The elemental stoichiometry (C, Si, N, P) of the Hebrides Shelf and its role in carbon export
Painter, S.C.; Hartman, S.E.; Kivimäe, C.; Salt, L.A.; Clargo, N.M.; Daniels, C.J.; Bozec, Y.; Daniels, L.; Allen, S.; Hemsley, V.S.; Moschonase, G.; Davidson, K. (2017). The elemental stoichiometry (C, Si, N, P) of the Hebrides Shelf and its role in carbon export. Prog. Oceanogr. 159: 154-177. https://dx.doi.org/10.1016/j.pocean.2017.10.001
In: Progress in Oceanography. Pergamon: Oxford,New York,. ISSN 0079-6611; e-ISSN 1873-4472, more
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| Author keywords |
Stoichiometry; Dissolved nutrients; Particulate organic matter; NW European shelf sea |
| Authors | | Top |
- Painter, S.C.
- Hartman, S.E.
- Kivimäe, C.
- Salt, L.A.
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- Clargo, N.M., more
- Daniels, C.J.
- Bozec, Y.
- Daniels, L.
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- Allen, S.
- Hemsley, V.S.
- Moschonase, G.
- Davidson, K.
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| Abstract |
A detailed analysis of the internal stoichiometry of a temperate latitude shelf sea system is presented whichreveals strong vertical and horizontal gradients in dissolved nutrient and particulate concentrations and in theelemental stoichiometry of those pools. Such gradients have implications for carbon and nutrient export fromcoastal waters to the open ocean. The mixed layer inorganic nutrient stoichiometry shifted from balanced N:P inwinter, to elevated N:P in spring and to depleted N:P in summer, relative to the Redfield ratio. This patternsuggests increased likelihood of P limitation of fast growing phytoplankton species in spring and of N limitationof slower growing species in summer. However, as only silicate concentrations were below potentially limitingconcentrations during summer and autumn the stoichiometric shifts in inorganic nutrient N:P are considered dueto phytoplankton nutrient preference patterns rather than nutrient exhaustion. Elevated particulate stoichiometriescorroborate non-Redfield optima underlying organic matter synthesis and nutrient uptake. Seasonalvariation in the stoichiometry of the inorganic and organic nutrient pools has the potential to influence theefficiency of nutrient export. In summer, when organic nutrient concentrations were at their highest and inorganicnutrient concentrations were at their lowest, the organic nutrient pool was comparatively C poor whilstthe inorganic nutrient pool was comparatively C rich. The cross-shelf export of these pools at this time would beassociated with different efficiencies regardless of the total magnitude of exchange. In autumn the elementalstoichiometries increased with depth in all pools revealing widespread carbon enrichment of shelf bottom waterswith P more intensely recycled than N, N more intensely recycled than C, and Si weakly remineralized relative toC. Offshelf carbon fluxes were most efficient via the inorganic nutrient pool, intermediate for the organic nutrientpool and least efficient for the particulate pool. N loss from the shelf however was most efficient via thedissolved organic nutrient pool. Mass balance calculations suggest that 28% of PO43−, 34% of NO3− and 73% ofSi drawdown from the mixed layer fails to reappear in the benthic water column thereby indicating the proportionof 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 andhigher trophic levels are considered the most likely fate for these missing nutrients. |
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