Quantifying the Journey of a Turbidity Current: How Water and Sediment Discharges Vary with Distance in Monterey Canyon
Abstract
Turbidity currents transport vast quantities of sediment across the seafloor and form the largest sediment accumulations on Earth. Such flows pose a hazard to strategically important seafloor infrastructure and are important agents for the transport of organic carbon and nutrients that support deep-sea ecosystems. It is therefore important to quantify the scale of these flows, how much sediment they transport, and how their discharge evolves over time and space along their flow path. Two modes of flow evolution have been proposed based on experimental and numerical models. The first is termed ignition, where flows entrain seafloor sediment and become more voluminous and powerful and increase in discharge. The second is dissipation, where sediment falls out of suspension, flows decelerate and lose discharge. Field-scale turbidity currents have only been measured at a handful of sites worldwide, however, and never at multiple locations along their full course. Therefore, it has not been possible to determine when, where and why flows diverge into these two modes in the deep sea and how discharge of the flows varies. The ambitious multi-institution Coordinated Canyon Experiment measured turbidity currents at seven instrumented moorings along the Monterey Canyon, offshore California. Fifteen flows were recorded, including the fastest events yet measured at high resolution (>8 m/s). This remarkable dataset provides the first opportunity to quantify down-channel sediment and flow discharge evolution of turbidity currents in the deep sea. To understand whether flows ignite or dissipate, we derive total and sediment discharges for each of the flows at all seven mooring locations down the canyon. Discharges are calculated from measured velocities, and sediment concentrations derived using a novel inversion method. Two distinct flow modes are observed, where most flows rapidly dissipated in the upper reaches of the canyon, while three ran out for the full 50 km array length. We then explore why only these three flows ignited and discuss the implications for canyon and channel capacity and evolution.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMEP13C1627C
- 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