Preliminary Results of the CASCADE Cruise (Gulf of Lions)

R/V l’Atalante, 01 - 23 March 2011CEFREM, 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

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Difference phases of open-sea convectionPreconditionning

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

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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)

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Jan 2008 Jul 2008 Jan 2009 Jul 2009 Jan 2010

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Pot. temperature (deg. C)

Current speed (cm/s)

Number of photon per seconds

Jul 2010

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Potential temperature (°C) Chlorophylle (µg/L)

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250012.90 13.25 0 0.15

4 march8 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 1st 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 stormTransect after the stormContinuous recording with moorings

Current, turbidity, and particle fluxes

ADCP Echo amplitude

(count)

ADCP current speed (cm/s)

1st storm 2nd 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 1st 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