Vol. 254: 3–9, 2003

MARINE ECOLOGY PROGRESS SERIES Mar Ecol Prog Ser

Published June 4

Nitrate supply and demand in the mixed layer of the ocean
Trevor Platt1,*, Shubha Sathyendranath1, 2, Andrew M. Edwards1, 2, David S. Broomhead3, Osvaldo Ulloa4
1

Biological Oceanography Section, Bedford Institute of Oceanography, Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada 2 Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada 3 Department of Mathematics, University of Manchester Institute of Science and Technology, PO Box 88, Manchester M60 1QD, United Kingdom 4 Centro de Investigación Oceanográfica en el Pacífico sur-Oriental and Departamento de Oceanografía, Universidad de Concepción, Casilla 160-C, …ver más…

It has been inferred that such systems are, in some way, biologically limited (Martin et al. 1990b): otherwise, the nutrients would be consumed, with a concomitant increase in phytoplankton biomass (as indexed by chlorophyll concentration). Iron, an essential element for autotrophic physiology, has been identified as a potentially limiting resource (Martin & Fitzwater 1988), with the corollary that
*Email: tplatt@dal.ca

addition of iron to the ocean would enhance photosynthesis by phytoplankton (Martin et al. 1990a, Coale et al. 1996), leading to complete utilisation of the ambient nitrate. Here, we show that HNLC regimes need not be considered as anomalous marine ecosystems; rather, they should be seen as elements of a continuum in which the biological dynamics are controlled by the ratio of nutrient supply to the nutrient demand of the local primary production, which is determined by the bio-optical characteristics of the pelagic ecosystem. We introduce a new dimensionless number, S, that captures the dynamics and diagnoses whether a given region will be HNLC, either in its pristine condition or after treatment with iron.
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Mar Ecol Prog Ser 254: 3–9, 2003

That the nitrate is not exhausted (by definition) in HNLC regions is an indication