Impact of dense shelf water cascading on the transfer of organic matter to the deep western Mediterranean basin

Abstract

During winter 2005–2006, particle fluxes and near‐bottom currents were measured in and around the Lacaze‐Duthiers and Cap de Creus submarine canyons (western Gulf of Lion). Current anomalies show the occurrence of a major dense shelf water cascading event down to the slope, the latest recorded up to date in the area. Concomitant increased total mass fluxes highlight the ability of cascading waters to transport large amounts of coarse sediment and organic matter, which is predominantly of terrestrial origin. In addition, results reveal that the current regime and associated grain size sorting is the responsible for a geochemical gradient of settling organic particles along the slope.

Trophic state of benthic deep-sea ecosystems from two different continental margins off Iberia

“…mainly from the Rhone River) resuspended on the shelf and transported down canyon and down slope Sanchez-Vidal et al, 2008Pasqual et al, 2010). Moreover, stable isotope and biochemical analyses revelead that this organic material settling on the seafloor was relatively labile (Sanchez-Vidal et al, 2008. Therefore, our results suggest that such episodic events involving massive organic particle transport from the shelf to the deep margin and basin can represent an important mechanism which fuels the benthic systems of the Catatan margin with bioavailable N-rich compounds.…”

“…Such huge inputs of organic material to the deep margin and basin are represented not only by organic particles of marine origin (due to the phytoplankton bloom occurring concomitantly on the shelf), but also by large amounts of organic particles of terrestrial origin (i.e. mainly from the Rhone River) resuspended on the shelf and transported down canyon and down slope Sanchez-Vidal et al, 2008Pasqual et al, 2010). Moreover, stable isotope and biochemical analyses revelead that this organic material settling on the seafloor was relatively labile (Sanchez-Vidal et al, 2008.…”

“…The head of Cap de Creus canyon is 12 km from the coastline and the canyon extends for 95 km basinwards till entering the deeper Sete canyon at about 2150 m depth. Recent studies conducted on the Catalan margin reported that Cap de Creus canyon represents a preferential pathway of particle transport for the entire Gulf of Lion and that dense shelf water cascading (DSWC) events occurring during winter periods represent one of the main mechanisms of sediment export towards deeper waters Sanchez-Vidal et al, 2008;Palanques et al, 2012). Two major DSWC events occurred in winter/early spring 2005 and 2006, a few months before the sediment sampling in October 2005 and August 2006.…”

“…These events, driven by exceptionally strong, dry northern winds, spread down to the Catalan margin with maximum near-bottom current velocities of ca. 1 m s −1 Palanques et al, 2012) conveying large amounts of organic material into Cap de Creus canyon and the adjacent southern open slope Sanchez-Vidal et al, 2008Pasqual et al, 2010). Primary production in the Gulf of Lion ranges between 78 and 142 g C m −2 yr −1 (Lefevre et al, 1997).…”

“…They can represent either a sink for particulate matter of autochthonous origin (i.e. derived from biological productivity of surface waters and/or exported from the land), or a source of organic material fueling the deep ocean's interior by lateral transport (Buscail and Germain, 1997;Bauer and Druffel 1998;Canals et al, 2006;Sampéré et al, 2008;Sanchez-Vidal et al, 2008;Masson et al, 2010;Pusceddu et al, 2010). Nevertheless, the extent to which such material is transported and distributed downslope is not consistent along latitudinal or longitudinal gradients, nor constant in time, mainly due to differences in hydrodynamic, topographic, climatic and ecological conditions (Liu et al, 2010).…”