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| Titel |
Impact of river discharge, upwelling and vertical mixing on the nutrient loading and productivity of the Canadian Beaufort Shelf |
| VerfasserIn |
J.-É. Tremblay, P. Raimbault, N. Garcia, B. Lansard, M. Babin, J. Gagnon |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 17 ; Nr. 11, no. 17 (2014-09-11), S.4853-4868 |
| Datensatznummer |
250117589
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| Publikation (Nr.) |
 copernicus.org/bg-11-4853-2014.pdf |
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| Zusammenfassung |
| The concentrations and elemental stoichiometry of particulate and dissolved
pools of carbon (C), nitrogen (N), phosphorus (P) and silicon (Si) on the
Canadian Beaufort Shelf during summer 2009 (MALINA program) were assessed
and compared with those of surface waters provided by the Mackenzie river as
well as by winter mixing and upwelling of upper halocline waters at the
shelf break. Neritic surface waters showed a clear enrichment in dissolved
and particulate organic carbon (DOC and POC, respectively), nitrate, total
particulate nitrogen (TPN) and dissolved organic nitrogen (DON) originating
from the river. Silicate as well as bulk DON and DOC declined in a
near-conservative manner away from the delta's outlet, whereas nitrate
dropped non-conservatively to very low background concentrations inside the
brackish zone. By contrast, the excess of soluble reactive P (SRP) present
in oceanic waters declined in a non-conservative manner toward the river
outlet, where concentrations were very low and consistent with P shortage in
the Mackenzie River. These opposite gradients imply that the admixture of
Pacific-derived, SRP-rich water is necessary to allow phytoplankton to use
river-derived nitrate and to a lesser extent DON. A coarse budget based on
concurrent estimates of primary production shows that river N deliveries
support a modest fraction of primary production when considering the entire
shelf, due to the ability of phytoplankton to thrive in the subsurface
chlorophyll maximum beneath the thin, nitrate-depleted river plume. Away
from shallow coastal bays, local elevations in the concentration of primary
production and dissolved organic constituents were consistent with upwelling
at the shelf break. By contrast with shallow winter mixing, nutrient
deliveries by North American rivers and upwelling relax surface communities
from N limitation and permit a more extant utilization of the excess SRP
entering through the Bering Strait. In this context, increased nitrogen supply
by rivers and upwelling potentially alters the vertical distribution of the
excess P exported into the North Atlantic. |
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