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Alexandre Normandeau, Geological Survey of Canada - Atlantic, Dartmouth, Canada
Patrick Lajeunesse, Université Laval, Québec, Canada
Guillaume St-Onge, Institut des sciences de la mer de Rimouski, Université du Québec, Rimouski, Canada
Daniel Bourgault, Institut des sciences de la mer de Rimouski, Université du Québec, Rimouski, Canada
Urs Neumeier, Institut des sciences de la mer de Rimouski, Université du Québec, Rimouski, Canada
Sediment density flow activity in sediment-starved submarine canyons (Pointe-des-Monts, Eastern Canada)

Submarine canyons are known to be main conduits for the transport of sediments to deep-sea basins. Sediment density flows occurring in submarine canyons are mostly triggered by river floods, small to large slope failures and advection of shelf sediment offshore. In these contexts, sediment supply is necessary to maintain canyon activity over time. In 2007, a high-resolution mapping of small-scale submarine canyons offshore Pointe-des-Monts (NW Gulf of St. Lawrence, Eastern Canada) revealed a series of incisions characterized by the presence of confined crescentic bedforms. The repeat mapping of the canyons in 2012 and 2015 revealed that the bedforms migrated upslope, indicating that they are cyclic steps produced by supercritical flows. Surprisingly, the comparison of multibeam surveys revealed the absence of slope failures that could have triggered the sediment density flows responsible for the migration of the bedforms. Additionally, the rocky shores and sediment-starved coastal shelf do not supply sediments to the canyons, thus excluding hyperpycnal flows or sediment density flows triggered by advection of shelf sediment. We thus suggest that hydrodynamic processes are responsible for suspending in-situ sediments, which then may flow as turbidity currents. ADCPs deployed for 3,5 months during the summer of 2015 revealed along-canyon currents following tidal cycles with speeds up to 0.4 m/s, which were not strong enough to produce bedform migration. Therefore, the currents responsible for bedforms occur during infrequent events or during winter conditions, both of which require longer instrument time-series to be observed. The retrieval of a 1 year long mooring ADCP during the summer of 2016 will hopefully allow us to gain insights on the triggers of turbidity currents in a sediment-starved shelf.

Special Session 1: Sediment Transport monitoring in submarine canyons
Oral Presentation
Cyclic steps; Monitoring; Sediment-starved; Repeat multibeam