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. 2021 Apr 6;12:2069. doi: 10.1038/s41467-021-22258-1

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 1 — a A diurnal tidal inflow of ferruginous seawater creates an anoxic Fe(II) layer over oxygenic phototrophic Cyanobacterial mats. Photosynthetic oxygen creates green rust (GR) in the upper boundary layer by partial oxidation of Fe(II) during the day. Closer to the Cyanobacterial mats, Fe(III) is the dominant species, as Fe(II) and precipitating GR is completely oxidised. b During the night time, no oxygen is produced by photosynthesis and the littoral zone becomes ferruginous with precipitated Fe(III) oxides and/or GR, produced in the daytime, at the bottom layer. c Tidal outflow transports GR and Fe(III) in the anoxic open ocean, where the remaining Fe(III) can react with Fe(II) to GR. GR and/or Fe(III) sink to the bottom and form deep ocean sediments. High oxygen levels during the day oxidise Fe(II) from the pelagic zone and thereby prevent Fe(II) from reaching the littoral zone. Surplus oxygen not consumed by the oxidation of Fe(II) escapes into the atmosphere leading to localised land weathering, thereby releasing additional nutrients. Additional weathering at the oxygen-rich microbe–mineral interface cannot be excluded. Image created from references^{6, 12, 13, 17, 18}.