Iron cycling in continental margin sediments and the nutrient and oxygen balance of the ocean

• Applicant: Professor Dr. Florian Scholz
• Subject Area: Oceanography ; Mineralogy, Petrology and Geochemistry
• Term: from 2016 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 283168947

• Final Report Year: 2025

Final Report Abstract

The ICONOX project, conducted between 2016 and 2025, focused on unraveling the complex biogeochemical feedbacks between iron (Fe), nitrogen, and trace metal cycling in the water column and sediments of oxygen minimum zones. Through participation in multiple research expeditions, the project team investigated the environmental conditions under which sedimentary Fe is released into the water column, where it may support biological productivity in the surface ocean. In addition, paleo-records were analyzed to identify potential feedback mechanisms linking sedimentary Fe release or retention to carbon and nutrient cycling and oxygen consumption in the ocean's interior. These empirical findings informed the development of numerical models designed to explore how coupled cycles of Fe, nutrients, and carbon may respond to ongoing, human-driven ocean deoxygenation. The project demonstrated that the release and redistribution of Fe from sediments is a widespread phenomenon in oxygen-deficient marine environments. However, only a limited fraction of the mobilized Fe ultimately reaches the surface ocean to support primary productivity. Instead, much of it is retained or transformed within the water column or sediments. One of the key insights from the project was the identification of chemical weathering on land as a primary control on the supply of reactive Fe to marine sediments. Additionally, the transformation of silicate minerals, including their alteration, partial dissolution, and neoformation, was found to significantly influence the mobility of sedimentary Fe. Modeling results showed that sedimentary Fe release responds dynamically to decreasing oxygen concentrations in bottom waters. These findings imply that continued ocean deoxygenation could stimulate further Fe release from sediments, potentially alleviating Fe limitation in certain regions and amplifying oxygen demand in subsurface waters through enhanced biological activity. The ICONOX project thus provides important insights into how elemental cycles in the ocean are interlinked and how they may evolve under future climate conditions.

Publications

• Chromium isotope cycling in the water column and sediments of the Peruvian continental margin. Geochimica et Cosmochimica Acta, 257, 224-242.
  Bruggmann, S.; Scholz, F.; Klaebe, R.M.; Canfield, D.E. & Frei, R.
  
• Dissolved benthic phosphate, iron and carbon fluxes in the Mauritanian upwelling system and implications for ongoing deoxygenation. Deep Sea Research Part I: Oceanographic Research Papers, 143, 70-84.
  Schroller-Lomnitz, U.; Hensen, C.; Dale, A.W.; Scholz, F.; Clemens, D.; Sommer, S.; Noffke, A. & Wallmann, K.
  
• Cretaceous oceanic anoxic events prolonged by phosphorus cycle feedbacks. Climate of the Past, 16(2), 757-782.
  Beil, Sebastian; Kuhnt, Wolfgang; Holbourn, Ann; Scholz, Florian; Oxmann, Julian; Wallmann, Klaus; Lorenzen, Janne; Aquit, Mohamed & Chellai, El Hassane
  
• Development of Iron Speciation Reference Materials for Palaeoredox Analysis. Geostandards and Geoanalytical Research, 44(3), 581-591.
  Alcott, Lewis J.; Krause, Alexander J.; Hammarlund, Emma U.; Bjerrum, Christian J.; Scholz, Florian; Xiong, Yijun; Hobson, Andrew J.; Neve, Lesley; Mills, Benjamin J. W.; März, Christian; Schnetger, Bernhard; Bekker, Andrey & Poulton, Simon W.
  
• A new view on the evolution of seawater molybdenum inventories before and during the Cretaceous Oceanic Anoxic Event 2. Chemical Geology, 582, 120399.
  Siebert, Christopher; Scholz, Florian & Kuhnt, Wolfgang
  
• Constraining Global Marine Iron Sources and Ligand‐Mediated Scavenging Fluxes With GEOTRACES Dissolved Iron Measurements in an Ocean Biogeochemical Model. Global Biogeochemical Cycles, 35(8).
  Somes, Christopher J.; Dale, Andrew W.; Wallmann, Klaus; Scholz, Florian; Yao, Wanxuan; Oschlies, Andreas; Muglia, Juan; Schmittner, Andreas & Achterberg, Eric P.
  
• Persistent deep water anoxia in the eastern South Atlantic during the last ice age. Proceedings of the National Academy of Sciences, 118(49).
  Riedinger, Natascha; Scholz, Florian; Abshire, Michelle L. & Zabel, Matthias
  
• Recycling and Burial of Biogenic Silica in an Open Margin Oxygen Minimum Zone. Global Biogeochemical Cycles, 35(2).
  Dale, A. W.; Paul, K. M.; Clemens, D.; Scholz, F.; Schroller‐Lomnitz, U.; Wallmann, K.; Geilert, S.; Hensen, C.; Plass, A.; Liebetrau, V.; Grasse, P. & Sommer, S.
  
• Updated estimates of sedimentary potassium sequestration and phosphorus release on the Amazon shelf. Chemical Geology, 560, 120017.
  Spiegel, Timo; Vosteen, Paul; Wallmann, Klaus; Paul, Sophie A.L.; Gledhill, Martha & Scholz, Florian
  
• Environmental changes affect the microbial release of hydrogen sulfide and methane from sediments at Boknis Eck (SW Baltic Sea). Frontiers in Microbiology, 13.
  Perner, Mirjam; Wallmann, Klaus; Adam-Beyer, Nicole; Hepach, Helmke; Laufer-Meiser, Katja; Böhnke, Stefanie; Diercks, Isabel; Bange, Hermann W.; Indenbirken, Daniela; Nikeleit, Verena; Bryce, Casey; Kappler, Andreas; Engel, Anja & Scholz, Florian
  
• Nutrient turnover by large sulfur bacteria on the Namibian mud belt during the low productivity season. Frontiers in Marine Science, 9.
  Chuang, Pei-Chuan; Anderson, Chloe H.; Kossack, Michael; Fabian, Jenny; Su, Chih-Chieh; Vosteen, Paul; Zabel, Matthias; Scholz, Florian; Schulz-Vogt, Heide N.; Sommer, Stefan & Dale, Andrew W.
  
• Smaller fish species in a warm and oxygen-poor Humboldt Current system. Science, 375(6576), 101-104.
  Salvatteci, Renato; Schneider, Ralph R.; Galbraith, Eric; Field, David; Blanz, Thomas; Bauersachs, Thorsten; Crosta, Xavier; Martinez, Philippe; Echevin, Vincent; Scholz, Florian & Bertrand, Arnaud
  
• Uranium isotope cycling on the highly productive Peruvian margin. Chemical Geology, 590, 120705.
  Bruggmann, S.; Gilleaudeau, G.J.; Romaniello, S.J.; Severmann, S.; Canfield, D.E.; Anbar, A.D.; Scholz, F. & Frei, R.
  
• Benthic-pelagic coupling and isotopic fractionation of barium in Kiel Bight, SW Baltic Sea. Frontiers in Marine Science, 10.
  Scholz, Florian; Cheng, Jun; Zhang, Zhouling; Vosteen, Paul; Siebert, Christopher & Frank, Martin
  
• Coastal El Niño triggers rapid marine silicate alteration on the seafloor. Nature Communications, 14(1).
  Geilert, Sonja; Frick, Daniel A.; Garbe-Schönberg, Dieter; Scholz, Florian; Sommer, Stefan; Grasse, Patricia; Vogt, Christoph & Dale, Andrew W.
  
• Dominance of benthic fluxes in the oceanic beryllium budget and implications for paleo-denudation records. Science Advances, 9(23).
  Deng, Kai; Rickli, Jörg; Suhrhoff, Tim Jesper; Du, Jianghui; Scholz, Florian; Severmann, Silke; Yang, Shouye; McManus, James & Vance, Derek
  
• Sedimentary molybdenum and uranium cycling under seasonally contrasting redox conditions on the Namibian Shelf. Geochimica et Cosmochimica Acta, 358, 174-191.
  Kossack, Michael; Scholz, Florian; Anderson, Chloe H.; Vosteen, Paul; Su, Chih-Chieh; Mohrholz, Volker & Zabel, Matthias
  
• Early Diagenetic Controls on Sedimentary Iodine Release and Iodine‐To‐Organic Carbon Ratios in the Paleo‐Record. Global Biogeochemical Cycles, 38(2).
  Scholz, Florian; Hardisty, Dalton S. & Dale, Andrew W.
  
• Refining the roles of productivity, redox, and remineralization on the cadmium isotope composition of marine sediments. Geochimica et Cosmochimica Acta, 372, 134-153.
  Tegler, Logan A.; Nielsen, Sune G.; Wang, Yi; Scholz, Florian; Owens, Jeremy D.; Peterson, Larry; Auro, Maureen; Kinsley, Christopher W.; Lam, Phoebe & Horner, Tristan J.
  
• Stable tungsten (W) isotope systematics in marine sediments: a potential paleo-proxy for deep ocean oxygenation. Earth and Planetary Science Letters, 660, 119346.
  Yang, Ruiyu; Gutjahr, Marcus; Scholz, Florian; Kurzweil, Florian; Eroglu, Sümeyya & Münker, Carsten
  
• Trace metal evolution of the Late Cretaceous Ocean. Chemical Geology, 671, 122477.
  Sun, Mingzhao; Archer, Corey; Scholz, Florian; Sweere, Tim & Vance, Derek