(CNN) The level of microplastics on the seafloor is at its highest ever level, with up to 1.9 million pieces covering just one square meter.

Researchers said they were "shocked" by the volume of microplastics found on the seafloor bed.

The accumulation of floating plastic accounts for less than 1% of the 10 million tons of plastic that enter the world's oceans each year, according to research spearheaded by the University of Manchester in the UK.

The missing 99% is thought to accumulate in the deep ocean, but until now it has not been clear just where it has ended up.

A study published Thursday in the journal Science reveals that deep sea currents act as conveyor belts, transporting tiny plastic fragments and fibers across the seafloor.

This graphic shows how microplastics are transported by currents.

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