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Effect of iron supply on Southern Ocean CO2 uptake and implications for glacial atmospheric CO2

Nature volume 407, pages 730–733 (2000)Cite this article

Abstract

Photosynthesis by marine phytoplankton in the Southern Ocean, and the associated uptake of carbon, is thought to be currently limited by the availability of iron1,2. One implication of this limitation is that a larger iron supply to the region in glacial times3 could have stimulated algal photosynthesis, leading to lower concentrations of atmospheric CO2. Similarly, it has been proposed that artificial iron fertilization of the oceans might increase future carbon sequestration. Here we report data from a whole-ecosystem test of the iron-limitation hypothesis in the Southern Ocean4, which show that surface uptake of atmospheric CO2 and uptake ratios of silica to carbon by phytoplankton were strongly influenced by nanomolar increases of iron concentration. We use these results to inform a model of global carbon and ocean nutrients, forced with atmospheric iron fluxes to the region derived from the Vostok3 ice-core dust record. During glacial periods, predicted magnitudes and timings of atmospheric CO2 changes match ice-core records well. At glacial terminations, the model suggests that forcing of Southern Ocean biota by iron caused the initial ∼40 p.p.m. of glacial–interglacial CO2 change, but other mechanisms must have accounted for the remaining 40 p.p.m. increase. The experiment also confirms that modest sequestration of atmospheric CO2 by artificial additions of iron to the Southern Ocean is in principle possible, although the period and geographical extent over which sequestration would be effective remain poorly known.

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Figure 1: Seawater f CO 2 in surface water measured from the RV Tangaroa as a function of time during the experiment.
Figure 2: Vostok ice-core record3 of dust and atmospheric CO2 compared to the atmospheric CO2 concentration from our carbon-cycle model.

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Acknowledgements

We thank K. Tanneburger, U. Schuster, and the officers and crew of the RV Tangaroa for their support. This work was supported by the United Kingdom Natural Environment Research Council and the New Zealand National Institute for Water and Atmospheric Research. We acknowledge support from the CEFIC iron salts committee.

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Authors and Affiliations

  1. School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK

    A. J. Watson, D. C. E. Bakker & A. J. Ridgwell

  2. Department of Chemistry, NIWA Centre for Chemical and Physical Oceanography, University of Otago, Dunedin , New Zealand

    P. W. Boyd

  3. Centre for Coastal and Marine Studies, Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH, UK

    C. S. Law

Authors
  1. A. J. Watson
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  2. D. C. E. Bakker
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  3. A. J. Ridgwell
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  4. P. W. Boyd
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  5. C. S. Law
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Correspondence to A. J. Watson.

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Watson, A., Bakker, D., Ridgwell, A. et al. Effect of iron supply on Southern Ocean CO2 uptake and implications for glacial atmospheric CO2. Nature 407, 730–733 (2000). https://doi.org/10.1038/35037561

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