Sediment dynamics in the Gulf of Lion (NW Mediterranean Sea) during two autumn–winter periods with contrasting meteorological conditions

International audienceA simulation based on a hydro-sedimentary model was conducted for the period between summer 2010 andspring 2012 in the Gulf of Lion (northwestern Mediterranean Sea) to understand the spatial and temporalvariability of sediment transport, erosion and deposition on the continental shelf and slope. Datasets of bothsimulated and observed current, temperature and suspended matter from the shelf and the Cap de Creus Canyonwhich is the main export route towards the continental slope, were first compared to assess the reliability of thesimulation. The simulation shows the massive sediment accumulation near the Rhone River mouth (~56 % of theinputs), the accretion along the mid-shelf mud belt, and the impact of dense shelf water cascading on sedimentresuspension and erosion inside the Cap de Creus Canyon. The two studied autumn–winter periods were stronglycontrasted in terms of meteorological conditions and subsequent impacts on the sediment dynamics. During thefirst period (2010–2011) dominated by marine storms, the shelf sediment underwent strong changes, the RhoneRiver sediment load accumulated in a relatively small area, stock of littoral sands moved to the inner shelf(20–40 m) while inner shelf fine particles fed the mid-shelf mud belt and the upper Cap de Creus Canyon. Duringthe second period (2011–2012) with very little marine wind and a particularly cold winter, sediment on the shelfunderwent little change except for a southwestward growth of the Rhone River prodeltaic deposit. Sediment fromthe southwestern end of the shelf as well as from the upper Cap de Creus Canyon was flushed toward deeperreaches by dense shelf water cascading. Cascading also had a more moderate impact in the various canyonsincising the continental shelf. Our work supports the view of an unbalanced sedimentary system, with a deficitmainly over the inner shelf, whose main driver is probably the strong and fast reduction of particulate matter inputs from the Rhone river