Abstract
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 to the deep sea floor through the canyons 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.
Highlights
Ocean ScienceContinental margins are the edges of continents and represent a zone of strong interactions between the continent, the open ocean, and the atmosphere (Weaver at al., 2004).These interactions drive margin’s hydrodynamic conditions, which in turn control the dispersal of particulate matter fluxes on the shelf and towards thSeoolpiden Eseaa r(tLhevin and Dayton, 2009)
We investigated the biochemical composition of particulate organic matter and its bioavailability to benthic consumers, settling down along the water column during one year-long (November 2008–November 2009) intensive sampling activity carried out comparatively inside the Blanes canyon and on its adjacent open slope (Catalan Margin, NW Mediterranean Sea), at the same water depth
Such a striking difference has been already described for the Blanes canyon, where the total mass flux (TMF) continuously increases from the head of the canyon at 300 m depth until 1500 m depth, unlike in the adjacent open slope where the TMF decrease with the distance to coast (Lopez-Fernandez et al, 2013)
Summary
Continental margins are the edges of continents and represent a zone of strong interactions between the continent, the open ocean, and the atmosphere (Weaver at al., 2004). These interactions drive margin’s hydrodynamic conditions, which in turn control the dispersal of particulate matter fluxes on the shelf and towards thSeoolpiden Eseaa r(tLhevin and Dayton, 2009). Many previous investigations have shown that continental margins may represent a reservoir of particulate organic matter (often derived from river discharge) which, while transported downslope, represents a key food source for the port to btheentdheoesp(WseaalTsihsh,m1e9ed9Ci1a)tr.eydOortghsarponuihcghecarvrebeortnica(Ol Cflu)xterasnos-f particles, which in turn are influenced by the general climate (Smith et al, 2009), local hydrodynamic conditions (Bonnin et al, 2008) and the presence of different benthic habitats (Pusceddu et al, 2010a). Submarine canyons may act as a major forced conduit of material to the deep sea (Canals et al, 2006)
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