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Examining the interaction between free-living bacteria and iron in the global ocean
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  • Anh Le-Duy Pham,
  • Olivier Aumont,
  • Lavenia Ratnarajah,
  • Alessandro Tagliabue
Anh Le-Duy Pham
Georgia Institute of Technology

Corresponding Author:[email protected]

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Olivier Aumont
Laboratoire d'Océanographie et du Climat: Expérimentations et approches numériques, Unité Mixte de Recherche 7159 CNRS / IRD / Université Pierre et Marie Curie/MNHN
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Lavenia Ratnarajah
Department of Earth, Ocean and Ecological Sciences, School of Environmental Sciences, University of Liverpool
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Alessandro Tagliabue
University of Liverpool
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Marine free-living bacteria play a key role in the cycling of essential biogeochemical elements, including iron (Fe), during their uptake, transformation and release of organic matter. Similar to phytoplankton, the growth of free-living bacteria is regulated by resources such as Fe, and the low availability of these resources may influence bacterial interactions with phytoplankton, causing knock-on effects for biogeochemical cycling. Yet, knowledge of the factors limiting free-living bacterial growth and their role within the Fe cycle is poorly constrained. Here, we explicitly represent free-living bacteria in a global ocean biogeochemistry model to address these questions. We find that although Fe can emerge as proximally limiting in the tropical Pacific and in high-latitude regions during summer, the growth of free-living bacteria is ultimately controlled by the availability of labile dissolved organic carbon. In Fe-limited regions, free-living bacterial biomass is sensitive to their Fe uptake capability in seasonally Fe-limitation regions and to their minimum Fe requirements in regions perennially Fe-limited. Fe consumption by free-living bacteria is significant in the upper ocean in our model, and their competition with phytoplankton for Fe affects phytoplankton growth dynamics. The impact of free-living bacteria on the Fe distribution in the ocean interior is small due to a tight coupling between Fe uptake and release. Moving forward, future work that considers particle-attached bacteria and different bacterial metabolisms is needed to explore the broader role of bacteria in ocean Fe cycling. In this context, the global growing ’omics data from ocean observing programs can play a crucial role.