CAMPAGNE CASCADE

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					    Preliminary Results of the CASCADE Cruise
                   (Gulf of Lions)




   CASCADE: CAscading, Storm,
   Convection, Advection and Downwelling Events

R/V l’Atalante, 01 - 23 March 2011
CEFREM, ICM-CSIC, UB, UPM, IFREMER, LA, HCMR, LOV, LMGEM, LOMIC, UA
Wind-driven mixing and cooling of the upper layer of
the ocean during winter


Cascading :
Down-slope cascade of
dense water formed
along the coast




                    Open-Sea convection : Deepening of the mixed layer
                    thickness in the open ocean
Situation for the Gulf of Lions




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     Marin
Open-sea convection event




                            02 Feb - Chlorophylle




                            05 Mar - Chlorophylle
Difference phases of open-sea convection
                                   Preconditionning                          Mixing


                       Radiale L
General circulation                                   Heat loss
           Radiale M



                                                      associated with
and winds combine
                                                      the wind exceed
to predispose some                                    some critical
part of a gyre to                                     level and initiates




                                                                                        After Helen Johns (http://puddle.mit.edu/~helen/oodc.html)
locally overturn                                      convection
                                     Sinking                                Spreading




Sinking and                                           Dispersion of
restratification of                                   newly formed
the water column,                                     deep mixed
once the surface                                      water
forcing decline


 Transfer and sequestration of organic matter in the deep basin
 Response of deep ecosystems
Hints of pelagic ecosystem response to convection

                             104   Number of photon
                                   per seconds
Bursts of deep (near-        103
bottom) bio-luminescence    102
measured by
                             10
photomultiplier following
convection events                       Pot. temperature (deg. C)
                            13.3

                            13.2

Both mechanical             13.1
stimulation (current-




                                                                                                       After Tamburini et al ( submitted to Science)
                            13.0
induced)
                            12.9

                             40
and                                     Current speed (cm/s)
                             30

spontaneous stimulation      20
(bacterial growth due to
nutrients inputs from        10
surface and sediment)         0
                             Jan 2008        Jul 2008      Jan 2009   Jul 2009   Jan 2010   Jul 2010
Sinking and spreading
                                                  0




Rapid shift from a convective
                                                 500
(homogenized) to a stratified
                                                                  Levantine
regime within few days
                                                                  Intermediate
                                                                  water
Capping of newly formed
                                                1000
deep water by Levantine


                                    Depth (m)
intermediate water                                               New
                                                                 deep water
                                                1500
Export of dissolved and
particulate, organic and                                   Mixed layer depth
inorganic matter and
bacterial activity (preserving in
                                                2000
situ hyperbaric conditions)
during and outside convective                                    Old
periods in old and new deep                                      deep water                        4 march
                                                                                                   8 march
waters                                          2500
                                                       12.90      Potential 13.25   0                         0.15
                                                               temperature (°C)         Chlorophylle (µg/L)
Storm, Downwelling and Cascading Event
                                                                10 March - Turbidity
Simulation of bottom currents for March 13, 2011
(peak of the 1st storm)




                                                                18 March - Turbidity




                                                       (cm/s)


             Suspended sediment concentration (mg/l)
Monitoring of the storm
In the Cap de Creus Canyon
2 days of fixed CTD YoYo-ing during the storm
Transect after the storm
Continuous recording with moorings


                                      Moorings




                    CTD station and transect
Current, turbidity, and particle fluxes

 ADCP                                  ADCP Echo
 current                                amplitude   Large current (up to 90
 speed                                    (count)   cm/s), turbidity
 (cm/s)                                             (up to 25 mg/l), and
                                                    particles fluxes




              1st storm    2nd storm


 Sediment traps samples (36h interval)              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
Transect performed after the 1st storm
(March 14, 2011)




                                            2011 : warm and
                                            wet winter with
                                            weak formation of
Salinity                                    dense shelf water.
                              Turbidity
                                            Export of existing
                                            dense water
                                            possible due to the
                                            occurrence of E-SE
                                            storms that flushed
                                            the shelf


Oxygene                       Temperature

				
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