Submarine channel shape controls combined turbidity current–contour current flow

Abstract

Turbidity currents transport sediment, organic carbon, nutrients, and pollutants from the continental shelf to the deep sea. They can flow over hundreds of kilometers through submarine canyons and channels. Along their trajectory, these flows may interact with contour currents, creating a mixed turbidite–contourite depositional system. Examples of such systems in the oceans exhibit a variety of channel shapes that are often asymmetrical. The effect of channel shape on turbidity currents and their interaction with contour currents remains unclear, yet understanding this could link flow characteristics to seafloor morphology. To this end, purely gravity-driven flows (turbidity currents) and combined flows were simulated in five different channel shapes (three symmetrical and two asymmetrical). The experiments show that firstly, combined flows have less steep vertical velocity gradients than purely gravity-driven experiments. The contour current advects momentum of the turbidity currents out of the channel onto the overbank, reducing the downslope flow velocity in the channel. Secondly, channel asymmetry results in asymmetrically overspilling flows, even without a contour current. Specifically, the overspilling flow is thicker and faster over the steep channel margin than over the gentle margin. Lastly, two types of secondary flow cells were formed. Channel cells, which are confined to the channel, and front cells, which form near stationary fronts in combined flows. These findings suggest that channel asymmetry alone is not diagnostic for inferring paleo-contour current directions. However, channel asymmetry can help to infer velocity distributions inside channels when only bathymetric data is available.