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Novel acoustic method provides first detailed measurements of sediment concentration structure within submarine turbidity currents

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

Authors

M Azpiroz-Zabala

M J B Cartigny

M A Clare

C Cooper

E L Pope

E J Sumner

P J Talling



Abstract

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.

Journal Article Type Article
Publication Date 2020-05
Journal Journal of Geophysical Research: Oceans
Print ISSN 2169-9291
Publisher American Geophysical Union
Peer Reviewed Peer Reviewed
Volume 125
Issue 5
Article Number e2019JC015904
APA6 Citation Simmons, S. M., Azpiroz-Zabala, M., Cartigny, M. J. B., Clare, M. A., Cooper, C., Parsons, D., …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), https://doi.org/10.1029/2019jc015904
DOI https://doi.org/10.1029/2019jc015904
Keywords Turbidity current; Submarine canyon; Suspended sediment; Acoustic inversion
Publisher URL https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JC015904
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