Scientists have discovered something concerning in the deep submarine canyons of Earth’s oceans, and it appears to be growing.
New insights into deep ocean explorations showcase how even deep regions like the Mariana Trench are becoming host to the accumulation of plastic waste, revealing a broader picture of the problems posed by plastic pollution in ecosystems worldwide.
Current estimates hold that millions of tons of plastic waste enter marine environments annually. During explorations of the trench in 2019, scientists discovered a plastic bag had made its way to an astounding depth of close to 36,089 feet (11,000 meters).
While experts know the accumulation of much smaller plastic particulates that can easily reach the seabed, the 2019 discovery represents just one example of how larger plastic waste is reaching deep ocean regions.
Now, new research is revealing how a phenomenon known as turbidity currents plays a significant role in the movement of plastic waste to the seabed.
The Hidden Effects of Turbidity Currents Unveiled
Turbidity currents involve the mass movement of sediment-rich ocean water, a phenomenon primarily driven by natural gravitational processes. These currents produce flows that can reach speeds of up to 65 miles per hour and cause ocean floor erosion, widening deep undersea canyons.
Another previously unforeseen effect of turbidity currents is their ability to deposit large amounts of sediment—including plastic pollution—in some of the deepest regions of the ocean.
“Manned submersible dives in the northwest South China Sea encountered substantial amounts of plastic litter accumulated at the base of scours along the floor of a submarine canyon, which may associate with the depositional behaviors of turbidity currents,” report the authors of a new study describing the effects of this phenomenon that appeared recently in Geophysical Research Letters.
Simulating Deep Ocean Plastic Pollution
For their study, the team, led by Dr. Yupin Yang of China’s Southern University of Science and Technology, undertook simulations that employed field-scale bathymetric data to help assess continuities between flow processes that appear to contribute to the accumulation of seafloor trash accumulation and canyon floor shapes and appearance.
According to Yang and his team, consistency between the patterns of sediment deposition that emerged from their simulations revealed that canyon morphology “may exert a dominant influence on turbidite deposition” due to what the team describes as a significantly lower shear velocity as turbidity currents in the team’s simulations make their way across deep ocean canyon floors.
Additionally, the team’s simulations revealed crucial evidence that plastic pollutants undergo processes that carry them to similar locations as other sediments deposited at the base of submarine canyons by turbidity currents.
Yang and the team relied on video footage obtained between 2018 and 2020 to complement the simulations. This footage allowed the team to gauge hydraulic parameters and other factors, ultimately revealing predictions involving the allocation of sediments of various sizes and concentrations, as well as their distribution and flow dynamics.
Canyon Morphology is Key
Ultimately, deep ocean canyon morphology was identified as the main factor behind the current turbidity deposition of plastic wastes in these locations, with concave regions or “scours” up to 30 meters deep identified as particular areas of plastic accumulation in four separate locations.
The team’s findings are significant because they help to identify the fundamental drivers of plastic accumulation on the seafloor. This has proven challenging in the past, mainly due to differences in the behavior of plastics compared to other sediments carried within turbidity flows. This is primarily because of plastic’s natural buoyancy, which helps it travel extremely long distances compared to other waste materials.
This buoyancy, paired with plastics’ ability to persevere over long periods, whereas other forms of waste will naturally break down more quickly, presents an especially dangerous combination capable of having a long-lasting impact on oceanic and other ecospheres.
Yang and the team’s research paper, “How Does Plastic Litter Accumulate in Submarine Canyons?” was recently published in Geophysical Research Letters.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.