The Calypso Abyss, located in the Ionian Sea at a depth of 5112 meters, has one of the highest concentrations of marine debris in the deep sea: another example of the increasingly worrying human footprint that has turned the ocean into a giant garbage dump. Image source: CaladanOceanic
The research results were published in detail in the Marine Pollution Bulletin. Lead authors include Miquel Canals from the School of Geosciences at the University of Barcelona, Georg Hanke from the European Commission's Joint Research Center (JRC), François Galgani from the French Institute for the Exploitation of the Sea (IFREMER) and Victor Vescovo from the US company Caladan Oceanic.
To reach the bottom of the trench, a key challenge in the research, the team used Limiting Factor, a state-of-the-art manned submersible. Images taken by the bathymetric vehicle (DSV) show that marine debris is not limited to coastlines, surface waters or shallow seabeds, but also accumulates in the deepest and most remote places of the Mediterranean. This area of the sea is particularly vulnerable to human influence.
The discovery of rubbish in the deep sea of Calypso by an international team warns that global policy action is needed to reduce marine litter and encourages citizens to change their consumption habits and reduce litter to protect the world's oceans.
The Calypso Deep is a depression 60 kilometers west of the Peloponnese coast of Greece, within the so-called Hellenic Trench, where there are several other similar but shallower depressions. The depression is located in an earthquake-prone area due to active faults and is surrounded by a rather steep terraced terrain with a slope of several kilometers and an almost flat bottom. The depth inside the trench is more than 5,000 meters, kidney-shaped, about 20 kilometers long and 5 kilometers wide.
But how did the garbage sink so deep? Garbage at the bottom of the Calypso Deep "comes from a variety of sources, both terrestrial and marine. Garbage may have arrived through a variety of routes, including long-distance transport by ocean currents and direct dumping," explained Miquel Canals, a professor in the Department of Earth and Ocean Dynamics and director of the Sustainable Blue Economy Chair at the University at Buffalo.
"Some lightweight litter, such as plastics, comes from the coast and escapes into the deep sea of Calypso, just 60 kilometers away from the coast. Some plastics, such as bags, float on the seafloor until they are partially or fully buried, or break down into smaller pieces," he said.
"We also found evidence of rubbish bags dumped by ships, with different types of rubbish piled together to form an almost straight gully, illustrating the huge accumulation of rubbish. Unfortunately, in the case of the Mediterranean, it can be said that 'not an inch is clean'," the expert warned. The Calypso Trench captures and deposits anthropogenic material that reaches the bottom: "It is a closed depression that facilitates the accumulation of garbage inside. The weak currents in the trench - about two centimeters per second, and in special cases, 18 centimeters per second - also facilitate the deposition of light debris on the bottom."
Floating objects carried by ocean currents come mainly from the southern Ionian Sea and further south. Ocean currents also tend to form surface eddies that concentrate floating debris inland. "When these eddies are above the Calypso Trench, some of the flotsam tends to slowly sink to the seafloor, while degradation mechanisms and ballasting processes increase the density of the flotsam. Currents can also carry Adriatic flotsam north through the Strait of Otranto and the waters off northwestern Greece."
Accessing the deepest ocean basins is a huge challenge that requires the use of cutting-edge technology. In this case, the innovation is the LimitingFactor submarine made by TritonSubmarines. Deployed from a specially prepared mother ship, the submarine is capable of carrying two passengers to the deepest trenches. While examining the seabed, this unique technological device moves slowly (approximately 1.8 kilometers per hour) to obtain high-quality images.
In CalypsoDeep, LimitingFactor can stay on the seafloor for 43 minutes and travel a distance equivalent to 650 meters in a straight line. "Each dive typically takes more time descending and ascending the submersible to the surface than inspecting the seafloor. Each complete dive typically takes several hours," Canals noted.
The technique made it possible to calculate the density of marine debris at the bottom of the trench, although no significant impact on marine life was found because this abyss of the Ionian Sea is particularly barren. The image only shows the presence of Coryphaenoides mediterraneus and Acanthephyraeximia shrimp.
"However, in more biodiverse places, there are different types of interactions between garbage deposited on the seafloor and organisms, such as fishing, burial, hooking or ingestion, and there are also animals that use garbage as a substrate to grow, hide or lay eggs," Canals noted.
The world's first evidence of garbage found on the seafloor dates back to 1975, in the Skagerrak Strait in the North Atlantic. Canyons and seamounts are major accumulation sites for trash that can be buried, broken up or moved by gravity, ocean currents and other ocean factors.
Today, the Mediterranean is a marine area particularly affected by this environmental problem. A 2021 study has identified the Strait of Messina as the area with the highest known density of marine debris in the world (Miquel Canals et al., Environmental Research Letters). This is a real hotspot with huge amounts of rubbish piling up.
"The Mediterranean is a closed ocean surrounded by humans, with heavy maritime traffic and extensive fishing activities. Our study provides evidence that should shake up global efforts, especially in the Mediterranean region, to reduce the dumping of waste, especially plastic, into the natural environment and ultimately into the ocean, in line with the joint The United Nations Global Plastics Pact, which still needs to be ratified. Even the May 2015 papal encyclical Laudato Si’ and some declarations from the G7 world summit move in this direction, although we are still far from achieving a huge social impact on seabed litter,” Canals points out.
Unlike other popular places, such as beaches or coastlines, "the seabed is still poorly understood by society as a whole, which makes it difficult to raise social and political awareness for the protection of these spaces, and scientists, communicators, journalists, media, influencers and others with social influence must work together. The problem is there, and even if it is not directly visible, it is widespread. We should not forget it," Miguel Canals concluded.
Compiled from /ScitechDaily