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An international research project has revealed the highest levels of microplastics ever recorded on the seafloor, with up to 1.9 million pieces in a thin layer that covers just one square meter.
More than 10 million tons of plastic waste enter the oceans each year. Floating plastic debris in the sea has captured public interest thanks to the “Blue Planet Effect” by seeing movements to discourage the use of plastic straws and carry bags. However, such accumulations represent less than 1% of the plastic that enters the world’s oceans.
Instead, the 99% missing is believed to occur in the deep ocean, but until now it was unclear where it actually ended. Published this week in the journal Science, research by; The University of Manchester, the National Center for Oceanography (United Kingdom), the University of Bremen (Germany), IFREMER (France) and the University of Durham (United Kingdom) showed how deep water currents act as conveyor belts, transporting small plastic fragments and fibers across the seabed.
These streams can concentrate microplastics within large accumulations of sediment, which they called “microplastic hot spots.” These critical points appear to be the equivalents on the sea floor of the so-called “garbage patches” formed by currents on the ocean surface.
The study’s lead author, Dr. Ian Kane of the University of Manchester, said: “Almost everyone has heard of the infamous floating plastic ocean ‘trash patches’, but we were surprised by the high concentration of microplastics that we find in the depths.
“We discovered that microplastics are not evenly distributed in the study area; instead, they are distributed by powerful currents of the seabed that concentrate them in certain areas. “
Microplastics on the seafloor are mainly composed of textile and clothing fibers. These do not filter effectively into domestic wastewater treatment plants and easily enter rivers and oceans.
In the ocean, they settle slowly or can be quickly transported by episodic turbidity currents, powerful underwater avalanches, that travel through underwater canyons to the deep seafloor (see the group’s previous research in Environmental Science and Technology).
Once deep in the sea, microplastics are easily collected and transported by continuously flowing seafloor currents (“bottom currents”) that can preferentially concentrate fibers and fragments within large sediment streams.
These deep ocean currents also carry water and oxygenated nutrients, which means that microplastic hot spots on the seafloor can also host important ecosystems that can consume or absorb microplastics. This study provides the first direct link between the behavior of these currents and seabed microplastic concentrations and the findings will help to predict the location of other microplastic hot spots in deep water and direct research on the impact of microplastics on the Marine life.
The team collected sediment samples from the seabed of the Tyrrhenian Sea (part of the Mediterranean Sea) and combined them with calibrated models of deep ocean currents and detailed mapping of the seabed. In the laboratory, the microplastics were separated from the sediment, counted under the microscope, and further analyzed by infrared spectroscopy to determine the types of plastic. With this information, the team was able to show how ocean currents controlled the distribution of microplastics on the sea floor.
Dr. Mike Clare of the National Center for Oceanography, who was co-leader of the research, stated: “Our study has shown how detailed studies of seafloor currents can help us connect microplastic transport routes in depths of the sea and find the ‘missing’ microplastics. The results highlight the need for policy interventions to limit the future flow of plastics in natural environments and minimize impacts on ocean ecosystems. “
Dr. Florian Pohl, Department of Earth Sciences, Durham University, said: “It is unfortunate, but plastic has become a new type of sediment particle, which is distributed across the seabed along with sand, Mud and nutrients. Therefore, sediment transport processes such as seafloor currents will concentrate plastic particles at certain locations on the seafloor, as our research demonstrates. “
Reference
Microplastic hot spots on the sea floor controlled by circulation in deep waters. Ian A. Kane et al. Science Apr 30, 2020: eaba5899, DOI: 10.1126 / science.aba5899.
This article has been reissued from the following materials. Note: the material may have been edited for length and content. For more information, contact the source cited.
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