Simmons, S.M. and Azpiroz-Zabala, M. and Cartigny, M.J.B. and Clare, M.A. and Cooper, C. and Parsons, D.R. and Pope, E.L. and Sumner, E.J. and Talling, P.J. (2020) 'Novel acoustic method provides first detailed measurements of sediment concentration structure within submarine turbidity currents.', Journal of geophysical research : oceans., 125 (5). e2019JC015904.
Turbidity currents transport prodigious volumes of sediment to the deep‐sea. But there are very few direct measurements from oceanic turbidity currents, ensuring they are poorly understood. Recent studies have used acoustic Doppler current profilers (ADCPs) to measure velocity profiles of turbidity currents. However, there were no detailed measurements of sediment concentration, which is a critical parameter because it provides the driving force, and debate centers on whether flows are dilute or dense. Here we provide the most detailed measurements yet of sediment concentration in turbidity currents via a new method using dual‐frequency acoustic backscatter ADCP data. Backscatter intensity depends on size and concentration of sediment, and we disentangle these effects. This approach is used to document the internal structure of turbidity currents in Congo Canyon. Flow duration is bimodal, and some flows last for 5‐10 days. All flows are mainly dilute (< 10 g/l), although faster flows contain a short‐lived initial period of coarser‐grained or higher‐concentration flow within a few meters of the bed. The body of these flows tends towards a maximum speed of 0.8‐1 m/s, which may indicate an equilibrium in which flow speeds suspend available sediment. Average sediment concentration and flow thickness determine the gravitational driving force, which we then compared to average velocities. This comparison suggests surprisingly low friction values, comparable to or less than those of major rivers. This new approach therefore provides fundamental insights into one of the major sediment transport processes on Earth.
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|Publisher Web site:||https://doi.org/10.1029/2019JC015904|
|Publisher statement:||Simmons, S.M., Azpiroz-Zabala, M., Cartigny, M.J.B., Clare, M.A., Cooper, C., Parsons, D.R., Pope, E.L., Sumner, E.J. & Talling, P.J. (2020). Novel acoustic method provides first detailed measurements of sediment concentration structure within submarine turbidity currents. Journal of Geophysical Research: Oceans 125(5): e2019JC015904. 10.1029/2019JC015904. To view the published open abstract, go to https://doi.org/ and enter the DOI.|
|Date accepted:||30 March 2020|
|Date deposited:||16 April 2020|
|Date of first online publication:||14 May 2020|
|Date first made open access:||14 November 2020|
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