1. Shelf-to-canyon sediment supply mechanisms in the Gulf of Lions and Eel margins
Pere Puig
Institut de Ciències del Mar, CSIC
With contributions from:
ICM-CSIC: Albert Palanques, Jorge Guillén, Jacobo Martín, Marta Ribó
UB: Antoni Calafat, Joan Fabrés, Miquel Canals
CEFREM: Xavier Durrieu de Madron, Serge Heussner
UW: Andrea Ogston, Beth Mullenbach, Chuck Nittrouer, Dick Sternberg

2. Gulf of Lions Mistral Wind Tramontane Wind Llevant Wind
Map of the Gulf of Lions showing the bathymetry (characterized by a broad shelf and a slope dissected by a large number of submarine canyons), the network of rivers discharging in this margin that drain from the Alps (green), Massif Central (pink) and Pyrenees (blue), the two principal wind directions (Tramontane and Mistral), the surface sediment distribution on the shelf and the regional current direction towards the SW (black arrow).
Llevant Wind

3. EuroSTRATAFORM monitoring efforts
Winter 2004
Winter 2005
Along-margin
Shelf-to-canyon

4. Forcing conditions Winter 2004 Winter 2005 Wave-storms & floods
Continuous northerly winds
4 Dec
21 Feb

5. Canyon heads (winter 2004)
4 Dec
21 Feb

6. Canyon heads (winter 2004)
> 68 mg/l
4 Dec
21 Feb

7. Canyon heads (winter 2004) Net fluxes (mg/m2s) 29 7 321 11 12 10 5
Swath bathymetry conducted by Ifremer

8. Cap de Creus Canyon (winter 2005)
Upper canyon monitoring
145 m
200 m
500 m
750 m
Swath bathymetry conducted by AOA, Fugro and UB

9. Cap de Creus Canyon (winter 2005)
Temperature (ºC)
Current speed (cm/s)

10. Cap de Creus Canyon (winter 2005)
SSC (mg/l)
Cumulative flux (Tm/m2)
(1 mab)

11. HERMES & HERMIONE monitoring efforts
Winter 2006
Winter Present
Across-margin
Canyon head monitoring
Rhone River
See Palanques et al. poster M-25

12. Time series (1)
140 mg/l
175 mg/l
> 68 mg/l

13. Time series (2)
140 mg/l
175 mg/l
> 68 mg/l
0.4
2.9
7.1
7.3
2.7

14. Storm resuspension & cascading advection (1)
February 2007
FALTA COMPROVAR ELS FLUXOS COREGITS !!!!!!

15. Storm resuspension & cascading advection (2)
January 2008
FALTA COMPROVAR ELS FLUXOS COREGITS !!!!!!

16. Eel margin
S 60

18. Shelf (S 60) time series
28 Oct
~ 8 g/l

19. Eel Canyon time series
28 Oct
108 mg/l

20. Storm resuspension at the canyon head

21. Storm-induced sediment gravity flows (1)

22. Storm-induced sediment gravity flows (2)

23. Wave-supported sediment gravity flows

24. Liquefaction by excess pore water pressure
WAVE
INFILTRATION
PRESSURES
SHEAR INDUCED
EXCESS PORE
WATER PRESSURE
ZONE A
Highly disturbed,
liquefied, transportable
ZONE B
Non liquefiable
Added stress may induce failure
LIQUEFACTION CRITERIA
ZONE C
Pore water pressures from wave infiltration
ZONE D
No pore pressure response
Penetration below seafloor
From: Clukey et al Geo-Marine Letters, 5:

25. Conclusions
Contemporary shelf-to-canyon sediment supply in the studied margin is controlled by event-driven transport processes.
Wave-storm resuspension events concurrent with dense shelf water cascading are the major contemporary shelf-to-canyon sediment transport mechanisms in the Gulf of Lions margin, while deep cascading events contribute to redistribute the sediment deposited in canyon head regions down to deeper parts of the margin (see Palanques et al. poster M-25).
Wave-storm events are also the main shelf-to-canyon sediment transport process in the Eel margin, but the supply mechanism is controlled by wave-load sediment liquefaction at the shelf edge and upper canyon head regions.
Cascading of dense shelf waters is a global oceanographic phenomenon whose effects on sedimentation processes on continental margins have been poorly studied and largely underestimated. The north-western Mediterranean is one of the regions of the world where massive dense water formation occurs because of cooling and evaporation of surface waters during winter-time. Recent observation within the frame of successive research initiatives found that, concurrent with the well known open-sea convection process, coastal surface waters over the wide shelf of the Gulf of Lions also become denser than the underlying waters and cascade downslope during sustained periods of time until reaching their equilibrium depth. Through this climate-driven phenomenon, dense shelf waters carrying large quantities of particles in suspension and as bed load are rapidly advected hundreds of meters deep, mainly through submarine canyons, acting as an efficient sediment transport and sea floor shaping process. Several evidences of sediment erosion and deposition within canyons attributed to this phenomenon have been identified (e.g. sedimentary furrows, sand-filled axial channels, sediments waves), providing an alternative explanation to the classical view that turbidity currents and associated processes are the main sediment transport mechanisms from shallow to deep-sea regions. At least, during highstands of sea level, dense shelf water cascading in the Gulf of Lions appears to effectively contribute to cross-margin sediment transport. Our findings allow anticipating that under present conditions dense shelf water cascading sites identified worldwide can constitute preferential regions for active contemporary sediment transport processes through submarine canyons, from the coastal ocean to the deep basins.