Morphodynamics in sediment-starved inner-shelf submarine canyons (Lower St. Lawrence Estuary, Eastern Canada)

The contemporaneous activity and sedimentary processes in a series of inner-shelf submarine canyons located in the Lower St. Lawrence Estuary were examined using high-resolution multibeam bathymetry and backscatter data. The presence of crescent-shaped bedforms (CSBs) displaced upslope at the bottom of the canyons between 2007 and 2012 indicates that they are currently active through the remobilization of sediment by gravity flows. However, the shelf and shores of the region are characterized by the absence of sediment. Our results indicate that gravity flows currently eroding the canyon floors do not transport new material downslope coming from the shelf but rather remobilize in-situ deglacial sediments within the canyon thalweg. We suggest that slope failures and internal tides/waves are responsible for sediment remobilization in these canyons, although their role in the upslope migrating CSBs is unclear. This paper provides evidence that sediment supply is not a prerequisite for the modern activity of inner-shelf submarine canyons when processes such as slope failures and internal tides/waves are frequent enough to remobilize in-situ sediments.