Article

Nature 407, 695-702 (12 October 2000) | doi:10.1038/35037500; Received 6 January 2000; Accepted 4 September 2000

A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization

Philip W. Boyd1, Andrew J. Watson2, Cliff S. Law3, Edward R. Abraham4, Thomas Trull5, Rob Murdoch4, Dorothee C. E. Bakker2, Andrew R. Bowie6,3, K. O. Buesseler7, Hoe Chang4, Matthew Charette7, Peter Croot8, Ken Downing4, Russell Frew9, Mark Gall10, Mark Hadfield4, Julie Hall11, Mike Harvey4, Greg Jameson3, Julie LaRoche12, Malcolm Liddicoat3, Roger Ling3, Maria T. Maldonado13,14, R. Michael McKay15, Scott Nodder4, Stu Pickmere11, Rick Pridmore11, Steve Rintoul16, Karl Safi11, Philip Sutton4, Robert Strzepek17, Kim Tanneberger2, Suzanne Turner2, Anya Waite18 & John Zeldis10

  1. National Institute of Water and Atmosphere, Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, Dunedin, New Zealand
  2. School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK;
  3. Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, Devon PL1 3DH , UK;
  4. National Institute of Water and Atmosphere, Greta Point, PO Box 14-901, Wellington, New Zealand ;
  5. Antarctic Co-operative Research Centre, University of Tasmania, GPO Box 252-80, Hobart, Tasmania, 7001, Australia;
  6. Department of Environmental Sciences,University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK;
  7. Department of Marine Chemistry and Geochemistry MS25, Woods Hole Oceanographic Institute, Woods Hole, Massachusetts 02543, USA;
  8. Netherlands Institute for Sea Research (NIOZ), Department of Marine Chemistry and Geology, Postbus 59, 1790 AB Den Burg – Texel, The Netherlands;
  9. Department of Chemistry, University of Otago, PO Box 56, Dunedin, New Zealand;
  10. National Institute of Water and Atmosphere, Christchurch , PO Box 8602, Christchurch, New Zealand ;
  11. National Institute of Water and Atmosphere, Hamilton , Box 11-115, Hamilton, New Zealand ;
  12. Institut fuer Meereskunde, Universitaet Kiel, Duesternbrooker Weg 20 D-24105 Kiel, Germany;
  13. Biology Department, McGill University, 1205 Avenue, Dr. Penfield, Montreal, PQ H2T 2V8, Canada;
  14. Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403, USA;
  15. CSIRO Division of Marine Research, GPO Box 1538, Hobart, Tasmania, 7001, Australia;
  16. University of British Columbia, Departments of Botany and Oceanography, 6270 University Boulevard, Vancouver, BC, Canada, V6T 1Z4;
  17. Centre for Water Research, Department of Environmental Engineering, University of Western Australia, Nedlands 6907, Western Australia, Australia.
  18. Present address: School of Marine Sciences, University of Maine, Orono, Maine 04469, USA.

Correspondence to: Philip W. Boyd1 Correspondence and requests for materials should be addressed to P.W.B. (e-mail: Email: pboyd@alkali.otago.ac.nz).

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Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis'. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.