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Diatom carbon export enhanced by silicate upwelling in the northeast Atlantic

Nature volume 437, pages 728–732 (2005)Cite this article

Abstract

Diatoms are unicellular or chain-forming phytoplankton that use silicon (Si) in cell wall construction. Their survival during periods of apparent nutrient exhaustion enhances carbon sequestration in frontal regions of the northern North Atlantic. These regions may therefore have a more important role in the ‘biological pump’ than they have previously been attributed1, but how this is achieved is unknown. Diatom growth depends on silicate availability, in addition to nitrate and phosphate2,3, but northern Atlantic waters are richer in nitrate than silicate4. Following the spring stratification, diatoms are the first phytoplankton to bloom2,5. Once silicate is exhausted, diatom blooms subside in a major export event6,7. Here we show that, with nitrate still available for new production, the diatom bloom is prolonged where there is a periodic supply of new silicate: specifically, diatoms thrive by ‘mining’ deep-water silicate brought to the surface by an unstable ocean front. The mechanism we present here is not limited to silicate fertilization; similar mechanisms could support nitrate-, phosphate- or iron-limited frontal regions in oceans elsewhere.

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Figure 1: Ocean colour-image of the northeast Atlantic.
Figure 2: Sections from each of the three SeaSoar surveys (7–17 June 2001).
Figure 3: The results of Si(OH) 4 uptake incubation experiments.
Figure 4: Diagnosed (QG) vertical motion (positive upwards).

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Acknowledgements

FISHES was a multidisciplinary experiment conducted as part of the Biophysical Interactions and Controls on Export Production core strategic programme. We thank R. Pollard for initiating and developing the FISHES experiment, which fully met its objectives owing to the enthusiasm and professionalism of all the officers, crew and scientists of RRS Discovery cruise 253. We thank the Defence Evaluation and Research Agency (now the Defence Science and Technology Laboratory) for their support of a number of staff involved in FISHES through the development of the Techniques for Optimising Environmental Sampling Joint Grant Scheme project. We thank the Natural Environment Research Council for their support of the George Deacon Division, and the National Oceanography Centre for their commitment to core strategic science funding.

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Authors and Affiliations

  1. National Oceanography Centre, SO14 3ZH, Southampton, UK

    John T. Allen, Louise Brown, Richard Sanders, C. Mark Moore, Alexander Mustard, Sophie Fielding, Mike Lucas, Stephanie Henson & Dan Mayor

  2. Environmental Research Institute, North Highland College, UHI Millenium Institute, Thurso, KW14 7JD, Caithness, UK

    John T. Allen

  3. School of Geography and Geosciences, University of St Andrews, Irvine Building, North Street, St Andrews, Fife, KY16 9AJ, UK

    Louise Brown

  4. NATO Undersea Research Centre, 19138, La Spezia, Italy

    Michel Rixen

  5. Queen's University of Belfast Marine Laboratory, BT22 1PF, Portaferry, UK, Northern Ireland

    Graham Savidge

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Correspondence to John T. Allen.

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Allen, J., Brown, L., Sanders, R. et al. Diatom carbon export enhanced by silicate upwelling in the northeast Atlantic. Nature 437, 728–732 (2005). https://doi.org/10.1038/nature03948

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