Underwater Avalanches Transport Pollution to the Deep Sea

It seems as though nowhere is safe from the unsanitary and unsightly effects of manmade pollution, as even the bottom of the deep blue sea has been thoroughly contaminated. These are the findings of a new study from the Italian National Research Council and the University of Rome, whose collaborative investigation into the seafloor of the Strait of Messina found it inundated with trash.

Using geophysical data acquisition and processing alongside remotely operated vehicle (ROV) video collection and analysis, the authors of the report were able to document the level of pollution at depths that had not been previously been plumbed in the name of environmentalism. It is believed that underwater avalanches cause the pollution to tumble to the bottom of the ocean floor, where it has little chance of seeing the light of day ever again.

An unexpected discovery

The researchers behind the Italian study were carrying out a routine assessment of the condition of the Strait’s seafloor when they made an unexpected discovery: an old car was resting on the bottom of the seabed at depths of over 1,600ft (almost 500m) one mile off the shore of the coastline.

Resolving to investigate further, they used ROVs to record footage of transects of four different large submarine channels. The zones being charted were approximately half a mile away from Sicily and Cantabria and the footage was used to document, identify and map types of litter found across the seafloor.

Plastic the chief culprit

The overwhelming majority (70%) of the pollution consisted of plastic items, with soft plastic such as packaging, plastic bags and single-use items making up 52% of the total waste. That’s perhaps little surprise after it was recently discovered that there are 5.25 trillion pieces of plastic in our seas and oceans around the world. Other materials such as bricks, textiles and scrap metal made up the rest of the refuse.

In conducting their results, the researchers also noticed the presence of many rocks, stones and pebbles among the debris. This discovery gave birth to the theory that underwater avalanches play an important role in transporting pollution to the profound depths of the seafloor, from where it is unlikely to ever surface again.

What next?

The rubbish often finds its way into the oceans in the first place due to illegal dumping of trash in the dry riverbeds that are dotted all over southern Italy in the scorching hot summer months. Once the river begins to fill up, it only takes around two feet of flowing water to generate enough momentum to propel a car along. From here, it reaches the sea, where it is eventually swept to the bottom of the ocean.

Clamping down on this illicit fly-tipping is one way to prevent the pollution entering the sea in the first place. As for the 5.25 trillion pieces of plastic which are already there, scientists are working hard to develop new and innovative ways (such as the unlikely union of forensic science and artificial intelligence) to tackle the problem.