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Microbial sequestration of phosphorus in anoxic upwelling sediments

Nature Geoscience volume 3, pages 557561 (2010) | Download Citation

Abstract

Phosphorus is an essential nutrient for life. In the ocean, phosphorus burial regulates marine primary production1,2. Phosphorus is removed from the ocean by sedimentation of organic matter, and the subsequent conversion of organic phosphorus to phosphate minerals such as apatite, and ultimately phosphorite deposits3,4. Bacteria are thought to mediate these processes5, but the mechanism of sequestration has remained unclear. Here, we present results from laboratory incubations in which we labelled organic-rich sediments from the Benguela upwelling system, Namibia, with a 33P-radiotracer, and tracked the fate of the phosphorus. We show that under both anoxic and oxic conditions, large sulphide-oxidizing bacteria accumulate 33P in their cells, and catalyse the nearly instantaneous conversion of phosphate to apatite. Apatite formation was greatest under anoxic conditions. Nutrient analyses of Namibian upwelling waters and sediments suggest that the rate of phosphate-to-apatite conversion beneath anoxic bottom waters exceeds the rate of phosphorus release during organic matter mineralization in the upper sediment layers. We suggest that bacterial apatite formation is a significant phosphorus sink under anoxic bottom-water conditions. Expanding oxygen minimum zones are projected in simulations of future climate change6, potentially increasing sequestration of marine phosphate, and restricting marine productivity.

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Acknowledgements

We thank K-C. Emeis for cruise coordination, V. Salman and H. Schulz-Vogt for providing extra sediment samples and microscope imaging, and H. Filthuth for support and advice in using the digital autoradiograph. This work has been supported through DFG Research Center/Excellence Cluster ‘The Ocean in the Earth System’.

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Affiliations

  1. MARUM—Center for Marine Environmental Sciences, University of Bremen, 28334 Bremen, Germany

    • Tobias Goldhammer
    • , Timothy G. Ferdelman
    •  & Matthias Zabel
  2. Department of Geological Sciences, Stockholm University, 10691 Stockholm, Sweden

    • Volker Brüchert
  3. Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany

    • Timothy G. Ferdelman

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Contributions

T.G., onshore laboratory work, data analysis and paper writing, V.B., concept and study design, shipboard experiments, data analysis and paper writing, T.G.F., concept for 33P as a radiotracer for microbial P cycling, M.Z., data interpretation and paper writing.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Tobias Goldhammer or Volker Brüchert.

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DOI

https://doi.org/10.1038/ngeo913