Southern Ocean Iron RElease Experiment

The data and their authors.

Cruise data (password access only)

Scientific Rationale

A strong, as yet circumstantial case can be made that iron limitation is important in the Southern Ocean today. During the Southern Ocean Iron Enrichment Experiment (SOIREE) from 31 January to 1 March 1999 on R.V. Tangaroa a patch of seawater has been enriched in iron to test the hypothesis that iron indeed limits the primary production of phytoplankton.

Pre-site survey

During a desktop survey by Mark Hadfield of the National Institute of Water and Atmospheric Research, New Zealand, an optimal site for the experiment had been defined in the polar Southern Ocean. Upon arrival in the area a 72-hour hydrographic survey using CTD and XBT confirmed the choice of the site and provided data on the physical, chemical and biological conditions in the area before the experiment.

The iron release

The release of iron and SF6 (sulphur hexafluoride) as a tracer was initated on 10 February (Boyd et al., 1999). The site had a mixed layer of roughly 65 m depth and low chlorophyll a levels. We raised the dissolved iron concentrations to levels considerably greater than ambient over 50 square kilometers. The elevated dissolved iron level quickly decreased toward the ambient level, necessitating three more infusions during the 13-day experiment. The patch moved about 40 nautical miles, generally eastward and expanded in size to about 150 square kilometers over this period.

Preliminary results

The response of the biota to iron fertilisation was slow in comparison to IRONEX I and II in the equatorial Pacific Ocean (Boyd et al., 1999). Five days after the release significant increases in algal photosynthetic competence were observed, followed by elevated algal biomass. Chlorophyll a levels increased markedly by the time of our departure. Macronutrient levels, the partial pressure of CO2 and the content of total dissolved inorganic carbon decreased from the initial levels. Upper ocean levels of dimethylsulfide increased during the experiment. Daily underway surveys and CTD-casts outside the patch indicate little change in biomass, photosynthetic competence or macronutrient levels. The effect of phytoplankton on surface water parameters was still increasing as R.V. Tangaroa left the area on 23 February.

The data and their authors

Results of the experiment have been presented at the 2000 Ocean Sciences Meeting (EOS Transactions, Vol 80, No 49), in three Nature articles, in a Special Issue of Deep-Sea Researchch and in several other publications. The data are on the CD-Rom Appendix of the Deep-Sea Research Special Issue on SOIREE (DSR II, 2001, 48, 11-12).

Meet the SOIREE science team

Participating institutes and universities

National Institute of Water and Atmospheric Research, NZ
McGill University, Canada
Netherlands Institute for Sea Research
Plymouth Marine Laboratory, U.K.
University of British Columbia, Canada
University of East Anglia, U.K.
University of Otago, NZ
University of Plymouth, U.K.
University of Tasmania, Australia
University of Western Australia
Woods Hole Oceanographic Institution, USA

Publications and Presentations on SOIREE

Dr. Dorothee Bakker
School of Environmental Sciences
University of East Anglia
Norwich NR4 7TJ, United Kingdom
Tel.+44 1603 592648
Fax. +44 1603 591327