Powerful turbidity currents driven by dense basal layers.

Area of Science:

• Oceanography
• Geology
• Sedimentology

Background:

• Seafloor sediment flows, or turbidity currents, are critical for deep-sea sediment transport but poorly understood.
• Direct observations are scarce, leaving key flow characteristics, like the presence of a dense basal layer, uncertain.

Purpose of the Study:

• To provide the most detailed direct observations of oceanic turbidity currents to date.
• To investigate the physical characteristics and driving mechanisms of these powerful sediment flows.

Main Methods:

• Direct observation of turbidity currents in Monterey Canyon.
• Measurement of flow speeds and inferred sediment transport dynamics.

Main Results:

• Turbidity currents exhibit frontal speeds up to 7.2 m/s.
• Heavy objects (800 kg) were transported at speeds ≥4 m/s.
• Flows likely comprise dense, near-bed layers from seafloor remobilization, overlain by faster, dilute clouds.
• Some flows occurred without obvious triggers like storms or earthquakes.

Conclusions:

• Turbidity currents possess dense basal layers capable of significant sediment and object transport.
• Seafloor remobilization of sand likely fuels these dense layers.
• The occurrence of turbidity currents is not solely linked to major perturbations, suggesting other initiation mechanisms.
• This study offers a revised understanding of sediment transport dynamics in submarine canyons to the deep sea.