EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-3486 Temporal variability in offshore Fe fluxes in the Peruvian oxygen minimum zone across an El Niño termination Chen Guanghui 1 Rapp Insa 2 Sieber Matthias 3 4 Achterberg Eric P. 2 Conway Tim J. 3 Gledhill Martha 2 Hopwood Mark J. https://orcid.org/0000-0002-9743-079X 2 5 Xie Ruifang C. https://orcid.org/0000-0002-6628-9236 1 2 6 State Key Laboratory of Submarine Geoscience and School of Oceanography, Shanghai Jiao Tong University, Shanghai, 200030, China GEOMAR Helmholtz Centre for Ocean Research, Kiel, 24148, Germany College of Marine Science, University of South Florida, St. Petersburg, 33701, USA Department of Earth and Planetary Sciences, ETH Zürich, Zürich, 8092, Switzerland Department of Ocean Science and Engineering, Southern University of Science and Technology, Shenzhen, 518055, China Key Laboratory for Polar Science, Polar Research Institute of China, Ministry of Natural Resources, Shanghai, 200136, China 25 06 2026 2026 1 21 Copyright: © 2026 Guanghui Chen et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3486/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3486/egusphere-2026-3486.pdf

Offshore fluxes of Fe in the Peruvian oxygen minimum zone are sensitive to seawater redox state, and potentially modulated by the El Ni&ntilde;o-Southern Oscillation. However, observational data on what controls such temporal variation in offshore Fe fluxes remain scarce. Here, we report seawater concentrations of dissolved Fe (dFe), particulate Fe (pFe), and their isotopic compositions (&delta;<sup>56</sup>dFe and &delta;<sup>56</sup>pFe) from two transects at 12&deg; S and 14&deg; S across the Peruvian shelf. Our data show clear shelf-to-slope dFe and pFe plumes with negative &delta;<sup>56</sup>Fe signatures. Maximum Fe concentrations at 12&deg; S decreased from 13 to 4 nmol kg<sup>&minus;1</sup> (dFe) and 122 to 13 nmol kg<sup>&minus;1</sup> (pFe) over a month across an El Ni&ntilde;o event termination. We link these variations to an intensifying Peru-Chile Undercurrent which enhanced oxygen supply and thereby weakened sedimentary reductive Fe effluxes. Off shelf, elevated &delta;<sup>56</sup>dFe and low &delta;<sup>56</sup>pFe in anoxic waters are attributed to organic ligand binding and authigenic Fe formation.