External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea

Abstract

Abstract. Particle fluxes (including major components and grain size), and oceanographic parameters (near-bottom water temperature, current speed and suspended sediment concentration) were measured along the Cap de Creus submarine canyon in the Gulf of Lions (GoL; NW Mediterranean Sea) during two consecutive winter-spring periods (2009–2010 and 2010–2011). The comparison of data obtained with the measurements of meteorological and hydrological parameters (wind speed, turbulent heat flux, river discharge) have shown the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea. Indeed, atmospheric forcing during 2009–2010 and 2010–2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14.2 × 103 W m−2) in winter 2009–2010 that triggered a pronounced sea surface cooling compared to winter 2010–2011 (1.6 × 103 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009–2010, which cascaded at high speed (up to ∼1 m s−1) down Cap de Creus Canyon as measured by a current-meter in the head of the canyon. The lower heat losses recorded in winter 2010–2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation and downslope transport of dense shelf water. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter-spring 2009–2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to the middle canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010–2011. The dominance of the lithogenic fraction in mass fluxes during the two winter-spring periods points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated with the plankton spring bloom during March and April of both years.

Impact of storms on residence times and export of coastal waters during a mild autumn/winter period in the Gulf of Lion

“…Two winter regimes have been distinguished regarding the characteristics of shelf water export: a first one driven by storms and concerning light shelf water, and a second, for which the waters formed on the shelf are very dense, potentially denser than those of the Western Mediterranean deep basin (Dufau-Julliand, 2004;Palanques et al, 2006;Canals et al, 2006;Ulses et al, 2008a,c;Durrieu de Madron et al, 2013;Rumín-Caparrós et al, 2013).…”

“…During the mild winter of 2010-2011, only brief, weak cascading was recorded (Rumín-Caparrós et al, 2013). In March, the CASCADE (CAscading, Storm, Convection, Advection and Downwelling Events) experiment documented the hydrological and hydrodynamic characteristics of the south-western GoL shelf and export zone during a period of low loss of buoyancy (Bourrin et al, 2015;Martín et al, 2013).…”

Particle fluxes and their drivers in the Avilés submarine canyon and adjacent slope, central Cantabrian margin, Bay of Biscay

“…Other authors have also pointed out that in some continental margins, particles from the shelf reach the deep margin and basin after experiencing several cycles of deposition and resuspension (e.g. Palanques et al, 2012;Rumín-Caparrós et al, 2013).…”

The deep ocean under climate change

“…Furthermore, short-term events that accelerate exchange between surface and deep waters are regulated by atmospheric processes (storm-induced convection, mesoscale eddies, and dense water cascading) and, hence, are climate sensitive. These events can affect deepsea benthos through habitat disturbance and enhanced POC fluxes (25), governing the capacity of deep-sea ecosystems to sustain fisheries and provide major regulating services (26).…”