When we think of pollution in the seas, what generally comes to mind are oils spills, great pacific garbage patch, wildlife entanglement, and microplastic, a commonality between all these is the easy exposure due to proximity to the surface because of this less is known of the majority of pollutants affecting the oceans, are in the deep seas.
In the scope of plastic waste, over 99 percent of it is present on the ocean’s floors or midway at around 180 meters to 460 meters below sea level as opposed to the surface, to make this comparison more visceral, consider the notorious imagery of “the great pacific garbage patch” which amounts to merely a 0.29 % of the total plastic waste present in the seas due to some of the research on the distribution of plastic content in the oceans it is reasonable to assume there are four times as much present in the depths below the garbage patch. It has even been found in some of the deepest most remote parts of the Mariana trench.
Concerns arise even further when we apply this phenomenon to the other form of plastic formed due to overtime degradation of its debris, microplastics. Microplastics are known for contaminating entire ocean food chains and scientists have discovered that large quantities are carried by bottom currents to concentrated spots to form microplastic hotspots, one example is located in the Tyrrhenian Sea. These same currents are also responsible for transporting nutrients and oxygenated water, implying that the microplastic hotspots form in the same regions as significant ecosystems filled with marine life.
Another notable scope of pollution that affects the deep sea comes in the form of chemical waste most significantly as pesticides, toxic metals, and pharmaceuticals, which come to about 100 million tons currently present, out of these the most alarming toxins identified by researchers were persistent organic pollutants, PCBs and PBDEs, both of which have been slowly phased out from widespread usage but as the category “persistent organic pollutants” suggests they stuck around in the environment to this day. Their effect can be illustrated through research conducted in the aforementioned marina trench. They are capable of traveling great distances indicative of their presence in such a remote area like the Marina trench, and they don’t dissolve well in water and favor sticking to the surface of materials such as we mentioned before deep-sea plastics. Creatures attracted by the colorful allure consume them, where the “persistent organic pollutants” remain building up in their fat tissue. Upon death, their bodies sink to the ocean floor to be consumed by deep-sea crustaceans, thus incorporated into the food web.
Interceptor technology for rivers prevents plastic discarded in them to reach the ocean, creating an artificial coastline to remove the garbage, and several other measures undertaken to clean up the oceans are encouraging examples indicating a brighter future for the oceans, but the lack of initiatives towards the deep sea is equally as concerning.