Bioavailability of sinking organic matter in the Blanes canyon and the adjacent open slope (NW Mediterranean Sea)

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

Major consequences of an intense dense shelf water cascading event on deep-sea benthic trophic conditions and meiofaunal biodiversity

“…Recent innovations in remote sensing techniques allowed the discovery that deep-sea habitats are more complex, heterogeneous and dynamic than previously hypothesized. There is increasing evidence that the deep-sea habitats may respond quickly to shifts in upper-ocean variables occurring over medium (months) to long-term (years) temporal scales Smith et al, 2009;Glover et al, 2010;López-Fernández et al, 2012), as well as to a variety of anthropogenic stressors, from fisheries (e.g. Bailey et al, 2009;Puig et al, 2012) to pollution (Unger et al, 2008;Ramirez Llodra et al, 2012).…”

“…Deep-sea ecosystems respond rapidly to the seasonal primary productivity pulses leading to the exportation of OM from the upper ocean (Billet et al, 2001;Wigham et al, 2003). However, an increasing number of studies now documents atmosphere and climate-driven episodic events, that might favour the transfer of sedimentary OM from the upper part of the continental margin down to the deep margin and basin (Klein et al, 1999;Heussner et al, 2006;Sanchez-Vidal et al, 2008, 2009, 2012López-Fernández et al, 2012). Table 4.…”

“…Some canyons have the head very close to the shoreline (Amblàs et al, 2006). The topographic and hydrodynamic features of some submarine canyons make these sites of intense exchange between the continental shelf and the deep margin and basin (Nittrouer and Wright, 1994), by intercepting and trapping coastal sediment drifts and driving the collected material towards the deep (Lewis and Barnes, 1999;Schmidt et al, 2001;Palanques et al, 2005;Flexas et al, 2002Flexas et al, , 2008Heussner et al, 2006). Canyons can favour or even amplify the effects of DSWC (Allen and Durrieu de Madron, 2009).…”