Anatomy of a turbidity current: Concentration and grain size structure of a deep-sea flow revealed by multiple-frequency acoustic profilers
Abstract
Turbidity currents are responsible for transporting large volumes of sediment to the deep ocean, yet remain poorly understood due to the limited number of field observations of these episodic, high energy events. As part of the Monterey Coordinated Canyon Experiment high resolution, sub-minute acoustic velocity and backscatter profiles were acquired with downward-looking acoustic Doppler current profilers (ADCPs) distributed along the canyon on moorings at depths ranging from 270 to 1,900 m over a period of 18 months. Additionally, three upward-looking ADCPs on different frequencies (300, 600 and 1200 kHz) profiled the water column above a seafloor instrument node (SIN) at 1850 m water depth. Traps on the moorings collected sediment carried by the flows at different heights above the seafloor and sediment cores were taken to determine the depositional record produced by the flows. Several sediment-laden turbidity flows were observed during the experiment, three of which ran out for more than 50 km to water depths of greater than 1,900 m and were observed on all of the moorings. Flow speeds of up to 6 m/s were observed and individual moorings, anchored by railroad wheels, moved up to 7.8 km down-canyon during these powerful events. We present results based on a novel analysis of the multiple-frequency acoustic data acquired by the ADCPs at the SIN integrated with grain size data from the sediment traps, close to the deepest mooring in the array where the flow thickened to the 70 m height of the ADCP above the bed. The analysis allows, for the first time, retrieval of the suspended sediment concentration and vertical distribution of grain size structure within a turbidity in spectacular detail. The details of the stratification and flow dynamics will be used to re-evaluate and discuss our existing models for these deep-sea flows.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMEP13C1628S
- Keywords:
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- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3045 Seafloor morphology;
- geology;
- and geophysics;
- MARINE GEOLOGY AND GEOPHYSICS;
- 4262 Ocean observing systems;
- OCEANOGRAPHY: GENERAL;
- 4558 Sediment transport;
- OCEANOGRAPHY: PHYSICAL