Two scientists have developed a geographic and temporal atlas of microplastics found in the ocean. A precious help in tracking down this pollution.
Every year, humanity dumps 10 million tonnes of plastic into ecosystems and this number could triple by 2040. This pollution threatens animals, plants and humans through food. The danger is posed in particular by a tiny form of plastic: microplastics. These can be a degraded form of the plastic already present in ecosystems, or come from our clothes, for example, whose microplastics flow into the Arctic.
This microscopic form of pollution is all the more problematic as it is very difficult to track down. It is for this reason that scientists in Michigan have developed a new tool, which they show in a video and a study published in June 2021.
« It is known that the concentrations of microplastics in the ocean vary considerably from place to place. », Remind the authors in the introduction to their work. The concentration is particularly high in the northern Atlantic and Pacific. The methods of measuring the microplastic concentration are generally based on plankton net trawling, then, from there, by models which predict the circulation of this pollution from the ocean circulation. ” However, global measures of the distribution of microplastics and their temporal variability are lacking. », Regret the authors.
A geographic and temporal method
The tool developed by Michigan scientists works like a world atlas of microplastics. The method is based on CYGNSS, an eight microsatellite program launched in 2016 that monitors the weather conditions of large storm systems around the world. CYGNSS satellites have radar measuring the roughness of the ocean surface. However, it is precisely on this roughness that Madeline C. Evans and Christopher S. Ruf, the two scientists behind the microplastic atlas, are counting.
Originally, roughness measurements were used to ” measure wind speed “, more ” we knew that the presence of certain elements in water modified its reactivity to the environment », Explains Christopher Ruf on the university’s website. So the scientists came up with the idea of doing this backwards, ” using changes in reactivity to predict the presence of substances in water “. In short: measuring the roughness at the surface of the oceans helps predict the concentration of microplastics. Indeed, we know that microplastics are accompanied by surfactants, oily, soapy compounds. They are “surfactants” which lower the surface tension on the surface of a liquid – and which therefore modify its roughness.
« Areas of high concentration of microplastics, such as the North Pacific Waste Vortex, exist because they are located in areas of convergence of ocean currents and eddies. Microplastics are carried by the movement of water and eventually collect in one place. Surfactants [évoqués plus haut] behave similarly, and it is very likely that they act as some sort of tracer for microplastics. »
This is how Madeline C. Evans and Christopher S. Ruf were able to develop a geographical and temporal map of the microplastics present in the ocean.
The tool is already useful for clarifying our scientific knowledge on the circulation of microplastics in the oceans. The two authors discovered that this pollution tends to vary according to the seasons: a peak is notably reached in the North Atlantic and the Pacific during the summer months.
In the northern hemisphere, the largest amounts of microplastics accumulate in June and July in the North Pacific Waste Vortex. In the southern hemisphere, concentrations are highest in January and February (summer months in this hemisphere). The explanation is to be found in the ocean circulation, the currents being stronger in winter, which breaks the concentrated plumes of microplastic.
Madeline C. Evans and Christopher S. Ruf also spotted peaks at the Yangtze River, which is believed to be one of the main sources through which microplastic is discharged. And this is often the case with rivers. ” What makes plumes from the mouths of large rivers worthy of interest is that they are a source in the ocean, as opposed to places where microplastics tend to accumulate. »
For both authors, their work has major ecological utility, for example in identifying where to send search and clean-up vessels. They are already in discussions with the organization The Ocean Cleanup, but also hope to get in touch with Unesco, which has a research group on innovative methods to track microplastic discharges in water.
The continuation in video