Multiple canyons incise the continental slope at the seaward edge of the continental shelf in the Gulf of Lions and are actively involved in the transfer of sediment from shelf to deep sea. Two canyons in the southwest region of the Gulf of Lions, Lacaze-Duthiers Canyon and Cap de Creus Canyon, were instrumented with bottom-boundary-layer tripods in their heads to evaluate the processes involved in sediment delivery, resuspension and transport. In both canyons, intense cold, dense-water flows carry sediment across the slope. In the Lacaze-Duthiers canyon head (located ∼35 km from the shoreline), dense-water cascading into the canyon was episodic. Currents were highly variable in the canyon head, and responded to interactions between the along-slope Northern Current and the sharp walls of the canyon. Inertial and other high-frequency fluctuations were associated with suspended-sediment concentrations of ∼5mg/l. In Cap de Creus canyon head (located ∼14km from the shoreline), downslope currents were higher in magnitude and more persistent than in Lacaze-Duthiers canyon head. Greater suspended-sediment concentrations (peaks up to 20mg/l) were observed in Cap de Creus Canyon due to resuspension of the canyon seabed during dense-water cascading events. The similarities and contrasts between processes in these two canyon heads emphasize the importance of the interaction of currents with sharp canyon bathymetry. The data also suggest that cold, dense-water flows have more potential to carry sediment to the slope on narrow shelves, and may more efficiently transfer that sediment to the deep sea where a smooth transition between shelf and slope exists

This work was conducted with funding from ONR Grants N00014-04-1-0376 (Ogston) and N00014-04-1-0379 (Puig). We gratefully acknowledge Dr. G. Kineke for providing the CTD data under ONR Grant N00014-04-1-0333, and Dr. X. Durrieu de Madron for sharing data from the Tet buoy and providing a thorough review of the manuscript

Special issue Sediment Dynamics in the Gulf of Lions; the Impact of Extreme Events.-- 17 pages, 11 figures

Peer reviewed