TECTONIC GEOMORPHOLOGY OF SUBMARINE CANYON SYSTEMS OFFSHORE OF SOUTHERN CASCADIA
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Submarine canyon
It is a widely held opinion that submarine canyons were cut during the glacial stages of low sea level and now are essentially dormant features, disturbed only on rare occasions by high-speed turbidity currents of torrential proportions. Published in 1979 after a 10-year study, this volume contradicts this concept of the canyons, with years of measurements of currents in the axes of canyons and in other types of sea valleys. It expands upon the previous publications of brief notes relative to currents measured in a few places on the deep seafloor, covering topics such as alternating current directions, turbidity currents, and crossvalley currents, clncluding with support data from studies of the California submarine canyons, British Columbia canyons, Mexican canyons, U.S. East Coast canyons, West indies canyons, Pacific Island canyons, and the Congo canyon.
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Abstract. Submarine canyons are sites of intense energy and material exchange between the shelf and the deep adjacent basins. To test the hypothesis that active submarine canyons represent preferential conduits of available food for the deep-sea benthos, two mooring lines were deployed at 1200 m depth from November 2008 to November 2009 inside the Blanes canyon and on the adjacent open slope (Catalan Margin, NW Mediterranean Sea). We investigated the fluxes, biochemical composition and food quality of sinking organic carbon (OC). OC fluxes in the canyon and the open slope varied among sampling periods, though not consistently in the two sites. In particular, while in the open slope the highest OC fluxes were observed in August 2009, in the canyon the highest OC fluxes occurred in April–May 2009. For almost the entire study period, the OC fluxes in the canyon were significantly higher than those in the open slope, whereas OC contents of sinking particles collected in the open slope were consistently higher than those in the canyon. This result confirms that submarine canyons are effective conveyors of OC to the deep sea, particles transferred are predominantly of inorganic origin, significantly higher than that reaching the open slope at a similar water depth. Using multivariate statistical tests, two major clusters of sampling periods were identified: one in the canyon that grouped trap samples collected in December 2008, concurrently with the occurrence of a major storm at the sea surface, and associated with increased fluxes of nutritionally available particles from the upper shelf. Another cluster grouped samples from both the canyon and the open slope collected in March 2009, concurrently with the occurrence of the seasonal phytoplankton bloom at the sea surface, and associated with increased fluxes of total phytopigments. Our results confirm the key ecological role of submarine canyons for the functioning of deep-sea ecosystems, and highlight the importance of canyons in linking episodic storms and primary production occurring at the sea surface to the deep sea floor.
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It is a widely held opinion that submarine canyons were cut during the glacial stages of low sea level and now are essentially dormant features, disturbed only on rare occasions by high-speed turbidity currents of torrential proportions. Published in 1979 after a 10-year study, this volume contradicts this concept of the canyons, with years of measurements of currents in the axes of canyons and in other types of sea valleys. It expands upon the previous publications of brief notes relative to currents measured in a few places on the deep seafloor, covering topics such as alternating current directions, turbidity currents, and crossvalley currents, clncluding with support data from studies of the California submarine canyons, British Columbia canyons, Mexican canyons, U.S. East Coast canyons, West indies canyons, Pacific Island canyons, and the Congo canyon.
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