University of Hawaii System; University of Hawaii Manoa; University of California System; University of California Los Angeles; University of Southern California; University System of Maryland; University of Maryland Center for Environmental Science
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2532929123
• 发表日期: 2026-05-05
• 页码: e2532929123
• 关键词: iron geochemistry; particulate; hypoxia; continental margin; dissolved iron; trace-metals; oxygen; fe; biogeochemistry; sedimentary; variability; NEWPORT; plume; dust

摘要

Continental margins are sources of iron (Fe), a critical oceanic micronutrient limiting productivity over nearly a third of the ocean. Paradoxically, they are also sinks of Fe and other particle-reactive elements that are sequestered in margin sediments. When dissolved Fe is released from reducing sediments, most is retained on the shelf by oxidative scavenging (Fe trapping), severely constraining cross-shelf export of dissolved Fe. However, observations from the Oregon shelf in 2021 show that cross-shelf export is overwhelmingly dominated by particulate Fe, forming persistent, particle-rich plumes that extend well beyond the shelf-slope break. Particles accumulate in a 30 m thick benthic nepheloid layer within hypoxic zones overlying the continental shelf sediments, previously shown to be a strong source of reduced iron. Surprisingly, resuspended particulate Fe includes both nonlithogenic and lithogenic components, suggesting that hypoxia influences particle buoyancy and resuspension, consistent with recent advances in organic geochemistry. A physical-biogeochemical model that incorporates oxygen-dependent particle sources and realistic settling velocities reproduces the distribution of particle-rich plumes, highlighting the dynamic physical processes driving cross-shelf export of particulate Fe. We propose that increases in particle buoyancy is a previously unrecognized mechanism linking hypoxia and Fe mobilization acting in tandem with well-established redox processes. Particles settle on the continental slope and supply large Fe plumes extending westward from the slope from 200 m to 2,000 m. Simulations with an inverse model show that these plumes outcrop in Fe-limited high nutrient low chlorophyll regions. Thus, local and regional hypoxia on the margins could have basin-scale biogeochemical impacts.