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Andrea S. Ogston, School of Oceanography, University of Washington, Seattle, US
Laurenz Thomsen, Jacobs University Bremen, Germany
Pere Puig, Institute of Marine Sciences, CSIC, Barcelona, Spain
Jacopo Aguzzi, Institute of Marine Sciences, CSIC, Barcelona, Spain
Corrado Costa, Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di ricerca per l’ingegneria agraria, Italy
Fabio C. De Leo, Ocean Networks Canada, University of Victoria, Canada
Sediment dynamics within Barkley Canyon: impact of dynamical processes on particles in suspension and their potential sources

Many canyons incising continental slopes are disconnected with their sediment source, yet may remain sites of active dynamics due to potential transport pathways on the continental shelf and focusing of energy within the canyon.  Thus, they remain conduits for particulates that contribute to deep-sea sedimentation. Canyons are logical settings to study impacts of many seabed environments within a temporally varying hydrodynamic regime, and have great potential for studying interactions between lithogenic, pelagic-organic, and benthic-organic particles. Active processes in Barkley Canyon located off Vancouver Island, Canada, along with strong physical forcing and regions of stable gas hydrates at the seafloor provide an ideal environment to investigate linkages between a range of benthic environments and aggregate/sediment dynamics.

Using nearbed current, turbidity, and chlorophyll data collected using sensors mounted on a remotely operated vehicle tethered to the Ocean Networks Canada observatory in the winter 2010-2011, we performed initial analyses to investigate sediment dynamics on a small plateau located at 870 m depth within the canyon.  At this site during the winter season, persistent down-canyon (~230°) flows that oscillate on tidal frequencies lead to downcanyon net fluxes of particles, and are effective at all times over the winter period.  The negative correlation between turbidity and current speed implies a settling signal for these particles in suspension, not resuspension from the bed, and suggests that particles are being held in suspension in the bottom boundary layer, which builds and collapses with current speed.  The temporal change in turbidity response to tidal velocity throughout the winter further suggests that particles of variable density are in suspension. Potentially denser, faster settling particles associated with very low chlorophyll signals near the seabed are likely sourced from other locations within the canyon; and less dense, slower-settling particles associated with higher levels of chlorophyll may be sourced from outside the canyon.  The rich data set that has been collected at this NEPTUNE observatory site provides novel and effective means of studying active sedimentary processes within canyon environments with limited sediment supply, a topic of interest in a variety of modern global environments.

Special Session 2: Interdisciplinary studies in Barkley Canyon
Oral Presentation
turbidity, canyon, tides, downwelling