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Marine biogenic humic substances control iron biogeochemistry across the Southern Ocean

Author

Listed:
  • C. S. Hassler

    (University of Geneva
    Ecole Polytechnique Fédérale de Lausanne
    University of Lausanne)

  • R. Simó

    (ICM-CSIC)

  • S. E. Fawcett

    (University of Cape Town
    University of Cape Town)

  • M. J. Ellwood

    (Australian National University
    Australian National University)

  • S. L. Jaccard

    (University of Lausanne)

Abstract

Iron, which is an essential element for marine photosynthesis, is sparingly soluble in seawater. In consequence, iron bioavailability controls primary productivity in up to 40% of the world’s ocean, including most of the Southern Ocean. Organic ligands are critical to maintaining iron in solution, but their nature is largely unknown. Here, we use a comprehensive dataset of electroactive humics and iron-binding ligands in contrasting regions across the Southern Ocean to show that humic substances are an important part of the iron binding ligand pool, as has been found elsewhere. However, we demonstrate that humics are mostly produced in situ and composed of exopolymeric substances from phytoplankton and bacteria, in contrast to other regions where terrestrially-derived humics are suggested to play a major role. While phytoplankton humics control the biogeochemistry, bioavailability and cycling of iron in surface waters, humics produced or reprocessed by bacteria affect iron cycling and residence time at the scale of the global ocean. Our findings indicate that autochthonous, freshly released organic matter plays a critical role in controlling primary productivity and ocean-climate feedbacks in iron-limited oceanic regions.

Suggested Citation

  • C. S. Hassler & R. Simó & S. E. Fawcett & M. J. Ellwood & S. L. Jaccard, 2025. "Marine biogenic humic substances control iron biogeochemistry across the Southern Ocean," Nature Communications, Nature, vol. 16(1), pages 1-11, December.
  • Handle: RePEc:nat:natcom:v:16:y:2025:i:1:d:10.1038_s41467-025-57491-5
    DOI: 10.1038/s41467-025-57491-5
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    References listed on IDEAS

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    1. Alessandro Tagliabue & Kristen N. Buck & Laura E. Sofen & Benjamin S. Twining & Olivier Aumont & Philip W. Boyd & Salvatore Caprara & William B. Homoky & Rod Johnson & Daniela König & Daniel C. Ohnemu, 2023. "Authigenic mineral phases as a driver of the upper-ocean iron cycle," Nature, Nature, vol. 620(7972), pages 104-109, August.
    2. Alessandro Tagliabue & Andrew R. Bowie & Philip W. Boyd & Kristen N. Buck & Kenneth S. Johnson & Mak A. Saito, 2017. "The integral role of iron in ocean biogeochemistry," Nature, Nature, vol. 543(7643), pages 51-59, March.
    3. Jakob Weis & Zanna Chase & Christina Schallenberg & Peter G. Strutton & Andrew R. Bowie & Sonya L. Fiddes, 2024. "One-third of Southern Ocean productivity is supported by dust deposition," Nature, Nature, vol. 629(8012), pages 603-608, May.
    4. David A. Hutchins & Amy E. Witter & Alison Butler & George W. Luther, 1999. "Competition among marine phytoplankton for different chelated iron species," Nature, Nature, vol. 400(6747), pages 858-861, August.
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