LAUSR

Abstract An instrumented seabed lander was deployed in the head of Logan Canyon in ~280 m water depth in 2005 to obtain the first observations of near-bed hydrodynamics and sediment transport processes in a shelf incising canyon on the glaciated Scotian Slope under strong influence of storms and ocean currents. The seafloor at the head of Logan Canyon is quite dynamic. Hourly mean current speeds can reach 35 cm/s while the maximum instantaneous currents are up to 70 cm/s. Under the forcing of semi-diurnal tides, the bottom currents are dominated by high frequency alternating up- and down-canyon current pulses of internal tides that cause periodic bedload and suspended load sediment transport. The current and sediment transport processes of the internal tides likely extend down to 800–1000 m depths along the canyon to contribute to the observed distribution of Holocene fine sand in the head and talweg of Logon Canyon. The high-frequency current and sediment concentration data show that the temporal changes of the current pulses are well correlated with the changes of temperature and sediment resuspension to demonstrate strong asymmetric patterns. The amplified currents of the internal tides cause the fine sands at the head of Logan Canyon to be transported as bedload in 2.1% of the time and in suspended-load in 1.2% of the time. Suspended-load transport is dominant over bedload transport. The maximum suspended sediment concentrations may reach ~100 mg/l in strong current events. As down-canyon transport is generally stronger and more frequent and the residual current is down-canyon, the net transport of sediment is in the down-canyon direction. Summer storms do not seem to directly impact the bottom currents at the head of Logan Canyon. However, sediments resuspended on the shelf during storms can be advected down slope into the canyon to cause events of substantially high sediment concentration enhancing sediment supply and transport at the head of Logan Canyon.