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Physical and biological processes over a submarine canyon during an upwelling event

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Short, shelf-break canyons are shown to have a substantial influence on local water properties and zooplankton distribution. Barkley Canyon (6 km long) off the west coast of Vancouver Island was extensively sampled in July 1997 and found to have water property and current patterns similar to those observed over Astoria Canyon (22 km long) off the coast of Washington State. Results from Barkley Canyon reveal that the canyon influence can occur very close to the surface (at the thermocline depth of 10 m) and that, near the canyon rim, the stretching vorticity generated over the canyon is strong enough to produce a closed cyclonic eddy of sufficient strength to trap deep passively drifting tracers. Most zooplankton species are advected by the currents; those near the ocean surface pass over the canyon, while those at depth are advected toward the coast. Euphausiids (Euphausia pacifica and Thysanoessa spinifera), the strongest swimming zooplankton collected in the 1997 study, were most prevalent in the closed eddy region near the head of the canyon. The observed aggregation of these animals appears to be linked to their ability to remain at specific depths combined with advection by horizontally convergent flows in the eddy.

Les courts canyons sur les bordures escarpées du plateau continental peuvent exercer une grande influence sur les propriétés hydrologiques locales et sur la répartition du zooplancton. Une étude détaillée en juillet 1997 du canyon Barkley (6 km de longueur) au large de la côte occidentale de l'île de Vancouver a révélé que les propriétés hydrologiques et les patterns de courants qui y règnent sont semblables à ceux qui ont été observés au canyon Astoria (22 km de longueur) au large de la côte de l'état du Washington. L'influence du canyon Barkley se manifeste jusque près de la surface (à 10 m, la profondeur de la thermocline); près de la bordure du canyon, l'étirement du tourbillon généré dans le canyon est suffisamment fort pour produire un tourbillon cyclonique fermé assez puissant pour retenir des traceurs qui dérivent passivement en profondeur. La plupart des espèces du zooplancton sont advectées par les courants; celles qui sont près de la surface de l'océan passent au-dessus du canyon, mais celles qui sont plus en profondeur sont advectées vers la côte. Les euphausiidés (Euphausia pacifica et Thysanoessa spinifera), les meilleurs nageurs dans le zooplancton récolté en 1977, se retrouvent surtout dans la région du tourbillon fermé près du sommet du canyon. La répartition contagieuse de ces animaux semble s'expliquer par leur capacité de se maintenir à des profondeurs particulières, ainsi que par l'advection par les courants horizontaux convergents dans le tourbillon.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2001

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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