Preliminary Results of the CASCADE Cruise (Gulf of Lions) R/V l’Atalante, March 2011 CEFREM, ICM-CSIC, UB, UPM, IFREMER, LA, HCMR, LOV, LMGEM, LOMIC, UA CASCADE: CAscading, Storm, Convection, Advection and Downwelling Events

Cascading : Down-slope cascade of dense water formed along the coast Wind-driven mixing and cooling of the upper layer of the ocean during winter Open-Sea convection : Deepening of the mixed layer thickness in the open ocean

Situation for the Gulf of Lions Marin Quantification of the export of dissolved and particulate organic and inorganic matter, as well as microorganisms (free and attached bacteria, phytoplankton) => validation of coupled models

Open-sea convection event 02 Feb - Chlorophylle 05 Mar - Chlorophylle

Radiale L Radiale M Difference phases of open-sea convection Preconditionning General circulation and winds combine to predispose some part of a gyre to locally overturn Mixing Heat loss associated with the wind exceed some critical level and initiates convection Sinking Sinking and restratification of the water column, once the surface forcing decline Spreading Dispersion of newly formed deep mixed water  Transfer and sequestration of organic matter in the deep basin  Response of deep ecosystems After Helen Johns (

Hints of pelagic ecosystem response to convection Bursts of deep (near- bottom) bio-luminescence measured by photomultiplier following convection events Both mechanical stimulation (current- induced) and spontaneous stimulation (bacterial growth due to nutrients inputs from surface and sediment) Jan 2008Jul 2008Jan 2009Jul 2009Jan Pot. temperature (deg. C) Current speed (cm/s) Number of photon per seconds Jul 2010 After Tamburini et al ( submitted to Science)

Depth (m) Potential temperature (°C) Chlorophylle (µg/L) march 8 march Sinking and spreading Rapid shift from a convective (homogenized) to a stratified regime within few days Levantine Intermediate water Old deep water Mixed layer depth New deep water Capping of newly formed deep water by Levantine intermediate water Export of dissolved and particulate, organic and inorganic matter and bacterial activity (preserving in situ hyperbaric conditions) during and outside convective periods in old and new deep waters

10 March - Turbidity 18 March - Turbidity Storm, Downwelling and Cascading Event (cm/s) Suspended sediment concentration (mg/l) Simulation of bottom currents for March 13, 2011 (peak of the 1 st storm)

Monitoring of the storm In the Cap de Creus Canyon Moorings CTD station and transect 2 days of fixed CTD YoYo-ing during the storm Transect after the storm Continuous recording with moorings

Current, turbidity, and particle fluxes ADCP Echo amplitude (count) ADCP current speed (cm/s) 1 st storm2 nd storm Sediment traps samples (36h interval) Large current (up to 90 cm/s), turbidity (up to 25 mg/l), and particles fluxes Export of dissolved and particulate organic and inorganic matter, as well as microorganisms (free and attached bacteria, phytoplankton) on water, trap samples, and sediment

Signature of dense water plume Turbidity Temperature Salinity Oxygene Transect performed after the 1 st storm (March 14, 2011) 2011 : warm and wet winter with weak formation of dense shelf water. Export of existing dense water possible due to the occurrence of E-SE storms that flushed the shelf