Letters to Nature

Nature 407, 727-730 (12 October 2000) | doi:10.1038/35037555; Received 20 December 1999; Accepted 4 September 2000

Importance of stirring in the development of an iron-fertilized phytoplankton bloom

Edward R. Abraham1, Cliff S. Law2, Philip W. Boyd3, Samantha J. Lavender2,4, Maria T. Maldonado5,4 & Andrew R. Bowie7,2

  1. National Institute for Water and Atmospheric Research (NIWA), PO Box 14-901, Kilbirnie , Wellington, New Zealand
  2. Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, Devon PL1 3DH, UK
  3. NIWA Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, Dunedin , New Zealand
  4. Department of Biology, McGill University , 1205 Dr. Penfield Avenue, Montreal, PQ H2T 2V8, Canada
  5. Department of Environmental Sciences, Plymouth Enivronmental Research Centre, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK
  6. Present addresses: Institute of Marine Studies, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, UK (S.J.L.); School of Marine Sciences, 5741 Libby Hall, University of Maine, Orono, Maine 04469, USA (M.M.)

Correspondence to: Edward R. Abraham1 Correspondence and requests for materials should be addressed to E.A. (e-mail: Email: e.abraham@niwa.cri.nz).

The growth of populations is known to be influenced by dispersal, which has often been described as purely diffusive1, 2. In the open ocean, however, the tendrils and filaments of phytoplankton populations provide evidence for dispersal by stirring3, 4. Despite the apparent importance of horizontal stirring for plankton ecology, this process remains poorly characterized. Here we investigate the development of a discrete phytoplankton bloom, which was initiated by the iron fertilization of a patch of water (7 km in diameter) in the Southern Ocean5. Satellite images show a striking, 150-km-long bloom near the experimental site, six weeks after the initial fertilization. We argue that the ribbon-like bloom was produced from the fertilized patch through stirring, growth and diffusion, and we derive an estimate of the stirring rate. In this case, stirring acts as an important control on bloom development, mixing phytoplankton and iron out of the patch, but also entraining silicate. This may have prevented the onset of silicate limitation, and so allowed the bloom to continue for as long as there was sufficient iron. Stirring in the ocean is likely to be variable, so blooms that are initially similar may develop very differently.