Topographic constraints of submarine canyon walls on near-bottom currents

Abstract

To investigate the topographic constraints caused by submarine canyon walls on near-bottom currents, four moorings arrays were deployed in the Blanes Canyon (NW Mediterranean) at ~600 m water depth during winter and spring 2020. Two moorings were placed at a main canyon head and two at the head of a canyon tributary, in regions characterized by narrow gorges and the presence of vertical canyon walls. This study was carried out during the Spanish ABRIC Project aimed to investigate sediment transport mechanisms and their influence on suspension feeder benthic communities. Preliminary results reveal that near-bottom currents were aligned with the canyon wall orientations and oscillated up- and down-canyon mainly at inertial frequencies. The highest current velocities measured at both study sites were ~35 cm/s and directed up-canyon, although the residual flows in both monitored sites were predominantly downcanyon. Suspended sediment concentrations did not exceed 4 mg/L and they mainly increased during down-canyon flows, which contributed to a continuous and persistent transfer of suspended particles towards deeper parts of the canyon. These new findings reveal a complex interaction between local hydrodynamics and steep canyon morphologies, which ultimately affect the ambient suspended sediment transport throughout the canyon, potentially driving the settlement and development of benthic communities inhabiting submarine canyon walls