Turbidity current flow structure and its modulation by contour currents: Insights from 3D flume experiments

Turbidity currents are the main agent transferring sediment, carbon, nutrients and pollutants (e.g. micro-plastics) from the continents to the deep sea. They flow through submarine canyons, connecting the continents to the oceans. Along their trajectory, these flows may interact with a suite of oceanographic processes, such as geostrophic contour currents, forming a mixed system, entraining material from the turbidity current into the large-scale ocean system. Turbidity current–contour current interaction is scarcely evaluated and their combined three-dimensional flow structure is poorly constrained. We conducted experiments showing the 3D flow structure of turbidity currents and how this structure is modified by contour currents for different contour current velocities, channel depths, and morphologies. Secondary flow cells are observed in the experimental turbidity currents inside the straight channel. This secondary flow is bi-cellular for the purely gravity-driven experiments. Contour currents collapse this bi-cellular structure into a single cell constrained to the downstream channel margin. Additionally, the contour currents modulate the overspilling behavior of the flow by reducing overspill on the upstream overbank and making overspill thicker and faster on the downstream overbank. Our results illustrate the importance of secondary circulation in turbidity currents and their structural modulation by contour currents.