author: academic headlines, title figure from: Vision China

It is generally believed that microplastic particles on the surface of the ocean will directly settle to the bottom of the ocean. The missing 99% of the ocean plastic may reach the deep sea, but its specific location is still unclear. In the recent “Science” magazine, researchers from the University of Manchester, the British National Oceanographic Center, the University of Bremen, Germany, IFREMER University, and Durham University in the United Kingdom used the Tyrrhenian Sea (outside the west coast of Italy) Sampling high-resolution sediment data and digital models finally clarified the missing 99% marine plastic (Tiny plastic fragments and fibers) location and content.

The lead author of this study, Dr. Ian Kane of the University of Manchester, said: “Almost everyone has heard of the infamous marine litter floating plastics, but we are shocked by the high concentration of microplastics found on the bottom of the deep sea. , These microplastics are not evenly distributed in the ocean area. On the contrary, they are distributed along with the powerful ocean currents, which concentrate them in certain areas .

Microplastics: Haizhong PM2.5

As early as 2004, Thompson and others of the University of Plymouth in the United Kingdom published a paper on plastic debris in ocean waters and sediments in Science magazine, which first proposed the concept of “microplastics”.

It is reported that “microplastic” refers to plastic fragments and particles with a diameter of less than 5mm, and is also known as “PM2.5 in the sea”. Due to the small diameter of the “microplastic” particles,Small volume means higher specific surface area (specific surface area refers to the surface area per unit mass of porous solid material) , the larger the specific surface area , The stronger the ability to adsorb pollutants. Therefore, compared with non-degradable “white pollution” plastics, “microplastics” are more harmful to the environment.

As we all know, “microplastics” that carry industrial and domestic wastewater can enter the ocean from rivers, and ocean currents control the distribution of plastics on the surface of the world’s oceans, thus forming floating garbage on the ocean surface. However, the concentration of plastic on the ocean surface only accounts for 1% of the global ocean plastic. Most of the plastic has sunk into the deep sea. At present, the location of these plastics at the bottom of the deep sea is still unclear.

Finally, research teams from the University of Manchester, the National Oceanographic Centre, the University of Bremen in Germany, the University of IFREMER in France and the University of Durham in the UK collected data from the Tyrrhenian Sea (Part of the Mediterranean) sediment samples from the ocean floor, and combine these samples with a calibrated deep ocean current model and detailed ocean floor mapping. In the laboratory, microplastics are separated from the sediment, counted under a microscope, and then further analyzed by infrared spectroscopy to determine the type of plastic. Using this information, the research team was able to show how ocean currents control the distribution of plastic particles on the ocean floor.

It was found that the ocean bottom current can control the flow of these “microplastics”, they can carry the microplastics to the submarine canyon, and then transport them on the seabed through the “bottom water flow”, and finally deposit these fine particles to accumulate a large amount Sediments. Researchers call these deposits “microplastic hot spots.” These hotspots seem to be the “garbage belt” of the deep sea.

In addition, these deep ocean currents also carry oxygenated water and nutrients, which means that the seabed “microplastic hotspot” can also accommodate important ecosystems that can consume or absorb these microplastics .


1.9 million microplastics per square meter

It turns out that microplastics are mainly concentrated in the depths of 600 to 900 meters of the ocean, where the interaction between ocean currents and the seabed is the largest. They either settled slowly, or were quickly transported deep into the submarine canyon by the occasionally turbid ocean currents — powerful underwater avalanches. Once microplastics enter the deep sea, the slow-flowing ocean current near the bottom of the ocean will promote the flow of microplastics. These ocean currents can preferentially concentrate fibers and debris in a large amount of sediments, thereby forming microplastic hot spots in the sediments of the deep sea.

At present, almost all subsea samples contain microplastics, most of which are fibers. These subsea microplastics are mainly composed of fibers from textiles and clothing. These pollutants are not effectively filtered in domestic sewage treatment plants and can easily enter rivers and oceans, while microplastics with the highest concentration can accumulate on the contour rocks. Importantly, given that ocean currents can provide oxygen and nutrients for deep-sea organisms, similarly, these toxic microplastics may enter hot spots of biodiversity, thereby increasing the opportunities for deep-sea organisms to ingest.

Microplastics are transported to the ocean through rivers carrying industrial and domestic wastewater, and then brought to the submarine canyon by powerful sediments (turbid currents), and then through “Underflow” is transported on the seabed and deposited in sediment (Source: Dr Ian Kane)

In addition, Researchers found that the microplastics hotspots produced by ocean currents are also terribly high in microplastics content, up to 1.9 million microplastics per square meter, the highest ever reported in the global seabed environment. Level.

The author of this study, Dr. Mike Clare of the National Oceanographic Center, said: “Our research shows that detailed studies of ocean currents can help us find microplastic transport routes in the deep sea, which can help us find the lost microscopic Plastics. Such a result emphasizes the use of policy interventions to limit naturalThe environment and the need to minimize the impact on the marine ecosystem. “

Ocean underflow controls the deep-sea fate of microplastics (Source: Science)

Dr. Florian Ball, Department of Earth Sciences, Durham University, UK, said: “Unfortunately, microplastics have become a new type of sediment particles, which are distributed on the sea floor along with sand, soil and nutrients. Therefore, our research shows that sediment transport processes, such as ocean currents, concentrate plastic particles at certain locations on the ocean floor. “


Reference:
https://science.sciencemag.org/content/early/2020/04/29/science.aba5899https://www.manchester.ac .uk / discover / news / scientists-find-highest-ever-level-of-microplastics-on-seafloor / https: //www.eurekalert.org/pub_releases/2020-04/aaft-scm042720.php


author: academic headlines, title figure from: Vision China