1. National Oceanography Centre, Southampton SO14 3ZH, UK
2. Environmental Research Institute, North Highland College, UHI Millenium Institute, Thurso, Caithness KW14 7JD, UK
3. School of Geography and Geosciences, University of St Andrews, Irvine Building, North Street, St Andrews, Fife KY16 9AJ, UK
4. NATO Undersea Research Centre, 19138 La Spezia, Italy
5. Queen's University of Belfast Marine Laboratory, Portaferry BT22 1PF, Northern Ireland, UK

Correspondence to: John T. Allen^1,2 Correspondence and requests for materials should be addressed to J.T.A. (Email: jta@noc.soton.ac.uk).

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 phosphate^{2, 3}, but northern Atlantic waters are richer in nitrate than silicate⁴. Following the spring stratification, diatoms are the first phytoplankton to bloom^{2, 5}. Once silicate is exhausted, diatom blooms subside in a major export event^{6, 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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