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Turbidity current flow structure and its modulation by contour currents: Insights from 3D flume experiments
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Three-dimensional flume experiments on turbidity current-contour current interactions found that contour currents collapse the normally bi-cellular secondary flow structure of turbidity currents into a single cell, altering how sediments and pollutants including microplastics are transported through submarine canyons. The results show contour current direction and intensity control both cross-channel material distribution and overbank flow dynamics.
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. • Bi-cellular secondary flow cells can form in straight submarine channels independent of Coriolis or contour current forcing. • Contour currents modify secondary flows to a single-cell circulation, displacing the cell along-slope, away from the thalweg. • The contour current direction and intensity, and the channel depth, modulate overbank flow thickness and velocity.
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This doctoral thesis investigated sediment dynamics in combined turbidite-contourite systems through laboratory experiments and computer simulations, directly measuring three-dimensional flow dynamics to link active flow processes to their sedimentary deposits. The experiments showed that contour currents alter turbidity currents through enhanced vertical mixing and sideways transport, and results were compared with samples from the Mar del Plata region off Argentina, with implications for understanding how microplastics are dispersed across the seafloor.
Echoes from the Deep
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Laboratory experiments and computer simulations recreating combined turbidity and contour current flows revealed that contour currents enhance vertical mixing in turbidity currents, fundamentally altering deep-sea sediment deposition patterns confirmed by natural samples from the Argentine margin. Understanding these combined flow dynamics has direct implications for predicting how microplastics and other pollutants are transported and archived across the deep ocean floor.
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Researchers used numerical simulations of turbidity currents in a South China Sea submarine canyon to explain observed plastic litter accumulation patterns, finding that canyon floor morphology—specifically scour features that reduce shear velocity—controls where both sediment and plastic debris are deposited by underwater flows.
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Researchers studied how turbidity currents circulate within continental slope minibasins, which are natural depressions that trap sediment-laden flows carrying materials including microplastics. The study established new experimental methods revealing circulation cell structures within these basins, improving understanding of how pollutants are transported and deposited on the seafloor.
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