Data from a rotary sonar instrument shows pits in the sediment at Barkley Canyon (400 m depth). The pink areas are acoustic reflections off the instrument platform on which the sonar is mounted, with the acoustic shadow of the platform beyond it.​

Time series of sonar scans of bottom sediment in Barkley Canyon, Saanich Inlet and the Strait of Georgia show depressions or pits and resuspension events that come and go over time scales of weeks to months. Camera images suggest that benthic flatfish form these pits in Barkley Canyon. These flatfish and other bottom sea creatures can resuspend the surface sediments, completely turning over the surface layer within 100 days. Observations demonstrate that animals are important contributors to sediment mixing (bioturbation), which liberates nutrients back into the ocean where they support plankton growth.

Two flatfish species commonly observed in Barkley Canyon. The fish in the foreground is a Pacific halibut (Hippoglossus stenolepsis); the one in the background is a Pacific Dover sole (Microstomus pacific us).

Tidally forced resuspension and transport at the base of the Fraser River Delta are critical for the redistribution of seasonal deposits from the sediment-laden river freshet. Continued long-term monitoring enhances understanding of the response of marine ecosystems to changes in turbulence and currents on the seafloor. 

To learn more contact staff scientists Fabio De Leo and Martin Scherwath.

During spring freshet, muddy silt-laden waters of the Fraser River form a front with salty, clear waters in the Salish Sea, British Columbia. Photo by Ed McNichol.