STUDY OF DEEP DYNAMIC IN THE LIGURO-PROVENÇAL SUBBASIN DURING WINTER 2005-2006

Historical data have identified the Gulf of Lion as the main important site for the formation of dense water responsible for the ventilation of the deep water in the western Mediterranean basin. report interesting episodes of deep convection also in the Ligurian Sea indicating significant changes in temperature and salinity of the Western Mediterranean Deep Water (Smith et al 2008, Marty et al 2010). Between 2004 and 2009, in the framework of the ENVAR long term monitoring program, six moorings were deployed along a distance of about 70 km and at variable depths starting from 500 m down to 2300 m. Although the primary goal of the project was the study of the Var submarine canyon system, a large amount of current data were also gathered. This led to the realization of a long term series essential to characterize the deep dynamics of this area. The analysis of this huge current dataset revealed long periods of strong near bottom currents not attributable to the turbidity flows acting along the submarine canyon, but rather imputable to processes of water sinking due to lateral mixing or pushed down by surface forcing. This is the case of the event recorded from February 2006, which shows abrupt increases of current speed (with peaks reaching 40 cm s-1) persisting for more than four months. This variation, recorded simultaneously by all current meters deployed, highlighted the occurrence of a mesoscale phenomenon whose effects transfer on a vast thickness of the water column (about 500 m). In support of this study, monthly hydrological profiles of temperature and salinity were retrieved from the Ifremer SISMER (Système d’Informations Scientifiques pour la MER) data bank. The combined analysis of both hydrographic and current data allowed us to obtain a synoptical view of the events acting in the whole Var area and to verify that the strong current speed signals measured on winter 2006 may be effectively related to deep convection processes already observed in this area and not only to the activity of the submarine Var canyon.