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The elemental stoichiometry (C, Si, N, P) of the Hebrides Shelf and its role in carbon export

The elemental stoichiometry (C, Si, N, P) of the Hebrides Shelf and its role in carbon export
The elemental stoichiometry (C, Si, N, P) of the Hebrides Shelf and its role in carbon export
A detailed analysis of the internal stoichiometry of a temperate latitude shelf sea system is presented which reveals strong vertical and horizontal gradients in dissolved nutrient and particulate concentrations and in the elemental stoichiometry of those pools. Such gradients have implications for carbon and nutrient export from coastal waters to the open ocean. The mixed layer inorganic nutrient stoichiometry shifted from balanced N:P in winter, to elevated N:P in spring and to depleted N:P in summer, relative to the Redfield ratio. This pattern suggests increased likelihood of P limitation of fast growing phytoplankton species in spring and of N limitation of slower growing species in summer. However, as only silicate concentrations were below potentially limiting concentrations during summer and autumn the stoichiometric shifts in inorganic nutrient N:P are considered due to phytoplankton nutrient preference patterns rather than nutrient exhaustion. Elevated particulate stoichiometries corroborate non-Redfield optima underlying organic matter synthesis and nutrient uptake. Seasonal variation in the stoichiometry of the inorganic and organic nutrient pools has the potential to influence the efficiency of nutrient export. In summer, when organic nutrient concentrations were at their highest and inorganic nutrient concentrations were at their lowest, the organic nutrient pool was comparatively C poor whilst the inorganic nutrient pool was comparatively C rich. The cross-shelf export of these pools at this time would be associated with different efficiencies regardless of the total magnitude of exchange. In autumn the elemental stoichiometries increased with depth in all pools revealing widespread carbon enrichment of shelf bottom waters with P more intensely recycled than N, N more intensely recycled than C, and Si weakly remineralized relative to C. Offshelf carbon fluxes were most efficient via the inorganic nutrient pool, intermediate for the organic nutrient pool and least efficient for the particulate pool. N loss from the shelf however was most efficient via the dissolved organic nutrient pool. Mass balance calculations suggest that 28% of PO43−, 34% of NO3− and 73% of Si drawdown from the mixed layer fails to reappear in the benthic water column thereby indicating the proportion of the nutrient pools that must be resupplied from the ocean each year to maintain shelf wide productivity. Loss to the neighbouring ocean, the sediments, transference to the dissolved organic nutrient pool and higher trophic levels are considered the most likely fate for these missing nutrients.
0079-6611
154-177
Painter, Stuart C.
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Hartman, Susan E.
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Kivimäe, Caroline
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Salt, Lesley A.
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Clargo, Nicola M.
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Daniels, Chris J.
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Bozec, Yann
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Munns, Lucie
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Allen, Stephanie
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Hemsley, Victoria S.
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Moschonas, Grigorios
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Davidson, Keith
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Painter, Stuart C.
29e32f35-4ee8-4654-b305-4dbe5a312295
Hartman, Susan E.
951bae25-3ce8-4305-8739-3e564631ab34
Kivimäe, Caroline
cdb7aa39-e076-4eb6-bf11-02caf1f93d24
Salt, Lesley A.
db67166e-401a-46a3-abab-441ad60372fb
Clargo, Nicola M.
7cb02f13-8df7-4f59-b8c0-c2f2ddd4bf41
Daniels, Chris J.
e4a51f9d-efe6-413a-8d3f-3f1eda5ce79f
Bozec, Yann
8845b447-a496-4608-a635-b25af5cc4d66
Munns, Lucie
c8a870d6-4252-4f4b-a357-4f5cda2d233b
Allen, Stephanie
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Hemsley, Victoria S.
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Moschonas, Grigorios
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Davidson, Keith
a7b8cf91-5373-469f-a60b-23c43f355b2c

Painter, Stuart C., Hartman, Susan E., Kivimäe, Caroline, Salt, Lesley A., Clargo, Nicola M., Daniels, Chris J., Bozec, Yann, Munns, Lucie, Allen, Stephanie, Hemsley, Victoria S., Moschonas, Grigorios and Davidson, Keith (2017) The elemental stoichiometry (C, Si, N, P) of the Hebrides Shelf and its role in carbon export. Progress in Oceanography, 159, 154-177. (doi:10.1016/j.pocean.2017.10.001).

Record type: Article

Abstract

A detailed analysis of the internal stoichiometry of a temperate latitude shelf sea system is presented which reveals strong vertical and horizontal gradients in dissolved nutrient and particulate concentrations and in the elemental stoichiometry of those pools. Such gradients have implications for carbon and nutrient export from coastal waters to the open ocean. The mixed layer inorganic nutrient stoichiometry shifted from balanced N:P in winter, to elevated N:P in spring and to depleted N:P in summer, relative to the Redfield ratio. This pattern suggests increased likelihood of P limitation of fast growing phytoplankton species in spring and of N limitation of slower growing species in summer. However, as only silicate concentrations were below potentially limiting concentrations during summer and autumn the stoichiometric shifts in inorganic nutrient N:P are considered due to phytoplankton nutrient preference patterns rather than nutrient exhaustion. Elevated particulate stoichiometries corroborate non-Redfield optima underlying organic matter synthesis and nutrient uptake. Seasonal variation in the stoichiometry of the inorganic and organic nutrient pools has the potential to influence the efficiency of nutrient export. In summer, when organic nutrient concentrations were at their highest and inorganic nutrient concentrations were at their lowest, the organic nutrient pool was comparatively C poor whilst the inorganic nutrient pool was comparatively C rich. The cross-shelf export of these pools at this time would be associated with different efficiencies regardless of the total magnitude of exchange. In autumn the elemental stoichiometries increased with depth in all pools revealing widespread carbon enrichment of shelf bottom waters with P more intensely recycled than N, N more intensely recycled than C, and Si weakly remineralized relative to C. Offshelf carbon fluxes were most efficient via the inorganic nutrient pool, intermediate for the organic nutrient pool and least efficient for the particulate pool. N loss from the shelf however was most efficient via the dissolved organic nutrient pool. Mass balance calculations suggest that 28% of PO43−, 34% of NO3− and 73% of Si drawdown from the mixed layer fails to reappear in the benthic water column thereby indicating the proportion of the nutrient pools that must be resupplied from the ocean each year to maintain shelf wide productivity. Loss to the neighbouring ocean, the sediments, transference to the dissolved organic nutrient pool and higher trophic levels are considered the most likely fate for these missing nutrients.

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Accepted/In Press date: 3 October 2017
e-pub ahead of print date: 5 October 2017
Published date: 1 December 2017

Identifiers

Local EPrints ID: 415114
URI: https://eprints.soton.ac.uk/id/eprint/415114
ISSN: 0079-6611
PURE UUID: 61a5a62a-6048-4490-b199-b7e0f928b08b

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Date deposited: 31 Oct 2017 17:30
Last modified: 02 Dec 2019 18:46

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Contributors

Author: Stuart C. Painter
Author: Susan E. Hartman
Author: Caroline Kivimäe
Author: Lesley A. Salt
Author: Nicola M. Clargo
Author: Chris J. Daniels
Author: Yann Bozec
Author: Lucie Munns
Author: Stephanie Allen
Author: Victoria S. Hemsley
Author: Grigorios Moschonas
Author: Keith Davidson

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