Fertilization of the ocean by adding iron compounds has induced diatom-dominated phytoplankton blooms accompanied by considerable carbon dioxide drawdown in the ocean surface layer. However, because the fate of bloom biomass could not be adequately resolved in these experiments, the timescales of carbon sequestration from the atmosphere are uncertain. Here we report the results of a five-week experiment carried out in the closed core of a vertically coherent, mesoscale eddy of the Antarctic Circumpolar Current, during which we tracked sinking particles from the surface to the deep-sea floor. A large diatom bloom peaked in the fourth week after fertilization. This was followed by mass mortality of several diatom species that formed rapidly sinking, mucilaginous aggregates of entangled cells and chains. Taken together, multiple lines of evidence—although each with important uncertainties—lead us to conclude that at least half the bloom biomass sank far below a depth of 1,000 metres and that a substantial portion is likely to have reached the sea floor. Thus, iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments.

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  1. 1.

    Hain, M. P. & Haug, G. H. The polar ocean and glacial cycles in atmospheric CO2 concentration. Nature 466, 47–55 (2010)

  2. 2.

    et al. Wind-driven upwelling in the Southern Ocean and the deglacial rise in atmospheric CO2. Science 323, 1443–1448 (2009)

  3. 3.

    Glacial-interglacial CO2 changes: the iron hypothesis. Paleoceanography 5, 1–13 (1990)

  4. 4.

    et al. Southern Ocean iron enrichment experiment: carbon cycling in high- and low-Si waters. Science 304, 408–414 (2004)

  5. 5.

    et al. Mesoscale iron-enrichment experiments 1993–2005: synthesis and future directions. Science 315, 612–617 (2007)

  6. 6.

    et al. The Southern Ocean biological response to aeolian iron deposition. Science 317, 1067–1070 (2007)

  7. 7.

    et al. Volcanic ash fuels anomalous plankton bloom in subarctic northeast Pacific. Geophys. Res. Lett. 37, L19604 (2010)

  8. 8.

    et al. Material supply to the abyssal seafloor in the Northeast Atlantic. Prog. Oceanogr. 50, 27–63 (2001)

  9. 9.

    , , , & Extensive phytoplankton blooms in the Atlantic sector of the glacial Southern Ocean. Paleoceanography 21, PA1013 (2006)

  10. 10.

    , , & Role of marine biology in glacial-interglacial CO2 cycles. Science 308, 74–78 (2005)

  11. 11.

    . Geoengineering the Climate: Science, Governance and Uncertainty. RS policy document 10/09 (The Royal Society, 2009)

  12. 12.

    , , & Global observations of large oceanic eddies. Geophys. Res. Lett. 34, L15606 (2007)

  13. 13.

    , , , & Comparison between Eulerian diagnostics and finite-size Lyapunov exponents computed from altimetry in the Algerian basin. Deep Sea Res. Part I Oceanogr. Res. Pap. 56, 15–31 (2009)

  14. 14.

    , , & Mixing in cyclonic eddies in the Antarctic Circumpolar Current. J. Mar. Res. 67, 1–23 (2009)

  15. 15.

    , , & Mixed layer analysis of a mesoscale eddy in the Antarctic Polar Front Zone. J. Geophys. Res. 113, C05017 (2008)

  16. 16.

    , , , & Mesopelagic carbon remineralization during the European Iron Fertilization Experiment. Glob. Biogeochem. Cycles 22, GB1023 (2008)

  17. 17.

    & The oceanic phosphorus cycle. Chem. Rev. 107, 563–576 (2007)

  18. 18.

    , , & Robotic observations of enhanced carbon biomass and export at 55° S during SOFeX. Science 304, 417–420 (2004)

  19. 19.

    A model of the formation of marine algal flocs by physical coagulation processes. Deep-Sea Res. 37, 1197–1211 (1990)

  20. 20.

    & The relationship between physical aggregation of phytoplankton and particle flux: a numerical model. Deep-Sea Res. A 39, 1085–1102 (1992)

  21. 21.

    et al. Synthesis of iron fertilization experiments: from the iron age in the age of enlightenment. J. Geophys. Res. 110, C09S16 (2005)

  22. 22.

    et al. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean. Nature 446, 1070–1074 (2007)

  23. 23.

    et al. Southern Ocean deep-water carbon export enhanced by natural iron fertilization. Nature 457, 577–580 (2009)

  24. 24.

    in Oceanography and Marine Biology. An Annual Review (eds , & ) 171–232 (Taylor & Francis, 2002)

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We thank C. Balt, K. Loquay, S. Mkatshwa, H. Prandke, H. Rohr, M. Thomas and I. Vöge for help on board. We are also grateful to U. Struck for POC and PON analyses. The altimeter products were produced by Ssalto/Duacs and distributed by Aviso with support from Cnes. We thank the captain and crew of RV Polarstern (cruise ANT XXI/3) for support throughout the cruise.

Author information

Author notes

    • Victor Smetacek
    •  & Christine Klaas

    These authors contributed equally to this work.


  1. Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany

    • Victor Smetacek
    • , Christine Klaas
    • , Volker H. Strass
    • , Philipp Assmy
    • , Boris Cisewski
    • , Ulrich Bathmann
    • , Joachim Henjes
    • , Martin Losch
    • , Ilka Peeken
    • , Oliver Sachs
    • , Eberhard Sauter
    • , Jill Schwarz
    • , Anja Terbrüggen
    •  & Dieter Wolf-Gladrow
  2. National Institute of Oceanography, Dona Paula, Goa 403 004, India

    • Victor Smetacek
  3. Norwegian Polar Institute, Fram Centre, Hjalmar Johansens Gate 14, 9296 Tromsø, Norway

    • Philipp Assmy
  4. Ecology and Evolution of Plankton, Stazione Zoologica Anton Dohrn, Villa Comunale, 80121-Napoli, Italy

    • Marina Montresor
  5. Johann Heinrich von Thünen Institute, Institute of Sea Fisheries, Palmaille 9, 22767 Hamburg, Germany

    • Boris Cisewski
  6. Department of Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium

    • Nicolas Savoye
  7. Univ. Bordeaux/CNRS, EPOC, UMR 5805, Station Marine d’Arcachon, 2 rue du Professeur Jolyet, F-33120 Arcachon, France

    • Nicolas Savoye
  8. Oceanography Department, University of Cape Town, Private Bag X3, Rondebosch, 7701 Cape Town, South Africa

    • Adrian Webb
  9. LOCEAN-IPSL, CNRS/UPMC/IRD/MNHN, 4 Place Jussieu, 75252 Paris Cedex 5, France

    • Francesco d’Ovidio
  10. Department of Biological Oceanography, Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg, The Netherlands

    • Jesús M. Arrieta
    • , Santiago Gonzalez
    •  & Gerhard J. Herndl
  11. Department of Global Change Research, Instituto Mediterraneo de Estudios Avanzados, CSIC-UIB, Miquel Marques 21, 07190 Esporles, Mallorca, Spain

    • Jesús M. Arrieta
  12. Leibniz Institute for Baltic Sea Research Warnemünde, Seestraße 15, 18119 Rostock, Germany

    • Ulrich Bathmann
  13. Bjerknes Centre for Climate Research, University of Bergen, Allegaten 55, N-5007 Bergen, Norway

    • Richard Bellerby
    •  & Craig Neill
  14. Norwegian Institute for Water Research, Thormøhlensgate 53 D, 5006 Bergen, Norway

    • Richard Bellerby
  15. Department of Environmental Earth System Science, Stanford University, Stanford, California 94305, USA

    • Gry Mine Berg
    •  & Matthew M. Mills
  16. Helmholtz Centre for Ocean Research Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany

    • Peter Croot
    •  & Linn J. Hoffmann
  17. Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway, Quadrangle Building, University Road, Galway, Ireland

    • Peter Croot
  18. Phytolutions GmbH, Campus Ring 1, 28759 Bremen, Germany

    • Joachim Henjes
  19. Department of Marine Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria

    • Gerhard J. Herndl
  20. School of Environmental Sciences, University of Liverpool, Room 209 Nicholson Building, 4 Brownlow Street, Liverpool L69 3GP, UK

    • Harry Leach
  21. Wealth from Oceans Flagship, Commonwealth Scientific and Industrial Research Organisation, Castray Esplanade, Hobart, Tasmania 7000, Australia

    • Craig Neill
  22. MARUM – Center for Marine Environmental Sciences, University of Bremen, Leobener Strasse, D-28359 Bremen, Germany

    • Ilka Peeken
  23. Institute for Coastal Research, Helmholtz-Zentrum Geesthacht, Center for Materials and Coastal Research, Max-Planck-Strasse 1, 21502 Geesthacht, Germany

    • Rüdiger Röttgers
  24. Eberhard & Partner AG, General Guisan Strasse 2, 5000 Arau, Switzerland

    • Oliver Sachs
  25. Centre for Biomolecular Interactions Bremen, FB 2, University of Bremen, Postfach 33 04 40, 28359 Bremen, Germany

    • Maike M. Schmidt
  26. School of Marine Science & Engineering, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK

    • Jill Schwarz


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V.S. and C.K. wrote the manuscript. V.S. directed the experiment and C.K. carried out the budget calculations. V.H.S., P.A., M.M. and D.W.-G. contributed to the preparation of the manuscript. V.H.S., B.C., H.L. and M.L. contributed physical data on mixed-layer depth dynamics, eddy coherence, patch movement and transmissometer data. N.S. provided thorium data. A.W. provided nutrient data. P.A. and J.H. provided phytoplankton and BSi data. F.D. carried out the Lagrangian analysis based on delayed-time altimetry. J.M.A. and G.J.H. provided bacterial data. C.N. and R.B. provided inorganic carbon data. G.M.B., C.K. and M.M.M. provided POC and PON data. P.C. provided the iron data. S.G. and A.T. provided DOM data. I.P. and L.J.H. performed the 14C primary production measurements and provided high-pressure liquid chromatography data. R.R. provided data on photochemical efficiency (Fv/Fm). C.K., M.M.S. and A.T. provided Chl data. U.B., E.S., O.S. and J.S. provided data on the eddy core from a subsequent cruise and satellite Chl images.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Victor Smetacek or Christine Klaas.

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    Supplementary Information 1

    This file contains Supplementary Text and Data 1-5 (see contents). Each section also includes Supplementary Figures, Supplementary Tables and additional references.

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    Supplementary Information 2

    This file contains Supplementary Methods, additional references, Supplementary Figures 1-7 and Supplementary Tables 1-3. This file was replaced on 20 July 2012, as the figures that appeared in the original file were incorrect.

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