Large Sediment Waves Formation by Dense Shelf Water Cascading over the Gulf of Roses Continental Slope (NW Mediterranean)

Abstract

Dense shelf water cascading (DSWC) and eastern storms control the off-shelf sediment transport in the northwestern Mediterranean Sea. Previous studies in the Gulf of Lions have shown that most of the sediment transport during these high-energetic events occurs through the Cap de Creus Canyon (Fig 1). However, it is known that part of the bottom currents and the associated sediment transport is advected southwards, channelized between the Cap de Creus promontory and the submarine canyon flank. Recently acquired swath bathymetry and seismic datasets on the Gulf of Roses continental slope, obtained during the FORMED Project (Ref: CGL2012-33989), revealed the presence of large sediment waves (wavelengths of ~ 2000 m and maximum heights of ~ 60 m) developed between 200 and 400 m depth (Fig. 1A). The analysis of seismic profiles showed the general architecture of the late Quaternary deposits over the Gulf of Roses outer shelf and slope, where five unconformity-bounded seismic units are differentiated, with sediment waves developed in all of them (Fig. 1B). The sediment waves over the continental slope are presumably generated by bottom currents intensified during major DSWC events flowing downslope in an oblique angle with respect the main bathymetry, whereas the outer continental shelf is characterized by morphological erosional features that erodes the upper part of the most recent seismic unit. While most observations of sediment dynamics over the study area have focussed in the transfer of sediment from the continental shelf into the deeper areas through the Cap de Creus Canyon, these findings suggest that this transfer also occur across the slope, associated with the overflow of DSWC south of the Cap de Creus coastal promontory, in agreement with the expected hydrodynamic conditions and the morphological configuration of the continental margin