Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

Abstract : Since 2010, an intense effort in the collection of in situ observations has been carried out in the northwestern Mediterranean Sea thanks to gliders, profiling floats, regular cruises, and mooring lines. This integrated observing system enabled a year-to-year monitoring of the deep waters formation that occurred in the Gulf of Lions area during four consecutive winters (2010-2013). Vortical structures remnant of wintertime deep vertical mixing events were regularly sampled by the different observing platforms. These are Submesoscale Coherent Vortices (SCVs) characterized by a small radius ($5-8 km), strong depth-intensified orbital velocities ($10-20 cm s 21) with often a weak surface signature, high Rossby ($0.5) and Burger numbers O(0.5-1). Anticyclones transport convected waters resulting from intermediate ($300 m) to deep ($2000 m) vertical mixing. Cyclones are characterized by a 500-1000 m thick layer of weakly stratified deep waters (or bottom waters that cascaded from the shelf of the Gulf of Lions in 2012) extending down to the bottom of the ocean at $2500 m. The formation of cyclonic eddies seems to be favored by bottomreaching convection occurring during the study period or cascading events reaching the abyssal plain. We confirm the prominent role of anticyclonic SCVs and shed light on the important role of cyclonic SCVs in the spreading of a significant amount ($30%) of the newly formed deep waters away from the winter mixing areas. Since they can survive until the following winter, they can potentially have a great impact on the mixed layer deepening through a local preconditioning effect.