Description

Context:

New research in “ACS Environmental Science & Technology” shows that microplastics are being carried to the deep sea by turbidity currents via underwater canyons, even in places that don't get their water supply from rivers (like Whittard Canyon off Ireland).

What are Turbidity Currents?

Water rapidly flowing downslope with a high concentration of sediments increases its density; this phenomenon is known as a turbidity current.

Just like underwater avalanches, these are set off by:

Seismic Events

Seafloor landslides

Natural disasters such as slope collapses

Key Features:

Density and Transparency	As turbidity increases, water becomes denser and less transparent.
Erosional Action	These flows erode the seafloor, forming and enlarging submarine canyons.
Sediment Deposition	Sediment is deposited in graded layers – coarser particles settle first, followed by finer ones.
Geological Role	They contribute to deep-sea sedimentation and shape oceanic topography.

Factors Responsible for Turbidity Currents

Factor	Description
Hyperpycnal Plume	Occurs when river water, heavily loaded with sediment, becomes denser than seawater, forming a downward-flowing plume. However, actual sediment concentrations needed are much higher than typical river input.
Sedimentation in Reservoirs	Turbidity currents transport sediment into narrow mountain reservoirs, accumulating near dams and potentially affecting inflow/outflow. Can be controlled using solid/permeable barriers.
Underwater Earthquakes	Seafloor tectonic activity can fluidize sediments, triggering turbidity currents. Such events are major causes of sediment deposition, especially in favorable physiographic conditions.
Canyon-Flushing	Canyons may experience self-sustaining turbidity currents due to previously introduced sediment from littoral drift storms or smaller currents.
Slumping	Excess sediment on continental shelves may slump and slide due to overloading, generating turbidity currents with a downward movement.
Convective Sedimentation	Dense, sediment-laden river plumes cause buoyancy-driven currents beneath the plume, initiating secondary turbidity currents along the ocean floor.

Submarine Canyons

Often stretching from the continental shelf into the deep ocean, submarine canyons are tiny underwater valleys with steep sides that can be found on continental slopes and rises.
Erosional forces, such as turbidity currents, primarily carve them out, much like river canyons do on land.
Underwater canyons make up around 9,477 of the world's known canyons, which account for nearly 11% of the area of the continental slopes.
Tectonically active zones, where canyons are found, are characterised by steeper and shorter canyons than passive edges, which are characterised by more gradual canyons.
Their walls are unstable and can collapse at any moment, adding silt to turbidity floods.