A JRC-led study recently published in Marine Pollution Bulletin has revealed that the deepest point of the Mediterranean Sea, the Calypso Deep, has one of the highest concentrations of marine litter.

An astonishing 26,715 litter items per square kilometre were found at this place, which is located more than 5 km deep in the Ionian Sea. This is one of the highest concentrations of plastic debris ever recorded in a deep-sea environment, surpassed only by observations in two canyons in the depths of the South China Sea.

The study, conducted using a deep-sea submersible vehicle, by Caladan Oceanic, found that plastics accounted for 88% of the identified litter items. The majority of the plastic debris in the Calypso Deep consists of items such as heavy-duty sacks, shopping bags, and cups.

Marine litter items likely originate from human activities on land and at sea, including littering, sewage, and discarded fishing gear.

To collect this data from the deepest depth of the Mediterranean, a state-of-the-art submersible vehicle was employed to dive to the bottom of the Calypso Deep and capture footage of the seafloor.

The vehicle was equipped with high-resolution cameras that recorded images, which were later analysed to identify and count plastic debris. Additionally, the team employed photogrammetry techniques to estimate the surveyed area and the distance covered by the submersible.

This method enabled them to calculate the density of plastic debris and compare their findings with those of other deep-sea studies. In total, the researchers analysed 167 items, of which 148 were confirmed to be litter, while 19 were suspected but unconfirmed.

Deep sea as a sink for litter: a call for action

The findings of this study serve as a stark reminder of the urgent need to reduce plastic pollution in our oceans, suggesting the importance of increasing recycling efforts, improving waste management systems, and reducing the use of single-use plastics to address this growing crisis.

The Mediterranean Sea, being a semi-enclosed body of water with limited exchange with the open ocean, is particularly vulnerable to pollution, while also experiencing heavy maritime traffic - over 30% of the world’s shipping passes through its waters.

The discovery of plastic debris in one of the deepest parts of the Mediterranean highlights the far-reaching impact of human activities on marine ecosystems. A wake-up call to take stronger action in protecting our oceans and marine life, the study calls for greater international cooperation to tackle plastic pollution at its source.

The upcoming Global Treaty on Plastic Pollution and the UN Agreement on the conservation and sustainable use of marine biological diversity of areas beyond national jurisdiction are new and strong global policy tools, which should be implemented in a way to protect also the deep-sea ocean environment.