1. nepheloid transport vs gravity flows gravity flows and sea level narrow, steep shelves receive much sed different type of gravity flow mass and chemical transport important RECENT OBSERVATIONS OF GRAVITY FLOWS IN SUBMARINE CANYONS C. Nittrouer, P. Puig, A. Ogston T., B. Mullenbach, J. Walsh, T. Drexler, A. DeGeest, G. Kineke, S. Kuehl

2. IMPORTANCE OF MODERN CANYONS To document modern sediment fluxes to the deep ocean To understand mechanisms of lowstand sedimentation SOME RECENT STUDY AREAS Narrow shelf:Eel canyon (northern California) No shelf:Sepik canyon (northern Papua New Guinea) Cold water:Cap Creus canyon (northeastern Spain)

3. 41 o 00’ 40 o 50’ 40 o 40’ 124 o 40’ 124 o 30’ 7 0 0 6 0 0 5 0 0 4 0 0 3 5 0 3 0 0 2 5 0 2 0 0 1 5 0 1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 Eel River Drainage Basin ~9000 km 2 Study Area 0 m 350 1400 Elevation California Eel margin

4. S 60 

5. from Traykovski et al., 2000 mid-shelf gravity-flow processes

6. Signals of Episodic Sedimentation on the Eel Shelf

10. Normalized 210 Pb dpm/(g clay) 10 depth (cm) 0 4 8 12 3020 % 253545 Clay content 7 Be dpm/g 2610 ND Larry entrance Eel River sediment is quickly deposited in the Canyon

15. 0 cm 10 20 30 Core 1Core 2Core 3 A B 90m 110 130 Core 1 Core 2 Core 3 90 100 110 120 Water depth (m) A B 050100150200250300 Distance along transect (m) tripod 124 o 27.83’27.50’ 40 o 39.5’ 39.33’ Larry thalweg A Channelized sediment transport and deposition Formed by gravity-driven sediment flows

16. sand silt clay A B C D E 60cm 90 120 150 180 Sand, silt and clay content (%) Total Pb-210 activity (dpm/g) Non-steady-state profiles in thalwegs Cs-137 Multiple seasonal deposits are preserved

17. MT160B Jul 98 MT450 Jul 98 180cm 210 90cm 120 0 50 100 150 200 250 0 50 100 150 200 250 Depth (cm) 1 10 Total Pb-210 activity (dpm/g) 1 10 Total Pb-210 activity (dpm/g) Moe 160 m Moe 450 m Evidence of sediment removal over decadal time scales

18. PNG Study Areas

19. SEPIK CANYON narrow shelf (<5 km) and…

20. April 1999 Courtesy of Gail Kineke

21. Plume bifurcates ~15% sed mass as surface plume ~85% sed mass as bottom plume Courtesy of Gail Kineke

22. 0.5.94 0.8 0.8 0.2 1.5 0.2 1.3 0.3 0.6 5.1 3.5 0.7 1.8 1.0 0.6 Kadovar Island Bam Island Blupblup Island Wei Island 4 o 30’ S 144 o 30’ E Sepik River 500 m 1000 m 10 km 100 m 1.0 3.9 Accumulation Rate (cm/yr) 4.0 - 5.0 3.0 - 4.0 2.0 - 3.0 1.0 - 2.0 0.3 - 1.0 Kuehl et al. 2000

24. KC16 Pb210

25. KC16 Th234

26. Gravity-flow Deposition

27. Primary sediment source for Gulf of Lions is Rhone River

28. Some sediment reaches submarine canyons on the continental slope

29. (courtesy of Orange et al.) Cap Creus Canyon

30. Courtesy of Amy DeGeest Sediment accumulation rates ~mm/y

31. Along-marginAlong-margin Shelf-to-canyonShelf-to-canyon Winter 2004-05 Winter 2003-04 EuroSTRATAFORM Monitoring Courtesy of Pere Puig

32. Durrieu de Madron et al., Prog. Oceanogr. (2005) & Heussner et al., Mar. Geol. (2006) 10 February 1995 Lacaze-Duthiers Canyon Long-term Monitoring Courtesy of Pere Puig

34. 0.4 2.9 7.1 7.3 2.7 Courtesy of Pere Puig

35. Time series recorded at 500 m water depth (5 - 30 mab) Courtesy of Pere Puig Coarse sediment also observed to be transported

36. Adapted from Fohrmann et al., J. Phys. Oceanogr. (1998) Mixing Neutral density level INLs Heat flux Courtesy of Pere Puig Dense shelf water cascades down continental slope

37. (courtesy of Orange et al.) Cap Creus Canyon

38. 750 m Courtesy of Pere Puig Deep-towed side-scan sonar survey

39. Courtesy of Pere Puig Furrow orientation controlled by bottom currents

40. Deposition during weak flows Erosion during strong flows Flood, Geological Society of America Bulletin (1983) Cap de Creus Canyon sedimentary furrows Maximum width = 50 m Wavelength = 100 m Maximum height = 10 m Type 1C Erosive Courtesy of Pere Puig Sedimentary Furrow Formation

41. CONCLUSIONS Much sediment can enter submarine canyons today especially on collision margins Canyon heads commonly are located in shallow depths fluvial/estuarine processes (turbidity max) surface gravity waves (liquefaction, resuspension) shelf water masses intercepted Turbid water transported into canyon head regularly sed gravity flows (fluid mud, hyperpycnal flows) cold-water gravity flows also observed Autosuspending gravity flows occur less frequently turbidity currents flush canyon heads?