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

Novel acoustic method provides first detailed measurements of sediment concentration structure within submarine turbidity currents
Novel acoustic method provides first detailed measurements of sediment concentration structure within submarine turbidity currents
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 toward 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.
2169-9275
1-24
Simmons, S.M.
1aa65c10-98f2-4e55-aa91-9e6edcd9c5ab
Azpiroz‐zabala, M.
d26dcdf2-afdd-4788-a6ca-b70360f238c5
Cartigny, M.J.B.
d252d7b1-16c6-47b1-bf86-8087070934ce
Clare, M.A.
b26da858-9c08-4784-aaa9-7092efcd94bd
Cooper, C.
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Parsons, D.R.
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Pope, E.L.
2043c317-9ba0-4cbb-a47f-a36f9020417e
Sumner, E.J.
dbba4b92-89cc-45d9-888e-d0e87e5c10ac
Talling, P.J.
1cbac5ec-a9f8-4868-94fe-6203f30b47cf
Simmons, S.M.
1aa65c10-98f2-4e55-aa91-9e6edcd9c5ab
Azpiroz‐zabala, M.
d26dcdf2-afdd-4788-a6ca-b70360f238c5
Cartigny, M.J.B.
d252d7b1-16c6-47b1-bf86-8087070934ce
Clare, M.A.
b26da858-9c08-4784-aaa9-7092efcd94bd
Cooper, C.
fedb5a0e-4ed9-4d66-84cd-cb9b6da23efb
Parsons, D.R.
53a48efb-7db1-458b-b86e-d9a60c7ec5d1
Pope, E.L.
2043c317-9ba0-4cbb-a47f-a36f9020417e
Sumner, E.J.
dbba4b92-89cc-45d9-888e-d0e87e5c10ac
Talling, P.J.
1cbac5ec-a9f8-4868-94fe-6203f30b47cf

Simmons, S.M., Azpiroz‐zabala, M., Cartigny, M.J.B., Clare, M.A., Cooper, C., Parsons, D.R., Pope, E.L., 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), 1-24, [e2019JC015904]. (doi:10.1029/2019JC015904).

Record type: Article

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 toward 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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Accepted/In Press date: 30 March 2020
e-pub ahead of print date: 6 April 2020
Published date: 1 May 2020

Identifiers

Local EPrints ID: 442941
URI: http://eprints.soton.ac.uk/id/eprint/442941
ISSN: 2169-9275
PURE UUID: 44724751-8a8a-419b-9d06-2f2bc114f7cd

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Date deposited: 03 Aug 2020 16:49
Last modified: 06 Oct 2020 22:54

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