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Carbonate counter pump stimulated by natural iron fertilization in the Polar Frontal Zone

Nature Geoscience volume 7, pages 885–889 (2014)Cite this article

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Abstract

The production of organic carbon in the ocean’s surface and its subsequent downward export transfers carbon dioxide to the deep ocean. This CO2 drawdown is countered by the biological precipitation of carbonate, followed by sinking of particulate inorganic carbon, which is a source of carbon dioxide to the surface ocean, and hence the atmosphere over 100–1,000 year timescales1. The net transfer of CO2 to the deep ocean is therefore dependent on the relative amount of organic and inorganic carbon in sinking particles2. In the Southern Ocean, iron fertilization has been shown to increase the export of organic carbon3,4,5, but it is unclear to what degree this effect is compensated by the export of inorganic carbon. Here we assess the composition of sinking particles collected from sediment traps located in the Polar Frontal Zone of the Southern Ocean. We find that in high-nutrient, low-chlorophyll regions that are characterized by naturally high iron concentrations, fluxes of both organic and inorganic carbon are higher than in regions with no iron fertilization. However, the excess flux of inorganic carbon is greater than that of organic carbon. We estimate that the production and flux of carbonate in naturally iron-fertilized waters reduces the overall amount of CO2 transferred to the deep ocean by 6–32%, compared to 1–4% at the non-fertilized site. We suggest that an increased export of organic carbon, stimulated by iron availability in the glacial sub-Antarctic oceans, may have been accompanied by a strengthened carbonate counter pump.

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Figure 1: Annual and seasonal inorganic carbon (CaCO3) fluxes.
Figure 2: Impact of the carbonate counter pump (CCP) and the contribution of CaCO3 fractions and foraminifer species in reducing deep-ocean CO2 storage.
Figure 3: Comparison of particulate geochemical signatures comprising Southern Ocean flux.

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Acknowledgements

Sediment trap deployments were funded through the NERC programmes CROZeX (PI: Pollard, R.T) and Benthic Crozet (PI: Wolff, G.A.). P.Z. was funded through the projects CGL2009-10806 (MinECo) and 265103 (EC-FP7). We are grateful to the captain and crew of R.R.S. Discovery for their support throughout the cruises D285, D286 and D300. We thank D. Bakker for sharing published DIC and TA data, calculating omega values and her detailed comments. M. Rembauville assisted in the preparation of Fig. 3. We are also grateful to M. C. Nielsdóttir and S. Blain for commenting on earlier versions of the manuscript. Finally we acknowledge the scientific participants of the CROZeX and Benthic Crozet programmes.

Author information

Authors and Affiliations

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

    Ian Salter

  2. Sorbonne Universités, UPMC Univ Paris 06, CNRS UMR 7621, Laboratoire d’Océanographie Microbienne, Observatoire Océanologigique, F-66650 Banyuls/mer, France

    Ian Salter

  3. Université d’Angers, UMR CNRS 6112, LPG-BIAF - Bio-Indicateurs Actuels et Fossiles, 2 Boulevard Lavoisier, Angers 49045, France

    Ralf Schiebel & Aurore Movellan

  4. Universitat Autònoma de Barcelona, ICREA-ICTA, Edifici Z, Carrer de les columnes, E-08193 Bellaterra, Barcelona, Spain

    Patrizia Ziveri

  5. Department of Earth Sciences, Vrije Universiteit Amsterdam, FALW, De Boelelaan 1105, 1081 HV Amsterdam, The Netherlands

    Patrizia Ziveri

  6. National Oceanography Centre, Ocean Biogeochemistry and Ecosystems, Waterfront Campus, European Way, Southampton SO14 3ZH, UK

    Richard Lampitt

  7. University of Liverpool, School of Environmental Sciences, 4 Brownlow Street Liverpool L69 3GP, UK,

    George A. Wolff

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Contributions

I.S. formulated the idea and together with R.S. designed the analytical approach. I.S. wrote the manuscript with all co-authors commenting. I.S. and R.S. performed all preparation and classification measurements on the foraminifer and pteropod fractions. A.M. measured calcite and aragonite mass of individual tests and R.S. and I.S. synthesized data. P.Z. performed ICP-AES measurements on the fine fraction. I.S. performed all bulk chemical analyses. G.W. and R.L. provided access to the sediment trap samples collected during the Benthic Crozet and CROZeX research programmes, respectively. All co-authors contributed to the manuscript.

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Correspondence to Ian Salter.

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The authors declare no competing financial interests.

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Salter, I., Schiebel, R., Ziveri, P. et al. Carbonate counter pump stimulated by natural iron fertilization in the Polar Frontal Zone. Nature Geosci 7, 885–889 (2014). https://doi.org/10.1038/ngeo2285

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