Nepheloid layer

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Nepheloid layer or nepheloid zone is a particle-rich layer above the ocean floor, from Greek: nephos, "cloud"; the particles in the layer may come from the upper ocean layers and from stripping the sediments from the ocean floor by currents. Its thickness depends on bottom current velocity and is a result of balance between gravitational settling of particles and turbulence of the current.

In a similar way, a surface nepheloid layer may be created, due to particle flotation, while intermediate nepheloid layers may be formed at the slopes of the ocean bed due to the dynamics of internal waves.

The existence of the nepheloid layer complicates bathymetry: one has to take into account the reflections of lidar or ultrasonic pulses from the upper interface of this layer, as well as their absorption within the layer.