Variability of open-sea deep convection and deep water masses in the northwestern Mediterranean basin over the recent period (2007-2011) from in-situ measurements

The recent modification of the Western Mediterranean Deep Water (WMDW) thermohaline characteristics in 2005 (known as the Western Mediterranean Transition, WMT) showed an abrupt increase in the deep heat and salt contents, and a modification in the deep stratification. We present here new in-situ observations collected between 2007 and 2011 in the convection region to characterize the deep water formation variability and subsequent thermohaline changes. During this period, mooring's time series together with CTD and gliders profiles reveal three consecutive deep convection events that modified dramatically the deep water characteristics, inducing a salinity increase of 0.01 and a temperature increase of 0.03°C in 4 years. We attempt to assess the role of the interannual variability of the atmospheric forcings and of the water column stability on the intensity of the open-sea convection. The spreading of the newly-formed deep waters in the NW Mediterranean basin is also addressed.