The deep ocean is one of the most unexplored places on Earth. But recently, scientists took the first measurements of organic pollutants in deep ocean trenches, and the results are not promising.
Researchers from the University of Aberdeen in the United Kingdom found high levels of man-made pollutants in shrimp-like crustaceans called amphipods. The amphipods were collected from two deep-ocean trenches—the Mariana Trench in the western Pacific Ocean and the Kermadec Trench near New Zealand.
Prior to these findings, researchers had studied pollutants as far as 2,000 meters below sea level. The amphipods in this study were found at depths between 7,000 and 10,000 meters, giving scientists the first glimpse into how trenches are affected by man-made pollutants.
The pollutants found in the trenches are particularly hard to break down, meaning they may be under the sea for the long haul. Here’s Jane Qiu reporting for Nature:
In both trenches, the amphipods contained polychlorinated biphenyls (PCBs)—used to make plastics and as anti-fouling agents to stop barnacles growing on ships’ hulls—and polybrominated diphenyl ethers (PBDEs), which are used as flame retardants.
Both chemicals are man-made and belong to a category of carbon-based compounds called persistent organic pollutants (POPs) because they are hard to break down. Production of PCBs—which are carcinogens—has been banned in many countries since the late 1970s; PBDEs, which animal studies suggest may disrupt hormone systems and interfere with neural development, are only now being phased out.
The Mariana Trench had a much higher concentration of PCBs in its amphipod population, more than 15 times greater than the concentration found in the Kermadec Trench. The concentration even topped PCB levels in two of the most polluted rivers in China—the Pearl River and the Liao River.
However, the PBDE levels in the Kermadec Trench were five times greater than those in the Mariana.
This leads scientists to believe that pollutants that get dumped into the ocean sink until they can’t sink anymore. This ultimate chemical resting place tends to be deep-ocean trenches, which then accumulate pollutants that have nowhere to go.
The deep ocean is still relatively undiscovered, which makes the high POP levels all the more concerning for scientists. The fact that so much is unknown about this environment means the deep-ocean canyons are “untapped natural resources”. They are home home to organisms that could aid in drug discovery and other commercial applications.
More importantly, scientists believe that the deep ocean could be an essential carbon sink. In the trenches, carbon is pushed into the Earth as tectonics plates are thrust underneath each other. The trenches also contain microbes that process carbon-containing chemicals into forms other than carbon dioxide. Scientists believe these processes may affect the carbon cycle as a whole.
As the carbon dioxide levels affect global warming, these deep-sea trenches could be valuable resources. But for these natural processes to continue, scientists must look into the effect of these man-made pollutants, and if they pose a tangible problem to the system.